PREFACE
Indian Consultancy Company M/s WAPCOS was engaged by Zimbabwe Power
Company to augment the depleted skills at their biggest Thermal Power Station at
Hwange. M/s WAPCOS has mobilised for the assignment since 1st week of February
2011. The WAPCOS Engineers are sharing their experiences and expertise and are
actively involved in day to day operation at Hwange power Station. In our due
diligence report it has been agreed to update all Operators by providing them the
basics of the Power Plant along with various schemes in Boiler, Turbine, Generator
and other ancillary plant like Coal Handling Plant, Ash handling plant, Water
Treatment Plant etc.
Training sessions have already been conducted for Operation staff, which
includes Operation Superintendant, Senior Unit controllers, Boiler-Turbine
operators, Coal and Ash Plant Operators. The training programmes are continued
and it is covering all Operators and Technicians in phases. The faculty members,
being the WAPCOS Engineers and local Engineers from ZPC. In the training
programmes M/s WAPCOS specialists have tried to enlighten the Operators with the
existing plant and schemes and update them with latest developments in the field
of Power Generation to facilitate them to operate the plant to the best of their
ability and improve the Generation.
In view of the above background it is proposed to provide the Operators with
a manual consisting of the specification, plant description and operating procedures
along with the various schemes of the power station with schematic and equipment
drawings. The write-ups have been prepared by the M/s WAPCOS and schematic
layouts and drawings are provided as a complementary to one another.
The Hwange Power Station is preparing for ISO 9001:2008 certification. All
the operating procedure have already been well formulated and documented. The
contents of this write-up are taken from the various O & M Manuals and the
material available from Hwange Power Station.
It is our effort to enhance the knowledge and skill of the Operators for
improving the Generation of the Power Plant and to provide a consolidated and
handy instruction booklet for the easy reference of the operation personnel.
WAPCOS LTD. INDIA,
HWANGE, AUG. 2011
Prepared by
(C.S.Chaudhari)
Sr. Unit
Controller
(WAPCOS)
Checked by
(A.R.Joshi)
Advisor to
Ops. Manager
(WAPCOS)
Approved by
(L.K.Shumba)
Operating
Manager
(HPS, ZPC, Hwange)
1
1. INTRODUCTION TO HWANGE POWER STATION:
Hwange is mine mouth Power Station situated in the north west of Zimbabwe, about
100 KMs from the world famous Victoria Falls, at the Zambia border. The Power Station has
an installed capacity of 920 MW, comprising of 6 units which were commissioned in two
phases as follows:
Stage I - 4 x 120 MW units were commissioned in the year 1983 to 1986, Comprising Boiler
of Internal Combustion (S. Africa) and Turbo Generators of MAN/Alsthom Atlantique.
Stage II - 2 x 220 MW units – 1986 to 1987 (Comprising Boiler of Babcock Power Limited
London make and Turbo Generators of Ansaldo, Italy.
The Power Station is currently generating with 6 units. The station uses coal received from the
nearby collieries as its primary fuel with diesel as secondary fuel. Water for station operations is being
supplied from Zambezi River through pumping station at Deka, via a 44 KMs long pipe lines and
delivered to two utility type reservoirs of 100 M x 100 M size. The ash generated is disposed of to the
Ash Bund, which is @ 5 Km away from the Power Station.
CIRCULATING WATER SYSTEM:
❖
❖
The cooling water system is of the closed loop type utilising natural draft cooling towers
The cooling towers are of natural draft type having a capacity of 135,00 litres/sec and a cooling
range of 12 OC. The re-cooled temperature is 32 OC. With a wet bulb temperature of 18 OC. Each
tower is 120 Mtrs high with a pond diameter of approx. 81.8 Mtrs. The cooling tower fill is of
corrugated asbestos supported on R.C. Columns.
❖
The main circulating water pumps are of horizontal split casing type of APE-Allen limited
manufacture. Each pump is capable of delivering 4700 Litres/sec against a generated head of 20
Mtrs.
❖
Stage-I Four Units consists of:
❖
A Water tube Boilers, natural circulation, balanced draft type. MCR capacity and steam
conditions are 134.72 Kg/sec at 89 Bar (Gauge) at Super heater outlet 518
Feed water at 205
❖
OC
from
OC.
A non-reheat turbines, 2 cylinder, tandem compound with two exhaust, the steam
conditions at the turbine stop valves being 83 Bar at 510 OC, 5 stage feed heating with
2 x 100% Condensate Extraction pumps and 2 x 100% Boiler Feed pumps.
❖
An Alternators of 120 MW, 10.5 KV, hydrogen cooled, with static thyristor excitation
supplied from a Transformer connected to the primary terminals of the alternator.
Manufactured by a consortium of West Germany (Turbines) and Alsthom – Atlantique
of France (Alternators, feed heating and condensing plant)
2
II.
PREDICTED PERFORMANCE
A. BOILER
LOAD
UNIT
M.C.R.
80 %
70 %
Evaporation
Kg/sec
134.722
107.78
94.307
Design pressure for high press portions
MPa (gauge)
11.0
11.0
11.0
Working press at Super heater outlet
MPa (gauge)
8.9
8.9
8.9
OC
518
518
518
MPa (gauge)
9.995
9.621
9.458
OC
205
194
188
kg/Sec
15.36
12.514
11.066
Steam temp. at Super heater outlet
Working press in boiler steam
Feed temperature at Economiser inlet
Wt. Of coal of GCV 24630 kj/kg consm
Flue gas temp. Entering Economiser
O
C.
610
576
551
Flue gas temp. Leaving Economiser
O
C.
300
268
252
Flue gases leaving Air Heater
O
C.
140
131
126
Water temp. entering Economiser
O
C.
205
194
188
Water temperature leaving Economiser
O
C.
294
283
275
Temperature of Air leaving Air Heater
O
C.
223
204
192
Flue gases leaving furnace
O
C.
1116
1063
1032
%
15.87/3.72
15.87/3.72
15.87/3.72
Qty. Of Combustion Air
kg/Sec
75.64
61.497
56.216
Qty. Of Re-circulated Air
kg/Sec
5.905
9.701
11.237
Qty. Of Total Air
kg/Sec
80.543
70.567
64.932
CO2 / O2 at Air Heater inlet
Air temp. Entering Air Heater
O
C.
54.4
63.9
67.8
Air temp. Leaving Air Heater
O
C.
223
204
192
B.
TURBINE
TYPE
Continuous Maximum Rating
Speed
Turbine Stages
Turbine intended for
Coupling
Line of Shafts
Casings
Exhaust flows
Exhaust Casing
Foundation
Turbine rotation (from HP front)
Live steam at turbine inlet
Exhaust steam downstream pressure
Bleed points
Feed water heaters
Deaerator specification
Condensing Turbine T 1A 120, 10-2F, 470
120 MW
3000 r.p.m.
HP- 16 stages, LP- 2x5 stages
Alternator Drive
Rigid
1, Tandem (coarse)- Multiple shafts
2
2
1
Concrete
Anti clockwise
Pressure- 8.4 Mpa, Temperature- 510 OC
11.8 Kpa
5
5 (2 HP Heaters, 2 LP Heaters and a Deaerator
Horizontal, spray, trays, with horizontal storage tank
3
CONDENSER SPECIFICATION
½
580o m2
9,972 tubes, 7478 mm in length, 25x1.2 mm diameter,
made of CuZn 28 SnF 33
Condenser Shell
Steam side
Water side
Volume
20 m3
95 m3
O
Design temperature
120 C
50 OC
Design gauge pressure
-100 kPa /70 kPa
280 kPa
Test pressure
Leakage test
520 kPa
C.W. Inlet temperature
32 OC
C.W. Cooling Method
Natural Draught Wet Cooling Towers
Turbine Gland Sealing Steam
Supplied from Auxiliary Steam Distributor
Turbine Bearing & Lubricating Oil System
Number of journal bearings
4
Type of journal bearings
Lemon-bore type
Thrust Bearing
Location
HP/IP bearing pedestal
Type
Kingsbury JJ 17 (6x6)
Bearing surface
932 cm2 (144.5 sq. Inch)
Number of pads
6 on loaded side / 6 on unloaded side
Speed
3000 r.p.m.
Oil inlet temperature
45 OC
Lubricating/control oil pumps
Main oil pump
Driven from Turbine shaft via a gear, supplies bearing oil
Discharge pressure 2 MPa
& control oil during normal operation.
Transfer pump
Driven by Oil Turbine operating on the bearing oil off
Discharge pressure 0.48 MPa
branched from full flow of MOP & reduced to bearing oil
press, in turbine. Delivers oil from oil tank to suction of
MOP
Auxiliary bearing oil pump (a.c. driven)
Serves bearings during start-up. Discharge pr- 0.37 MPa
Auxiliary control Oil pump (a.c. driven)
Serves hydraulic control equipment till MOP takes over.
Discharge pressure – 1.6 MPa
D.C. Emergency Oil pump
Serves during total a.c. failure Discharge pr.- 0.2 MPa
OIL COOLERS
Number of Oil coolers / Type
2 x 100 % duty / Vertical
Cooling area
200 m2 /
Number of passes-- Water / Oil
4/1
Oil flow/ Cooling water flow
140 m3/h / 300 m3/h
Oil temperature inlet/Outlet
58 OC / 45.7 OC
Cooling water temperature inlet / outlet
38 OC /40.3 OC
Oil Purifier Specification
Type
OS 2000
Capacity
Approx. 2000-3500 Ltr/hr turbine lubricating oil
Viscosity
12x10-6 m2/s at 70 OC, 26 x 10-6 m2/s at 40 OC
Bearing jacking oil pump pressure
15 MPa
Speed of Turbine on Barring Gear
50 r.p.m.
Number of water flows/passes
Cooling area
Condenser tubes
4
C.
GENERATOR
A-
General characteristic
-
Rating
…
…
…
…
133.33 MVA
-
Active output
…
…
…
…
120 MW
-
Voltage
…
…
…
…
10500 V
-
Current
…
…
…
…
7331 A
-
Power factor
…
…
…
…
0.90
-
Nominal speed
…
…
…
…
3 000 r.p.m
-
Over speed
…
…
…
…
3 600 r.p.m
-
Frequency
…
…
…
…
50 Hz
-
Relative gas Pressure
…
…
…
…
2
-
Short circuit ratio
…
…
…
…
0.463
-
Class of insulation
…
…
…
…
B
-
Standards
…
…
…
…
I.E.C
-
Type of cooling…
Stator core
:
with gas flow
•
Stator winding
:
without water, with gas flow
•
Rotor
:
with axial and radial gas flow
•
B -
Excitation Characteristics
Excitation: STATIC – SHUNT
Excitation output
…
…
…
…
…
354 KW
Excitation voltage
…
…
…
…
…
246 V
Excitation current
…
…
…
…
…
1438 A
...
…
…
664 V
…
…
…
0.1712 Ohm
Excitation ceiling voltage (5 sec)
Rotor resistance at
C.-
bars
75o
C
…
Mechanical Characteristics
WR2 of generator and exciter
….
…
…
…
2940 kg. m2
First critical speed
….
…
…
…
1520 r.p.m.
Second critical speed
….
…
…
…
4160 r.p.m
…
…
± 1120 KN
Static load on the foundation (on each side)
In the case of short-circuiting
D.
….
…
End Shield Bearing Characteristics
a) Journal Bearing Supply
-
Oil flow of the two generators journal
-
Bearing at nominal speed :
...
420
Ltr/min
-
Maximum inlet oil temperature:
…
50
OC
-
Oil type :
…
0TE
Light
-
Maximum journal temperature :
…
90
oC
5
b) Gas Seal supply
-
Differential pressure between oil and gas
-
Total shaft seal oil blow at stands still
-
(2.00 bar absolute)
-
Total shaft seal oil flow at rated speed
-
(2.00 bars absolute)
-
Total shaft seal oil flow at over-speed
-
(2.00 bars absolute)
…
….
…
…
…
…
1.0
bar
….
….
…
1.2
Ltr/min
….
….
….
13.0
Ltr/min
….
…..
….
15.0
Ltr/min
E. Cooling System Characteristics
▪
Gas used
.....
Hydrogen
▪
Gas pressure (absolute)
…..
3 bars
▪
Gas flow
….
30.4 m3/s
▪
Maximum cold gas temperature
…..
46oC
▪
Maximum warm gas temperature
....
60oC
▪
Number of gas coolers
…..
4
▪
Rated capability with a cooler out of operation
….
93 MVA
▪
Maximum looses to be dissipated by gas
….
1340 KW
▪
Rated pressure of gas cooling water (absolute)
.…
11 bars
▪
Maximum pressure of gas cooling water (absolute)
….
17 bars
▪
Maximum inlet temperature of cooling water
…..
38oC
▪
Maximum outlet temperature of cooling water
….
43.2oC
When cooling gas of generator is hydrogen, we need following characteristics.
-
-
-
-
Generator useful volume
Minimum purity in hydrogen cylinders
…..
Volume of CO2 to scavenge air
….
Minimum volume of H2 to scavenge the CO2
…..
Minimum volume of C02 to scavenge H2
Volume of air to scavenge CO2
…
Hydrogen consumption at filling at 0.035 bar …
Hydrogen consumption at filling at 1 bar
Hydrogen filling time at design pressure
Daily guaranteed hydrogen consumption at 0.035 bar
Daily guaranteed hydrogen consumption at 1 bar
Required hydrogen purity in stator during operation
Alarm trips for purity level of
……
Generator stops for a purity level of
…..
….
….
…
….
…..
….
….
….
….
...
…..
…..
…..
…..
❖ GENERATOR Xmer AND AUXILIARIES:
The ratings of the various main transformers are as follows:
Generator Transformer
–
133 MVA
Station Transformer
–
15 MVA
Unit Transformer
–
10 MVA
6
….
99
72,5
116
203
72,5
145
203
6 to 7
5
10
98
96
92
58
m3
%
m3
m3
m3
m3
m3
m3
hours
m3
m3
%Alarm trip
%
%
III. DESCRIPTION OF THE MAIN PLANT:
A.
BOILER PLANT
INTRODUCTION:
•
•
•
•
•
•
•
•
•
The Boiler unit is comprised of a single furnace suspended from the Boiler roof steel work. The
furnace exit channel is continuous with the rear gas pass in which the feed water economiser and
the first superheater stage are housed. The second superheater stage is suspended from the
furnace roof.
The furnace is provided with 4 corner-mounted burner boxes, each burner box accommodating 4
coal burners and 2 oil lighting-up burners. The burners are of the tilting type for control of the
superheat steam temperature.
It is a Water tube, natural circulation, balanced draft type. MCR capacity and steam conditions are
134.72 Kg/sec at 89 Bar (Gauge) at Super heater outlet 518 OC from Feed water at 205 OC.
Furnace wall and roof are of membrane wall construction.
ICAL PF corner fired, tangential, burners- 4 rows (capable of tilting ICAL tip, recirculation type oil
burners- 2 per corner.
Super heat temperature control by inter stage spray water attemperator.
Tubular Air Heaters of ICAL make.
Electrostatic precipitator of Brandt make
ID Fans – Airtec Davidson, 2 per Boiler, backward bladed aerofoil section, inlet vane control,
electric motor drive.
Note: Mechanical draft plant (FD and ID fans has margin in capacity of 15 % by volume and 33 % in
pressure above MCR requirements.
•
•
•
ICAL Loesche LM 16/1220 PF mills, 4 per Boiler, 3 required for MCR duty. The mills are of the
pressurised table and roller type. The PF is fed direct to the burners.
Fineness of PF specified 72 % through 200 mesh BS test sieve. 99.7% through 52 mesh BS test
sieve.
Primary Air fans- Airtec Davidson, 4 per Boiler (each utilised for coal mills). Backward aerofoil
bladed, radial inlet control electric motor drive.
FURNACE CONSTRUCTION:
The walls of the furnace are constructed of welded tube panels. The tubes are fin welded to
form complete sections. These sections are then welded together to a completely gas tight enclosure.
The water walls rise from the lower furnace headers, with the tubes welded to the stubs on the
drum. These tubes form the front, side and rear walls of the furnace.
The furnace ash hopper has been with sufficient slope to prevent build-up of deposits.
REAR GAS PASS:
The rear gas pass contains the primary superheater stage and the economiser. The roof, sides
and the rear wall are formed by the superheater tubing.
The gas pass is divided into two separate gas flow passages on reaching the economiser to
form the economiser gas outlet.
INSULATION:
The furnace and rear convection gas pass are insulated with a suitable thickness of insulating
slabs, which are covered with IBR sheeting.
7
ACCESS DOOR:
❖
❖
❖
Access and inspection doors are provided to allow entry into the Boiler for maintenance and
cleaning.
Observation doors are provided for checking combustion conditions.
All the doors are air tight and sealed with an asbestos sealing ring. The doors are made from
cast iron.
SUPERHEATER:
(Ref. Diagram no. HPS/WAPCOS-02)
The superheater forms an integral part of the Boiler and its purpose is to raise the temperature
of the steam to a level which gives maximum plant efficiency without subjecting the superheater tubes
and turbine to excessive temperature.
The final superheater outlet temperature is automatically controlled by two spray-type nozzle
de-super heaters which are parallel and located between two stages of superheater.
Automatic control of the superheater spray is effected through a measurement of the steam
temperature at each of the two final outlets, each outlet being independently controlled.
SUPERHEATER PRIMARY STAGES:
(Ref. Diagram HPS/WAPCOS-02)
The first stage superheater is a two-flow horizontal convection stage and consists of mild steel
U-loop elements situated in the rear main gas pass immediately above economiser.
SUPERHEATER SECONDARY STAGES:
(Ref. Diagram HPS/WAPCOS-02)
The second stage superheater is three-flow vertical-type, consisting of 33 Chromomemolysteel elements situated in the upper furnace local to the furnace nosing.
These elements are also fitted with rows of heat resisting steel slip and plate spacers in the
vertical section.
SPRAY DE-SUPER HEATERS:
The spray-type de-super heater is a device by means which the temperature so the steam
flowing along a pipe can be reduced to a desired lower figure.
The formation of a fine spray (which is commonly termed as atomisation) is obtained either by
passing high pressure water through a special nozzle.
The two inter stage spray de super heaters each consists of an alloy steel shell with welded
joints at both inlet and outlet.
SUPERHEATER PROTECTION:
Excessive temperature of the super heater elements may result in tube failure and can only be
prevented by the cooling action of the steam through the tubes, or by reducing the temperature of the
gas surrounding them by controlling the firing rate.
STEAM DRUM AND INTERNAL FITTINGS:
(Ref. Diagram HPS/WAPCOS-03)
The Boiler is provided with a 125-150 mm thick drum of fusion welded construction, stand
pipes, fittings and mountings or stub tubes connecting to circulating tubes and welded to the drum.
A hinged and easily operated manhole door is installed in each end of the drum. The drum is
fitted with internal fittings comprised of: Feed distribution pipes, directional baffles, tube separators
and corrugated plate baskets and mesh to obtain the following:1.
An even distribution of the entering water and steam mixture over the full effective length of the
drum.
2.
Uniform drum metal temperatures during rapid increases and decreases in boiler output.
3.
Stable water level during rapid and wide variations in load.
4.
An arrangement whereby the efficiency of steam separation is not affected by wide variations in
load or drum water level.
8
STEAM AND WATER FLOW THROUGH THE STEAM DRUM:
The water and steam mixture from the water wall is introduced at the rear of the drum. The
mixture then enters the separators, which are arranged in three rows across the length of the drum. A
separating force is created by vanes which gives the mixture a spinning action as it travels upward
through the separators. The concentrated layer of water, flowing upward along the surface of the
primary tube, is schemed off at the top and directed downwards through the outer concentric tube,
and discharged below the water-line with a minimum of disturbance to the water level.
PRINCIPLE OF SEPERATOR: The steam and a small quantity of entrained water continue upward
through a steam collector nozzle and turn horizontally into the secondary separator. This consists of
closely spaced corrugated plates and is designed to force out the entrained water from the steam.
The velocity at this point is relatively low and the water cannot be re-entrained from the
wetted surfaces and runs off the plates through opening located away from the steam outlets. The
steam then leaves the separators and flows upwards through the steam dryers located at the top
centre of the steam drum.
The internal feed pipe is positioned below the water level and is arranged to feed directly over
the down comers in such a way that mixing with the re-circulated saturated water in the drum occurs
just at the down comer inlets. The steam therefore does not come into contact incoming feed water
and no measurable condensation occurs.
Initially bi-colour Gauge glass was provided for the drum level indication and control. The
same is changed to hydra-step technology.
BURNERS AND BURNER BOXES:
Four pulverised fuel burner boxes are provided, incorporating eight lighting-up tip shut-off recirculating pressure jet oil burners.
The burner boxes are arranged one in each corner of the combustion chamber per mill group.
The burners directed on to a firing in the furnace plane and by this method of tangential firing, high
turbulence is maintained in the furnace.
Each burner box accommodates four coal burners and two oil lighting-up burners. The burners
are of the tilting type for control of the steam temperature.
FUEL OIL SYSTEM:
Storage Tanks
-
a. 2 x 300 Tonnes capacity for Dissolve or equal for st. I
b. 2 x 500 Tonnes capacity for Dissolve or equal for st. II
Transfer pumps
-
Two off each 30,000 kg/h capacity-centrifugal type
Pressure pumps
-
Three of each 13,500 kg/h capacity-screw type
Provisions only for heaters.
OIL LIGHT UP EQUIPMENTS:
➢
➢
➢
➢
➢
2 Storage Tank of capacity 300 Tonnes each are provided.
3 Fuel oil pumps of capacity 30000 Kg/hr at a discharge pressure of 3.5 Mpa are provided to
supply the fuel oil to the burners.
8 Oil burners (2 at each corner) of capacity 770 kg/hr and working press of 3.1 MPa are provided
with a minimum oil press for atomisation at 2.4 MPa.
2 Nos. Ignitor Air Fans to supply air at 1960 Pa are provided.
Gas Electric Burner Igitors working at 0.3 bar (gauge) gas supply press are provided to ignite
the fuel oil burners.
9
a.
MILLING PLANT:
The boiler unit is provided with four pressurised type mills. Each mill is driven by a high torque
constant speed motor, the motor being directly coupled by means of a flexible (Bibby) coupling to the
input shaft of the mill gear box.
The coal to be ground is fed to the mill from the top and falls on to the grinding table, which is
mounted on the gear box output shaft and rotates at constant speed. The coal is pressed under the
two grinding rollers which grind the coal. It is whirled round and carried upwards on a strong air
current to leave the mill. The hot/cold air mixture of temperature above 75-100 OC is supplied by the
Primary Air Fan to lift and supply the pulverised fuel to the coal burner.
THEORY OF CLASSIFICATION:
The classifier which is mounted on top of the mill, allows only particles up to a certain size to
leave the separator. The oversize material returns to the grinding table for further grinding.
The fine particles of the pulverised fuel leave the classifier as a fuel/air mixture and are
conveyed via the pulverised fuel pipes to the burner. The hot air sweeping through the mill from the
primary air fans dries the coal in addition acting as the carrying agent.
The layout of the piping is such that each mill will supply four burners comprising one
complete horizontal bank of burners simultaneously so that perfect balance of firing is obtained, and
the balance will not be upset when a mill group is taken off or put on load.
Two-way distributor pieces (Riffle boxes) are incorporated in the pipe work. They are specially
constructed with internal riffles, so that a coal and air mixture is evenly distributed to each branch and
burner.
DETAILS OF LOESCHE ROLLER MILL
INTRODUCTION:
LOESCHE roller Mills are sophisticated systems for pulverizing.
The description which follows, refers to drawing number HPS/WAPCOS/04
OPERATION:
The raw coal is fed from the coal feeder through the feed pipe onto the centre of grinding
table, which is firmly bolted to the gear box palm flange and revolves at a constant speed. As a result
of the rotary motion of the grinding table, the coal is evenly distributed over the grinding table by the
two cone-shaped grinding rollers which roll, over it. Pressure as well as friction plays their part in the
process of grinding which is rendered particularly effective by the hydro-pneumatic spring action
applied to the rollers. When the rollers roll onto the coal, the piston of the loading cylinder, actuated
by rocker arms and spring rods, is moved upwards and displaces the oil from the cylinder into
nitrogen-filled hydraulic accumulators, compressing the gas and making it act as a spring. A balloon
shaped “diaphragm” separated the nitrogen from the oil.
The ground coal is flung outwards by centrifugal force and spills over a dam ring of predetermined height into the area above the louver ring surrounding the grinding table. From there it is
blasted upwards by the stream of hot air, from the primary fan through the mill body annulus into the
classifier. In this stream of hot air, the intimate contact between the ground coal and the hot air
evaporates moisture, reducing it to a content of approximately 0.5 %.
Depending on how it is set, the classifier will reject ground coal which has not been reduced to
the desired size. Such rejected coal is returned via the oversize return duct to the grinding table for
further grinding. Meanwhile the finished product passes the classifier at the desired degree of fineness.
From the classifier outlet the pulverised coal is conveyed by the hot primary air through the pulverised
fuel piping to the corner burners.
The mill is driven by a three-phase motor through a 2-stage bevel/spur gearbox. The drive is
by squirrel-cage induction motor, started and stopped from the central control panel. In the gearbox, a
hydro-dynamically lubricated thrust bearing takes up the forces exerted by the grinding rollers
hydraulically lifted, the mill may be started directly, even when filled with coal.
10
MILL BASE:
CONSTRUCTION:
The assembly is made up of the boxed base frame (102), with primary hot air duct
connections (836) and ducts for sealing air which are all integrated into the main frame.
HOT AIR SUPPLY:
The hot primary air ducts are bolted to the base connections from where the hot air is directed
into the annular louver ring positioned around the grinding table. The bottom of the air compartment
forms a chute, allowing foreign bodies to collect before discharge from the mill base.
On the inside of the hot air duct adjoining the grinding table is a seal which is fed with sealing
air from the seal air fan via internal air connecting duct.
CONNECTIONS FOR SEALING AIR:
This mill is designed for direct firing of P.F. and is operated at higher than atmospheric.
Pressure seals are therefore required wherever moving parts of the mill pass to the outside through
openings in the casing. Since such seals should preferably not be subject to wear whilst operating,
sealing air is employed. It is fed into specially designed chambers close to the places to be sealed.
Since the sealing air is under higher pressure than that found in the grinding space, sealing air will
flow into the mill and to the outside.
On a top corner of the mill base a sealing air connection (120) is provided and is supplied from
the seal air fan. Seal air ducts are formed integrally with the base fabrication. Flexible hoses (1013) in
turn connect the shafts of the rocker arms to these ducts.
A cast iron air manifold surrounds the neck of the grinding table. This is supplied with cold seal
air from the duct (837) through the pipe connection.
OPERATION:
The mill base has two functions. It supports the mill housing and classifiers and grinding rolls
while conducting the hot air to the Louvre ring which surrounds the grinding table (located in the mill
body above the air chambers).
Grinding forces are transmitted from the rollers to the grinding table, and then to the mill
gearbox output shaft and to the base. Forces originating from the rocker arms and hydro-pneumatic
units will also be transmitted to the mill base.
The cross sectional area of the hot air passage is so dimensioned that it offers as little
resistance as possible to the flow of hot air and largely reduces the kinetic energy of the hot air stream
by converting this into static pressure. This ensures optimum and even distribution of hot air through
the Louvre ring into the grinding space without substantial ‘streaming’.
Foreign bodies ejected through the Louvre ring by the rotating table as well as any coal which,
in the event of electricity supply failure, falls outside the table ring are caught by the scrapers below
the grinding table and thrown into the reject space at the bottom of the air compartments.
Suitable liners are provided at the reject openings to obviate air duct plate wear.
GRINDING ROLLERS:
Number and Arrangement:The mill is fitted with two rollers spaced at 180 deg. Each roller ism attached to a rocker arm.
With no coal they are supported on the grinding table with roller shafts inclined at 15 deg. to the
horizontal.
11
HYDRO-PNEUMATIC SPRING SYSTEM:General:
The mills are fitted with a hydro-pneumatic spring system operating on the grinding rollers.
This system is actuated from the hydraulic cabinet placed next to the mill. In the cabinet an oil
pumping unit is mounted which supplies high-pressure hydraulic oil to the spring system. The pump is
stopped and started by high and low limit pressure switches connected to the H.P. line.
Operation:
With the mill in operation, the oil pressure on the piston rod side of the cylinders forces the
pistons of the cylinders down and consequently the grinding rollers are pulled down onto the grinding
bed on the table via spring rods and rockers arms.
During the process of grinding, the rollers move up and down through a slightly curved arc due
to the non-homogenous nature of the coal bed and the pistons follow such movement. When coal
forces the roller up, oil is discharged from the piston rod side cylinder space into the hydraulic
accumulators (1322), where the nitrogen-filled rubber bladders of the hydraulic accumulators are
compressed; the nitrogen thus acts as a spring.
In order to raise the grinding rollers before the mill is started, control valves in the hydraulic
cabinet arrange for the oil to be pumped into the space below the pistons. Oil then flows out of the
piston rod space into the hydraulic accumulators. The roller with lowest oil flow resistance will be
raised first until the movement is arrested when the piston contacts the cylinder end. The second roller
is then raised until the rocker arm actuates an electric switch which stops the raising action.
The rollers are again lowered from the hydraulic cabinet by switching the control valves back
for normal position.
HYDRAULIC ACCUMULATOR:
The hydraulic accumulator of the hydro-pneumatic spring system is a nitrogen-filled bag type.
Its functioning and the length of its service life depend decisively upon the correct ratio between
nitrogen filling pressure and the hydraulic operating pressure.
The maximum filling pressure of the nitrogen must not exceed 0.8 of the minimum hydraulic
operating pressure (to be read off the pressure gauge on the hydraulic cabinet). The minimum
nitrogen filling pressure is 0.25 of the maximum hydraulic operating pressure with the mill operating.
If the pressure is not kept within these limits, there is a danger that the accumulator bag may be
caught and damaged by the valve at the bottom of the accumulator, allowing the nitrogen to diffuse
into the oil and rendering the accumulator inoperative.
REJECT SYSTEM:
General:
The reject gates are fixed to the hot air compartment of the mill and comprise reject box
(833), shut-off doors (834) and access doors (835). The reject gates make it possible to extract
foreign bodies and waste material from the mill into the reject boxes. The reject boxes must therefore
be sealed off probably from the mill internal air pressure when the rejects are removed to the outside.
12
CLASSIFIER:
Description: A double-cone static classifier is mounted on top to the mill body.
The Classifier comprises:a.
b.
c.
d.
e.
Outer housing, flange connected to the mill body.
Concentric guiding cone.
Extension hopper mounted below guiding cone.
Inverted cone attached to the raw coal pipe.
Seal flaps supported from inverted cone. Flaps prevent P.F. laden air from bypassing swirl
vanes.
f. Adjustable swirl vanes which effect separation of fine and coarse coal particles.
g. The raw coal feed pipe leading raw coal from the top of the mill into the grinding space.
h. The classifier outlet duct from where the P.F. is conveyed to the burners.
Operation:
The ground P.F. from the grinding section is conveyed by the blast of hot air in a swirling
motion through the annular spaces between the outer housing and guiding cone to the top of the
classifier The P.F. laden warm air flows past the swirl vanes sufficient swirl is imparted to it to separate
out oversize material before leaving the classifier. After another turn in direction via the outlet to the
burners, the coarse coal separated out by the swirl and direction change and acceleration then swirls
down along the guiding cone towards the seal flaps. The seal flaps, which are gravity loaded by
counter weights, open when sufficient coarse coal is collected to overcome the counterweight effect
and discharge coarse pulverised coal onto the grinding area together with the raw coal flowing through
the central feed pipe from the feeders mounted above it.
The coarse coal is then further reduced in size together with raw coal and is carried up in the
hot air stream as before.
The seal on the raw coal side is affected by the head of raw coal above the feeder.
During commissioning, the swirl vanes position is set to an optimum angle by sampling of P.F.
extracted from the P.F. pipes during the various loading conditions of the boiler/pulverisers. The vane
angle should be equalized and a record dept of the setting for future reference after maintenance.
Loss of Performance:
Due to natural wear of the grinding parts, a gradual loss of performance takes place which
depends largely on the coal quality. The main reason for the decreasing output is due to an increase in
the gap between roller and table due to wear of these parts. Readjust the roller height. Ensure that
the grinding rollers do not touch the grinding tables. The grinding pressure would not be affected by
such re-adjustments.
PULVERISED FUEL EQUIPMENT
COAL FEEDERS:
Manufacturer:
Type
Number per Boiler
Type of Drive
Range of Capacity kg/hr
STOCK EQUIPMENT
VOLUMETRIC BELT CONVEYOR
4
VARIABLE SPEED EDDY CURRENT CLUTCH
33403 to 5344
Unit
Number of Feeders I/s per Blr
Electric input to Motor
Boiler
M.C.R.
3
1.4
Nos
kW
13
80%
M.C.R.
3
1.2
70
MCR
3
1.1
%
Max
Pulv
capacity
3
1.5
PULVERISERS:
Type
Number per Boiler
Type of Drive
Minimum No. of Mills required
LOESCHE LM 16/1220 D
4
DRIVE COUPLD CONSTANT SPEED MOTOR
for stable ignition without oil burners --- 2
Unit
Number of pulverisers I/s per Blr
Output of each pulveriser
Electric input to Motor
Temp. Of drying agent
Nos
Kg/sec
KW
O C.
Boiler
M.C.R.
3
5.345
190
205
80% M.C.R.
3
4.355
172
194
70
%
MCR
3
3.851
158
183
Max Pulv
capacity
3
6.417
214
210
COAL BURNERS
Manufacturer
N.E.I.(I.C.L. derby)
Type
TILTING TANGENTIAL
No. Per Boiler
16
Position
4 in each corner
Capacity of burners
Maximum kg/hr --5775,
Minimum kg/hr --1996
1 Seal Air Fan per coal mill of 29.2 KW capacity is provided for sealing the coal mill.
SAFETY VALVES
Manufacturer : DEWRANCE
DRUM SAFETY VALVES :
Type
Size
Number
Total Capacity kg/h.
Setting pressure, MPa
MAXIFLOW
76.2 and 63.5
2 and 2
244014 and 154800
11 x 2 off
10.9 x 2 off
SUPERHEATER SAFETY VALVES:
Type
Size
Number
Total Capacity kg/h.
Setting pressures, MPa :
Without Electric Assistance
With Electric Assistance
MAXIFLOW
63.5
2
109428
9.7
9.6
SOOT BLOWERS
Manufacturer
Total Steam consumption per cycle
FOREST INTERNATIONAL
4500
Furnace
Type
Number per Boiler
Blowing press at the nozzle MPa (Gauge
Steam Consumption kg/hr
Effective blowing radius (~)m
F144
6
1.35
282
2.5
14
F356
2
1.257
761
1.8
F356
1
1.6
962
1.8
Superheater
F356
F356
2
2
1.1
1.0
1346
1150
1.8
1.8
PRIMARY AIR FANS
Unit
Number of Fans I/s per Blr
Air Temp at Fan inlet
Press at inlet to Fan
Press at outlet of Fan
Electric input to Motor
Max press rise across the fan
Max electrical input to Fan
Boiler
M.C.R.
3
205
981
8581
126
Nos
C.
Pa
Pa
KW
mm wg
KW
O
80%
M.C.R.
3
194
637
7746
120
70 %
MCR
3
183
490
7375
110
9880
163
Max Pulv
capacity
3
210
981
10860
163
DRAUGHT PLANT
2 NOS. INDUCED DRAUGHT FANS – DUTIES PER FAN:
Unit
Volume of Gas at fan inlet
Temp of Gas at fan inlet
Electric input to Motor
Boiler
M.C.R.
104.67
140
280
M3/sec
O
C.
KW
80%
M.C.R.
83.15
131
210
70 %
MCR
72.7
126
180
Max Pulv
capacity
120.36
140
383
2 NOS. FORCED DRAUGHT FANS – DUTIES PER FAN:
Unit
Volume of Air at fan inlet
Temp of Air at fan inlet
Electric input to Motor
Boiler
M.C.R.
82.1
49
310
M3/sec
O
C.
KW
80%
M.C.R.
73.79
58
260
70 %
MCR
68.75
62
190
Max Pulv
capacity
94.4
49
471
@@@@@ $$$ @@@@@
(B)
TURBINE PLANT:
The four 120 MW condensing turbo-sets No. 1 to 4 for the Hwange Power Station of Electricity
Supply Commission, Salisbury, Zimbabwe, were built in 1980 and 1981 by Maschinen-fabrik AugsburgNurnberg Aktiengesellschaft, Nurnberg Works. The turbine is of the tandem compound axial flow
impulse type rigidly coupled to hydrogen-cooled Atlantique generators. For cross-section of turbine,
please refer drawing No. HPS/WAPCOS-05.
Each turbine comprises an HP section and a two-flow LP section. The live steam enters the
turbine at 8.4 MPa, 510 OC and expands in the 16 stages of the HP section to about 0.36 MPa, 140 OC.
Steam for feed heating and deaerating is taken from the HP section through three bled steam points.
At the end of the HP section the steam passes through two cross-over pipes to the LP section. In the
LP section the steam expands in two five-stage flows to the condenser pressure of 12 kPa. Two bled
steam points are provided in the LP section for feed heating. The exhaust steam is condensed in a
surface condenser designed for a circulating water temperature at 32 OC. The circulating water is recooled in a wet cooling tower.
Each turbo-set is equipped with a mechanical hydraulic control system, which regulates the
steam supply to the turbine via two groups of valves, one at each side of the turbo-set. Each valve
chest is provided with an emergency stop valve and two control valves. The steam admission to the
emergency stop valve is vertical from below and the inlet pipes from the control valves to the HP
casing are short and flexible. Both valve chests are supported on swing links and are able to follow the
heat expansion of the casing.
15
The two rotors of alloy steel are of the integral type i.e. shaft, discs and coupling flanges
machined from a solid forging. The wheels are discs of uniform thickness. In order to reduce end
thrust, the wheel discs of the HP rotor are provided with axial holes (Pressure equalising holes). The LP
rotor is of balanced thrust type and therefore no holes are provided. The two rotors are rigidly coupled
together by means of flanged couplings and each mounted in two plain bearings.
The turbine and Generator bearings are fitted with additional HP lubrication for starting and
rundown. The vibration behaviour of the individual rotors and the rotor line has been carefully tuned.
There is an adequate margin between the coupled critical speeds of the rotors and their operating
speed. The arrangement of the thrust bearing in the front bearing pedestal results in a favourable
differential expansion behaviour of the moving parts relative to the casings. The rotor position, as well
as the expansion and vibration behaviour of the rotors is monitored continuously by means of
electrical instrumentation.
The HP casing consists of heat-resistant cast steel and is of two shell construction (nozzle
chest plus 3 diaphragm carriers) which, due to the graduation of pressures and temperature results in
a substantial reduction of mechanical and thermal stresses in the casing walls. The LP casing which is
welded throughout is braced by struts inside. The exhaust casing is welded solidly to the spring
mounted condenser.
All bearing pedestals are solidly fixed to the foundation. The anchorage for the absolute
expansion of the HP casing is at the HP/LP turbine bearing. From there the HP casing and the
thrust bearing, which is a sliding fit in the stationery front bearing pedestal, move forward. The HP
casing and LP casing are not coupled, the latter being individually located near the first LP flow.
Steam is admitted to the single row HP control stage through 4 nozzle groups. All guide vanes
and moving blades are made of stainless steel. All moving blades have a wrought profile and fixing in
the wheel discs is by means of pinned tenon roots. The HP moving blades have integral shroud decks
and tenon roots. The shroud decks are in solid contact with each other to form a continuous shroud
ring over the steam passage. The moving blades of the LP exhaust stages are of the cantilever type
and have a taper profile. To avoid detrimental vibrations, these blades are tied or around. Tying is by
means of arch-shaped elements braced in a hole in each air foil and warranting stiff bracing in the
circumferential direction.
The nozzles of the HP control stages are machined from solid blanks. All other diaphragms are
of welded construction. The HP guide vanes are milled and the LP guide vanes are stainless steel
pressings.
The shaft glands of the casings and the diaphragm seals are of the non-contacting radial
clearance labyrinth type, where the seal strips of the stationary parts register in turned grooves in the
rotor. The use of spring backed seal ring segments effectively prevents damage to the shaft glands
and seals. The automatic seal steam supply is controlled by a pressure and temperature control loop.
Vapours developing at the shaft glands and valve stem glands are removed by an exhauster
and discharged separately into a vapour condenser.
The mechanical/hydraulic control system provides speed control during non-synchronised
operation of the turbine. After synchronisation, it serves for load control and frequency stabilisation.
Further more, there is a main steam control loop and a vacuum limit pressure control loop, which can
be activated via the set point adjusting motor of the contr9ol system. The speed governor is of the
proportionate action type and geared to the turbine shaft. Its output is transformed into a hydraulic
control signal and transmitted to the hydraulically operated control valves.
16
A hydraulic protection and test system with duplicated trips monitors essential parameters and
permits all protective devices including the emergency stop valves to be tested during operation.
Superimposed on it is a single-channel electrical protective system, also arranged for line testing, for
the parameters of the other criteria categories. The transmission of the trip signal to the emergency
stop signal is hydraulic. Operation of the control and emergency stop valves is fail-safe with opening
being effected by pressure oil acting against the force of the springs. If the oil pressure fails, all valves
will close the air control bleed valves have the emergency trip signal applied by an oil/air relays.
The oil supply for the turbo-generator in normal operation is maintained by the main oil pump
which is geared to the turbine shaft and which has oil delivered to it by a transfer pump. The oil flow
intended for bearing lubrication is passed through an oil turbine, which drives the transfer pump, to
reduce the pressure to the level required in the bearings. The bearing oil and control oil flows are
passed through a fabric insert type filter. Two changeover type full-flow oil coolers are provided for
cooling the bearing oil.
During starting of the turbo-generator, 2 AC operated auxiliary oil pumps deliver oil to the
bearing oil and control oil circuits until the main oil pump reaches its full output. The auxiliary bearing
oil pump is also automatically cut in if the oil pressure downstream of the main oil pump or the bearing
oil pressure should fall below a predetermined limit. If the pressure falls below the predetermined limit
for the bearing oil pressure, the DC operated emergency oil pump would be started automatically. Two
HP gear oil pumps are provided to supply oil at 150 bar to produce a hydrostatic lift under the turbine
and generator shaft journals during starting and during operation of the turning gear.
With the exception of the main oil pump, which is geared to the turbine shaft, all oil pumps are
accommodated, in an oil room which also houses the oil tank, the oil coolers, oil filters and oil purifying
plant. Grouping these items together facilitates servicing and maintenance of this group.
To reduce heat radiation losses, the high pressure casing, the valve chests and the main steam
inlet pipes are provided with sprayed insulation. The crossovers to the LP turbine are covered with
matting for insulation.
The control valve chests and the HP casings can be heated to permit a rapid start up of the
turbine from cold or semi-warm condition. For this purpose, steam is introduced through a heating
pipe into the two control valve chests whence it flows through the steam admission pipes into the HP
casing. In this manner all sections of the casing are subjected to intensive heating before the turbine
is started. This results in almost uniform axial expansion conditions of the rotor and casing and largely
eliminates the risk of any rubbing.
The heating steam is steam at a pressure of 1.5 MPa (abs.) and a temperature of 340 *C from
the auxiliary steam header. The flow rate is roughly 6 ton/h, so that with a good vacuum the turbine
speed remains beneath 1000 rpm.
The supply of steam from the auxiliary steam header is controlled by a manual isolating valve,
the steam flowing via motorised valve SA11 SO52 trip valve SA11 SO51 and check valve SA11 S552
to the control valve chests on the left and right of the HP casing.
A check valve SA11 S551 is arranged downstream of the heating valves to protect the heating
pipe system against the entrance of steam from the turbine. An angle pattern safety valve SA11 S550
is arranged in the heating pipe line as a further safeguard in the event of any leakage of the heating
valves. The safety valve is set to open at a certain pressure rise to 18 bar and only has a warming
function. On response do not fail to look for and remedy the trouble.
=====#=====
17
CONDENSER DETAILS
(For cross sectional details of condenser, please refer drawing No. HPS/WAPCOS-06)
a) Steam Space
The condenser shell enclosing the steam space is rectangular structure made of steel plates
in welded construction.
The tube plates are made of muntz metal.
The condenser tubes are positively expanded into the tube plates. A controlled torque
expander is used to expand the tubes into the tube plates. The condenser shell is welded to the
exhaust neck of the turbine. The condenser is mounted on spring supports for freedom of vertical
expansion under heat.
The lower part of the condenser shell is the hot-well, which is of extra large size to hold a
larger quantity of condensate under abnormal operating conditions without flooding the condenser
tubes and impairing steam condensation.
The condensate collecting in the condenser shell is discharged at the bottom through the
condensate' suction connection ahead of which a strainer is located in the condenser shell to prevent
any foreign matter from gaining access through the suction pipe into the pumps.
The steam space of the condenser has a number of connections, nozzles and tapping points
for the admission of extraneous steam, condensates and make-up water for monitoring and
maintenance purposes.
Above and below the tube bundle, there is a manhole in the steam space for cleaning and
inspection work. The manhole covers are hinged and thus easy to open.
The air collecting in the condenser is discharged through air cooling bundles arranged at the
centre of the two tube nests. The two air cooling bundles are arranged such that the air flows from the
tube nest carrying the warmer cooling water via the air cooling bundle to the tube nest carrying the
colder cooling water.
At the side of the condenser there are two flash boxes. Each flash box has a steam side
connection on the condenser neck and a small condensate connection on the hot-well via a syphon
loop. One flash box takes the drains and vents of the heat exchangers of the feed heating system. The
other flash box takes the drains from the turbine steam pipes. Where hot steam is admitted into the
flash boxes, they are equipped with a condensate injection system.
The extraction pipes of the last extraction stages are taken from the low pressure turbine
through the condenser neck to atmosphere. The penetration of this pipe through the condenser shell is
of double pipe design for thermal flexibility.
The condensate level at the bottom of the steam space is indicated outside by a solenoid
controlled water level indicator. The water level indicator is connected to a collecting pipe to which also
a number of level monitors and a level Transducer are connected. The collecting pipe is connected at
the top and bottom to the condenser shell by one shutoff valve each. These shut off valves and filling
connection enable the level monitor to be checked at any time.
b) Water Space:
The surface condenser is divided on the cooling water side for one water flow and two water
passes, The two tube bundles for each water pass are arranged side by side. Each tube has a separate
rectangular water box at the front and rear made of steel plate, in welded construction. The front
boxes have cooling water inlet and outlet connections at the bottom. The rear water boxes are
connected on the cooling water side.
Each water box is equipped with an adequate number of manholes which are fitted with hinged
bolts and hinges to facilitate access for maintenance purposes.
For positive venting all water boxes are equipped with vent connections at the highest point to
warrant a satisfactory flow of cooling water through all condenser tubes. Each water box is also
equipped with a drain connection at the lowest point.
18
c)
Condenser supports
To accommodate thermal expansion, the condenser is placed on springs which are capable of
taking up expansion in the vertical and horizontal directions. The springs are of the cup type (Belleville
washers) placed in pairs against each other.
The design of the condenser supports is in such a manner that in normal operation a down pull
acts on the turbine exhaust casing. Further, allowance has been made for the fact that when the
condenser water spaces are empty, the uplift of the springs should not exceed the deadweight of the
turbine exhaust casing so that a load is maintained on the turbine deck.
The spring supports are provided with devices for blocking the spring columns upwards
and downwards in order to keep away from the turbine excessive down pulls when, for instance,
the steam space is filled with water. Adjusting screws fitted in cast base plates facilitate
alignment of the condenser relative to the turbine and also make it possible to replace individual
cup springs at any time.
Deaerator Details (Refer Drawing No.
HPS/WAPCOS-07)
The deaerator comprises a heating and deaerating unit placed over the water reserve,
composed of three parts:
•
an upper stage in which the water is sprayed through a suitable number of nozzles,
heated, and partially deaerated,
•
an intermediate stage with one perforated tray, which completes the heating of the
water,
•
a lower stage which completes the deaeration by bubbling steam through the previouslyheated water. The equipment for inserting the steam is so designed as to increase the
period of contact between the water and the steam.
This deaerator is of the counter-flow type
The feed water spray system consists in a supply casing welded on the upper inside part
of the shell, The casing is provided with 8 spray nozzles, The perforated tray consist in two
longitudinal sections 4000 x 800 mm with perforated area 430 mm width on either side is
provided with 12 mm diam. holes.
The ratio of total area/hole= 0.3. The upper part of the shell is provided with two lateral
longitudinal vertically placed" perforated sheets (one on each side) with 12 mm diam. holes and
30% drilling area are designed·, to make the steam bubble into water to be deaerated.
Both ends of the shell make up steam casings intended to distribute the heating and:
deaerating steam introduced into the shell by one supply nozzle on each shell end. The steam is
inserted further to get in touch with water into two lateral longitudinal casings
The daerator is associated with the storage tank by:
•
one daerated water outlet nozzle (E.D. 400mm)
•
two balancing steam nozzles (E.D. 900mm)
The three nozzles welded to storage tank shell form the daerator system as well.
The storage tank itself is supported by two ground located cradles. The daerated water
runs out from daerator into storage tank through two pipes with outlets reaching the bottom
tank on either of the shell.
By contrast the feed water outlet is located nearer to the shell midpoint. This layout improves
the feed water blending in the tank. The deaerating system includes an electric auxiliary device
running automatically during off-load periods.
It consists in:Horizontal centrifuge recycle pump 1450 rpm (48,000 KG/H at 18 m of generated
head) with a driving motor 5.5 KW.
-Electric resistance heater 12 KW in the pump outlet pipe.
-Circulating pipe with suction in the deaerator storage tank and discharge connected to deaerator
upper part including one spray nozzle of the same type and size as the spray nozzles of the main set.
19
Operating Description
The deaerator plays multiple role in the power station unit performance:
▪
▪
▪
▪
▪
▪
▪
It eliminates all non-condensable with the object of avoiding corrosion damage to the steam
generator
It heats the feed water.
It provides a water reserve for the feed water circuit
It provides the necessary positive suction head for the boiler feed water pumps.
it recovers HP water drains.
it collects feed pump balance leakages
it collects feed pump leak-off valve discharge when running at minimum flow.
The steam supply system to daerator depends on the case of operation:
During the stages of rise to the operating temperature and during start up the auxiliary
steam circuit will provide the steam supply. The recycle pump is in operation. The motorised vent
valve is open to the atmosphere.
▪
When the turbine reaches about 10% of nominal load i.e. as soon as bled steam (5) pressure
reaches 1.3 bar absolute (0.13 M Pa) the auxiliary inlet steam control valve closes. and recycle
pump stops and the bled steam (5) inlet control valve opens. The motorised vent valve to
atmosphere shall be closed and the vent valve to condenser opens.
▪
As and when the turbine load increases bled steam (5) supply is gradually replaced by bled
steam (3). As soon as the pressure of bled steam.(3) reaches 1.4 bar absolute (0.14 MPa) - at
about 40% of nominal load - the bled steam (3) only provides the steam supply to deaerator
while the bled steam (5) fully .supplies the HP heater 2.
The role of recycle pump/electric heater consists in keeping the deaerator temperature up to
100·C thus the pressure up to atmospheric during off-load period to avoid air inlet into de aerator
system.
The desuperheater manifold spray nozzle operates when superheated steam is introduced into
deaerating system. The temperature controller with a set point at 200·C acts on spray nozzle feed
water control valve. Under normal operating conditions with saturated heating bled steam 3, the spray
nozzle control valve is closed.
Performance particulars at 120 MW:
▪
▪
Maximum oxygen content of the condensate
at the deaerator outlet at continuous
maximum rating of the tubro-gen. set.
Storage capacity at normal working level
Feed water
▪
▪
▪
▪
▪
Feed water flow per spray nozzle
Pressure drop through spray nozzle
Inlet temperature
Outlet temperature
Operating pressure
0.007 ppm
74200 Kg
48,000 Kg/h
0.064 MPa
114.5 °C
138.3 °C
0.3447 MPa abs
Heating Steam
▪
▪
▪
▪
▪
Auxiliary steam /start up
Max flow
Max pressure upstream control valve
Max temp. before desuperheater
Desuperheated steam temp
6000 Kg/hr
1.5 MPa abs
350 °C
200 °C
Bled steam 3/Normal operation:
▪
▪
Flow
Pressure at heater
Saturated Temperature
17460 Kg/hr
0.3447 MPa abs
138.3 °C
20
a.
REGENERATIVE FEED HEATING
I. Condensate /Feed water flow from Condenser to Boiler:
The steam from the exhaust of the double turbine flow L.P. Turbine enters the condenser.
The exhaust steam is condensed in the surface condenser by circulating water. The condensate is
collected in the hot well.
The condensate from the condenser hot well is then extracted by 2 Nos. 100% capacity
condensate extraction pumps. Only one .pump is normally in service and the other is standby.
The discharge of the' condensate extraction pump goes through the coolers of the main
ejectors, for extracting the heat in the steam used in ejectors. The steam to these main ejectors
is tapped from auxiliary steam distributor. In addition to three 50% capacity 2 stage main
ejectors, a starting ejector is also provided to pull vacuum during starting-up of the machine.
Steam to starting ejector is also tapped from the auxiliary steam distributor.
The condensate is then passed through gland steam condenser (G.S.C). The penultimate
recesses in the shaft seals of both H.P. & L.P. turbines are connected to the shell of gland steam
condenser, in which a small vacuum is maintained by an exhauster. Hence the leak off steam
from this part of the glands is drawn into the shell of G S C, which is condensed by the
condensate flowing through the tubes under the influence of condensate extraction pump. A bypass line to gland steam condenser is also provided on the condensate line to by-pass the
condensate during higher loads when the condensate flow is more than what can be passed
through tube nest of G S C without undesirable pressure drop.
After the gland steam condenser, a line is provided which can re circulate the water back
to main condenser. This is mainly intended for recirculating the condensate from this point back
to hotwell so as to maintain a minimum flow through the ejectors and G.S.C., without affecting
the hot well level, during low load conditions when the condensate flow drops due to less steam
being condensed in the condenser. Connections are also provided to rout the water through
condensate polishing plant and for discharge to waste during start - up when water quality is not
acceptable. A line to send the water to R. F. W. tanks is also provided.
The condensate further, flows to LP heaters I & II via drain cooler RN 108, where the heat
from the drain of LP heaters is extracted by condensate. The LP heaters are two in numbers and
the extraction steam for these is bled from LP turbine. The LP heaters are of vertical type with U
tubes design. A common by-pass line for both LP heaters is provided. The drain formed due to
condensation of extraction steam, in the shell of the LPH-II, is taken to LP heater-I and that of
LP-I goes to condenser through the drain cooler RN 108. This cooler has arrangement for by
passing of condensate as well as drain.
After the LP heaters the condensate further goes to Deaerator. The deaerator performs
two functions viz, removing the oxygen from water as well as heating of the water. The steam for
the dearator can be taken from three sources. They are (1) from H P turbine outlet for normal
load (2) from the extraction steam line of HP heater II during low load' operation and (3) from
auxiliary steam header during starting.
The heated/deaerated condensate then enters the storage tank of deaerator and forms the
feed water to boiler. The feed water from storage tank is coming to boiler feed pump. Two Nos. 100%
capacity boiler feed pumps are provided of which one is running and the other is standby. Before the
discharge valve of the pump, a recirculation line is provided to take a certain quantity of water back to
storage tank. This is meant for providing a minimum flow through the boiler feed pump, during startup and low load operation. The valve on recirculation line closes after a minimum flow is established
on boiler side. Balance leak off lines from the pump are also taken to feed water tank. Strainers are
provided on suction lines to the boiler feed pumps.
The water from the Boiler feed pump then flows to HP heater I and HP heater II. The HP
heaters are of vertical type and of U tube design. The extraction steam for these heaters is bled from
HP turbine. Individual by pass on feed water side is provided for these heaters, in case of tube
leakage. Drain of HP II is cascaded to HP I and then to Deaerator under rated load or above certain
load conditions when the pressure in the HP heater I is adequate to send the drain to deaerator. The
drain of these HP heaters flows to condenser under low load conditions.
The feed water from the HP heaters then enters the Boiler in the economiser via feed control
station.
21
BOILER FEED PUMPS:
Old Boiler Feed pumps are being replaced by new Clyde Union (Weir pumps) having a
maximum feed flow of 559 M3/hr at a head of 1311 Mtrs, Suction pressure- 15 Bar, Discharge
pressure- 161.3 Bar. The motor is having a capacity of 2875 KW at 3.3 KV having full load current of
556 Amps.
b.
GLAND SEALING SYSTEM (REFERTO DRAWING NO.
HPS/WAPCOS-08)
1. FUNCTIONS OF BASIC LAY OUT
The gland steam system is designed, firstly, to prevent the ingress of air into those of the
turbine in which a vacuum exists and, secondly, to prevent leakage of steam from all shaft and
spindle penetrations into the turbine bay. In addition to the steam piping (seal steam, leak steam
and vapour exhaust circuit) this involves a source of seal steam, and appropriate control system
for pressure and temperature which acts upon the gland steam system as required during the
various modes of operation, a vapour exhaust system as well as suitable drain devices.
The turbine shaft glands are provided with a number of inner annuli through which most
of the leak steam flows through the pipes to the main discharge pipes of the turbine casings .All
shaft glands have two low-pressure annuli at their extreme ends, the penultimate chamber in
each case being connected to the gland steam system in which a slight positive: pressure of
about + 10 mbar is maintained; the outermost chamber are maintained at a slight negative
pressure of about -10 mbar, which is maintained by the vapour exhaust system which
incorporates a vapour exhauster.
The valve stem seals have low-pressure annuli arranged and connected in a similar
manner, with exception of the emergency stop valves. Because the latter are never exposed to a
vacuum, they are not steam sealed; instead they have a single annulus through which the steam
leakage is extracted into vapour system. All valve stems are back-seated to prevent leakage of
steam in the fully open position.
As a result there is no steam leakage of the emergency stop valves in normal operation
the control valves produce gland steam from the time the turbine starts, the rate of steam
depending on the live steam pressure. By successive opening of the control valves (seal by
second seat) the steam leakage decreases gradually until at full load the leakage is zero.
2. GLAND STEAM SYSTEM (+10mbar)
a) Pressure Control System
The control system has the function of keeping a constant steam pressure in the seal
steam system where the seal steam demand varies according to the load at a low adjustable
,pressure of about + 10 mbar. This is done by admitting seal steam from an auxiliary steam
distributer via a supercritical gland steam control valve.
In the event of a steam surplus, an automatic overflow valve with free-floating disc
assumes the function of maintaining the pressure at about 15 mbar by directing the leak steam
overflow into the vapour system at - 1 0 mbar negative pressure. The steam is distributed in the
process according to the operation of the turbine.
Before evacuation is started, the auxiliary steam distributor and seal steam pipe are
preheated to an adequate temperature by opening the motive steam valve on the hogging ejector
and the seal steam warming-up valve. When the limit temperature is reached the seal steam
warming-up valve is closed and the seal.
During evacuation and after the seal steam starting valve has opened, the seal steam
control valve supplies steam from the auxiliary steam circuit to all glands. The maximum seal
steam flow rate is attained at full vacuum, shortly before starting the turbine.
22
As the turbine load increases, the seal steam demand is reduced as initially less and less
steam is required by the HP glands. These then produce an increasing amount of leak .steam
which is supplied to the LP glands along with the stem leak steam until seal steam supply for the
LP glands is obtained in the turbine in the upper load range.
The overflow safety valve prevents an unintentional increase in pressure in steam system
above a positive pressure of about 40 mbar.
The overflow valve has the characteristic of a spring less safety valve for particularly low
differential pressure If necessary; its function can be taken over by a manually-adjustable
overflow throttle valve.
b) Temperature control arrangement
To limit the seal steam temperature for the cold LP shaft glands, a leak steam cooler is
provided with condensate atomizing nozzles. A temperature controller apportions the necessary
condensate flow by operating a control valve and reduces the varying steam temperature to a
constant value of 150° C. A changeover-type twin filter with differential pressure alarm
eliminates clogging of the spray nozzles.
2. Vapour Exhaust System (-10 mbar)
The pressure differential existing between· the two circuits at the glands causes a
continuous flow of steam vapours into the vapour exhaust system and discharging into the
vapour condenser. The air leaking through each shaft gland and valve stem gland from the
outside mixes with the steam vapours and, after these have been condensed in the vapour
condenser, is removed by an exhauster which at the same time produces the suction pressure
(about -10 mbar) in the exhaust system.
The vapour exhaust system is operated by two vapour exhausters each rated for 100%
with one being used as a standby. Both are designed to operate on suction and are of the wet
steam type designed for a pressure differential of about 20 mbar.
The exhauster non-return flap prevents a bypass backflow through the standby unit.
The external air adjusting damper permits the admission of external air to ensure that the
exhauster .operates in a stable range.
In bypass operation to the vapour condenser and with the exhauster off, it is possible. to
operate non-condensing through the automatic relief valve, in which case the vapour condenser
check valve will close automatically and thus prevent any overheating of the vapour condenser.
The shaft gland check valve prevents stem leakage from the HP emergency stop valve
from penetrating into the turbine when operating non-condensing while the boiler is still under
pressure and the turbine generator already shut down.
Drains
The drains in the gland steam system comprise various circuits designed to meet the
respective requirements. After the warming-up valve is closed the seal steam piping is drained
via the seal steam preheating system through a thermal steam trap.
o
The vapour condenser drain system includes the drain for the vapour extraction system.
o
It is sized for large cooling pipe leakages and leads to the makeup tank with a geodetic
head.
o
The gland steam drain system is connected to the makeup tank in the same manner.
o
Both drain systems are provided with suitable pipe loops to prevent abnormal pressures.
23
c. GENERAL DESCRIPTION OF TURBINE LUBRICATION OIL SYSTEM
(I) Oil Circuit (Refer Drawing No. HPS/WAPCOS-09)
The oil supply system is one of the most important items for safe and dependable
operation of the turbo-set. On M.A.N. turbine the circulating system is employed which ensures
ample supply of lubricating oil to the bearing and gearboxes as well as control oil to the hydraulic
governing and supervisory equipment. In addition to the most careful planning and construction
of the, system, routine maintenance and checking according to the operating and maintenance
instructions is necessary for economical operation with the least possible deterioration of the
turbine oil.
In the interests of the operator, only high steam quality steam turbine oils on a mineral
oil basis should be used. Where possible with suitable additives and in conformity with the
requirements of German Standard, DIN 51 515 as well as suppliers oil specifications
.
To guarantee operational dependability and economy of turbine service the oil supply
system is divided in three separate main circuits, these being:
1)
The bearing oil circuit for lubrication and cooling of turbine, generator and exciter bearings,
as well as for lubrication oil supply to turning gear, gearboxes, etc. The bearing oil circuit
also serves the generator sealing oil system.
2)
The control oil circuit for all hydraulic control and governing equipment and safety devices.
The control oil circuit provides the emergency supply for the generator sealing oil system.
3)
The high pressure oil circuit for jacking the rotor line on starting in order to reduce the
breakaway torque (jacking oil system).
These oil circuits differ both in respect of oil pressure and oil flow. They are therefore
supplied by different oil pumps:
During normal operation bearing oil and control oil supply for the turbo-set is from the
main oil pump. This pump, rated for the maximum consumer pressure, is a single-stage
horizontal centrifugal pump. It is located in the front bearing housing of the turbine with drive
from the turbine shaft via a gear.
To eliminate suction problems from the oil tank arranged in the oil room underneath the,
a transfer pump is used to deliver the oil to, the main oil pump. The transfer pump is two-stage
Francis oil turbine which operates on the bearing oil off branched from the off branched from the
main oil pump and reduced to bearing oil pressure in' the oil turbine.
As the main oil pump must run at a speed of roughly 2700 rpm, before It operates at its
full output, the turbine is started on a.c. driven auxiliary oil pumps, i.e. the auxiliary bearing oil
pump and the .auxiliary control oil pump.
o
The auxiliary bearing oil pump serves the bearings during the start up phase until the main
oil pump has taken over. It also serves to fill the complete bearing and control oil system
prior to start up. During turbine start up it assumes the function of the transfer pump until
the latter has taken over.
o
In the start up phase the auxiliary control oil pump serves the hydraulic control equipment
with oil until the oil supply of the control system has been taken over by the main oil
pump.
Oil supplied during emergency run-down of the turbo-set in the event of possible total
failure of the a. c, three-phase grid are provided by the emergency oil pump. This pump
receives its power from a 220 V. d. c. battery and is switched on automatically via a pressure
monitor in the bearing oil pipe. The feed by the emergency oil pump, as opposed to other
bearing oil pumps, is downstream of the oil coolers so as to bypass the flow resistance in the
oil coolers. Due to this arrangement the capacity of the pump could be reduced to the
minimum necessary for safe run-out of the turbo-set.
24
The transfer pump, the auxiliary bearing oil pump and d. c. emergency oil pump are
vertical single-stage centrifugal pumps. The auxiliary control oil pump is a 5-stage highpressure centrifugal pump of the modular type. All these pumps are immersed pumps and
located inside the oil tank.
The system incorporates two high-pressure gear pumps, one of which being a standby
unit, for jacking the turbine and generator bearings. These pumps supply high-pressure oil at
15 M Pa (150 bar). The pumps are protected by pressure relief valves in the discharge. The
jacking pumps are located at the side of the oil tank. The oil flow from the oil tank to the
jacking pump is by gravity.
The bearing oil is cooled by two 100%-duty oil coolers of vertical design in welded
construction. The oil coolers can be switched over during operation for cleaning purposes. The
tube bundles are removable for cleaning.
The full control oil and bearing oil flows are each routed via a filter system capable of
separating particles down to a size of 0.02 mm (fabric-type tubular filters). The oil flow to the
jacking oil pumps is also filtered. The oil filling can be cleaned independent of turbine operation
by an oil purifier connected to the oil tank.
From the consumers the oil flows by gravity back into the return pipes to the oil tank.
The oil tank is made of welded steel plate and closed airtight at the top by cover plates. It is
dimensioned to circulate the oil filling roughly 8 times an hour, the residence time of the oil in
the tank being adequate for good separation of dirt and air. The separated air and the oil
vapours forming above the oil level and in the oil return pipes are exhausted by an exhauster
located on the oil tank. The oil sludge can be discharged through a sludge lock without any loss
of oil.
The enclosed, fire - proof oil room is located a certain distance away from the turbine. It
accommodates the oil tank with all auxiliary oil pumps as well as the jacking pumps, the oil
coolers, the oil filters and the oil purifier. This facilitates maintenance and monitoring of the
equipment besides affording good fire protection.
The oil pipes running to the turbine are arranged in an oil tunnel at the side of the
foundation and routed in branch ducts in the topping concrete of the foundation deck. The oil
tunnel system is covered by chequered plating. In the event of a fire hazard the oil room can
readily be screened.
The oil room and tunnel and trenches in the turbine foundation block are protected from
fire by automatic high velocity sprays within the room, tunnel and trenches. In the even t of a
fire inside the oil room the ventilation of the room will be automatically shut down.
Prior to start up of the turbo-generator, the cold oil in the oil tank must be circulated by
means of the motor-driven auxiliary oil pumps to heat it to operating temperature.
One portable oil pump is provided for the four units to discharge the oil from the oil
reservoirs into the station oil main. I n addition the portable oil pump can be used to transfer
any oil into the station dirty oil tank which has leaked from the oil systems to the oil troughs of
the oil rooms.
(II) Oil Coolers
General
The oil coolers serve for cooling of the lubricating oil of turbine and generator bearings
by water. There are two oil coolers provided in this plant.
One of the two oil coolers is sufficient for operation. A two-stage three-way valve allows
change-over from the oil cooler in service to the stand-by cooler during operation. In this
manner cleaning work on one cooler can be undertaken without interrupting turbo set
operation. In particularly extreme circumstances parallel operation of the two coolers is
possible. The tube bundle can be withdrawn for cleaning purpose.
25
Normal Mode of Operation
The water flow should be regulated to maintain the desired cold oil temperature. In
order to reduce the cooling water consumption and the pump output and to maintain the oil
temperature at the desired level, a good heat transfer from oil to water through the tubes is
necessary In view of this the oil cooler should be cleaned at the water side and the oil side
from time to time.
In the event of extensive· shut-down periods the water should be drained off from oil
cooler: If the cooling water has aggressive components it is advisable to dry out the' parts in
contact with the water by means of compressed air.
III. Oil Purifiers
The oil purifiers supplied for purifying the oil consist of following parts.
1. Coarse oil filter
It is equipped with a single - mesh metal screen to retain coarse dirt particles 0.2 mm
permanent magnet to retain the smallest Iron particles.
2. Indirect heated electric oil heater
Connected value 80 kW, 380 volt 'switched in three steps of 26.6 kW each
An interlock system is incorporated to ensure that the heating system cannot be started
until the circulating pump is in operation.
3.
Oil separator
The oil separator, dirty and clean oil pumps are driven by a ~80 V A.C. three phase
motor. The oil pumps (gear pumps) are fitted with a pressure relief valve. On the separator hood there
IS a connection with isolating valve for hot water.
4.
Anti -flood system
A solenoid valve in the dirty oil inlet pipe protects the oil separator against flooding
when the drum is filled with sludge.
5.
Pipe system
6.
Oil tank
To hold the contents of the drum, when the separator is out of operation.
7.
Control panel
Containing:
8.
o
motor protection switches for the separator and the circulating pump.
o
Air contactors for the oil heater
o
1 Ammeter and 1 Volt metre as well as the necessary, switches and terminals for the
lead, for the connection to 380V, AC 3 phase, 50Hz.
electric
Base frame
Rugged base frame with metal covering to carry the afore-mentioned with lifting eyes. Metal
covering in the form of a trough for leakages
9.
Water Heater
Connected value 3 KW, 380 V with safety valve, temperature regulator and temperature
limiter, to supply approx. 10.1/h hot water at 90°C and for connection to the water pipe system at a
pressure of 0.4. - 0.6 MPa (4-6 bar). The water heater is bracket-mounted on the wall of the oil room.
Operation Instructions for Oil purifier
The oil heater is filled with heat-transmitting oil BP Transcal N. Refilling is accomplished
through the funnel, with valve below the funnel opened.
In cold condition the heat-transmitting oil has to stand in the middle of the oil level
26
If the heating system is in operation the heat-transmitting oil will expand and rise into the
conservator
Set adjustable pointer of the thermostat provided on the oil heater for the heattransmitting medium to 120°C,· that of the thermostat provided in the piping for the oil that must
be purified to 60–70 OC. If required (for example to prevent emulsification) set this thermostat by
10-20 OC higher.
Adjust the thermostat of the water heater by 5 °C higher than the temperature on the
thermostat for the oil that must be purified, therefore at 65-75°C. The temperature limitation for
the water heater is fixed to 95 GC.
The cold-water supply will be connected on the below connection piece of the water
heater. (Operating pressure - max. 6 bar). First of all valves and cocks must be closed.
Set the plant up horizontally and connect it by means of special rubber hoses or a firm
·piping to the oil tank.
Connect the plant to the electric supply main.
Check the direction of rotation of the circulating pump for heat transmitting oil.
Make the separator ready for operation.
Connect the hot-water outlet of the water heater by means of a tube with the make-up
water regulating valve of the water separator.
Putting in Operation
o
Start the heating system for the oil heater. If several heating groups are provided one of
they will suffice to heat up the heat transmitting oil.
o
Start the circulating pump for the heat transmitting oil.
o
Open the stop cock in the cold-water supply pipe for the water heater.
o
Then switch on the heating system for the water heater.
o
After the heat-transmitting oil has obtained a temperature of 90OC put the oil separator in
the time of 6 minutes 1 he separator will reach its full speed.
o
Then open the water regulating valve located on the separator hood, slowly, until is coming
out from the sight glass for water outlet.
o
Throttle the water regulating valve so that only 1-2% water per hour can flow to oil
separator. (Referring to hourly oil flow quantity) Open slowly the stop cock for the oil flow
to the plant and switch on the remaining heating elements.
o
The oil in the separator shall not rise higher than to the below edge of the right side glass
of the separator, otherwise the oil will flow out in the water chamber of the separators
Coming out at the water outlet of the separator.
o
The setting screen mounted on the oil supply pump is adjusted to the capacity of separator
drum. By increasing pollution of the separator drum the oil will flow out of the Pipe of the
separator, first by drops, but then more and more.
o
In this case the solenoid valve in the oil - inlet pipe will be closed automatically by means
of a float switch in the overflow pipe. Then the oil inlet is closed. The heating system in
the oil heater and in the oil separator stops automatically. For safety, switch out all
heating elements and the separator by hand on the switch panel. Then after stopping of
the separator clean the separator drum according to the operating instruction.
o
After the housing for the float switch in the overflow piping of the separator is emptied by
opening the drain cock; the separator and the heating system for the oil heater can be
switched on again. A limit switch provided on the separator prevents starting the
separator by opened hood.
27
Putting out of operation:
Switch out the heating system for the oil heater and the water heater by hand on the
switch panel. After switching out, the oil shall flow for 2-3 minutes through the plant because
the heating elements continue to heat after having been disconnected. Then close the stop cock
for the oil supply to the plant and switch out the circulating pump for the heat-transmitting oil.
Close the stop cock for the cold-water supply to the water heater. Close the water regulating
valve on the separator hood. Switch out the oil separator if no more oil flows out of the oil
outlet of the plant. After stopping of the separator drum the remaining oil flows out in an oil-tub
through the over-flow respectively emptying piping. After that the float housing must be
emptied, otherwise a new operation is not possible.
Important remarks
o
Because of the hot-water supply in the separator drum, water of condensation can
accumulate into the float switch housing. It is necessary to discharge the water of
condensation from time to time in order that float switch does not switch off the plant
when the condensate level rises.
o
The vacuum metre in the piping between oil coarse filter and oil pump indicates a vacuum
of approx. 0.2 bar by normal passage.
o
When this vacuum rises to 0,6 bar the filter element in the oil coarse filter must be cleaned
or replaced. For this purpose the oil purifying plant must be put out of operation.
o
The thermostats for the oil heater and the water heater are switching the heating system
on and off automatically. These instruments must be supervised from time to time.
o
In the event of danger by overheating (which may be due to failure of these thermostats)
stop the heating systems (by hand on the switch panel).
o
When purifying dehydrated oils the hot-water supply for the separator is not necessary.
The separator drum must then be adjusted according to operating instruction.
o
In the condition of the heat - transmitting oil should be controlled every 6 months. If its
colour is dark, filtering it is advisable as this will prolong its usability for years. If sludge
has formed the oil must be replaced. Be sure to refill the same sort of oil.
(IV)
Hydraulic Jacking System for Journal Bearings
All journal bearings are equipped with a hydraulic jacking system to provide a hydrostatic
lift to establish an oil film and reduce the breakaway torque during starting.
At the lowest point of the lower shell of the journal bearing a port is provided which
communicates with an oil sump, Oil is injected through this port at a pressure of 15 M Pa by
means of high-pressure pumps. This produces a high hydrostatic pressure under the journal
which raises the rotor on a film of oil and facilitates rotary movement due to a reduction of the
original friction coefficient.
The high - pressure oil is introduced through a nozzle which is screwed and locked oil
tight in the bearing shell before babbitting the bearing. A relief groove with a relief duct Is
provided to protect the bearing from high-pressure oil penetrating between the shell and the
babbit lining.
The pressure of the high - pressure oil is kept at a constant level by a pressure limiting
valve. The oil throughput of each bearing is controlled by a flow regulating valve to give the
desired amount of rotor lift. A check valve is arranged in the oil admission pipe to prevent any
disturbance of the journal bearing during normal operation when the jacking system is not in
use.
@@@@@$$$@@@@@
28
d. GOVERNING, PROTECTIVE SYSTEM
A)
1.
Governing System (Ref- Drg No. HPS/WAPCOS-10)
General.
For the Hwange power Station No. 4-1 units, Woodward flyweight speed governor is used
with nozzle governing system: There are four No control valves, which are required to open to
give the desired linear output vs. 'frequency characteristic.
The governing system is also provided with Automatic. Pressure unloading gear and
vacuum unloading gear. When the Boiler outlet steam pressure falls below a set value, the
machine is unloaded proportionately from full load to no load to match the steam consumption
in the turbine equal to the steaming capacity of the Boiler. Similarly when the condenser
vacuum falls below a set value, the machine is unloaded proportionately.
Provision is also made to prevent excessive overshooting of the speed when large load
(dp/dt) occur, by temporarily closing all the control valves through a load shedding relay.
2.
Description of Woodward Speed Governor
Principle of Operation
The schematic diagram Dwg. No. ( HPS/WAPCOS-11) shows the essential parts of the
governor. Two accumulators are provided for pressure oil storage capacity; the maximum
pressure of governor oil is regulated by-pass ports in the accumulator cylinders.
There is always full accumulator oil pressure on the top area of the power piston
(regardless pilot valve position) which will turn the terminal shaft in the direction to shut off
fuel if there is no pressure (or low enough pressure) on the bottom area of the power piston.
The pilot valve supply this small oil pressure to the bottom area of the power piston if the valve
moved down far enough to open the control port Due to the difference of areas on the on top
and bottom of the piston, a greater force on the bottom will then overcome the force on the top
side and will move the power piston up, turning the terminal shaft in the direction to increase
fuel.
If the pilot valve is moved up, the area under the piston is opened to sump, reducing the
force exerted on the bottom of the piston. The force exerted by the oil pressure on the top will
then be greater and will move the piston down, turning the terminal shaft in the direction to
decrease fuel.
The governor drive shaft, gear pump pilot valve bushing assembly and ball head rotate
together. A laminated drive shaft interconnects the gear pump and ball head driver gear.
The spring under the pilot valve supports the weight of the pilot valve and floating lever.
The spring above, the actuating compensating piston acts to .eliminate lost motion in the
compensation linkage and 'has no effect in the normal operation of the governor.
Increase of Load
Assume the load on the prime mover is increased, resulting in a decrease in speed.
As speed decreases the flyweights move in, allowing the speeder spring to lower the
speeder rod and the inner end of the floating lever, thus lowering the pilot valve plunger and
uncovering the control port of the pilot valve bushing. The opened control port admits pressure
oil to the bottom of the power cylinder. Since the bottom area of the power piston is greater
than the top area, oil pressure will move the piston up and rotate the terminal shaft in the
direction to increase fuel.
As the power piston moves up: rotating the terminal shaft, the actuating compensating
piston moves down and forces the receiving compensating piston up, compressing the lower
compensating spring and raising the outer end of the floating lever and pilot valve plunger.
Movement of the power piston, terminal shaft, actuating compensating piston, receiving
compensating piston and pilot valve plunger continues until the control port in the pilot valve
bushing is covered by the .control land on the plunger. As soon as the control port is covered,
the power piston and terminal shaft are stopped at a position corresponding to the increased fuel
needed to run the engine at normal speed under increased load.
As the actual unit speed returns to normal, the flyweights and speeder rod return to
normal position. The receiving compensating piston is returned to normal position by the
compensating spring at the same rate as the flyweights, thus keeping the control port covered
29
by the control land on the pilot valve plunger. Flow at' oil through the compensating needle
valve determine, the rate at which the receiving compensating piston is returned to normal. At
the completion of this cycle, flyweights, speeder rod, pilot valve plunger and receiving
compensating piston are in normal positions; power piston and terminal shaft are stationary at a
position corresponding to increased fuel necessary to run the prime mover at normal speed
under increased load.
Decrease of Load
Assume now that load on the prime mover is decreased and speed increases. As the speed
increases, the flyweights move out raising the speeder rod and the inner end of the floating
lever, thus raising the pilot valve plunger and uncovering the control port in the pilot valve
bushing. As the control port is opened, the bottom of the power cylinder is opened to sump and
the oil pressure on the top of the power cylinder forces tile power piston down and rotates the
terminal shaft in the direction to decrease fuel.
As the power piston moves down, rotating the terminal shaft, ,the actuating compensating
piston moves up and draws the receiving compensating piston down, compressing the, upper
compensating spring and lowering the outer end of the floating lever and 'the pilot valve
plunger. Movement of the power piston, actuating compensating piston, receives compensating.
Piston and pilot valve plunger continues until the control port in the pilot valve bushing is
covered by the control land on the pilot valve plunger.. As S00n as the control port is covered,
the power piston and terminal shaft are stopped at a position corresponding to decreased fuel
needed to run the engine at normal speed under decreased load.
As speed decreases to normal, the flyweights return to normal position lowering the
speeder rod to normal position. The receiving compensating piston is returned to normal
position by the compensating spring at the same rate as the flyweights thus keeping the
control port in the pilot valve bushing covered by the control land on the pilot valve plunger.
Flow of oil through the compensating needle valve determines the rate at which the receiving
compensating piston is returned to normal.
At the completion of this cycle, the flyweights, speeder rod, pilot valve plun ger and
receiving compensating piston are in normal positions; the power piston and the terminal shaft
are stationary at a position corresponding to decreased fuel necessary to run the prime mover
at normal speed under decreased load.
In actual operation, the events described occur almost simultaneously, rather than step
by step.
This description is based upon speed changes resulting from load changes. However, the
same sequence of governor movements would occur if a difference between actual governor
speed and governor (and prime mover) speed setting is produced by turning the speed control
shaft on the lever type governor or the synchronizer control knob on the dial type governor.
Cross-sectional View
The cross - sectional view, shows the position of the governor parts with the mover
running at normal speed under steady load. The centrifugal force of the flyweights (due to the
speed of rotation) balances the opposing force of the speeder spring with the flyweights in the
vertical position. In this position, the flyweights hold the pilot valve plunger in its centred
position, with the control land just covering the control port in the pilot valve bushing. With the
control port closed, oil pressure is balanced across the power piston and the power piston and
terminal shaft are held stationary.
3.
Mechanical/Hydraulic Control System
▪
for the Hwange Power Station No. 4 - 1 Units
MODULATION OF HP CONTROL VALVES
Functions of turbine control system
▪
The speed of unloaded or solo-operating turbine must be capable of being varied by
indexer. In the range of rated speed,' these adjustments must be sensitive enough for
synchronizing the turbo-generator with the electric grid.
@@@@@|||@@@@@
30
(C) GENERATOR DESCRIPTION
a)
i)
Stator Winding
Composition
The winding is of the ROEBEL Type two simple bars per slot. The end windings are helically
arranged on a cone opening; very slightly so as to reduce the front magnetic field.
The high
values of the total current per slot require a particularly delicate wedging
arrangement of the windings to withstand the alternating hammering at 100 Hz on the bottom of the
slot without damage, as well as the electro-dynamic forces which develop in case of short-circuit the
machine.
ii)
Insulation
The bars are composed of basic, electrolytical copper strands, permutated all along the
magnetic core according to the ROEBEL System which allows the additional losses produced by the
transverse field of the slot to be reduced to a very low value.
These strands are insulated from one other by means of a silionne based lapping impregnated
with epoxy resin.
They are checked for insulation at 220 V during manufacturing
Each bar is insulated over its whole length, in the straight part and in the end-winding by
means of continuous taping following ISOTENAX procedure.
The ISOTENAX tape is composed of two very fine glass tissues between which is trapped a thin
layer of mica formed of micro-splitting called SAMICA.
The support assembly and SAMICA paste is impregnated with epoxy resin.
During manufacturing, the bars are dried under vacuum, then the insulation is hot-polymerised
under constant hydrostatic pressure.
To avoid corona the bars are then coated with a semi-conducting paint for the parts located in
the punchings and with a resistant paint in the end windings.
An internal electrode system regularly reduces the potential in the end windings
Each bar is subject to dielectric controls after manufacturing.
The variation of the tangent of the angle of losses is about 3/1000 for a voltage variation going
from 20 % to 80% of the rated voltage with an extremely low dispersion showing the regularity of
manufacture.
The instantaneous dielectric rigidity is 28kv/mm in kV r.m.s. at 50 Hz
Thermal conductibility is 3.4 MW/Cm-oC
Thermal ageing tests under dielectric stress have shown that, up to 155 oC under a gradient of
3.2 KV/mm, there appears to be no deformation.
Measurement readings have shown perfect adhesion between insulation and copper and the
perfect firmness of the ISOTENAX during relative expansions between bars and the magnetic core,
causing the phenomenon of creeping encountered on the windings insulated by means of continuous
asphalt taping to disappear.
31
b)
Terminals
The ends of the three winding phases are connected on six H.V terminals located in the upper
part of the generator on the excitation end.
The H.V bushing of the stator winding are hollow and cooled directly by an internal hydrogen
flow.
c)
o
o
o
o
o
o
1.
a)
Resistance thermo-Detectors and checking Devices
The thermo-coupes, the sensitive element of which is in copper –constantan, are used in order
to check the stator winding temperature.
Each thermo-coupe is located between two bars in one same slot.
They are fitted at the inlet and at the middle of the iron core turbine end and at excitation end.
They are distributed throughout the winding and connected to a terminal box fixed to the outside
of the frame.
They allow heating up of the winding to be measured constantly,
The gas temperature is continually checked by means of: thermo-couples, thermometer and
thermostats which are fitted in the gas circuit of the generator.
Rotor
Shaft
o
The generator rotor is constituted of a forged monobloc piece, the ingot having been worked in
an electric furnace and cast under vacuum.
o
o
It is solid shaft in alloy steel with high tensile strength (greater than 640 N/mm2
86 000 Psi)
The characteristics of the steel are measured on test pieces taken on the forging at its periphery.
o
Moreover ultra-sonic checks allow the homogeneousness of the piece to be checked as also the
absence of inclusions.
o
The slots for housing the inductor windings are mille din the central table of the rotor and
distributed so as to engender a magnetic force wave close to the sinusoid.
The central non-coiled part of each of the posed contains small slots used only for
lodging dampers which, with those present in the coiled slots, form a complete cage which
allows preservations of:
o
Contract surface between retaining-ring and rotor shaft, against the passage of parasite
currents.
o
The rotor against the effect of the inverse field when operating in unbalanced regime.
o
As the arrangement of the coils is asymmetrical, since the excitation winding only covers
approximately 2/3 of the periphery, it causes inequality of the moments of inertia according in
the two main planes of the rotor.
o
To avoid double frequency vibrations of the electrical frequency, this inequality is compensated
for by cross slots, milled perpendicularly to the axis of rotation in the non coiled parts of the
shaft, so that the rotor then behaves like an isotropic body.
o
The sizing of the rotor is determined so that the second critical speed is well above the over
speed.
o
Shaft tightness is ensured excitation end by rubber gaskets easily accessible without removing
the rotor.
32
b)
Winding
o
The conductors are composed of slightly silver alloyed copper and are cold-rolled to a slight
deg.(5%)
They are bonded together under pressure per half-coil with their intermediary insulators and
inserted together into the slots already provided with ground insulation composed of a glass
tissue impregnated with epoxy resin.
This conductor assembly is then joined up by means of brazing in the pole centreline to the
corresponding conductors of the second half-coil, so constituting the field winding coils.
The end windings kept in place by the retaining rings are inter wedged with insulators in
bakelited asbestos and insulated from the retaining rings by means of cylindrical rolls of glass
strata
The dampers cage which covers the coils is also in copper of unequal thickness with a low silver
content, slightly cold hammered in the slots and harder for the end plates upon which act
mechanical and thermal stresses.
All the end plates are electronically silvered to improve protection of the contact surface between
retaining-ring and rotor shaft.
The windings and dampers are retained in the slots against the action of centrifugal force by
means of brass wedges with high mechanical resistance.
The end windings are rigidly wedged against the centering rings in the axial direction.
The expansion caused through heating are absorbed by the copper elasticity.
An insulating cylinder, composed of layers of soft (NOMEX) and hard materials (stratified Epoxy
Glass), formed of two half-shells, separated by a 10 mm gap (04 In) in the interpolar axis is
placed between the end windings and the retaining rings.
It allows radial expansions in the latter caused by centrifugal force, and this, without any risk of
tear in the insulating mattress.
The first three layers of the insulating cylinder are stuck together at an angle of 45 o on the either
side of polar axis.
The lower layer is it self stuck on the upper copper strips of the end-windings while the upper
layer is coated with film of Teflon (PTFE).
This Teflon process carried out between the insulating layers of the copper strips on the one
hand, and the insulating layer in contact with the retaining ring on the other, facilitates the
relative movement previously described, while preventing deformation of the insulator between
the end windings and the retaining ring.
o
o
o
o
o
o
o
o
o
o
o
o
o
c) Non Magnetic Retaining ring And Centering Ring
o
The end turns of the rotor windings are subjected to centrifugal force and expansion due to
heating up of the copper.
o
They are kept in place by means of cap centred only on the shaft and which completely covers
them.
o
This cap is composed of a retaining-ring in non magnetic steel and a disc, the centering ring.
o
The retaining rings are the parts of the alternator which are subjected to the greatest
mechanical stresses.
o
Moreover, they are weighted in an asymmetrical fashion, considering the distribution of the
excitation winding.
o
This is why they are made from forged pieces in non magnetic steel of high characteristics,
obtained by cold hammering resulting from cold hydraulic expansion.
o
However, the arrangement of the 2-pole winding does not ensure natural equalisation of the
weighting of the two axes.
33
o
Thus compensating weights located against the centering rings prevent the retaining ring from
being ovalized.
o
The retaining ring centering ring assembly only rest on the rotor on one-side at the shaft
entrance (floating retaining rings).
The clamping rates:
▪
Of the retaining ring onto the rotor shaft on the one hand
▪
Of the retaining ring onto the centering ring on the other are such that they allow to
maintain a residual rate of clamping sufficient for the over speed.
▪
The retaining-rings are locked in the axial direction by means of a system of locking ring,
prohibiting any longitudinal displacement during running.
d)
Fans
o
On each side of the rotor a fan is fitted which draws cold hydrogen leaving the coolers and
discharges it to the inlet, across the magnetic core, the front parts of the stator winding, the
rotor and the terminal box extension.
o
The fans are of the axial type with separate blades, in aluminium alloy of fine mechanical
quality.
o
The blades are fitted and bolted onto a forged collar of the shaft on the turbine end and on a hot
shrunk-on plate, on the excitation end.
e) Coupling
o
At the turbine end the shaft end in a forged flange.
o
The generator rotor is rigidly coupled by this flange, using bolts, to the connecting sleeve of the
turbine rotor.
f) Excitation
The turbo-generator is excited by a static-shunt system.
g) Shaft Surveillance
o
The behaviour of the rotating shaft is checked and constantly analysed by means of vibrations
sensors connected to control system (amplifiers switch and recorders). Used both for the turbine
and the generator.
h) Lubrication of Journal Bearing
o
The rotor is fitted into the end-shield bearings by way of spherical seat journal bearings.
o
The latter are lubricated under oil pressure by the general lubricating system of the turbinealternator shaft line.
o
The proper operation of the end-shield lubrication system may be controlled on both turbine and
excitation end.
o
By measuring the temperature of the warm oil at the journal bearing outlet by means of a
pyrometric probe (Thermo-couple)
34
GENERATOR COOLING SYSTEM
1
General Cooling
a) General
The main cooling fluid in the generator is gas. It removes all the losses, other than those of
the journal bearings-removed by lubricating, that is to say:
o Rotor losses
o Stator core losses
o Stator winding losses
o Friction losses
o Ventilation losses
o And transmits them to the gas-water coolers.
The four gas water coolers are arranged vertically in the cooler housing them located impairs
at each end of the frame.
They are arranged symmetrically in relation to the vertical planes passing on the one hand
though the centre of the frame, on the other hand through the longitudinal axis of the stator.
Each of the coolers is composed of a fine network of finned tubes opening into water boxes the
covers of which are removable.
The water inlet-outlets are situated under the generator.
The internal compartments of the generator allow, due to adequate arrangement, the
dissymmetry due to operation with a cooler out of service.
To obtain cold gas temperature approximately equal, the hydrogen coolers are supplied, in
parallel on the general cooling water circuit.
Advantage of Hydrogen Cooling
The advantages of hydrogen as a ventilation agent are due mainly to its physical properties :
its density is fourteen times lower and its thermal conductibility seven times higher than that of air.
In addition, the heat transfer factors are approximately 50% higher in hydrogen than in air.
The advantages of hydrogen are:
o
o
o
o
Reduction of the constant losses, at all loads, exceeding 0.4% of the power of the machine:
from which there arises a marked increase in efficiency especially at low loads.
Impossibility of ozone being formed around the windings, and consequently no premature
ageing of the insulations.
Running without danger of fire, thus dispensing of all extinguishing equipment.
Relatively quiet operation and protected from any dust.
Hydrogen Explosive Properties
o
o
o
o
o
o
Pure hydrogen does not burn, but mixed with air in a proportion of 5 to 75% of the total volume
of gas and submitted to a temperature greater than 760 oC (1430oF), the mixture ignites and
explodes.
The most dangerous mixture is that composed of 35% H2 and 65% air.
The risk of creating an explosive mixture in the alternator is removed by the fact that the
hydrogen therein is kept at a degree of purity exceeding 98% during normal operation.
On the other hand, before filling the generator with hydrogen, the air is displaced by carbon
dioxide (CO2) which is an inert gas.
In addition to protect the power station staff from possible explosions, the generator casing is
designed to withstand the pressure that the Hydrogen would be liable of producing with out
exaggerated stress.
The hydrogen equipment, for its part, is arranged so t hat hydrogen coming from a leak escapes
to the atmosphere.
35
It is necessary nevertheless to take the following precautions:
o
o
Prevent the hydrogen accumulating in a closed space
Avoid putting a naked flame or incandescent particle near the enclosure in which the hydrogen is
likely to be discharged.
b)
Generator Gas Cooling Circuit
o
o
o
o
o
o
o
o
o
Special arrangements confirmed by tests, are taken to ensure efficient cooling of all the
elements in the machine
The gas circulation in the generator is ensured by two axial fans mounted on the shaft ends on
each side of the stator core.
The ventilation of the generator by gas is effected in a closed circuit.
To ensure gas circulation from the periphery towards the air-gap, then from the air-gap to the
coolers, the frame I divided axially into five compartments.
Two of the latter are located in a symmetrical manner in the central area of each half of the
frame and are designed to bring the fresh gas into the air-gap.
The other three are outlet compartments, i.e. warm gas packets of laminations separated by
radial vents 8 mm (0.315 in) wide
The frame is divided so as to establish certain equilibrium for the flow as also for the gas drop in
the coolers.
Then, a common circuit reserved for fresh gas brings the latter to the ends of the machine from
where it is drawn by fans which discharge it to the inside of the generator.
The ventilation of certain components at the stator ends, where temperature rise may be
considerable, is particularly meticulous.
This especially concerns:
o
o
o
The clamping stator frame flanges
The cooper flux screens
The clamping fingers for the teeth.
c)
Rotor Cooling
o
The direct method of cooling is used.
o
The gas circulation in the rotor occurs in the axial-radial direction, the general supply being at
each side under the retaining-ring.
o
Each copper-strip is provided in its straight part with elongated holes in the form of slits
obtained by punching, and in its front part with an axial half- conduit.
o
The super imposition of the two copper – strips forms an electrical conductor, the from parts of
which are cooled by means of an axial gas circulation through the canal formed by the super
imposition of the two half – canals, the central part being cooled by means of radial slits or
slotted – holes.
o
The axial canals of the end – windings are supplied turn by turn through side inlets, removal
being ensured in the first slotted –holes at each end of the rotor.
o
The central slotted – holes are supplied by means of an axial passage milled in t he shaft under
each slot, i.e. the sublot.
o
The radial removal of the warm gas which has passed through the slotted – holes is ensured by
holes contrived in the closure wedges of the rotor slots.
o
This radial slotted – holes cooling system allows a fairly uniform distribution of the gas
throughout the slots thus avoids any possibility of the thermal unbalance and renders hot
balancing of the rotor useless.
36
d)
Stator Winding Cooling
o
Gas flow circulates through the radial gas ducts of the magnetic core and removes not only the
iron core losses, but also those of the stator winding.
o
The stator winding is of conventional cooling type by means of gas: the heat generated in the
copper conductors crosses through the ISOTENAX grounding insulation, and is transferred to the
magnetic plate laminations before being evacuated by gas flow circulating through the radial gas
ducts
o
The temperature difference between the copper and the magnetic core remains slight, due to the
very good temperature conductibility of the insulation which for the same voltage allows a lower
thickness in comparison with the previous insulation of the mica-bituminous type.
o
Wedging of stator end turns is secured in such a way that the coil ends present a large cooling
surface to the gas.
o
Special arrangements are made to insure active cooling of stator ends: ventilation between
clamping finger of teeth and ventilation of the flux screens.
2)
Gas supply
a) Supply Racks
The hydrogen supply to generator is ensured by one rack fixed in the upper part of the frame,
and of the terminal box extension.
A second rack situated in the lower part of the frame is for letting out CO 2 to displace the air
or hydrogen in the machine.
c)
H2 and CO2 Supply (Ref- Drg No. HPS/WAPCOS-13)
Before admission to the generator, hydrogen coming from the bottle frames undergoes two
expansion stages:
o
o
The first one from the pressure of the bottles up to 5 bars occurs in the first expansion Station,
generally located outside the power station buildings.
The second one, from 5 bars to the pressure used in the machine, occurs in the second
expansion, station located near the hydrogen seal supply system.
In order to avoid an explosive mixture being formed during filling, the air is displaced by
carbon dioxide before hydrogen is let into generator.
Delivered in liquid form in bottles, it is gasified at 60 bars, and passes through a heater so that
expansion does not cause it to freeze.
Carbon dioxide is generally used for draining the generator
The expansion stations include the necessary control and checking devices: pressure reducers,
manometers, stop valves, governing valves.
d)
Hydrogen Pressure in the Generator
The increase of the hydrogen pressure increases its density and consequently its head
absorption power.
The losses through ventilation and friction are obviously increased, but this slight disadvantage
remains negligible nevertheless when compared to the improvement to the cooling of the machine.
This increase in pressure may be used, either to increase the power of the machine, the
coolers supply water temperature being constant, or inversely to allow operation at rated power but
with warmer water, the temperatures reached by the active parts of the machine remaining lower than
the anticipated limits.
37
3. Gas Coolers
a) Introduction
The generator is provided with four water cooled gas coolers of the two pass type, located in a
vertical position.
They are located at each end of the frame and symmetrically mounted with respect to the
median plane of the latter.
▪
▪
Each cooler is chiefly composed of:
o
o
o
o
o
o
o
o
o
o
b)
A casing made up to two staggered copper tube banks in which the cooling water flows and
each end of which is expanded into steel tube sheets.
Two steel water–boxes located at each end of the cooler.
Each assembly is mounted in a frame which rests on the upper part of the vertical stator
cooler housings by means of the corresponding tube sheet (upper part, or fixed end).
The hot gas stream, sucked by the fans, flows first through the tube banks in the axial
direction of the turbine generator, and after having been cooled, is discharged by the fans
into the various cooling circuits.
The frame is made-up of two vertical walls of mild steel sheets, which ensure the lateral
closing of the cooler and guide gas by forcing it through he tube banks.
The lower water-box is divided into two compartments, and is provided with two pipes, each
terminating in a flange, and which ensure the cooling water inlet and outlet.
Water inlets and outlets are so arranged as to obtain a counter flow between the gas to be
cooled and cooling water.
Thus hot gas flowing into the cooler, meets the warmest water first, that of the outlet circuit,
while fresh gas, arriving at the exchanger outlet is in contact with the cold tubes through
which the inlet circuit water flows.
The four coolers are symmetrically arranged, both in the frame and in the gas circuit and are
connected in parallel on the cooling water circuit.
Each cooler is provided with a filling checking device and a water leakage alarm with
electrical contract, to prevent any considerable water leakage into the stator should a cooler
tube split.
Adjustment Of Generator Cooling Water Flow
o
o
o
o
o
A flow relation is provided for the cooling water of generator gas coolers, although the
cooling water temperature is not subject to excessive or sudden changes.
In fact the power station operator’s attention must be drawn to the following point:
Gas coolers and exciter air coolers have been designed for an inlet raw water temperature of
45 to 46o C maximum.
However make sure that the temperature
Of air in exciter
Does not drop below 20 to 22oC, which approximately corresponds to a cold raw water
temperature of 15 to 18oC according to the cooler fouling level and to the load.
This value must be respected in order to limit:
o
o
o
Shaft embrittlement
Thermal cycling of windings
Differential expansion between stator winding bars and magnetic core punchings.
Should the raw water temperature be liable to drop below 15 to 18 oC in winter, it will be
necessary to adjust the primary cooling water flow in order to keep a sufficient thermal level inside the
generator.
The adjustment is ensured by means of a device installed on the cooling water circuit of
generator gas coolers.
38
GENERATOR SEAL OIL SYSTEM (Ref- Drg No. HPS/WAPCOS-14)
1.
Functional Role and Design of System
The generator frame, it’s and shield bearings and the central shaft bore are designed to be
hydrogen sealed.
The purpose of the hydrogen “oil – seal” system is to make the generator shaft and seals tight
by means of pressurized oil circulation.
In order to set up an effective hydrogen barrage, the oil pressure at the seals is automatically
kept at a value greater than that of the existing hydrogen pressure in the machine.
At the seal outlet the oil escapes in two separate flows and the system treats the oil containing
air and that containing hydrogen separately.
This system is interconnected with the shaft line lubricating system, which ensures the
preliminary treatment and the cooling of the oil used for the seals.
2.
Description of Equipment
The following represents the principal equipment ensuring oil treatment and circulation:
o
o
o
o
2.1
Gas detraining tank on the air side : CE 10
Gas detraining tanks on the hydrogen side CE 19 AND CE 20
Hydrogen anti-leak tanks : CE 12 and CE 13
Motor driven pump units
Gas detraining tank on the air side : CE 10
This is supplied by the oil returns form the journal bearings and oil seals on the air side. It
also takes in oil from the anti-leak tank when the unit is turning.
A series of baffles in this detraining tank forces the oil to spread out in a layer and in this way
the air bubbles are released, and possibly the few hydrogen bubbles it may contain.
These bubbles burst and the gaseous mixture is discharged to the outside air through the gas
extractor: SU10 D009 which is a centrifugal fan, designed to withstand the possibility of a hydrogen
explosion and not produce sparks.
The siphon located on the degassed oil return prevents any hydrogen which may have
accidentally entered the journal bearing block compartment from penetrating the main lubricating
tank.
This detraining tank is usually located on the lubricating oil returns, at the side of the turbogenerator foundation, close to the magnetic centre-line of the generator and 300 mm lower than the
hydrogen detraining tanks.
2.2
Detraining tanks on hydrogen side : CE 19 and CE 20
This equipment is composed of two tanks connected together by a siphon in order to avoid
hydrogen circulation due to a pressure difference between the ends of the generator. They are
supplied by oil returning from the seals on the hydrogen side and are at the same pressure as the
generator.
They are suspended as high as possible, beneath the table, close to the magnetic centre-line
of the generator.
On each detraining tank a pipe allows the gaseous mixture coming from the annular chamber
to be trapped off and discharged to the atmosphere through a flow-meter and scavenging analyser.
39
2.3
Anti leak system: “pressure” unit
This composed of a tank divided into two compartments:
o
o
CE 12 compartment used in normal operation
CE 13 emergency compartment
In normal operation, the CE 12 compartment is supplied with oil coming from the detraining
tank on the hydrogen side, through valve R 105.
The oil returns through filter FL 11 the ballcock RF 10 and valve R 106, either towards the
detraining tank on the air side when the generator is operating or towards the pump intake MP 13 or
MP 14 through valve R 111 and the non-return valve RR 11 when the unit is at shutdown.
The ballcock RF 10, which closes when the level drops serves to keep the oil level constant in
the middle of the compartment so avoiding hydrogen escaping to the atmosphere through the air side
detraining tank and gas extractor. Should the ball-cock be defective, non closure of which is detected
by the low level controller SP 11 L 312 and non opening controlled by an overflow in the hydrogen side
detraining tank, therefore liquid detection in the tank CE 17, the overflow of this tank pours into the
emergency compartment CE 13 which comes into operation. This compartment contains ballcock RF
11 Which closes when the level drops, valve R 108 being open permanently.
The level controllers SP 11 L313 and SP 11 L315 defect respectively a low and a high level in
this compartment should the ballcock not operate.
In case of failure, the two compartments may be isolated and the flow sent into the by-pass,
including a tank CE 14 fitted with a visible level, and valves R 109 and R 110.
In addition this system includes:
o
o
o
2.4
The hydrogen returns to the detraining tanks through valves R 208 and R 211.
Drains at the top through R 207 and R120
Valves R209 and R 212 which allow compartments CE 12 and CE 13 to be drained
“Motor driven pump” Units
2.4.1 Main pump : SU 10 D 001
This pump driven by an asynchronous motor ensures the normal seal oil supply.
It is provided with a non-return valve RR 15, a pressure-switch SP11-P316 located at the
discharge point, and its pressure is set by the valve RD 11 which discharges part of the oil into the air
side detraining tank CE 10 through the pipe fitted with valve R 142.
It may be isolated from the circuit by means of valves R140, R141 and R142
2.4.2 Emergency pump: MP 14
This pump is driven a D.C motor, supplied by the standby battery.
It is fitted with a non-return valve RR17, its pressure is adjusted using the valve RD 12 which
discharges part of the oil into the air side detraining tank through the pipe fitted with valve R 152.
It may be isolated from the circuit by valves R150, R151 and R152.
The “motor driven pump” units are mounted on the “pressure” unit.
2.5
Differential pressure regulator: RP 10
This direct action governing valve is composed of a diaphragm of large sec tonal area
subjected to pressure on each surface. The high pressure is exerted on the upper surface (oil) and on
the lower surface the low pressure (hydrogen). The obturator located on the pipes of the fluid to be
controlled is connected to the diaphragm by a stem. A nut screwed onto the rod compresses the
spring and regulates the differential pressure.
40
The pressure difference between the oil pressure at the oil seal inlet and the hydrogen
pressure contained in the generator acts on the governing valve and in this way enables the oil-seal
pressure to be regulated.
This pressure difference remains approximately constant and must be about 0.35 bars during
normal operation.
The governing valve may be isolated by valves R101 and R 102.
passes through the pipe fitted with valve R 170.
The oil-seal circuit then
The regulator is mounted on the “pressure” unit.
2.6
Oil Filtering
A certain number of filters are arranged on the circuit
Fine mesh filters FL 11 and FL 12, at the outlet of the anti-leak tanks, filter the return oil.
The cylindrical fine mesh filter FL 13, located at the lubricating oil inlet, ensures protection of the
pumps SU 10D001 and SU10D003, and cleanliness of the sealing oil.
The cylindrical fine mesh filter FL 10, protects the differential pressure regulator.
Filter FL 17 with a degree of filtration of 20 microns, located on the feeding pipe of the seal oil,
o
o
o
o
protect the sealing ring.
The cylindrical filters are composed of cartridge constituted of superimposed disc and star
o
shaped piece the thickness of the latter determining the mesh. The impurities which are
deposited on the outside surface of the cartridge are removed when the filtering element rotates
due to fixed scrapers, and are collected in vessel provided for this purpose. Theses pieces of
equipment are cleanable in operation, without dismantling, by simply turning the handle.
The filter mounted on the feeding pipe of the seal oil is double component: the elements each
o
contained in a filter casing, work in alternating sequence under normal operation conditions.
This allows a filter casing to be changed without interrupting the flow, by a single movement of
o
the change- over lever.
An element is cleaned by means of a back flow.
o
2.7
Second emergency system
This is composed of:
The pressure reducer DP 10 which lowers the pressure of the turbine governing system oil to the
normal operating valve
This pressure reducer is set to obtain a minimum oil flow during normal operation of the pumps.
The discharge valve RD 13 which protects the circuits against any overpressure due to failure of
the pressure reducer DP 10.
The second emergency system may be isolated form the circuit by valves R 161 and R163
o
o
o
o
3..
Definition of Equipment
3.1
Technical data
3.1.1 Motor driven pump units
For a relative hydrogen pressure of 2 bars in the generator.
o
o
o
The maximum oil flow necessary for the two seals may reach 60 Ltr/min, when the speed of
the unit is 3 000 r.p.m
This flow is only 10 Ltr/min approximately when the unit stops.
The theoretical pressure of the oil at the seals inlet is fixed at 2.35 bars.
41
Table of the motor driven pump units.
Pump
Designation
Ref.
Flow
Pressure
Speed
MotorOutput
Main
SU10D001
80 Lit/min
10 bars
1450 r.p.m
4 Kw
D.C Emergency
SU10D003
80 Lit /min
10 bars
1500 r.p.m
3.7 Kw
3.1.2 Air side de-training tank : CE 10
This is designed as a function of two criteria:
o
In volume, it constitutes an oil reserve for operation upon shut down of the unit: it contains
about 500 litres permanently.
o
Due to small diameter, but considerable length, it ensures that the oil is spread out with a view
to detraining.
3.1.3. Hydrogen side detraining tank : CE 19 AND CE 20
Each tank contains approximately 40 litres of oil in normal operation
3.1.4 Other tanks
The buffer volume in the anti-leaks is about 700 litres
The circuits and tanks in the “hydrogen oil-seal” system contain about 1,400 litres of oil in
normal operation
3.1.5 Gas extractor : SU10 D009
This is designed for a flow of 180m3/hr with a total manometric height of 60 mm W.C. The
rating of the drive motor is 0.75 KW
It is fitted against a pillar, close to and above the air side detraining tank.
3.2
Sensors
3.2.1 Gauges
They give local information on the value of the different physical quantities.
1) Mounted on the “pressure” unit:
SP11 P510 : Pressure at pumps discharge
SP11 P514 : Differential oil-hydrogen pressure
2) Mounted on the second emergency system:
SP11 P516 : oil pressure at the second emergency system outlet
3) Mounted at the oil-seals inlet :
SP11 P511 : Pressure in the oil-seals in front bearing block.
SP11 P512 : pressure in the oil-seal in rear bearing block.
3.2.2 Transmitter sensor
SP11 P011 : mounted on the “pressure “ unit, transmits in 4-20 Ma signal, the differential oilhydrogen pressure.
4.
4.1
Operation of the installation
Normal operation
The oil flow is determined by the hydrogen seals and arrives from the main lubricating tank
through valve R112, non return valve R 13, filter FL 13 and the isolating valve R 140 of the main
pump.
The main pump SU10D001 sucks in this oil coming from the main lubricating tank, and
discharge it to the seals by means of the following circuit; non – return valve RR 15, isolating valve R
141 and R 101, filter FL10, differential pressure regulator RP 10 and valve R 102.
42
Part of the oil flow discharged by the pump SU10D001 goes to the detraining tank CE 10,
through the discharge valve RD 11 and the pipe equipped with the valve R 142.
The oil leaving the seals divides into two flows, one containing air which mixes with the
bearing block lubricating oil and returns with it to the detraining tank CE 10, the other containing
hydrogen which flows into the detraining tanks CE 19 and CE 20.
The gas liberated in the tank CE 10 is discharged to the atmosphere through the gas extractor
SU10D009.
Continuous admission of pure hydrogen in the generator to the annular chamber discharges
the air-hydrogen mixture analysers ST11A342 and ST11A343, and flow meters ST 11F540 and
ST11F541.
From the detraining tanks CE 19 and CE 20, the oil flows into the anti-leak tank CE 12 through
the valve R 105.
This tank is at the same pressure as the generator. The small part of the hydrogen released
again returns to the detraining tank CE 20 through the pipe equipped with valve R 208.
The ballcock RF 10 serves to keep a constant oil level in the middle of the tank. When the
generator is at atmospheric pressure, this compartment is full of oil and the level is established in the
pipe equipped with valve R 105 as the same level than the detraining tank CE 10.
As soon as the gas pressure increases in the generator, the level in the aforementioned pipe
drops, the level difference being due to the gas overpressure. At rated hydrogen pressure the balance
cannot be kept and the level in the tank CE 12 is maintained by the ball-cock RF 10 which closes when
the level drops, so avoiding hydrogen escaping to the atmosphere.
From the compartment described, the oil rises up to the air side detraining tank CE 10 across
the filter FL 11, ball-cock RF 10 and the isolating valve R 106.
4.2
Special permanent types of operation
Failure of a certain number of components equipping the system does not prevent operation at
normal output on condition that a few precautions are taken.
4.2.1 Operation with emergency pump SU10D003
Should the pressure drop at the discharge on the main pump, detected by the pressure switch
SP11P316 and due to a mechanical pump failure, tripping of the motor or voltage failure, the
automatic control system orders start up of the emergency pump SU10D003F.
The emergency pump SU10D003 is driven sucks in oil coming from main lubricating tank
through the same circuit as the main pump SU10D001. The oil is discharged through non-return valve
RR 17 and valve R 151. The circuit configuration is similar to that in normal operation. The discharge
valve RD 12 allows the excess oil to escape into the air side detraining tank through valve R 152.
4.2.2 Failure of tank CE 12
Failure of the ballcock RF 10 is signified either by a level drop in the compartment CE 12
detected by the level controller SP11L312, or by clogging of the detraining tanks CE 19 and CE 20
detected by a high level in the liquid detector CE 17.
In both cases, the compartment CE is isolated by the valves AR 105and R 106. The CE 13
compartment with its ballcock RF 11 after manual opening of the valve R 107 ensures the same
function and consequently allows continued operation of the unit and intervention on the CE 12
compartment
43
4.2.3 Oil circulation at unit shutdown
The generator being stopped, the lubricating circuit is no longer under pressure and the
hydrogen oil seal flows in a closed circuit: autonomous operation.
The return oil from the seals coming from the detraining tank CE 10 and compartment CE 12,
is drawn in to the pump SU 10D001 through the valve R 111 and obturator RR 11 which is then open.
The rest of the circuit is unchanged in relation to normal operation
The oil flow to the seals is far significant than in normal operation
The emergency start up of pump SU10D003 remains assured as during normal operation
4.3
Transition emergency circuit
In case of simultaneous failure of the main and emergency pumps, a second emergency device
is provided to supply the oil-seals, allowing the time to lower the hydrogen pressure in the generator
to a value below block supply oil pressure. The second emergency is only available for a few minutes
in case of turbine shutdown.
This emergency device uses high pressure oil coming from the HP pump driven by the turbine.
It is automatically put into service as soon as the pressure of the pumps SU10D001 and SU10D003 is
reduced by a certain valve.
The oil arrives through the pipe fitted with valve R 161, flows into pressure reducer DP 10, the
isolating valve R 163, the return valve RR 19, valve R 164, and arrives in the normal seal supply
circuit against any overpressure due to failure of the pressure reducer DP 10. A discharge pipe is
provided on this pressure reducer to remove slight leakage possibly occurring during operation, when
the pressure accidentally exceeds the set pressure.
4.4
Operation at reduced load
4.4.1 Supply of the oil seals directly using lubricating oil.
In case of failure of the main pump SU10D001 and emergency pump SU10D003, the second
emergency system will be put into service to supply the oil-seals, allowing time to lower the hydrogen
pressure in the generator, and then be able to ensure the permanent oil supply of the seals directly
from the lubricating circuit. It is then essential to lower the generator load to avoid abnormal heating
up.
The hydrogen pressure in the generator must be 0.35 bar lower than the lube oil pressure
measured at the inlet to the seals in these conditions the second emergency system may be put out of
service.
The oil arrives directly from the lubricating circuit through valve R 112 and the non-return
valves RR 13 and RR 20 which are open, by – passing the motor driven pump units, and supplies the
seals across the differential pressure regulator, as in normal operation. The rest of the circuit remains
unchanged.
4.4.2 By-pass for anti-leak compartments
In case of simultaneous failures of the ball-cock RF 10 of compartment CE 12 and ball-cock RF
11 of compartment CE 13, and in order to avoid unit shutdown, these two tanks may be isolate.
It is then necessary to lower the Hydrogen pressure in the Generator to a compatible value, by
means of easy manual adjustment using valve R 110 and maintaining the oil level in the tank CE 14.
This value is determined during the compressed air tests. The Generator load must be reduced to a
value compatible with the new hydrogen pressure.
GENERATOR AND AUXILIARIES:
The ratings of the various main transformers are as follows:
Generator Transformer
–
133 MVA
Station Transformer
–
15 MVA
Unit Transformer
–
10 MVA
@@@@@@@@@@@@@@@
44
(D)
GENERATOR – EXCITATION SYSTEM (Ref- Drg No. HPS/WAPCOS-15 to 17)
GENERAL PRINCIPLE OF OPERATION:
In the Static Excitation System, the AC Power is tapped off from the Generator terminal
stepped down and rectified by fully controlled thyristor bridges and then fed to generator field thereby
controlling the generator output. A high controlled speed is achieved by using an internal free control
and power electronic system. Any deviation in the generator terminal voltage is sensed by an error
detector and causes the voltage regulator to advance or retard the firing angle of thyristor thereby
controlling the field excitation of Alternator. Refer General layout of excitation system.
FUNCTIONS OF STATIC EXCITATION SYSTEM:
1.
2.
3.
4.
Regulate stator Voltage of the machine.
Meet excitation power requirements under all normal operating conditions.
Enable maximum utilisation of machine capabilities.
Regulate MVAR (Reactive Power) loading within limits.
STATIC EXCITATION SYSTEM CONSISTS OF:
1.
2.
3.
4.
Excitation Transformer
Thyristor bridge Rectifier
Excitation start-up and field discharge equipment
Regulator and Operational control circuit
In Hwange Power Station, Unit 1,2 and 4 are equipped with Analog Voltage Regulators.
Unit 3- is equipped with P320 Automatic Voltage Regulator by M/s Alsthom.
Unit 5&6- are equipped with Digital Voltage Regulator by M/s Ansaldo.
PRINCIPLE OF OPERATION:
a)
Power Circuits
i)
ii)
iii)
iv)
Excitation panel feeding system
Power conversion system
De-energising system
Field monitoring system
CONTROL ELECTRONICS:
Manual Regulator
Digital Setting Device
Delayed Rotor Limit
Firing circuits:
o
o
o
o
o
Synchronism
Amplitude/Phase Shift Conversion
Max Load Angle Limitation
Firing Pulse formation
Firing Pulse Amplification
Limit lag and Voltage Control
Power Supply Transient Control.
AUTOMATIC REGULATOR:
o
o
o
o
o
o
o
o
o
Machine voltage regulation loop.
Corrective circuits for positive and negative compound
Stabilizing signals
Voltage/frequency limit
Under excitation limit
Over excitation limit
Minimum/ Maximum excitation current limit
Delayed limits
Joint voltage control
45
SIGNALLING AND PROTECTIVE PANEL:
o
o
o
o
o
Fault string counter
Maximum Instantaneous current
Crow bar triggering
Thyristor thermal protection
Annunciator
CONTROL LOGIC:
-
Field flashing
Supervisor for Auto-manual regulation
Protection logic
Battery
- Field breaker control
- Joint voltage control
- Lock out controls
EXCITATION SYSTEM 1,2,3, AND 4 (STAGE-I)
Power circuits:
Excitation Panel Feeding System:
This system feeds the Convertor with the alternating current from the Generator Output
terminals.
The system includes:
-
Step down transformer for convertor feeding (TRE)
Synchronising Transformers (TSA-TSM), transmitting the necessary signals to the firing circuit.
Voltage Transformers (TVR) and current transformers (TA ½) for voltage and current signals to
regulator.
EXCITATION TRANSFORMER:
▪
The transformer is outdoor, oil immersed, three phase units with cooling by natural oil circulation
and natural air circulation. The rating is 3 x 500 KVA, 10.5 KV primary and 640 V on Secondary
side for Stage-I, whereas for Stage-II the rating is 1780 KVA with primary voltage as 17 KVA
and Secondary voltage as 810 Volts.
BUCHHOLZ RELAY:
Gas actuated relays have 2 contacts (Tripping and Alarm) and can operate one closed and the
other open. It is used to protect transformer from internal faults like Fire and etc.
POWER CONVERSION SYSTEM:
AC side Protections”
The Convertor is provided with D2A protection class, which characteristics are indicated here
below:
Fuse triggering selectivity
Protection against over voltages with crow bar.
Convertor protection with thermal image relay
Damaged fuse number limiting for shortcut.
RECTIFIERS:
A set of thyristor connected in series and in parallel, the function of which might be performed
by a single thyristor is called bridge branch. The no. of parallel strings per branch is determined
according to the field currents calculated in faulty conditions; metering points are provided to check
the rectified correct operation.
-
Alternate feeding voltage
Rectified voltage
-
Gate voltage
46
DC SIDE PROTECTION:
On the DC side, the thyristor shunt (crow bar) and non linear resistor protect the exciter in
case of dangerous voltages when the machine falls out of step.
The crowbar triggering of which is automatic enables the discharge of overvoltage’s caused by
inductive current cut offs in the rotor through the discharge resistance.
The feedback voltage transformer (TVR) is transmitting the information required for the
system monitoring to the voltage regulator.
COOLING SYSTEM:
The conversion modules are cooled by ventilation. The Thyristor Bridge is cooled by closed
circuit ventilation.
DE-ENERGISING SYSTEM: A helicoidally fan MV
Air flow - 0.9 m3/s,
Speed - 2850 rpm,
Power absorbed – 0.6 KW
FIELD BREAKER:
The field breaker consists of a bipolar breaker with arcing pole, the contacts of which are
provided with magnetic blow arc chutes.
The field breaker is draw-able and provided with contacts for anti-hunting (a circuit which
prevents the discharge switch from opening and closing continually so called hunting).
DISCHARGE RESISTANCE:
The discharging resistance has the purpose of dissipating the energy stored in the rotor of the
synchronous machine, thus allowing a fast suppression of the field current, it is cut in during deenergising for in case of crow bar triggering.
FIELD MONITORING SYSTEM;
ETR Transducers:
It is used for monitoring of field voltage and current.
Electrical transducer for Reactive power:
REGULATOR OPERATION:
The Microprocessor works out three basic types of functions:
-
Interface functions
-
Trace function
Operative functions
OPERATIVE FUNCTIONS:
o
o
o
o
o
o
Regulation signals transduction
Basic Regulation Loops
Reactive Power or power factor regulation
Compound PSS and V/Hz limitations
Under-excitation and rotor current limit functions
Rotor over load function.
The auxiliary supplies are:
o
o
o
o
110
380
380
380
V
V
V
V
DC from battery for Electronics, Logics and auxiliary circuits.
AC, 50 Hz, 3 Phase for internal lights, fan, heaters
AC, 50 Hz, 3 Phase for field flashing
AC, 50 Hz, 3 Phase for the power supply of the motor fans.
47
WARNING (ALARMS):
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
16)
17)
18)
19)
20)
AVR (i) FAULT- SERIOUS OR BUCHHOLZ ALARM
The maximum temperature 1O level
Buchholz 1 O level
The minimum oil level
The maximum oil level
Rectifier fuses
Rectifier – Maximum temperature
Rectifier current unbalance
Cooling rectifier
Water flow
Water temperature
Air flow
Air temperature
24 V DC Back up supply missing
Crow bar firing missing
Maximum rotor temperature
Field flashing bypass
Over-voltage protection fault
PLC failure
Excitation transformer fault
ANNUNCIATOR:
Excitation Transformer:
o
o
o
o
o
High temperature
High temperature trip
Buchholz triggering
Buchholz triggering trip
Over current trip
Power convertor:
o
o
o
High thyristor temperature
First string failure
Rectifier instantaneous over-current trip
Cooling system:
o
o
o
o
o
High air temperature
Low cooling fan water flow
Fans not available
Standby fan running
Fans failed.
Field Breaker:
o
Field breaker not available
Field flashing:
o
Field flashing too long
Crow bar:
o
o
Operating crow bar
Crow bar over-load trip
Electronic supply:
o
o
MVR electronic DC supply failure
Signal/Protection panel DC supply failure
48
CONTROL LOGIC:
Field flashing:
When the excitation system is fed by the machine incoming feeder, an
auxiliary excitation source, represented by the central battery is required for a very short time to
trigger self energising.
Supervisors for Auto/manual Regulation:
Change over from one control system to another occurs by suppressing the firing circuit pulses
of the non-operating regulator. Before operating, the 98 M and 90V firing circuit control voltages shall
be equal to prevent change over from causing changes in the reactive load or lockout due to maximum
current or voltage.
+ 15 V Voltage is used to feed the following circuits:
Regulation Circuits
Protective Circuits
Firing Circuits
Signalling Circuits
+ 24 V Voltage is used to feed the pulse generator for tryristor, transducers, the signalling and trigger
logic and read relays for signalling, protective and Regulating functions.
MANUAL REGULATOR:
Principle of operation:
The voltage manual Regulator is a control system providing for
thyristor convertor driving by means of a firing circuit and based upon the reference set by operator
through the setting device.
AUTOMATIC REGULATOR:
Principle of operation:
As a result of processing the analogue, signals of the quantities to set,
the automatic regulator gives a signal suited to the plan requirements, which drives the power stage
(thyristor Convertor) of the excitation system.
CONTROL ELECTRONICS:
The control monitoring and protection circuits of the excitation system are of semi-conductor
static type, accomplished with printed circuits on draw out cards.
o
o
o
Manual regulated
Automatic Regulator
Protection and signals
( 98 M)
( 90 V)
( 98 S)
FEEDERS:
Each type of Electronic circuits is provided with power supply unit. These units are in turn
powered both in alternating and direct power supply.
Each circuit consists of
o
o
o
o
Transformers
Diodes
Convertors 1 & 2
Voltage Control System by means of Relays.
Each feeder unit has four operating voltages; Two stabilized (+ 15V) and two semi-stabilised
(+ 24V), Insulated from one another and from the supply mains.
SIGNIFICANCE OF MACHINE CAPABILITY
REQUIREMENTS OF EXCITATION SYSTEM:
DIAGRAM
AND
OPERATIONAL
Capability diagram of Generators give the safe operating regimes and limitations. This is of
great help to the operating Engineers to ensure operations of the machine accordingly.
Operational requirements of excitation system essentially call for a fast response particularly
High Initial Response excitation system, High degree of Reliability and also suitable arrangement of
field discharge.
Capability diagram gives information regarding full load rotor current, max. Rotor angle during
steady state leading power factor zone operation, are essential for proper setting of various limiters in
the excitation control system. Refer Limitation drawing PQ diagram--=====*****=====
49
50
IV.
DESCRIPTION OF GENERAL PLANT:
a.
COAL HANDLING PLANT (Ref- Drg No. HPS/WAPCOS-18 to 22)
General Description:
1.
SUMMARY
Hwange Power Station is the base load station for Zimbabwe. It was built in two stages; Stage
1 of 4 x 120WM units and Stage 2 of 2 x 220 MW units. The total generating capacity of the station is
920 MW.
The coal handling plant services both Stage 1 and 2 for their respective coal requirements.
Stockpile Capacity is 450000 Tonnes. Average rate of Consumption is @0.5 ton per Mwh.
2.
General Description of plant
Junction tower 1
Junction tower 1 is the terminal point for the colliery overland. The overland conveyor deposits
coal into a hopper. The bunker discharges coal onto the main coal feeding belt (C1) that supplies coal
to junction tower 2. There is a magnetic separator at the discharge head of the overland conveyor for
removing tramp iron.
There is also a coal sampling system located here. The distance between tower 1 and 2 is
approximately 100 meters.
Junction tower 2.
The main coal conveyor (C1) discharge coal via a diverter chute to a belt (C2) that feeds the
station directly or to 2 conveyors (C9 & C10) that feed the coal stockpiles. Diverter chute actuation is
performed by electro/hydraulic rams. A diverter chute determines which stockpile is fed. Stock pile
stacking is performed manually using front end loaders. The distance between junction tower 2 and
junction tower 3 is approximately 200 meters.
The active stockpiles have a storage capacity of 5500 tonnes.
•
•
C2- width 1350 mm – capacity 1575 t/h
C9 & C10 – width 1350 mm – capacity 1575 t/h
Diverter chute travel approx. 600mm
Junction tower 3.
Junction 3 is the starting point for the incline conveyors that feed the station mill bunkers.
The incline conveyors are fed from 2 sources:
Direct feed
Coal is fed directly from junction tower 2 through a diverter chute. The diverter chute
determines which incline conveyor (C3 & C4) is to be placed in service. Diverter chute actuation is by
electro/hydraulic rams.
Reclaim feed
The incline conveyors can be fed from 2 separate reclaim hoppers.
Reclaim hopper 1
The hopper has 4 discharge gates. At each discharge point there are vibrating feeders. The
vibrating feeders have a capacity of 520t/h. The vibrating feeders are paired and dedicated to two
under belt conveyors (C7 & C8). The under belt conveyors feed the incline conveyors. Magnetic
separators are installed at the discharge heads of C7 & C8.
Reclaim hopper 1 has a storage capacity of 375 tonnes.
51
Reclaim hoppers 2.
Both hoppers are manually filled by using scrapers.
De-watering
At each hopper discharge point are de-watering pipes that feed water into the de-watering
sumps. Each reclaim hopper has its own de-watering sump. Both de-watering sumps have 2 sump
pumps.
The distance between junction tower 3 and junction tower 4 is approximately 200 meters.
•
•
•
•
C3 & C4 width 1050 mm – capacity 950 t/h
C7 & C8 width 1050 mm – capacity 950 t/h
C11-width 1350 mm – capacity 1575 t/h
Diverter chute travel-approx. 600mm.
Junction tower 4
The incline conveyors (C3 &C4) feed into 2 separate hoppers. Each hopper has a separate coal
sampling conveyor that feeds a common coal sampling system. The hopper discharges feed into a
common discharge chute. A diverter chute determines whether stage 1 or stage 2 is to be supplied.
Diverter actuation is by electro/hydraulic rams.
Discharge to stage 1
A diverter chute determines which travelling tripper car/belt (C5 &C6) is to be supplied. The
tripper car/belt fills the mill bunkers. The tripper car/belt length is approximately 150 meters long.
Discharge to Stage 2
Stage 2 also has 2 travelling tripper car/belts (C12 & C13) and service is determined by a
diverter chute. The tripper car/belt length is approximately 80 meters.
2.2
C5 & C6 width 1050 mm
C12 & C13 width 1050 mm
Capacity 750 t/h
capacity 750 t/h
Diverter chute travel approximately-
600mm
Coal plant instrumentation
Belt Weighers
Belt weighers are located on the main conveyor C1 and the incline conveyors C3 &C4. The
weighers are rated at 3000t/hr.
Belt alignment/Under-speed/pull ropes
All the conveyor belts are equipped with under speed, pull rope and belt alignment detection.
The detectors are hard wired and act directly on the switchgear.
2.3
Electrical
All the conveyor plant switchgear is rated at 3.3KV and 380 V AC. The driven side of the
conveyors are quipped with solenoid operated brakes. The 3.3 KV is supplied from the station board 1
and 2. The 380 vac for coal and ash plant is supplied through the coal plant substation.
The coal plant has an independent substation for supplying the plant. The 380vac switchgear
is located in the building located below the coal handling plant control room.
@@@@@$$$@@@@@
52
b.
ASH HANDLING PLANT
1.1
GENERAL DESCRIPTION
The ash handling plant removes ash from the furnace ash hoppers hydraulically and transports
it via high velocity sluiceways to an ash sump from where it is pumped via discharge pipelines to the
ash disposal area.
The plant is designed to remove 100 tonnes of ash from the ash hopper of each boiler unit
during a working period of 14 hours on the basis of the four boiler units teaming at one time.
The high velocity sluiceway feeds the ash to a clinker grinder mounted in a pit within the ash
plant house, where it is ground to a suitable size before being deposited into the ash sump below the
grinder. Two clinker grinders are provided, one duty and one standby. The sluiceways are arranged so
that ash may be fed to either of the clinker grinders. To ensure that removal of either clinker grinder
for overhaul does not interfere with the overall operation of the plant a by-pass complete with grid, is
provided to feed the ash directly to the sump. Two lifting liners are incorporated in the section of the
sluiceway within the ash plant house for this purpose. Slurry pumps are provided, mounted in a pit
within the ash plant house, to pump the ash and water mixture from the ash sump via the discharge
pipelines to the ash disposal area. Three slurry pumps are provided, one duty and two stand by. Each
pump is capable of dealing with the ash and water at the maximum rate at which it will be fed to the
sump in the course of the removal of ash from the furnace hopper. Two discharge pipelines are
provided to the ash disposal area. The output from any one of the three slurry pumps may be routed
to either or the discharge pipeline as required. Each discharge pipeline is fitted with a pneumatically
operated emergency isolating valve to prevent drain back from the discharge piping. High pressure
pumps within the ash plant house draw water via a common strainer from the reservoir adjacent to
the ash plant house and supply high pressure water for operation of the plant. Three high pressure
pumps are provided, one duty and two standbys. Level detectors within the ash sump control the
operation of a pneumatically operated make-up valve which is turn, control the admission of make-up
water to the sump. The make-up water is taken from the reservoir adjacent to the ash plant house.
Two electrically driven vertical spindle bilge pumps are provided, one for draining the slurry pump pit
and the other for dealing with drainage in the ash sump during non-ashing periods.
DUST HANDLING PLANT
GENERAL DESCRIPTION
The dust handling plant removes the dust collected in the hoppers of the electrostatic
precipitators, economiser hoppers and chimney hoppers by means of water ejectors operated by water
supplied by the high pressure pumps in the ash plant house, and transports it via gravity type
sluiceways to the high velocity sluiceway which carries it to the ash sump from where it is pumped to
the ash disposal area. A slide plate dust valve is mounted each hopper outlet to control the flow of
dust to the ejector for the hopper outlet. A spectacle plate valve is fitted between the slide plate dust
valve and hopper outlet to facilitate maintenance of the slide plate valve.
@@@@@$$$@@@@@
53
54
c.
ELECTRICAL SUPPLY SYSTEM FOR HWANGE POWER STATION
INTRODUCTION: (Ref- Drg No. 23 to 27)
Electrical supply system for auxiliaries is the most important part of a thermal power station.
The failure of Electrical supply even to small equipment could result in the station losing load or being
put out of commission. Therefore, the auxiliary supply system at Hwange Power Station has been
designed and installed very carefully to serve the reliable and dependable power source to their
various auxiliaries.
TYPE OF AUXILIARIES:
The auxiliaries can be classified as1. Boiler auxiliaries such as draught fan, Coal mills, fuel and ash handling facilities, feed pumps etc.
2. Turbo-Generator and condenser auxiliaries such as circulating Water Pumps, Auxiliary Cooling
Water/Bearing Cooling Water pumps, Condensate Extraction Pump, Lub oil and Seal oil pumps etc.
3. Common auxiliaries comprising of Compressors, Over-head Cranes, and Water Treatment Plant
equipments, service pumps, fire-fighting, elevator, lighting etc.
SOURCE OF SUPPLY:
As regards the source of supply is concerned, auxiliaries can be divided into main groups.
i)
Unit auxiliaries: These are associated with running of a unit, whose loss would cause an immediate
reduction in unit output.
ii) Service auxiliaries: These are common auxiliaries associated with one or more units. Their loss
would not affect the output of the station until after considerable time interval.
At Hwange P.S. “Unit system” has been adopted. In this system one boiler, one turbo- generator,
one step up Transformer with auxiliary transformer and exciter transformer operate as a unit. When
unit is in operation auxiliary supply is available from unit auxiliary transformer connected to Unit
Board. To obtain the auxiliary supply during start-up, station transformers have been installed to feed
the auxiliaries from grid through station board.
In stage-I all 120 MW units are switched to 330 KV power system with the help of 10.5/330 KV
step-up generatoer transformer and stage-II both 220 MW units are switched to grid through 17.0/330
KV step up transformer.
RATING OF SERVICE VOLTAGE:
1) In stage-I for high rating equipments 3.3 KV and for low rating equipments 380 V supply Voltages
have been arranged as:
2) For Stage II- 11 KV, 3.3 KV and 380 V LT supply have been provided for equipments depending
upon their rating.
METHOD OF OPERATION:
To start up a unit, a supply is taken from 330KV Grid via the Station Board to the unit board.
Under this condition breaker of unit auxiliary transformer must be in open position. When the
generator has been brought up to normal speed, synchronised with grid and loaded about 10% of its
rating, then unit transformer supply breaker is closed and disconnect station supply from unit board.
Thus unit auxiliaries are continued to fed from unit auxiliary transformer. During changeover of supply,
paralleling duration of both station and unit supply shall be as minimum as possible.
LAYOUT OF SUPPLY ARRANGEMENT AT HWANGE POWER STATION1.
Station supply of Stage I:
There are two 3.3 KV station Boards in Stage-I. These Boards are fed from 15 MVA 33 KV/3.3
KV Station Transformer I and II. 33 KV Bus Bar feeding the Station Transformer I & II, receives the
Power from 330 KV grid via three 330/33 KV Transformers 1A, 2A and 3A. 33 KV/3.3 KV station
transformer I feed to station board I and station transformer II feed to station board II.
Interconnection between station board I and unit board I and unit board 3 have been provided.
55
Similarly station board II is also interconnected with unit board II and unit board IV. Station board I
and II are also interconnected. 3.3. KV station board I feeds 3.3 KV/380 V transformer which in turn
feed to 380 V board I installed in boiler House, turbine House, Water Treatment plant, Coal Plant,
Lighting board. Similarly station board II provide the supply to 380 V board II installed at locations as
mentioned above. Single line diagram of station board I is given in drawing no. HPS/WAPCOS-23.
2.
Station supply of Stage II:
In stage-II there are two Nos. 11 KV station boards known as 11 KV station board 3 and 11 KV
station board 4. These boards are fed from two No. 30 MVA, 33/11 KV station transformer 3 and 4
respectively. From 11 KV station board 3 interconnection to 11 KV unit board 6, 11 KV unit bnoard 5
and 11 KV unit board 4 have been provided. In stage-II 3.3 KV station boards known as 3.3 KV station
board 3 is also available. This board is fed from 11 KV station board 3 through 8.5 MVA, 11/3.3 KV
Transformer, 3.3 KV station board 3 is also interconnected with 3.3 KV station board of Stage-I. 3.3
KV station board 3 in turn feed to 380 V board 3 provided at Turbine house, boiler house and lighting
board 3. Single line diagram (SLD) of station supply system is given in drawing no. HPS/WAPCOS-24
and HPS/WAPCOS-25.
3.
Unit supply of Stage –I
Single line diagram of unit supply is given in Figure 1. In stage I, 3.3. KV unit auxiliaries are
fed from their respective 3.3 KV unit board which in turn get supply from 10.5/3.3 KV 10 MVA unit
transformer connected directly to generator terminals and 380 V auxiliaries is being fed from 380 V
auxiliary board A & B receiving power from 3.3 KV unit board through 750 KVA, 3.3 KV/380 V auxiliary
transformer. 3.3 KV auxiliaries fed from 3.3 KV unit board 1 are as follows:
❖
❖
❖
❖
❖
❖
❖
Mill 1A, 1B, 1C & 1D
Condensate Extraction Pump 1A, 1B
B.F.P. 1A
C.W.P. 1
PA Fan 1A, 1B, 1C & 1D
FD Fan 1A, 1B
ID Fan 1A, 1B
It may be noted that 2nd B.F.P. of units of 1 stage is not connected to their respective 3.3 KV
unit board. 2nd B.F.P. of unit 1 and 3 is connected on 3.3 KV station board 1 and of unit 2 and 4 to 3.3
KV station board 2.
4.
Unit supply of Stage –II:
SLD of 11 KV and 3.3 KV unit supply system is given in fig. 2 & 4. Here 11 KV unit board
receives power from 20 MVA, 11/17 KV unit transformer directly connected to generator terminals and
3.3 KV unit boards are charged from 11 KV unit boards through 8.5 MVA, 11/3.3 KV board 5A, 5B, 6A
& 6B transformers shown in fig. 3. In stage-ii all three BFP’s are connected to 11 KV boards of their
respective unit boards and C.W. Pumps 6&7 are connected to 11 KV station board 3 & 4 respectively.
C.W. pump 5 is fed from station board 3. Other auxiliaries are connected to 11 KV or 3.3 KV unit board
depending upon their voltage rating.
5.
380 V Essential supplies boards:
Each unit has one no. 380 V essential supply board to cater the requirements of most
important auxiliaries of turbo-generator. For these boards main supply is arranged from Turbine board
and Standby from DG supply system. On these boards auxiliaries connected are Aux. Bearing Oil
Pump, Barring Gear, Hydrogen Seal Oil Pump, Jacking Oil Pump, Hydrogen Extraction Fan and Oil
Vapour Fan. SLD of Essential supplies boards are given in drawing no. HPS/WAPCOS-26.
6.
D.G. Supply System:
To meet the power requirement of essential auxiliaries and services during the Grid Failure,
5 no. Diesel Generating (DG) Sets have been provided and kept on auto start. These DG Sets start
automatically whenever the A.C. supply is not available in the Plant. This system supplies the power to
these auxiliaries which are necessary to the safety of Turbo-generator and other equipments. Single
line diagram of system is given in drawing no. HPS/WAPCOS-27.
$$$$$$$$$$$$$$$$$$$$$$$
56
WATER TREATMENT
d)
NEW REVERSE OSMOSIS PLANT (RO PLANT)
INTRODUCTION:
The existing Water Treatment Plant at Hwange Power Station is very old and refurbishing may
not lead to a long term solution. Hence, Reverse Osmosis Plant is being introduced to cater for the
D.M. Plant requirements of the Power Station. Reverse Osmosis Plant incorporates latest technology
and are easy to operate and maintain. This plant requires less spares and the cost of generating water
is much lower than the conventional DM Plant. The Reverse Osmosis Plants are being extensively used.
The plant is supplied by M/s Ion Exchange (India) Ltd which is a company having good
background and is a leading water treatment company in India and one of very few in the world with a
comprehensive range of technologies, products and services, which cover the entire spectrum of water
and waste water treatment.
▪
PROCESS DISCRIPTION:
ON LINE AUTOMATIC FILTRATION:
Pressurised water from raw water tank enters a coarse screen “On-line Filter” where large
particles are pre-filtered.
The water then enters fine screen “Gravity Sand Filter” and then goes to the filter water sump
when the fine screen becomes contaminated, a pressure differential across the screen is sensed
causing the electric control unit to open the hydraulic flush valve.
The entire cleaning cycle takes approximately 5-20 seconds. It should be noted that even
during the back-flush cycle, clean water flow to the system is not interrupted.
▪
RO PLANT:
ANTISCALANT DOSING:
From filter water sump, water is fed to “Static Mixer”. Dosing is done to the “Static Mixer” of
Antiscalant to prevent “RO Membrane” from scaling. Ph adjustment is also done in the Static Mixer.
▪
MICRON CARTRIDGE FILTER:
The filtered water will then pass through “Micron Cartridge Filter”. The chemically conditioned
and filtered water from the “Micron Cartridge Filter” is then fed into “RO Unit” via RO high-pressure
pumps.
▪
REVERSE OSMOSIS SYSTEM RO:
The pressurised flow enters to “RO System”. 38 No. of segments are provided in “RO System”.
They are divided into 19. 13 and 6 segments. Water from each zone enters the other and finally pure
water comes out. Due to high pressure, a portion of the feed water permeates through the semipermeable RO Membrane as pure water while the balance of the flow exists the system as reject.
Pressure switches are provided at the RO high-pressure feed pump delivery, to protect the membrane
from high pressure exposure. A flow meter is provided on the RO Skid on product line which shall give
indication about permeate flow. The conductivity transmitter is provided on the RO permeate line,
which monitors the product water quality. Auto dump valve is provided to drain the product water if
the conductivity at RO outlet is not within the set limits.
After every shut down, RO system shall be flushed with permeate water from the Clients
permeate water storage tank.
▪
CLEAN IN PLACE SYSTEM (cip):
A cleaning system is provided for the RO chemical cleaning as well as to clean the membranes
as per the system requirements.
A system cleaning is required when the normalised permeate flow is reduced by 10-15%, or
the differential pressure (DP) increases by 15 percent from the reference conditions.
57
The operation of cleaning has to be initiated manually for each bank; the cleaning solution
preparation operation is totally manual. The micron cartridge type guard filter is provided after the
cleaning pump to prevent passage of suspended solids removed during the CIP cycle back onto the RO
Membranes. The RO Cleaning pump will flow cleaning solution through each stage of RO train. The
overall rate is based on the number of RO vessels in a train and each step of the cleaning process is
controlled manually at the pump delivery.
▪
DEGASER:
▪
MIXED BED EXCHANGER:
Water from the R.O. System goes to the Degaser for removal of any gas
before it is fed to the Mixed Bed Exchanger.
Mixed Bed Exchanger is a final unit, which acts as a polishing unit to achieve Ultimate Quality
of DM Water; Mixed Bed Exchanger consists of Cation Exchange Resin and anion Exchange Resin in a
mixed form. Cation Exchange Resin is regenerated using Sulphuric Acid and the anion Exchange Resin
re regenerated using Sodium Hydroxide.
R.O. High
Press pump
REVERSE OSMOSIS PLANT
58
TECHNICAL SPECIFICATIONS OF THE R.O. PLANT
S.N.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
DESCRIPTION
RAW WATER STORAGE TANK – BY CLIENT
ON-LINE FILTER
Flow Rate
500 m3/hr
FILTER WATER STORAGE TANK – Using existing gravity filter water
RO FEED PUMP WITH MOTOR
Capacity
225 m3/hr
ANTISCALENT DOSING
DOSING TANK
Capacity
1200 Lit
DOSING PUMP
Capacity
50 lph
pH ADJUSTMENT DOSING
DOSING TANK
Capacity
1200 Lit
DOSING PUMP
Capacity
50 lph
MICRON CARTRIDGE FILTER
Capacity
225 m3/hr
RO HIGH PRESSURE PUMP WITH MOTOR
Capacity
113 m3/hr
RESERVE OSMOSIS UNIT
Feed flow rate
225 m3/hr
Permeate flow rate
180 m3/hr
Recovery
80%
RO CLEANING UNIT
TANK
Capacity
2.5 m3
PUMPS
Capacity
135 m3/hr
MICRON CARTRIDGE FILTER
Capacity
135 m3/hr
RO WATER STORAGE TANK- Using existing degasser water storage sump
Capacity
60 m3
MB FEED PUMP WITH MOTOR
Service flow rate
180 m3/hr
MIXED BED EXCHANGER
Design flow rate
180 m3/hr
Service time
80 Hrs.
Resin Make and type a) Cation resin b) Anion
INDION 225 H+INDION GS300
resin
Type of Regeneration
Sequential
Quantity of 100 % H2SO4
374 kg
Quantity of 100 % NaOH
342 kg
MIXED BED AIR BLOWER WITH MOTOR
Capacity
20 m3/hr
MB REGENERATING UNIT
ACID MEASURING TANK
ACID DOSING PUMP
Capacity
1200 LPH
CAUSTIC DOSING PUMP
Capacity
2400 LPH
REGENERATION PUMP WITH MOTOR
Service Flow rate
m3/hr
DM WATER STORAGE TANK- Using existing DM Water Storage Tank
@@@@@$$$@@@@@
59
60
e.
DEKA PUMPING STATION
1.0
INTRODUCTION:
Hwange Power Station, (2x220 MW + 4x120 MW) is one of the largest Power Stations in
Zimbabwe, supplying 50% electricity needs of Zimbabwe. The water required for steam generation
and all the housing schemes is drawn from the Zambezi River. The raw water is transported from a
Low Lift Pump Station to the settling tanks from where suction is taken to the High Lift Pump Station.
From High Lift pump station, the water is delivered to 2 Raw Water Reservoirs of capacity 1,50,000 M3
constructed on a hill adjacent to the Power Station. From the discharge of the High lift pumps, a
tapping is taken to the water purification works. After purification, one tapping goes to the Baobab and
associated Housing complex. The second pipeline goes to the potable water reservoirs near Power
Station.
From the two Reservoirs, pipeline goes to a Valve Pit. From the valve pit, supply is given to the
Stage-I and Stage-II C.W. make-up. Further supply from the valve pit is also given to clarifier, Firefighting and Ash Handling Plant. From the Clarifier water goes to the sand filter. The water required for
the D.M. Plant is taken after this sand filter. A tapping is taken from the sand filter which is a suction
to the two potable pumps, which deliver water to the circular potable water reservoir situated near the
Power Station. From the Circular Potable Water Reservoir, suction is taken for two potable pumps
which deliver water to the header tank. From the header tank, potable water supply comes to the
power Station and Ingagula Housing complex.
To facilitate water supply to the water purification works, in case of failure of High lift pumps, a
tapping is taken from the discharge of the two reservoirs to a Pressure Breaking Tank, which supplies
water back to the water purification works.
All the pipe lines in the system are provided with cathodic protection.
Electric power required for the Deka Pumping Station is taken from a 88 KV sub-station near
the entry of Power Station.
The 88 KV line goes to Deka where two no. 88/11 KV Transformers of 7.5 MVA capacity are
provided.
Two 11 KV buses are provided at Deka. From one bus supply is given to the 11 KV High Lift
Pumps. From 2nd bus supply is given to two 11 KV/380 V, 1 MVA Transformers for giving supply to the
Low Lift Pumps.
The complete layout of the system is given.
DEKA PROJECT:
➢
The WAPCOS Engineers visited Hwange site for Deka Project and have prepared a project
report. It covers the following:
➢
The rehabilitation of pumps, valves and other equipment needing Replacement/ refurbishing.
➢
De-silting of intake and other sumps.
➢
Addition of one more line to cater for station expansion.
➢
Replacement of old switch gear and controls including PLC and SCADA system.
➢
Rehabilitation and expansion of water supply to Hwange Town and Deka community.
@@@@@###@@@@@
61
62
V. OPERATING INSTRUCTIONS
(A)
BOILER ----
1.0
INTRODUCTION
1.1
GENERAL NOTES:
1.1.1
Automatic control does not preclude intelligent interpretation and anticipation by the Operator
in charge.
Operating experience may dictate further refinement to the procedures outlined.
One of the most common causes of trouble and dislocation in bringing large boiler/turbine
units on load is delay in bringing feed water heating plant into commission during the initial
stages of loading on the unit.
The operator in charge should ensure that the feed heating plant is available for immediate
use as and when steam flow conditions through the turbine permit.
If this is not done, trouble will be experienced in control of both steam and metal temperatures
on the boiler due to over-firing to maintain load, this happening at a time when the turbine
differential expansions are usually critical and will result in a shut down of the machine/boiler.
In connection with the above, desuperheater spray water supplies should always be available
during run up, ready to be used when required.
During pressure raising and whilst awaiting loading on the turbine final circulation drains
should be regulated to give a continuous flow of steam through the superheater, and must be
used to maintain control of the final steam temperature when running up the turbine.
Pressure raising and initial loading should be done using the lower of P.F. mill groups.
However, when unit is on normal steady load as much use as possible should be made of the
upper P.F. mill groups especially when unit load is below MCR. This applies more to new units
when the boiler is clean and soot blowing equipment is in good condition, and avoids arriving
at a situation when only upper P.F. mill groups are available due to maintenance on the lower
mill groups usually at a time when soot blowing equipment also require outages for
maintenance.
Ashing out of the boiler should take place immediately after soot blowing, thus preventing high
steam temperature due to ingress of air through ash hopper doors. In the event of ash hopper
doors jamming open, especially on low load, total air flow must be reduced until doors are
closed, and if necessary oil burners commissioned to maintain stable conditions. It is
preferable to blow soot and remove ash at the beginning of a shift in order to prevent overlap
at a time when unstable conditions may occur.
During initial loading of a turbine surges of water level will occur due to increase firing
rates/steam flow rates, therefore drum level should be maintained below normal level at this
time, especially on hot starts with block loading.
If a loss of feed water heaters should occur on load then the operator should change to as
many lower P.F. mill groups as possible and also reduce unit load to keep steam/metal
temperatures within the design parameters.
It is normal to do a complete soot blowing sequence prior to shutting a boiler down. However,
if it is known that the shut down is ,likely to be for an extended period it is sometimes
advantages to leave the superheaters dirty in order to assist in keeping steam temperatures
down on cold start. Boiler is then not heated fast to achieve this temperature.
A careful log should be kept of draught differentials across the boiler system. If slagging of
superheater tubes is evident, reduce load and increase excess air. Then operate the
appropriate soot blowers.
The bypass valves around the desuperheater spray water control valves should be opened
gradually and communication should be maintained between the spray station and the control
panel at all times to avoid possible swamping of the superheater.
It is It is essential that unit operators should study and memorise the maximum and operating
limits within the design parameters of all items of plant under their control. This will assist in
avoiding confusions and unnecessary shut down when abnormal conditions arise during
operation.
1.1.2
1.1.3
1.1.4
1.1.5
1.1.6
1.1.7
1.1.8
1.1.9
1.1.10
1.1.11
1.1.12
1.1.13
63
1.2
DESIGN LIMITATIONS:
1.2.1
1.2.2
1.2.3
1.2.4
1.2.5
Maximum saturated steam temperature change is 80 OC per hour.
Maximum gas inlet temperature to the secondary superheater on start-up is 500
positive steam flow is achieved.
The precipitator gas inlet maximum temperature is 155 OC.
The recommended air heater average cold end temp (metal) for coal is 98 OC.
Maximum mid-wall metal temperature primary superheater 520 OC
2.0
PRESSURE RAISING FROM ZERO (FROM COLD CONDITIONS)
2.1
STATE OF PLANT: (COLD CONDITION)
2.1.1
2.1.2
Boiler is empty and clean, Steam lines cleaned. Safety valves are set.
Furnace and gas passes previously inspected and all access and observation doors are
closed.
All ‘Permits to Work’ are cancelled and plant de-isolated.
All electrical and pneumatic supplies are available for controls and boiler auxiliaries.
All instrumentation is in service i.e. shut off valves, cocks, isolating switches etc. To be in
the normal operating position, and also gas temperature probes.
All auto/manual control stations selected for manual operations.
All cooling water supplies are ON.
Precipitators ready for service and all hoppers are empty.
Power supply to panels and propane gas ignition switched on and available. All gas
connections are made up and tight.
Oil fuel system fully commissioned. L.P. circulating oil pump running and fuel oil circulating
to oil burners, oil burner guns inserted into burner boxes and clamped up. Manual valves
open. Control valves closed.
Check that sufficient milling plant and associated equipment is available.
Carry out per-start checks and ensure that adequate lubrication is available and cooling
water supplies are flowing to the following items:a) I.D. and F.D. Fans and Motors.
b) P.A. Fans and Motors.
c) Mill Gearboxes and roller arms, feeders and S.A. Fans
d) Control air Compressors.
e) Steam and Water sample coolers.
f) Drum water level indicators.
Also ensure that common boiler services plant is operating correctly:
Fuel Oil Pump
Demineralised Water Plant
Control and Station Air Compressors
Cooling Water Supplies.
Also that coal and ash handling plant will be available when required.
Check that oil burner and furnace monitoring photoelectric cells are clean and ready for
service.
Lockheed hydraulic pump for damper operation is available.
Electrical supply to electrically assisted safety valves switched on.
The sequential detailed procedure for starting an empty boiler from cold follows.
H.P. Feed water supply available.
All draught plant is fully commissioned and ready.
Fire extinguishing equipments operational.
Soot blowers adjusted and available.
2.1.3
2.1.4
2.1.5
2.1.6
2.1.7
2.1.8
2.1.9
2.1.10
2.1.11
2.1.12
2.1.13
2.1.14
2.1.15
2.1.16
2.1.17
2.1.18
2.1.19
2.1.20
2.1.21
64
OC
until
BOILER COLD START (As per HOI 001)
3.0
Step
BOILER FILLING:
ACTION
ADDITIONAL INFORMATION
3.1
Fill Deaerator to normal working level
3.2
3.4.1
Prime boiler feed Pump and charge HP Feed system as per
HOI 32
Check C.W. system I/S and Put ACW & BCW system in
service as per HOI 34. Put Condensate system I/S
Start B.F.P. when system is fully primed and the discharge
valve fully open.
Start LP dosing pump
Check Generator H2 pressure
is normal at 0.06 Mpa
Inform
Main
C.R.
before
starting BFP
LP dosing to BFP suction
3.4.2
Using top up line, fill boiler to clear the low level alarm
Normal Drum level 565 mms
3.4.3
3.4.4
Change the LP dosing to the Condensate Extraction pump
discharge
Stop BFP only when Feed regulators are passing, otherwise select top up line on auto
3.5
Check valves and dampers set as per valves & dampers status sheet (Appendix A)
3.6
Check HP Chemical Dosing pump available
4.0
Establishing Air and Gas Circuits
4.1
Flame intensity monitors & purge air Fans available
4.2
Pre Start Checks complete on :
3.3
3.4
Inform Lab to charge D/A with
chemicals
For Boiler dosing
ID Fans, FD Fans, Mill Groups, Fuel Oil system, COG system
5.0
NATURAL PURGE
5.1
5.9
Select SGC natural Purge to auto & start sequence.
Following dampers & vanes will be opened by sequences:
*ID/FD discharge damper & inlet vanes
*A/H air outlet and bypass dampers
*Precipitator inlet dampers
*All 16 secondary air dampers
Once the 20 mins. Is timed out, it will close all dampers
except related air heater & precips. Set Natural purge
programme.
The Draught Fans are started on (SCG) sequence Group
Control
&
this
control
does
dampers
operation
automatically.
To enable the program one draught group must be in
service with purge required signal & no flame detected
All ID, FD & Sec. Air dampers are set for auto operation. FD
control loop set to fixed flow set point
One FD vane, one ID vane & 3 sec. Air dampers per firing
level on auto & total air is > 25 %. Signal
5 min. Timer starts. FD fixed flow set point resets.
5.91
PURGE COMPLETE
5.92
BMFT resets. Inform other units and open
Fuel oil v/vs.
Pr.----- > 2.5 Mpa
COG v/v
Pr.----- > 54 Kpa
Propane v/v
Pr.----- > 0.2 Mpa
ESTABLISHING FIRING:
Initiate 1st Oil burner. (Open final drains). Maintain Drum
level at normal working all the time
5.2
5.4
5.6
5.7
5.8
6.0
65
Ensure
Lockheed
pump
running. Start Natural Purge
programme. At Step 1- will
open all air/gas dampers to
create natural draught.
Programme
Changes
to
Natural Purge in progress at
this stage. (Also refer to PF
code of practice for above)
Draught group crossover is not
selected.
Natural
Purge
programme is completed.
Total Air flow must be > 25 %
of MCR
Other unit will take a note to
check appropriate fuel oil
pressure at their unit also.
1st burner must be initiated in
5 min or further 5 min purge
will be required. Check flame
Step
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.91
6.92
7.1
ACTION
ADDITIONAL INFORMATION
Drum metal temp Top/Bottom should never exceed 50 deg
C. Rotate burner firing for even heating.
Rate of Saturation temp rise should not exceed 55OC in 1st
hr. And < 70 OC per hr. thereafter
At 0.2 Mpa Close all air release valves and primary
superheater drains.
Flash blow primary S/H for 1 min every 1 Mpa rise
Flush primary drains at every 1
Mpa steam press rise.
Refer start up curve
Raise press/temp as permissible in Sheet 11A of HOI 28.
Insert oil burners as per requirement.
At 2 Mpa Open Main Steam Stop bypass valves to warm HP
legs.
Open Main steam stop valves and close bypasses. Charge
Aux steam from self unit by @ 20 %. Close all Boiler side
drains.
Continue firing to get 350 OC and 4 Mpa in 5 hrs. for turbine
cold start. Aux steam fully from self.
Closely monitor superheater
metal temp
For 20 min. Start Turbine
Control Oil pump. Stop LOP
Charge Aux. Steam self supply
to establish steam flow to raise
steam temp/press
Run lower Mill group as per
7.0,
in
case
poor
performance of burners
Open A/H air outlet & close A/H air bypass damper at gas
outlet temp >98 deg C. Maintain gas temp above
Start mill group as the turbine loading and boiler
pressure and temp raising allows
66
To remove water from tubes
As per operations HOI 21
BOILER WARM/HOT START (As per HOI 002)
(Superheater outlet pressure > 1.0 Mpa, Temperature > 190*C)
1.0
Check the STATE OF PLANT as per 2.1 above
STEP
ACTION
ADDITIONAL INFORMATION
Check Condenser level, Deaerator level and Drum level is at
normal working. CW/ACW/BCW & condensate systems are
in service. All Cooling water systems are normalised.
Inform Lab Chemist for dosing
arrangements of chemicals.
Check Generator H2 press
>0.05 Mpa
Check C.W. system I/S and Put ACW & BCW system in
service as per HOI 34. Put Condensate system I/S
Inform Main C.R. before boiler
firing.
Start B.F.P. when system is fully primed and the discharge
valve fully open.
Stop BFP only when Feed regulators are passing, otherwise select top up line on auto
1.16
Check valves and dampers set as per valves & dampers status sheet (Appendix A)
Establishing Air and Gas Circuits
2.0
Pre Start Checks complete on :
ID Fans, FD Fans, Mill Groups, Fuel Oil system/COG system, Propane gas
NATURAL PURGE
2.3
Select SGC natural Purge to auto & start sequence.
Following dampers & vanes will be opened by sequences:
*ID/FD discharge damper & inlet vanes
*A/H air outlet and bypass dampers
*Precipitator inlet dampers
*All 16 secondary air dampers
2.4
Once the 20 mins is timed out, it will close all dampers
except related air heater & precips. Set Natural purge
programme.
Ensure
Lockheed
pump
running. Start Natural Purge
programme. At Step 1- will
open all air/gas dampers to
create natural draught.
Programme
Changes
to
Natural Purge in progress at
this stage. (Also refer to PF
code of practice for above)
2.7
2.10
to
The Draught Fans Both ID, Both FD are started on (SGC)
sequence Group Control.
Natural Purge programme is
completed.
2.11
2.14
to
All ID, FD Fan discharge dampers open. Select Sec. Air
dampers on auto operation. Increase air flow to start force
purge and clear FD fan fixed air flow set point reset”
Or start forced purge program
on SGC.
2.15
During force purge, set furnace press to -50 pa, Set
Windbox pressure to 250-400 Pa & burner tilts to -5 O
5 min purge. If Air flow falls
below 40 Kg/s, the force purge
will stop.
2.16
Fuel oil supply & return vlv, main COG valve and Ignitor gas
trip valve should open on auto once the BMFT resets. Purge
Air fans I/s, press> 90 Kpa
Sec. Air damper master have
to be adjusted to achieve
required wind box press
3.0
ESTABLISHING FIRING:
1st burner must be initiated in
5 min or further 5 min purge
will be required. Check flame
Initiate 1st Oil burner. (Open final drains). Maintain Drum
level at normal working all the time
67
STEP
ACTION
ADDITIONAL INFORMATION
3.2
Open superheater circulating drains. Operate to regulate
pressure and temperature raising.
BM48/1 and BM48/2
3.3
Flush blow primary SH drains at every 1 Min every 30
minutes interval.
BM46/1 and BM46/2
3.4
Open Desuperheater drains
BM112/1 and BM112/2
3.5
Insert additional oil burners as necessary.
Saturation temp rise not to exceed 80 OC
of
Refer start up curve. Temp rise
not to exceed 80OC/hr
3.6
Monitor air heater gas exit temp. The temp must not drop
below 98*C
A/H air bypass damper opens if
gas outlet temp <100 OC
3.6
At 0.2 Mpa Close all air release valves and primary
superheater drains.
3.7
Maintain boiler drum at normal working level. 565 mms via
topping up line on auto unless if defective
Keep main feed reg vlv on
auto.
3.8
At satisfactory Superheater outlet temperature, open boiler
stop vlvs bypass vlvs.
SH outlet temp should be at
least 20*C above ESV inlet
3.9
At 2 Mpa after charging main steam legs, Open Main Steam
Stop valves fully. close bypasses.
20* C above turbine HP inlet
casing temp
3.10
Increase firing rate by oil burners. If not satisfactory put
lower mill group in service and Charge Aux steam from self
unit. Close all Boiler side drains.
3.11
Reset and run up the turbine
4.0
TURBINE READY FOR SYNCHRONISING
Rate
As per the turbine operating
instruction
Soak the turbine and close turbine side drains, put mill
groups in service one by one and load the turbine as the
parameters permit.
@@@@@|||@@@@@
68
Put LP and HP Heaters
service appropriately.
in
BOILER NORMAL SHUT DOWN (As per HOI 3)
HWANGE OPERATING INTRUCTION (HOI: - 006)
STEP
ACTION
ADDITIONAL INFORMATION
1
Carry out soot blowing
complete To avoid disturbances
2
Test Oil/COG burners for termination of PF firing
3AD & 3BC needed minimum
3
Sequence for stopping Mills:
Take out C,B,D,A groups
Reduce load by taking Mills out as per PF Code of Practice
3.6.1 to maintain furnace stability
4
Shut down mill groups on selected groups if combustion &
loading conditions permit.
5
At @ 40 MW load
1 mill load +oil burner support
6
At @ 20 MW load
6 Oil burners load. No mills
6.1
Feed water controls to manual- maintain drum level
Using Main & Top up line
6.2
Take précis out of service
Leave rappers running
6.3
Maintain turbine load as per rate of boiler pr drop
60 Bar pr reqd for shut down
6.4
Open Economiser recirculation valve
LAH10AA101
Over a ten-minute period reduce to three oil burners and
load to Zero
Operate drains to maintain temperature
BM48/1 and 48/2
7
7.1
8
8.1 to
8.4
8.5
9
10
10.1 to
10.4
11
12
With total air flow-30%, withdraw all burners
Check fuel oil pr-0, solenoid valve closed, Close manual
iso vlv to FO system, Close Propane iso vlv
Check all fires out in boiler and withdraw all Oil burners
min 60 cms
Force purge complete, Reduce ID/FD vanes to zero
Force purge will start (6 min)
Sec air damper at @40%
Of57; of 58; COG v/v & Propane
v/v. Of 29 and Of 34
4 x BC and 4 x AD
Furnace pr. @ at -100 Pa
Take Fans out of service
1st FD; 1st ID then 2nd FD; 2nd ID
To box Boiler, close Air Heater gas outlets A & B and all
secondary air dampers
After Turbine vacuum broken and indicating zero
12.1
Open A and B boiler stop valve bypass valves
12.2
Close A and B boiler stop valves
12.3
Close Boiler Stop Valves’ bypass valves
XK5 (2 off)
BM1?1 and BM1/2
13
Maintain drum level between 4-6 Greens
For 1 Hr. After coming off load
14
Ash and dust Boiler as required at the earliest
Ash removal is easier in hot
condition
@@@@@|||@@@@@
69
70
(B) TURBINE OPERATING INSTRUCTIONS
TURBINE COLD START (HOI-025) (Ref- Drg No. HPS/WAPCOS-28)
STEP
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
2.0
2.1
2.2
2.3
2.4
2.5
2.6
3.0
3.1
3.2
4.0
4.1
4.2
4.3
4.4
5.0
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
5.11
5.12
OPERATION
STATE OF PLANT:
Turbine
CW system I/S, ACW system in service
Oil system
All auxiliaries and Plant
All Instrumentation
Condensate system, CEP’s, Feed Heating
system, Feed Pumps
Alternator- Check rectifier is On & in right
mode
Lub Oil system
Put Oil Purifier I/S, Start AC Lub Oil Pump
Start AC control Oil Pump
Check Oil Vapour Fan I/S
Start jacking Oil pump at Lub oil temp >25OC.
Don’ t run 2 JOP at times
Select Control Oil Pump & AC Lub Oil Pump on
auto
Start DC L.O.P. to test for availability
Barring Gear
Turn rotor manually, if free start Motor
Check turbovisory indications if current isCondensate system
Prime condensate system to normal level
Close- LP Hood Spray, Flash box spray
Inlet/Outlet valves of Main ejector, vapour
condenser are open
Pre-start check & start EXTRACTION pump
Turbine sealing & vacuum raising
Check Aux steam from live steam isolating
valve is shut
Check Manual Isolating valves for Turbine
heating, Deaerator heating, Gland steam &
ejectors on Aux. Manifold are closed
BOILER REQUIREMENTS:Start one vapour exhauster Fan
Open MS Leg Drains, MS pipe drains, Boiler
Stop valve bypass valves
MS Leg pressurised. Open boiler Main valves
Commission aux steam, Open steam to
Deaerator
Commission Gland sealing system
Select LP Hood Spray to Auto
Check Gland steam condensate spray
isolating valves is open
REMARKS
At gland Steam temp 240 OC Open inlet
valves (electrical)
Set Gland steam temp/press on auto
Confirm barring
71
Stationery(metal temp <120 *C
ACW Primed
Available
Available
Available and in service
Available
Gassed up with Hydrogen 2.0 bar. See below
2.3 below
0.25 Mpa, 58 amps
1.7 Mpa, 50 Amps
For Gas in Generator it is essential.
Amps 72, Solenoid vlv energises >30 Amps,
JOP I/S until 100 r.p.m.
Check ‘Not on auto’ alarm clear
“DC Lub Oil Pump” signal for confirmation
➢
Amps 13-14, RPM- 52.
14 Amps
Gland steam temp control valve
HOI 42
To avoid damaging aux steam safety valve
Or Auxiliary steam from station range
1.4 Amps. Check CEP is must running.
ESV warm up valves shut be shut until leg
metal temp > 150 OC
Turbine should be always on barring
Temp- 160 OC, Press- 1.5 Kpa
STEP
5.13
5.14
5.15
6.0
6.1
STEP
6.2
6.3
6.4
6.6
6.7
6.8
6.9
6.10
OPERATION
Open turbine flash box spray valve
Shut Gland steam warm up valve
PULL VACUUM
Turbine Warming:
Ensure that all alarms and trips are reset &
turbovisory instrumentation working. Startup-device MAD10 AA101 closed
OPERATION
Reset Turbine by actuating “Heating bypass
Reset” on POS: Turbine controls- Turbine
reset- “HTNG”. This resets heating bypass
emergency Trip valve-LBG50AA201.
Open heating bypass control valve- LBG50
AA101 slowly to @40% for 20 Min to heat
pipe work upto control valve chests.
When pre-heating is complete, close ‘Heating
bypass CV’ LBG50 AA101
If all permissive are met, select “LO” ramp on
POS: Turbine Controls – Ramp Up/Down
The DDCS will issue a start permissive and a
run command to the 505
The 505 will now start increasing the speed
reference set point
Monitor the speed reference set point on POS
(Turbine Controls)
As the Speed Reference Setpoint increase
to 1400 rpm, the 505 will start raising
governor oil press, opening turbine control
vlvs as it tries to get turbine speed to
increase to 1400 rpm
REMARKS
This opens on auto at Temp > 240 OC
As per HOI 24
Start up device closes on auto when ESV’s
close. Ensure all group drains & ESV warming
up connections are open
REMARKS
This resets Turbine Trip system, but leaves
ESV’s closed. Start-up device opens 100%
Ensure this, else drive manually open
Ensure
LHS/RHS
ESV’s
warming
up
connection drains and start up drain valves is
open during this.
The required permissive are :
ESVs closed,
HP Inlet Casing flange temp <220*C
Heating bypass control vlv closed
Heating bypass trip vlv open
Pre heating complete- as per 5.3
Turbine reset
BMFT reset or boiler trip on bypass
Speed reference set point will be increasing
while the actual speed remains at 52 rpm
At @ 0.3 Mpa governor control oil press, 1 st
CV begin to open. Monitor Governor
Actuator
demand
increasing
towards
100%. At 100% governor control oil press
should reach +- 1.0 Mpa (On POS)
6.11
505 continues raising governor oil press to
1.0 Mpa, since turbine actual speed remains
at 52 rpm since heating bypass control valve
is still closed
All control valves 100% open at 1.0 Mpa
governor pin oil pressure
6.12
Once actuator demand reached to 100% and
the Operator is satisfied that all are under
control (e.g. No speed rise), the heating
bypass CV- LBG %) AA101 must be opened to
20-25%. Turbine speed will increase to
approx 1000 rpm
Actual speed on 505 will start increasing.
Monitor speed rise during this operation.
Observe turbo-visory indications as turbine
runs up.
6.13
6.14
At 100 rpm stop barring gear and JOP
After 30-35 mins open Heating bypass CV to
35%. At 1400 rpm, the speed reference,
without intervention, will start ramping up to
the actual Low Idle speed of 1450 RPM.
72
Turbine speed will increase to 1450 RPM
STEP
OPERATION
REMARKS
6.15
Once speed reference setpoint & actual speed
reaches 1450 rpm, Operator can issue
command “Hi” on POS: Turbine controlsRamp Up/Down. Speed reference set point
will now increase to 1925 rpm
Turbine actual speed at 1400-1500 rpm,
monitor HP inlet casing 4 and Flange centre
temp rise. When this temp stops increasing
raise speed to 1900 rpm by opening heating
bypass CV
Continue to monitor HP inlet casing 4 and HP
outer casing flange centre temp.
Turbine speed will now increase above 1450
rpm over next hour.
Turbine heating is complete when the
following temp are achieved:
HP inlet casing 4 temperature> 200 OC,
HP outer casing flange centre >100 OC
Close heating bypass control valve LBG50
AA101
Trip the Turbine
The turbine warming can continue if the
boiler is not yet ready to run up the turbine.
6.16
6.17
6.18
6.19
6.20
6.21
6.22
6.23
Monitor turbine speed so that jacking oil
pump and barring gear motor can be started
when speed drops below 100 rpm
Boiler requirements for turbine start up:
Steam temp: 350 – 400 OC
Steam press: 5.0 Mpa
Proceed to run up Turbine as per Warm/ Hot
start procedure Turbine Run Up Steps 6.3
Avoiding lingering in the 1500-1900 rpm
critical speed range. Speed not to exceed
1950 rpm during heating. Turbine is set to
trip, should its speed rise to 2400 rpm during
warming.
Inform other units supplying aux steam so
that adjust press to avoid lift of safety vlv
This operation is to be done manually on the
POS.
HOI 26
@@@@@$$$@@@@@
73
TURBINE HOT START (HOI-026) (Ref Drg no. HPS/WAPCOS-29 & 30)
STEP
1.0
1.1
1.2
OPERATION
STATE OF PLANT
Turbine on Barring
C.W. System, ACW System, Condensate
system in service. Condenser, Deaerator &
Boiler Drum level Normal
1.3
Oil Vapour Extractor Fan in service
1.4
A.C. Lub Oil Pump in service
1.5
A.C. Control Oil Pump in service.
Stop A.C. Lub Oil pump- Stand bye
1.6
D.C. Emergency Lub Oil pump
1.7
Seal Oil pump in service
1.8
Hydrogen in Generator at normal press
1.9
Auxiliary steam to Deaerator I/S
1.10
ALL PERMIT TO WORK CANCELLED
2.O
Lub Oil System
2.1
Start D.C. LOP & check signal “D.C. Lub Oil
pump” on control desk
2.2
Switch off D.C. LOP & select on Auto
2.3
Select A.C.LOP & Control Oil Pump on auto
3.0
Condensate System
As per HOI 25, 4.0 (4.1 to 4.4 and HOI 42 for CEP)
4.0
Turbine Sealing and Vacuum Raising
4.1
Check all manual & electrical operated drain
valves on turbine are Open
4.2
Put Auxiliary Steam Manifold I/S
4.3
Check starting steam drain is open
4.4
Check Gland Steam isolating valve shut.
Steam trap bypass valve shut.
4.5
Open manual iso valve for Gland Seal system
and Ejectors on aux. Steam manifold
4.6
Start one vapour exhauster Fan
4.7
Open Gland steam warming up valve
4.8
Select LP Hood spray to auto
4.9
Check manual isolating valve to Gland Steam
temp control valve is open
4.10
Open gland steam electric iso valve
4.11
Set press & temp controllers to auto
4.12
Open turbine flash box spray water valves
STEP
OPERATION
4.13
Close gland st warming up valve at >240 OC
4.14
Close vacuum breaker
4.15
Raise vacuum by Quick Start Ejector and
change to main ejectors at a vacuum of
10kPa. Close deaerator vent to atmosphere &
open vent to condenser at 40 MW when
extraction 5 steam takes over steam supply
to deaerator
5.0
Turbine Main Steam Pipe Warming
5.1
Check Main Steam Stop valves are Open
5.2
Open turbine main st. Leg and ESV warming
up connection drain valves
74
REMARKS
14-15 Amps
0.25 Mpa, 58 Amps
1.70 Mpa, 50 Amps
Stand bye
Seal Oil/Hydrogen diff press < 35 Kpa
2 bar
Deaerator water @ 120 OC
16 Amps with A.C. LOP I/S, 29 Amps, 226
kPa with A.c. LOP O/S
Check “not on auto” alarms clear
Group 1 and 2
As per HOI 24A Operating Instructions
SH10 A109
SG10 S005
SA11 S052
1.4 Amps CEP must be I/S
SH10 S052
Will not open below 240 OC
Press- 1.5 kPa, Temp- <240 OC
REMARKS
SH10 S052 opens automatically at <240 OC
When a vacuum of 10 kPa is achieved the
turbine is ready for rolling.
STEP
5.3
5.4
6.0
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10
6.11
6.12
OPERATION
Warm main steam legs by opening boiler stop
bypass Valves
When Main St. Pipe charged, Open boiler stop
valves and close bypass valves
Turbine Run-Up
Final Main Steam conditions i.e.
Pressure 5 MPA. Temp as per graph
Inform Main Control Room about turbine
rolling
Reset all trip alarms & check turbine and
turbovisory instrumentation. Reset turbine by
selecting “TURB” on POS: Turbine Controls—
Turb reset. The power oil press rises to 6 bars
and ESV’s open as indicated on POS. Turbine
can also be reset locally by raising hydraulic
control unit for 10 sec
Turbine is now ready to run. If we get all
permissives, select “LO” on POS: Turbine
Controls- Ramp Up/Down.
The 505 now raises turbine speed to the low
Idle Speed of 1450 RPM.
Once turbine reaches & stabilizes at 1450
rpm, select “HI” on POS: -Ramp Up/Down
The 505 will ramp turbine to Hi Idle set point
and hold turbine at speed 1950 rpm.
Once turbine reaches & stabilises at 1950
rpm, select “RTD” on POS: Turbine ControlsRamp Up/Down. Once the rated command
is issued, turbine will start ramping from
1950 rpm to 3000 rpm.
At 3000 rpm, carryout turbine protection test
sequences.
Stop AC LOP and Control Oil Pump
Put Gen Xmer Cooler Fans I/S on POS: Unit
Co-ordinator, set load setpoint to 2MW
Once Turbine speed reaches to 3000 rpm, the
ECR will have automatic control over turbine
speed setpoint. Inform MCR
After synchronisation, breaker closure will
automatically set 505 to auxiliary (load)
control & automatically raise the load to 2 MW
to avoid motoring.
After synchronisation, continue to load the
machine by selecting the load setpoint on
Unit Master.
75
REMARKS
For approx 10 minutes
Adjust leg drainage to suit boiler temp and
press raising.
Final steam temp must be >20 OC above
turbine inlet casing 4 temp
The required permissives are:
ESV’s opened > 3.7 MPa
Main steam temp > 350 OC
HP Inlet flange temp > 100 OC
HP Inlet casing temp > 200 OC
Heating bypass control vlv closed
Heating bypass trip valve closed
330 KV breaker not closed Turbine
RESET
This resets the turbine trip system and opens
the ESV’s.
The start-up device opens automatically to
100%, ensure, otherwise drive manually
open.
Turbine will be held at 1450 rpm till “HI”
command is issued from POS.
Take note of the Turbine critical speed ranges
1500 – 1900 rpm
2100 – 2400 rpm
Observe the vibrations.
Over-speed trip, Lub. Oil trip, vacuum trip,
and turbine trip(system 1&2).At 2950 rpm
Oil supply taken over by shaft driven MOP
Unit must not be synchronised with load
set point not reset on OS Unit Master
This is indicated on POS: turbine controlsMonitor speed during synchronising. Once
synchronised, ECR has no control on Gov.
Breaker closure can be monitored from the
POS. The remote auxiliary enable turns from
white to green on POS.
The turbine pressure controller must be
selected to manual.
STEP
7.0
7.1
7.2
7.3
7.4
OPERATION
TURBINE LOADING
Close turbine steam pipe drains
At 7MW load, LP Hood Spray will close
Soak machine between 10 and 20 MW. Unit
flange centre temp is > 330 OC
At 330*C flange centre temp is achieved,
soaking is complete & machine can be loaded
in relation to Boiler Pressure as mills are put
I/S
7.5
At 20 MW close group 1and2 drains and HP
flash box spray water valve
7.6
Observe
value as machine is loaded
and keep within acceptable margin
7.7
At a load greater than 40 MW commission HP
Heaters and close aux steam to Dearator.
Close group 2 drains 7,8 and 12
Continue loading machine to full load as you
commission mills on the Boiler
7.8
7.9
REMARKS
M.S.Pipe, ESV Warming connec, leg drains
Unless selected to manual
Rate of metal temp rise below a flange centre
temp of 450*C is 1.5*C/minute
Before putting 1st mill I/S check Boiler sprays
are available. Machine loading rate
Metal temp < 150 OC – 0.5 MW/min.
Metal temp < 300 OC – 1 MW/min.
Metal temp < 450 OC – 3 MW/min.
Metal temp > 450 OC – 5 MW/min.
Except drains 7,8 and 12 for HP Heaters.
Alarm at 0*C, Trip at – 20 OC
Boiler de-superheater sprays are fully
effective at load greater than 30 MW. Temp
control of steam is governed by boiler steam
press and turbine flange centre temperature.
When HP Heaters are fully I/S, Normal
loading rate and metal temp rise above
450*C flange centre temp are:
5 MW/Min.
0.75 OC /min.
@@@@@$$$@@@@@
76
C. GENERAL SUGGESTIONS FOR
UNIT ROLLING/LOADING AT STAGE-I
1.
Check C.W. pump is running. Check hydrogen pressure in Generator. Fill H2 if
required upto 0.06 Mpa H2 pressure.
2.
Check ACW and BCW pumps are running. Check RFW tank level.
3.
Check turbine lubricating oil cooler and good filter is in service. If choked up,
change the same to another and send note to the concerned for cleaning.
4.
Check auxiliaries cooling water is in service wherever it is necessary.
5.
Check turbine and boiler side drains/vents are open as per the procedure
recorded in the pre start checks.
6.
Check for normal level of Condenser, Deaerator and Boiler drum.
7.
After purge complete, fire the boiler with AD & BC elevation Oil burners one
by one to maintain steam temperature rise not exceeding 80 OC/hour. .
8.
Start Condenser extraction pump on recirculation. Maintain condenser and
deaerator level.
9.
Close Boiler vents at 0.2 MPa drum pressure.
10. Open Boiler outlet valves at 1.5 MPa press. Start Control oil pump and
stop AC lub oil pump.
11. At pressure 1.5 MPa, Open 10 % Aux. Steam from own unit for raising the
steam temp and pressure. Close Boiler side drains. Start coal mill A or D to
raise the press and temp faster.
12. At 2.0 MPa pressure and >280 deg C, fully charge aux. Steam from own unit.
13. If HPT parameters are for hot rolling, raise boiler pressure to the extent to get
steam temp more by 50OC but not more than 100OC w.r.t. max HPT
metal temp.
77
14. At proper temp of aux steam, start gland sealing and starting ejector to pull
the vacuum. Maintain condenser, deaerator & drum level. At 17 KPa vacuum,
start main ejectors and at 10 KPa vacuum stop starting ejector. Check
air valve tight closure.
15. For resetting the turbine, stop the coal feeder and restart immediately
after resetting the turbine.
16. Maintain boiler drum level on slightly –ve side and start rolling the machine
after reaching steam parameters 50OC more than HPC body max temp.
17. Keep the coal feeder running till turbine speed reaches to 3000 rpm. Keeps the
load setting at 5 MW only.
18. Inform MCR to synchronise the machine and stop the coal feeder. Take aux
supply from range in case synchronising is delayed by more than 5 minutes.
Close own unit aux steam valves by 90 % so as to restrict the pressure drop.
19. When machine is synchronised, take coal feeder in service and raise the load
maintaining the steam pressure so as to maintain the proper steam
temp difference i.e. more than 50OC but not more than 100OC; than HP
cylinder In Casing temperature. Slowly raise the steam pressure and
temperature as HP in casing temp rises. Close all turbine drains as per
procedure. Stop control oil pump.
20. On stabilising HPC metal temp, raise steam pressure gradually to raise the
steam temp also. Charge HP heaters from steam side at @ 40 MW load and
check proper cascading of both HP 1 and 2 keeping the heater levels normal.
21. Take 2nd coal mill and raise the load. Check the steam pressure rise gradual
and not erratic. Do not allow steam pressure to drop while raising the
load.
To
control
the
pressure,
load
variation
should
be
done.
Remember pressure is the key to maintain proper temperature and
faster stabilising of HPT metal temperatures.
@@@@@$$$@@@@@
78
V. PF CODE OF PRACTICE
This document is the Property of ZESA and can not be used, reproduced, transmitted and /
or disclosed without permission.
MILL FIRES
▪
▪
▪
▪
▪
▪
General
Fire in a Standing Mill
Fire in a Running Mill
Action after a Mill Fire
or High Temperature condition
P.F. Pipe Fires
Section 6
5.1.1. To 5.1.3
5.2.1 to 5.2.4
5.3.1 to 5.3.7
5.4.1
5.5.1 to 5.5.6
MALFUNCTIONING OF DAMPERS
AND CONTROL EQUIPMENT
6.1.
Section 7
LOSS OF IGNITION
1–7
Appendix 1
P.F. CODE OF PRACTICE
INTRODUCTION
1.1.
The danger of explosion from Pulverized Fuel cannot be too highly stressed and to appreciate
the factors that may lead to fires and explosions the following notes are presented.
1.2
The rate of the reaction differentiates normal combustion in the furnace from an explosion.
In normal combustion the rate of release of energy is low. The development of an explosive
accumulation in the furnace follows the failure to ignite an incoming cloud of fuel or loss of
ignition during operation. Hence care must be taken to prevent an accumulation of unburnt
fuel building up in the furnace.
1.3
Fire risks in mills and P.F. pipes occur if coal is allowed to deposit and accumulate. A
minimum transport velocity of 20m/sec should prevent deposition in P.F. pipe work.
1.4
Spontaneous combustion of the deposited fuel may occur depending on the temperature of
the surrounding air. Another possible source of mill fires is flashback from the furnace. This
can take place if the velocity of the flame at the burner is greater than the velocity of the
air/fuel stream at the burner.
1.5
The following procedure is for the guidance of all operators associated with boilers.
important that the procedure laid down be followed at all times.
Section 2
It is
GENERAL PRECAUTIONS
2.1
Cleanliness and Care in Operation
2.1.1
Extreme cleanliness and care in operation of the entire plant must be observed. P.F. and
coal spillages must not be allowed to accumulate and any oil or grease spillage must be
cleaned up without delay.
2.1.2
P.F. leaks should be reported as soon as they are located. P.F. leaks should be sealed by a
permanent repair. When a mill is required in service to increase availability, and the
strength of the P.F. system is in doubt, a temporary repair is permissible.
2.2
TEMPERATURE OF STANDING (OR SHUT DOWN) MILLS
2.1.3
A standing mill is defined as a mill that is not in service, but is available for use as required.
The temperature of such a mill should be restricted to a maximum of 45C to prevent any
risk of spontaneous combustion of trapped coal dust.
2.1.4
A standing mill should be run at least once per day to keep the burner quarls clear of slag, to
exercise dampers and prove coal flow. If the temperature of a standing mill rises above
45C check that the hot air damper is closed.
79
2.3
MAINTENANCE AND OPERATION OF DAMPERS AND SAFETY VALVES
2.3.1
All dampers and Safety Devices must be maintained in good working order and regularly
checked for operation once per shift. All control dampers on a running mill should be
checked for freedom of movement on ‘auto’ and ‘manual’ control.
2.3.2
On a standing mill the following damper positions should apply.
Hot air isolating damper
- shut
Attemperating air damper
- shut
Mill inlet damper
- shut
Burner flap damper
– shut
GAS/OIL BURNER EQUIPMENT
2.3.3
This equipment must be maintained and operated in such a manner as to ensure the
complete combustion of the fuel oil / gas used for ignition. To assist in good oil /gas burner
performance the gas/oil burners should be cleaned and tested on a routine basis, i.e. once
per shift. Defects should be processed on a priority basis.
2.4
USE OF OIL AND GAS BURNERS FOR FLAME STABILIZATION
2.4.1
If it is known that unstable firing conditions may occur the P.F. burner flame should be
stabilised by the use of oil /gas burners associated with the mills in service
2.4.2
If slight instability occurs, i.e. fluctuating furnace draught but no ‘low furnace pressure’
alarm, inserts oil /gas burners to regain stability.
2.4.3
If ‘furnace suction’ alarm initiates with one mill or two lightly loaded mills in service, initiate
‘Boiler Firing Trip’.
2.4.4
If furnace suction alarm initiates with two highly loaded or three mills in service and it does
not stabilise within 20 seconds initiate “Boiler Firing Trip”.
2.4.5
If in the opinion of the Unit Controller the furnace conditions are such as to cause potential
danger to personnel or plant, he or she should initiate the ‘Boiler Firing Trip’.
2.5
MILL REJECTS
2.5.1
The mill reject boxes should be checked at frequent intervals and emptied as required. The
time between emptying will be dictated by the mechanical condition of the mill, type of coal
being ground, mill loading and the air/fuel ration. The optimum time will be found by
operating experience. All running mills should be checked initially at least once per hour.
Any sign of rejects being on fire or excessive in quantity, it should be reported to the
Operations Superintendent and recorded in the Unit Controller’s logbook.
2.5.2
The method of emptying rejects is as follows:Shut inner reject door. Carefully open outer door in case inner door is passing. Empty
contents of reject box and inform Unit Controller if any pieces of metal are observed
among the pyrites. Reject box fires are usually caused by hot air passing through the outer
door seal. Therefore defective door seals should be attended to on a priority basis.
2.6
MILL AIR CASING AND CLASSIFIER
2.6.1
The mill air casing and classifier should be examined whenever a mill is opened up to ensure
they are in good condition and free from accumulations of coal dust and/or debris.
2.6.2
Any internal feature or defect causing such conditions should be reported to the Operations
Superintendent.
2.7
PRECIPITATOR ASH AND GRIT COLLECTING HOPPERS
2.7.1
When operating conditions are such as to lead to incomplete combustion of fuel (including
fuel oil) the Ash Supervisor is to be informed in order that precipitators, ash and grit
collecting hoppers can be emptied more frequently. If for any reason the emptying of these
hoppers is delayed, the Ash Plant Supervisor should inform the Operations
Superintendent.
80
2.7.2
Before ashing of a boiler is carried out, permission must be obtained from the Unit
Controller. The Unit Controller must be informed when ashing is completed. During
ashing operations the firing of gas/oil burners is at the discretion of the Unit Controller
depending on the conditions of the boiler stability and ash levels.
2.7.3
Personnel engaged on ash removal duties must be warned of impending or suspected
unstable operating conditions.
2.7.4
If the dust is black in colour when removed from the hoppers, then the Operating
Superintendent should be informed. This indicates an accumulation of unburned coal.
Section 3:
MILLING PLANT
3.1
Lighting up the furnace.
3.1.1
Before lighting up a furnace a 20-minute ‘natural draught’ purge must be carried out. The
fans must be run to clear the combustion chamber and boiler passes of flammable gas and
dust in a further 5-minute forced purge. A clean flow of air, equal to at least 25% and not
more than 40% of that required for maximum output should be passed through the furnace
for duration of at least 5 minutes.
3.1.2
Check propane pressure is > 200KPa and that the supply to the boiler front is on. Check
that the fuel oil pressure is at 3MPa when purging is completed and first gas/oil burner is
initiated.
C.O.G. Level should be health >20%
C.O.G. Pr
52 Kpa
Temperature should be around 20oC
3.1.3
Initiate first oil or gas burner. If the burner does not light within 5 minutes it will time out
and a further 5-minute purge will be required. (Secondary air dampers may require closing
on a burner to obtain gas/oil burner ignition. Reopen dampers after ignition.)
3.1.4
Establish the group of oil or gas burners associated with the mill to be brought into service.
A minimum of three oil/ gas burners must be established before the P.A. Fan will start but all
four gas/ oil burners of that group, MUST be put into service so that each P.F Burner is lit by
its own gas/ oil burner.
3.1.5
Immediately check that satisfactory combustion is being obtained, i.e. a clean flame free
from ‘sparklers’ or smoke and unburnt oil dripping into the furnace.
If satisfactory
combustion cannot be achieved then the oil burner must be withdrawn from service and
examined. Also check that no spillage is taking place into the furnace from oil burners not in
use.
3.2
PREPARING THE FIRST MILL
3.2.1
Refer to the logbook for conditions at the previous shutdown.
3.2.2
Ensure that all gas /oil burners are in service as in 3.1
3.2.3
Establish that the mill reject boxes are empty and that there is no evidence of fire existing in
any part of the milling system. If a fire is suspected the mill must not be put into service.
The Operating Superintendent must be informed immediately and actions taken as
detailed in 5.2.
3.2.4
Ensure Mill and Feeder doors and outer reject doors are shut.
3.2.5
Adjust burner tilt to -5C.
3.2.6
Ensure all mill group dampers are closed.
3.2.7
A minimum of 3 gas/oil burners associated with mill group is put in service.
3.2.8
Sound ‘Boiler Evacuate’ alarm. Ensure that the mill is not being worked on.
3.2.9
Start seal air fan.
3.2.10
Start P.A fan.
81
3.2.11
Open hot air isolating damper.
3.2.12
Open mill inlet damper
3.2.13
Start mill motor when mill exit temperature is 75 oC.
3.2.14
Adjust attemperating air damper to adjust rate of rise of mill temperature.
3.2.15
Set the primary air fan suction vanes to minimum position to give a mill air flow of 60% of
M.C.R. 3.2kg/s and a maximum of 8.4kg/s
3.2.16
Check P.F. Flaps local to P.F. burners are open.3/4 flaps should be open for feeder to start.
3.3
BRINGING FIRST MILL INTO SERVICE
3.3.1
Start mill feeder when mill exit temperature is >75 oC and increase feeder speed control.
Note that the minimum load of any mill for steady state running is not to be less than
8m3/hr of coal. Ensure the air/fuel mixture is below the explosive range and a P.A. flow of
not less than 3.2kg/s vane setting, to ensure the mixture is above the minimum transport
velocity of 20m/sec.
3.3.2
Check ignition of P.F. at the burners. Indication will be given by rise in furnace pressure and
furnace flame intensity meters.
3.3.3
If an established stream of P.F is not ignited within ten seconds of it appearing at the
burners, trip the P.A. Fan, purge the furnace with oil burners in service for 5 minutes and
proceed as from 3.2.8.
3.3.4
If ignition of P.F. is established, set the coal feeder to ‘auto’ control.
3.3.5
Adjust the P.A suction vanes to give a minimum P.A. flow of 3.2kg/s and observe the mill
differential pressure.
3.3.6
Adjust the secondary air damper setting and Windbox pressure as necessary to give
satisfactory combustion.
3.3.7
Select mill to auto control as soon as conditions are stable.
3.3.8
Check and empty mill rejects.
3.4
INCREASING LOAD
Increase load, when required, in stages.
To increase load open P.A Fan suction vanes a small amount to increase P.A. differential. If
on ‘auto’ P.A Fan vanes will open on decreasing boiler pressure.
3.4.1
Coal feeder speed will then increase to maintain air/fuel ratio if on ‘auto’ control. Otherwise,
if on ‘manual’ raise coal feeder speed, to satisfy the predetermined air/fuel ratio curve.
3.4.2
Inspect mill reject boxes during the load increase and then at the frequency found necessary
for that particular mill, but at least every hour.
3.4.3
For operation at full output the P.A differential should be maintained at 95%.
3.5
MILLS BRINGING ADDITIONAL INTO SERVICE
3.5.1
Establish three or four oil/ gas burners in the appropriate group before attempting to start
any mill group.
3.5.2
Then proceed with operations for a normal mill start as detailed in section 3.2 where
applicable and all of section 3.3.
82
3.6
TAKING A MILL OUT OF SERVICE (NORMAL SHUTDOWN)
3.6.1
Check for evidence of fire in the mill system. If any evidence of fire exists within the mill
system, the mill should be kept running if this is possible. For action in this case refer to
section 5.3
NB: Feeder speed RPM x 1.5 – amount of P.A. flow required.
3.6.2
Sound ‘Boiler Evacuation’ alarm (if fitted).
3.6.3
Adjust P.A Fan suction vanes and if necessary attemperating air damper to limit mill
temperature rise. Mill outlet temperature should not exceed 93C and should not decrease
below 60C while firing coal.
3.6.4
Reduce load in stages by adjusting mill output with P.A. Fan vane control. Reduce feeder
speed to maintain air/fuel ratios and empty mill.
3.6.5
Take coal feeder out of service and open attemperating damper fully.
3.6.6
When mill is empty as indicated by an ammeter reading of 25A, and the mill differential
reduced to a minimum, purge the mill for a further five minutes with a P.A. flow of >3.2kg/s.
3.6.7
Shut mill inlet damper, shut hot air to mill damper. Ensure P.F. flaps are closed. Mill and PA
fan motors will trip.
3.6.8
Take seal air fan out of service after approximately 20 minutes when mill temperature has
returned to 45C. (It is appreciated that plant conditions make it difficult to reduce the
temperature to 45C, this being the desired temperature. The temperature should be
reduced to as low as is practicable and if the mill is purged as in 3.6.6. the risk of P.F.
ignition is minimised.)
3.6.9
Shut secondary air dampers – 2.5kg/s/damper airflow.
3.6.10
Ensure that the mill reject boxes are empty, the inner doors are left open and the outer
doors are closed.
3.6.11
If there is an excessive airflow through the reject boxes’ it should be reported to the Unit
Controller.
3.6.12
The mill outlet temperature will rise slowly after the shutdown. If there is a rapid rise in
temperature however, this may be due to a fire in the mill and action as detailed in 5.2
should be applied.
Section 4: OPERATING PROCEDURE TO DEAL WITH ABNORMAL OCCURRENCES
a.
Loss of Coal Feed
4.1.1
Loss of coal feed when the mill is on ‘auto’ is indicated by a decreased mill differential and
P.A Fan differential pressure. The mill outlet temperature will also increase. Feeder trips on
‘no coal on belt’
4.1.2
In the event of losing coal feed, sound the ‘Boiler Evacuation’ alarm.
4.1.3
If burner ignition has not been lost put appropriate gas/ oil burners in service.
4.1.4
Switch mill attemperating air damper to ‘hand’ and stop any rise in temperature of mill.
4.1.5
Reduce coal feeder setting to zero and gradually reduce P.A. differential ensuring that P.A
Flow does not fall below 3.2kg/s.
4.1.6
If coal cannot be stabilised take mill group out of service as detailed in 3.6.6. to 3.6.14.
4.2
MILL TRIPPED WHILST CONTAINING COAL
4.2.1
If a mill has been tripped whilst still containing coal there is a danger of this coal igniting
unless steps are taken to cool the mill as soon as possible. In addition, P.F. will have been
deposited in the pipelines to the burners. This must be blown into the furnace and burned
off to avoid risk of fire or flashback in these lines. Furthermore it may well be impossible to
start the mill until the mill grinding zone has been cleared of coal.
4.2.2
The following procedure should be adopted whenever a mill has tripped whilst still containing
coal.
4.2.3
Select mill attemperating air damper to ‘hand’ and open it.
83
4.2.4
Put appropriate gas/oil burners in service and sound the ‘Boiler Evacuation’ alarm. (if fitted)
The mill and P.F pipes should then be purged until the Mill differential falls to a steady value.
NOTE: If the mill is choked with coal it may not be possible to pass purging air through it.
This condition will be indicated by a low P.A Fan differential, low P.A Fan current and high
mill differential. In this case, if there is no indication of a fire in the mill, the mill and P.A
duct need to be opened and the coal cleared.
4.2.5
After purging, attempt to restart the mill. If the mill starts satisfactorily shut it down and
clear the reject boxes. Restart mill and check if inner reject box doors can be closed. If not,
shut down mill and clear reject boxes. Continue until all coal is removed and inner reject
doors will close. A maximum of three starts/hr is permitted with 20-minute intervals.
Return mill to service if required.
4.3
MILL OUTLET TEMPERATURES
4.3.1
The minimum mill outlet temperature controls are set at 75C with a high temperature alarm
set to operate at 100C and a mill trip at 110C.
4.3.2
Failure to control at the set temperature should be immediately investigated. If only one
mill is affected the control equipment should be suspected.
4.3.3
If high outlet temperature exists on all mills check that the air recirculation dampers are
shut. (On the air heater).
Section 5: MILL FIRES
5.1
General
5.1.1
A high mill outlet temperature, excessive outside casing temperature or P.F. pipe
temperatures will detect a fire in a P.F. system.
5.1.2
If the mill is on load abnormal fluctuations in draught gauges and mill amps may occur.
5.1.3
If these indications are received it should be assumed that a fire exists and the action
detailed below should be taken and the Ops Superintendent informed.
5.2
FIRE IN A STANDING MILL
5.2.1
Ensure mill is not approached for 30 minutes after fire is detected. Make sure that air is
excluded from mill by closing Mill inlet damper, Hot air damper, Attemperating Air damper
and stopping Seal Air Fan.
5.2.2
Shut reject box doors.
5.2.3
Do not attempt to put the mill on load.
5.2.4
When temperature has fallen to 50C and its casing cool open reject doors first, and then
open up mill for inspection and clearing.
5.3
FIRE IN A RUNNING MILL
Sound ‘Boiler Evacuation’ alarm! (if fitted)
5.3.1
A fire in a running mill will usually be extinguished by an increase in coal flow to the
maximum practicable level and opening attemperating air damper fully, thus helping to
reduce the mill temperature.
5.3.2
The shutting down of a mill containing a fire may result in an explosion as the air/fuel ration
passes through the explosive range. Therefore the mill is to be tripped at full load if any of
the following circumstances exist.
5.3.3
Persistent fire.
5.3.4
The mill in mechanical danger, as assessed by the Ops Superintendent.
5.3.5
Coal feed is lost.
5.3.6
Mill temperature continues to rise.
5.3.7
The mill will trip automatically when the temperature reaches 110C
84
5.4
ACTION AFTER A MILL FIRE OR HIGH TEMPERATURE CONDITION
5.4.1
Treat as a fire in a standing mill 5.2
5.5
P.F. Pipe Fires
These sometimes occur in the elbow adjacent to the Windbox.
5.5.1
Trip mill group.
5.5.2
Ensure P.F Flap valves closed.
5.5.3
Ensure P.A Fan isolating damper is closed.
5.5.4
Ensure Seal air fan is shut down.
5.5.5
Ensure Secondary air dampers are shut.
5.5.6
Connect up hosepipe. Allow P.F. pipe to cool naturally but if a fire can be seen through
cracks in the lagging, and then it should be put out using the fire hose.
Section 6: MALFUNCTIONING OF DAMPERS AND CONTROL EQUIPMENT
5.6.1
Should faults develop on the dampers system such that control of mill temperature is likely
to be lost the mill should be taken out of service until the faults can be put right. Manual
Operation of the dampers may be necessary to contain temperatures until the mill is shut
down, and hence avoid the possibility of a trip due to high outlet temperature.
Section 7: LOSS OF IGNITION
5.7.1
A loss of ignition will cause a Unit trip. The following procedure should be used to purge the
furnace. Make sure the following valves are closed:
➢
fuel oil supply and return valves
➢
propane valve
➢
C.O.G main valve
Slowly open all dampers and fan vanes in the air and flue gas passages of the unit to the wide
open possible to ventilate the boiler. Opening fan dampers shall be timed or controlled to avoid
excessive positive or negative furnace pressure transients during fan coast-down. Maintain this
condition for a period that will result in not less than five changes in volume, but in any case not less
than fifteen minutes. During the purge all secondary air dampers shall be open and the F.D. and I.D
Fan vanes maintained in the full open position. At the end of this period close the flow control vanes
and immediately start the fan(s)
Gradually increase airflow to at least 25% of full load airflow. These limits shall be adhered to
unless adequate tests on a specific Unit demonstrate satisfactory purging with different values of flow
and time.
If it is not possible to start for some extended period of time, a flow of air through the Unit to
prevent accumulations of combustible gases shall be maintained.
###############
85
vii.
120 MW UNIT FULL LOAD LIMITING PARAMETERS
BOILER LIMITING PARAMETERS AT MAXIMUM CONTINUOUS RATING
LOAD
MW
120
Eco
I/let
OC
205
LH
Top
OC
1250
FD
Water
Kg/s
134
Steam
T/Air
Coal
Kg/s
134
Kg/s
155
Kg/s
16.5
Eco Outlet
LH / RH
OC
OC
290
290
RH
Top
OC
1250
Spray Water
LH/RH
Kg/s
Kg/s
6.3
6.3
Steam-Water Pressure
Eco I/let| Drum |Main st|
Mpa
Mpa
Mpa
12
9.5
8.6
Steam Water Temperatures
Final SH Outlet
De-SH Inlet
LH / RH
LH / RH
OC
OC
OC
OC
518
518
450
450
Pyro Temperatures
LH
RH
Mid
Mid
OC
OC
1250
1250
LH
Bot
OC
1250
RH
Bot
OC
1250
De-SH Outlet
LH / RH
OC
OC
400
400
Eco Gas In/Out
L/R
L/R
In
Out
OC
OC
610
300
A/H Gas Inlet
LH
RH
OC
OC
300
300
A/H Gas Outlet
LH
RH
OC
OC
140
140
A/H Air Outlet
LH
RH
OC
OC
280
280
FD Flow
LH
RH
Kg/s
Kg/s
75
75
ID Suction
LH
RH
Pa
Pa
-1650
-1650
Wind box pressure at corners
1
2
3
4
Pa
Pa
Pa
Pa
750
750
750
750
pH
value
Condu
ctivity
9
<0.5
Mill
A
B
C
D
Burner tilt in Degrees
|Corn 1| Corn 2|Corn 3|Corn 4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
A
Kg/s
8.6
Drum
Sat.
OC
305
A/H Air Inlet
LH
RH
OC
OC
38
38
Primary Air Flow to Mills
B
C
D
Kg/s
Kg/s
Kg/s
8.6
8.6
8.6
O2 in Gas
LH
RH
%
%
3.7
3.7
Secondary air dampers
Corn 1
2
3
60
60
60
40
40
40
30
30
30
50
50
50
%
4
60
40
30
50
TURBINE LIMITING PARAMETERS AT MAXIMUM CONTINUOUS RATING
Vacuum
Kpa
11.8
End
Thrust
KN
<200
Bearing
temp
OC
90
Eco
Out
OC
290
BFP
Current | press
Amp
Mpa
566
13.6
Diff
Expn
mm
<6.5
Shaft
Posn
Mm
<3.5
Main Steam
Press | temp
OC
Mpa
8.4
510
Cond
temp
OC
49
Lub oil
temp
OC
32-38
86
Cond
LP2 O
OC
115
Dea
Outlet
OC
138
Circulatg water
Inlet | Outlet
OC
OC
32
44
FW
HP1 O
OC
175
CEP
Amp/Pr
...|Mpa
50/2.0
FW
HP2 O
OC
205