COGENERATION PROJECT
PERFOMANCE OF THE COGEN PLANT
1998
BY
GAIQUI Vivian
FUEL Steam & Power Generation
Existing Plant No. 1
BOILER
Fives Cail Babcock
Rating:110T on Bagasse Mode
90T on Coal Mode
Steam Pressure:45bars
Steam Temp: 450°c
TURBO GENERATOR GROUP
Creusot Loire/Jeumont Sneider
Power: 21.7 Mw
Extraction Pressure:1,5bar
Condensor Capacity:110t
FUEL Steam & Power Generation
Power Plant No. 2
BOILER
John Thompson Africa
Single Pass/Suspended boiler
Rating:100 T on Bagasse Mode
80 T on Coal Mode
Steam Pressure:45 Bars
Steam Temp: 450 °c
TURBO GENERATOR GROUP
ABB/SIEMENS Extraction & Condensing
Power: 18.8 Mw
Extraction Pressure:1,5bar
Condensor Capacity:100t
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POWER PLANT 1 & 2 (steam & Power)
Advantages
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High overall efficiency
Any type of fuel may be used
(Bagasse/Coal)separately or in combined
mode
Heat to power ratios can be varied
through flexible operations
Ability to meet more than one site heat
grade requirement
Wide range of sizes available
Long working life
THE BOILER
The choice was a JOHN THOMPSON AFRICA Boiler
with operating pressure of:
- 4500 Kpa with a mean temp. of 440ºc
(same working pressure as Boiler No.1)
These specific conditions were chosen to
optimize the power generation capacity while
at the same time refraining the need for
sophisticated and high cost of water
treatment.
THE DEMIN PLANT
After a survey of the existing Demin Water Plant
and in addition of the return condensate from the
Sugar Factory Process Results shows that the
existing DEMIN WATER PLANT was enough efficient
and sufficient for the 2 boilers need.
Flow Rate service:15m³/hr
Capacity:250m³ nett. Between regeneration
Raw water quality: Cations 91mg/l
Anions 71mg/l
pH
6,5-7,5
Operating pressure: 500kpa
JTA BOILER EFFICIENCY
To maintain the steam temp.within the close limits
required by the 18.8Mw/h Extraction/Condensing
turbo alternator.
The single pass boiler is fitted with two stage
superheaters and interstage attemperator.
(This differenciate with others conventional boilers which are
usually fitted with spray Attemperator and requires a high
quality water)
While in this case of the JTA Boiler, the
attemperation is achieved by passing a
portion of the steam through a heat
exchanger heated in the of the boiler
water drum.
EFFICIENCY OF COMBUSTION CONTROL
Grit refiring is also in operation to improve
combustion efficiency on coal mode.
Optimal boiler efficiency is achieved by
reducing the flue gas temperature to 130ºc by
means of a heated economisers,So as to avoid
risk of dew point corrosion in the lower banks of
economiser tubes while firing coal,a feed water
heater preheats the feed water to approx. 135 ºc
(steam from turbine MP outlet)
WET SCRUBBER
The outlet flue gas passes through a
wet gas scrubber to reduce
particulate emissions to below
120mg/nm³ both on Bagasse and
coal,ensuring the running of the plant
“ ENVIRONMENTAL FRIENDLY”
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THE BAGASSE & COAL HANDLING
Once again the existing installation was
upgraded to Feed the Boiler No.2
- COAL HANDLING
With slight modification to of COAL HANDLING
installation /distribution equipments,the BOILER 2 is
feeded correctly.
- BAGASSE HANDLING
On the other side by adding 3 New belt conveyors,the
routing of Bagasse Feed to BOILER 1 & 2 are being done
sufficiently.
The Turbo Generator Group
The ABB/Siemens reaction Turbine with:
- Rating of 18.8Mw
- Working INLET Pressure 45bars/440°c steam and
- Medium Steam Temperature at 6bars/135°c
- Extraction Steam 2bars for the Sugar Factory Process
- Turbine speed 6800rpm
- Voltage system:6.6
- Alternator speed:1500rpm
And fitted with:
-100T/h surface condensor
-Aero cooling Tower of 3 Units
Performing with INLET Water Temp Max.35°c
The Turbine General Description
For the conversion of Thermal energy into mechanical power,the
Turbine receives Superheated steam of 44bars/430°c from the
main steam line.The live steam coming from the main steam line
passes through the Live-steam emergency stop Valve,the three
control valves,the control stage nozzles and the control-wheelblades entering the wheel chamber and flow through the reaction
part.The enthalpy drop of steam across the 18stages of the
turbine is transformed into energy in a continuos process.Steam
flow through the control valves and the control wheel into the
turbine.
The Turbine is equiped with an Extraction line,where it is possible
to lead steam after the 12th reaction stage into Extraction line.
A bleed line make possible to lead steam after the 9th reaction
stage into the bleed line.
The steam turbine is equiped with a control wheel to enable a
good efficiency at partial load points due to flow control without
throtting losses.
STEAM & POWER GENERATION
INTERCROP
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During INTERCROP season the Two Power
Plants namely:
Power Plant No. 1 Max Rating: 21.7Mw
&
Power Plant No.2 Max Rating: 18.8 Mw
Export Max off crop:32Mgw/h
STEAM & POWER GENERATION
CROP SEASON
-The Two POWER PLANTS operates on Extraction
Mode and Bagasse firing
Export Max :22Mw
- Extraction Steam to FACTORY PROCESS
*Steam Flow to Factory:300t/h
*Steam Pressure:2bars
*Condensate Return from process at Full load:130t
Performance 2008:
Cane Crushed:976,000t
Bagasse:312,500t
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BOILER EFFICIENCY on BAGASSE MODE
Bagasse has a calorific value of 19,250 KJ/kg at
0% moisture content.The nett calorific value of
bagasse at 48% moisture content is approx.
8,000KJ/kg.Moisture content is the most
determinant parameter.A lower moisture content
result in a higher calorific value.
However,most mills in MAURITIUS produce a
bagasse with 48% moisture.During combustion,
steam to bagasse ratio is normally taken as 2.2.
By working out the recorded datas the efficiency
is:1t of Bagasse =2.1t/Steam
END