INDEX
SR.NO.
PARTICULARS
PAGE NO.
1
INTRODUCTION
2
2
SIGNIFICANCE
3
3
OPERATION
4
4
EQUIPMENT
5
5
FURNACE PURGE
7
6
LIGHTING UP WARM UP ELEVATION
10
7
LIGHTING UP HEAVY OIL ELEVATION
16
8
MILL
18
9
FAN CONTROL
25
10
CONTROLS OF WIND BOX DAMPER
26
11
FSSS PROTECTION TO BOILER
27
12
FSSS ANNUNCIATIONS
13
CARE OF FSSS
28
29
INTRODUCTION
Furnace safeguard supervisory system popularly called FSSS
continuously monitors the operations related to fuel admission and some
other vital parameters to ensure safety of the Boiler.
Generally furnace oil or any kind of fuel is susceptible to explosion
hazards. Majority of explosion occurs during start up, shut down and
low load operations. There are many steps that must be followed by the
operator to admit a fuel in to the furnace safely and properly. In high
capacity boilers, where fuel input rate is very high major furnace
explosions can result from the ignition of unburnt fuel accumulated in
the first one or two seconds. Human reaction time to such situations is
inadequate. So there a proper burner management system called as FSSS
is installed in the Boilers. Every operation related to fuel admission is
accomplished through FSSS.
SIGNIFICANS
The furnace explosion occurs due to:
a) Improper purging of the furnace and air.
b) Inadequate ignition procedures.
c) Maintaining fuel supply for too long a period without establishing
combustion.
d) Re-lighting burners too soon after previous flame out.
e) Introduction of main fuel without ensuring adequate ignition
energy.
So furnace burning any and all kinds of fuels is susceptible to
explosion hazards. FSSS helps in achieving basic objectives repeatedly
without error to safe-guard the furnace against hazardous effect by
means of
a) Ensuring certain Safe condition established and proved in the
furnace before light up can proceed.
b) In the case of unstable furnace flame condition, to help the
operator to introduce additional ignition energy.
c) In the event of flame failure fuel supply is immediately cut off and
furnace, air and gas paths purged before any attempt is made to
relight the burners.
OPERATION
Furnace safeguard supervisory system comprises of controls,
indications, logic to carry out following:
1) To start and complete furnace purge when all technological
conditions are fulfilled.
2) To start and monitor igniters.
3) To start warm up or heavy oil guns when permissive condition
exits. The guns are allowed to burn so long as proper
combustion conditions are ensured.
4) To start mills and coal feeders when safe conditions exist.
5) To trip out mills and coal feeders when satisfactory conditions
cease.
6) To trip out all boiler fines when boiler safety is threatened
7) To monitor furnace flame.
8) To start and stop igniter and scanner fans.
9) To indicate auxiliary and fuel air damper close and modulation
indications.
10) To release damper interlocks for secondary air control.
11) To provide boiler trip signal to other equipment such as PA
fans, turbine generator etc.
EQUIPMENT
So, FSSS system is designed to offer a maximum safety, minimum
trips, minimum power consumption and maximum life for the
component used. The logic is functionally divided into unit logic,
elevation logic and corner logic.
Unit Logic: it supervises the overall furnace condition by monitoring all
critical parameters of fuel firing system and also supervises furnace
purge.
Elevation Logic: start up and stopping actions for the elevation are
carried out through this logic.
Corner Logic: it controls and supervises the corner was that is oil
valves, atomizing valves.
FSSS Equipment can be group under three heads:
Operating and indicating console insert on the operators desk: this
consist of all the switches for initiating controls and also indications of
status of all fuel firing equipment and their auxiliaries. The operator is
mainly concerned with this desk only provided other two are functioning
properly.
Relay logic cabinets:
This cabinet consists of relays, timers, circuit breakers for AC,
DC, and control supplies flame scanner. The control the process
logic.
Field Equipment:
Field equipment are those which help in actual operation of fuel
firing equipment and those which provide the status to the operating
consol and relate logic cabinet. Field equipments are trip was valves
on the main oil headers, hydro motor valves on oil lines of individual
corner, oil guns and atomizing medium of oil gun assembly, igniters,
flame scanners, pressure and temperature switches, scanner fans,
igniter fans, mill discharge valves, hot air gate, cold air gate, tram
iron gate, seal air gate etc. the connection form field equipment to
relay logic cabinet is through cables. Connection from operating
console to relay logic cabinet is by cables for easy maintenance.
FURNACE PURGE
Furnace purge is required after a boiler trip out, before relighting
the boiler to expel all unburnt full particles, vapor etc, form the boiler so
that when spark is introduced during light up, possibility of explosion
are avoided.
FSSS ensure a proper furnace purge in following manner:- “Purge
Ready” signal when appear only when following conditions are fulfilled.
 110V AC and 220V DC supply to FSSS panel is switch on.
 Boiler Drum water level normal.
 At least one ID and one FD fan running.
 Establish 30% full load air flow as seen in total air flow recorder.
 Igniter trip valve closed.
 Warm up trip valve closed.
 Heavy oil trip valve closed.
 All igniter valves closed.
 All warm up and oil gun valve closed.
 All auxiliary air damper modulating to maintain air flow can
adequate wind box to furnace differential processing?
 All coal mills off.
 All raw coal feeders off.
 All flame scanners show no flame.
 All mill hot air gates closed and cold air damper are less than 5
degree open.
 No boiler trip command.
When above conditions are met, signal “purge ready” will
disappear, even during purging process. When signal “purge ready”
appears, press button “push to purge after the expiry of purging time
signal “purge complete” appears.
454
LIGHTING UP WARM UP ELEVATION
Now we are ready for Boiler light up.
a) Lighting up warm up elevation AB
Elevation AB has capability to be used for either burning light oil
or heavy oil. So select “light oil” on the consol for AB elevation ensure
warm up oil tips are provided is guns of that particular elevation.
b) I] Igniter trip valve:
Press igniter trip valve “open” push button igniter trip valve oil
open provided the following condition are fulfilled.
Igniter oil supply pressure adequate (more than 12.1 kg/cm2)
All igniter valves closed.
No boiler trip command.
In addition, instrument air supply must be available to actuate trip
valve.
If igniter fan is not started, it will start when first igniter start
Command is given.
II] Opening light oil trip valve:
Light oil trip valve will open if following condition is met:
 No boiler trip.
 Elevation AB LO valves on guns is closed.
Light oil pressure adequate i.e. they should not less than 1.4
kg/cm2 for more than 25 sec. and light oil trip valve open push button
pressed.
The following figure shows logic diagram for “warm up oil trip
valve control”. Before Boiler light up with Light Diesel oil, LOTV must
be open by giving “open” command from push button switch on the
desk.
Output form “OPEN” push button switch goes to an AND gate.
Other input to this gate are_
1. No Boiler Trip
2. All Corner Valves closed
3. LDO Pressure Adequate
4. LOTV “Close” command not persisting
When all these inputs are TRUE, OPEN command causes AND
gate to give a TRUE output causing LOTV to open.
LOTV closes when
1. Close command through push button switch is initiated OR
2. Boiler trips OR
3. After a delay of 3 second when any warm up oil elevation’s Corner
valve is NOT CLOSE AND
i) If LDO Pressure drops to LOW valve OR
ii) If P between atomizing air and LDO is low.
Dia fig3 455
c) Starting Igniter:
When igniter is started for 1st 10 sec period, oil and atomizing air
are admitted though the valve and simultaneously a spark is applied. The
spark lights up the oil spray and flame is sensed by flame sensor in the
igniter. This happen within 10 secs, the valve is held ‘open’ allowing
igniter to continue.
There are no separate igniter start push buttons, pressuring any one
pair of oil gun start or stop push button will give starting impulse to all
four igniter of that elevation. To start the oil guns press either 1and 3 or
2 and 4 start button. This gives commands for igniter start provided the
following condition is met:
 DC power available.
 No boiler trip command.
 Burner tilt horizontal and air flow less than 40%.
 Igniter trip valve open.
 L.O. trip valve are open.
Igniter start causes following gives a start command to spark plug.
This command holds for 10 secs by which time if flame is in the igniters.
Now in this way at least three igniters on selected elevations are
proved command is given for selected LO guns to advance and light up
provided:
o Atomizing air valve open
o Warm up oil valve open.
o Corresponding igniter proved.
Under this condition, first one gun will advance, atomizing air will
open the next gun of will undergo similar operation with time log off
25 secs in this at least three guns have to be proved, otherwise oil guns
will trip out. When guns trips , the gun will not retract , it must be
retracted locally immediately to avoid any fire accident.
Warm up guns will trip under following conditions:
 Pressing stop push button.
 Moving local switch from ‘Remote’ to any other position.
 Gun advanced or engaged limit switches are released.
 Corresponding igniters trip out.
 Air or oil is elevating valve are closed.
 Oil valve is not proven to be open within 90seconds.
 Any boiler trip command.
 At any time when warm up guns are in service, it more than
one igniter is off all warm up guns oil trip.
LIGHTING UP HEAVY OIL ELEVATION
I] Lighting up Heavy Oil Elevation.
Healy oil can be fired on any three elevation AB,CD and EF.
Heavy oil guns are supposed to be self sustaining. Once three oil guns
are tilt, their flow (gun loading in that particular elevation) is more than
30% or Boiler load more than 30% and flame scanners are sensing flame
under these condition light oil can be withdrawn without affecting oil
guns.
II] Now the heavy oil valves open under following condition are met.
 Header oil pressure adequate.
 All heavy oil hydra motor valve of AB, CD, EF oil guns are
proven closed.
 No boiler trip command.
 Heavy oil pressure not low less than 1.4 kg/cm2 for more than 2
secs. When valve open signals open appears on the panel.
Starting igniter command oil materialize only when heavy oil is
ready for light up with oil temperature more than 1050C .
Now taking heavy oil guns service in elevation AB.
Gun will advance provided:
 Atomizing steam isolating valve open.
 Heavy oil manual isolating valve open.
 Heavy oil igniter on.
Under this condition oil gun advance.
MILL
FSSS controls the salve starting, running and stopping of mills.
a) Pulverizer Ready for start
This is common to all six mills signal pulverizer ready will appear
when all the following conditions are fulfilled.
 Mills outlet temperature is less than 900C.
 Seal air valve open.
 Cold air gate open.
 Feeder inlet gate open,
 Pulverizer discharge valve open.
 Tramp iron hopper gate open.
 No Pulveriser trip command.
 Burner tilt horizontal and air flow less than 40% for
subsequent mills, the first R.C. feeder ON. Energizes relay by
passing burner tilt and air flow conditions.
Dia fig 4. 456
b) Ignition permissive :
It is presumed that P.A. fan is running, seal air fan is running, P.A.
header pressure is normal before we can actually start the mill, another
conditions that of providing sufficient ignition energy near the burner
nozzle of the mill has to be ensured so that, once coal flow is established
through mill, the pulverized coal will light up inside the boiler without
any loss of time.
At least three oil guns (Heavy oil or warm up) are in service for the
first mill to be started A or B, C or D, E or F.
For second mill to be start ignition energy is given by either: Three oil Guns being in service adjacent to mill or
 Boiler load is more than 30%.
 Adjacent mill running with RC feeder speed in excess of
5rpm or Pulverizer A or C in service at igniter than 50%
loading.
 This ignition energy must be continuously available for three
minutes after starting RC feeder.
Even though the logic permits removal of ignition energy after
three minutes operationally it will be required for even longer period till
boiler flame conditions are stable.
The following figure shows Logic Diagram for Ignition Permissive
for Pulverizer A and B. Similar requirements are applicable for other
Pulverizers:
1) Pulverizer B is running with 50% loading AND Boiler Load is More
than 30% OR
a) Elevation AB in service with 3 out of 4 Guns established.
2) Puloverizer B Ignition Permissive is available if
a) Pulverizer A or C running at 50% loading AND Boiler load is
more than 30% OR
b) Oil Elevation AB in service with 3 out of 4 Guns established.
Dia fig. 457
Actual starting of the mill
If conditions are met and if local key release push button is
released mill can be started by pressing the start push button on console.
 As soon as mill starts, cold air damper opens full.
 Hot air gate can now be opened provided temperature after mill
still remains less than 900C. If the temperature exceeds 900C, the
white signal ‘ Pulverizier ready’ will disappear but the mill will
continue to run. Pulversier ready can disappear for other reason
also.
However if discharge damper closes mill will trip immediately.
 After opening the hot air gate, cold air and hot air damper can be
regulated to achieve an after mill temperature of 60 0C to750C and
P.A. fan flow about 52 T/hrs. During manipulation of air, take care
load P.A. fan so, that P.A. header pressure does not fall below
650mm.
 If the ignition energy continuous to be present after starting mill,
feeder can be started and mill loaded.
 As soon as feeder is started, signal given to panel to modulate fuel
air accelerator to speed of feeder. When feeder stops, fuel air
damper is shut. This is to facilitate quick light up of fuel when a
mill is started.
 After 50 seconds of feeder starting relay energizes to permit feeder
to be controlled by boiler pressure auto.
PULVERIZER START
When ignition energy available and Pulverizer ready condition are
establish for the respective Pulverizer. The Pulverizer may be place in
service as follows:
a) Start the Pulverizer by pressing start push button
b) When Pulverizer is proven on as indicated by its on indication
or by amp on UCR open, hot air gate and allow pulverize to
come adequate temp (750C) and PA flow of about 52 T/hr with
the help of cold air damper.
c) When Pulverizer is up to temp 1400C start feeder and set at
minimum and associated elevation of fuel air damper proven
close.
Coal flow must be proven either by coal flow detector or
satisfactory Pulverzier amp within 5 secs after feeder started. When
minimum of the two feeders are establish at greater than 50% loading,
associated elevation of oil guns may be shutdown provided feeder has
been on for minimum 3 of 3 minute.
FAN CONTROL
Igniter and scanner fans:
Igniter fan:Igniter can be started from control desk otherwise it get set started
automatically when any igniter or oil elevation start is initiate at least
one ID and more than one FD fan must be service for the igniter fan to
start on stopping igniter fan from control desk will remove the
associated igniter fan service provided all of igniter valve are closed.
Scanner Fan Control:It can be started from control desk otherwise it get started
automatically when the scanner air duct to differential pressure falls
below 4.5”w.g. low differential pressure more than 10 secs will alarm,
the scanner emergence damper open on interlock when both ID/FD fan
are off, this allows the fan to draw ambient air for the cooling scanner
when unit is bottled up on stopping fan from control desk will remove
the scanner fan from service provided the scanner duct to furnace desk.
Pressure is above 4.5”w.g.
CONTROLS THE WIND BOX DAMPERS
1] Auxiliary Air Dampers:
 During furnace purge and when load is less than 30%. FSSS
modulates are auxiliary air dampers to maintain a low wind box
pressure (30mm).
 When load increases beyond 30% the modulation is for a higher
wind box pressure (60mm), which is achieve by closing dampers
near elevation not in service.
 When warm up oil is in service, the auxiliary air damper of AB
elevation opens to a predetermined position.
 When heavy oil is in service, the auxiliary air is allowed to be
controlled by opening depending on oil pressure.
 When one FD fan trips, then all auxiliary and fuel air damper open
wide.
2] Fuel air dampers:
 All the air dampers are shut on elevations where there are no
feeders in service.
 After starting of feeder, the fuel air damper of that elevation
is allowed to be controlled with feeder speed.
FSSS PROTECTS THE BOILER
By tripping out all fuel i/p under the following condition:
 Loss of D.C. to FSSS
 Furnace pressure inadequate.
 Less than fire ball load and loss of A.C. on any elevation in
service.
 Drum level high or low.
 Flame failure trip.
 Both PA fan off.
 Low air flow.
In this way FSSS protect the boiler hence it is said to be furnace
safeguard supervisory system.
FSSS ANNUNCIATIONS
F.S.S.S. Provide the following Annunciations/ contacts:
 Both ID & FD fans (one pair) off.
 Air flow is less than 30% when boiler load is less than 30%.
 Scanner fault alarm.
 Stand by scanner fan started.
 Furnace pressure high/low.
 Both P.A. fans off when any pulverizer is ON.
 Drum level high/low.
 Turbine trip.
 Heavy oil Header Pressure low.
 Loss of A.C. power.
CARE OF FSSS
To get maximum utilization out of FSSS the following are
recommended:
These notes serve as a guide for boiler operation engineers. Relay
numbers have been given for their understanding only. No repair o
tinkering on FSSS panel is allowed by operation engineers. Relay logic
panel must be handled by only the control maintenance engineers
deputed for the purpose.
 All check and repair must be based on engineering drawing.
 FSSS panel and console must be kept clean. Periodic vacuum
cleaning or air blowing is advised.
 FSSS panel must be kept closed and locked if necessary.
 Earth fault relay occur in the panel wiring and relays. Frequent
source or fault lie in the field equipment and connecting with FSSS
must be periodically inspected; leakages eliminated, kept clean and
smooth working should be constantly at relay panel to make good
failures of field equipment.
 Gun advance retract mechanisms, limit switches, hydra motor
valve, trip valves pressure, temperature switches etc. require
periodic cleaning, lubrication and other appropriate maintenance.