The presentation details about the Boiler Operation specifically while lightup of boiler and loading of boiler. the course participants discuss in details about the operations carried in their respective power stations

1. Boiler Light Up & Loading
Manohar Tatwawadi
Director, tops
mtatwawadi@gmail.com
+91 9372167165

2. Topics Covered
• Cold Start Up
– Preparations
– Initial Firing Precautions
– Boiler Lightup Procedure
• Loading and Unloading Procedure
• Normal Shutdown to Cold
• Normal Shutdown to Hot S/B
• Hot Restart
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3. Cold Startup
A Preparations for Boiler Lightup
It is assumed that at this time the following preparatory work has been
completed:
• The unit has been chemically cleaned, that the steam lines have been
blown, that the safety valves have been set and that the unit has been
filled to slightly above the normal operating level with properly treated
feed water. The feed water tank should have been filed with water.
• All control systems have been checked and are available for service.
• All instrumentation and associated mechanical equipment have been
checked and are available for service. Check all safety interlock system
prior to startup to ensure proper functioning.
• The oil firing equipment has been checked out to assure proper
functioning.
• Recheck items such as:
– Oil guns inserted and properly coupled. (Check gaskets between unions).
– All manual valves open.
– All control valves closed.
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4. Preparations….
• The pulverizers and feeders have been checked and are available for
service. "Refer Mill starting sequence" under Mill Operating Procedure.
• The wind boxes have been checked for proper damper positioning, tilts at
horizontal, etc.
• The feedwater system, instrumentation and equipment, have been
checked and are available for operation. It is recommended that during
start ups the feed water is controlled remote-manually, until a continuous
flow is established. To avoid possibility of oxygen corrosion in the boiler,
the use of undeaerated feedwater temperature less than 100 deg.C is not
recommended.
• All air handling equipment have been checked and are available for
service. All air and gas duct dampers should be in the start up position.
Refer to Notes and caution below;
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5. Preparations
• I.D. Fan outlet shut off gate closed. Inlet regulating
vanes/dampers are in closed position during starting.
• Keep the FD. Fan outlet shut-off dampers closed. Keep the F.D.
Fan regulating
• Vanes/Blades in the minimum position.
• Primary air fan outlet shut off gate and inlet control dampers
are closed.
• Wind box (secondary) auxiliary air dampers open.
• Scanner emergency air damper closed.
• Pulveriser seal air fan shut off dampers open.
• Air and gas dampers around airheater open.
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6. Preparations
• Notes:
• Refer to the Fan Manufacturers instructions for operating
details.
• It is assumed that the unit will be started with both F.D.Fans
and I.D. Fans. If the unit is started with only one set of fans
and airheaters, the corresponding dampers associated with
the equipment to be kept open. Dampers associated with
idle equipment should be closed.
• Caution:
• The ID Fans are generally capable of developing drafts in excess of
the furnace design pressure. Therefore, the operator must take
care to establish and maintain an air flow path through the unit
prior to starting the ID. Fan and prior to opening the ID.Fan inlet
damper by ensuring that other dampers in the system are in the
start up positions indicated above.
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7. Preparations
• The ID. Fan inlet damper must be kept closed until after the fan is
started. This procedure will minimize the possibility of developing
excessive negative pressure in the unit during the starting
procedure. The operator must take care to maintain the furnace
draft within safe limit at all times. He must be especially careful
when draft and air low controls are in the "Manual mode. He must
be alert at all times for possible malfunctions of automatic control
equipment resulting in abnormal excursions in furnace pressure
either negative or positive .
• Check that the airheaters have been prepared for service, than an
adequate means of extinguishing airheater fires is available and
ready for use. Refer to Air Preheater instructions for details.
• The soot blowing equipment has been checked for proper
operation and the system is in the start up condition. (All blowers
retracted, main steam supply valve open).
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8. Preparations
• All Desuperheater Spray Water Control Valves and
block valves are closed.
• All Boiler, Superheater and Reheater drain and vent
valves are in the start up position. Refer to the Valve
Operating Diagram.
• The furnace gas temperature probe is in working order
and available for service.
• The turbine generator is available for service and has
been prepared for service as described in the
manufacturer's instructions.
• Cooling water and compressed air service is available.
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9. Initial Firing Precautions
To Ensure a maximum safety margin during start-ups. It is
mandatory that at least 30% of full load air flow be maintained in
order to produce the following conditions:
• An air-rich furnace atmosphere. This precludes the possibility
of an accumulation of explosive mixtures in the event of poor
or delayed ignition after fuel is introduced in to the furnace.
• High excess air through the air heater. This minimises the
dilution of combustion air by inerts, carried over by the air
heater rotor.
• Air flow should be increased when the boiler reaches a load
where additional air is required to maintain the rated operating
excess air.
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10. Initial Firing Precautions
• During start-ups, lighting off is done with the lower ignitors
and warm up oil guns. Warming up can be accomplished with
either the warm-up oil guns or fuel oil firing. In either case, the
required firing rate must permit operation of an entire
elevation of fuel nozzles without exceeding the furnace exit gas
temperature limitation as described in the following paragraph.
• NOTE: To minimize the possibility of adverse visible stack
emission it is desirable to use the warmup oil guns till attained
to at least 35 Kg/cm 2 drum pressure and 177 deg. C secondary
air temperature before firing pulverised coal.
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11. Initial Firing Precautions
• When bringing the unit up to pressure and temperature, the saturated
(steam temperature rise must be limited to 110 deg. C per hour as per the
startup curve. The stat-up curve also shows the corresponding rate of drum
pressure increase.
• The capacity variation curve shows the capacity pressure relationship
required for proper waterwall circulation. At reduced drum pressure the
steam flow must not exceed the corresponding maximum allowable
capacity (% design capacity) shown on the curve.
• During all start-ups the firing rate should be controlled to keep the
maximum furnace exit gas temperature below 540 deg.C (as measured by
the furnace outlet gas temperature probe) until adequate flow is
established through RH by cutting in the HP/LP Bypass. After rolling the
turbine, the steam temperature and pressure rise at the turbine throttle
should at all times be in accordance with the limits prescribed by the
turbine manufacturer.
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12. Initial Firing Precautions
• NOTE: It is recommended that during initial start
of a new unit a relatively slow rate of pressure
increase be followed, in order to allow sufficient
time for checking expansion movements and to
permit the operators to become familiar with the
characteristics of the unit and its auxiliaries. Once
these characteristics have been established,
subsequent startups may be made at the fastest
rate consistent with maintaining the furnace exist
gas temperature limitation of 540 deg. C until the
HP/LP Bypass is cut - in.
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13. Boiler Light up Procedure
• Start both air preheaters. Then start two I.D. Fans and both F.D. Fans. After starting
the F.D. Fan, open the shut - off dampers for minimum. 30% air flow by variable
pitch control (See Note below and "Caution" under Section "Preparation for
Lighting up").
NOTE: Although it is sufficient to operate one set of fans until the turbines, carry a
light load, it may be desirable to light off with both sets of fans in order to avoid
unbalancing of the air flow when load is being carried.
• Open the air preheater air bypass duct.
• Start the scanner and seal air fans.
• Adjust the fan and windbox dampers to permit a purge air flow of atleast 30% of
total air flow and a furnace draft of approximately 12.7mm wg.
• When the fans are started, the secondary air damper control should adjust the
auxiliary air dampers to obtain approximately 37mm wg windbox to furnace
differential pressure.
• Check that all other purge permissives are satisfied.
• Initiate a furnace purge. Upon completion of purge cycle, check that all firing
prerequisites are satisfied.
• Place the temperature probe in service
• Initiate a light off sequence of the lower elevation of ignitors and warmup oil guns.
Refer to the "Furnace Safeguard Supervisory System". "Ignitor" and Air cooled Oil
Gun" Instructions for details.
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14. Boiler Light up Procedure
• During warming up period keep open the economiser recirculating line valve.
• Blow down the unit as required to maintain the drum water level in sight in the
gauge glass.
• The firing rate should be controlled to keep the furnace exit gas temperature
below 540 deg. C until steam flow through Reheater is established. Establish a
slight flow through superheater by opening its start-up vent. More superheater
drains/vents may be opened, if necessary, for increasing the steam temperature to
match turbine conditions.
NOTE: HP-LP By pass Station helps the unit to be quickly synchronised.
• Increase the firing rate as required within permissible limit of 110 deg.C hr. to raise
the pressure, if necessary with fuel oil.
• While the unit is heating up, frequent checks should be made of the boiler
expansion movements. Special attention should be given to expansion of the lower
part of the boiler relative to building steel. Expansion movements should be
recorded for comparison with future start-ups. Refer to the expansion movements
diagrams.
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16. Boiler Light up Procedure
• Maintain drum water level at normal and check boiler water concentrations and constituents
as frequently as required to maintain proper boiler water conditions.
• Close the economiser recirculation valve when continuous feed water flow is established.
• Before raising a vacuum in the condenser, make sure that all reheater vents or drains that
open to the atmosphere are closed. Leave drains or vents connected to HP drain flash tank
open until the turbine is carrying a light load.
• As drum pressure increases, progressively throttle the final Superheater Outlet Header vent
(Start-up Vent) and other start-up drains used (main steam line drain, turbine drains, etc.,).
• Sufficient steam flow must be maintained at all times to assure clearing the superheater
elements of condensate. Increase the firing rate as necessary, without exceeding the
furnace exit gas temperature limitation.
• Do not close start-up vent completely until steam flow through the turbine is established.
• Start rolling the turbine as soon as the minimum permissible start-up pressure and
temperature, specified by the turbine manufacturer, are reached. Refer to turbine
manufacturer's instructions.
• When bringing the turbine up to speed, the firing rate should be controlled to prevent the
furnace exit gas temperature from exceeding 540 deg. C. When the turbine is up to speed, it
may be synchronized. At this point the gas temperature probe may be withdrawn and the firing
rate increased as required. In no case should the firing rate exceed than what is necessary to
satisfy steam demand.
• NOTE: If the unit is put on the line before design operating pressure is reached, further
increase of firing rate should be in accordance with the start-up rate. The steam flow must not
exceed the maximum allowable capacity.
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17. Boiler Light up Procedure
• If the unit was started with one set of fans then start the second set of fans.
• Place additional level of oil guns in service as the load demands replace the warm-
up oil guns with load carrying guns after the first level of main oil guns are in service
and fire is stable.
• If coal was not fired previously (See Note) the pulverizer serving the lowest
elevation of coal nozzle (adjacent to the warm up oil guns) should be prepared for
operation so that it can readily be started at this time. Refer to Section 'Furnace
Safeguard Supervisory System" for startup sequence and controls. Prior to placing
pulveriser in service, ensure that one of the P.A. fans developing adequate header
pressure is in service.
• Refer to the Furnace Safeguard Supervisory System instructions. The coal fuel-air
dampers should remain closed until ignition is established. Check to see that the
nozzle tilts are horizontal. Place the second Primary Air Fan in service, if not done
previously."
• NOTE: If a pulverizer was started during the warming up period increasing load
requirements can be met by increasing fuel flow through this pulveriser. When
pulveriser is put into service ensure that the corresponding seal air fan is also in
service.
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18. Boiler Light up Procedure
• When placing the first Coal mill in service, check that the pulveriser start
permissives (ignition energy, etc.,) are satisfied. (Check and Refer FSSS)
• If ignition does not take place immediately after coal appears at the coal
nozzles, stop the feeder. Determine the cause of the ignition failure before
attempting to restart the feeder.
• Maintain proper coal/air temperature leaving the pulverizers. Regulate the
hot and cold air damper to hold between 66 deg.C and 90 deg.C at the
pulveriser outlet. At no time should this temperature exceed 95 deg.C. If it
should exceed 95 deg. C, the hot air damper must be closed.
NOTE: Pulverizer start-up will cause a sudden and sharp increase of steam
pressure. This will level out rapidly as load is placed on the turbine.
• Take the second coal mill in service in a similar manner when the coal
feeding of the first mill has reached 90% of its maximum. (Refer FSSS)
• Refer FSSS for loading, unloading, shutting off of Mills and Furnace oil and
Light oil burners.
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19. Boiler Light up Procedure
• The Furnace Safeguard Supervisory System and Secondary Air Damper Controls
should close the auxiliary air dampers serving compartments adjacent to coal
nozzles which are out of service. When the boiler reaches 20% of full load increase
the wind box to furnace differential pressure to approximately 100 mmwc.
• It is essential that the air flow to the furnace is sufficient for the firing rate at all
times, Automatic control equipment is normally arranged to maintain such a
balanced condition. The Oxygen measuring devices which are often tied in with the
air flow control should be checked periodically to assure continuous and dependable
operation.
• Place additional pulverizers in service as the unit loading demands.
• Place the Steam Temperature Controls and Combustion Controls on 'Auto' when
firing conditions are stable and the temperature and pressure control set points
have been reached. Refer to the control manufacturer's instructions for specific
procedures.
• Adjust the feed water supply to the boiler as necessary to maintain normal water
level, as per drum level operating curve. Feed water control should be placed on
automatic as soon as possible and practicable when continuous feed water flow is
established.
• When the unit firing conditions are stabilised, all warmup oil guns and ignitors may
be taken out of service.
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20. Boiler Loading Unloading Procedure
Decreasing Load
• If the unit load decreases, the feeder speed can be reduced so as to reduce the load. The
feeder speed can be reduced upto 50% below which further reduction may affect the ignition
energy of the adjoining coal mill. (Refer to FSSS).
• To remove the pulveriser from service, refer mill normal shutdown procedure.
• Additional pulverisers can be taken out of service in a similar manner if required.
• Every effort should be made to keep adjacent ends in service. If, due to maintenance a
pulveriser is not available, skipping the coal elevation served by that pulveriser is permissible.
Skipping of two coal elevations is not recommended and is only permissible with the use of
auxiliary supporting fuel oil (associated warmup guns and ignitors).
• NOTE: Auxiliary supporting fuel should be used at any time and under any conditions in
which, in the operators 'judgement in stabilisation of ignition is necessary.
Increasing Load.
• If it is required to increase the load, the feeder speeds of all the coal feeders can be increased
in equal manner after a load decrease when pulverizer has been taken out of service.
• If the unit load is to be increased further by taking a pulveriser in service. (Refer FSSS).
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21. NORMAL SHUTDOWN TO COLD
• The following procedures for normal shutdown are based on the
assumption that the unit is operating at full load on automatic control and
that it is the intention to reduce the pressure to zero and cool the boiler
completely.
• Gradually reduce load on the unit; reduce the firing rate in line with the decreasing
steam flow. Allow the pressure to drop with the reduction in load to accelerate cooling.
• A) Reduce the steam temperature at the rate prescribed by the turbine
manufacturers.
• B) Steam temperature control, combustion control and feedwater
control may be left on automatic mode until the point is reached when
better control can be obtained on manual mode.
• Refer to FSSS for shutting down.
• As pulverisers are taken out of service the secondary air damper control system should
close the associate windbox dampers and throttle other dampers as required to
compensate for the reduction in firing rate.
• NOTE: It is recommended that the above consecutive elevation shutdown
sequence be followed. Firing coal at separated coal nozzle elevations
without auxiliary supporting fuel is not permitted.
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22. NORMAL SHUTDOWN TO COLD
• Operate all soot blowers. Refer to manufacturer's instructions.
• Reduce the air flow in line with fuel reduction until 30% of maximum air
flow is reached. Do not reduce the air flow below this rating until all fires
are out and the unit is off the line. See curve 3. To avoid firing instability
during this period of high relative air flow, the auxiliary air dampers at all
elevations should d open and reduce the windbox to furnace differential
pressure to its lower setting.
• Check the expansion movement of the unit as load is being reduced.
• Close the desuperheater isolating valves.
• After the last pulveriser end has been shut down, remove the warm-up
guns and the ignitors from service. Shut off the cooling water to the
pulverisers. All fires should be removed when the unit is off the line.
• Immediately after closing the turbine stop valves, open wide the
superheater outlet vents and drains and all reheater vents and drains.
Open other drains in the superheater system as required for further
pressure reduction. Open steam line and turbine drains as described by the
turbine manufacturer.
• Open the economiser recirculating valves.
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23. NORMAL SHUTDOWN TO COLD
During the shutdown period if it is not required to enter the unit immediately a slow
rate of pressure and temperature decay may be desirable. This can be
accomplished as follows:
• Purge the unit by running the induced draft and forced draft fans for atleast five
minutes (at 30% air flow) after the fires are extinguished.
• Reduce the air flow through the unit to a minimum. Keep the fans and airheaters in
service until the unit has cooled to the desired temperature.
• After stopping the fans stop the airheater.
• Keep the water level near normal in the gauge glass, add make up as required.
NOTE: Fans and Airheater should not be taken out of service until the airheater gas
inlet temperature has dropped to below 200 deg. C.
• Open the drum vents when the unit pressure has decayed to 2 kg/cm2 (g).
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24. NORMAL SHUTDOWN TO COLD
If it is desirable to accelerate the cooling process in order to
permit entry into the unit for maintenance, proceed as
follows:
• Purge the unit by running the induced draft and forced draft
fans for atleast five minutes (at a minimum of 30% air flow)
after the fires are extinguished.
• Continue running the fans to cool the unit at the desired rate.
The airheaters may be shutdown when the gas temperature at
airheater inlet has dropped to below 200 deg.C.
• Maintain the water level near normal in the gauge glass.
• Open the drum vents when the unit pressure has been
reduced 2 kg/cm2 (g).
• The boiler water temperature should be reduced to atleast 93
deg.C before draining.
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25. NORMAL SHUTDOWN TO HOT
STANDBY
• It is assumed that the boiler will be shut down for a relatively short period of time
and existing pressure and temperature condition will be substantially maintained.
A procedure similar to that for normal shutdown should be followed except:
– Do not reduce drum pressure in line with unit load reduction. The rate of
pressure drop should be much less than the rate followed during normal
shutdown. When the desired pressure at which the boiler is to be held is
reached after the turbine is off the line, the boiler may be bottled up closing
all super-heater drains and vents. Reheater drains and vents are kept open.
• NOTE: If it is expected that the Unit will be restarted in a very short period of time
in which the turbine metal temperatures will not decrease appreciably, it may be
desirable to cool the turbine metal to below 425 deg.C by reducing the steam
temperature and pressure, while the unit load is being reduced. This will reduce
the steam/turbine metal differential temperature upon restart.
– It is recommended that after all fires are extinguished (See Caution below) the
I.D. and F.D. Fans are kept running until the airheater gas inlet temperature
has dropped to below 200 deg.C (See Warning below). Close all gas duct,
secondary air duct and windbox dampers after the fans are shut down.
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26. NORMAL SHUTDOWN TO HOT
STANDBY
– CAUTION: If it is known or suspected that combustible deposits are present in
the air heater elements, the airheater gas inlet temperature must be reduced
to 200 deg.C before shutting down the F.D. Fans, I.D. Fans and airheaters. The
airheaters must be thoroughly cleaned to remove any combustible products
before it is shut down.
– WARNING: If it is decided to shut down the fans with the airheater gas inlet
temperature above 200 deg.C the airheaters MUST be kept rotating. However
running an airheater with the gas inlet temperature above 200 deg. C and no
air flow through it will result in seal damage and subsequent excessive leakage
during operation (Refer to airheater instructions). The decision to bottle up
the unit above 200 deg.C must be made with this in mind.
Keep the water level in sight in the gauge glass. As the unit cools and the water
shrinks, make up should be added intermittently to prevent the water from
dropping out of sight in the gauge glass.
• NOTE: The operator should observe the gauge glass periodically so that he
is always aware of the actual drum level and can take the appropriate
action to re-establish water level when the unit is being restarted.
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27. HOT RESTART
• Assuming the boiler has been down for a comparatively short period of time and
considerable drum pressure was maintained, the following procedures should be
used in restarting the unit.
– Make a general inspection of the boiler and check the points as mentioned
under normal start-up.
– If the airheater and fans were shutdown at reduced temperatures start the AH
and fans
– If the unit was bottled up hot with the airheaters still running, start the fans in
the normal sequence.
– Initiate a furnace purge and normal light off sequence of the warm-up oil
guns.
– Open wide all superheater drains to allow complete draining of superheater
headers and/or elements.
– After draining, close all drains, except the superheater steam cooled rear
outlet header and side steam cooled wall outlet header drains and the start-
up drain vent (Main Steam Line Vents and drains).
– Keep the steam cooled wall header drains slightly cracked open until steam is
admitted to the turbine.
– Keep the startup vent, drains open. Reheater drains and vents are open.
– Open the desuperheater isolating valves. Desuperheater control valves must
be closed.
– Close all reheater vents and atmospheric drains before pulling a vacuum in the
condenser.
Reheater condenser drains may be left open until the turbine is under light
load. They may be closed soon after HPLP Bypass has been cut into operation.
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28. Hot Restart
• When steam is admitted to the turbine for rolling, it is
desirable to have a minimum steam/turbine metal
temperature differential. This can be achieved by firing
at a maximum rate within the furnace exit gas
temperature limitation of 540 deg.C until HP-LP bypass
is cut in. In order to reach the exit gas temperature
limit it may be desirable to put more oil guns to start a
pulveriser at this time. Stabilize the firing conditions to
maintain the maximum furnace exit gas temperature
without exceeding it.
• Proceed as during normal start-up from cold.
• During a hot restart the turbine metal temperature will normally
require a rapid reloading of the unit and this is achieved by closing
the bypass as the turbine valve opens.
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