interview q and ans for tharmal power plant

5/26/2018 Interview q and Ans FOR THARMAL POWER PLANT

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Q. How to calculate heat rate?

Station heat rate = Specific fuel consumption * Calorific value of fuel

Turbine heat rate = (Main steam flow * Main steam enthalpy + Aux Steam flow * Aux steam

enthalpy - Feed water flow * Feed water enthalpy + Makeup water flow* Makeup water

enthalpy)/Power generationUnit of Heat rate is kcal/kWh, kJ/kWh,Mcal/MWh, MJ/MWh,

Turbine efficiency = 1/ turbine heat rate for Kcal/KWh is 860/ turbine heat rate

For kJ/kWh is 3600/turbine heat rate

Station efficiency = 1/ station heat rate for Kcal/KWh is 860/ station heat rate

For kJ/kWh is 3600/station heat rate

Heat rate is important. Changes in heat rate can indicate problems in unitproblems may

include instrument calibration drift, gas path fouling or foreign object damage (FOD). Although,

in most cases, performance losses due to FOD are noticeable without getting out the calculator.

There are only three numbers that go into the heat rate calculation, so it should be simple, right?

But, when you look at those three numbers a little closer, several questions can come up.

First, the calculation:

Heat Rate = Fuel Flow * Fuel Heating Value / Power Output

A heat balance helps us to identify avoidable and unavoidable heat losses.

Boiler efficiency tests help us to find out the deviation of boiler efficiency from the best

efficiency and target problem area for corrective action. The combustion process in a boiler can

be described in the form of an energy flow diagram.

The performance parameters of a boiler, like efficiency and evaporation ratio, reduces with time

due to poor combustion, heat transfer surface fouling and poor operation and maintenance.

Even for a new boiler, reasons such as deteriorating fuel quality and water quality can result in

poor boiler performance.

We will now discuss heat balance and boiler efficiency, which are important in assessing the


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boiler performance:

A heat balance helps us to identify avoidable and unavoidable heat losses.

Boiler efficiency tests help us to find out the deviation of boiler efficiency from the best

efficiency and target problem area for corrective action.

The goal of a Cleaner Production and/or energy assessment must be to reduce the avoidable

losses, i.e. to improve energy efficiency. The following losses can be avoided or reduced:

Stack gas losses: Excess air (reduce to the necessary minimum which depends from burner

technology, operation, operation (i.e. control) and maintenance) and Stack gas temperature

(reduce by optimizing maintenance (cleaning), load; better burner and boiler technology).

Losses by unburnt fuel in stack and ash (optimize operation and maintenance; better

technology of burner).

Blow down losses (treat fresh feed water, recycle condensate)

Condensate losses (recover the largest possible amount of condensate)

Convection and radiation losses (reduced by better insulation of the boiler).

Boiler efficiency direct metnodThe parameters to be monitored for the calculation of boiler

efficiency through the direct method are: Quantity of steam generated per hour; the quantity of

fuel used per hour; the working pressure and superheat temperature if any; the temperature of

feed water; the type of fuel and gross calorific value, GVC, of the fuel.

hg=the enthalpy of saturated steam in kcal/kg of steam

hf= the enthalpy of feed water in kcal/kg of water

Bo iler efficiency ind irect metho d-------

The data that is required to calculate boiler efficiency according to the indirect method include:Ultimate analysis of fuel in terms of H2, O2, S, C, moisture content and ash content.

Percentage of oxygen or CO2 in the flue gas; flue gas temperature; ambient temperature and

humidity of air; as well as GCV of fuel. In case of solid fuels, the percentage combustible in ash

and GCV of ash.

Q. What are the engineering units on these values?


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In the US, Heat Rate is most often shown in Btu/kWh. Fuel Flow can be in a number of

different units, the most common being KPPH (thousands of pounds per hour), PPS (pounds

per second) or SCFM (standard cubic feet per minute). Fuel Heating Value might be provided

in Btu/SCF or Btu/lb. Power Output is nearly always in either kW or MW.

For places outside the US, Heat Rate is most often shown in kJ/kWh. Fuel Flow might bereported in m3/hr (standard cubic meters per hour) or kg/hr. Fuel Heating Value may be in

GJ/kg, or GJ/m3. Power Output is still in either kW or MW.

Q.Steam Turbine Exhaust Hood Temperature

A) High exhaust temperature is the result of followings

Excessive wear on impulse wheelIneicient tip sealing arrangementHigh inlet steam temperature.

B) The Heat Drop from the Steam, is very less due to very low load. Hence the temperature ofsteam flowing through the turbine is higher and hence the hood is having more temperature,

wich in turn depends upon the surface radiation level also.

C) There is no single value for a minimum acceptable exhaust temperature. Steam temperature,

pressure and flow rate are all very much related. So, even the manufacturer has to know the

rest of the parameters in you operating case/mode to tell you the acceptable exhaust

temperature. The more pressure drops from the inlet, the more temperature drop from the inlet.

The temperature should be above the saturation curve to avoid condensation; especially in the

turbine is design to runs against a back pressure.

Heat will then accumulate in the condenser at almost atmospheric condition or just to the limitsto avoid a trip on poor vacuum on the condenser. This already in most power plants is a

problem. After a unit trips the temperature will continue to increase in the machine and this will

show-up at the back-end of the machine.

Also some warm-up drains in our machine with super heated steam are redirected to the

condenser so this just compounds the back-end temperature problems.

Why steam turbine exhaust temperature rise during start up?The air passes through an adiabatic compression, when it's volume shrinks, it's temperature

rises.

During low steam flow condition, the velocity and density of the steam is greatly reduced. Thisproduces 2 effects:

First, windage losses increase. Windage is essentially friction which occurs when the turbineblades contact the near-stationary steam. The windage losses cause heating of the blades inthe last few stages of the turbine.


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Second, there is insufficient steam to absorb the heat from the blades. During higher flowconditions, the steam provides a cooling medium for the blades. That heat is carried by thesteam into the condenser. The lower density and lower mass flow rate of the steam results inless heat transfer capacity. The temperature in the exhaust hood rises as less heat is removedto the condenser and more stays in the hood area.

Q.How to Determine Calorific Value Fuel?

Calorific value is the amount of heat energy released by burning one kg of a fuel.For example if the calorific value of a particular quality coal is given as 4500 Kcals/kg, it impliesby burning 1kg of coal 4500 Kcalories of heat energy is released.The more the ash content in the coal the lesser is the calorific value.Fuels like bio gas, firewood,rice husk etc. will have different calorific values

Q.Turbine SOP

1. Ensure the oil Tank level is 90%2. Start Auxiliary cooling water pumps and ensure water flows through Oil coolers and

Generators3. Vent the oil Coolers and Generator water box4. Keep running oil cooler inlet and outlet valves in throttled condition5. Start the Auxiliary oil Pump and vent the Oil Cooler and Filters.6. Check the AOP and EOP auto start interlock.7. Ensure Standby AOP and EOP in Auto Mode..8. Start the Vapor extractor Fan ( Ensure the oil tank level is not high)9. Ensure the Overhead tank Overflow thro Flow Glass and High level Switch actuation.10. Ensure the oil temperature is >42Deg C11. Ensure the oil flow and pressure to all the bearings12. Start Barring Gear Motor Locally and check for normal running13. Open the main steam line warm-up and drain line.14. Start Condensate extraction pumps and keep in re-circulation mode.15. Ensure CEP discharge flows through Ejector and Gland Seal Condenser.16. Open the following steam Drains.Turbine Casing Drain orifice bypass and main valveTurbine Control valve Drain orifice bypass and main valveLP bleed before ON /OFF valve drain orifice bypass and main valveMP bleed before ON/OFF valve drain orifice bypass and main valveFront and rear gland leak off steam drainsDrains before and after PRDS valves17. Ensure the Auxiliary steam pressure from PRS as per manual for cold startup.18. Maintain the front gland steam pressure 0.02 to 0.1 Kg/cm2 by PCV or available system in

maral.

19. Maintain the rear gland steam temperature as 160180 Deg C or as per manual.20. Ensure the Vacuum release valve is fully closed21. Achieve the vacuum of >-0.750 kg/cm2 by Hogger Ejector.22. Open the main steam stop valve gradually23. Ensure the main steam ParametersMain steam Pressure at Turbine Inlet = >as per manual (maral)Main steam Temperature at Turbine Inlet = >as per manual24. Ensure the Lube oil temperature before TG startup >45 Deg C


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25. Check the Turbine Trip Logic Screen in DCS for any trip except Shutdown command fromGovernor Ensure the Following before Giving reset Command:

EOP ready and Kept in Auto ModeOverhead oil tank Overflow thro Flow glassOverhead oil tank Level highBoiler and Turbine Main steam stop valves fully opened.

26. Check the Emergency push button status Turbine Control Panel.27. Give reset command in DCS and ESV opens automatically .28. Give Start permissive and Run Command from Turbine Control Panel.29. Ensure the Turbine Startup is Accordance to the Start up Curves.30. During Speed up the Following parameters to be carefully monitored.

Barring Gear Dis engage.

Lube Oil Temperature (Must be between 4550 Deg C).

Vibrations

Bearing Temperatures.

Bearing inlet oil pressure.

Main steam parameters.

Exhaust steam Parameters. Lube oil System Operation

Abnormal noise.If any abnormality found in any of above, machine speed / runup should be holded or tripped.

31. At full Rpm switch off AOP and put in Auto Mode..32. The following drains shall be closed after reaching to the rated speedTurbine Casing Drain orifice bypass valve onlyTurbine Control valve Drain orifice bypass valve onlyWarm up line.

All drain main valve should be always in Open Condition.

42. If the TG set is running smoothly, excite the Generator and Synchronize with the grid andthereafter load the machine.43. Load the Turbine firstly to 2.0 MW or 10% and check all the parameters.44. Gradually increase the load from Governor according to the loading Curve.45. Loading of the TG set.Cold Start up Sync to Full Load = 104 minWarm Start up Sync to Full Load = 50 minHot Start up - Sync to Full Load = 20 min46. During normal run, you must log all the operating parameters every hour and significant

values in the logbook.

Procedure for Turbine Shutdown / During Turbine Trip:

Whenever turbine trips, immediately open the main steam warm up line and drain. Ensure AOP cut-in during Coasting down Period. Open all the Flash Tank Drains. Please establish the reason for tripping before restarting.


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For Long Shutdown period following Procedure to be followed:

Machine should be on Barring Gear till 72 Hours. CEP shall be kept running till the Turbine Exhaust temperature Reaches to > 40 Deg. Auxiliary cooling water Pumps and Fans shall be kept running till the DT of condenser inlet /

Outlet water comes to < 2 Deg C.

Procedure for charging Extraction Steam: Ensure Extraction line drain to flash tank is kept open condition Ensure LP extraction line to header valve is in fully open condition. Ensure Turbine load > 5 MW or as per maral turbine sop. Open all line drains upto LP header. Open the ON / OFF valve. Press F3 and enable extraction control. Ensure the set Pressure as per manual. After reaching extraction line temperature 200 Deg C close drain to flash tankonly orifice

bypass valve. Gradually increase the load if extraction demand increases.

Procedure for charging MP Bleed steam:

Ensure MP bleed line drain to flash tank is kept open condition Ensure MP extraction line to header valve is in fully open condition. Ensure Turbine load > as per maral turbine sop. . Open all line drains upto MP header. Maintain the Open the ON / OFF valve. After reaching extraction line temperature 200 Deg C close drain to flash tankonly orifice

bypass valve. Gradually increase the load if extraction demand increases.

MAINTAINED PARAMETERS AS PER MARAL TURBINE MANAUL

Q.C.V OF FUEL (COAL)

The calorific value or heat of combustion or heating value of a sample of fuel is defined as the

amount of heat evolved when a unit weight (or volume in the case of a sample of gaseous fuels)

of the fuel is completely burnt and the products of combustion cooled to a standard temperature

of 298 degree K.

It is usually expressed in Gross Calorific Value (GCV) or Higher Heating Value (HHV) and Net

Calorific Value (NCV) or Lower Calorific Value (LHV). The difference being the latent heat of

condensation of the water vapor produced during the combustion process. Gross calorific value

assumes all vapor produced during the combustion process is fully condensed. Net calorific

value assumes the water leaves with the combustion products without fully being condensed.


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Fuels should be compared based on the net calorific value. The calorific value of coal varies

considerably depending on the ash, moisture content and the type of coal while calorific value of

fuel oils are much more consistent.

Energy content of the Indian Coal is expressed in Useful Heating Value (UHV) basis. Indian

coal (non-coking) is classified by grades (A-G) defined on the basis of Useful Heat Value (UHV).UHV is an expression derived from ash and moisture contents for non-cocking coals as per the

Government of India notification. UHV is defined by the formula:

UHV kcal/kg = (8900-138[percentage of ash content +percentage of moisture content])

In the case of coal having moisture less than 2% and volatile content less than 19%, the UHV

shall be the value arrived as above, reduced by 150 kcal/kg for each 1% reduction in volatile

content below 19% fraction pro-rata. Both moisture and ash shall be determined after

equilibrating at 60% relative humidity and 40C temperature as per relevant clauses of the

Indian Standard Specification No. IS:1350-1959.

The quality of coal depends upon its rank and grade. The coal rank arranged in an ascending

order of carbon contents is Lignite sub-bituminous coal bituminous coal anthracite

Chemical composition of the coal is defined in terms of its proximate and ultimate (elemental)

analysis. The parameters of proximate analysis are moisture, volatile matter, ash, and fixed

carbon. Elemental or Ultimate analysis encompasses the quantitative determination of carbon,

hydrogen, nitrogen, sulfur, and oxygen. The calorific value Q, of coal is the heat liberated by its

complete combustion with oxygen. Q is a complex function of the elemental composition of the

coal. Gross Calorific value Q is mostly determined by experimental measurements. A close

estimate can be made with the Dulong formula:

Q = (144.4 %[C])+(610.2 %[H])-(65.9 %[O])+(0.39 %[O]2)

Q is given in kcal/kg or Btu/lb.

Values of the elements C,H, and O, are calculated on a dry ash-free coal basis. Empirical

Relationship of GCV, UHV, and NCV UHV:

Useful heat value = 8900 138(A+M)

GCV: Gross Calorific Value = (UHV + 3645 -75.4 M)/1.466NCV: Net Calorific Value = GCV

10.02M

UHV, GCV, NCV in kcal/kg, A is %age Ash; M is %age Moisture.

Q. AFBC SOP

Cold startup .pre-startup inspections

Pror to the start up, the following plant system and services should be available.


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Operating staff, clearance from maintenance group, electrical power , control power and

system, air compressor for instrumentation air, dm plant for dm water,feed water system

including feed water pumps, deaerator and control valve , cooling water system, chemical

dosing system, coal feeding, bed material feeding system, emission control system air and gas

side clearance, ect

Before going to startup following things are to be checked

Air and gas circuit

ID FANS

INLET DAMPERS (MOTORIZED) CLOSED

OUTLET DAMPER (MOTORIZED) OPENED

ID FAN INLET CONTROL DAMPER (PNEUMATIC) MINIMUM POSITION

FD FANS

INLET VANES ( PNEUMATIC) MINIMUM POSITION

FD O/L DAMPERS-CLOSED

AIR HEATER BYPASS DUCT ISOLATION DAMPER- OPENED

AIR HEATER INLET DUCT ISOLATION DAMPER-CLOSED

ALL THE BED COMPARTMENT ISOLATION DAMPERS- CLOSED

PA FANS

INLET VANES-CLOSED

PA O/L DAMPERS-CLOSED

PA AIR TO FUEL FEED LINE DAMPERSALL CLOSED

PA AIR TO INDIVIDUAL FUEL FEED LINE DAMPERSOPENED

ESP

FREE FROM MAN AND FOREIGN MATERIAL

ESP HOPPERS ARE FREE FROM FLY ASH

ENSURE THE EXP MAN HOLE DOORS ARE TIGHTLY CLOSED

CHIMNEY

IS FREE FROM MEN AND FOREIGN MATERIAL


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MAN HOLE DOOR IS CLOSED

FUEL HANDLING SYSTEM

CHECK AND ENSURE THE AVAILABILITY OF DRY FUEL OF RECOMMENDED SIZE IN THE

BUNKER,DRIVES AND CONTROL SYSTEM ARE READY FOR SERVICE, HORIZONTAL

AND VERTIEAL FUEL FEED LINES ARE CLEAR.

START UP BURNERS

BMS IS READY FOR SERVICE

COMBUSTOR

RECOMMENDED SIZE BED MATERIAL FILLING INTO THE COMBUSTOR

FUEL FEED LINE VERTICAL DRAINS ARE CLOSED PROPERLY

FILL THE COMPUSTOR WITH THE SPECIFIED DRY BED MATERIAL AS PER BEDMATERIAL FILLING PROCEDURE TO HE REQUIRED LEVEL IN ALL THE

COMPARTMENTS.

D.P TEST

Before going to bed material filling, we must know the cleanliness of bubble caps, the

fluidization depends on this aspect, hence for checking bubble caps cleanliness, we have

conduct DP test ( differential pressure test on the boiler)

Closed all PA line bottom gates, close all PA line individual dampers as well as compartment

main PA header dampers. Close all overfeed secondary air dampers.

Start ID fan first and boiler furnace draft nearly about -5mmwc

Then check for interlock release in FD fan individual display on ID fan path open. Before starting

FD fans ensure that, all individual compartment secondary air wind box dampers are in shut or

close position.

Start FD fan slowly increase the airflow by adjusting inlet guide vane opening, while doing this

furnace draft is to be maintained nearly about -5 mmwc

For a boiler having a total air requirement of 125 TPH for carrying out DP test required air flow

need to be maintained. For example boiler is having 5 compartments.

Normally, out of the total air requirement, about 30% of air will be pressurized PA fans and this

air is used to convey the coal through PA lines which means 70% of total air requirement will

pass through wind box.

Primary air quantity= 30% of total air ( 37.5 TPH)


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Air passing through wind box=(Total airprimary air) =87.5 TPH

INDIVIDUAL COMPARTMENT AIR REQ=87.5/5=17.5 TPH

So adjust the air flow near about 20 TPH and open first compartment damper (furnace draft -

5mmwc) and than take the first compartment wind box pressure reading. After noting down the

reading close the first compartment damper then open the second compartment wind box

damper and note down the wind box reading continued for all five compartment.

Then increase the airflow to 87.5 TPH and open all five compartment windbox dampers, note

down wind box pressure readings

After DP test we can ensure the cleanness of bubble caps.after that note down the wind box

pressure reading at 100 TPH air flow keeping all the compartment dampers in open condition.

The same quantity of air flow should be maintained through-out filling time and start filling of bed

material into furnace.

Record the wind box pressure readings intermittently so that outside itself we can judge the bed

height like fluidzation, for hudgeing the height, we have to subtract the initial wind box pressure

reading from present wind box pressure reading. This will give us the approximate bed height

inside the furnace.therfore,

Bed height= (present wind box pressure-initial wind box pressure

Check water and steam circuit drain valves , isolation valves etc..Fill the bed material to a height

of 300 mm in all compartments. Fluidize all the compartments together provided the fan motor

amperes area below the limits. If not possible, fluidize two compartments together for leveling.

Then the next compartment can be fluidized separately. The start up compartment is to be

fluidized separately. When this is done, a portion of the bed material spills to the adjacent

compartment and builds a mount along the edge of the compartment. Further bed material is to

be added to the start up compartment so that the bed height of 200 225 mm is maintained.

BOILER LIGHT UP

The lighting up of the boiler is to be done with the help of charcoal and kerosene. The start up is

to be done only for a single compartment. After stabilizing with a single compartment fire is

transferred to other compartments as per the procedure explained separately.PREPARATIONS

Inspect the boiler prior to starting and check the following.

All access doors are closed.

All personnel cleared.

All foreign materials are removed from furnace and pressure parts.


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Starting equipment and interlocks are in position.

Boiler is filled with DM water above the low level limit.

Check the following equipments for adequate lubrication and readiness for service.

Fans and drives.

Feed pumps and drives.

Fuel feeders and controllers.

Check dry fuel (0-6) mm is available in the bunker, the gates blow the bunker is open and fuel is

available at feeder inlet.

Check the instrument air is available at the required pressure of 7Kg/cm for instrumentation

and control.

Check the following valves in the boiler drum are closed.

Feed control valve and its bypass valve.

Blow down valve.

Main steam stop valve.

Drain valves of water level gauge.

Check the following valves are kept open.

Air vent on top of drum.

Water level gauge, pressure gauge and level transmitter / isolation valves.Valves before and after the feed control valve in the feed line.

Valves on the feed line connecting to the feed pumps in operation.

Check the bed material is filled in the furnace and fluidisation study is complete.

BOILER FILLING

Before starting the filling up, keep the vent on the drum open and close the blow down and drain

valves. The filling up is to be done by running the feed pumps but the rate of flow is controlled

by means of feed control valve. During the filling up check the operation of blow down valve and

drain valves and then close them. The boiler is filled up completely till water comes through the

drum vent and is drained to bring the water level at low level alarm limit.

FLUIDISATION STUDY

During the fluidisation studies, expect for large compartments the fuel transport air need not be

introduced, as it would disturb the bed.


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Observe the fluidisation of the start up compartment by varying the airflow gradually. Mark the

position of dampers when the bed material begins to fluidize. In the case of pneumatically

operated dampers, note the input signal PSI from the manual loaders.

The on set fluidisation may also be observed by plotting the bed pressure drop against the air

flow.

Set the air flow at 5 mm P.

Measure the Sporger Header pressure, P1 mmwc.

Add the gas plenum pressure P2 to P1 (P1+(P2)) is the pressure drop across the Sporger

Header and bed.

Subtract P3 mmwc, which is the pressure drop across Sporger Header, alone which is

measured in DP study. i.e., (P1+(P2))-P3 would be the pressure drop across the bed.

The pressure drop across the bed is thus obtained for various airflows. The readings may be

plotted in a graph as shown.

The airflow at which fluidisation starts is noted. This valve is to be maintained for the purpose of

mixing at the time of startup.

Once the fluidization study is completed, the fans shall be switched off and boiler shall be taken

for light up.

The boiler light up is done using charcoal and kerosene as explained below.

A fixed quantity of dry charcoal is spread uniformly over the start up compartment.

A fixed quantity of kerosene mixed charcoal is spread uniformly over the dry charcoal layer.

The fire is initiated using swab.

Further by proper air flow control, fire can be spread and the heat released by charcoal is

utilized to heat the bed material to a temperature above the ignition temperature of the fuel.

In the process of preheating bed material the required fluidisation velocity is maintained in the

bed by suitably opening the FD fan inlet damper.

Further, the fuel feed rate is adjusted to maintain a bed temperature of 800C to 850C.

The charcoal of size below 15 mm shall not be accounted for the above quantity.Keep the ID fan damper open at the time of lighting up. This would reduce the possibility of

furnaces puff.

Initiate the fire bushing number of swabs. Throw the swabs in such a way that the fire spreads

uniformly over the entire furnace. If the spreading of the fire is non-uniform sprinkle some

kerosene choked charcoal and throw it to the locations where fire is not there. Unless the fire is


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more or less present over the entire surface, it is advised not to proceed with the light up.

Unless the top layer or charcoal gets ignited, further charcoal would not get ignited.

BED TEMPERATURE AND AIR FLOW CONTROL

The thermocouples are located in such a way that they are well utilized for start up.

The top-level bed thermocouple is located at a height to read the temperature just at the burning

charcoal layer. The bottom level thermocouple is located to read the bed material temperature

at a height of 100 mm from nozzle level.

After the introduction of fire, top-level thermocouple temperature will go up. It is very important

to increase the airflow gradually in order to increase the top-level temperature to 800C. At first

the ID fan damper opening alone allows some leakage of air. Further opening of FD fan damper

will add some more air to increase the bed temperature. Now close ID fan and FD fan inlet

dampers. Start ID fan then FD fan. Open ID fan and FD fan inlet dampers step by step to

increase the top level temperature to 800C to 850C. Till this period the bottom level

thermocouple would not have shown increase in temperature. Once the top level temperature

reaches 800-850C, the burning top layer of charcoal shall be mixed with rest of the bed. The

mixing is done by increasing the airflow so as to fluidise the bed. The mixing airflow should not

be higher than that of the airflow established during the fluidisation study. For this purpose the

markings made on damper positions shall be used. If the mixing is done at other airflow, the

burning charcoal will spill into the adjacent compartment. More than a loss of charcoal in the

start up compartment, the bed height will reduce in start up compartment. This would lead to

defluidisation, as the air would tend to bypass at bed heights lower than 100 mm.

The duration of mixing shall be between 20-30 seconds. During the mixing process, the top-

level temperature would start reducing. At the same time, bottom level temperature would begin

to rise.

Soon after the mixing is completed the airflow is brought to a minimum. Open the man hole door

and visually ensure through mixing has been done. If top layer charcoal is not been disturbed at

some places, mixing shall be carried out once again.

After ensuring thorough mixing, the airflow shall be brought down to minimum and then shall be

increased in steps. The airflow shall be increased gradually so as to raise the bed temperature.

The airflow shall be brought up at MCR airflow in process of raising bed temperature above

600C.

Once the bed temperature shoots above 600C, the fuel transport lines are to be dechoked and

fuel flow shall be established.


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Switch on the PA fan.

Open the fuel transport air dampers of the start up compartment.

Check the suction at the mixing nozzle. If suction is not available, open the respective bottom

drain gates of fuel pipes to dechoke, if any. After the choking of fuel feed pipe is cleared close

the gates.

In the case of larger compartments it is advisable to initiate minimum airflow in fuel pipelines just

before mixing process to avoid choking of the fuel lines.

Adjust the PA fan suction damper, to maintain the header pressure in between 700 to 900

mmwc.

Initiate the fuel flow by switching on the fuel feeders. The fuel flow shall be kept minimum at the

beginning. At the time of fuel feed initiation, the charcoal might not be burnt fully. Hence it is

most important to initiate fuel feed gradually.

Excess fuel feed will increase the bed temperature uncontrollably. Though the bed temperature

can be controlled by increasing the airflow, it is advisable to take care at the time of fuel feed

initiation. Stabilize the start up compartment operation with a bed temperature of 850C and with

the MCR air flow.

On the waterside watch the drum level. If the level goes down switch on feed pump and regulate

the feed control valve. ON/OFF operation of feed pump should be avoided to the extent

possible. If the feed pump is auto operated, keep the selector switch in auto mode. Here again

regulate feed control valve to avoid frequent start/stop of pump.

Close the drum vents at 2kg/cm pressure if the boiler is provided with super heater. This is

done so that super heater coils are cooled better by more steam flow through them. Ensure the

vents, start up vents, drains are open in super heater lines. The condensate in super heater

coils and main steam pipe should have been removed earlier. In the case of non-drainable

sections of super heater coils it is possible that condensate leads to water hammer.

In case of power cut during start up after the mixing, it will not be possible to access how much

charcoal is burnt out. It is advised to cool thoroughly and drain the bed material in start up

compartment and do a fresh light up.

However, if the power cut had occurred before mixing one may attempt to light up as below.

Sprinkle kerosene soaked charcoal through manhole evenly over the start up compartment. The

charcoal quantity shall be the same as that for light up.

Throw swabs and light up.

Follow the same procedure as discussed in a regular light up.


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if the power cut occurs after mixing and provided the duration is also short, it may be possible to

light up.

Fluidize the bed minimally. Check the bed temperature. If the bed temperature is more than 400Cadd dry charcoal to the bed. The charcoal should be thrown uniformly over the entire bed. Observethe rise in temperature. If there is no improvement in bed temperature it is better to cool the bed

Never allow the bed to be static in this method. If the bed is static, clinker formation will start.

interview q and ans for tharmal power plant

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