Working

Q 1a) What is Mill

Mill is a system which is used to pulverize the coal in to the fine particles (as per required size).

Mill duty is to:

Grind coal

Evaporate moisture

Classify coal into fine particles

Discharge acceptable fine powder pneumatically

b) Describe its importance in thermal power plant. (Purpose/role)

The economic motives for the introduction of mills are:

i) Efficient utilization of cheaper low grade coals.ii) Flexibility in firing with ability to meet fluctuating loads.iii) Elimination of banking losses.iv) Better reaction to automatic control.v) Ability to use high combustion air temperature; increasing the overall efficiency of boiler.vi) High availability

c) What type of problem may occur in its absence?

If it’s not there then coal will not be pulverized and not be burnt properly in the furnace. So in all it will reduce the efficiency of the plant and will lead to increase operating cost of plant as that unburnt coal is to be sent again to the furnace.

d) What are the two most popular type of it?

Bowl Mill

The bowl mill is one of the most advanced designs of coal pulveriser presentlyManufactured. The advantages of this mill are:a) Lower power consumption.b) Reliability.c) Minimum maintenance.d) Wide capacity.

Ball and tube mills

Forged balls, varying in size from 25 to 100 mm in diameter, are the grinding medium inside the cylindrical casing protected by bolted manganese steel liners, which last several years. About a quarter of the drum volume is filled with the balls. Grinding takes place by a combination of impact and attrition.

Types of pulverisers Speed

Low 10 to 20 rpm

Medium 40 to 70 rpm

High 900 to 1000 rpm

Type Ball tube mills Bowl MillBall & race Mill

Hammer mill, beater mill or fan mill

Dominating Principal Attrition Crushing Impact

e) Why these are popular give reason.

Advantages of ball and tube mills.

Easy maintenance. Only periodic ball charge is necessary. Cast liners last for years. (But they need long downtime for replacement.) The maintenance cost over time is about the same as for vertical mills. Constant capacity and fineness. No effect of foreign material. Large reserve capacity and hence quick response. Usefulness for hard and abrasive fuels.

Advantages of bowl mills:-

As the balls wear out, a filler ball is inserted to prolong the running. The fineness of the product increases with time. Only a part of mill is moving. The force exerted by springs can be adjusted by the screws. Milling performance is very high. The coal supply to the burners is regulated automatically by the combustion control. Low power is required.

f) What is the operational procedure of it.

Ball-Tube MillsThis type of mill consists of a rotating tube filled with cast alloy balls. Coal is introduced through two hollow trunnions on each side of the tube. As the tube rotates, the balls tumble onto the coal, crushing and pulverizing it.

Impact MillsGrinding Action is carried out by a series of hinged or fixed hammers revolving in an enclosed chamber with wear resistant plates. The hammers impact on the coal, crushing it against the plates. Further pulverization isachieved as the smaller coal particles are ground through attrition against each other and the grinding face.

g) During operation which type of problem may occur?

WEAR:-Wear is the main concern in mills. Wear is a progressive loss of material due to abrasion (Sand papering effect parallel to the surface) or erosion (due to particle impingement at an angle).

MILL FIRES: - Precautions should be included at the design stage. Two types of fires can occur in two different areas of the mill.

1. In the air-inlet chamber, which has the highest air temperature, if the coal dust finds its way to the chamber because of low throat velocity or accumulation soon after a mill trip, fi re may occur suddenly.

2. In the cooler part of the mill, which has a high concentration of fuel, a fire can slowly simmer over a long time and under favorable conditions, pick up momentum and destroy a mill.

Q 2a) What is BFP

A boiler feed pump is a specific type of pump used to pump feed water into a steam boiler. The water may be freshly supplied or returning condensate produced as a result of the condensation of the steam produced by the boiler. It is the device which consumes maximum auxiliary power consumption in plant. so now a days motor driven BFP’s are replaced by turbine driven bfp’s. BFP’S are multistage centrifugal type pump for continuous flow and high pressure output.


The main purpose of the BFP is to pump feed water to the boiler drum To give the required pressure to the Feed water before entering into boiler


In the absence of BFP there is no water supply to the boiler drum. So starvation occurs which ultimately leads to failure of tubes in boiler.

d) What is the operational procedure of it?

Start auxiliary oil pump. Close discharge valve and by pass of discharge valve. Open the recirculation valve. Scoop control to its minimum position and to shift controller to manual mode Start motor and open circulating valve. Open by pass valve to discharge valve. Open discharge valve. Close by pass valve to discharge valve. Shift scoop control to auto mode.

e) During operation which type of problem may occur.

Vibrational problems may occur during part load condition. Uneven expansion due to thermal stress Damage of impeller blade due to cavitation. Leakage of water due to high pressure difference.

Q 3a) What is ID Fan

1. Air or flue gases are maintained above atmospheric pressure; normally it is done with the help

of a forced draft fan.2. Draft is obtained by forcing air into the furnace by means of FD fan. Air is often passed through

an air heater, heats the air going into the furnace in order to increase the overall efficiency of the boiler.

3. Dampers are used to control the quantity of air admitted to the furnace. Forced draft furnaces usually have a positive pressure.

4. Keep the positive pressure in the stack. 5. Intake fans are forced draft fans that increase the pressure inside a boiler's combustion

chamber. 6. Increased combustion chamber pressure allows the fuel inside the boiler to burn more

efficiently and reduces the waste associated with incomplete combustion


1. For the proper and the optimized heat transfer from the flue gases to the boiler tubes draft

holds a relatively high amount of significance. 2. The combustion rate of the flue gases and the amount of heat transfer to the boiler are both

dependent on the movement and motion of the flue gases. 3. A boiler equipped with a combustion chamber which has a strong current of air (draft) through

the fuel bed will increase the rate of combustion (which is the efficient utilization of fuel with minimum waste of unused fuel).

4. The stronger movement will also increase the heat transfer rate from the flue gases to the boiler (which improves efficiency and circulation)


1. The FD Fan supplies combustion and in the absence of it the adequate air – fuel mixing is not possible.

2. In the absence of FD fan there may be a chance of the coming in contact with the nozzle. 3. The furnace cannot operate at under pressure and flue gases cannot be exhausted from the

chimney. 4. There may be a chance of water tubes getting melted in the boiler.

d) What is the operational procedure of it?

1. Ensure all debris tools, rags, etc. are removed from the fan and driver area. 2. Give fan and driver a visual check; look for loose nuts, plates or bolts disconnected rods etc. 3. Ensure that the fan inlet screen is clean and clear of frost, rags or debris. 4. Checks the damper and damper drive connection for tightness 5. Check the oil in the fan and driver bearing. If the level is low, fill it to the correct level with

recommended oil. 6. Open cooling water to the water –cooled bearings. 7. Generally look for any condition which might impair the proper operation of the unit. 8. If the driver unit is the steam turbine open drains and slightly open the steam supply and

exhaust valve to warm up the unit 9. Start fan, listen the unusual noises, fill bearing and fan casing for excessive vibration, check

bearing lubrication check for fan leaks especially around seals.


1. Leakage of oil, water & air. 2. Unusual noises. 3. Unusual smells, such as those caused by hot bearings, leakage of gases motor shorts , etc. 4. High temp and vibration in bearings. 5. Improper blade pitching may leads to high current. 6. Improper damper control may lead to high current. 7. Pollutants at the inlet may chock the screen of the FD fan. 8. Dirt collecting on the blades of an intake fan reduces the amount of air the fan can feed into the

boiler combustion chamber.

Q 4a) What is FD Fan

A fan called forced draught fan is installed at the inlet of the boiler. This fan forces the atmospheric air through the boiler furnace and pushes out the hot gases from the furnace through super heaters, re heaters, economizers, air heaters etc. to the stack.


1. For the proper and the optimized heat transfer from the flue gases to the boiler tubes draft holds a relatively high amount of significance.

2. The combustion rate of the flue gases and the amount of heat transfer to the boiler are both dependent on the movement and motion of the flue gases.

3. A boiler equipped with a combustion chamber which has a strong current of air (draft) through the fuel bed will increase the rate of combustion ( which is the efficient utilization of fuel with minimum waste of unused fuel).

4. The stronger movement will also increase the heat transfer rate from the flue gases to the boiler (which improves efficiency and circulation)

c) What type of problem may occur in its absence.

1. The FD Fan supplies combustion and in the absence of it the adequate air – fuel mixing is not possible.

2. In the absence of FD fan there may be a chance of the coming in contact with the nozzle.3. The furnace cannot operate at under pressure and flue gases cannot be exhausted from the

chimney.4. There may be a chance of water tubes getting melted in the boiler.

d) What is the operational procedure of it.

1. Ensure all debris tools , rags, etc. are removed from the fan and driver area.2. Give fan and driver a visual check; look for loose nuts, plates or bolts disconnected rods etc.3. Ensure that the fan inlet screen is clean and clear of frost, rags or debris.4. Checks the damper and damper drive connection for tightness5. Check the oil in the fan and driver bearing. If the level is low, fill it to the correct level with

recommended oil.6. Open cooling water to the water –cooled bearings.7. Generally look for any condition which might impair the proper operation of the unit.8. If the driver unit is the steam turbine open drains and slightly open the steam supply and

exhaust valve to warm up the unit

9. Start fan, listen the unusual noises, fill bearing and fan casing for excessive vibration, check bearing lubrication check for fan leaks specially around seals.


1. Leakage of oil, water & air. 2. Unusual noises.3. Unusual smells, such as those caused by hot bearings, leakage of gases motor shorts , etc.4. High temp and vibration in bearings.5. Improper blade pitching may leads to high current.6. Improper damper control may lead to high current.7. Pollutants at the inlet may chock the screen of the FD fan.8. Dirt collecting on the blades of an intake fan reduces the amount of air the fan can feed into

the boiler combustion chamber.

Q 5a) What is PA Fan

Supply high pressure primary air through APH needed to dry & transport coal directly from the coal mills to the furnace.Ambient air is drawn into the primary air ducting by two 50% duty, motor driven axial reaction fans. Air discharging from each fan is divided into two parts, one passes first through a air pre-heater then through a gate into the P.A bus duct. The second goes to the cold air duct. The mix of both is used to carry the pulverized coal to the boiler


It is very important because it performs following vital functions:

1. Supply air for combustion in the furnace and for evacuation of the flue gases formed from the combustion.2. Maintain Balanced Draft inside the furnace.3. Supply air for cooling of equipments which are working in hot zones.4. Supply air for sealing of gates, feeders & mills bearings etc.


PA fan is very important in a power plant as it has a very vital role to play which is to carry coal from mills to the furnace. It also dries up the coal. If its not there then coal cannot be transported to the furnace. Also it wont be dried up which will reduce the efficiency of the system. It also extracts a part of heat energy from the exiting flue gases failing which the flue gas exit temperature will rise, which will further reduce the efficiency.


CHECK that all PA fans start permissive is satisfied. PA fan bearing temp NOT HIGH (<60oC.). PA lub oil pressure is ADEQUATE. PA fan inlet guide vanes are at MINIMUM position. PA fan FSSS start command is AVAILABLE (BOILER MFR: RESET & all mill cold air dampers are less

than 5% OPEN). PA fan discharge damper is CLOSED

START PERMISSIVES

Blade pitch/IGV minimum Lube oil pressure adequate Bearing temp. not high Discharge damper closed. Lube oil tank level adequate No MFT & Cold air damper closed At least one FD fan is running and PAPH A/B in service & respective air inlet/ outlet dampers are open CHECK that PA fan is locally line up for starting. PA fan lub oil coolers are CHARGED from waterside. PA Fan LOP : ON and other pump is on AUTO PA fan lub oil tank level is ADEQUATE. PA fans EPBS are in RELEASED position. PA fan guide vanes are on REMOTE. Instrument air pre. is AVAILABLE. PA fan discharge damper is OPERATIONAL and power supply is AVAILABLE. CHECK. if air system is lined up before starting PA fan. APHs primary air isolation dampers are OPEN. Seal air fans are LINEDUP and their suction dampers are OPEN. Mills' cold air dampers on REMOTE. Instrument air pre. is AVAILABLE. Furnace purging is COMPLETED and MFTRs are in RESET condition.


1. Leakage of oil, water & air. 2. Unusual noises.3. Unusual smells, such as those caused by hot bearings, leakage of gases motor shorts , etc.4. High temp and vibration in bearings.5. Improper blade pitching may leads to high current.6. Improper damper control may lead to high current.7. Pollutants at the inlet may chock the screen of the FD fan.

8. Dirt collecting on the blades of an intake fan reduces the amount of air the fan can feed into the boiler combustion chamber.

Q 6a) What is CEP

A condensate pump is a specific type of pump used to pump the condensate (water) produced in an HVAC (heating or cooling), refrigeration, condensing boiler furnace or steam system. They may be used to pump the condensate produced from latent water vapour in any of the following gas mixtures:

Conditioned (cooled or heated) building air Refrigerated air in cooling and freezing systems Steam in heat exchangers and radiators The exhaust stream of very-high-efficiency furnaces


Condensate recovery systems helps to reduce three tangible costs of producing steam:

Fuel/energy costs Boiler water make-up and sewage treatment Boiler water chemical treatment


If its not there then our condensate cannot be transported in further & our system will fail as our power generation system has close cycle. Also it is required for sealing of glands of valves, temperature control of LP Bypass system for other important purposes.


Before starting Condensate Extraction Pumps (CEPS), ensure that the following permits are met:-

Condensate water system lineuped.Condenser Level > NPSHR.CEP inlet valve OPEN.CEP Motor Bearing Temperature.CEP Motor Winding Temperature.

http://en.wikipedia.org/wiki/Furnaces

http://en.wikipedia.org/wiki/Steam

http://en.wikipedia.org/wiki/Water_vapor

http://en.wikipedia.org/wiki/Steam

http://en.wikipedia.org/wiki/Condensing_boiler

http://en.wikipedia.org/wiki/Refrigeration

http://en.wikipedia.org/wiki/HVAC

http://en.wikipedia.org/wiki/Water

http://en.wikipedia.org/wiki/Condensation

http://en.wikipedia.org/wiki/Pump

OPEN CEP A Suction Valve. Ensure CEPs Discharge Valves are CLOSED. Place Recirculation Control Valve in MANUAL and fully OPEN.START Condensate Extraction Pump (CEP) and establish recirculation flow through the GSC back to the Condenser.Place CEP B on STANDBY.

Operation: - Ensure that the Suction and Discharge Valves of the Condensate Delivery Pumps (DPs) are OPEN.Ensure Electrical Supply is available to the Condensate Delivery Pumps.Fill the Condenser Hot well Level to 60% using Condenser Water Filling motor operated valve (MOV).Maintain the Hot Well Level using Condenser Water pneumatic control valve (PCV) and Condenser Water Storage pneumatic control valve tank in manual.After maintaining level at normal level, place the Control Valves in AUTO and set suitable Set point of control valve.Ensure the Condensate Flow path for all the Low Pressure (LP) Heaters and Gland Steam Condenser (GSC) is through. If not, OPEN the GSC inlet & Outlet Valves, LP Heater (in condenser) & inlet & Outlet Valves).



Q 7a) What is CW Pump

A circulator pump is a specific type of pump used to circulate gases, liquids, or slurries in a closed circuit. They are commonly found circulating water in a hydronic heating or cooling system. Because they only circulate liquid within a closed circuit, they only need to overcome the friction of a piping system (as opposed to lifting a fluid from a point of lower potential energy to a point of higher potential energy).


Cooling water pump is very much required to circulate water within the system. It brings the hot water from the condenser to cooling towers and cold water from cooling towers to condenser.

http://en.wikipedia.org/wiki/Hydronics

http://en.wikipedia.org/wiki/Water

http://en.wikipedia.org/wiki/Slurry

http://en.wikipedia.org/wiki/Liquid

http://en.wikipedia.org/wiki/Pump


In its absence the water cannot be recirculated and reused in the system. If we do not incorporate it in the system then efficiency of our system will reduce drastically.


1. The plant Distributed Control System (DCS) monitors and controls the circulating water pumps, the pump discharge valves, and the cooling tower fans so these components can be operated from the main control room operating stations. To ensure safe remote operation of the system, pump discharge valve controls include electronic "permissive" interlocks to ensure the valve is shut before the associated pump can be started.

2. Other pump-start permissive interlocks require that the main condenser water boxes must be full of water, there must be a minimal water level in the cooling tower water basin, and there must be minimal cooling water flow to the pump bearings.

3. The circulating water chemical feed systems inject five chemicals at various points in the system flow cycle.

4. Operators shall regularly monitor the conditions and parameters listed below in order to anticipate, recognize, and respond to any associated alarm or automatic "trip".

e) During operation which type of problem may occur?


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