We prepared an article on Power Plant Interview Questions & Answers which covers basics about power plant operation.
1. Name the four major circuits in steam power plant.
2. What consists of air and flue gas circuit?
Air and flue gas circuit consists of forced draught fan, air pre heater, boiler, furnace, super heater, economiser, dust collector, induced draught fan and chimney.
3. What consists of feed water and steam flow circuit in steam power?
The feed water and steam flow circuit consists of feed pump, economiser boiler drum super heater, turbine and condenser.
4. What consists of cooling water circuit and coal & ash circuit in steam power plant?
The cooling water circuit consists of a pump, condenser and cooling tower. The coal and ash circuit consists of coal delivery, preparation of coal, handling of coal to the boiler furnace, ash handling and ash storage.
5. What is the main purpose of the reservoir?
The main purpose of reservoir is to store water received from catchments areas during the rainy seasons and supply the same during the dry season.
6. What is the main purpose of the dam?
The main purpose of the dam is to increase the height of water level and also to increase the working head of the hydraulic power plant.
7. Why trash rack is used?
The trash rack is used to prevent the entry of debris, which might damage the turbine runners and chock up the nozzle of impulse turbine.
8. What is the use of surge tank?
The surge tank is used to provide better regulation of water pressure in the system. The surge tank controls the water when the load on the turbine decreases and supplies water when the load on the turbine increases. Thus, surge tank controls the pressure variations resulting from the rapid changes in water flow in penstock and hence prevents water hammer.
9. What is the function of Fore bay?
Fore bay is considered as naturally provided surge tank. It is temporary water storage when the load on the plant is reduced and provides water for initial increment on increasing load.
10. Explain about penstock?
The pipe between surge tank and prime mover is known as penstock. It is designed to withstand high pressure. It is made up of reinforced concrete. In very cold areas, the penstock is buried to prevent ice formation and to reduce the expansion joints.
11. What is the use of spill Ways?
Spillway is like a safety valve of the dam. It discharges major flood without damaging the dam. It keeps the reservoir level below the maximum level allowed.
12. Write about prime movers?
Prime mover converts the kinetic energy of water into mechanical energy to produce electrical energy. Pelton wheel, turbine, Francis turbine, Kaplan turbine and Propeller turbine are prime movers used in hydraulic power plants.
13. What are the uses of air filter and superchargers in diesel engine power plant?
The purpose of air filter is to filter the air from dust and other suspended particles. The purpose of super charger is to increase the pressure of the engine to increase power of the engine.
14. What is the use of draft tube?
The draft tube is used to regain the kinetic energy of water coming out of reaction turbine. It enables the reaction turbine to be placed over tailrace level.
15. What is the function of cooling system in Diesel power plant?
The function of cooling system is to remove heat from the engine cylinder to keep the temperature of the cylinder in low range and extend engine life.
16. What consists of lubrication system in diesel engine power plant?
The lubrication system consists of oil pumps, oil tanks, filters, coolers and connecting pipes. The purpose of the lubrication is to reduce the friction of moving parts and also pipes to reduce the wear and tear of moving parts.
17. What is the purpose of intercooler in gas turbine power plant?
Since the power required to compress the air is less in isothermal process it is required to maintain the, temperature of air constant as far as possible. Hence the air leaving the L.P. compressor is cooled by intercooler and then passed to the H.P compressor.
19. Define turbo charging in combined gas turbine and diesel cycles?
In the combined cycle, the exhaust gas from the diesel engine is expanded in the turbine, which is coupled with compressor which supplies pressurized air to the diesel engine. This increases diesel engine output. This arrangement is known as turbo charging.
20. What is the main purpose of high-pressure boilers?
The high-pressure boilers are used to increase the efficiency of the plant and to reduce the cost of electricity production.
22. Name important high pressure boilers?
23. Write about La Mont boiler? What is the major disadvantage of La Mont boiler?
La Mont boiler is a forced circulation high pressure water tube boiler.
The major disadvantage is the formation of bubbles, salt and sediment on the inner surfaces of the heating surfaces. This reduces the heat flow and steam generation.
24. Write about Benson boiler? State some important advantages of Benson boiler?
Benson boiler is the high pressure, vertical fire tube boiler. This boiler has no drum and is ~designed to operate at critical pressure of 225 bar. Benson boiler has no drum.
So the total weight of the Benson boiler is reduced by 20%, when compared to other boilers. The erection of Benson boiler is easier and quicker.
25. Write about Loeffler boiler?
The major disadvantage in La Mont boiler is the deposition of salt and sediment on the inner surface of the water tubes. It reduces the heat transfer and ultimately the steam generating capacity.
In Loeffler boiler, this problem is solved by preventing water from flowing through the boiler tubes. The steam is generated outside the tubes.
26. Explain Reheat cycle?
If the dryness fraction of steam leaving the turbine is less than 0.88, then, corrosion and erosion of turbine blades occur. To avoid this situation, reheat is used.
In the reheat cycle, the expansion of steam takes place in one (or) more turbines. Steam is expanded in the HP turbine first, and then it is reheated. The reheated steam is again expanded in. the LP turbine.
27. What are the important advantages of Re heating?
29. Define bleeding in steam power plant?
Assume I kg of steam is expanded in the turbine. Before complete amount of steam is expanded, some amount of steam (m kg) is extracted ‘ Extracting the steam in the turbine before exhaust is called bleeding. This bled steam is used to heat the feed water.
30. Explain the term Regeneration?
Regeneration means heating the feed water by steam taken from the turbine. The steam is exhausted (bled) from the turbine at several locations before exhaust and is supplied to regenerator (feed water heater) to heat the feed water.
31. State some advantages of Regeneration cycle?
33. Define the term waste heat recovery?
Waste heat is the heat which is not at all used and exhausted out as a waste product. Waste heat is normally available from the industry in the form of process steam and water at high temperature.
Also, the waste heat is discharged with the exhaust gases in so many industries. This heat can be recovered for useful purpose. This process is known as waste heat recovery.
35 Write about waste heat boilers?
The waste heat boilers use the waste heat in gases coming out of diesel engines and gas turbines at high temperature (or) use the waste as a fuel in the incineration.
Some boilers use the industrial dirty gases for power generation.
36. Write about fluidised bed boilers?
When the high velocity gas is passed through a packed bed of finely divided solid particles, the particles become suspended in the gas stream and the packed bed becomes a fluidised bed. When the gas velocity is very high, the fluidised bed become turbulent and rapid mixing of particles occurs. Ultimately, the, behaviour of mixture solid particles and gas become a fluid. Burning of a fuel in such a state is known as Fluidised Bed Combustion. The boiler plant using this fluidised bed combustion is known as fluidised bed boilers.
39. Write about out plant handling?
Out plant handling includes the handling of coalmine to the thermal power plant. These handlings are outside the plant in the following ways.
40. Write about inplant handling of coal?
In order to handle large quantity of coal inside the plant, some mechanical handling systems are provided f6r smooth, easy and better controlled operation. The inplant coal handling is divided, into following categories.
41. Why the preparation of coal is necessary?
The coal from coal nines cannot be directly fed into the furnace. Proper preparation of coal should be done before feeding the coal to the furnace. In the coal preparation, the coal passes through the different equipments like 1. Crushers 2. Sizers 3. Driers and Magnetic Separators.
42. Name the different types of coal transforming equipments?
The coal transfer starts by carrying of coal from unloading point to the storage site.
43. What is the use of belt conveyors?
Belt conveyors are mostly used for transporting coal over long distance with large quantity. An endless belt is made to run over a pair of end drums and pulleys and supported by series of roller at regular intervals.
44. Write about screw conveyor and bucket conveyors?
In screw conveyor, an endless helicoid screw is fitted to the 9haft. On one end of the shaft, the driving mechanism is fitted and the other end of the shaft is supported on a ball bearing. While the screw is rotating, the coal is transferred` from one end to the other end.
Bucket conveyors are used as vertical lifts. The coal is loaded at the bottom and unloaded at the top in the bucket conveyors.
45. Define draught, what is the use of draught in thermal power plants?
Draught is defined as a small pressure difference required between the fuel bed (furnace) and outside air to maintain constant flow of air and to discharge the gases through chimney to the atmosphere. Draught can be obtained by chimney, fan, steam jet (or) air jet (or) combination of these.
46. Write about classification of draught?
Draught is classified as
The artificial draught is further classified as
(a) Steam jet draught
(b) Mechanical draught
(c) Induced draught
(d) Forced draught
47. Define the term Natural draught and what are the advantages of natural draught system?
The tall chimney creates the natural draught by the temperature difference between hot gases in the chimney and cold atmospheric air outside the chimney.
The advantages are
48. Write about artificial draught?
In modem power plants, the draught should be flexible to meet the fluctuating loads and it should be independent of atmospheric conditions. To achieve this, the aid of draft fans becomes must and by employing the draft fans, the height of the chimney would be reduced.
49. Write about forced draught system?
In this system, the blower (forced draft fan) is located at the base of the boiler near the grate. Air is forced to the furnace by forced fan and the flue gases are forced to chimney through economiser and air preheater.
50. What are the advantages of forced draught system
51. How the induced draught is working?
In an induced draught system, a blower (induced draft fan) is placed near (or) at the base of the chimney. The fan sucks the flue gas from the furnace creating a partial vacuum inside the furnace. Thus atmospheric air is induced to flow through the furnace to aid the combustion of fuel. The flue gases drawn by the fan passes through chimney, to the atmosphere.
52. Why the balanced draught system is preferred than other system?
In the induced draught system, when the furnace is opened for firing, the cold air enters the furnace and dilate the combustion. In the forced draught system, when the furnace is opened for firing, the high pressure air will try to blow out suddenly and furnace may stop.
Hence the furnace cannot be opened for firing (q) inspection in both, systems. Balanced draught, which is a combination of induced and forced draught, is used to overcome the above stated difficulties.
53. What is the difference between stocker firing and pulverised fuel firing?
The stocker firing method is used for firing solid coal where as pulverised firing method is used for firing pulverised coal.
54. What are the different types of stockers?
1. Over feed stockers
55. What is the use of pulveriser and name different types of pulverising mills?
The pulveriser is used to pulverise the coal in order to increase the surface exposure. Pulverised coal enables rapid combustion.
The different types of pulverising mills are
1. Ball mill
2. Hammer mill
3. Ball and race mill.
60. Name different types of dust collectors?
2. Cyclone. Separators
3. Elector Static Precipitator (ESP)
61. What is the main purpose of chimney?
The main purpose of chimney is to emit the flue gases at a considerable height to avoid nuisance to the surrounding people.
62. What are the different types of load act on the chimney?
64. Define forced draft and induced draft cooling towers
If the fan is located at the bottom of the tower and air is blown by the fan up through the descending water it is called as forced draft cooling towers.
If the fan is located at the top of the tower and air enters through the louvers located on the tower’s side and drawn up and discharge through the fan casing, it is called as induced draft.
67. What are the factors that affect the rate of evaporation of water in cooling towers?
68. What is the working principle of Cooling Towers?
The hot water is sprayed from the top of the tower, while the air is made to flow from the bottom of the tower to the top. This air cools the hot water in the cooling tower. Air vaporises a small percentage of water, there by cooling the remaining water.
The air absorbs the heat and leaves at the top of the tower and cooled water leaves at the bottom and recirculated to the condenser.
69. Name different types of cooling towers?
The cooling towers are classified as follows.
(a) According to the construction of material
1. Timber for small tower
2. Ferro concrete for large capacity stations.
3. Multi deck concrete towers for large steam stations
4. Metallic
(b) According to the nature of air draught
1. Atmospheric (or) Natural draught cooling system
2. Mechanical draught cooling tower.
70. How the atmospheric (or) natural draught cooling towers are classified?
In atmospheric (or) natural cooling towers, the natural air provides the required cooling without the use of fans.
71. How mechanical draft cooling towers are classified?
Mechanical draft cooling tower is classified into three types
72. How the dry type cooling towers are classified?
The dry type cooling towers are classified into two types ‘as follows.
73. What are the methods to reduce the effects of particulates?
74. What are the equipments used for ash collection?
75. What is meant by ‘Desulphurisation’ and name the methods adopted for desulphurisation?
77. Write about C02 recorders?
In thermal power plants, it is necessary to keep the concentration Of C02 as low is necessary as possible. To achieve this, a constant recording of concentration Of C02
79. What is the purpose of automatic, combustion c61ritrol?
The main purpose of automatic combustion’ control system is to maintain load against demand, to prevent smoke, to increase boiler house efficiency, to carry out routine adjustments and to provide interlocking safe guards.
80. What are the appliances known as boiler accessories?
The appliances used to increase the efficiency of the boiler are known as boiler accessories.
82. Write about C02 recorders?
In thermal power plants, it is necessary, to keep the concentration of C02 as low as possible.
To achieve this ‘ a constant recording of concentration of C02 is necessary.
83. What is the necessity of Automatic controls for feed water?
The electrical load on power plant varies irregular manner. The automatic man control provided at a steam power plant successfully meets over the variable load. The automatic control for feed water is necessary sine the supply of feedwater depends upon plant load.
84. Name some of the automatic controlling methods for feed water?
85. What is the purpose of automatic combustion control?
The main purpose automatic combustion control system is to maintain load adjust demand, to prevent smoke, to increase boiler house efficiency, to carry out routine adjustments and to provide interlocking safe guards.
86 What is the use of air preheater?
Air pre heater is used to transfer heat from the flue gases to the air before it passes into the furnace for combustion. It is placed between the economizer and chimney. The overall efficiency of the plant may be increased by 10 per cent by the use of air preheater.
87. Write about boiler mountings?
The devices used for the efficient operation, proper maintenance, and safe operation boiler mountings.
88. What is meant by boiler trial?
Steam is generated in boilers under certain conditions of feed water and exists as steam while a certain amount of fuel is burnt.
To study the performance of boiler, some experiments are conducted by operating, the boiler for a certain length of time and recording the data. This procedure is known as boiler trial.
91. Define load curve?
Load curve is a graphical representation between load in kW and time in hours. It. shows variati6n of load at the power station. The area under the load curve represents the energy generated in a particular period.
92. Define load factor?
Load factor is defined as the ratio of average load to the peak load (or) maximum demand.
93. What includes fixed cost?
94. What includes operating cost?
Operating cost includes the following cost.
95. What is the need of depreciation cost?
Depreciation cost is the amount to be set aside per year from the income of the plant to meet the depreciation caused by the age of service, wear and tear of the machinery and equipments. Depreciation amount collected every year helps in replacing and repairing the equipment.
96. Write about atomic number?
The nucleus contains protons and neutrons. The number of protons in a given atom is an atomic number (Z). The atomic number for H is 1 and He is 2.
97. Write about isotopes of an element?
Some elements have the same number of protons in the nucleus but different number of neutrons. As a result, these elements have the same atomic number but different mass number. Such type of elements which ‘ have the same atomic number – same number of protons the same chemical properties but different mass numbers due to different number of neutrons, are known as I the isotopes of an element.
99. Define multiplication factor of a fission process.
k =number of neutrons of any one generation/number of neutrons of immediately preceding generation.
100. Define fertile materials and breeding in reactors
There are materials like U235 and Th232 which are not fissile but can be converted into fissile materials by the bombardment of neutrons. Such materials are known as fertile materials.
The process of converting more fertile material into fissile material in a reaction is known as breeding.
103. Name few types of reactors.
Fast reactors, Thermal reactors, natural fuel reactors, Enriched Uranium reactors, water moderated reactors, heavy water moderated reactor, graphite moderated reactor, gas cooled reactors and Sodium cooled reactors.
107. What are the advantages of Sodium in fast-breeder reactors?
109. What is the working principle of magneto hydrodynamic power plant?
The working principle of MHD is as like that of dynamo. Instead of solid conductor high temperature plasma is passed through the magnetic field at sonic speed. When the gas is passed through magnetic field, current is induced. Electrodes collect this induced current.
110. What is the purpose of control rods?
The control rods are used to start the chain reaction, maintain the chain reaction at required level and to shut down the reactor during emergency.
112. What is meant by Nuclear fission?
Uranium exists in different isotopes of U238, tP34 and U235. Out of these, EP35 is most unstable.
When unstable heavy nucleus is bombarded with high-energy neutrons, it splits up roughly into two equal fragments and about 2.5 neutrons are released and a large amount of energy is produced. This process is called nuclear fission.
113. Name the different components of nuclear reactor?
1. Nuclear fuel 2. Moderator 3. Control rods 4. Reflectors
5. Reactor vessel 6. Biological shielding 7. Coolant
Also Read : Self-Actuated Valves
116. What is breeding in nuclear reactor?
The process of producing fissionable material from a fertile material such as uranium 238 (U238) and thorium 232 (Th 232 ) by neutron absorption is known as breeding.
118. What is the necessity of Automatic controls for feed water?
The electrical load on power plant varies in an irregular manner. The automatic control provided at a steam power plant successfully meets over the variable load. The automatic control for feed water is necessary sine the supply of feed water depends upon plant load.
