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important Questions and Answers: Coal Based Thermal Power Plants

Mechanical and Electrical - Power Plant Engineering - Coal Based Thermal Power Plants



1. What are the types of power plants?


1. Thermal Power Plant

2. Diesel Power Plant

3. Nuclear Power Plant

4. Hydel Power Plant

5. Steam Power Plant

6. Gas Power Plant


7. Wind Power Plant

8. Geo Thermal

9. Bio –Gas

10.            M.H.D. Power Plant


2. What are the flow circuits of a thermal Power Plant?


1. Coal and ash circuits.

2. Air and Gas

3. Feed water and steam

4. Cooling and water circuits


3. List the different types of components (or) systems used in steam (or) thermal power plant?


1. Coal handling system.

2. Ash handling system.

3. Boiler

4. Prime mover

5. Draught system.

a. Induced Draught

b. Forced Draught


4. What are the merits of thermal power plants?


Merits (Advantages) of Thermal Power Plant:






1. The unit capacity of thermal power plant is more. The cost of unit decreases with the increase in unit capacity


Life of the plant is more (25-30 years) as compared to diesel plant (2-5 years)

3. Repair and maintenance cost is low when compared with diesel plant

4. Initial cost of the plant is less than nuclear plants

5. Suitable for varying load conditions.


5. What are the Demerits of thermal power plants?


Demerits of thermal Power Plants:


1. Thermal plant are less efficient than diesel plants

2. Starting up the plant and brining into service takes more time

3. Cooling water required is more

4. Space required is more.


6. What are the various steps involved in coal handling system?


1.     coal delivery

2.     Unloading,

3.     Preparation

4.     Transfer

5.     Outdoor storage

6.     Covered storage

7.     In-Plant handling

8.     Weighing and measuring

9.     Feeding the coal into furnace


7. After coal preparation, How the coal transfer?


1.     Belt conveyors

2.     Screw conveyors

3.     Bucket elevation

4.     Grab bucket elevators

5.     Skip hoists

6.     Flight conveyor.


8. Write the advantages of belt conveyor?


1.     Its operation is smooth and clean,

2.     It requires less power as compared to other types of systems.

3.     Large quantities of coal can be discharged quickly and continuously,

4.     Material can be transported on moderate inclines.



9. What are the systems used for pulverized coal firing?

1.     Unit system or Direct system

2.     Bin or Central system


10.            Write the classification of Mechanical Stokers?


1.     Travelling grate stoker

2.     Chain grate stoker

3.     Spreader stoker

4.     Vibrating grate Stoker

5.     Underfeed stoker.


11.            What are the three major factor consider for ash disposal system?


1.     Plant site

2.     Fuel source

3.     Environmental regulation


12.            Write the classification of Ash handling system?


1.     Hydraulic system,

2.     Pneumatic system

3.     Mechanical system


13.            What are the Ash discharge equipments?


1.     Rail road cars

2.     Motors truck

3.     Barge


14.            Define Draught.



Draught is defined as the difference between absolute gas pressure at any point in a gas flow passage and the ambient (same elevation) atmospheric pressure.


15. What are the purpose of Draught.



(i) To supply required amount of air to the furnace for the combustion of fuel. The amount of fuel can be burnt per square foot of grate depends upon the quantity of air circulated through fuel bed.


(ii)To remove the gaseous products of combustion.



16. Write the classification of Draught?


The following flow chart gives the classification of draughts

17. Define artificial draught?


If the draught is produced by steam jet or fan it is known as artificial draught.


18. Define Induced draught?


The flue is drawn (sucked) through the system by a fan or steam jet.


19. Define Forced draught?


The air is forced into the system by a blower or steam jet.


20.            Write the merits of Natural Draught?


1.     No external power is required for creating the draught

2.     Air pollution is prevented since the flue gases are discharged at a higher level

3.     Maintenance cost is practically nil since there are no mechanical parts

4.     Its has longer life,

5.     Capital cost is less than that of an artificial draught.


21.            Write the De-merits of Natural Draught?


1.   Maximum pressure available for producing draught by the chimney is less,


2.   Flue gases have to be discharged at higher temperature since draught increases with the increase in temperature of flue gases.


3.    Heat cannot be extracted from the fluid gases for economizer, superheater, air pre-heater, etc. Since the effective draught will be reduced if the temperature of the flue gases is decreased.



22.            Write the merits of steam Jet draught?


1.     This system is very simple and cheap in cost,

2.     Low grade fuel can be used

3.     Space required is less


23.            Write the De-merits at steam jet draught?


1. It can be operated only when the steam is raised

2. The draught produced is very low


24.            Define Condenser?


A condenser is a device in which the steam is condensed by cooling it with water. The condensed steam is known as condensate.


25.            Write the essential elements of a steam condensing plant?


1.     A closed vessel in which the steam is condensed.

2.     A pump to deliver condensed steam to the hot well from the condenser.

3.     A dry air-pump to remove air and other non-condensable gases,

4.     A feed pump to deliver water to the boiler from hot well.


26.            What are the sub division of jet condensers?


1.     Low level counter flow jet condenser

2.     High level (or) Barometric jet condenser

3.     Ejector condenser.


27.            Write the surface condenser?


1.     Down flow condenser

2.     Central flow condenser

3.     Evaporative condenser


28.            Write the advantages of surface condenser?


1.     The condensate can be used as boiler feed water


2.     Cooling water of even poor quality can be used because the cooling water does not come in direct contact with steam


3.     High vacuum (about 73.5 cm of Hg) can be obtained in the surface condenser. This increases the thermal efficiency of the plant.

29.                        Write the disadvantages of surface condenser?


                     The capital cost is more,

                     The maintenance cost and running cost of this condenser is high,

                     It is bulky and requires more space.


30.Name any two heat saving devices used in a thermal power plant?


                     Air pre heater


8. Differentiate propeller and Kaplan turbine?



In the propeller turbine the runner blades are fixed and non-adjustable. In Kaplan turbine, which is a modification of propeller turbine the runner blades are adjustable and can be rotated about the pivots fixed to the boss of the runner.


9. What are the Element of Hydel Power Plant?


Elements of Hydel Power Plant:


1.     Water reservoir,

2.     Dam,

3.     Spillway,

4.     Pressure tunnel,

5.     Penstock,

6.     Surge tank,

7.     Water turbine,

8.     Draft tube,

9.     Tail race,

10.                        Step-up transformer,

11.                        Power house.


10.            Write the Advantages of Hydro-electric power plants?



1.     Water is a renewable source of energy. Water which is the operating fluid, is neither consumed nor converted into something else,


2.     Water is the cheapest source of energy because it exists as a free gift of nature. The fuels needed for the thermal, diesel and nuclear plants are exhaustible and expensive.


3.     There is no ash disposal problem as in the case of thermal power plant.


11.            Write the classification of Hydro turbines?


Hydraulic turbines are classified as follows:


1) According to the head and quantity of water available,

2) According to the name of the originator,

3) According to the action of water on the moving blades,

4) According to the direction of flow of water in the runner,

5) According to the disposition of the turbine shaft,

6) According to the specific speed N.



12. Define Governing Mechanism?



When the load on the turbine changes, the speed may also change. (i.e., without load the speed increases and with over load, the speed decreases). Hence, the speed of the runner must be maintained constant to have a constant speed of generator. This is done by controlling the quantity of water flowing on the runner according to the load variations. This speed regulation is known as governing and it is usually done automatically by a governor.


13.            What are the functions of draft tubes?


1)    Increase in efficiency,

2)    Negative head.


14.            Write the two types of Draft tubes?


The draft tubes are of the following three types:

1) Conical or divergent draft tube,

2) Elbow type draft tube,

3) Hydracone or Moody spreading draft tube.


15. Define Kaplan turbine?



The Kaplan turbine is an axial flow reaction turbine. It is suitable for relatively low heads. Hence, it requires a large quantity of water to develop high power. It operates in an entirely closed conduct from the head race to the rail race.


16.            Write the advantages of small Hydro-power plant (SHP)?


a)    Readily accessible source of renewable energy,

b)    Can be installed making use of water head as low as 2 m and above,

c)     Does not involve setting up of large dams,

d)   Least polluting.


Working principle

Figure: Kaplan turbine



The water from the scroll casing flows over the guide vanes. It is deflected through 90° between guide vanes and runner. Then, it flows axially into the runner. The blades are shaped such that water flows axially in the runner. The force exerted on the blades causes the runner shaft to rotate. This rotation is transmitted to the generator which is couple to the runner shaft. After passing through the runner, the water enters the tailrace through a draft tube.



Governing of Kaplan turbine



A Kaplan turbine has adjustments in both guide vanes and runner vanes. Generally, double regulators are provided in a Kaplan turbine. The governor regulates the guide blade opening as well as the runner vane angles simultaneously. The adjustment of guide vanes is similar to that of a Francis turbine. The runner vanes are regulated by a separate Servomotor. The control valves for both the runner and guide vanes are interconnected to ensure a define runner vane angle for the given vane opening.


Figure: Governing of Kaplan turbine.



The runner vane angles may be adjusted while the turbine is in motion. The piston rod of the servomotor (of the runner vanes) pass through the hollow turbine shaft as shown in figure. The movement of the piston is transmitted to the runner of the piston is transmitted to the runner vane by a small crank connected to cross head. The servomotor acts as the coupling between the turbines shaft and the generator shaft. Oil from the governor is admitted to the upper or lower side of the servomotor piston through pipes. This will reduce or increase the blade angle. The governor actuates simultaneously both the guide vane and the runner vane. Thus for all loads, the turbine is able to maintain high efficiency.

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