UNIT 4
POWER PLANT
QUESTIONS
Question 1)Explain efficiency of a Thermal Power Station?
Answer 1) A huge amount of heat is lost in various stages of the plant. Major part of heat is lost in the condenser. That is why the efficiency of thermal plants is quite low.
Thermal Efficiency: The ratio of 'heat equivalent of mechanical energy transmitted to the turbine shaft' to the 'heat of coal combustion' is called as thermal efficiency.
Thermal efficiency of a steam power station= heat equivalent of mechanical energy transmitted to the turbine shaft / heat of coal combustion.
Thermal efficiency of modern thermal power stations is about 30%. It means, if 100 calories of heat are produced by coal combustion, the mechanical energy equivalent of 30 calories will be available at the turbine shaft.
Overall Efficiency: The ratio of 'heat equivalent of electrical output' to the 'heat of coal combustion' is called as overall efficiency.
The overall efficiency of a thermal plant is about 29% (slightly less than the thermal efficiency).
Question 2) Explain boilers and types?
Answer 2)
BOILER- A boiler (or steam generator) is a closed vessel in which water, under pressure is converted into steam. The heat is transferred to the boiler by all three modes of heat transfer i.e. conduction, convection and radiation.
Major types of boilers are: (i) fire tube boiler and (ii) water tube boiler
Generally water tube boilers are used for electric power stations.
Fire Tube Boiler
• The boiler is named so because the products of combustion pass through the tubes which are surrounded by water.
• Depending on whether the tube is vertical or horizontal the fire tube boiler is divided into two types
1. Vertical tube boiler
2. Horizontal tube boiler
• A fire tube boiler is simple, compact and rugged in construction. Its initial cost is low.
• Water being more and circulation being poor they cannot meet quickly to changes in steam demand.
• As water and steam both are in the same shell, higher pressure of steam are not possible. The maximum pressure which can be had is 17.5 kg/cm2 with a capacity of 15,000kg of steam per hour.
• For the same output the outer shell of a fire tube boiler is much larger than that of a water tube boiler.
• In the event of a sudden and major tube failure. Steam explosions may be caused in the furnace due to rush of high pressure water into the hot combustion chamber which may generate large quantities of steam in the furnace.
• Fire tube boilers use is therefore limited to low cost small size and low pressure plants.
Water Tube Boilers
• In this boiler, the water flows inside the tubes and hot gases flow outside the tube.
• Water tube boiler are classified as
1. Vertical tube boiler
2. Horizontal tube boiler
3. Inclined tube boiler
• The circulation of water in the boiler is may be natural or forced.
• For Central steam power plants large capacity of water tube boilers are used.
• The tubes are always external to the drum they can be built in smaller size and therefore withstand high pressure.
• The boiler drum contains both steam and water, the former being trapped from the top of the drum where the highest concentration of dry steam exists.
Question 3) what is feed water heater?
Answer 3) Feed Water Heaters: These heaters are used to heat the feed water by means of blend steam before it is supplied to the boiler. Necessity of heating feed water before feeding it back to the boiler arises due to the following reasons.
• Feed Water heating improve overall efficiency.
• The dissolved oxygen which would otherwise cause boiler corrosion are removed in the feed water heater.
• Thermal stresses due to cold water entering the boiler drum are avoided.
• Quantity of steam produced by the boiler is increased.
• Some other impurities carried by steam and condensate, due to corrosion in boiler and condenser, are precipitated outside the boiler.
Question 4) Write efficiency of nuclear power plant?
Answer 4) The Efficiency of the Nuclear Power Plant
The nuclear power plant efficiency can be decided equally to other heat engines because technically the plant is a large heat engine. The sum of electric power generated for every unit of thermal power will provide the plant is thermal efficiency & because of the thermodynamics second law, there is a higher limit to how efficient these power plants can be.
The normal nuclear power plants attain efficiencies approximately 33 to 37%, equivalent to fossil-fuel plants. High temperature & more current designs such as the Generation IV reactors could acquire above 45% efficiency.
Question 5) Describe types of nuclear power plant?
Answer 5) Types of Nuclear Power Plant
There are two types of nuclear power plants such as pressurized water reactor and boiling water reactor.
Pressurized Water Reactor
In this kind of reactor, regular water is used as a coolant. This is kept at extremely high force so that it does not get a boil. A heat exchanger in this reactor transfers the heated water where the water from the secondary coolant circle is changed into vapour. Therefore, this loop is totally free from the material of radioactive. In this reactor, the coolant water works as a moderator. Because of these benefits, these reactors are used most frequently.
Boiling Water Reactor
In this kind of reactor, a single coolant loop is only available. The water is permissible to heat within the reactor. The steam is produced from the reactor when it heads out from the reactor & the steam will flow throughout the steam turbine. The main drawback of this reactor is, the coolant water approaches the fuel rods & the turbine. So, radioactive material could be located over the turbine.
Question 6) In India, how many nuclear plants are there?
Answer 6) there are seven nuclear plants available in India
1) Kudankulam Nuclear Power Plant, located in Tamil Nadu
2) Tarapur Nuclear Reactor, located in Maharashtra
3) Rajasthan Atomic Power Plant, located in Rajasthan
4) Kaiga Atomic Power Plant, located in Karnataka
5) Kalapakkam Nuclear Power Plant, located in Tamil Nadu
6) Narora Nuclear Reactor, located in Uttar Pradesh
7) Kakarapar Atomic Power Plant, located in Gujarat
Question 7) Explain advantage and disadvantage of nuclear power plant
Answer 7)
Advantages
The advantages of nuclear power plants include the following.
1) It uses less space compared with other power plants
2) It is extremely economical and generates huge electric power.
3) These plants are located near the load center because there is no requirement of huge fuel.
4) It generates a huge amount of power in the process of each nuclear fission
5) It uses less fuel to generate huge energy
6) Its operation is reliable
7) When compared with steam power plants, it is very clean and neat
8) The operating cost is small
9) It doesn’t produce polluting gases
Disadvantages
The disadvantages of nuclear power plants include the following.
1) The cost of primary installation is extremely high when compared with other power stations.
2) The nuclear fuel is expensive so recovering is difficult
3) High capital cost compare with other power plants
4) Technical knowledge is required to operate this plat. So maintenance, as well as salary, will be high.
5) There is a chance of radioactive pollution
6) The response is not efficient
7) The requirement of cooling water is double compare with a steam power plant.
Question 8) Explain the difference between nuclear power plant and thermal power plant?
Answer 8) difference between nuclear power plant and thermal power plant are given below:
Question 9) Explain the difference between thermal power plant and hydroelectric power plant?
Answer 9)
Question 10) Difference between PWR and BWR?
Answer 10) Differences between PWR and BWR
Pressurized Water Reactor (PWR) | Boiling Water Reactor (BWR) |
Pressurized Water Reactor (PWR) power plants consist of two loops—(i) primary loop or coolant loop that takes away heat from reactor, and (ii) secondary loop or working fluid loop that drives the turbine. A heat exchanger (HE) is employed to transfer heat from primary loop to the secondary loop. | Boiling Water Reactor (BWR) power plants consist of a single loop where the coolant that takes away heat from the reactor is directly fed to the turbine. Thus no heat exchanger is desired. |
In the primary loop, normal water (H2O) acts as coolant-cum-moderator. In the secondary loop, the normal water acts as working fluid. However, water from one loop is not allowed to mix with the water of other loop. | Since it has only one loop, so normal water (H2O) serves all three purposes – cooling, moderation, and working fluid. |
Normal water in the primary loop that acts as moderator-cum-coolant is not allowed to boil. That means the water remains in liquid phase throughout the cycle of primary loop. However, the water in the secondary loop is allowed to boil. | Here the normal water (H2O) is allowed to change its phase. Thus the water (liquid phase) is first converted into steam (gaseous phase) within the reactor, and then the steam is again condensed to water before pumping back to reactor. |
Here steam is generated in a heat exchanger outside the nuclear reactor. | Here steam is generated within the reactor itself. |
Here the water in the primary loop is maintained at high pressure (15 – 17 MPa) to avoid boiling at reactor exit. | Here water pressure remains comparatively low (7 – 8 MPa) as it is allowed to boil. |
A pressurizer is required to use mandatorily to maintain water pressure in such a way that it does not evaporate even at very high temperature. | No such pressurizer is employed as evaporation of the water is desired. |
The temperature of the water at the reactor exit is kept around 310°C (corresponding to the working pressure to avoid boiling). | Steam temperature at reactor exit remains comparatively low (around 285°C). |
PWR has comparatively low thermal efficiency owing to two different loops. | BWR offers higher thermal efficiency. |
In PWR, the control rods are inserted from the top of the nuclear reactor. | In BWR, the control rods are inserted from the bottom of the nuclear reactor. |
Since the fluid is maintained at high pressure, so the PWR core volume is less. | For the same power generation, core volume of the BWR is comparatively larger. |
Since the working fluid loop is separated from the primary loop, so PWR is less risky in spreading of radioactive materials owing to leakage. | Since same fluid passes through the reactor and turbine in BWR plants, so any leakage in the turbine can spread radioactive elements into the atmosphere. |
UNIT 4
POWER PLANT
QUESTIONS
Question 1)Explain efficiency of a Thermal Power Station?
Answer 1) A huge amount of heat is lost in various stages of the plant. Major part of heat is lost in the condenser. That is why the efficiency of thermal plants is quite low.
Thermal Efficiency: The ratio of 'heat equivalent of mechanical energy transmitted to the turbine shaft' to the 'heat of coal combustion' is called as thermal efficiency.
Thermal efficiency of a steam power station= heat equivalent of mechanical energy transmitted to the turbine shaft / heat of coal combustion.
Thermal efficiency of modern thermal power stations is about 30%. It means, if 100 calories of heat are produced by coal combustion, the mechanical energy equivalent of 30 calories will be available at the turbine shaft.
Overall Efficiency: The ratio of 'heat equivalent of electrical output' to the 'heat of coal combustion' is called as overall efficiency.
The overall efficiency of a thermal plant is about 29% (slightly less than the thermal efficiency).
Question 2) Explain boilers and types?
Answer 2)
BOILER- A boiler (or steam generator) is a closed vessel in which water, under pressure is converted into steam. The heat is transferred to the boiler by all three modes of heat transfer i.e. conduction, convection and radiation.
Major types of boilers are: (i) fire tube boiler and (ii) water tube boiler
Generally water tube boilers are used for electric power stations.
Fire Tube Boiler
• The boiler is named so because the products of combustion pass through the tubes which are surrounded by water.
• Depending on whether the tube is vertical or horizontal the fire tube boiler is divided into two types
1. Vertical tube boiler
2. Horizontal tube boiler
• A fire tube boiler is simple, compact and rugged in construction. Its initial cost is low.
• Water being more and circulation being poor they cannot meet quickly to changes in steam demand.
• As water and steam both are in the same shell, higher pressure of steam are not possible. The maximum pressure which can be had is 17.5 kg/cm2 with a capacity of 15,000kg of steam per hour.
• For the same output the outer shell of a fire tube boiler is much larger than that of a water tube boiler.
• In the event of a sudden and major tube failure. Steam explosions may be caused in the furnace due to rush of high pressure water into the hot combustion chamber which may generate large quantities of steam in the furnace.
• Fire tube boilers use is therefore limited to low cost small size and low pressure plants.
Water Tube Boilers
• In this boiler, the water flows inside the tubes and hot gases flow outside the tube.
• Water tube boiler are classified as
1. Vertical tube boiler
2. Horizontal tube boiler
3. Inclined tube boiler
• The circulation of water in the boiler is may be natural or forced.
• For Central steam power plants large capacity of water tube boilers are used.
• The tubes are always external to the drum they can be built in smaller size and therefore withstand high pressure.
• The boiler drum contains both steam and water, the former being trapped from the top of the drum where the highest concentration of dry steam exists.
Question 3) what is feed water heater?
Answer 3) Feed Water Heaters: These heaters are used to heat the feed water by means of blend steam before it is supplied to the boiler. Necessity of heating feed water before feeding it back to the boiler arises due to the following reasons.
• Feed Water heating improve overall efficiency.
• The dissolved oxygen which would otherwise cause boiler corrosion are removed in the feed water heater.
• Thermal stresses due to cold water entering the boiler drum are avoided.
• Quantity of steam produced by the boiler is increased.
• Some other impurities carried by steam and condensate, due to corrosion in boiler and condenser, are precipitated outside the boiler.
Question 4) Write efficiency of nuclear power plant?
Answer 4) The Efficiency of the Nuclear Power Plant
The nuclear power plant efficiency can be decided equally to other heat engines because technically the plant is a large heat engine. The sum of electric power generated for every unit of thermal power will provide the plant is thermal efficiency & because of the thermodynamics second law, there is a higher limit to how efficient these power plants can be.
The normal nuclear power plants attain efficiencies approximately 33 to 37%, equivalent to fossil-fuel plants. High temperature & more current designs such as the Generation IV reactors could acquire above 45% efficiency.
Question 5) Describe types of nuclear power plant?
Answer 5) Types of Nuclear Power Plant
There are two types of nuclear power plants such as pressurized water reactor and boiling water reactor.
Pressurized Water Reactor
In this kind of reactor, regular water is used as a coolant. This is kept at extremely high force so that it does not get a boil. A heat exchanger in this reactor transfers the heated water where the water from the secondary coolant circle is changed into vapour. Therefore, this loop is totally free from the material of radioactive. In this reactor, the coolant water works as a moderator. Because of these benefits, these reactors are used most frequently.
Boiling Water Reactor
In this kind of reactor, a single coolant loop is only available. The water is permissible to heat within the reactor. The steam is produced from the reactor when it heads out from the reactor & the steam will flow throughout the steam turbine. The main drawback of this reactor is, the coolant water approaches the fuel rods & the turbine. So, radioactive material could be located over the turbine.
Question 6) In India, how many nuclear plants are there?
Answer 6) there are seven nuclear plants available in India
1) Kudankulam Nuclear Power Plant, located in Tamil Nadu
2) Tarapur Nuclear Reactor, located in Maharashtra
3) Rajasthan Atomic Power Plant, located in Rajasthan
4) Kaiga Atomic Power Plant, located in Karnataka
5) Kalapakkam Nuclear Power Plant, located in Tamil Nadu
6) Narora Nuclear Reactor, located in Uttar Pradesh
7) Kakarapar Atomic Power Plant, located in Gujarat
Question 7) Explain advantage and disadvantage of nuclear power plant
Answer 7)
Advantages
The advantages of nuclear power plants include the following.
1) It uses less space compared with other power plants
2) It is extremely economical and generates huge electric power.
3) These plants are located near the load center because there is no requirement of huge fuel.
4) It generates a huge amount of power in the process of each nuclear fission
5) It uses less fuel to generate huge energy
6) Its operation is reliable
7) When compared with steam power plants, it is very clean and neat
8) The operating cost is small
9) It doesn’t produce polluting gases
Disadvantages
The disadvantages of nuclear power plants include the following.
1) The cost of primary installation is extremely high when compared with other power stations.
2) The nuclear fuel is expensive so recovering is difficult
3) High capital cost compare with other power plants
4) Technical knowledge is required to operate this plat. So maintenance, as well as salary, will be high.
5) There is a chance of radioactive pollution
6) The response is not efficient
7) The requirement of cooling water is double compare with a steam power plant.
Question 8) Explain the difference between nuclear power plant and thermal power plant?
Answer 8) difference between nuclear power plant and thermal power plant are given below:
Question 9) Explain the difference between thermal power plant and hydroelectric power plant?
Answer 9)
Question 10) Difference between PWR and BWR?
Answer 10) Differences between PWR and BWR
Pressurized Water Reactor (PWR) | Boiling Water Reactor (BWR) |
Pressurized Water Reactor (PWR) power plants consist of two loops—(i) primary loop or coolant loop that takes away heat from reactor, and (ii) secondary loop or working fluid loop that drives the turbine. A heat exchanger (HE) is employed to transfer heat from primary loop to the secondary loop. | Boiling Water Reactor (BWR) power plants consist of a single loop where the coolant that takes away heat from the reactor is directly fed to the turbine. Thus no heat exchanger is desired. |
In the primary loop, normal water (H2O) acts as coolant-cum-moderator. In the secondary loop, the normal water acts as working fluid. However, water from one loop is not allowed to mix with the water of other loop. | Since it has only one loop, so normal water (H2O) serves all three purposes – cooling, moderation, and working fluid. |
Normal water in the primary loop that acts as moderator-cum-coolant is not allowed to boil. That means the water remains in liquid phase throughout the cycle of primary loop. However, the water in the secondary loop is allowed to boil. | Here the normal water (H2O) is allowed to change its phase. Thus the water (liquid phase) is first converted into steam (gaseous phase) within the reactor, and then the steam is again condensed to water before pumping back to reactor. |
Here steam is generated in a heat exchanger outside the nuclear reactor. | Here steam is generated within the reactor itself. |
Here the water in the primary loop is maintained at high pressure (15 – 17 MPa) to avoid boiling at reactor exit. | Here water pressure remains comparatively low (7 – 8 MPa) as it is allowed to boil. |
A pressurizer is required to use mandatorily to maintain water pressure in such a way that it does not evaporate even at very high temperature. | No such pressurizer is employed as evaporation of the water is desired. |
The temperature of the water at the reactor exit is kept around 310°C (corresponding to the working pressure to avoid boiling). | Steam temperature at reactor exit remains comparatively low (around 285°C). |
PWR has comparatively low thermal efficiency owing to two different loops. | BWR offers higher thermal efficiency. |
In PWR, the control rods are inserted from the top of the nuclear reactor. | In BWR, the control rods are inserted from the bottom of the nuclear reactor. |
Since the fluid is maintained at high pressure, so the PWR core volume is less. | For the same power generation, core volume of the BWR is comparatively larger. |
Since the working fluid loop is separated from the primary loop, so PWR is less risky in spreading of radioactive materials owing to leakage. | Since same fluid passes through the reactor and turbine in BWR plants, so any leakage in the turbine can spread radioactive elements into the atmosphere. |
