This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Cooling Water System, Air & Fuel Gas System”.
1. What type of draught fan is used to draw air from air heater?
a) Balanced draught fan
b) Induced draught fan
c) Forced draught fan
d) Artificial draught fan
Explanation: Forced draught fan is used to draw the air. This is installed near the base of boiler and air is forced to pass through the furnace, economizer and to the air stack. This is also called as positive draught system because pressure and air is forced to flow through the system.
2. In what form are the products of combustion in steam powered plant?
a) Air products
b) Flue gas
d) Hot water
Explanation: The products of combustion are in form of flue gas. Flue gas is the gas which is exiting to the atmosphere via a flue, which is channel for releasing exhaust gas from steam power plant. The flue gas is high in the contamination of nitrogen, oxygen and carbon dioxide. And also it contains a small amount of pollutants, such as soot and other types of oxides.
3. How flue gas is made use of in steam power plant?
a) To maintain the constant pressure inside boiler
b) To heat the water in the tubes of boiler
c) To increase or decrease the pressure inside the boiler
d) To remove all unnecessary chemical constituents
Explanation: The flue gases are circulated in the furnace to heat the water in tubes. First it is passed over economizer and then to the pre-heater. And the finally after making maximum utilization of the flue gas they are exhausted through chimneys.
4. How is flue gas discharged through the chimneys?
a) By using induced draught fan
b) By using balanced draught fan
c) By using forced draught fan
d) By using mechanical draught fan
Explanation: After extracting maximum possible heat by circulating the flue gas in furnace. Induce draught fan is used to remove the left over gas via chimney. This is located near the base of the chimney. The air is sucked in by reducing the pressure below atmosphere. The draught produced is independent of temperature of hot gases.
5. What is the purpose of chimney?
a) To provide air ventilation
b) To eliminate noise produced in the system
c) To exhaust flue gases those is induced
d) To help in to suck the air required for system
Explanation: Chimneys are actually used to remove exhaust gases or products of combustion by using induced draught system. Almost all chimneys are constructed by bricks vertically and at a certain height in order easily release flue gases into atmosphere. The height of the chimneys shows its ability to transfer flue gases. The deposits of flue gas contaminations are made on the inner walls of the chimney.
6. What is the advantage of using flue gas inside a boiler?
a) Heats up boiler water tube quickly
b) Reduces the amount of amount of exhaust
c) Speeds of the process of boiler
d) Reduces the green house of effect
Explanation: Using flue gas to heat up the water tubes reduces the greenhouse effect indirectly by making use of its heat to turn the water in water tubes into steam. This will be used in steam power plant to rotate the turbine and to produce electricity. And also plant operators can operate at best heat rate efficiency.
7. How is water pumped into condenser tubes in the steam power plant?
a) Water clarifier plant
b) Draught systems
c) Hydraulic capacity electric motor pump
d) Drawing through water
Explanation: The water is pumped into condenser tubes through water clarifier plant. Clarifier helps in suspending solids from water in order to avoid damages to condenser tubes. Clarifiers are available in wide varieties of capacities of capacities and shapes depending on the steam plant.
8. When is cooling tower preferred?
a) When there is plenty of water available
b) When there is scarcity of water
c) When the plant is of large capacity
d) When the amount of flue gas produced is very high
Explanation: Cooling tower is preferred when there is scarcity of water. Instead of circulating the water directly, it is sprinkled in the cooling tower to condense the exhausted steam coming from the turbine. The loss of water due to evaporation is compensated by supplying water directly from the river.
9. What type of system is it, when the water is directly is used to condense the steam?
a) Closed system
b) Open system
c) Closed loop system
d) Open loop system
Explanation: Water is pumped through the water clarifier plant and is used to circulate through the condenser in order to condense the steam coming out from the turbine. Water leaving the condenser is discharged to the downward side of the river. The amount of water in taken from river, the same amount of water is discharged back to river with the minimal temperature difference. And this following system is called open system.
10. How is the amount of cooling required by steam power plant determined?
a) By the capacity of plant
b) By the amount of exhausted gas
c) By its thermal efficiency
d) By the type of fuel used (coal or uranium)
Explanation: The amount of cooling required by the steam power plant is determined by its thermal efficiency. It has nothing to do whether it is fueled by coal or uranium; neither has it depended on the type of power plant (nuclear, thermal or hydel). Nuclear power plants have lower thermal efficiency than the thermal plants. Higher the thermal plants lower the water usage for cooling.
11. How much amount of water does typical 1GWe plant uses for cooling per day?
a) 30 mega litre
b) 45 mega litre
c) 55 mega litre
d) 75 mega litre
Explanation: Water is used in a plant to convert it into steam and utilize it for developing mechanical energy as well as it is used for the cooling of the steam produced. This water is supplied by the large water bodies like river or big lakes. The amount of utilized from water body is all discharged back at the end.
12. What type of system is it when the cooling tower is preferred?
a) Closed system
b) Open system
c) Closed loop system
d) Open loop system
Explanation: When there is scarcity of water a cooling tower is installed, such system is known as the closed system. In this system the condensed water is cooled by passing it through the cooling tower and water is sprinkled over steam. The loss of water due to evaporation is compensated by supply of water directly from the river.
13. What is the alternative cooling method for the thermal plant?
a) Wet cooling
b) Evaporation cooling
c) Dry cooling
d) Central air damping
Explanation: The alternative way of cooling method is dry cooling. Where in this method the heat is directly transferred to air via high flow forced drafts [industrial sized fans]. This is less efficient compared to wet cooling method since it uses very high amount of power to rotate the fans. Dry cooling method is very useful in the desert areas, where water scarcity is a huge problem.
14. How can we achieve high thermal efficiency in a power plant?
a) Drawing high output with limited input
b) Decreasing the working temperature
c) Increasing the working temperature
d) Maintain large temperature differential
Explanation: The amount of heat discharged to environment depends on the plants thermal efficiency. High efficiency is achieved by having a large temperature differential. Irrespective of whether it comes from high internal heat or low temperature external environment, or both. The thermal efficiency of today’s nuclear power plant is around 35% whereas hotter coal burners can reach 40% or more. At last higher thermal efficiency is required to lower the water usage.
Sanfoundry Global Education & Learning Series – Energy Engineering.
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