Power Plant Questions and Answers – Cogeneration of Power & Process Heat

This set of Power Plant Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Cogeneration of Power & Process Heat”.

1. Having two separate units for process heat and power is?
a) useful
b) useless
c) pollution reducing
d) none of the mentioned
View Answer

Answer: b
Explanation: Having two separate units for process heat & power is wasteful, for of the total heat supplied to the steam generator for power purposes, a greater part will normally be carried away by the cooling water in the condenser.

2. A plant producing both, electrical power & process heat simultaneously is?
a) Cogenital plant
b) Cogenerial plant
c) Cogeneration plant
d) Conglomerate plant
View Answer

Answer: c
Explanation: Cogeneration plant is defined as a plant which produces electrical power and processes heat simultaneously.

3. In a back pressure turbine _____________
a) pressure at the exhaust from the turbine is the saturation pressure corresponding to the temperature desired in the process
b) pressure at the entrance of the turbine is the saturation pressure corresponding to the temperature desired in the process
c) pressure at the exhaust from the turbine is the saturation pressure corresponding to the pressure desired in the process
d) none of the mentioned
View Answer

Answer: a
Explanation: The name back pressure turbine is given because pressure at the exhaust from the turbine is the saturation pressure corresponding to the temperature desired in the process.
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4. In a by-product power cycle?
a) the power is produced initially
b) power production is in the middle stages of the cycle
c) power production is after the cycle has ended
d) none of the mentioned
View Answer

Answer: c
Explanation: When the process steam is the basic need, and the power is produced incidentally as a by-product, the cycle is often called as the by-product power cycle.

5. Back pressure turbines are usually _________________ with respect to their power output.
a) large
b) small
c) very large
d) very small
View Answer

Answer: b
Explanation: Back pressure turbines are usually small with respect to their power output because they have no great volume of exhaust to cope with, the density being high.
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6. In terms of cost per MW compared to condensing sets of the same power, the back pressure turbines are?
a) more expensive
b) cheaper
c) costly
d) none of the mentioned
View Answer

Answer: b
Explanation: Back pressure turbines are usually small with respect to their power output because they have no great volume of exhaust to cope with, the density being high. They are usually single cylinder and hence, usually cheaper in terms of cost per MW.

7. Which of these is not an application of back pressure turbine?
a) desalination of sea water
b) filtration of water
c) process industries
d) petrochemical installations
View Answer

Answer: b
Explanation: The applications of back pressure turbine are desalination of sea water, process industries, petrochemical installations, district heating and also for driving compressors and feed pumps.
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8. Back pressure turbine is placed between ____________
a) Turbine & Pump
b) Boiler & Pump
c) Turbine & Heat Exchanger
d) Boiler & Turbine
View Answer

Answer: d
Explanation: In a cogeneration plant, the back pressure turbine is placed between the boiler & turbine.

9. Which of the following is a good medium for constant temperature heating?
a) Water
b) Steam
c) Coolant
d) Diesel
View Answer

Answer: b
Explanation: For constant temperature heating (or drying), steam is a very good medium since isothermal condition can be maintained by allowing saturated steam to condense at that temperature and utilising the latent heat released for heating purposes.
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10. The cogeneration plant efficiency nCO if WT, Qi, QH represents turbine work, heat input, heat output respectively is given by?
a) nCO = (WT + Qi) / QH
b) nCO = (WT – Qi) / QH
c) nCO = (WT + QH) / Qi
d) nCO = (WT + QH) / Qi
View Answer

Answer: d
Explanation: The cogeneration plant efficiency nCO if WT, Qi, QH represents turbine work, heat input, heat output respectively is,
nCO = (WT + QH) / Qi.

11. The electricity fraction of total energy output if W1 and Q1 represents the turbine work and heat output is given by?
a) W1 / (W1 + Q1)
b) W1 / (W1 – Q1)
c) W1 / (W1Q1)
d) W1 / Q1
View Answer

Answer: a
Explanation: The electricity fraction of total energy output if W1 and Q1 represents the turbine work and heat output is,
W1 / (W1 + Q1).

12. If e is the electricity fraction of the total energy output, m is the electric plant efficiency and n is the steam generator efficiency; the heat added per unit total energy output is given by?
a) (1 / m) + ((1 – e) / n)
b) (1 / n) + ((1 – e) / m)
c) (1 / m) + ((1 + e) / n)
d) (1 / n) + ((1 – e) / m)
View Answer

Answer: a
Explanation: If e is the electricity fraction of the total energy output, m is the electric plant efficiency and n is the steam generator efficiency; the heat added per unit total energy output is given by?
(1 / m) + ((1 – e) / n).

13. Pass-out turbines are used in which of these cases?
a) relatively high back pressure
b) small heating requirement
c) only relatively low back pressure
d) both relatively high back pressure and small heating requirement
View Answer

Answer: d
Explanation: Pass-out turbines are used in cases of relatively high back pressure and small heating requirements. They are used in cases where a certain quantity of steam is continuously extracted from the turbine at an intermediate stage for heating purposes at the desired temperature and pressure.

14. Which of these is not considered economical for cogeneration?
a) a high fraction of electric to total energy
b) a low fraction of electric to total energy
c) a low fraction of total energy to electric energy
d) none of the mentioned
View Answer

Answer: b
Explanation: A low fraction of electric to total energy is considered as an economical condition for cogeneration. Cogeneration plant is defined as a plant which produces electrical power and processes heat simultaneously.

Sanfoundry Global Education & Learning Series – Power Plant Engineering.

To practice all areas of Power Plant Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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