# Thermal Engineering Questions and Answers – Steam Generators – Water Tube Boilers

This set of Thermal Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Steam Generators – Water Tube Boilers”.

1. Water tube boilers are further classified into horizontal straight tube and bent tube boilers.
a) True
b) False

Explanation: Water tube boilers are further classified into horizontal straight tube (Babcock and Wilcox boiler) and bent tube boilers (Stirling boiler). Horizontal straight tube boilers are further classified into longitudinal and cross drum boilers.

2. Which of the following is a horizontal straight tube boiler?
a) Lancashire boiler
b) Babcock and Wilcox boiler
c) Stirling boiler
d) Locomotive boiler

Explanation: Lancashire and locomotive boilers are fire tube boilers. Babcock and Wilcox and Stirling boilers are water tube boilers out of which the former one is a horizontal straight tube boiler and the latter one is a bent tube boiler.

3. What is the correct range of diameter of the drum for a Babcock and Wilcox boiler?
a) 0.61 – 1.02 m
b) 1.22 – 1.83 m
c) 2.87 – 3.52 m
d) 4.89 – 5.66 m

Explanation: Babcock and Wilcox boiler is a water tube (horizontal straight tube) boiler. The diameter and length of the boiler drum are in the range of 1.22 to 1.83 m and 6.096 to 9.144 m respectively.

4. For a Babcock and Wilcox boiler, what is the correct range of size of the water tubes?
a) 1.22 to 1.44 cm
b) 4.98 to 6.02 cm
c) 7.62 to 10.16 cm
d) 12.25 to 15.54 cm

Explanation: The correct answer is 7.62 to 10.16 cm. Babcock and Wilcox boiler has multiple water tubes as it is a multi-tube boiler. These tube join the uptake header with the down take header. These water tubes are made of mild steel.

5. What is the correct range of size of superheater tubes in Babcock and Wilcox boiler?
a) 1.20 to 2.10 cm
b) 2.12 to 2.84 cm
c) 3.84 to 5.71 cm
d) 5.84 to 6.25 cm

Explanation: The correct answer is 3.84 to 5.71 cm. The range of size of water tubes is 7.62 to 10.16 cm. The presence of superheater increases the efficiency of the boiler. Babcock and Wilcox boiler has an efficiency of 60 to 80%.
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6. What is maximum working pressure of Babcock and Wilcox boiler?
a) 40 bar
b) 50 bar
c) 60 bar
d) 80 bar

Explanation: The maximum working pressure of a Babcock and Wilcox boiler is 40 bar. Babcock and Wilcox is used when pressure above 10 bar and steam capacity greater than 7000 kg/hr is required. It is a water-tube boiler.

7. What is the maximum steam capacity of a Babcock and Wilcox boiler?
a) 20000 kg/hr
b) 30000 kg/hr
c) 40000 kg/hr
d) 50000 kg/hr

Explanation: The maximum steam capacity of a Babcock and Wilcox boiler is 40000 kg/hr. This boiler is used when a steam capacity greater than 7000 kg/hr is required. The maximum working pressure of the boiler is 40 bar.

8. In Babcock and Wilcox boiler, just before entering the superheater the steam enters _____
c) main stop valve
d) antipriming pipe

Explanation: The steam is collected in the drum. The steam first enters the antipriming pipe and then it enters the superheater. The steam then reaches the main stop valve. The water from the drum flows to down take header and then to uptake header through the inclined pipes.

9. Babcock and Wilcox boiler is a forced circulation boiler.
a) True
b) False

Explanation: Babcock and Wilcox boiler does not use a pump for circulation of water. The water flows though the down take header, inclined pipes and the uptake header by means of natural convection current. Hence Babcock and Wilcox is not a forced circulation boiler but a natural circulation boiler.

10. Which of the following statements is FALSE for a cross drum Babcock and Wilcox boiler?
a) The alignment of boiler drum is different in cross drum and longitudinal drum boilers
b) Any number of connecting tubes can be used
c) Steam of pressure 100 bar could be generated
d) Steam capacity is 45000 kg/hr

Explanation: Steam having pressure 100 bar and steam capacity of 27000 kg/hr could be achieved with the help of cross drums. Cross drum and longitudinal drum are placed differently with respect to the axis of the water tubes. In case of cross drum boiler, there is no limitation to the number of connecting tubes.

11. Stirling boiler is _____
a) a fire tube boiler
b) a bent-tube (water tube) boiler
c) a horizontal straight tube (water tube) boiler
d) a high pressure boiler

Explanation: Stirling boiler is a water tube boiler that comes under the category of bent tube boilers. The drums and headers in the boilers are connected by bent tubes. It has a steam capacity of 50000 kg/hr.

12. What purpose do baffle plates serve in a Babcock and Wilcox boiler?
a) They direct the flow of water
b) They direct the flow of steam
c) They direct the flow of hot gases
d) They direct the flow of air to combustion chamber

Explanation: The baffle plates are provided to direct the flow of hot gases around tubes containing water. The water absorbs the heat from the hot gases and the temperature of hot gases is dropped. The hot gases are ultimately directed to the chimney through which they escape to atmosphere.

Sanfoundry Global Education & Learning Series – Thermal Engineering

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