This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Boiler Classification”.
1. On what basis are fire and water tube boilers are classified?
a) Depending the combustion products formed
b) Depending the state of fuel
c) Depending on the steam formation rate
d) Depending tubular heating surface
View Answer
Explanation: Based on the contents of the tubular heating surface, boilers are primarily classified as fire tube boiler and water tube boiler. Fire tube boilers those in which production of combustion pass through the tubes and water tube boilers are those in which the products of combustion surround the water tubes from outside.
2. Cornish boiler is an example of which type of boiler?
a) Fire tube boiler
b) Water tube boiler
c) Vertical tube boiler
d) Externally fired boiler
View Answer
Explanation: Cornish boiler is an example of fire tube boiler and also includes Cochran, Lancashire, and Locomotive and scotch marine boilers. Fire tube boilers are those in which the products of combustion pass through the tubes and water lies around the outside of tubes. These boilers operate at moderate pressure (16-20bar) and more suitable to generate 3-8 tons of steam per hour which is used in process heating.
3. Stirling boiler is an example of which type of boiler?
a) Inclined tube boilers
b) Mobile boiler
c) Fire tube boiler
d) Water tube boiler
View Answer
Explanation: Water tube boilers are those in which the products of combustion (Hot flue gas) surround the water tubes from outside. Cold water enters the tubes and leaves hot. These boilers operate at very high pressures and are used for power generation.
Ex: Babcock-Wilcox boiler, Stirling boiler.
4. Which of these is a stationary boiler?
a) Locomotive boiler
b) Marine boiler
c) Mobile boiler
d) Babcock-Wilcox boiler
View Answer
Explanation: If the boilers are used at one place only they are termed as stationary boilers. These boilers are used for either process heating in industries or for power generation in steam power plants. These are used at central station utility power plants, for plant process etc. Ex: Babcock-Wilcox boiler, Fluidized Bed Combustion (FBC) boiler.
5. Which of these is a mobile boiler?
a) Lancashire boiler
b) Stirling boiler
c) Locomotive boiler
d) Cochran boiler
View Answer
Explanation: The boilers, if they are portable, i.e., if they can be moved from one place to other place those are known as mobile boilers. Such boilers are used in locomotives and ships to get the engine moving. And also small units are used for temporary at working sites. Ex: Locomotive boiler, Marine boiler etc.
6. Which type of boiler is it when the furnace is placed in the region of boiling water?
a) Internally fired boiler
b) Externally fired boiler
c) Babcock-Wilcox boiler
d) Stirling boiler
View Answer
Explanation: If the furnace region is placed in the region of boiling water, the boilers are termed as internally fired boilers. Ex: Lancashire boiler. If the furnace is placed outside the boiling water region, the boilers are known as externally fired boilers. Ex: Babcock-Wilcox boiler.
7. Are boilers defined on the basis of heat source.
a) Yes
b) No
View Answer
Explanation: Boilers can be classified based on fuel used for combustion or heat generation source. Various heat sources are: heat generated by the combustion of fuel in solid, liquid or gaseous form. Heat generated by hot waste gases as byproducts of other chemical processes. Heat generated by electrical energy and nuclear energy.
8. What is the steam pressure limit of natural circulation boilers?
a) 650bar
b) 180bar
c) 400bar
d) 550bar
View Answer
Explanation: Water is purely circulated by density difference with most of the heat from the fuel flame being radiated to the water walls directly. The steam pressure of such boilers is limited to about 180bar, with water and steam being separated in the boiler drum.
9. Which type of boilers use orifice to control the flow circulation?
a) Natural circulation boilers
b) Forced convection boilers
c) Once-through boilers
d) Positive forced circulation boilers
View Answer
Explanation: In these boilers water is circulated by using an additional pump. These boilers often use orifices to control the flow circulation. Orifices are located at the bottom of the tubes that ensure even distribution of flow through water wall tubes. These boilers can generate steam upto about 200 bar.
10. Which of the given boilers operate above critical pressure?
a) Natural circulation boilers
b) Forced circulation boilers
c) Once-through boilers
d) Water tube boilers
View Answer
Explanation: Once-through boilers operate above critical pressure i.e., above 221.2bar. As the density of water and steam are same above the critical pressure there will be no recirculation. These types of boilers are also called as positive forced circulation boilers.
11. Which type of boilers are called drum-less boilers?
a) Natural circulation boilers
b) Fire tube boilers
c) Positive forced circulation boiler
d) Forced circulation boiler
View Answer
Explanation: In positive forced boilers, water enters the bottom of the tubes and completely transforms into steam as it passes through the tubes and reaches at the top. Thus, these boilers do not need a steam drum and hence often referred as drum-less boilers. These boilers work at very high pressures.
12. What is the advantage of having smaller ratio of water to steam space?
a) Steam can be generated at a faster even if the boiler is cold
b) Increases the rate of evaporation
c) Water is made cyclic, i.e., from boiler drum to water tube and back to drum
d) Helps in mobilizing the boiler
View Answer
Explanation: Rate of evaporation is more as area of heating surface is more due to presence of large small diameter tubes. Due to that smaller water ratio is allowed to steam space where in the steam can be generated as a faster rate even if the boiler is cold. As the rate of evaporation is more, it is preferred in steam power plants for power generation.
13. Chances of sediments depositing inside the water tubes in the shell is less due to?
a) Low working pressure
b) Natural circulation of water
c) Partial circulation of water
d) High working pressure
View Answer
Explanation: Due to high working pressure and positive circulation of water, chances of sediments depositing inside water tubes in the shell is less. This high working pressure of boiler in the shell can withstand high temperature or thermal stresses.
14. Out of the given option choose the advantage that supports fire tube boilers?
a) Water circulation is cyclic
b) Used as a mobile boiler
c) Water circulation is limited inside boiler shell
d) Bursting of flue tube does not cause any explosion
View Answer
Explanation: Water circulation is limited inside the boiler shell. Water need not be that much pure and needs minimum treatment like passing through a pressure filter. Cleaning and repairing is not easy due to inaccessible parts, furnace cannot be altered and is used for one fuel only.
15. Which are the major types of boilers that are operated in world today?
a) Natural circulation boiler
b) Forced circulation boiler
c) Fire tube boiler
d) Once through boiler
View Answer
Explanation: The once through boiler has higher load response characteristics due to the fact that it does not have drum and has much lower water inventory. Many times load change response is dictated by the firing system and its controls rather than the boiler, per-say.
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