This set of Energy Engineering test focuses on “Types of High Pressure Boilers – 2”.
1. Which of the given boilers velocity of flue gases is greater than velocity of sound?
a) Benson boiler
b) La-Mont boiler
c) Schmidt-Hartmann boiler
d) Velox boiler
Explanation: Velox boiler is a forced circulation water tube boiler. In this boiler, the velocity of the flue gas is greater than the velocity of sound, which causes more heat transfer from gas to the water, which increases the steam generation rate. It is mostly used in gas turbine. Due to this reason it is one of the important boilers.
2. Which boiler is most successful boiler in the gas turbine industries?
a) Because it has greater flexibility
b) It is easy to control, it’s fully automatic
c) It has higher thermal efficiency of all
d) Can increase heat transfer without changing its size
Explanation: When the velocity of gas is greater is greater than speed of the sound, its heat transfer rate also increases. More heat is transferred from the gas to water comparatively when the heat transfer is at subsonic speed. This boiler can increase the heat transfer or can say steam generation rate without increasing boiler size. This is why; Velox boiler is most successful boiler in the gas turbine industries.
3. What is done to increase the rate of heat transfer in the Velox boiler?
a) The boiler is heated upto very high range of temperature
b) The size of the boiler is changed as it is flexible
c) High grade fuel is made use for the combustion
d) Combustion gases are circulated through tubes with supersonic speed
Explanation: This boiler uses oil or gaseous fuel inside furnace for its combustion. The combustion gases are circulated through the tubes with supersonic speed velocity to increase the heat transfer rate between the hot gases and feed water.
4. What type of boiler is a Velox boiler?
a) Forced circulation boiler
b) Natural circulation boiler
c) Positively forced circulation boiler
d) Once- through boiler
Explanation: Velox boiler is a forced circulation boiler. It has gas turbine driven air compressor, which compresses the air. This compressed air enters into the vertical combustion chamber; as a result, high rate of heat is released from the fuel, which increases the flue gas velocity up to the sound velocity. In this boiler pump is used to circulate water inside tube.
5. What is used to heat the feed water which is used for recirculation through tubes?
d) Water Clarifier
Explanation: The combustion gas coming out of the super heater is used to run gas turbine which runs at air compressor. The exhaust gases coming out of the gas turbine are passed through the economizer to heat the feed water. Feed water is recirculated with the help of a pump.
6. How many circuits are there in the Schmidt-Hartmann boiler?
Explanation: There are 2 circuits in S-H boiler, in the primary circuit distilled water from the water drum passes through the primary evaporator and steam produced is passed over drum and in secondary circuit, feed pump supplies impure water from hot well to the evaporator drum through feed preheater.
7. Which type of circulation is incurred in Schmidt-Hartmann boiler?
a) Natural circulation
b) Positive forced circulation
c) Forced circulation
d) Once-through circulation
Explanation: Natural circulation is used in the primary circuit of a Schmidt-Hartmann boiler and this is sufficient enough to affect the desired rate of heat transfer and to overcome the thermo-siphon head of height about 2 to 10 meters. This boiler has got 2 pressure cycles.
8. Why pressure gauge and safety valve are made use of in the Schmidt-Hartmann boiler?
a) Safety against fire causes
b) To control the burst/blast of the boiler due to variance in pressure
c) Safe guard against leakage accidents
d) Act as controller against overheating of water in the boiler and boiler tubes
Explanation: In normal circumstances, replenishment of distilled water in the primary circuit is not required as every care is taken in the design and construction to prevent leakages. But as a safeguard against leakage accidental loss, a pressure gauge and safety valve are fitted in the Schmidt-Hartmann boiler’s circuit.
9. Why are salts deposited on the evaporator drum?
a) Due to continuous circulation of water
b) Due to usage of hard water containing calcium content
c) Due to circulation of impure water
d) Due to the chemicals added in water
Explanation: The salts are deposited in the evaporator drum (steam generator) due to the circulation of impure water can be easily cleaned by blowing off the water with pressure or by removing the submerged coil from the drum.
10. Overheating doesn’t occur in components of primary circuit Schmidt-Hartmann boiler?
Explanation: There is a rare chance of overheating or the burning of the highly heated components of the primary circuits there is no danger of salt deposition as well as there is no chance of interruption to the circulation either by rust or any other material. The highly heated parts run safe throughout the life of the boiler.
11. What is feature of the Loffler boilers?
a) Evaporating water by super heated steam
b) Provide better efficiency by re-circulating gas coming out of turbine
c) Produce better steam quality by heating the boiler furnace above critical degrees
d) Eliminate the extra components used
Explanation: The novel feature of the Loffler boiler is to evaporate water solely by means of superheated steam. The furnace heat is supplied only to economizer and super heater. In other words, steam is used as a heat absorbing medium.
12. What is the major difficulty of the La-Mont boiler?
a) Unstable water circulation
b) Deposition of salts
c) Overheating of the components
d) Boiler working is slow
Explanation: Major difficulty experienced in La-Mont boiler is deposition of salt and sediment on the inner surfaces of water tubes. The deposition reduces the heat transfer, ultimately, the generating capacity. This difficulty was solved by Loffler boiler by preventing the flow of water into the boiler tubes.
13. At what temperature is the water in convection super heater is heated of Loffler boiler?
Explanation: Steam coming out of the radiant super heater enters the convection where it is finally heated to the desired temperature of 500oC. The convection superheater receives heat from the flue gases entered by convective heat transfer. Both radiant and convective super heaters are arranged in the series in the path of flue gases.
14. Which is the most recent economical method of power generation from boilers?
a) Natural circulation boiler
b) Fire tube boiler
c) Forced circulation
d) Super critical boiler
Explanation: Varying fuel costs have constantly persuaded power engineers to search for more economical methods of power generation. The most recent method is super critical boiler which operated at pressure of 3200psi or 22Mpa therefore facilitates in converting water into steam instantly.
15. Which of the following boilers has the highest heat transfer capacity?
a) Subcritical boiler
b) Critical boiler
c) Forced circulation boiler
d) Supercritical boiler
Explanation: The heat transfer rates of supercritical boilers are large compared to any other boilers. The steam side heat transfer of subcritical is 165000 kJ/m2hroc when the steam pressure and temperature are 180 bar and 538oC whereas, the steam side heat transfer coefficients of supercritical boiler is about 2, 20,200 kJ/m2hroC when the steam is generated at 240oC.
Sanfoundry Global Education & Learning Series – Energy Engineering.
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