Diploma Thermal Engineering 2 Important Questions
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We have added Diploma Thermal Engineering 2 Important Questions 3 Marks for the unit 3
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Diploma Thermal Engineering 2 Important Questions
Thermal Engineering 2
Unit 3 – THERMAL POWER PLANT, STEAM TURBINES AND CONDENSERS
3 Marks
1. What are the four imporant circuits of thermal power plant?
1) Fuel (coal) and ash circuit
2) Water and steam circuit
3) Air and flue gas circuit
4) Cooling water circuit
2. Mention the essential equipments of a steam power plant.
Feed pump, economiser, air preheater, boiler, superheater, turbine, generator, condenser, cooling tower, etc.
3. Mention the major pollutants from thermal power plants.
1) Sulphur di-oxide (SO2)
2) Oxides of nitrogen (NOx)
3) Carbon di-oxide (CO2)
4) Carbon monoxide (CO)
5) Dust particles
4. Name any three devices used to remove dust particles from the flue gas in thermal power plants.
1) Cyclone separators
2) Wet scrubbers
3) Electrostatic precipitators
5. What is the use of wet scrubbers?
Wet scrubbers are used in boiler operations to remove fumes, smokes and soluble gases such as SO2, H2S, etc. in the flue gases.
6. List out the advantages of electrostatic precipitator.
1) Removes very small particle like fly ash, smoke, mist, etc.
2) Suitable for removing dust from high dust loaded gas.
3) The removal of dust is easy, as it is collected in dry form.
7. Mention any three methods of controlling nitrogen oxides in flue gas from boiler furnace.
1) Lowering the temperature of combustion zone
2) Reducing the staying time of combustion gases in high temperature zone and
3) Using fluidised bed combustion.
8. How the emission of sulphur oxides can be controlled in boiler operations.
1) Using wet scrubber and electrostatic precipitators.
2) Adding lime-stone to the coal before it is pulverised.
3) Burning fuels with less amount of sulphur.
9. What is meant by fluidised bed combustion. State its uses.
A fluidised bed may be defined as the bed of solid particles behaving as a fluid. The combustion of fuel in a fluidised bed is called fluidised bed combustion. It is a new method used in boiler operations to reduce the emission of sulphur dioxide and oxides of nitrogen.
10. How thermal pollution can be reduced in thermal power plants.
Thermal pollution of the atmosphere can be reduced by using the exhausted steam for other applications. It can be used to run the absorption refrigeration system in summer or to run the heating system in winter.
11. What are the sources of noise pollution in thermal power plants? How it can be reduced?
The sources of noise in a thermal power plant are turbo alternators, fans and power transformers. The noise can be reduced by using sound proofing insulation to the turbine body and piping.
12. Name the thermodynamic cycles used in steam power plants.
1) Carnot cycle
2) Rankine cycle
3) Modified Rankine cycle
13. Why Carnot cycle is not suitable for steam power plants?
1) It is difficult to partially condense the steam.
2) Isothermal heat addition or rejection is difficult.
3) The feed pump has to handle water and steam.
4) The specific volume of steam is more. Hence large size feed pump and more work input is required
14. Classify steam turbines according to the direction of flow of steam.
a) Axial flow turbine
b) Radial flow turbine
c) Tangential flow turbine
d) Mixed flow turbine
15. What are the functions of guide blades in reaction turbines.
1) To change the direction of flow of steam
2) To guide the steam to enter the next moving blade
3) To allow the steam to expand to a higher velocity
16. What is the necessity of compounding?
In simple impulse turbine, the steam is expanded from the boiler pressure to condenser pressure in one stage. Hence, the speed of the rotor becomes very high. Due to the high velocity of steam at the exit of turbine, a considerable amount of kinetic energy is lost. Hence, compouding should be done to reduce the high speed of the rotor and loss of kinetic energy,
17. What is compounding of turbines?
To reduce the high speed of the rotor and loss of kinetic energy, number of blade rings are used in impulse turbines to absorb the kinetic energy of steam. This method of absorbing the jet velocity in stages when the steam flows over moving blades is known as compounding.
18. What are the methods of compounding of impulse steam turbines?
a) Velocity compounding
b) Pressure compounding
c) Pressure – velocity compounding
19. State the difference between velocity compounding and pressure compounding.
- If the velocity of the steam is reduced in stage by stage, then it is called velocity compounding.
- If the pressure of the steam is reduced in stage by stage, then it is called pressure compounding.
20. Differentiate between impulse and reaction turbines.
| Impulse turbine | Reaction turbine | |
| 1 | It consists of moving blades and nozzles | It consists of fixed blades and moving blades, which act as nozzles. |
| 2 | Expansion of steam takes place in stationary nozzle | Expansion of steam takes place in the moving blades |
| 3 | Steam impinges the blades with kinetic energy | Steam passes over the moving blades with pressure and kinetic energy |
| 4 | Steam pressure remains constant when it flows through the moving blades | The pressure reduces gradually |
21. Name any three industrial (special) turbines.
1) Back pressure turbine
2) Bleeder turbine or pass out turbine
3) Exhaust turbine
22. List out the applications of back pressure turbine.
- Chemical industries
- Paper industries
- Textile industries
- Sugar mills, etc.
23. Mention the applications of bleeder (pass out) turbine.
- Paper industries
- Textile dyeing
- Sugar refining, etc.
24. What is the application of exhaust turbine?
Exhaust turbine is mainly used where there are many noncondensing type reciprocating steam engines working intermittently.
25. What is steam condenser?
A steam condenser is a device used to condense the steam by circulating cooling water. The condensed steam is known as condensate.
26. State the advantages of steam condensers.
1) Efficiency of power plant is increased.
2) Steam consumption is reduced for the given output.
3) The condensate is reused as boiler feed water.
27. Name the elements of a steam condensing plant.
1) Condenser
2) Condensate pump
3) Dry air pump
4) Feed pump
5) Cooling water pump
6) Cooling tower
28. List out the different types of jet condensers.
(a) Parallel flow jet condensers
(b) Counter flow jet condensers
(c) Low level jet condensers
(d) High level jet condensers
(e) Ejector jet condensers
29. What are the different types of surface condensers.
(a) Down flow surface condensers
(b) Central flow surface condensers
(c) Single pass surface condensers
(d) Multi pass surface condensers
(e) Evaporative surface condensers
30. List out the merits of jet condensers.
1) Quantity of cooling water required is less.
2) Simple design.
3) Low initial cost.
4) Less space is required.
31. Mention the merits of surface condensers.
1) It maintains high vacuum than jet condensers.
2) It increases the thermal efficiency.
3) Any type of cooling water can be used.
4) Condensate can be reused as feed water directly.
5) Waer supply is not affected by drop in vacuum.
32. Distinguish between jet condensers and surface condensers.
| S.No | Jet condenser | Surface condensers. |
| 1 | Cooling water and steam are mixed together. | Cooling water and steam are not mixed together |
| 2 | It requires less quantity of cooling water. | It requires more quantity of cooling water. |
| 3 | It requires less space. | It requires more space. |
| 4 | More power is required for operating the pumps. | Less power is required for operating the pumps. |
33. What are the sources of air in jet condensers?
1) Exhaust steam from the turbine
2) Leakage of atmospheric air through various joints.
3) Cooling water.
4) Leakage of air through relief valves.
34. Define condenser vacuum.
The pressure existing inside the condenser is always below the atmospheric pressure. This low pressure is referred as condenser vacuum. It is expressed in mm of Hg.
35. Why vacuum is maintained in condenser?
The pressure of exhaust steam from the turbine is very low after expansion. The pressure in the condenser must be lower than the steam pressure so that the steam can easily flow to the condenser and to extract more work from the steam in the turbine. Hence a vacuum is always maintained in the condenser.
36. Define vacuum efficiency.
Vacuum efficiency is defined as the ratio of actual vacuum to maximum possible (ideal) vacuum in a perfect condensing plant.
37. Define condenser efficiency.
Condenser efficiency is defined as the ration of actual rise in temperature of cooling water to the maximum possible rise in temperature of cooling water circulated through the condenser.
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