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Ex/PM40D/26/2008

FINAL B. E. MECHANICAL PART-IIA EXAMINATION, 2008

ENERGY CONVERSION METHODS - A

Time : Three hours Full Marks : 100

Answer Any Five(5) Questions.

Use of Steam Table or Mollier Chart is permitted.

Assume suitable data, if any.

1. a) Sketch and label a shaped steam generator showing all

the heat transfer surface and the air-flue gas path. 15

b) Sketch the pressure distribution of a high pressure coal

fired boiler, that is based on balanced draught. 5

2. A steam generator operates on following condition.

Coal composition (% weight) : Carbon-60.0, Hydrogen- 4.0,

Oxygen-3.0, Nitrogen-2.0, Sulfur-1.5, Moisture-4.5, Ash-25,

GCV-21 MJ/kg.

Other parameters : Moisture in air-0.014 kg/kg of dry air,

Ambient temperature - 30o Backend Temperature - 150o, Sp.

Heat of the flue gas-1.05 kJ/kg K. GCV of carbon-33820 kJ/

kg, Unburnt carbon loss - 20% of GCV of coal. Other losses

- 3%. Excess air - 20%. Determine the boiler efficiency. 20

3. The following data apply to a steam generator with economizer

and air preheater. Steam output 100 t/h, blowdown - 2%, gas

flow - 140 t/h, gas temperature to economizer - 410 oC, gas

temperature leaving airpreheater - 150oC, air flow - 110t/h,

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water temperature to economizer - 210oC water temperature

from economizer - 225oC, air temperature to air preheater -

44oC, heat transfer surface area of economizer - 380 m2, heat

transfer surface area of air preheater - 5000 m2

,. Calculatemaking needed assumptions, (a) the gas temperature leaving

economizer, (b) the air temperature leaving air preheater,

(c) heat transfer co-efficient of both economizer and air

preheater. Take Cp of air and gas as 1.005 and 1.05 kJ/kg K

respectively. 20

4. a) State different methods of controlling temperature of

superheated steam (only name). Describe any one. 3+5

b) What is the fundamental difference between superheater

and reheater ? 4

c) What do you mean by circulation ratio ? What are the

major differences between natural and forced circulation

boilers ? 2+6

5. a) With simple flow diagram how the fundamental difference

between hot PA and cold PA scheme for coal fired boilers.

What are the advantages of cold PA over hot PA ? 6+4

b) With simple sketch show the major components of a ball

& race mill. State advantages of this type of mill. 6+4

6. a) Clearly explain when and why a fluidized bed is called a

bubbling fluidized bed (BFB). What are the advantages and

disadvantages of the bubbles in a BFB ? 6+2

b) How a BFB boiler can be operated at lower load ? 4

c) How fuel feed system is classified for a BFB boiler ?

Briefly describe them. 8

7. a) A power s ta tion has to supply load as follows : 12

Time (in hours) 0-6 6-12 12-14 14-18 18-24

Load (MW) 30 90 60 100 50

Draw load curve and load duration curve. Also calculate

average load and load factor.

b) The input-output relationship for two generating units A

and B of a power plant are as follows :

2A A AI 0 0333P 25P 30= + + and

2B B BI 0 040P 20P= +

40+ where IA, IB are the fuel cost in rupees and PA, PB

are the power output in MW. Determine the economic

loading of the two units when the total load supplied by the

plant is 200 MW. 8

8. Write short note on (any four) on 45 5=20a) Proximate analysis of coal, (b) Air preheater (c)

Electrostatic Precipitator, (d) Mechanical Dust Collector(e) Drum internals (f) HGI, (g) Supercritical boiler.