Week 1

Question 1

Give facts about steam turbines

Answer 1

-Efficiency=40%
-High specific work ratio
-Can utilise any fuel

Question 2

Give facts about gas turbines

Answer 2

-Low efficiency=20%
-Low specific work ratio
-Utilise gas and fuel only

Question 3

Advantages of steam turbines

Answer 3

-Doesn’t use fuel directly
-Very efficient

Question 4

Disadvantages of steam turbines

Answer 4

Slow start up (preheating required)

Question 5

Advantages of gas turbines

Answer 5

-High flexibility (quick start-up and high performance)
-Available in large range of sizes

Question 6

Disadvantages of gas turbines

Answer 6

-Requires high energy fuel
-Low efficiency

Question 7

How can efficiency of gas turbine be increased

Answer 7

-Use exhaust gas to heat air entering combustion chamber.
-Use exhaust gas to form steam for steam cycle (Combined gas and steam)
-Use exhaust to produce hot water for heating (CHP)

Question 8

Explain scheme A combined gas and steam

Answer 8

Steam and gas cycle are independent processes. If unfired boiler is used, low cost plant is possible. Efficiency= 40%

Question 9

Explain scheme B combined gas and steam

Answer 9

Combustion chamber not required (for gas cycle) as air is combusted in boiler then sent to gas turbine. Increases efficiency to 59%

Question 10

Explain the difference between a fired and unfired boiler

Answer 10

Fired (fuel supplied).
Unfired (no added fuel).

Question 11

Advantages of CHP

Answer 11

-Increased efficiency
-Reduces fuel combustion (less pollution)
-Reduces operating cost.
-Increases jobs

Question 12

Explain pass-out arrangement of steam turbine

Answer 12

Steam used at intermediate temp + pressure. Ideal heat to power ratio= 3:1

Question 13

Explain back pressure arrangement of steam turbine

Answer 13

Controller used to control pressure to meet heat demand (Eg higher demand=higher pressure). Ideal heat to power ratio= 9:1

Question 14

What is the ideal heat to power ratio for a gas turbine

Answer 14

3:1

Question 15

What is trigeneration

Answer 15

Heat, power and cooling produced simultaneously.

Question 17

What are the advantages to tri-generation

Answer 17

-Fuel cuts
-Emission reduction
-Increased reliability of supply

Question 18

What technologies are required for trigeneration

Answer 18

-CHP plant to produce electricity and heat
-Heat powered cooling system eg-absorption or adsorption system

Question 19

Explain how the refrigeration cycle works

Answer 19

1) Evaporator: Extracts heat from environment.
2) Compressor: Increases pressure
3) Condenser: Rejects heat to surroundings
4) Expansion valve: Reduces pressure

Operates in a cycle

Question 20

What is absorption

Answer 20

Chemical substance that pumps refrigerant is in liquid phase. More efficient than adsorption. Eg- Lithium bromide/water

Question 21

What is adsorption

Answer 21

Chemical substance that pumps refrigerant is in solid phase.Eg- Silica gel/water

Question 22

Explain the absorption cooling cyle

Answer 22

Chemical (eg-lithium bromide solution) circulated form one container to other.
Absorbs gas on cool side, releases on hot side.

Question 23

Explain the adsorption cooling cycle

Answer 23

Adsorbent packed in beds.
Bed is called adsorber when connected to the evaporator, absorbs refrigerant vapour.
Bed is called desorber when connected to condenser and is heat to generate refrigerant vapour at high pressure.

Question 24

Adsorption vs absorption

Answer 24

Absorption- requires pump to circulate solution (power consumption)

Adsorption- more complex valve control system, more tolerance to vibration, more bulky (hence more expensive).