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UST ChE Department

Improving Thermal Efficiency

of the Steam Power Cycles

Summary of Equations

b 2 1Q ( ) H H

c 4 3Q ( ) H H net b c

2 1 4 3

Q ( ) Q + Q

= H H H H

t 3 2W ( ) H H

p 1 4 4 1 4W ( ) H H V (P P )

net T P 3 2 1 4W ( ) W + W = H H H H

net 2 1 4 3 net-W H H H H Q

Summary of Equations (With

Irreversibility of Turbine and Pump)

t 3 2 t 3 2W ( ) H H (H' H )

4 1 4p 1 4

p

V (P P )W ( ) H H

net T P 3 2 1 4W ( ) W + W = H H H H

net 2 1 4 3 net-W H H H H Q

3 3 2H' based on S S

t pturbine efficiency; pump efficiency 1. Increasing Boiler Pressure (Normal Limit

=10 MPa)

2. Increasing Superheated Temperature

(Normal Limit = 600oC)

3. Lowering Condensing Temperature

(Limited by Ambient or Climate

Temperature)

4. Increasing Feedwater Temperature in

stages (Regenerative Cycle)

Increasing Thermal Efficiency

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More Exercises:

1. Recalculate previous example if the

boiler steam is just saturated;

2. Recalculate previous example if the

boiler steam is at 10 MPa, 600oC;

3. Recalculate previous example if the

condenser pressure is at 8 kPa

4. Recalculate previous example if the

boiler steam is at 10 MPa, 600oC and

condenser pressure is at 8 kPa

Solution if Saturated Boiler Steam

Solution if Boiler Steam is at

10 MPa, 600oC Solution if Condenser @ 8 kPa

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Solution if Boiler Steam at 10MPa,

600oC and Condenser @ 8kPa Reheat Rankine Cycle

Reheat Rankine Cycle Reheat Rankine Cycle

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Example Using Reheat Cycle

Resolve the original example if the Reheat Cycle

is used with the superheated steam from the boiler

expanding isentropically to saturated steam in the

first stage turbine, and then reheated before expanding

again isentropically in the second stage turbine to

saturated steam and then passing the condenser

Diagrams

Solution to Reheat Cycle (Saturated

Steam from 2 Turbines)