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PROPRIETARY MATERIAL.

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2011 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission. 10-41 10-52 A steam power plant operates on an ideal regenerative Rankine cycle with two open feedwater heaters. The net power output of the power plant and the thermal efficiency of the cycle are to be determined. Assumptions

1 Steady operating conditions exist.

2 Kinetic and potential energy changes are negligible. Analysis (a) From the steam tables (Tables A-4, A-5, and A-6), ? ? ? ?? ? kJ/kg

95 .

137 20 .

0 75 .

137 kJ/kg

0 2 .

0 m kPa

1 kJ

1 kPa

5 200 /kg m 0.001005 /kg m

001005 .

0 kJ/kg

75 .

137 in ,

1 2

3 3

1 2

1 in ,

3 kPa

5 @

1 kPa

5 @

1 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? pI pI f f w h h P P w h h v v v ? ? ? ?? ? ? ? ? ?? ? kJ/kg 10.35 m kPa

1 kJ

1 kPa

600 10,000 /kg m 0.001101 /kg m

001101 .

0 kJ/kg

38 .

670 liquid sat. MPa

6 .

0 kJ/kg

13 .

505 42 .

0 71 .

504 kJ/kg 0.42 m kPa

1 kJ

1 kPa

200 600 /kg m 0.001061 /kg m

001061 .

0 kJ/kg

71 .

504 liquid sat. MPa

2 .

0 3

3 5

6 5 in ,

3 MPa

6 .

0 @

5 MPa

6 .

0 @

5 5 in ,

3 4

3 3

3 4

3 in ,

3 MPa

2 .

0 @

3 MPa

2 .

0 @

3 3 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? P P w h h P w h h P P w h h P pIII f f pII pII f f v v v v v v kJ/kg

8 .

2821 MPa

6 .

0 K kJ/kg

9045 .

6 kJ/kg

8 .

3625 C

600 MPa

10 kJ/kg

73 .

680 35 .

10 38 .

670 8

7 8

8 7

7 7

7 in ,

5 6 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? h s s P s h T P w h h pIII ? ?? ? kJ/kg

7 .

2618 6 .

2201 9602 .

0 71 .

504 9602 .

0 5968 .

5 5302 .

1 9045 .

6 MPa

2 .

0 9

9 9

9 7

9 9 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? fg f fg f h x h h s s s x s s P

1 2

10 s T

7 9 0.6 MPa

5 kPa 0.2 MPa

1 - y - z

4 y

3 6

5 8

1 - y

10 MPa

7 8

9 10

1 2

3 4

5 6 Turbine Boiler Condenser fwh I fwh II P I P II P III PROPRIETARY MATERIAL. ?

2011 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission. 10-42 ? ?? ? kJ/kg

0 .

2105 0 .

2423 8119 .

0 75 .

137 8119 .

0 9176 .

7 4762 .

0 9045 .

6 kPa

5 10

10 10

10 7

10 10 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? fg f fg f h x h h s s s x s s P The fraction of steam extracted is determined from the steady-flow energy balance equation applied to the feedwater heaters. Noting that

0 Δpe Δke ? ? ? ? W Q ? ? , FWH-2: ? ? ? ?

5 4

8 5

5 4

4 8

8 out in (steady)

0 out in

1 1

0 h h y yh h m h m h m h m h m E E E E E e e i i system ? ? ? ?? ? ? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? where y is the fraction of steam extracted from the turbine ( ? ? / ? m m

8 5 ). Solving for y,

07133 .

0 13 .

505 8 .

2821 13 .

505 38 .

670 4

8 4

5 ? ? ? ? ? ? ? h h h h y FWH-1: ? ? ? ?

3 2

9 3

3 2

2 9

9 1

1 h y h z y zh h m h m h m h m h m e e i i ? ? ? ? ? ?? ? ? ? ?? ? ? ? ? ? ? ? ? ? where z is the fraction of steam extracted from the turbine ( ? ? / ? m m

9 5 ) at the second stage. Solving for z, ? ? ? ?

1373 .

0 07136 .

0 1

95 .

137 7 .

2618 95 .

137 71 .

504 1

2 9

2 3 ? ? ? ? ? ? ? ? ? y h h h h z Then, ? ?? ? ? ?? ? kJ/kg

2 .

1388 8 .

1556 0 .

2945 kJ/kg 1556.8 137.75 2105.0

1373 .

0 07133 .

0 1

1 kJ/kg

0 .

2945 73 .

680 8 .

3625 out in net

1 10 out

6 7 in ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? q q w h h z y q h h q and ? ?? ? MW 30.5 ? ? ? ? kW

540 ,

30 kJ/kg 1388.2 kg/s

22 net net w m W ? ? (b) The thermal efficiency is 47.1% ? ? ? ? ? kJ/kg 2945.0 kJ/kg 1556.8

1 1 in out th q q ?