Examples Based on 600 Psig 750F Superheated Steam

Examples 4 through 6, which are illustrated in Figures 11 -50 through 11 -53, are based on the following conditions:

Inlet condition (hc)

Exhaust condition (hd) (condensing example)

Exhaust condition (hd) (back-pressure examples) Turbine efficiency (nj) Turbine efficiency (nj) Boiler efficiency (nB) Steam (mass) flow (ni) Condensate (ha) Condensate (ha) Makeup water Boiler feedwater (hb)

600 psig, 750°F — (1,380 Btu/lbm) 3 in. HgA (918 Btu/lbm — ideal)

70% (condensing example) 50% (back-pressure examples) 85%

40,000 lbm/h

83 Btu/lbm (condensing example) 180 Btu/lbm (back-pressure examples) 6% (18 Btu/lbm)

79 Btu/lbm (condensing example) 170 Btu/lbm (back-pressure examples)

Note:

In these examples, enthalpy per lbm of steam is rounded to the nearest Btu and cycle efficiencies include consideration of makeup water requirements. Footnotes listed under previous examples (1 through 3) based on operation with 250-psig steam apply to these examples (4 through 6) as well.

Example 4: Condensing Steam Turbine (Figure 11-50) A. Ideal Rankine Cycle

Ideal heat drop = hc - hd = 1,380 - 918 = 462 Btu/lbm

_ 2,545 Btu/hp-h 2,545 Btu/hp-h r ri ,, . TWR = _-_-_ = _-_ = 5.51 lbm/hp-h

Heat ate = TWR (hc - hb) = (5.51 lbm/hp-h) (U80 - 79) Btu/lbm = 8,434 Btu/hp-h nB 0.85

_ (hc- hd) ,, „, 462 Btu/lbm ^ 0 _ , Power output = m - = (40,000 lbm/h)- = 7,260 hp

Fig. 11-50 Condensing Turbine Operation.

B. Actual Conditions

Actual heat drop = (hc- hd)actud = Vt^c- hd)ideal = 0.70(1,380 - 918) = 323 Btu/lbm

Actual hd = hc - rjT (hc - h^i^i = 1,380 - 323 = 1,057 Btu/lbm

2,545 Btu/hp-h 2,545 Btu/hp-h ^ nn „ ,, , AWR = _-_-_ = _-_ = 7.88 lbm/hp-h

(hc- hd)actual 323 Btu/lbm

Heat rate = AWR (h - hb) = 7.88 lbm/hp-h 1,301 Btu/lbm = 12,061 Btu/hp-h % 0.85

Power output = m^ (h - hd)ideal = (40,000 lbm/h x 0.70) 462 Btu/lbm = 5,083 hp 2,545 Btu/hp-h 2,545 Btu/hp-h

Condenser Duty (P) = m (hd - ha)iutuuli = 40,000 lbm/h (1,057- 83) Btu/lbm = 38,960 MBtu/h

Example 5 - Back-Pressure Steam Turbine (Figure 11-51) A. Ideal Rankine Cycle rith =

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Renewable Energy 101

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