085

= Work output = 2,545 x 100% = 85% Net heat rate 2,994

Net thermal output to process = m (hd - ha)actuai = 20,000 lbm/h (1,129.0 - 180.0) Btu/lbm = 18,980 MBtu/h

Example 3 - Pressure Reducing Valve (Figure 11-48) vs. Back-Pressure Turbine (Figure 11-49)

A. Boiler and PRV Operation

Thermal output to process = m (hc - h) = 20,000 Ibm/h (1,201.7 - 180.0) Btu/lbm = 20,434 MBtu/h

Input to boiler = m h - hb) = 20,000 lbrn/h (1,201J- 1703 Btu/lbm = 24,268 MBtu/h F r]B 0.85

Pc = 250 psig Tc = 406°F hc = 1,201.7 Btu/lbm m = 21,532 lbm/h

Fuel QB 26,127 MBtu/h

Pc = 250 psig Tc = 406°F hc = 1,201.7 Btu/lbm m = 21,532 lbm/h

Fuel QB 26,127 MBtu/h

Usetul Heat To Process

Usetul Heat To Process

Fig. 11-48 PRV Operation.

B. Back-Pressure Steam Turbine Operation

Fig. 11-49 Back-Pressure Turbine Operation vs. PRV.

Net steam input required =

Net input to process with PRV 20,434 MBtu/h

Power output = m (hc - hd)actual- = 21,532 lbrn/h x_727 ^ = 615 hp

2,545 Btu/hp-h

2,545 Btu/hp-h

, ■ , • (hc — hb) 1Ifri„ ,, (1,201.7 —170.3) Btu/lbm ,, Input to boiler = m -— = 21,532 lbm/h ^---—-- = 26,127MBtu/h hB

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