Page 343 - Steam Turbines Design, Applications, and Rerating

Elliott Shortcut Selection Method for Steam Turbines 317

Alternatively, using a TSR table:
TSR = 28.08 lb/kWh

Using the basic definition of TSR:
3413 3413
ΔH = h 1 − h 2 = = = 121.5 Btu/lb
TSR 28.08
From Example 15.2, the optimum isentropic heat drop per Rateau stage =
58.0 Btu/lb
121.5
Approximate stages required = = 2.1 (thermodynamically)
58.0
The turbine will require two Rateau stages.
Assuming 80 percent stage efficiency:

121.5 × 0.80 = 97.2 Btu/lb
1305.7 − 97.2 = 1208.5 Btu/lb

Example 15.4: Curtis and Rateau staging Conditions: 1500 psig (1515 psia),
950°F, exhaust pressure 150 psig (165 psia). Find the number of 35-in-diameter
Rateau stages required, at 5000 r/min, when using one 25-in-diameter Curtis
stage, assuming optimum stage efficiencies. (See Fig. 15.8.)

(a) (b)
Figure 15.8 Isentropic heat drop and end points for Curtis and Rateau staging.
(Elliott Company, Jeannette, Pa.)