Page 72 - Handbook of Energy Engineering Calculations

Computing the steam rate and heat rate for the quarter-load points for this
turbine-generator we find:

3. Determine the internal steam rate of the turbine
(c) For the turbine and generator combined, E = 3413/(w )(H − H ), where
k
c
l
e
E = turbine engine efficiency; H = enthalpy of the steam at the condenser;
e
c
other symbols as given earlier. Since, from the steam tables H = 1398 Btu/lb
1
(3257.3 kJ/kg) and H = 912 Btu/lb (2124.9 kJ/kg), then (H − H ) = 486
c
1
c
Btu/lb (1132.4 kJ/kg).
From earlier steps, w = 356,000 lb/h (161,624 kg/h) at full-load; w =
s
s
32,000 lb/h (14,528 kg/h) at no-load. For the full-load range the total change
is 356,000 − 32,000 = 324,000 lb/h (147,096 kg/h). Then, w at 30 percent
s
load = [(32,000) + 0.30(324,000)]/0.30(40,000) = 10.77 lb/kWh (4.88
kg/kWh). Then, E = 3413/(10.77)(486) = 0.652 for combined turbine and
e
generator.
If the internal efficiency of the turbine (not including the friction loss) E ,
i
then E = 2545/(w ) (H − H ). Thus E = E /(turbine mechanical efficiency)
i
e
1
a
i
c
(generator efficiency). Or E = 0.652/(0.99) (0.98) = 0.672. Then, the actual
i
steam rate per horsepower (kW) is w = 2545/(E )(H − H ) = 2545/(0.672)
a
1
i
c
(486) = 7.79 lb/hp (4.74 kg/kW).
Related Calculations. Use this approach to analyze any steam turbine—
utility, industrial, commercial, marine, etc.—to determine the throttle steam
flow and heat rate.