Page 75 - Handbook of Energy Engineering Calculations

(c) Use the relation, ideal steam rate, l = 3413 Btu/kWh/h . Or, l =
w
r
r
3413/419.1 = 8.14 lb/kWh (3.69 kg/kWh).
4. Find the cycle efficiency of the ideal cycle
(d) Cycle efficiency, C = (heat converted into work/heat supplied). Or
e
h /(H − H ); substituting, C = 419.1/(1366 − 130.85) = 0.3393, or 33.9
1
3
w
e
percent.
5. Determine the combined steam rate
(e) The combined steam rate for the actual unit is R = lb steam
c
consumed/kWh generated. Or R = 307,590/29,760 = 10.34 lb/kWh (4.69
c
kg/kWh).

6. Find the combined thermal efficiency of the actual unit
(f) The combined thermal efficiency, TE = 3413/heat supplied. Or TE =
c
c
3413/10.34(H − H ) = 35413/10.34(1366 − 130.85) = 0.267, or 26.7 percent.
3
1
7. Compute the combined engine efficiency
(g) The combined engine efficiency TE /C , or 26.7/33.9 = 0.7876, or 78.76
c
c
percent.

Related Calculations. Use this general procedure to determine the percent
bleed steam, net work of each pound of throttle steam, ideal steam rate, cycle
efficiency, combined thermal efficiency, and combined engine efficiency for

steam-turbine installations in central stations, industrial, municipal, and
marine installations. Any standard set of steam tables and a Mollier chart are
sufficiently accurate for usual design purposes.

STEAM RATE FOR TURBOGENERATOR AT VARIOUS
LOADS

2
A 100-MW turbogenerator is supplied steam at 1250 lb/in (abs) (8612.5
kPa) and 1000°F (537.8°C) with a condenser pressure of 2 in (5.08 cm) Hg
(abs). At rated load, the turbine uses 1,000,000 lb (454,000 kg) of steam per