Page 97 - Handbook of Energy Engineering Calculations

of the turbine = W = ∑W = 102.3 + 97.7 + 115.0 + 100.9 = 415.9 Btu (438.8
e
kJ). The total W = ∑W = W + W + W + W = 4.7 + 1.7 + 0.5 + 0.1 =
p2
p3
p4
p
p
p1
7.0 Btu (7.4 kJ).
Since the station auxiliaries consume 6 percent of W , the auxiliary
e
consumption = 0.6(415.9) = 25.0 Btu (26.4 kJ). Then, net station work w =
415.9 − 7.0 − 25.0 = 383.9 Btu (405.0 kJ).

5. Check the turbine work output
The heat added to the cycle Q Btu/lb = H − H = 1474.5 − 505.5 = 969.0
a
2
1
Btu (1022.3 kJ). The heat rejected from the cycle Q , Btu/lb = (H – H ) (1 –
6′
7
r
m − m – m ) = (938.4 − 47.1) (0.6277) = 559.5 Btu (590.3 kJ). Then W −
1
2
e
3
W = Q − Q = 969.0 – 559.5 − 409.5 Btu (432.0 kJ).
r
a
p
Compare this with W − W computed earlier, or 415.9 − 7.0 = 408.9 Btu
e
p
(431.4 kJ), or a difference of 409.5 − 408.9 = 0.6 Btu (0.63 kJ). This is an
accurate check; the difference of 0.6 Btu (0.63 kJ) comes from errors in
Mollier chart and calculator readings. Assume 408.9 Btu (431.4 kJ) is correct
because it is the lower of the two values.
6. Compute the plant and turbine efficiencies
Plant energy input = Q /e , where e = boiler efficiency. Then plant energy
a b
b
input = 969.0/0.88 = 1101.0 Btu (1161.6 kJ). Plant thermal efficiency =
W/(Q /e ) = 383.9 = 1101.0 = 0.3486. Turbine thermal efficiency = W /Q =
e
a b
a
415.9/969.0 = 0.4292. Plant heat rate = 3413/0.3486 = 9970 Btu/kWh
(10,329.0 kJ/kWh), where 3413 = Btu/kWh. Turbine heat rate = 3413/0.4292
= 7950 Btu/kWh (8387.7 kJ/kWh). Turbine throttle steam rate = (turbine heat

rate)/(H – H ) = 7950/(1474.5 − 505.5) = 8.21 lb/kWh (3.7 kg/kWh).
2
1
Related Calculations. By using the procedures given, the following values

can be computed for any actual steam cycle: engine or turbine efficiency e ;
e
steam enthalpy at the main-condenser inlet; bleed-steam flow to a feedwater
heater; turbine or engine work output per section; total turbine or engine

work output; station auxiliary power consumption; net station work output;
plant energy input; plant thermal efficiency; turbine or engine thermal
efficiency; plant heat rate; turbine or engine heat rate; turbine throttle heat