Page 77 - Handbook of Energy Engineering Calculations

An industrial turbogenerator operates on the reheating-regenerative cycle

with one reheat and one regenerative feedwater heater. Throttle steam at 400
2
lb/in (abs) (2756 kPa) and 700°F (371°C) is used. Exhaust is at 2 in (5.1 cm)
2
Hg (abs). Steam is taken from the turbine at a pressure of 63 lb/in (abs) (434
kPa) for both reheating and feedwater heating. Reheat is to 700°F (371°C).
For the ideal turbine working under these conditions, find: (a) percentage of
throttle steam bled for feedwater heating, (b) heat converted to work per

pound (kg) of throttle steam, (c) heat supplied per pound (kg) of throttle
steam, (d) ideal thermal efficiency, (e) T-S, temperature-entropy, diagram and
layout of cycle.

Calculation Procedure:

1. Determine the cycle enthalpies, pressures, and entropies
Using standard steam tables and a Mollier chart, draw the cycle and T-S plot,

2
Fig. 12a and b. Then, P = 400 lb/in (abs) (2756 kPa); t − 700°F (371°C);
1
1
H = 1362.3 Btu/lb (3174 kJ/kg); S = 1.6396; H = 1178 Btu/lb (2745
1
2
1
kJ/kg); H = 1380.1 Btu/lb (3216 kJ/kg); S = 1.8543.
g
g

FIGURE 12 (a) Cycle diagram. (b) T-S diagram for cycle in (a).

(a) Percent throttle steam bled = (H − H )/(H − H ) = (196.15/1107.9) =
5
5
6
2
0.1771, or 17.71 percent.