Page 78 - Handbook of Energy Engineering Calculations

2. Find the amount of heat converted to work per pound (kg) of throttle
steam
(b) The amount of heat converted to work per pound (kg) of throttle steam =
(H − H ) + (1 − 0.1771) (H − H ) = 467.3 Btu/lb (1088.8 kJ/kg).
g
1
4
2
3. Compute the heat supplied per pound (kg) of throttle steam
(c) The heat supplied per pound (kg) of throttle steam = (H − H ) + (H −
6
g
1
H ) = 1299.1 Btu/lb (3026.9 kJ/kg).
2
4. Determine the ideal thermal efficiency
(d) The ideal thermal efficiency = [heat recovered per pound (kg) of throttle

steam]/[heat supplied per pound (kg) of throttle steam] = 467.3/1299.13 =
0.3597, or 35.97 percent. The T-S diagram and cycle layout can be drawn as
shown in Fig. 12a and b.

Related Calculations. This general procedure can be used for any turbine

cycle where reheating and feedwater heating are part of the design. Note that
the enthalpy and entropy values read from the Mollier chart, or interpolated
from the steam tables, may differ slightly from those given here. This is to be
expected where judgment comes into play. The slight differences are
unimportant in the analysis of the cycle.

The procedure outlined here is valid for industrial, utility, commercial, and
marine turbines used to produce power.

REHEAT-REGENERATIVE CYCLE STEAM RATE

2
Steam is supplied at 600 lb/in (abs) (4134 kPa) and 740°F (393°C) to a
steam turbine operating on the reheat-regenerative cycle. After expanding to
2
100 lb/in (abs) (689 kPa), the steam is reheated to 700°F (371°C). Expansion
2
2
then continues to 10 lb/in (abs) (68.9 kPa) but at 30 lb/in (abs) (207 kPa)
some steam is extracted for feedwater heating in a direct-contact heater.
Assuming ideal operation with no losses, find: (a) steam extracted as a
percentage of steam supplied to the throttle. (b) steam rate in pounds (kg) per
kWh; (c) thermal efficiency of the turbine; (d) quality or superheat of the