Page 114 - Handbook of Energy Engineering Calculations

by 10,160 − 9850 = 310 Btu/kWh (327.1 kJ/kWh). This is a reduction of 3.05
percent.
To determine whether this reduction in heat rate is appreciable, the
carrying charges on the extra heaters, piping, and pumps must be compared
with the reduction in annual fuel costs resulting from the lower heat rate. If

the fuel saving is greater than the carrying charges, the larger number of
heaters can usually be justified. In this case, tripling the number of heaters
would probably increase the carrying charges to a level exceeding the fuel

savings. Therefore, the reduction in heat rate is probably not appreciable.

Related Calculations. Use the procedure given here to compute the actual
heat rate of steam-turbine regenerative cycles for stationary, marine, and
portable installations. Where necessary, use the steps of the previous
procedure to compute the actual heat rate of a straight-condensing cycle

before applying the present procedure. The performance curves given here
are suitable for first approximations in situations where actual performance
curves are unavailable.

REHEAT-REGENERATIVE STEAM-TURBINE HEAT RATES

What are the net and gross heat rates of a 300-kW reheat turbine having an
2
initial steam pressure of 3500 lb/in (gage) (24,132.5 kPa) with initial and
reheat steam temperatures of 1000°F (537.8°C) with 1.5 inHg (5.1 kPa)
absolute backpressure and six stages of regenerative feedwater heating?
2
Compare this heat rate with that of 3500 lb/in (gage) (24,132.5 kPa) 600-
mW cross-compound four-flow turbine with 3600/1800 r/min shafts at a 300-
mW load.

Calculation Procedure:

1. Determine the reheat-regenerative heat rate
2
Enter Fig. 36 at 3500-lb/in (gage) (24,132.5-kPa) initial steam pressure, and
project vertically to the 300-mW capacity net-heat-rate curve. At the left,
read the net heat rate as 7680 Btu/kWh (8102.6 kJ/kWh). On the same
vertical line, read the gross heat rate as 7350 Btu/kWh (7754.7 kJ/kWh). The