Page 268 - Handbook of Energy Engineering Calculations

indicated. An intersection to the left of the FBP line indicates that some of the
steam to the brine heater is bypassed around the turbine regardless of the
cycle used. Since the intersection in Fig. 6 occurs to the right of the FBP line,
either an extraction or multishaft type of cycle could be used. The final
choice of a cycle would depend on the water output required.

Related Calculations. The data presented here were developed by W. H.
Comtois, Westinghouse Electric Corp., and were reported in Mechanical
Engineering. Studies made at Westinghouse show that:

1. The fixed-annual-charge rate exerts the greatest single influence on water

cost, increasing the cost by about two-thirds for a factor of 2 increase in the
rate. This effect is moderated somewhat for large plant sizes.

2. The plant load factor gives the expected result of decreasing product costs
with increasing load factor. The effect is a 1 to 2 percent decrease
(increase) for every percentage increase (decrease) in load factor in the

range from 75 to 95 percent.

3. Plant design life is of little consequence in the range normally considered
(30 to 40 years).

4. The range of maximum brine temperatures studied was 200 to 250°F (93.3
to 121.1°C). Without exception, the computed optimum brine temperature

was 250°F (121.1°C).

5. The single-shaft cycles (backpressure or extraction) enjoy a small (5 to 10
percent) water cost advantage over the multishaft cycle.