Page 174 - Steam Turbines Design, Applications, and Rerating

Governors and Control Systems 153

Figure 8.10 Extraction diagram. (Elliott Company, Jeannette, Pa.)

steam). The extraction lines show the total inlet steam flow for various
horsepower loads when the flow indicated is extracted. Thus, 32,500 hp
with an extraction flow to the extraction line of 250,000 lb/h would
require a total flow of 350,000 lb/h. By indulging in some “kitchen
arithmetic,” exhaust flow is obtained as the difference between total
flow and extraction flow, that is, 100,000 lb/h.
At 16,000 hp the 250,000-lb/h line terminates in the total extraction
line, and at 12,500 hp there is no 250,000-lb/h extraction line. The story
as told by the chart is that if the process needs 250,000 lb/h of steam,
the turbine must be loaded to at least 16,000 hp. At 12,500 hp the tur-
bine will give 200,000 lb/h for extraction flow, and if 250,000 lb/h is
required, an additional 50,000 lb/h must be supplied by a reducing
valve in the steam header system or by another source.