Page 338 - Steam Turbines Design, Applications, and Rerating

312 Chapter Fifteen

Figure 15.3 Part load steam rate correction for multivalve,
multistage turbines. (Elliott Company, Jeannette, Pa.)
From the curve, the hp correction is 1.04 and the r/min correction 1.05.
Total correction is 1.04 × 1.05 = 1.09. The part load steam rate is there-
fore 7.40 × 1.09 = 8.06 lb/hph.
Alternatively, the same procedure in metric units: In this example,
Fig. 15.2, an 18,500 kW, 5000 r/min turbine using steam at 40
bar/400°C exhausting to 150 mbar has an approximate efficiency of 77
percent.
Applying this approximate efficiency to the theoretical steam rate
(TSR), Table 14.4, results in a steam rate and steam flow as follows:

TSR = 3.52 kg/(kWh)

Approximate efficiency =η a = 77%

Approximate steam rate (ASR)
= TSR/η a = 3.52/.77 = 4.57 kg/(kWh)

Approximate steam flow = ASR × kW
= 4.57 kg/(kWh) × 18,500 kW = 85,550 kg/h

The Mollier diagram, Fig. 14.2, can be used to determine the TSR for
steam conditions not tabulated. Figure 15.3 can again be used to find
approximate steam rates for turbines operating at part load and speed.