Page 104 - Handbook of Energy Engineering Calculations

FIGURE 26 T-S diagram for multiple reheat stages.

POWER ENERGY OUTPUT ANALYSIS OF MECHANICAL-
DRIVE STEAM TURBINE

Show the effect of turbine engine efficiency on the condition lines of a
turbine having engine efficiencies of 100 (isentropic expansion), 75, 50, 25,
and 0 percent. How much of the available energy is converted to useful work

for each engine efficiency? Sketch the effect of different steam inlet pressures
on the condition line of a single-nozzle turbine at various loads. What is the
available energy, Btu/lb of steam, in a noncondensing steam turbine having
2
an inlet pressure of 1000 lb/in (abs) (6895 kPa) and an exhaust pressure of
2
100 lb/in (gage) (689.5 kPa)? How much work will this turbine perform if
the steam flow rate to it is 1000 lb/s (453.6 kg/s) and the engine efficiency is
40 percent?

Calculation Procedure:

1. Sketch the condition lines on the Mollier chart
Draw on the Mollier chart for steam initial- and exhaust-pressure lines, Fig.
27, and the initial-temperature line. For an isentropic expansion, the entropy
is constant during the expansion, and the engine efficiency = 100 percent.

The expansion or condition line is a vertical trace from h on the initial-
1
pressure line to h , on the exhaust-pressure line. Draw this line as shown in
2
Fig. 27.