Page 374 - Handbook of Energy Engineering Calculations

Figures 2 and 3 show a schematic and T-S diagram of a vapor-dominated
power system. Dry steam from the well (1) at perhaps 400°F (200°C) is used.
It is nearly saturated at the bottom of the well and may have a shut-off
pressure up to 500 psia (∼35 bar). Pressure drops through the well causing it
to slightly superheat at the well head (2). The pressure there rarely exceeds

100 psia (∼7 bar). It then goes through a centrifugal separation to remove
particulate matter and enters the turbine after an additional pressure drop (3).
Processes 1-2 and 2-3 are essentially throttling processes with constant

enthalpy. The steam expands through the turbine and enters the condenser at
(4):
Because turbine flow is not returned to the cycle but reinjected back into
the earth (Mother Nature is our boiler), a direct-contact condenser of the
barometric or low-level type may be used. Direct-contact condensers are

more effective and less expensive than surface-type condensers. (The latter,
however, are used in some new units with H S removal systems, below.) The
2
turbine exhaust steam at (4) mixes with the cooling water (7) that comes from
a cooling tower. The mixture of 7 and 4 is saturated water (5) that is pumped
to the cooling tower (6). The greater part of the cooled water at 7 is
recirculated to the condenser. The balance, which would normally be returned

to the cycle in a conventional plant, is reinjected into the ground either before
or after the cooling tower. The mass-flow rate of the reinjected water is less
than that originating from the well because of losses in the centrifugal
separator, steam-jet ejector (SJE), evaporation, drift and blow-down in the

cooling tower, and other losses. No makeup water is necessary.
A relatively large SJE is used to rid the condenser of the relatively large
content of noncondensable gases and to minimize their corrosive effect on the
condensate system.

This procedure and the data and illustrations presented in Related
Calculations are the work of M. M. El-Wakil, as presented in his book
Powerplant Technology, McGraw-Hill, 1984. At the time of publication he
was Professor of Mechanical and Nuclear Engineering at the University of

Wisconsin.

GEOTHERMAL AND BIOMASS POWER-GENERATION

ANALYSES