Page 376 - Handbook of Energy Engineering Calculations

and private-sector R&D programs have effectively overcome most of these
problems. Currently, there are more than 35 commercial plants exploiting
liquid-dominated resources. Of the 800 MW of power generated by these
plants, 620 MW is produced by flash-type plants and 180 MW by binary-
cycle units (Fig. 4).

FIGURE 4 Energy from hot-water geothermal resources is
converted by either a flash-type or binary-cycle plant (power)

The flashed-steam plant is best suited for liquid-dominated resources
above 350°F (177°C). For lower-temperature sources, binary systems are

usually more economical.
In flash-type plants, steam is produced by dropping the pressure of hot
brine, causing it to “flash.” The flashed steam is then expanded through a
conventional steam turbine to produce power. In binary-cycle plants, the hot

brine is directed through a heat exchanger to vaporize a secondary fluid
which has a relatively low boiling point. This working fluid is then used to
generate power in a closed-loop Rankine-cycle system. Because they use
lower-temperature brines than flash-type plants, binary units (Fig. 4) are

inherently more complex, less efficient, and have higher capital equipment
costs.
In both types of plants the spent brine is pumped down a well and
reinjected into the resource field. This is done for two reasons: (1) to dispose

of the brine—which can be mineral-laden and deemed hazardous by