Steam, geothermal

Table 23.2. Chemical compositions of water and steam discharged from wet-steam geothermal wells in Iceland (Arnorsson et al., 1983)...

Fig. 23.8. Calculated saturation indices (log Q/K) of various minerals for the Reyk-janes 8 wet-steam geothermal well. The well produces from seven intervals at temperatures varying from 274 °C to 292 °C. The calculated saturation indices suggest an equilibrium temperature between about 285 °C and slightly above 300 °C.

Figure 2.22b Dry-steam geothermal power plant without condenser.

Truesdell, A. H., Haizlip, J. R., Armannsson, H. D Amore, F. 1989. Origin and Uansport of chloride in superheated geothermal steam. Geothermics, 18, 295-304. 

The other components present in the direct steam geothermal cycle include ... 

A condenser used to condense turbine exhaust steam. Both direct contact and surface condensers are used in direct steam geothermal power plants. 

Flash steam is the steam produced when the pressure on a geothermal fluid is reduced. A flash steam cycle for a high-temperature liquid-dominated resource is shown in Fig. 5. This dual-flash cycle is typical of most larger flash steam geothermal power plants. Singleflash cycles are frequently selected for smaller facilities. 

Dry Steam Geothermal Plants - Conventional turbine generators are used with the dry steam resources. The steam is used directly, eliminating the need for boilers and boiler fuel that characterizes other steam-power-generating technologies. This technology is limited because dry-steam hydrothermal resources are extremely rare. The Geysers, in California, is the nation s only dry steam field. 

There are two general geothermal resourees, dry (steam) fields and wet (brine) fields. More than 800 MWe is being produeed from sueh dry geothermal steam fields in Northern California. The wet fields usually eannot be used in this manner and Rankine eyele-type systems, ealled binary plants, are being eonsidered at sueh loeations. At the wet fields found in the Imperial Valley of Southern California, the geothermal fluid is a 250°C brine, whieh does not lend itself for use in eonventional steam turbines. 

The flashed steam method is less efficient and its requirements for steam properties—cleanliness, high temperature, and high pressure— are usually unavailable in most geothermal fields. The situation is different with the binary cycle system, which is quite efficient and widely used. This wet system involves the transfer of heat from the hot well stream into a more manageable boiling fluid to generate power through a turboexpander. 

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