Abstract: For equal flows of hot water wells, the electric power which can be generated increases with feed water temperature. However, high temperature wells discharge greater flows than that of lower temperature wells of similar permeability, with the result of enhanced power potential. In fact, where fluids are exploited utilizing two-stage flash, these factors combine to give a power potential which is proportional to the cube of the feed water temperature in degrees celsius. Hence a feed of 315 C would generate twice the power of that of water at 250 C for wells of good permeability and where the reservoir exists under conditions of boiling point with depth. Higher temperature water (exceeding 300 C) has, however, a commensurate higher tendency to mineral deposition in reinjection water lines and this disposes design to single-stage flash with slightly reduced power, compared with the two-stage alternative.

Abstract: Although it is widely believed that silica solubility in low pressure (5 to 10 bar) geothermal steam is negligible, when one takes into account steam flows exceeding 10 million tonnes a year--at Wairakei, for instance--it is found that the amount transmitted in the vapor has the potential to give significant deposits on turbine nozzles and blades. A 150 MWe power station, when based on flows from a hot water reservoir at (a) 250 C or (b) 315 C, and with separator pressures of 6 bar, is found to carry about 100 and 200 kg/year respectively in the steam phase. In the case of a similar sized station exploiting a dry steam reservoir such as The Geysers, equivalent silica flows are obtained, dissolved in steam and carried as dust--the latter as solid particles precipitating from the vapor en route from source to turbine, and not preexisting in the formations as is commonly considered. Choking or coating of subterranean rock near such dry steam wells due to exsolving silica, may be the principal cause of declining steam discharge under production. Silica from completely dry or superheated steam can also seal the cap and sides of steam reservoirs when expanding below the …