Significant Silica Solubility in Geothermal Steam
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 criticus temperature (236 C) in a way previously thought possible only by hot water or wet steam.
- Research Organization:
- D.S.I.R., Wairakei, New Zealand
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AS03-80SF11459; AS07-84ID12529
- OSTI ID:
- 887164
- Report Number(s):
- SGP-TR-93-38; TRN: US200618%%165
- Resource Relation:
- Conference: Proceedings, Eleventh Workshop Geothermal Reservoir Engineering, Stanford University, Stanford, California, January 21-23, 1986
- Country of Publication:
- United States
- Language:
- English
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