Solid Waste Problems in Geothermal Operations

Abstract

Abstract The solid waste generated in geothermal operations is not limited to silica as often assumed. The silica by itself does not cause unsurmountable solid waste problems. However, numerous other solids coprecipitating with the silica cause major problems in many high temperature liquid-dominated fields. Depending upon (a) reservoir temperature, (b) reservoir fluid composition, (c) thermodynamics of steam and gas flashing, (d) types of flash and brine treatment facilities and, finally, (e) field operating conditions numerous other solids can be formed at various locations within the field and power plant. Thus, there exists a rather complex relation between the various field parameters and the types and amounts of the various solids. Solid waste disposal and/or utilization problems are further complicated by the relationships between the formation of scale, i.e., solid deposits adhering to the hardware, and suspended solids to be removed in the various brine treatment facilities prior to reinjection of the heat-depleted brine. All these complex relationships are explained in this paper by using the rough data from the MCR Mercer 2 field experiments published by DOE/DGE in 1981 and 1982. Approximately 2000 lbs. of a solid, rather impure iron hydroxychloride plus numerous other solid metal compounds are formed from the fluids per well and day. If these solids are comingled with substantial amounts of amorphous silica, a rather severe waste disposal and/or solid utilization problem becomes evident. At present, this set of problems seems to be the major hurdle for the development of numerous fields. The technical, economical and environmental problems regarding waste utilization and/or waste disposal are described. Solutions to these problems are far from being available. It is judged that presently developed processes will not solve the rather evident solid waste problems. The only alternative seems to be a combination of mineral recovery and waste disposal processes. This also hampered by numerous technical, economical and environmental problems as shown in the paper.