Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy...
Reexamination Certificate
1999-05-14
2003-03-25
Redding, David A. (Department: 1744)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
C435S262500, C423S027000, C423S028000, C423S335000, C423S340000, C423SDIG001
Reexamination Certificate
active
06537796
ABSTRACT:
The invention relates to a process for treatment of geothermal residue to produce commercially useful products such as silica from the geothermal waste and to reduce the amount of regulated and non-regulated waste resulting from geothermal power production.
BACKGROUND OF THE INVENTION
Geothermal energy is a major clean energy resource. However, large scale production of energy using geothermal sources produces considerable amounts of waste in the from of residual brine and sludge. The sludge contains solids which precipitate out during the power generation process and the sludge can be highly concentrated in a variety of metal salts, many of them toxic. The sludge also contains a large proportion of silica. High disposal costs and the long-term liability associated with hazardous waste disposal are a continuing problem in the production of geothermal energy. Even if the toxic metals are removed, the sludge still requires expensive disposal. The United States Congress has enacted legislation to oversee the disposal of solid and hazardous wastes (Resource Conservation and Recovery Act (RCRA), 42 U.S.C. Sections 6921 et seq.) A major objective of the RCRA was to provide assistance to state and local governments for the management of hazardous waste. The State of California has an even more stringent hazardous waste control law. Regulations were established for the handling, processing, use, storage, and disposal of hazardous wastes.
Examples of important geothermal sites are located in California, including the Geysers in Sonoma and Lake Counties north of San Francisco and the Imperial Valley of Southern California and geothermal waste is carefully regulated by the state. Geothermal waste determined to be hazardous must be disposed of at a Class I or Class II site. Discharges of nonhazardous waste will generally be at Class III sites. Disposal of regulated waste in all the classes, particularly in Classes I and II, is quite expensive. It would therefore be advantageous to convert geothermal waste to nonhazardous and even useful products.
Geothermal fluids can include steam and hot saline solutions ranging upward to concentrated brines. These fluids can contain exceptional concentrations of dissolved solids including NaCl, KCl, silica, and metals, also hydrogen sulfide. Concentrated brines can also contain appreciable levels of heavy metals, metal salts and oxides of metals such as iron, manganese, lead, zinc, cadmium, molybdenum, thallium, chromium, titanium, antimony, nickel, bismuth, tin, arsenic, antimony and mercury and radionuclides such as radium. Silver and gold may also be present. Wastewaters or condensates from geothermal plants are often reinjected through disposal wells. However, silica and carbonate depositions can cause blockages in rock fissures necessitating chemical processing of brines before reinjection to remove these materials. Solid waste materials from geothermal plants present even more difficult problems.
The technology used to convert geothermal resources to electricity include vapor-dominated (steam) systems and liquid-dominated (hot water) systems. Vapor-dominated systems are easier to exploit for the generation of electricity because steam can be directly expanded in a low pressure turbine. However, liquid-dominated systems are more readily available. The brine from a liquid-dominated system is usually flashed, i.e., abruptly reduced in pressure, to produce steam which is then used to drive a turbine. On cooling of hot geothermal fluids, a sludge is produced which is considered a mixed waste and therefore subject to regulatory constraints. Mixed waste containing heavy metals or radionuclides requires expensive disposal in a hazardous waste site. Processing of low salinity liquids also produces a chemical residue the disposal of which is regulated. The former is associated with Salton Sea type brines and the latter is associated with the Geyser type steam condensates. Brines from the Salton Sea geothermal area in California may contain total dissolved solids up to 350,000 ppm. In other areas such as the Geysers, the major contaminants are more likely arsenic and mercury.
Geothermal power plants generate waste during well drilling and plant operation. Well drilling waste includes drilling muds, brines and residue. Operational waste includes steam condensate and sludge from condensate cooling towers and hydrogen sulfide abatement systems. The sludge is dewatered resulting in a filter cake. All of this results in large volume of both non-regulated waste and hazardous waste which requires safe disposal.
U.S. Pat. No. 5,305,607 describes a method and apparatus for separating silica from scale in a geothermal power plant using silica seed particles and mechanical means based on viscosity. Before the silica separation, metallic sulfides and other hazardous materials are first precipitated in flash crystallizers. The silica filter cake is intended for simple sanitary refuse disposal.
U.S. Pat. No. 5,098,578 describes a method for precipitating a metal from spent geothermal brine by admixing the geothermal brine with steam condensate. The method stabilizes the scale-forming constituents, identified as compounds of silica and calcium, and these are disposed of in an injection well.
U.S. Pat. No. 4,437,995 describes a method for treating geothermal brines to control the precipitation of silica. A sulfate-rich liquid is introduced into residual geothermal brine to react with barium, calcium and/or lead salts to produce a colloidal suspension which accelerates the precipitation of silica from the brine. The product is a silica plus heavy metal sulfate-rich sludge. Although the cleansed brine can be pumped into an injection well, the sludge would require toxic waste disposal.
Inventors herein have suggested the desirability of treating geothermal byproducts to produce commercially acceptable silica products, e.g., Premuzic et al., “Recent Advances in Biochemical Technology for the Processing of Geothermal Byproducts”, BNL 62901, April 1996; Premuzic et al., Geothermal Brines and Sludges: A New Resource”, BNL 61972, June 1995. However, the recovery of commercially valuable products is only generally mentioned in these publications without any details or specifics of how the recovery might be accomplished.
It is an object of this invention to convert geothermal wastes into non-toxic disposable materials. It is a further object of this invention to convert geothermal wastes into commercially useful products.
SUMMARY OF THE INVENTION
Commercially useful amorphous silica can be obtained by at least once contacting geothermal residue with a depigmenting reagent under depigmenting conditions to produce a mixture comprising depigmented amorphous silica-containing solids and pigment-containing depigmenting reagent liquid. The solids and liquid can be separated from each other to yield amorphous silica product. Before or after the contacting, the geothermal residue or the depigmented amorphous silica-containing solids can be subjected to treatment with a metal salts solubilizing agent to detoxify the geothermal residue by removing metals. The silica product can be neutralized and then dried at a temperature from about 25° C. to about 300° C. The geothermal residue most advantageously processed is a geothermal waste generated after heat extraction in the plant which contains silica and metal salts.
In one embodiment, geothermal residue is first treated with a metal salts solubilizing agent, the contacting producing a first product which includes a) pigmented amorphous silica-containing components and b) solubilized metal-containing components. The metals which are preferably solubilized and removed are toxic metals which require hazardous waste deposition such as heavy metals and radionuclides. For example, in the State of California, regulated toxic metals include antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, lead, mercury, molybdenum, nickel, selenium, silver, thallium, vanadium and zinc.
Components a) and b) are separated from each other. Compone
Lin Mow S.
Premuzic Eugene T.
Bogosian Margaret C.
Brookhaven Science Associates LLC
Redding David A.
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