Stabilization of Highly Saline Geothermal Brines
- John L. Featherstone (Magma Power Co.) | Douglas R. Powell (Morrison-Knudsen Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 1981
- Document Type
- Journal Paper
- 727 - 734
- 1981. Society of Petroleum Engineers
- 4.3.4 Scale, 5.9.2 Geothermal Resources, 4.1.2 Separation and Treating, 5.2.1 Phase Behavior and PVT Measurements, 4.1.6 Compressors, Engines and Turbines, 4.1.5 Processing Equipment, 5.6.4 Drillstem/Well Testing, 4.2.3 Materials and Corrosion
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Severe scaling and plugging in a dual-flash test facility using hot brine from the Salton Sea geothermal resource has impeded the development of that resource. A brine treatment process proposed by Magma Power Co. appears to have eliminated these problems, making development of a 49-MW dual-flash power plant feasible.
In 1971, San Diego Gas and Electric Co. (SDG and E), acting through its subsidiary, New Albion Resources Co., joined with Magma Power Co. to begin geothermal exploration and development at the Salton Sea geothermal resource near Niland, CA. Subsequent geothermal discoveries and encouraging well-flow tests led to construction of the U.S. DOE/SDG and E geothermal Loop Experimental Facility (GLEF) on the resource.
GLEF was developed initially to serve two purposes: (1) to determine the technical and economic feasibility of the flash-binary cycle and (2)to establish the capacity and characteristics of the Salton Sea geothermal resource. This information was required to ensure design of a reliable, commercial hydrothermal power plant. The facility was operated initially as a four-stage flash system providing steam to cascading binary heat exchangers. A direct steam turbine cycle did not appear feasible because of the high volume of noncondensable gases in the brine. Subsequent operation and testing have demonstrated that instead of 3 wt% the non-condensable gases compose only about 0.2% of the brine. As a result, the facility was converted in 1976 to a dual-flash parallel flow system with the intent of gathering information to develop design data for a dual-flash direct steam turbine power plant.
The brine is characterized as an extremely high-salinity liquid with a total dissolved solids (TDS) concentration greater than 200,000 ppm and is supersaturated with silica and heavy metals. A typical analysis of this brine is presented in Table 1. The Salton Sea geothermal resource is believed to have the greatest potential for electric power generation of any of the reservoirs in Imperial Valley, CA. A preliminary engineering and cost analysis report has been prepared for a 49-MW dual-flash power plant which includes a spent-brine treatment system utilizing reactor-clarifiers and dual-media gravity filters.
The major risk in using the Salton Sea geothermal fluids involves controlling the brine during steam separation and spent brine injection. Extreme scaling at GLEF necessitates plant shutdown after only 1,000 hours of operation. Major scaling problems have occurred in the second-stage flash tank, the atmospheric flash tank, and the associated piping and valves. Also, supersaturated silica and suspended solids in spent brine have caused scaling and plugging of the injection pump casing and injection well formation. Magma has proposed changes in previously conceived designs which show potential for reducing brine-handling problems. These changes include (1)a reactor-clarifier and filtration process to precipitate scaling constituents (mainly silica) and to remove suspended particles from the brine before well injection and (2) seeding of the brine in the flash vessels to reduce scale formation.
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