Stabilization of Highly Saline Geothermal Brines

Abstract

Summary Severe scaling and plugging in a dual-flash testfacility using hot brine from the Salton Seageothermal resource has impeded the development ofthat resource. A brine treatment process proposed byMagma Power Co. appears to have eliminated theseproblems, making development of a 49-MW dual-flash power plant feasible. Introduction In 1971, San Diego Gas and Electric Co. (SDG and E), acting through its subsidiary, New Albion ResourcesCo., joined with Magma Power Co. to begingeothermal exploration and development at theSalton 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 twopurposes:to determine the technical and economicfeasibility of the flash-binary cycle andtoestablish the capacity and characteristics of theSalton Sea geothermal resource. This informationwas required to ensure design of a reliable, commercial hydrothermal power plant. The facility wasoperated initially as a four-stage flash systemproviding steam to cascading binary heat exchangers. A direct steam turbine cycle did not appear feasiblebecause of the high volume of noncondensable gasesin the brine. Subsequent operation and testing havedemonstrated that instead of 3 wt% thenon-condensable gases compose only about 0.2% of thebrine. As a result, the facility was converted in 1976to a dual-flash parallel flow system with the intent ofgathering information to develop design data for adual-flash direct steam turbine power plant. The brine is characterized as an extremelyhigh-salinity liquid with a total dissolved solids (TDS)concentration greater than 200,000 ppm and issupersaturated with silica and heavy metals. Atypical analysis of this brine is presented in Table 1.The Salton Sea geothermal resource is believed tohave the greatest potential for electric powergeneration of any of the reservoirs in ImperialValley, CA. A preliminary engineering and costanalysis report has been prepared for a 49-MWdual-flash power plant which includes a spent-brinetreatment system utilizing reactor-clarifiers anddual-media gravity filters. The major risk in using the Salton Sea geothermalfluids involves controlling the brine during steamseparation and spent brine injection. Extremescaling at GLEF necessitates plant shutdown afteronly 1,000 hours of operation. Major scalingproblems have occurred in the second-stage flash tank, the atmospheric flash tank, and the associatedpiping and valves. Also, supersaturated silica andsuspended solids in spent brine have caused scalingand plugging of the injection pump casing andinjection well formation. Magma has proposedchanges in previously conceived designs which show potential for reducing brine-handling problems.These changes include (1)a reactor-clarifier andfiltration process to precipitate scaling constituents (mainly silica) and to remove suspended particlesfrom the brine before well injection and (2) seedingof the brine in the flash vessels to reduce scaleformation. JPT P. 727^