Heat exchanger tests with moderately saline geothermal brine

Small-scale tube-in-shell heat exchangers were operated in the Imperial Valley near Heber, California, with geothermal brine containing 14,500 ppM dissolved solids and having a pH of 6.2. Scale deposits were experienced on tube surfaces exposed to the brine during the experiment, which caused the overall heat transfer coefficient to decrease linearly with operating time. The time rate of decline in heat transfer performance increases as the brine was cooled from 350 to 150 F. Scale deposition, indicated by the heat transfer coefficient, is a strong function of the brine temperature level and brine velocity. Brine-side pressure loss in the heat exchanger test unit was not significantly affected by the thin, uniform scale layer observed on tube surfaces exposed to geothermal brine. Chemical cleaning effectively removed the scale layer developed on tube surfaces after continuous exposure to the geothermal brine for 560 hr. Corrosion of the titanium tubes was not observed after the completion of the tests.