Binary Cycle Plant Design for Water-Dominated, Low Enthalpy Geothermal System

Abstract

Binary cycle technology allows the exploitation and development of low to medium temperature geothermal resources (i.e. 80 -180°C) at economically viable scales. The Bath geothermal reservoir in eastern Jamaica is located in the Blue Mountain Inlier (BMI) which undergoes tectonic uplift. Na-Cl-SO4-type waters discharge from an aerially-exposed and fissured suite of basalts, gabbros, and deep marine sedimentary deposits at temperatures of 51.3°C to 52°C. Reservoir temperatures estimated from a recent hydrogeochemical investigation and geothermometric analyses range from 82°C and 223°C. The minimal depth of circulation for the Bath hot springs-south (BTHS) water sample is 2.80 km based on the Truesdell (1977) silica geothermometer. The power potential estimated for the Bath geothermal reservoir ranges from of ≈28– 170 MWt assuming an average geothermal gradient of 30°C/km for the Caribbean region and reservoir temperatures estimated at 82-120°C. Cl/SO4 vs. Li/B ion ratios suggest the existence of a shallow, more accessible low enthalpy geothermal reservoir that warrants exploration drilling and resource development. Suggestions for the design and optimization of a 5 MWe geothermal binary power plant utilizing Organic Rankine Cycle (ORC) technology are proposed for future geothermal energy production from the reservoir.