MEDIUM-ENTHALPY GEOTHERMAL ENERGY SYSTEMS: NEW OPPORTUNITIES OF RENEWABLE ENERGY IN CHINA

High enthalpy geothermal fields (>150°C) are present in western China (eg. Yangbajing field in Tibet) and are exploited through steam- or "flash"-type thermoelectric power plants. Many other areas in China show lower, but interesting geothermal gradients, likely due of medium-enthalpy (90° -150° C) fluids at depth that could be exploited through binary cycle, 200 kW to over 30 MW power plants (e.g. in USA, Turkey, Iceland). These use a heat exchanger where the geothermal fluid yields heat to a low-boiling "working fluid" (i.e. Kalina or ORC systems) that operates within a sealed circuit feeding turbines in a saturated steam Rankine or a superheated steam Hirn cycle. Binary cycles systems, based on the total reinjection of all geothermal liquid and non-condensable gases at depth, eliminate any possible environmental pollution. CIRPS Florence Section proposes the evaluation of medium-enthalpy geothermal resources in the Chinese territory and their exploitation by binary cycle thermoelectric plants.