Cascading vapour absorption cycle with organic rankine cycle for enhancing geothermal power generation

Abstract

Novel concepts of coupling the absorption cycle to the organic Rankine cycle (ORC) driven by a low temperature geothermal heat source have been evaluated. One option involves the use of an absorption heat transformer (AHT) to upgrade the temperature of the fluid fed to the ORC vaporizer. A second alternative proposes the introduction of a vapour absorption chiller (VAC) to lower the temperature of the fluid fed to the ORC condenser. Computer simulations have been done to predict the performances of the combined cycles (AHT-ORC and ORC-VAC) as well as the conventional ORC. The results indicate that the ORC-VAC presents a promising stance for generating greater power output than the ORC. Although it requires a bigger heat transfer area per unit power output and a relatively larger prime mover, the economic gain in producing large power output can overcome the drawback of higher initial investment. It also has a lower Rankine fluid flow rate than the ORC in the order of 40–70%. Moreover, this option leads to a better exergetic efficiency proving that it can utilize the geothermal heat source to its best potential. On the other hand, the advantages that the AHT-ORC could offer are its smaller turbine size and low Rankine fluid flow rate.