Performance of a novel open double absorption heat transformer for freshwater

A recent alternative to obtain freshwater is the open single absorption heat transformer, which can produce freshwater at different points of the thermodynamic cycle with free energy (residual or renewable). To date, few studies on open single-absorption heat transformers with a distillation system have been reported in the literature. The use of an Open Double Absorption Heat Transformer (advanced cycle) used to desalinate water by single-effect evaporation is proposed for the first time to give continuity to this research field. The aim is to analyse the energy and exergy performance by using the first and second laws of thermodynamics, as well as its cost-effectiveness to determine its economic feasibility. The distillation system is coupled to the absorber at high pressure to remove useful heat, which is used in the evaporation process at medium pressure to obtain a part of the distilled water, while another part is obtained in the condenser at low pressure. This arrangement can distil water up to 1.634 kg/s (77.2 % is extracted at low pressure and temperature in the condenser, and 22.8 % at medium temperature and pressure in the evaporator). In comparison with a Closed Double Absorption Heat Transformer, this proposed coupling produces up to 2.57 times more distilled water (1.297 kg/s), a performance ratio of 3.38 times more (1.15), and a coefficient of operation of 1.83 times more (0.55), and from the exergy point of view, the evaporator presents the highest irreversibility of 36.6 % (205.6 kW), while the absorber/evaporator reaches the best exergy efficiency (0.91) with a high investment cost (34 % of total investment), considering an absorber temperature of 170 °C, and absorber/evaporator temperature of 130 °C. With respect to cost-effectiveness, the payback is 5.7 years with a projection of a useful life of 25 years using a flux relation in the absorber/evaporator of 13.08 and a flux relation in the absorber of 8.14.