Three-objective optimization of water desalination systems based on the double-stage absorption heat transformers

A new type of double-stage absorption heat transformer integrated with water desalination system is proposed and compared with four other types of absorption heat transformers i.e. a conventional type of double-stage and three different types of double-effect absorption heat transformers from the viewpoint of exergoeconomics, using Engineering Equation Solver software. Considering product unit cost, exergy coefficient of performance and mass flow rate of distilled water as objective functions, a three-objective optimization is performed to specify the optimal design point for all studied systems. The temperatures of evaporator, condenser, absorber and absorbing evaporator (low-pressure absorber for double-stage absorption heat transformers) are considered as decision variables and the related Pareto Fronts are plotted for all the studied cycles. The results show that the maximum gross temperature lift in the proposed type of double-stage absorption heat transformers is about 18-27% higher than that in other considered systems. Therefore, its evaporator temperature can be risen by up to about 120 °C. It is also observed that, under optimized conditions, the exergy coefficient of performance however, is found to be the highest for the type in which there is no split for the absorber inlet an exit streams (type 3).