Exergy cost assessment of CSP driven multi-generation schemes: Integrating seawater desalination, refrigeration, and process heat plants

Abstract

An exergy cost assessment of integrated solar multi-generation schemes, which includes cogeneration, trigeneration, and polygeneration schemes, for the joint production of electricity, fresh water, cooling, and process heat, is carried out. This evaluation process allows finding out the key equipment to improve the design, detect potential energy savings, and establish the best configurations of these schemes, in terms of unit exergy cost, total exergy cost, and exergy efficiency. The methodology includes modelling and evaluating the performance of solar multi-generation schemes and stand-alone systems, by applying the symbolic exergoeconomic methodology. The solar multi-generation schemes consider a concentrated solar power as the prime mover, which is coupled to a multi-effect distillation, an absorption refrigeration, and a process heat plant. Twenty-one configurations were investigated, twenty of them regarding solar multi-generation plants: eight of cogeneration, eight of trigeneration, four polygeneration schemes, and the other one considering stand-alone systems. This study reveals that the recommended configurations for the solar multigeneration schemes are those in which the desalination plant replaces the condenser of the power cycle, and the refrigeration plant, as well as the process heat module are coupled to turbine extractions. Furthermore, the main components contributing to the cost formation of electricity are, in this order, solar collectors, evaporator, and reheater. In the case of by-products generated, the main components are dissipative systems, solar collectors, and productive subsystems (multi-effect distillation, refrigeration, and process heat plants). In consequence, they constitute the key equipment that could be improved. Finally, solar multi-generation schemes are more cost effective than stand-alone systems. For instance, the best option within the polygeneration schemes analyzed allowed reducing the unit exergy cost about 6.8%, 59.2%, 45.6%, and 32.2% for electricity, water, cooling, and process heat respectively. Therefore, solar multi-generation schemes are identified as a promising alternative for zones with high irradiation conditions and scarcity of water, where the CSP technology can be the prime mover.