Exergoeconomic optimization of a new trigeneration system driven by biogas for power, cooling, and freshwater production

Anaerobic fermentation of crop straw/animal dug can be the most appropriate solution for biomass conversion into applicable renewable energy-based fuels. However, due to the imperfection matching between the biogas combustion process and energy conversion system, a painstakingly design procedure is required to devise high-efficient energy system for capturing biogas efficiently. For this aim, a new trigeneration system driven by biogas is devised for electricity, refrigeration, and potable freshwater generation. The devised system encompasses a gas turbine (GT) cycle, a new cooling/electricity cogeneration system based on organic Rankine cycle (ORC) and ejector cooling cycle (ECC), and a humidification-dehumidification (HDH) unit. To further enhance performance of the devised system, exergoeconomic optimization of the system is concurred. Five working fluids were screened through the new ORC/ECC system and ultimately Toluene was suggested since in the case the overall integrated trigeneration system had the highest refrigeration load of 249.8 kW and trigeneration-based gainoutput-ratio (TGOR) of 0.894 (as the main performance indicators). Using Toluene as refrigerant in the ORC/ECC system, it is found that optimization leads to the increment of the net electricity, refrigeration load, TGOR, and exergy efficiency of around 2.58%, 22.69%, 14.04%, and 13.26%, respectively, while unit cost of trigeneration (UCT) is decreased by 6.71%. Among all elements, combustion chamber is recognized as the highly destructive element by exergy destruction of 771.6 kW, followed by vapor generator with exergy destruction of 221.4 kW. At last, an intensive parametric evaluation of some influential parameters is presented.