Combined production of distillated water and cooling by application of Supercritical carbon dioxide refrigeration in multi-effect-desalination systems

Supercritical carbon dioxide refrigeration is a proposed system to provide extremely low temperatures. The waste heat from the gas-cooler is noticeable. So, it can be used as a promising heat source in other systems like multi-effect-desalination system (MED), in order to provide cooling and fresh water, simultaneously; as well as reduction of power consumption. In this paper, the energy analysis and comparison of two novel combined systems are carried out. The combined systems consist of CO2 refrigeration system and two MED's models, the Boosted model and the water preheaters (PH) model. The effect of operating parameters such as evaporator temperature, ambient temperature and compressor outlet pressure on system performances are studied. Results showed that for both combined systems, by decreasing the evaporator temperature or increasing the ambient temperature, the coefficient of performance (COP) and the distilled water flow rate, decreases and increases, respectively. On the other hand, increasing the compressor outlet pressure would increase COP and decrease distilled water flow rate up to an optimum point. Also, MED-Boosted could produce more fresh water compared to MED-PH. In order to decrease the power consumption of the combined system two methods are presented. In two compressors method the COP enhances 6.2% compared to the base system (consists of one compressor and an expansion valve). However, the produced fresh water would be reduced by 60%. On the other hand, the expander method could improve the COP by 23.4%, compared to the base system, while the amount of distillated water decreases less than 8%.