Thermodynamic Analysis of Adsorption-based Desalination Cycles

Adsorption-based desalination (AD) is attracting increasing attention because of its ability to use low-grade thermal energy to co-generate fresh water and cooling. In this paper, a thermodynamic model has been developed in order to study the factors that influence the fresh water production rate (FWPR) and energy consumption of silica gel based AD system. Water adsorption on the silica gel is modelled using a Langmuir isotherm and the factors studied are the silica gel adsorption equilibrium constant, and the heating and cooling water temperatures, which supply and remove heat from the silica gel respectively. The result shows that in terms of the energy consumption, a heating water temperature of 65oC is optimal for the conditions studied here. The cooling water temperature has far more significant impact on the both water productivity and energy consumption compared to the heating water temperature. The results also show that silica gel adsorption equilibrium constant, whilst related to the FWPR in a linear manner, has little impact on the energy consumption. The paper also discusses the impact of evaporator temperature on the thermodynamic cycle when the system is operated in desalination mode only.