Thermodynamic analysis of adsorption-based desalination cycles

Abstract

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 temperatures of the hot and cooling water which supplies and extracts heat from the silica gel based bed respectively. The result shows that in terms of the energy consumption, 65°C is apparently the optimum for the hot water entering the bed under the study condition. The temperature of the cooling water entering the bed during the adsorption process has significant impact on the both water productivity and energy consumption compared with the effect of hot water temperature. The results also show that silica gel adsorption equilibrium constant (K°I) and FWPR are linearly related, but has little impact on the energy consumption. Furthermore, the paper also discussed the impact of temperature of the evaporator on the thermodynamic cycle when the system is operated as desalinator only.