Joule heating membrane distillation enhancement with multi-level thermal concentration and heat recovery

Abstract

Self-heating membrane distillation process (MD) uses solar and electrical energy to directly heat a composite membrane for seawater desalination, has obvious advantages in terms of cost and energy consumption. However, there has been minimal research concerning the independent power supply for joule heating MD and desalination performance remains unsatisfactory. In this work, the thermal management measures of multi-level thermal concentration and multi-level heat recovery device were used in combination to improve the MD process. A tri-layer superhydrophobic composite membrane having good joule thermal conversion was prepared and its electrochemical impedance performance was analyzed. Joule heating MD experiments revealed that the multi-level thermal concentration could improve the MD performance, and reduce the membrane cost, due to the nonlinear relation of vapor transport and thermal concentration. The use of a multi-level heat recovery device further enhanced MD performance through recycling the energy from the condensing process. A highest freshwater obtained was approximately 2.77 kg m-2h−1 with energy consumption 0.36 kW h kg−1 and 99.9% salt removal. This highly efficient joule heating MD process could be combined with other MD processes to enhance freshwater productivity and reduce energy consumption, and could also lead to further development and applications of the MD process.