Performance evaluation of regeneration of high-concentration liquid desiccant using direct contact membrane distillation

Abstract

Membrane-based absorptive dehumidification is an attractive technique for humidity control that reduces energy consumption. The process involves a dehumidifier that absorbs moisture with a liquid desiccant, and a regenerator that concentrates the desiccant solution to complete the process cycle. In this study, a regeneration module employing a membrane distillation (MD) mechanism was developed, and its performance was evaluated theoretically and experimentally. Detailed theoretical investigations demonstrated the impact of the spacer on the convective thermal and material transport at the membrane surface at a high desiccant concentration. The module employs a hydrophobic and microporous composite membrane consisting of a polypropylene support layer and an active layer composed of polytetrafluoroethylene. For all the experiments, the desiccant solution used was an aqueous solution containing 25 wt% of lithium chloride. The transmembrane flux of the regeneration module was evaluated at different feed and permeate flow rates from 0.6 to 1.4 L/min at solution temperatures of 45 to 80 degrees C and a permeate temperature of 25 degrees C. The permeate flux of the regeneration module with the spacer-filled channel increased by more than 50 % compared with that of the empty channel. The regeneration module using spacers achieved a permeate flux ranging from 1.9 to 4.3 kg/m2h during desiccant regeneration at a solution temperature of 50 degrees C.