Novel structures of direct contact membrane distillation for brackish water desalination using distributed feed flow

Abstract

The productivity enhancement of a single threshold membrane distillation (MD) module is sought via distributed feed arrangement. The threshold module is 15 m long with a total feed flow rate of 1500 kg/h taken as a reference case study. Two redistributed feed structures were proposed, tested, and compared to the reference case study. For a fair comparison, the sum of the distributed feed branches equals the total feed flow rate of 1500 kg/h. The first structure resembles multi-stage short MD units in series such that the sum of the surface area of the individual stages is equal to that of the threshold module. The second structure uses the same threshold module but is divided into several sections at which the redistributed feeds are injected. The purpose of the distributed feeds for both structures is to boost the temperature of the interstage/section brine. The first structure managed to enhance productivity by 10 % due to temperature boosting and the fact that shorter modules produce higher water flux. The second structure failed to even maintain the productivity of the reference case. The reduced feed flow and the variable cold/hot flow rate ratios deteriorated the overall productivity of the second structure.