Solar powered membrane distillation for seawater desalination

Abstract

This thesis presents an investigation into the performance of a Membrane Distillation (MD) system used for seawater desalination. The research is focused on the effects of intermittent use of the MD module when powered with a solar energy collector. The aim is to assess the feasibility of directly powering an MD unit with a fluctuating input from a solar collector. An investigation into the effect of temperature on the microstructure of the membrane was carried out. In a series of experiments, samples of PTFE membrane were imaged while heated from 17 C to temperatures between 60 C and 80 C. It was found that the membrane pore size increased with increases in temperature. When heated to 80 C the pore diameter increased by 44%. Intermittent use of the system would cause the temperature of the MD module to fluctuate, therefore altering the membrane microstructure. An investigation was carried out to determine the in fluence of intermittent MD operation on the flux and conductivity of the distillate. The system was tested after overnight shutdown periods and was also tested with short term `on/off' periods of between 5 and 20 minutes, simulating the intermittent output from a concentrated solar collector. It was found that as the module was heated, the distillate flux produced increased, while the distillate conductivity decreased. Conversely, when the module cooled, the

flux decreased and the quality of the distillate worsened. This was the result of the dependancy of membrane pore size on temperature.