Numerical and experimental investigation of membrane distillation flux and energy efficiency

Abstract

While the field of desalination has matured for seawater desalination and similar applications, other markets such as the treatment of high salinity feed streams require novel technological innovations. This thesis considers membrane distillation (MD), one of the relatively less studied desalination technologies. The energy efficiency of MD in the sweeping gas (SGMD) configuration along with a multi-tray bubble column dehumidifer is analyzed and compared to other conventional configurations. The single stage SGMD systems studied have relatively low GOR (approximately 2-3) compared to other MD systems. The system mass flow rates and top and bottom temperatures together define optimal operating points of the system. An experimental apparatus designed to analyze scaling and fouling in MD is described in detail along with a discussion of the practical challenges faced and their solutions. Experiments are conducted at various feed temperatures, flow rates and salinities ,and a numerical model of heat and mass transport in MD is validated. MD can treat feed solutions at very high salinities (200 ppt) and still produce extremely pure permeate with salinity less than 0.1 ppt. The experimental apparatus is also used to study the effect of module inclination angle on Air Gap MD flux performance and these results compared with theoretical predictions to determine the optimal orientation of the AGMD apparatus.