More than 70% of the global population finds its fresh water from aquifers, rivers, and lakes. Global population estimated to approach 9 billion by 2050 and the standard of living of fast developing countries, such as Qatar, increases and the demand for fresh water is increasing dramatically. Qatar is located in an arid region where there is no source of surface fresh water give the very low precipitation per year. Qatar's primary source of fresh water is through seawater desalination. Thermal desalination processes (MSF and MED) and Reverse Osmosis (RO) are highly expensive due to high energy input requirements and high operating costs associated with maintenance and stress induced on the systems in harsh alkaline media. Beside that cost, environmental food print of these desalination techniques are significant; from damaging marine eco-system, to huge land use, to release of tons of GHG and huge carbon footprint. Other less energy consuming techniques based on membrane separation are being sought to reduce both the carbon footprint and operating costs. Membrane Distillation (MD) process involves the evaporation of a hot feed, typically below boiling point of brine at standard conditions, by creating a water vapor pressure difference across the thickness of a porous, hydrophobic membrane. To achieve the objective of this study, state of the art flat-sheet cross-flow DCMD bench scale unit was designed, commissioned, and tested. The objective of this study is to conduct an energy efficiency analysis of DCMD with varied process parameters. Comparison with available literature data is undertaken where appropriate. Energy efficiency analysis showed that, feed flow rate is an important factor and doubling feed flow rate can increase the energy efficiency by about 2 folds. Similarly, increasing feed temperature, increases energy efficiency significantly due to an increase in driving force and hence flux. Effect of concentration and permeate temperature also has been studied and showed increasing these factor cause lead to a decline in energy efficiency. MD has not yet been commercialized and to be practically implemented and feasible, MD should use free and cheap waste energy such as industrial waste heat from flue gas or other sources. Other factors in improving feasibility of MD might be optimization of process conditions, preparation of novel membranes, module configurations as well as spacers support.


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