oa Field testing of membrane distillation for desalination of brines discharge from thermal plants

Membrane Distillation (MD) is a hybrid thermal-membrane process that produces a high quality distillate from concentrated brine. It utilizes either low grade waste heat or solar energy to generate a vapor pressure difference across a hydrophobic membrane. A consortium composed of ConocoPhillips - Global Water Sustainability Center (GWSC), Qatar University (QU) and Qatar Electricity & Water Company (QEWC), was formed to conduct a pilot testing program to assess the suitability of MD at pilot scale to treat brines from thermal desalination plants. This research project aims toward ensuring a sustainable water supply in Qatar, one of the twelve grand research challenges identified recently by Qatar National Research Strategy (QNRS). This presentation summarizes the outcomes of the project including the most relevant conclusions and findings from the field testing program. Bids from the five leading MD technology providers were evaluated and the two most suitable technologies for Qatar environment were selected: a vacuum multi-effect MD unit from memsys in Germany and a single stage air gap MD unit from Xzero in Sweden. Initially, hydraulic testing was conducted at QU and then the pilots were relocated to the QEWC power/desalination plant at Ras Abu Fontas to operate under field conditions. Globally, this is the first study that benchmark MD technologies side by side at pilot scale. The performance of the MD pilot units was evaluated under different operating conditions (temperature, flowrate and feed salinity up to 70,000 mg/L TDS) with the objective of maximizing water production and lowering operational costs. The product stream was of distilled water quality (TDS < 10 ppm), independent of feed salinity. Typical flux values of 5 - 6 LMH were obtained at feed / cooling temperatures of 70oC / 20oC. Results also showed that pretreatment plays an important role on system performance. An important outcome of the project was related to the energy efficiency of the systems. Detailed energy balance showed that a multi-effect design significantly improves energy efficiency. The multi effect system has a performance ratio of 3.0, which was 3 times higher than the single stage system. The projected outcome of the testing program includes: * Sustainable augmentation of water production in Qatar * Reduction of environmental impact * Capacity building in Qatar