Design of a seawater desalination unit working with solar energy

Abstract

Solar thermal energy for membrane distillation desalination is a green and safe way for areas where water scarcity and solar irradiance are strongly correlated. In the desalination field, the membrane distillation (MD) is a new process of producing distilled water that has been developed and tested in recent years. In this thesis, the main studies include: (1) Effective study of operating parameters on the AGMD module for desalination. (2) Simulation and controlling study of the solar AGMD system small scale. (3) Development and optimization study of the solar AGMD system small scale. (4) Experimental, simulation and economic Study of the solar AGMD system large scale. - The first study presents the effect of the operating temperatures and the flow rates on the distillate flux that can obtain from a hydrophobic membrane having the characteristics: pore size of 0.15 µm; thickness of 130 µm; and 85% porosity. The new approach in the present numerical modeling has allowed examining effects of the nature of materials (Polyvinylidene fluoride (PVDF) polymers, copolymers and blends) used on thermal properties. The obtained results found that, copolymer P(VDF-TrFE) (80/20) is more effective than the other materials of membrane distillation (MD). The mass flux and efficiency reach 193.5 (g/m²s), and 83.29 % using turbulent flow and an effective area 3.1 m², respectively. - The second study presents the integrated single cassette AGMD module in the solar thermal desalination system which is validated and numerically simulated with the TRNSYS program. This model is studied to be ideal for obtaining a distilled water flow rate of 5.5 kg/h at different times under changing climatic conditions throughout the year in Ain-Temouchent weather, Algeria. Therefore, the energy needed is calculated for the auxiliary heater and is replaced by 10 photovoltaic panels, each one has an area of 1.6 m² using three of the energy storage batteries (12V, 100Ah) with 1.5 KW. It was found that when the inlet temperature of AGMD reaches 85 °C, the distilled water flow from the distillation membrane reaches 5.5 kg /h and that remains stable on different days throughout the year by relying solely on solar energy. - The third study presents a numerical study to investigate the solar AGMD system for seawater desalination. The solar MD system includes both flat plate collectors and photovoltaic panels with a total membrane area of AGMD: 0.2 m². Therefore, the photovoltaic system with the energy storage batteries (12V, 100Ah) is used to power electrically the pumps and sensors. It was found that the solar AGMD system is used for the production of 3-5 L/h of distilled water flow. Besides, the brine that contains the high salt concentration is completely dispensed with this process. In addition, the energy efficiency of the AGMD module and the collector efficiency values reach 68 % and 74 % respectively. - The fourth study presents an experimental study of the performance of a multi-channel spiral-wound AGMD module with an area 14.4 m² was carried out on a commercial scale. The lab-scale AGMD desalination pilot plant was driven by solar energy using the flat plate (FPC) and evacuated tube collectors (ETC) installed in Port-Said City, Egypt. The results showed that the permeate flux of AGMD with ETCs was 18.81%–30.44% higher than FPCs, and its cost was 22.48% lower. The STEC of the AGMD system ranged from 158.83 kWh/m3 to 346.55 kWh/m3. The maximum GOR reaches 4.4 at 52 °C, depending on the feed inlet temperature. The thermal efficiency of the air gap membrane distillation system is 72%. The proposed AGMD system produced 28.78 m3/year of fresh drinking water at a cost of USD 14.73/m3 with remarkable reducing in carbon dioxide emissions by 7,274.45 kg/year.