Concentrated solar power plant integrated with direct-contact membrane distillation system: Concept, simulation, performance, and economic evaluation

Abstract

Freshwater is an essential component for life, and its demand is increasing worldwide as population continues to grow. Although 75% of the earth’s surface is covered with water; however, a large portion of the water is saline. Desalination powered by renewable energy sources is considered to be a very promising way to cope with the growing demand of freshwater and corresponding energy requirements while mitigating environmental pollution. This dissertation presents an investigation on concentrated solar power (CSP) plant integrated with direct contact membrane distillation (DCMD) system for energy and freshwater production, respectively. Both the technologies were synergized by using seawater as cooling fluid in the condenser of the power plant, and then utilizing heated seawater from the condenser into the DCMD system. The ultimate objective of this dissertation is concept description, simulation, performance, and economic evaluation of CSP plants integrated with DCMD system. Three CSP plants, including parabolic trough (PT), solar power tower (SPT), and linear Fresnel reflector (LFR), were considered for assessments. The investigations of CSP plants were performed by utilizing System Advisor Model (SAM) software for the weather conditions of Abu Dhabi, United Arab Emirates. Whereas the investigations of DCMD system were carried out by solving DCMD mathematical model in MATLAB® software. The mathematical model was validated with the experimental data. A decent agreement was observed between the model results and experimental data. The main investigated variable for CSP plants was direct normal irradiance (DNI). Whereas investigated variables for DCMD system include inlet temperatures, flow rates, and concentration. The performance of CSP plant was evaluated in terms of electricity production, capacity factor, and gross-to-net conversion factor. Whereas performance of DCMD system was evaluated in terms of evaporation efficiency (EE), specific thermal energy consumption (STEC), and freshwater production. Moreover, economic evaluation of CSP plant and DCMD system was presented in levelized cost of energy (LCOE) and water production cost (WPC), respectively. The simulation results revealed that increase in the DNI increases the electricity production. The maximum and minimum electricity generation was achieved in summer and winter, respectively. Specifically, SPT plant produced maximum electricity with a highest capacity factor. In contrast, the LCOE of PT plant was lowest. The sensitivity analysis revealed that the solar multiple and solar field cost considerably affect performance of the CSP plant and LCOE, respectively. For DCMD system, increase in feed temperature from 30 °C to 45 °C exponentially increased the permeate flux from 5.19 kg/m2·h to 20.05 kg/m2·h. In addition, increase in flow rates increased the permeate flux and vice versa for permeate temperature and feed concertation. However, the influence of increasing feed temperature was prominent compared to the other operating conditions. Furthermore, an increase in feed temperature from 30 ºC to 45 ºC increased the EE from 39.2% to 54.98% and reduced STEC from 1865 kWh/m3 to 1330 kWh/m3, respectively. Average freshwater production by CSP plant integrated with DCMD system was found to be 36.79 m3/day with a WPC of 0.33 USD/m3. Specifically, PT plant integrated with DCMD system produced maximum freshwater. In contrast, the WPC of SPT plant integrated with DCMD system was lowest. Adequate electricity and freshwater production indicated that the performance of CSP plants integrated with DCMD system is quite satisfactory. In addition, low LCOE and WPC revealed economic feasibility of the proposed system. Therefore, integration of DCMD system with CSP plant could be a very promising way to cope with the growing demand of freshwater and corresponding energy requirements while mitigating environmental pollution.