Energy efficient multi-effect distillation powered by a solar linear Fresnel collector

Abstract

Solar-driven desalination is a potential solution to the problem of freshwater scarcity in many parts of the world. However, this technology requires considerable efforts to overcome a number of technical challenges such as high-energy consumption, intermittency of solar radiation, and high-water consumption. This paper proposes an optimized multi-effect distillation (MED) process driven by steam at 70 °C and 0.3 bar, which is provided by a linear Fresnel collector. The aim of the proposed integrated system is to reduce the equivalent mechanical energy of the MED process, and utilize the most cost-effective storage system. Moreover, we incorporated an air-cooled condenser instead of a water-cooled condenser, to reduce the water cooling facilities. A computer model was developed using the Engineering Equation Solver tool, to solve the mass and energy balance equations of the integrated system (under different operating conditions). Under the operating conditions of Qatar, the simulation results showed that 1 m2 of solar linear Fresnel collector produces 8.6 m3 of freshwater per year. The equivalent mechanical energy of the optimized MED desalination plant is 8 kWh/m3, which is 59% lower than that of existing commercial MED facilities with thermal vapor compression (19 kWh/m3). This significant reduction in equivalent energy consumption would reduce the required solar field size by 25%. This study also showed that using a water storage system (instead of thermal energy storage) results in a lower total system capital cost. Furthermore, by integrating an air-cooled condenser, the overall plant water consumption reduced by 2 m3 of sea water per m3 of feed water. The performance of the air-cooled condenser can vary by as much as 300% due to fluctuations in dry-bulb temperature and relative humidity.