Techno-economic evaluation of novel combinations of reverse osmosis with absorption and HDH desalination systems for energy utilization and sustainability

Abstract

Reverse osmosis (RO) is a widely used technology for water desalination nowadays, owing to its high water production. However, it suffers from high consumption of high-grade energy and the generation of large amounts of high-concentration brine, which is harmful to the environment. This study provided an innovative solar-powered hybrid desalination plant that integrates RO, an absorption (AB) desalination-cooling system, and a humidification-dehumidification (HDH) system for mitigating water shortage, optimizing energy utilization, and reducing carbon emissions. The rejected brine from the RO system is treated further by passing it through the AB and HDH desalination systems to produce additional fresh water and treat the rejected brine. In addition, the feed RO brine is passed through the absorber before entering the HDH system, which eliminates a separate heat source to preheat the fluid entering heat the fluid filling the humidifier. In this study, two configurations of hybrid systems were proposed and compared. In the first configuration (RO-AB-HDH), a simultaneous drinking water and cooling effect (from the AB system) can be obtained. In the second configuration, an energy recovery scheme is used between the condenser and evaporator (HR) of the AB to enhance the evaporation rate and the water production rate. Numerical models were developed to simulate and evaluate the performance and economic viability of the proposed systems for various operating conditions. Results showed that the proposed hybrid systems significantly improve the quality and quantity of desalinated water, as well as reduce the cost of freshwater, compared to the stand-alone RO cycle. For instance, the product freshwater salinity obtained by the proposed systems is decreased by 63 %, compared to the RO system for an applied pressure of 70 bar and feed salinity of 50,000 ppm. The first configuration is the most cost-effective at a high salinity of 45,000–50,000 ppm when the system is driven by solar energy with 2.2 $/m³ with an additional free-cooling effect of 17.6 kW at 85 °C. The second configuration is more effective when only a large amount of desalinated fresh water is needed.