An innovative closed-air closed-desiccant HDH system to extract water from the air: A case for zero-brine discharge system

Abstract

In a conventional HDH system, a constant feed of seawater is required to run the system. As a result of extracting freshwater from the saline water, it is rejected at higher salinity, thus it cannot be recirculated as a feed again. The aim of this study is to come up with a zero-brine discharge system that eliminates the continuous need for the supply of source and sink in the conventional system. Based on the fact that earth's atmosphere holds a vast amount of water that can be considered as a reliable freshwater resource, especially in coastal areas. A water-from-air system is proposed in this study. The proposed system configuration comprises of two parts, a basic HDH system that uses a liquid desiccant solution instead of saline water and a desiccant-based air dryer. The liquid desiccant leaves the HDH part at a higher concentration due to the extraction of freshwater. It then enters the air dryer where it is diluted by absorbing water vapor from the ambient air. This diluted desiccant is directed to the HDH part to close the desiccant loop. In this study, Lithium chloride is used as the working fluid of the proposed system. Mathematical modeling of heat and mass transfer processes between the air and desiccant in the humidifier and dehumidifier is developed to predict the performance of the desalination system. The proposed system produces about 8 kg of freshwater per hour.