Cleaner Engineering and Technology (Apr 2023)
Experimental and numerical investigation of a solar-thermal humidification-dehumidification desalination plant for a coastal greenhouse
Abstract
Meeting the water demand for agriculture is considered one of the most crucial challenges societies face worldwide. Seawater greenhouses are a promising irrigation water source for locations where it is necessary to source freshwater from saline groundwater or seawater. Coupled with hybrid humidification-dehumidification (HDH) plants, powered by solar-thermal collectors, they can provide valuable freshwater using a free and accessible energy resource. Compared to conventional desalination systems, they can reduce emissions associated with desalination, have lower operational and maintenance costs, and are more suitable for deployment in remote areas. In this work, an experimental and numerical study of a solar-powered HDH desalination system in a seawater greenhouse is presented, considering an open-air/open-water (OAOW) cycle. In addition to the development of a thermodynamic model of the plant, a pilot plant consisting of a full-scale greenhouse for crop production, a HDH unit, 15 solar-thermal collectors, a firebox hot water boiler and two spiral coil heat exchangers was constructed and field-tested in Bushehr, Iran, under real meteorological conditions. The freshwater production of the pilot plant approached 2000 L per day. Thanks to an optimised hydroponic irrigation system, which reduced irrigation water consumption to approximately 1000 L per day, the greenhouse was self-sufficient in terms of water consumption and generated a freshwater surplus. In the experimental work, where the hot water temperature at the humidifier inlet was limited to 70 °C to prevent fouling, a maximum gain output ratio (GOR) of 2.3 was achieved. The computational model was validated and found to be in good agreement with experimental data, with GOR predictions to within a maximum deviation of 25 %. The model was then used for parametric performance studies beyond the limits of the experimental arrangement. A maximum GOR of 3.2 was achieved at a humidifier inlet temperature of 80 °C. Results from this study demonstrate that solar-powered HDH seawater greenhouses can provide a cost-effective solution to water desalination in hot and dry coastal locations.
