Techno-Economic and Environmental Assessment of Solar-Driven Hybrid Adsorption Desalination-HDH Using Silica...

This study explores a solar-driven hybrid desalination approach developed for Saudi Arabian climatic conditions, combining adsorption desalination (AD) based on a silica gel/CaCl₂ composite with an ejector (EJ) and a HDH system. The proposed integration aims to enhance vapor utilization and reuse condenser heat to generate additional distillate. Two operating modes are examined, including a productivity-focused strategy that activates evaporator/condenser heat recovery (HR) when cooling is not required. Compared to raw silica gel (SG), the composite adsorbent improves adsorption cycle performance, raising the COP from about 0.38-0.43 to 0.55-0.63, and increasing SCP from roughly 130-240 W/kg to 320-675 W/kg. Without HR, the full AD-EJ-HDH system achieves SDWP of 52-100 m³/ton·day with GOR of 2.40-2.75 over the year. In HR-enabled operation, SDWP increases to 81-140 m³/ton·day and GOR rises to 2.7-2.95, reflecting stronger internal heat reuse and improved vapor management. Techno-economic results show that the solar-driven unit cost for AD-EJ-HDH decreases from winter values (2.7-2.9 $/m³) to a minimum around June (1.53 $/m³), while waste heat operation reduces the cost further to 0.49 $/m³ in June (rising to ~0.76-0.80 $/m³ in winter). With HR, the full AD-HR-EJ-HDH reaches around 1.44 $/m³ (solar, June) and 0.38-0.40 $/m³ (waste heat, summer), confirming the advantage of desalination-focused HR operation when cooling is not required. Finally, compared with SWRO, the AD-HR-EJ-HDH configuration delivers an approximately 90% lower carbon footprint on the same environmental assessment basis. The study highlights the environmental benefit of the intensified SG/CaCl₂ hybrid configuration.