Experimental study on the performance of integrated adsorption unit for bubble column HDH desalination system

Abstract The two bubble columns, humidifier and dehumidifier, have been introduced as a more efficient humidification-dehumidification (HDH) water desalination system. However, air leaving the dehumidifier is almost saturated, causing a considerable amount of water vapor to be lost. In this study, three identical bubble columns: humidifier, dehumidifier, and adsorber, as an HDH desalination system were constructed and experimentally evaluated. The evaluation parameters include the inlet temperatures of heating and cooling water, the air flow rate inlet to the system, and the freshwater collected by the adsorption unit. The results indicated that HDH process and system performance are significantly improved by increasing the air flow rate and heating water temperature and decreasing the cooling water temperature. Specifically, increasing the heating water temperature from 40 to 65 ºC increased the system productivity by 233%, and the gain output ratio (GOR) by 30%. Increasing the inlet air flow rate from 300 to 900 l/h increased productivity by 247%, and GOR by 81%. Decreasing the cooling water temperature, from 15 to 5 °C, increased the productivity by 100% and GOR by 129%, at 700 l/h air flow rate. Under any operating conditions, the relative humidity of air exiting the dehumidifier was 100% (saturated). Therefore, integrating the adsorption unit increased the productivity by 17% (at a cooling water temperature of 15 °C), and only by 4% (at a cooling water temperature of 5 °C). Accordingly, using an adsorption unit is recommended only when the cooling water temperature is high (e.g., tap water).