Water productivity enhancement in variable pressure humidification dehumidification (HDH) desalination systems using heat pump

Abstract

Variable pressure humidification dehumidification (VPHDH), humidification compression (HC), and conventional humidification dehumidification (HDH) processes are coupled to a heat pump (HP) for enhancement of their performances and desalination rates. Process simulation of the modified processes reveals the superiority of the proposed VPHDH-HP process to HC-HP, HDH-HP and the conventional HDH processes. Due to the superiority of VPHDH processes over conventional HDH processes, coupling them to HP units as a novel idea improves the desalination rate and energy utilization. The effects of dehumidifier to humidifier pressure ratio (PD/PH), humidifier pressure, and the inlet water to air mass flow rate ratio (w/a) on desalination rate and performance ratio (PR) are studied for the VPHDH-HP process as the superior process. Increasing PD/PH within 2.0 to 3.0 range, leads to an increase in desalination rate by 215%. Increasing w/a from 1.5 to 2.0 increases the desalination rate by 15%, while the same from 2.0 to 3 leads to a 53% decrease in the desalination rate for humidifier pressure of 0.5 bara. A cost analysis yields a water cost of US $4.68/m3 in VPHDH-HP system, indicating its performance superiority against its counterparts.