The exergo-economic analysis of two novel combined ejector heat pump/humidification-dehumidification desalination systems

Abstract

Two novel integrated cycles including ejector heat pump (EJR-HP)/humidification-dehumidification (HDH) desalination were investigated. The first scheme (EJR-single) uses the rejected heat of the HP condenser for heating both seawater and dry air streams of the HDH cycle. In the second scheme (EJR-double), the condenser rejected heat only heats the air, and the system includes double HDH units that use the rejected brine of the first HDH as the feed sweater of the second unit. Based on the results, the novel EJR cycles have better exergy efficiency (ηex), gained output ratio (GOR), and lower fresh water cost (COW) over the base cycle without EJR. Moreover, the GOR and ηex of the EJR-double cycle (7.10, 1.1%, respectively) are 1.88% and 12.45% higher than the EJR-single cycle, respectively. However, the electricity consumption of the EJR-single cycle is higher than the other EJR cycle due to higher pumping power. Due to the higher investment costs of the EJR-double scheme, the COW was obtained as 5.33 $/m3 which is slightly higher than that of the EJR-single cycle (5.18 $/m3). The increase of dehumidifier effectiveness (εdh) from 0.87 to 0.97 decreases the COW of the first and second schemes to 4.20 $/m3 and 4.30 $/m3, respectively.