Technoeconomic assessment of indirect-contact HDH desalination unit driven by boiler blowdown of steam power plant

Abstract

Humidification and dehumidification (HDH) desalination units compared with the other thermal desalination systems have relative advantages due to working under ambient pressure and low temperatures and are more attractive. In this research, the application of an HDH desalination unit with indirect-contact of air and water streams in a steam power plant is investigated. To increase the energy efficiency of the system, a closed air cycle has been considered. Also, by application of the closed water cycle in the humidifier, the recovery rate of the desalination unit increases according to the concentration of discharge flow. The flow rate of boilers blowdown in the studied steam power plant is around 2.2 kg/s and can be used as a unique source of required thermal energy in the desalination system to produce freshwater from power plant chemical effluents. On the basis of the available cooling water (30 m³/day), this stream is considered as the limiting flow in the modeling. The detailed design of different parts of the desalination unit, including the humidification tower, condensers, wet air circulation fans, the required pumps, and the heat exchanger, is presented in this study. The maximum production of freshwater and the minimum energy intensity are obtained for the circulating air flow rate of 4 kg/s. By 14% recovery of lost steam in the power plant, 20.8 m³/h of desalinated water is produced. The gain output ratio and the energy intensity of the system are 1.025 and 2201 kJ/L, respectively. The production cost with the proposed indirect-constant HDH system is equal to 0.56 $/m³ of freshwater.