Modeling of a direct-contact humidification-dehumidification desalination unit in a 256 MW steam power plant using effluent streams: Case study

Abstract

Considering the waste of fresh water in a 256 MW steam power plant located in the southeast of Iran, and to compensate a part of its water consumption, a humidification-dehumidification (HD) desalination system is proposed. Because of sedimentation problems in indirect-contact HD systems, in this research, the application of direct-contact HD method to recover the effluent stream in a steam power plant is presented. Considering unit cross-sectional area for HD towers and based on primary results of the modeling, up to 119 lit/hr can be produced when the height of both humidifier and dehumidifier is 1.8 m and the flow rate of air is 0.7 kg/s. Three different scenarios based on (I) full capacity of available steam from the blowdown of boilers, (II) available chemical effluent (salt water), and (III) available cooling water, are examined and compared in this research. As, required salt water or/and cooling water are much more than the available amounts in the power plant, scenario I and II are rejected. Based on obtained resulted from the scenario III, the cost of production is 0.8 $/m3 of fresh water, and the GOR of proposed HD desalination unit is 1.03. With consumption of less than 5% and 10% of the available steam and salt water in the power plant, respectively, more than 7.5 m3/day of fresh water can be produced by the proposed direct-contact HD desalination system.

Keywords

• Direct-contact HD desalination Unit
• Power plant
• Cooling water
• Energy recovery