Thermodynamics analysis of a direct contact membrane distillation with/without heat recovery based on experimental data

Abstract

The objective of this study is to analyze various performance parameters of a direct contact membrane distillation (DCMD) system using energy and exergy analysis based on experimental data. The effect of recovering the heat of the permeate stream exiting from the spiral wound MD module is investigated. The analysis is based on experimental tests for brackish waters. The results indicate the maximum water recovery ratio can reach 6.5% at feed flow rate and temperature of 300 L/h and 80 °C, respectively. The performance ratio is found to be 0.3 kg/MJ and can be increased to 1.15 kg/MJ when heat recovery is activated. The gain output ratio can reach a maximum of 2.7 at 150 L/h and 80 °C with the aid of heat recovery. The effect of feed temperature and flow rate on the system performance indicators has been also investigated. The feed temperature has a significant positive effect on performance parameters such as recovery ratio, performance ratio and energy efficiency mainly when the heat recovery is included. The impact of the feed flow rates on the system performance is marginal in particular when the heat recovery is included. The specific energy consumption (SEC) was also evaluated for the evaporator and condenser streams and the entire MD system as well and found to fall within the ranges given in the literature. The specific exergy consumption when the heat recovery is enabled can become as small as 12 kWh/m3, indicating that the present system has the potential to operate at high energy efficiency after some adjustments and optimization allowing further reduction of the irreversibility sources.