Development and evaluation of an integrated MED/membrane desalination system

Abstract

Driving the thermal desalination system by waste heat is typically proposed to save utilized energy and mitigate environmental impact. However, to evaluate the performance of desalination unit, it is necessary to define the exergy efficiency correctly to reveal the real source of irreversibilities. In this regard, a geothermal-based system combined with seawater desalination units to produce distillated water, cooling, power and hydrogen is developed and analyzed thermodynamically. To identify the major extent of generated entropy in multi-effect-desalination (MED) and direct-contact membrane-distillation (DCMD), in addition to exergy destructed in the system's components, the temperature disequilibrium and chemical disequilibrium are taken into account. The present results indicate that the desalination integrated system is capable of producing more than 165,600 kg freshwater per day. Also, under the specific operating conditions, the membrane evaporation efficiency, mass flux through the hydrophobic permeate in DCMD and GOR in MED can be achieved to 46.2%, 9.8 × 10−6 m/s and 5.6, respectively. As well as, the condenser in MED and membrane module in DCMD are the most exergy destructive elements. For MED condenser, it is owned to the large cooling water flow rate and for DCMD, membrane structure like thickness and pore size and also conduction loss are the main reasons of irreversibilities.