The Effect of Operating Conditions on the Performance of a Vacuum Membrane Distillation Unit Using PES Flat Sheet Membrane

Abstract

The desalination of seawater is considered a promising source of potable water in Egypt. Vacuum Membrane Distillation (VMD) is a new separation technology based on the evaporation of saline water through hydrophobic porous membranes by applying vacuum pressure on the permeate side of the membrane to desalinate brackish or seawater. A lab scale experimental model was constructed and operated using hydrophobic polyethersulfone flat sheet membrane (PES) with effective area of 0.049 m², pore size 0.2-0.4 µm and thickness 120-160 µm. Salt concentration ranging from 5000 ppm to 35000 ppm aqueous NaCl. Resultant permeate flux was measured for the following operating conditions: feed flow temperature (40-50-60-70 °C), flowrate (1-1.2-1.4-1.6 L/min), and vacuum pressure (0.2-0.3-0.4-0.5 Bar). Results showed an increase in permeate flux due to increased temperature, flow rate and vacuum pressure, while it decreased with the increase in salt concentration. The flux value obtained reached 15 kg/m².hr at T= 40°C, vacuum pressure= 0.4 bar, TDS= 5000ppm, and flow rate 1 L/min, while it reached 29 kg/m².hr at  T= 70°C, vacuum pressure= 0.5 bar, TDS= 35,000 ppm, and flow rate 1.6 L/min. Electric power consumed by the system reached 0.612 Kwh at  T=70°C, TDS =5000ppm, vacuum pressure = 0.4 bar, and feed flow rate 1 L/min.

Keywords: VMD, desalination, vacuum pressure, hydrophobic membrane.