Solar-assisted multi-stage vacuum membrane distillation system with heat recovery unit

• Design and performance evaluation of a SMVMD system with HRU and TM scheme
• Development and validation of an integrated theoretical SMVMD model
• Performance evaluation of a multi-stage VMD system for the different numbers of HRUs
• Annual performance evaluation of a SMVMD desalination system

This paper describes the development of a solar-assisted multi-stage vacuum membrane distillation (SMVMD) system. The proposed system employs heat recovery unit (HRU) for the energy recovery from the permeate vapor to the feed seawater. Temperature modulating (TM) scheme is also implemented for the attenuation of temperature fluctuations of the feed seawater. A commercial shell-and-tube capillary membrane module consisting of an array of polypropylene hydrophobic fibers has been adopted for the system design and mathematical model development. The SMVMD system is studied for the different numbers of HRUs using a mathematical model. For a solar-assisted VMD system with 24-stage, the total water production of SMVMD system with 10 HRUs is found to be 3.37 m3/day, which is about 34% higher as compared to the system with a single HRU. For a VMD system without solar-thermal unit, the overall specific thermal energy consumption (OSTEC) decreases by 20% with an increase in the number of HRUs from 1 to 10. For the different numbers of HRUs in the range of 1–10, the system OSTECs with solar-thermal system having 150 m2 of evacuated-tube collectors and 16 m3 seawater storage tanks are 28%–36% lower compared to those without the solar thermal system.