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

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. © 2015 Elsevier B.V. All rights reserved.

Solar-assisted multi-stage VMD (SMVMD) desalination system with the heat recovery and temperature modulating units has been designed and its performance has been evaluated with a developed rigorous mathematical model. Total water production of 24-stage SMVMD desalination 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. Without the solarthermal system, the overall specific thermal energy consumption (OSTEC) of the system with 10 HRUs decreases by 20% as compared to the system with a single HRU. It is observed that the installation of the HRU for each VMD stage does not necessarily improve the water production rate. For the different numbers of HRUs in the range of 1–10, the system OSTECs with the solar-thermal system having 150 m2 of evacuatedtube collectors and 16 m3 seawater storage tanks are 28%–36% lower as compared to those without the solar thermal system. Here, the annual solar fraction and collector efficiency of the 24-stage SMVMD system with the 10 HRUs are found to be 0.92 and 0.54, respectively.