Elsevier

Solar Energy

Volume 188, August 2019, Pages 1274-1282
Solar Energy

Experimental parametric study of membrane distillation unit using solar energy

https://doi.org/10.1016/j.solener.2019.07.025Get rights and content

Highlights

  • A sample of the measurements for a sunny day is presented and indicated a high productivity of 15.2 L/h.

  • The unit is very suitable and promising for remote areas in the North African regions.

  • The total amount of distillate gained on that day was about 86 L.

  • A good correlation between the system yield productivity and global solar energy is given.

Abstract

Solar distillation is a promising method for the supply of freshwater to rural communities because water is a vital factor for the survival of humans. Therefore potable water demand is increasing continuously because of the industrial, population and, fast agricultural applications. Nowadays, different techniques for water purification have been created to provide freshwater from salty and polluted water such as solar distillation method to distill brackish/saline water. This work presents an experimental study of the solar membrane distillation unit which is coupled with direct contact membrane (DCMD) which located at Kairouan University. The system is installed as part of a cooperation project research and development between Tunisian Electromechanical Systems Laboratory and German Institute for Solar Energy Systems entitled: Solar driven membrane distillation for resource efficient desalination in remote areas. For the heating of the hot feed water stream, a heat exchanger is included which can be operated with any external heat supply between 60 and 80 °C. For the cooling of the cold feed water stream, no heat exchanger is included. The cooling can be provided over the intake of cold feed water. The effect of solar irradiation and all temperature on the journal productivity of the unit has been presented.

Introduction

Water presents a basic element and a fundamental source of life. However, almost 97% of this resource on Earth is in the ocean, but 3% of all water sources in the world are potable. Less than 1% (of) fresh water is available for drinking and domestic usages (Singh, 2011). Today, potable water consumption is increasing because of the industrial, population and fast agricultural applications. The rapid evolution need for energy has focused attention on some renewable energy resources (Badran and Abu-khader, 2007). The use of solar energy in developing countries presents an important role in the brackish and seawater desalination process (Srithar, 2010, Al Hayek and Bardan, 2004). Solar energy can be used for distillation processes. Membrane distillation is a new membrane technology (Findley, 1967, Gore-Tex, 1982, Carlson, 1983, Schöfield et al., 1987, Andres et al., 1998, Banat et al., 2002). Contrary to membranes for reverse osmosis, MD membranes are hydrophobic. This signifies that up to a limiting pressure the M cannot be wetted by liquid. Thus, according to literature review, there are a lot of investigators who have developed and installed various solar membrane distillations, like, for example, in Spain, The Canary Islands can be considered a test laboratory for different technological desalination innovations of brackish/saline water (Peñate and García-Rodríguez, 2011, Sadhwani and Veza, 2008). Bier and Plantikow (1995) installed a solar-powered membrane distillation (SPMD) using an air–gap membrane distillation module (AGMD) and direct contact membrane distillation module (DCMD). Pilot plant fabricated by Hogan et al. Koschikowski et al. (2003) used a similar MD to that used by Bier et al. without heat storage tank. This unit can produce 150 L/d of freshwater in a southern country in the summer. Thus, according to literature review, the German Institute for Solar Energy Systems (ISE) has been working on the creation of MD modules since 2001 (Raluy et al., 2011, Banat et al., 2006, Cipollina et al., 2009, Rommel et al., 2008, Winter et al., 2011). A lot of experimental work has been studied out in the field of module yield production, investigation and improving (Rommel et al., 2008, Winter et al., 2011, Koschikowski, 2011). MD was first introduced and developed in the literature since 1967. MD is a hybrid process between membrane process and thermal distillation (Mericq et al., 2011, Banat et al., 2006, Cipollina et al., 2009, Rommel et al., 2008, Winter et al., 2011, Koschikowski, 2011, Safavi and Mohammadi, 2009). The MD process uses micro porous hydrophobic membrane for the separation. Fath et al. and Safavi et al. use some types of polymer for MD membrane such as polytetrafluorethylene (PTFE) and polypropylene (PP) (Fath et al., 2008, Safavi and Mohammadi, 2009). MD is classified in four types of configurations such as: vacuum MD (VMD) (Fath et al., 2008) air–gap MD (AGMD), sweeping gas MD (SGMD), and the one that is installed in this unit is direct contact MD (DCMD).

This paper presents an experimental parametric study of solar MD unit under the weather condition in Tunisia. This compact system was installed at Kairouan University and coupled with DCMD.

The newly designed system presented in the current work shows a number of attractive attributes that might open new promising opportunities for the advent of freshwater to environments with limited water resources and high solar irradiation rates. Based on the obtained results, the following conclusions can be drawn:

Indeed, the yield productivity of our unit increases with the decrease of inlet condenser temperature. The separation effect of these polymer membranes is based on their hydrophobic nature. This signifies that up to a certain limiting pressure, the surface tension retains liquid water from entering the pores, but molecular water in the phase of vapor can pass through the membrane.

  • The feed water does not usually need chemical pre-treatment before entering the modules, just a simple pre-filtration

  • The product water quality is practically independent of the feed water salinity.

Section snippets

Design of the system

The apparatus shown in Fig. 1 presents a schematic plan of the MD system. Figs. 2a and 2b illustrate respectively a side and front views photograph of the installed unit. The detailed specification of all components of the solar unit distillation is presented in Table 1. This MD unit has four major components: an MD module (DCMD) that is installed in this unit solar heater, a PV module and feed tank. The MD unit works with PV module for start-up of the pumps and all other electrical devices

Experimental results and discussion:

The measured climatic conditions; ambient temperature and solar radiation for a typical two days in August (summer time) in the City of Kairouan University, Tunisia are presented in Fig. 7, Fig. 8. Those Figs show an hourly variation of solar radiation and ambient temperature for various days (17/08/2017, 19/08/2017 and 01/09/2017). These days are characterized by clear sky conditions. One can observe that the maximum solar radiations that are at 13:00 h for these two experimental days

Economic analysis

The principal objective of the solar MD unit is to minimize the cost production per liter of freshwater. Economic analysis is used to estimate the MD cost because it may be technically very efficient. The economic analysis of the MD is used to show both the payback period of the experimental set up and the cost of the freshwater produced. Table 3 summarizes the cost of each component of the MD. The payback period of the experimental application of the MD unit is affected by the cost of

Conclusion

In this work, a solar membrane distillation coupled to a water collector and PV module was installed, fabricated and experimentally tested during daytime for sunny days (summer time) at the climatic conditions of the City of Kairouan, Tunisia.

The various temperatures like inlet and outlet evaporator temperature, the inlet and outlet condenser temperature, and the distillate flow rate of the unit are recorded by using thermocouples and the data is plotted. The unit is self-operating using a PV

References (25)

  • C. Bier et al.

    Solar powered desalination by membrane distillation

  • L. Carlson

    The new generation in sea water desalination — SU membrane distillation system

    Desalination

    (1983)
  • Cited by (33)

    View all citing articles on Scopus
    View full text