Membrane distillation configurations

Islam (2005) wrote a masters thesis on the purification of water contaminated by As, using the HVR (house-hold water purifier) system developed by the Swedish HVR Water Purification AB Company. The system includes a heated feed tank, a membrane module equipped with two flat membranes (total membrane area, 0.2 m ) and a water chiller. The membrane distillation configuration investigated was that with the air gap (1 mm thick) at the permeate side. 

Direct-Contact Membrane Distillation Configuration If the mean free path of the transported molecules is large in comparison with the membrane pore size (i.e., Kn > 1 or dp < X.,)> the molecule-pore wall collisions are dominant over the molecule-molecule collisions, and the Knudsen type of flow is responsible for mass transfer through the membrane pore. In this case the permeability through each pore in the Knudsen region was expressed as follows (Matsuura, 1994 Khayet et al., 2004a) ... 

Khayet, M., Godino, M. P., and Mengual, J. I. (2003c). Possibility of nuclear desalination through various membrane distillation configurations A comparative study. Int. J. Nucl. Desalin. 1, 30. 

The main advantages of the membrane distillation process over conventional distillation are the configuration of the evaporation surface can be made into various membrane modules with a compact area density, mist can be eliminated, and highly pure water can be obtained as product corrosion may be less than that with metal surfaces. 

We have shown in this book that any distillation configuration, no matter how complex, can be modeled using CPMs. The example shown here is an extension of this work. While previous Chapters 5 7 focused on distillation only, we include the addition of a membrane unit connected to CSs. 

Ding Z., Liu L., Li Z., Ma R., Yang Z. (2006), Experimental study of ammonia removal from water by membrane distillation (MD) The comparison of three configurations, / Membrane .,286,93-103. 

The most common configurations of PMRs with suspended photocatalyst are those utilizing pressure driven membrane processes, such as microfiltration (MF), ultraflltration (UF) and NF. In other types of PMRs, photocatalysis is combined with dialysis, pervaporation (PV) or direct contact membrane distillation (DCMD, MD) (Mozia, 2010). 

Figure 6.12 Common configurations used for membrane distillation (a) DCMD.direct contact membrane distillation (b)AGMD, air-gap membrane distillation (c) SGMD,sweep gas membrane distillation and (d)VMD, vacuum membrane distillation (Caputo etal.,2007).

There are different studies published in the literature on the use of membrane distillation for the treatment of waters contaminated by As, as reported in the following. Most of them deal with the DCMD configuration, although some experiments on the use of AGMD are also reported. Only recently, the potentialities of the vacuum configuration have been also explored. 

An aqueous solution colder than the feed solution is maintained in direct contact with the permeate side of the membrane, giving rise to the configuration known as direct-contact membrane distillation (DCMD). Both the feed and permeate aqueous solutions are circulated tangentially to the membrane surfaces by means of circulating pumps or are stirred inside the membrane cell by means of a magnetic stirrer. In this case the transmembrane temperature difference induces a vapor pressure... 

A stagnant air gap is interposed between the membrane and a condensation surface. In this case, the evaporated volatile molecules cross both the membrane pores and the air gap to finally condense over a cold surface inside the membrane module. This MD configuration is called air gap membrane distillation (AGMD). 

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