Direct contact membrane distillation module scale-up calculations: Choosing between convective and conjugate approaches

Soukane, Sofiane; Lee, Jung-Gil; Ghaffour, Noreddine

doi:10.1016/j.seppur.2018.07.052

Cited by 18 publications

(13 citation statements)

References 35 publications

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“…Membranes 2020, 10, 25 3 of 22 MD submerged modules presented in the literature were conducted using the capillary membranes of short length, usually not exceeding 20-30 cm. Therefore, a further development of the MD process requires additional testing of these modules also on a larger scale [26,34]. The submerged modules fabricated from capillary polypropylene membranes are currently offered by the ZENA Membranes company from the Czech Republic [42].…”

Section: Heat and Mass Transfermentioning

confidence: 99%

“…Therefore, a temperature of the boundary layer (T2) rises quickly, and the temperature in the distillate channel (TD) becomes close to the feed temperature ( Figure 2). For this reason, it is important to determine the useful length of the MD module, which will depend not only on the flow velocity of the streams and their initial temperature [29,34,47], but also on the diameter of the capillary membranes. The changes of the distillate and feed temperatures along the capillary membranes were calculated based on the balance equations formulated for a differential element (ΔL) presented in Figure 1:…”

Section: Heat and Mass Transfermentioning

confidence: 99%

“…Therefore, the hydrodynamic conditions are important since the occurrence of temperature polarization reduces in a significant degree the MD process efficiency [30]. Bubble aeration and mixing allow the cross-flow of feed through the membrane bundle [32], however, it is difficult to obtain such a high flow turbulence in the submerged modules as in the case of the conventional cross-flow module with housing [30,33,34]. Using a Vacuum Membrane Distillation (VMD) variant can enhance the values of the driving force in this case [26], however, the application of pressure difference (vacuum) also accelerates the membrane wetting [13,30].…”

mentioning

confidence: 99%

“…In this case, the feed flow in the submerged module system can be induced by the air bubbles introduced between the fibres. The effect of liquid movement in the feed tank can be also obtained by mechanical mixing [32] or by pumping of feed (recirculation) [36].An enhancement of flow turbulence on the feed side limits the negative effect of the temperature polarization [34][35][36][37][38][39][40]. However, the bulk temperature is also decreased during the MD process, hence, the achievement of higher degrees of water recovery will require the energy supply also in the case of application of the submerged MD modules.…”

mentioning

confidence: 99%

“…An enhancement of flow turbulence on the feed side limits the negative effect of the temperature polarization [34][35][36][37][38][39][40]. However, the bulk temperature is also decreased during the MD process, hence, the achievement of higher degrees of water recovery will require the energy supply also in the case of application of the submerged MD modules.…”

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confidence: 99%

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The Application of Submerged Modules for Membrane Distillation

Gryta

2020

Membranes

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This paper deals with the efficiency of capillary modules without an external housing, which were used as submerged modules in the membrane distillation process. The commercial hydrophobic capillary membranes fabricated for the microfiltration process were applied. Several constructional variants of submerged modules were discussed. The influence of membrane arrangement, packing density, capillary diameter and length on the module performance was determined. The effect of process conditions, i.e., velocity and temperature of the streams, on the permeate flux was also evaluated. The submerged modules were located in the feed tank or in the distillate tank. It was found that much higher values of the permeate flux were obtained when the membranes were immersed in the feed with the distillate flowing inside the capillary membranes. The efficiency of submerged modules was additionally compared with the conventional membrane distillation (MD) capillary modules and a similar performance of both constructions was achieved.Membranes 2020, 10, 25 2 of 21 the module channels. With regard to this, in order to achieve a higher degree of water recovery, the feed is circulated in the closed loop and simultaneously reheated before the feed water enters the module [11,12]. These operations are omitted by immersing the capillary membranes inside the feed tank. Thus, the application of submerged modules significantly simplifies a construction of installation, which also additionally reduces the heat losses in the MD process [13][14][15].During a long-term exploitation of the MD module, the water fills a fraction of the membrane pores, thereby the elimination of membrane wettability becomes a very important issue [16][17][18]. The MD process is not pressure-driven, however, the hydrostatic pressure is necessary in order to obtain the feed flow through the module channels. Although the value of this pressure is usually not high, this is one of the reasons accelerating the membrane wetting, especially if the surface tension of the feed solution is low [17,18]. The immersion of membranes inside a non-pressure feed vessel allows elimination of a hydrostatic pressure generated by feed pumping.Fouling is also one of the reasons causing the membrane wetting [19][20][21]. The application of air bubbling is commonly employed in the MBR in order to mitigate the fouling phenomenon and it also proves to be effective in the MD process [15,22,23]. Moreover, in the case of the presence of surface active agents, they are accumulated on the surface of air bubbles, which additionally limits the influence of these substances on the pore wetting [23]. Such a concept was successfully used in the MD process applied to the treatment of wastewater from the petrochemical industry and to the treatment of produced water generated during the extraction of gas and petroleum [2,24].The driving force in the MD process does not directly depend on the bulk feed temperature, but on the feed/membrane interfacial temperature [25][26][27][28][29][30][31]. Therefore, t...

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Section: Heat and Mass Transfermentioning

confidence: 99%

Section: Heat and Mass Transfermentioning

confidence: 99%