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Comparative characterization of three commercial spiral-wound membrane distillation modules

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Abstract

At Plataforma Solar de Almería (PSA), different commercial spiral-wound MD modules were tested coupled to a solar thermal field composed of stationary flat plate solar collectors. One of them is the Solar Spring module with a permeate-gap membrane distillation (PGMD) configuration. Two modules from Aquastill based on a configuration of air-gap membrane distillation (AGMD) were also tested. A characterization of the modules is presented based on an extensive set of experiments carried out using simulated seawater. The performance was evaluated by measuring the production of distillate per unit surface of membrane and the heat efficiency, calculated through the thermal energy consumption. Also, the quality of the product was evaluated by measuring the conductivity of the distillate. The tests were performed changing the most significant operational parameters in order to characterize their effect on the performance of the system. The feed flow rate was varied between 400 and 600 l h–1 and the temperature of the hot feed from 60 to 80°C. The results show that the internal design of the module is very important, and the differences in the channel length in these modules have a stronger effect in their performance for seawater desalination than the configuration of the gap.

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... This plant was totally described in the work in Ref. [25] and it is composed of: a solar thermal field, with a nominal capacity of 7 kW th at 90 • C, a slope angle of 7 • and facing south (azimuthal angle of 0 • ); a storage tank, with a volume of 1.5 m 3 ; and a Membrane Distillation (MD) module. Although there are several MD modules available at PSA, in this work we use the Aquastill module which has a total membrane surface area of 24 m 2 providing a maximum distillate production of around 30 L/h under the best operating conditions [26]. • Nanofiltration plant: This facility is also based on a pilot plant located at PSA. ...
... Similarly, the equivalent circuit for photovoltaic cells provides the field's performance (η D,1 ) via another user-defined function [30]. The desalination and nanofiltration plants have been an object of analysis to determine their features as well [26,27] and only the storage systems are hypothetical elements, as justified in Ref. [31]. In respect to the resources considered as outputs (demands) of the energy hub, the electricity consumption of the pumping systems of the solar collectors (0.1943 kW), the MD plant (0.1720 kW), and the nanofiltration plant (0.2502 kW) were taken into account in the problem separately, as device-dependent outputs (O 2 , O 4 , and O 6 , respectively), allowing us to relate them to the on/off state of each pump. ...
... In respect to the resources considered as outputs (demands) of the energy hub, the electricity consumption of the pumping systems of the solar collectors (0.1943 kW), the MD plant (0.1720 kW), and the nanofiltration plant (0.2502 kW) were taken into account in the problem separately, as device-dependent outputs (O 2 , O 4 , and O 6 , respectively), allowing us to relate them to the on/off state of each pump. In addition, the value of κ in O 5 = κη D,3 P 13 is fixed at κ = 121.25 kW/m 3 , considering the experimental data and model provided in Ref. [26]. The rest of the demands (O 1 , O 3 , and O 7 ) were calculated by processing the real historical data measured by the sensor systems of each of the plants considered in the agro-industrial district (see Figure 4). ...
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... Although PGMD has been studied by various researchers, most of them are based on flat sheet [7,[12][13][14][15] and spiral wound [10,11,16,17] membrane modules. In this research, a specifically designed PGMD module using hollow fiber membrane was manufactured and tested under various operating conditions, because hollow fiber membrane has a large specific area without any supporting structure [18]. ...
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... Fig. 13-b shows the corresponding velocity effect on the system performance. These predicted trends are in accordance with the results in (Aguirre et al., Jan. 2017) 4.2.1.3. Effect of channel height. ...
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... This is the reason that many current plants are powered by low-grade and/or renewable energy. As indicated in Table 1, twelve installations combine solar thermal and PV to supply the required energy [128,[132][133][134][138][139][140]142,[145][146][147][148]. Other plants use a combination of solar thermal and waste heat [133], electricity from the grid [144,150], geothermal energy [149] or a salinitygradient solar pond [141]. ...
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... 12 A model optimization for seawater desalination showed that for very low circulation rate and feed temperature 70°C, GOR could be up to 6-7, although permeate flux was only 1 l/h m 2 . 34 Similar values of GOR and flux were obtained by Ruiz-Aguirre et al. 35 with a larger module (24 m 2 ) with longer channels (5 m long) using four times more circulation feed rate. This can be explained using the heat exchanger theory applied to MD by Swaminathan et al. 36 Reducing the feed flow rate is equivalent to lengthening the channel, increasing the number of heat transfer units (NTU) and improving heat recovery. ...
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... These modules involved a plate and frame design with each featuring a 1 mm air gap, 2.3 m 2 membrane area, nine feeds and nine cooling channels (total stack thickness 17.5 cm). In another work, Aquastill spiral wound system based AGMD configuration was tested coupled to a solar thermal filed composed of stationary flat plate at PSA centre [248,249]. The performance plant was evaluated by measuring the flux and the heat efficiency. ...
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In this paper, a commercial spiral wound PGMD module was modeled and optimized for seawater desalination using Response Surface Methodology (RSM). Permeate flux (Pflux) and specific thermal energy consumption (STEC) were the main performance parameters to optimize, while evaporator inlet temperature (Tevap), condenser inlet temperature (Tcond) and feed flow rate (F) were the three operating parameters chosen. Analysis of variance (ANOVA) was used to evaluate statistically the response surface models. According to the study, Tevap had the strongest effect on Pflux and STEC, increasing the former and decreasing the latter, F increased both responses, and Tcond had a weak effect on Pflux and practically none on STEC. The models were validated with further experimental data and a good correlation between experimental and predicted values of the responses was obtained for Pflux and STEC respectively. An optimization was performed to determine the operating conditions that produce a maximum value of Pflux and a minimum value of STEC simultaneously. The result of the multiple responses optimization using desirability function was a maximum Pflux of 2.66 l/h·m² and a minimum STEC of 255.8 kWh/m³.
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