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Wpływ warunków hydrodynamicznych przepływu w module membranowym na proces rozdziału mieszaniny CO2/H2

Janusz-Cygan A., Tańczyk M., Warmuziński K.

Prace Naukowe Instytutu Inżynierii Chemicznej Polskiej Akademii Nauk

2009

nr 13

15-27

Przedstawiono wyniki symulacji numerycznych procesu rozdziału mieszaniny CO2/H2 dla dwu róż nych schematów przepływu gazu w module membranowym: z idealnym wymieszaniem faz po obu stronach membrany oraz z przepływem tłokowym po stronie zasilania i swobodnym odpływem permeatu. Stwierdzono, że warunki hydrodynamiczne w module membranowym znacząco wpływają na czystość i sprawność odzysku obu rozdzielanych składników mieszaniny zasilającej jedynie w zakresie wysokich ciśnień i niskich natężeń przepływu gazu zasilającego.

A proper choice of a model of the membrane separation process is determined by a construction of a membrane module and resulting hydrodynamic phenomena in the module. The model which assumes ideally mixed gas phases on the feed and permeate sides (described in Section 3) may be used to describe the separation in flat membrane modules. The model with plug flow on the feed side and unhindered permeate flow is used in the case of spiral wound modules. In order to study the impact of hydrodynamic conditions in a membrane module on CO2/H2 separation the two models were used in the simulations of the process. The simulations were performed for two polymeric membranes: PDMS and PEBAX, assuming that the mixture consists of 50% of CO2 and 50% of H2. It was also assumed that the pressure on the permeate side is 1 bar and the membrane thickness is 10 m. In order to assure a constant value of the permeation number R it was assumed that the PDMS membrane area is 1 m2 and the PEBAX membrane area is 50 m2. The results of simulations for the PDMS membrane are presented in Figs. 2, 4, 6 and 8, and for the PEBAX membrane in Figs. 3, 5, 7 and 9. Carbon dioxide recovery (η CO2), presented in Figs. 2 and 3, is defined as a ratio of CO2 amount in the permeate to CO2 amount in the feed gas. Hydrogen recovery (η H2), presented in Figs. 4 and 5, is defined as a ratio of H2 amount in the retentate to H2 amount in the feed gas. It is concluded that in the case of the model with ideally mixed gas phases on the feed and permeate sides, CO2 mole fractions in the permeate (Figs. 6 and 7) and H2 mole fractions in the retentate (Figs. 8 and 9) are somewhat lower than those obtained in the case of the model with plug flow on the feed side and unhindered permeate flow. It is also concluded that carbon dioxide recoveries calculated using the model with unhindered permeate flow are greater than those calculated using the other model. However, the differences are significant only for very high pressures and do not exceed 18%. It is observed that hydrogen recoveries are almost the same for both models. Based on the results of simulations it is concluded that, in the case of CO2/H2 membrane separation, hydrodynamic conditions have signifi cant impact on the product purities and recoveries only in a limited range of the process parameters (high pressures and low feed gas flow rates). From the practical viewpoint this means that preliminary design and optimization studies may be performed using the simplest models, regardless of the construction of the membrane module, that is, of the hydrodynamic conditions prevailing in the system. A similar conclusion was also given by Rautenbach [7] for the case of the membrane air separation.

Procesowa charakterystyka pracy stacji membranowej do odzysku wody z permeatu po nanofiltracji serwatki

Zander Z., Dąbrowski J., Zander L.

Inżynieria i Aparatura Chemiczna

2006

Nr 4s

154-155

A statistical description of process variables for an industrial two-stage reverse osmosis (HO) station used for water recovery from permeate remaining after whey nanofiltration was obtained. The permeation rates and resistance, mineral component content in the feed, RO permeate and retentate were evaluated.