Simulation of Water-Gas Shift Membrane Reactor for Integrated ...

Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 911-9268 the difference is negative) after which the rateof permeation becomes faster than the productionof H 2 . As seen from Fig. 8, the maximumdifference is reached around the 400 th sectionand the permeation rate becomes almost equal tothe reaction rate around the 4000 th section. Therate of reaction rises slightly at the end becauseat that point the concentration of H 2 is closeto zero and the effect of the backward WGSRalmost disappears. The increase in the reactionrate also causes the rate of permeation to increase,because more H 2 is produced, which immediatelypermeates through the membrane because theprocess is not permeation limited.in the retentate stream at the beginning and H 2converted from CO until that point permeatethrough the membrane. From that point on, onlythe H 2 that is converted from CO is permeatingthrough the membrane.Rapid permeation of H 2 is responsible formolar fractions of H 2 O and CO to experiencethe first inflection point around the 400 th section.The fractions reach the second inflection pointaround 2000 th section, where majority of H 2 onthe retentate side already permeated through themembrane. From that point on both fractionsgradually reduce towards the end of reactor wherethe consumption of H 2 O and CO again slightlyincreases on behalf of increase in the reaction rate.The molar fraction of CO 2 is increasing fastin the first 2000 sections because of H 2 permeationand because of CO conversion. This can be seenfrom a graph where after 2000 sections the rate ofCO 2 formation starts to decrease since virtuallyall of H 2 that was present in the stream permeatesthrough the membrane. At the end, the rate ofCO 2 formation slightly increases on behalf of theincrease in the reaction rate.Fig. 8. Difference between the rate of H 2production and the rate of H 2 permeation in eachsection of the reactorAs it can be seen from Fig. 9, the molarfraction of H 2 actually rises at the beginning eventhough the rate of permeation is greater as the rateof formation. By constantly extracting H 2 fromthe retentate stream, the joint molar flow alsodecreases. Since at the beginning the differencebetween the permeation and the production ratesof H 2 is not big enough, the H 2 molar flow inretentate stream is decreasing but not as fast as themolar flows of H 2 O and CO. As a consequence,the molar fraction of H 2 actually rises slightlyuntil the 64 th section where, on behalf of a sharpincrease in the permeation rate, H 2 starts to rapidlypermeate through the membrane.After reaching the peak at the 64 th sectionthe molar fraction of H 2 starts to decrease fastuntil the 1000 th section. Around the 2000 th sectionthe permeation already slows down considerablyand around the 4000 th section most of H 2 presentFig. 9. Change in molar fractions of species andthe CO conversion throughout the reactorBased on the input values, the calculatedmolar composition of the retentate stream ispresented in Table 3. Below, these values are alsocompared to the simulation results from AspenPlus.In order to keep the MR operating atisothermal conditions, approximately two thirdsof all heat, produced from the WGSR, would needto be removed from the reactor in the first 2000sections (see Fig. 10). The cooling tubes should bedistributed in such a way that they would insure920 Lotrič, A. ‒ Sekavčnik, M. ‒ Kunze, C. ‒ Spliethoff, H.