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

Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 911-926The reactor achieves only 50% COconversion because the extraction of H 2 is tooslow and it does not shift the equilibrium as far tothe product side as in the base case scenario.3.1.4 Influence of Reactor’s Surface Area andH 2 Molar Fraction in Permeated Stream on COConversionThe influence of the reactor’s surface areaon CO conversion was studied by varying thelength of the reactor. Additionally, the influenceof different molar compositions in the permeatestream was studied. By changing both parametersTable 4 was obtained.The table shows that reducing the molarfraction of H 2 in the permeate stream wouldfavour the CO conversion. This is due to the factthat the partial pressure of H 2 is lower and thus,enhances the flux through the membrane whichindirectly affects the CO conversion.Increasing the reactor’s surface, byextending the length of the reactor, also favoursthe CO conversion. By enlarging the membranesurface area, more H 2 can permeate through,which shifts the WGSR more to the product side,and helps improve the CO conversion.To further determine the influence ofsurface area, the reactor with 70 m in length andH 2 molar fraction x H2 = 0.45 was simulated. Thereactor achieved only 92.3% CO conversion. Thisshows that extending a reactor further would helpachieve better conversions, but from economicpoint of view investment costs would be enormousto build such a big reactor. As discussed in earlierchapters, it would be better to use the catalystbecause the surface area is already large enoughand in the latter part of the MR the limitingprocess is the WGSR rate.3.2 Simulation Results in Aspen PlusThe model simulated on the basis of thecalculations obtained from the Mathematica basecase model is presented in the previous subchapter.Table 4. CO conversion at different H 2 molar fractions and lengths of reactorL = 30 m L = 40 m L = 50 mX COn N2[mol/s]n P,H2[mol/s]X COn N2[mol/s]n P,H2[mol/s]X COn N2[mol/s]n P,H2[mol/s]x H2 0.5 87.0 2664.53 2664.49 89.1 2707.63 2707.57 90.2 2730.35 2730.30.45 88.0 3281.43 2684.73 90.1 3335.05 2728.57 91.2 3363.35 2751.820.55 86.0 2162.35 2642.9 88.0 2196.87 2685.16 89.1 2215.03 2707.32Table 5. Molar compositions of gas streams(see Fig. 13)Rawgas (on the exit from the gasifier)species CO H 2 H 2 O CO 2 Ar H 2 S N 2 COS HClx i 0.560 0.230 0.120 0.077 4.8∙10 -3 4.5∙10 -3 4.0∙10 -3 3.9∙10 -4 6.7∙10 -5Syngas (after quench)species H 2 O CO H 2 CO 2 Ar H 2 S N 2 COS HClx i 0.410 0.375 0.154 0.052 3.2∙10 -3 3.0∙10 -3 2.7∙10 -3 2.6∙10 -4 4.5∙10 -5Gas-2 (retentate stream on the exit of the MR)species CO 2 H 2 O CO Ar H 2 S N 2 H 2 COS HClx i 0.769 0.140 0.072 6.3∙10 -3 5.9∙10 -3 5.3∙10 -3 5.3∙10 -4 5.2∙10 -4 8.8∙10 -5Gas-3 (after catalytic burner)species CO 2 H 2 O SO 2 Ar N 2 O 2 CO H 2 H 2 Sx i 0.835 0.146 6.4∙10 -3 6.2∙10 -3 5.2∙10 -3 2.0∙10 -3 0 0 0GT-gas (permeate stream on the exit of the MR)species H 2 N 2 CO H 2 O CO 2 Ar H 2 S COS HClx i 0.5 0.5 0 0 0 0 0 0 0922 Lotrič, A. ‒ Sekavčnik, M. ‒ Kunze, C. ‒ Spliethoff, H.