Simulation of 12-Bed Vacuum Pressure-Swing Adsorption for Hydrogen Purification

This thesis discusses the design and development of a 12-bed vacuum pressure-swing adsorption (VPSA) simulation capable of purifying hydrogen from ternary mixture (H2/CO2/CO 75/24/1 mol%) derived from methanol-steam reforming. This process produces 9 kmol H2/h to polymer electrolyte membrane fuel cell (PEMFC) specifications (i.e., <2 ppm CO2, <0.2 ppm CO). Models of the process and cycle schedule were developed using Aspen Adsorption® (AspenTech®, 2020, V11) using the “uni-bed” approach. A parametric study on the removal of CO and CO2 in response to adsorption operating pressure, column height, activated carbon:zeolite ratio, and feed composition. The goal of the parametric study was to find adsorption column and process design parameters that reduced product stream CO and CO2 mole fractions below 0.2 ppm and 2 ppm, respectively, while maintaining as high a H2 recovery as possible. A 4-bed VPSA model that attains similar product purity results is then developed so that the recovery of the 4-bed and 12-bed VPSA models can be compared. The results show that both VPSA processes can successfully limit the mole fractions of product stream impurities. The required column height for the 12- bed VPSA is 1.2 m, and 2.35 m for the 4-bed VPSA. Adsorption occurs at 7 bar, and the activated carbon:zeolite ratio is 70%:30%. This design can successfully purify feed with CO as high as 3 mol%. For the 1 mol% CO feed case, the 12-bed VPSA model maintains a H2 recovery of 75.75%, while the 4-bed VPSA H2 recovery decreases to 61.34%. As a result, the 12-bed VPSA is considered the most viable process when strict H2 purity constraints are necessary in addition to high H2 recovery.