Effects of feed composition of coke oven gas on a layered bed H₂ PSA process

The effects of feed composition on the adsorption dynamics and the optimal process design were studied from the experimental and simulated results in the H₂ layered bed PSA with activated carbon and zeolite 5A. The breakthrough results using the "base composition" (56.4 vol% H₂; 26.6 vol% CH₄; 8.4 vol% CO; 5.5 vol% N₂; and 3.1 vol% CO₂) in various layered beds were compared with those using the "higher nitrogen composition" and the "no nitrogen composition". In the breakthrough dynamics, the propagation velocity of wave front of each component was closely related to the slope of isotherm estimated at its concentration in the feed. Breakthrough behavior at each layered bed in the "higher nitrogen composition" showed similar trends as that in the "base composition". However, the "no nitrogen composition" showed different breakthrough behavior from the other groups. In this feed composition, it was observed that the order of CO and CH₄ breakthrough times was reversed with a change in the carbon-to-zeolite ratio. Based on the adsorption dynamics and breakthrough behavior of each feed composition group in various layered beds, the effect of feed composition on a seven-step two-bed PSA process for the H₂ recovery from coke oven gas was investigated numerically to develop a well-designed H₂ PSA process under various operating conditions. As expected from the breakthrough results, the trends of the PSA performance in the "higher nitrogen composition" were similar to those in the "base composition" except for the slight decrease in the optimal carbon-to-zeolite ratio. However, in case of the "no nitrogen composition", high purity product was obtained from the activated carbon-rich layered bed PSA because the adsorption capacity of the activated carbon for impurities was superior to that of zeolite. As a result, the optimum carbon-to-zeolite ratio at each operating condition was slightly changed depending on the propagation velocity of each component on each layer.