Investigating PSA, VSA, and TSA methods in SMR unit of refineries for hydrogen production with fuel cell specification

In this paper a robust and reliable process is proposed for purification of hydrogen from syngas to approach to the specification of fuel cell application (H-2 purity >99.99, CO impurity <0.2 ppm). Three cyclic adsorption processes; Pressure Swing Adsorption (PSA), Vacuum Swing Adsorption (VSA) and Temperature Swing Adsorption (TSA), were proposed, modeled and optimized, comparatively, for hydrogen purification. The Response Surface Methodology (RSM) was implemented for statistical investigation and optimization of operating conditions. In all cases two-layered adsorption bed of activated carbon and 5A zeolite was considered in cyclic adsorption process. The effect of bed length, purge to feed ratio, vacuum level (for VSA) and steam temperature (for TSA) were investigated and they were proposed for each process to approach to the maximum H-2 purity (>99.99%) and minimum CO content of 0.2 ppm, with appropriate recovery and productivity. Among the studied processes, PSA re-pressurized with feed had limited ability to achieve fuel cell hydrogen specification whereas PSA re-pressurized with product could achieve these specifications; however the low recovery of the process made it unreliable from economical point of view. Considering high H-2 purity and acceptable recovery, TSA would be the appropriate process, but its low productivity is a great imperfection. Considering the purity of hydrogen, energy consumption and capital cost, VSA would be the most superior process compared with the other cyclic processes. At the optimal point of view, for a feed with 75mol% H-2, VSA has resulted productivity of 148 mol H-2/(kg(ads).day) with 940 kJ/kgH(2product) electrical energy consumption whereas TSA has resulted only 86 mol H-2/(kg(ads) day) productivity, with 420 kJ/kgH(2product), electrical energy and 45.2 MJ/kgH(2product) heating energy consumption. (C) 2016 Elsevier B.V. All rights reserved.