To produce a high-purity carbon monoxide (CO) stream, and a high-purity hydrogen stream, plus a…
Hydrogen PRISM PSA Process by Air Products and Chemicals, Inc.
Purify hydrogen from dedicated H2-production equipment and a wide range of offgas streams from refineries and hydrocarbon processing industries (HPI) to produce 95–99.999+% H2 purity. Feed: Wide range of H2-containing streams, typically with feed H2 greater than 50%, pressure from 70 psi to 600 psi (5–40 bar), and temperature from 60°F to 110°F. Examples of dedicated H2-production units include steam-methane reformers, naphtha-fired reformers and gasifiers. Hydrogen can be recovered from ethylene, propylene, styrene, and coke oven offgases; and various refinery streams such as cat reformer, hydrotreater/hydrocracker offgases.
Products: Hydrogen recovery is 83–90% for SMR applications, with CO from 1 ppm to 50 ppm. Purity is typically 95–99.9% for offgas plants, with recovery dependent on operating conditions. Integrated processes producing multiple products are practiced. For example, gasifier or refinery offgas pressure swing absorption (PSA) can be integrated with cryogenic processes for co-recovery of H2 with CO or hydrocarbons, respectively. PSAs are typically integrated with membranes in gasifier installations to coproduce high-purity H2 and a wide range of syngas compositions.
PSA purifies H2 by sequentially adsorbing impurities in multiple layers of adsorbents within a single PSA vessel. Adsorbent selection is critical, and is based on extensive R&D with verification from frequent plant performance tests. Hydrogen is produced from vessel(s) in their feed step, while other vessels are regenerated.
The number of vessels depends on the system capacity and the desired H2 recovery. For example, 4-bed PSA typically produces up to 15 million scfd H2. As capacity increases, it is generally economical to increase the recovery and number of beds. A 10-bed PSA unit can produce over 120 million scfd H2 at up to 90% recovery. Single-train capacities exceed 200 million scfd.
The systems are skid-mounted, requiring minimal fieldwork. These PSAs include all control valves, switch
valves and instrumentation required. Feed, product, and tail gas monitoring, isolation, and venting systems can be integrated into the skid design to further minimize field piping associated with the PSA. The system can be controlled using any commercial PLC or DCS products. Average reliabilities exceed 99.9%.
Economics: PSA costs vary with capacity and recovery. When compared to the other hydrogen recovery technologies (cryogenics and membranes), hydrogen PSAs fall in the medium-capital cost range and have moderate scaling economics. Using a PSA, H2 can typically be recovered for about 1.2-2X fuel value from offgas plants. When ultra-high-purity is required (e.g., ppm levels of CO, CO2 or other contaminants), PSA is typically the best technical and economic choice.
Licensor: Air Products and Chemicals, Inc.
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