Application: Pressure swing adsorption (PSA) process selectively adsorbing impurities from product streams. The impurities are adsorbed in a fixed-bed adsorber at high pressure and desorbed by “swinging” the adsorber from the feed to the tail gas pressure and by using a highpurity purge. Typically, the desired component is not adsorbed and is recovered at high purity.
Description: A PSA system operates as a batch process. However, multiple adsorbers operating in a staggered sequence are used to produce constant feed, product and tail gas flows.
Step 1: Adsorption. The feed gas enters an adsorber at a high pressure, impurities are adsorbed and high-purity product is produced. Flow is normally in the upwardly direction. When an adsorber has reached its adsorption capacity, it is taken offline, and the feed automatically switched to a fresh adsorber.
Step 2: Co-current depressurization. To recover the product trapped in the adsorbent void spaces, the adsorber is co-currently (in the direction of feed flow) depressurized. The product gas withdrawn is used internally to repressurize and purge other adsorbers.
Step 3: Counter-current depressurization. At the end of the co-current depressurization step, the adsorbent is partially regenerated by counter-currently depressurizing the adsorber to the tail-gas pressure, and thereby rejecting the impurities.
Step 4: Purge. The adsorbent is purged with a high-purity stream (taken from another adsorber on the cocurrent depressurization step) at a constant pressure to further regenerate the bed.
Step 5: Repressurization. The repressurization gas is provided from the co-current depressurization step and a slipstream from the product. When the adsorber has reached the adsorption pressure, the cycle has been completed. The vessel is ready for the next adsorption cycle.
UOP’s Polybed PSA system offers:
• High reliability (greater than 99.8% onstream time)
• Minimal manpower requirements due to automatic operation
• Reduced equipment costs and enhanced performance based on high performance adsorbents and advanced PSA cycles
• Lower operating and equipment costs for downstream process units
• Flexibility to process more than one feedstock
• Modular construction for improved delivery times and low installation costs
• Minimal feed pretreatment and utility requirements
• Adsorbents last for the life of the mechanical equipment (more than 30 years).
Installation: Since commercialization in 1966, UOP has provided over 800 PSA systems in more than 60 countries in the refining, petrochemical, steel and power-generation industries. The Polybed PSA System has demonstrated exceptional economic value in many applications, such as hydrogen recovery from steam methane reforming, refinery offgas, monomer recovery in polyolefin plants, hydrogen extraction from gasification syngas, helium purification for industrial gas use, adjustment of synthesis gas for ammonia production, methane purification for petrochemicals productions, and H2/CO ratio adjustment for syngas used in oxo-alcohols production. Feed conditions typically range from 100 to 1,000 psig (7 to 70 kg/cm2g) with concentrations of the desired component typically in the range of 30 to 98+ mole%. System capacities range from less than 1 to more than 350 MMscfd (less than 1,100 to more than 390,000 Nm3/hr). UOP provides unit and complex integration development support to ensure the PSA system meets the end-user’s processing objectives and worldwide service and technical support after startup.