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PSA (Pressure Swing Adsorption)

Pressure Swing Adsorption (PSA) is an economic and reliable method for separating a wide range of process gases and bringing them to a very high purity level.

Application Overview

Pressure swing adsorption is a process that separates single gases from a gas mixture. It is mainly used in chemical and petrochemical processes as well as the steel industry, for example to recover hydrogen (H2) from coking or conversion gases, or to separate oxygen (O2) and nitrogen (N2) from air.

The adsorption process is based on gas molecules binding to an absorbent material. The adsorbent bed is specially selected depending on the gas to be absorbed. Ideally, only the gas to be separated is adsorbed, while all other gases in the mixture pass through the adsorbent bed. Frequently, absorbents containing carbon (e.g. activated carbon or carbon molecular sieves) and oxide absorbents (e.g. zeolite) are used. The purity of the absorbed gas not only depends on the adsorbent used, but he temperature and pressure during the process are important as well. As a result, the control valves used also contribute considerably to the quality of the end product.

 

The Process

PSA units consist of multiple adsorber vessels containing one or more adsorbent layers.

Pressure is fluctuated between the vessels and the gas molecules will physically bind to the adsorbent material, causing a gas phase separation to take place.

The PSA process consists of four main stages:

  1. Adsorption - The adsorber starts off pressurized with pure gas. Feed gas (impure gas) is fed into the bottom of the adsorber, absorption takes place in the vessel, and pure gas is purged from the top of the vessel downstream. This takes place until the adsorber has reached its adsorption capacity, then it is taken off-line and the feed gas is fed to the next adsorber in the PSA unit.
  2. Depressurization - The adsorber is depressurized over in several small steps to recover additional pure gas still in the adsorber. Once all pure gas has been recovered, the desorbed impurities are dumped to the PSA offgas line.
  3. Regeneration - The adsorbent is purged with high-purity gas at constant offgas pressure to further regenerate the adsorbent bed.
  4. Repressurization - The adsorber is repressurized with pure gas and is now ready to receive more feed gas to start the process over. PSA units are used for several different applications, such as hydrogen recovery and purification, CO2 removal and purification, oxygen production, nitrogen generation, helium recovery, methane recovery, and others. PSA units can also be found in many different industries, including chemical, petrochemical, industrial gases (air separation), refining, and iron & steel production.

 

SAMSON Solutions

Control valves play an essential role in the PSA process and face some very unique challenges. SAMSON has a wealth of experience in PSA applications and offers several valves specifically designed to overcome these unique challenges.

3241 and 3251 PSA Valves
Size: 1/2" to 6"
ANSI Class: 150 to 600
Leakage Class: Class VI
Temperature Range: -20 to 430oF (-10 to 220oC)

Special Features
  • Meets strict fugitive emissions requirements
  • Low levels of vibration during operation
  • Easy maintenance
   
14p PSA Butterfly Valve
Size: 3" to 16"
ANSI Class: 150 to 300
Leakage Class: Class VIl
Temperature Range: -4 to 356oF (-20 to 180oC)

Special Features
  • Heavy-duty double-eccentric design
  • Tight bi-directional shut-off for gases
  • Flexible face-to-face dimensions

Bidirectional Flow

As an inherent part of the PSA processes, several of the control valves are required to operate bidirectional. SAMSON offers both rotary and globe control valves specifically designed to operate with flow in both directions.

Tight Shut-off

The internal leakage of the control valve has a direct impact on the efficiency of the PSA process. SAMSON offers optional high performance metal sealing to achieve leakage class V requirements and soft sealing options achieving leakage class VI.

Fast Acting

In order for the PSA process to run smoothly, control valves are often required to operate very quickly. SAMSON offers a wide variety of control valve accessories to meet the most stringent actuation time requirements, even on large valves sizes.

High Valve Noise

As a part of the PSA process, many control valves will see high differential pressures, causing high noise levels. SAMSON offers special trim technologies designed to reduced control valve noise emissions with bidirectional flow.

 

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