Various Pressure Swing Adsorption (PSA) / Vacuum Pressure Swing Adsorption (VPSA) processes are offered for gas separation and purification.
|Process||PSA||PSA||PSA VPSA||PSA VPSA|
The nitrogen plants consist oftwo towers operating on pressure swing adsorption process. Purified compressed air is passed through one tower whereinoxygen is adsorbed and the outlet gas contains high purity nitrogen. A portion of this nitrogen is used to regenerate the other tower which is in the regeneration cycle.The outlet gas from the regenerating tower is then vented into the atmosphere with 30-35% oxygen (by volume) content. The typical cycle time for the PSA process is 1 + 1 minute and achieved using specially designed change over valves.
The PSA hydrogen-unit consists of four or more adsorption towers. Each of these towers passes subsequently through the stages of pressure build up, adsorption, and regeneration. By this, a continuous supply of product gas can be achieved. The pressure build-up is carried out in one or more steps. The tower in adsorption is switched over to regeneration. During this step, hydrogen-enriched gas flows to another tower for the next adsorption step.
The remaining part of the pressure build-up is done with product gas. In the subsequent production step, the feed gas is passed through the adsorption tower and hydrogen with very high purity leaves the tower. The regeneration is also done in several steps.
After pressure equalization with the previously regenerated adsorption tower, the present adsorption tower is depressurized. This is followed by a purge step with a counter-current flow of hydrogen. In case there is a high concentration of heavy hydrocarbons in the feed gas, a pre-filter system is integrated into the PSA-process.
Pressure swing adsorption systemscan be used for the production of methane from a number of feed gases such as biogas from digesters, biogas from sewage treatment plants, biogas from liquid manure towers, landfill gases and coal bed methane.In case of feed gases with carbon dioxide as the main component to be removed, methane is produced at line pressure. Whereas in case the main components to be removed are nitrogen and oxygen, methane is produced at atmospheric pressure (during regeneration). For feed gases with equal quantities of carbon dioxide, nitrogen and oxygen, a two stage process is used.Methane of purity upto 99 % can be produced using the PSA process.
The methane production units generally consist of four adsorbers, each of which passes through three stages-pressure build up, adsorption, and regeneration. This configuration ensures a continuous flow of product gas.
The PSA process is especially suitable for the production of carbon dioxide since carbon dioxide is adsorbed to a higher extent as compared to other gases such as nitrogen, hydrogen, oxygen, methane orcarbon monoxide. The PSA plants for carbon dioxide recovery generally consist of multiple beds which are sequentially passed through the process steps of pressure build-up, adsorption and regeneration. These plants operate at adsorption pressures of 1.1 to 1.5 bar (g) and desorption pressures below 200 mbar (g). The feed gas for these units can be any carbon-dioxide rich gas.