From variable pressure adsorption (PSA) is a technology used to separate certain types of gas from a mixture of gases under pressure according to the molecular characteristics and affinity of species for adsorbiruûŝim material. He works in Middle temperature and significantly differs from cryogenic distillation gas separation technologies. Special adsorptive materials (e.g., zeolites, activated carbon, molecular sieves, etc) are used as traps, the preferred target species adsorption gas at high pressure. Then the process pumps with low pressure for the desorption of adsorbed material.
process
Process pressure swing adsorption expected at high pressure, the gases tend to be attracted to solid surfaces, or "adsorbed". The higher the pressure, the more gas is adsorbed; When the pressure is reduced, the gas is released, or desorbiruût. PSA processes can be used for the separation of gases in the mixture, since various gases, usually attracts a variety of hard surfaces more or less strongly. If the gas mixture, such as air, for example, pass under pressure through a vessel containing a layer of adsorbent of zeolite that attracts nitrogen more strongly than it does oxygen, part or all of the nitrogen will stay in bed, and gas coming from the vessel will be enriched with oxygen. When the bed reaches the end of its ability to adsorb nitrogen, It can be recovered by reducing the pressure, thereby releasing the adsorbed nitrogen. This is ready for the next round of air enriched with oxygen.
This is the process used in portable oxygen concentrators used by emphysema patients and others who are in need of air enriched with oxygen to breathe.
Using two adsorbent vessels allows almost continuous production gas target. It also allows the so-called pressure equalization, where gas leaves the pressure vessel is used to create pressure in the part of the second vessel. This results in significant energy savings, and is a common industrial practice.
Adsorbents
In addition to their ability to distinguish different gases, adsorbents for PSA systems are usually chosen because of their large specific surface is very porous materials. Typical adsorbents activated carbon, silica gel, aluminium oxide and zeolite. Though gas adsorbirovanny on these surfaces may consist of a layer only one or at most a few molecules thick, the surface area of several hundred square meters per gram enable absorption of a large part of the weight of adsorbent in Gaza. In addition to their selectivity for different gases, zeolites and some types of activated carbon called carbon molecular sieves, can use their molecular sieves characteristics to exclude some gas molecules from their structure based on the size of the molecules, thereby limiting the ability of larger molecules adsorbed.
applications
One of the main applications of the PSA is to remove carbon dioxide (CO2) as the final stage in the large-scale commercial synthesis of hydrogen (H2) for use in refineries, in the production of ammonia (NH3). Refineries often use PSA technology in the removal of hydrogen sulfide (H2S) from hydrogen feed and recycle streams of hydrotreating and hydrocracking. Another application of PSA is to separate carbon dioxide from biogas to increase the ratio of methane (CH4). Through PSA the biogas can be upgraded with a quality similar to natural gas.
The DOG is also used in
Hypoxia air fire prevention system to produce air with low oxygen.
With the aim of propylene plants through dehydrogenation of propane. They consist of selective media for the preferred adsorption of methane and ethane on hydrogen.
Small-scale production of reasonable purity oxygen or nitrogen from the air. PSA technology is of great use in the medical industry to produce oxygen, particularly in remote and inaccessible areas of the world where the main cryogenic or compressed in capacitive tank impossible.
Nitrogen generator units which use a technique to obtain high gas PSA nitrogen purity (up to 99.9995%) and from the compressed air source. But this DOG is more equipped to deliver intermediate ranges and flows:
for nitrogen: from 100 Nm 3/h at 99.9% purity to 9000 Nm 3/h, with 97% of purity;
for oxygen:. up to 1500 Nm ³/h with purity of 88% and 93% [2]
Research now for PSA to capture CO2 in large quantities from coal-fired power plants prior to geosequestration, in order to reduce the production of greenhouse gases from these plants