Analysis of the process principle of Sichuan pressure-variable adsorption and temperature-variable adsorption

In practical industrial applications, adsorption separations are generally classified into two main categories: pressure-variable adsorption and temperature-variable adsorption. From the adsorption isotherm of the adsorbent, it can be seen that the adsorbent has a large capacity to adsorb impurities at high pressure and a small capacity at low pressure. Also from the adsorption isobars of adsorbent, it can be seen that at the same pressure the adsorbent has a large adsorption capacity at low temperature and a small adsorption capacity at high temperature. The adsorption separation using the former property of the adsorbent is known as pressure shift adsorption (PSA) and the adsorption separation using the latter property of the adsorbent is known as temperature shift adsorption (TSA).

In practical industrial applications, the choice of TSA, PSA or TSA + PSA process is generally based on the composition of the gas source, pressure and product requirements.

Variable temperature adsorption process needs to be warmed up, so the cycle is long, the investment is large, but the regeneration is complete, usually used for the purification of trace impurities or difficult to desorb impurities; Variable pressure adsorption process has a short cycle, high utilisation of adsorbent, relatively small amount of adsorbent, does not need external heat exchange equipment, is widely used in the separation and purification of atmospheric volume, multi-group body.

In the industrial pressure swing adsorption (PSA) process, the adsorbent is usually adsorbed under normal temperature and high pressure to the easily adsorbable components in the mixed gases, and the components that are not easily adsorbable are discharged from one end of the bed, and then the pressure of the adsorbent bed is lowered to the atmospheric state to desorb the adsorbable components, which are discharged from the other end of the bed, so as to realise the separation and purification of the gases and at the same time, regenerate the adsorbent. At the same time, the adsorbent is regenerated.

However, in the usual PSA process, even if the adsorption bed pressure is reduced to atmospheric pressure, the adsorbed impurities can not be completely desorbed, then two methods can be used to make the adsorbent completely regenerated: one is to use the product gas to the bed "flushing", the more difficult to desorb the impurities rinsed down, the advantage of which is that it can be completed at atmospheric pressure, but the disadvantage of the loss of some product gas; the other is to use the product gas to "flush", to flush down the more difficult to desorb impurities. The advantage is that it can be done under atmospheric pressure, but the disadvantage is that it will lose part of the product gas; another is to regenerate the bed using vacuum, so that the impurities which are more difficult to be desorbed can be forcibly desorbed under negative pressure, which is commonly known as Vacuum Pressure Swing Adsorption (abbreviated as VPSA or VSA). The advantages of VPSA process are good regeneration effect, high product yield, and the disadvantage is the need to increase the vacuum pump. In the actual application process, exactly what kind of process is used, mainly depending on the composition of the raw gas conditions, flow rate, product requirements, as well as the capital and site of the plant and other circumstances to decide.