There are several factors affecting the dynamic adsorption capacity of molecular sieves in air separation equipment, among which the flow rate of fluid is one.
The effects are: high flow rate of fluid, too short residence time of adsorbate in the adsorption bed, poor adsorption effect, growth of mass transfer area and small dynamic adsorption capacity. However, the flow rate is too low, and the gas volume processed by the purification equipment per unit time is small. From the aspect of adsorption mechanism, the limit velocity of fluid is the adsorption rate. It can also be said that the shortest residence time should be the adsorption time. The so-called adsorption rate is the rate of completing the whole process of external diffusion, internal diffusion and adsorption. For physical adsorption, the adsorption rate mainly depends on the speed of diffusion stage, and the adsorption stage is only completed in an instant. Indeed, if the fluid flow rate is higher than the adsorption rate, that is, the residence time is shorter than the adsorption time, the adsorption will not occur, and its adsorption capacity is zero. Only when the fluid flow rate is less than the adsorption rate, can there be a law that the lower the flow rate, the smaller the adsorption capacity.
The flow rate used for adsorbent adsorption is usually the empty tower speed, that is, the cross-sectional flow rate of the inner cylinder without adsorbent.
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