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TAPERED BEAD SIZE IN PRESSURE SWING ADSORPTION BEDS

IP.com Disclosure Number: IPCOM000019373D
Publication Date: 2003-Sep-12
Document File: 2 page(s) / 68K

Publishing Venue

The IP.com Prior Art Database

Abstract

When the intra-particle mass transfer rate plays an important role in the adsorption process, it is desirable to reduce the particle size in order to reduce the length for mass transfer within the particle, and increase the surface area of the adsorbents. On the other hand, the reduced particle size increases the pressure drop across the adsorption bed. When the pressure of the system is low, the increase in pressure drop can significantly impact the power consumption of the PSA system. Therefore, the size of the particles cannot be too small, either.

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TAPERED BEAD SIZE IN PRESSURE SWING ADSORPTION BEDS

When the intra-particle mass transfer rate plays an important role in the adsorption process, it is desirable to reduce the particle size in order to reduce the length for mass transfer within the particle, and increase the surface area of the adsorbents. On the other hand, the reduced particle size increases the pressure drop across the adsorption bed. When the pressure of the system is low, the increase in pressure drop can significantly impact the power consumption of the PSA system. Therefore, the size of the particles cannot be too small, either.

One of the characteristics of the pressure swing adsorption processes is that typically the adsorption front where adsorption occurs moves from near the entrance of the bed to close to the end of the bed. The adsorbent that is saturated and that ahead of the front are not performing any separation. The only significant impact of these layers of adsorbent is to increase the pressure drop. Can we make use of at least some of the idle time of these adsorbent layers to improve the performance of the pressure swing adsorption process?

If the particle size of the adsorbent near the entrance of the adsorption bed is larger, it will take a longer time to saturate the adsorbent beads. On the other hand, the front will go forward before the adsorption capacity of such large beds is exhausted. When it reaches the end of the bed, impurities will break through and enter the product. Therefore, the adsorption step has to be stopped before such breakthrough occurs. However, if the beads there are too big in diameter, the intra-particle mass transfer will limit the level of saturation. Therefore, when the front breaks through the last layer of the adsorbent, the unsaturated inner core cannot be used before breakthrough. This is not desirable since the adsorbent near the exit end is not fully used. The ideal situation is that the particle size of the adsorption bed near the outlet of the adsorption step should be relatively small while that near the entrance is much larger. When the adsorbent near the entrance of the bed is exhausted, the front reaches the end of the bed. The particle size at the end of the bed is so small that as soon as the adsorption front reaches the particles at the end of the bed, the whole particle is saturated with impurities. The sizes of the particles in between can be tapered such that the centers of all the particles along the flow direction of the bed are saturated at the same time as the front reaches the last layer of the bed.

That is for adsorption only. In pressure swing adsorption processes, the...