Adsorption Wheel (Rotating Beds)
In this method of contacting, adsorbent in monolithic or particulate form are mounted on a rotor or wheel, which is turned by a motor. As shown in the Figure below, as the wheel rotates, the adsorbent is alternately contacted by the process gas and by a regeneration gas at an elevated temperature. The relative residence times of the adsorbent in each zone are set by the fractions of the circle covered by each of the zones, while the overall cycle time is set by the speed of rotation.
Figure not available
Not only do these wheels offer a degree of process simplicity through the use of only one vessel to house the whole process, but also the cycle times can be considerably shorter for wheel-based TSA processes, than for fixed bed TSA processes. This result in wheel-based processes requiring considerably less adsorbent per unit of gas processed per unit of time. However, adsorbent in monolithic form costs more than simple particles. Wheels had been made with diameters in excess of 4-m and are available with silicalite, alumina, silica gel, and other adsorbents.
A complication associated with adsorbent wheels is that there can be leakage of process gas into the regeneration section and of regeneration gas into the adsorption section. This cross-contamination leads to practical removals which are lower than can normally be achieved in fixed bed TSA processes. In addition, the mass transfer rate per unit length of bed traversed is not as high as that in packed bed of particles.
[ Back on Top ]