SIMULATED COUNTERCURRENT ADSORPTION PROCESSES - A COMPARISON OF MODELING STRATEGIES

The behaviour of simulated countercurrent adsorption processes may be modelled using two different approaches. The first method, known as the moving-bed approach, treats the simulated countercurrent process as equivalent to a true countercurrent system. The second technique, known as the fixed-bed approach, considers the simulated countercurrent process as a series of fixed beds and incorporates the actual flow switching of the process at fixed time intervals. In this work, theoretical predictions of the two approaches have been computed numerically by the method of orthogonal collocation. The moving-bed approach, although less realistic, gives results that are very similar to those obtained from the fixed-bed approach for the description of the final steady state behaviour of a Sorbex-type four-section simulated countercurrent process. However, in the case of a three-section simulated countercurrent process, there is significant deviation between the predictions calculated from the two approaches. This difference arises as a result of the flow switching procedure implemented in the three-section process, a feature that cannot be accounted for by the idealized moving-bed approach. The validity of the moving-bed approach is thus seen to be limited to the four-section type of simulated countercurrent process.