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 th e moving-bed approach, treats the simulated countercurrent process as equivalent to a true countercurrent system. The second technique, know n as the fixed-bed approach, considers the simulated countercurrent pr ocess as a series of fixed beds and incorporates the actual flow switc hing of the process at fixed time intervals. In this work, theoretical predictions of the two approaches have been computed numerically by t he 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 s tate behaviour of a Sorbex-type four-section simulated countercurrent process. However, in the case of a three-section simulated countercurr ent process, there is significant deviation between the predictions ca lculated from the two approaches. This difference arises as a result o f the flow switching procedure implemented in the three-section proces s, 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 l imited to the four-section type of simulated countercurrent process.