Abstract
Fixed bed adsorption processes such as pressure swing (PSA) and temperature swing (TSA), unlike other chemical engineering separation processes, are dynamic processes which do not produce a continuous or steady flow of either the adsorbate or lean (non-adsorbed) phase. Instead, they operate with multiple vessels in a cyclic operation. These processes, therefore, pose additional challenges which include amuch larger array of input parameters that control the individual steps within each PSA or TSA cycle. This work proposes an Aspen AdsorptionTM based Multi-Objective Optimisation (MOO) framework for PSA systems. The PSA systems can be optimised against different step times and process parameters suchas, blow down pressure, feed pressure, valve co-efficients etc. The proposed framework is demonstrated by considering an example of a PSA based Carbon Capture and Sequestration (CCS) unit, for the removal of CO2 from an entrained flow gasifier synthesis gas stream, downstream of the Water Gas Shift Reactors. The two objective functions maximise the CO2 capture rate and minimise the specific energy penalty associated with CO2 capture. A novel feature of this study is the purification of the CO2 produced by the PSA by condensing it, thereby, allowing it to be pumped up to a pressure of 100 bar. The off-gas from the separation has been constrained to have the same composition as that of the feed, which may be recycled to the PSA process or used for a different purpose. The MOO Pareto curves provide information on the most important variables for both the PSA and the refrigeration system.
