Rouse, Anna J.; (2004) Fast cycle low pressure drop systems for the separation of CO2. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In the effort to reduce CO2 emissions, industry is increasingly looking at sequestrating CO2. Estimates currently suggest that 50% of the total capture and storage costs lies in the CO2 separation stage. In this thesis one specific CO2 separation technology. Dual Piston Driven Pressure Swing Adsorption (DP-D PSA), has been evaluated, using both an experimental study and mathematical modelling. It was hoped that the process, which encounters very low pressure drops and could be operated at fast cycles, could be efficiently utilised for this low value separation. The initial mathematical studies undertaken centred on the validity of one of the modelling assumptions made for adsorption processes; the linear driving force (LDF) approximation used to describe mass transfer. Using both numerical simulations and analysis of analytical expressions a new approach to the LDF model for fast cycles was developed, and was verified for various cyclic adsorptions systems. Preliminary experiments began with characterisation of two monolithic adsorption columns, using chromatography and ZLC techniques. Experiments, which incorporated the activated carbon columns, were then conducted using a DP-D PSA test rig, operated both at total reflux and under production conditions. Runs were undertaken to analyse the behaviour of the rig under adsorbing and non adsorbing conditions, while the effect of rig parameters such as cycle speed and stroke length were also investigated. Mathematical models were then developed to simulate the system, incorporating both of the columns. Comparing the simulated and experimental results showed that the models represented system behaviour well under both adsorbing and non adsorbing conditions at total reflux. Results were reasonable but not as good when feed and product streams were considered and further work was suggested to improve agreement. Final comments were made with regard to the industrial feasibility of the process and possible improvements which could make the system more attractive.

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