Model based scale-up study of the calcium looping process

A 1-D dynamic calcium looping model was applied to a large scale calcium looping concept capturing CO2 from a 250 MWt power plant. Several new features were added to the existing model frame in order to successfully simulate the large scale unit. Models were needed for new material fractions, such as ash and CaSO4, sulfur capture and heat transfer in the solid return system. The plant was dimensioned based on the experience from large CFB units and the heat transfer design was evaluated based on initial simulations of the design case. The unit was then simulated in five load scenarios ranging from full load to zero load, no flue gas flow to the carbonator. The scale-up of the process is feasible from the model's point of view keeping in mind the assumptions and simplifications made in the modeling. The results from the simulations confirmed that successful operation of a large scale calcium looping unit requires good heat transfer design including cooling of the hot solids coming the calciner. Also the recirculation of flue gas in both reactors is necessary to ensure the sufficient fluidization for different flue gas flows from the source combustor. Solid circulation control is also critical because it affects heavily the thermal balance of the system as well as the capture efficiency and the CO2 balance. Results show that utilizing the experience gained from the large CFB-units coupled with new innovations, the scale-up of this process could be feasible in the near future. The ability to operate flexibly in different modes could give this technology an advantage needed for wide industrial utilization of the process.