Techno-economic optimization and off-design analysis of CO2 purification units for cement plants with oxyfuel-based CO2 capture

This paper evaluates the technical and economic performance, as well as the direct/indirect CO2 emissions of the CO2 Purification Unit (CPU) for cement plants equipped with oxyfuel-based CO2 capture. Two configurations, targeting two different outlet CO2 specifications (‘moderate’ 95% purity and ‘high’ 99.9% purity) are designed, modelled and optimized in order to minimize the incremental clinker production cost for different values of the carbon tax. Mass and energy balances are simulated with Aspen Plus, while the operating conditions are numerically optimized with Matlab. Results show that moderate purity can be achieved with an increased cost of clinker of 16.3 €/tclk (CO2 recovery 99.3%), while the base high purity configuration leads to a 19.3 €/tclk increase (CO2 recovery 96.1%). Sensitivity analyses are carried out on design parameters (fuel and air infiltrations in the oxyfuel calciner line) and exogenous factors (carbon tax, CO2 intensity of electricity). Air infiltration rate has the highest impact on the incremental cost of clinker (increased by 25% when air leakage grows from 0 to 10%) and on the selection of optimal operational conditions. Off-design analyses aimed at assessing the impact of air infiltration changing over time highlight the relevance of designing the CPU for the scenario with air infiltrations, while selecting reasonable temperature differences (e.g. 5K) to avoid operability issues in the cold box heat exchanger. For the base case CPU, the cost of clinker increases by 3 €/tclk when moving from zero to 10% air infiltration.