CO2 quality as a system-level decision variable in integrated capture-conditioning systems for steel plants - a techno-economic trade-off assessment

The steel industry is a significant emitter of CO2 and a critical target for decarbonization. This study develops a CO2 quality-driven, integrated capture-conditioning assessment framework to quantify system-level trade-offs, rather than optimising capture and conditioning systems independently. The framework is applied to a steel plant case using the DISPLACE solid sorbent-based capture technology, followed by a CO2 conditioning system including compression, dehydration, and cryogenic separation to meet pipeline transport specifications. Thirteen capture-side operating cases are analysed, spanning variations in carbon capture ratio, CO2 purity, and outlet pressure. Results show that CO2 quality strongly reshapes system-level energy and cost performance: energy demand varied by up to 23.5%, while the corresponding overall cost of CO2 avoidance varied by up to 15.5%. Conditioning costs account for only around 10% of the total capture-conditioning cost. Consequently, using the capture system to produce low-purity, low-pressure CO2 is an efficient economic lever, whereas the conditioning system can accommodate CO2 qualities at relatively low marginal cost, yielding a minimum overall cost of CO2 avoidance of 211.5 €/tCO2. Despite large differences in energy use and cost, CO2 quality has less impact on the overall CO2 avoidance, which remains relatively stable, varying by only about 3.5% across all cases. Additional sensitivity analysis shows that changes in electricity price and grid carbon intensity affect the absolute values of the main KPIs but do not alter the underlying trade-off structure. The gains in capture-side avoidance are offset by conditioning-related emissions and vented-CO2 losses. These findings demonstrate that CO2 quality should be treated as a system-level decision variable and provide guidance for the investigated steel-plant case.