Simulation and modelling study of a chemical absorption plant to evaluate capture effectiveness when treating high CO2 content iron and steel industry emissions

Humanity must decarbonise to prevent climate disaster associated with CO2 and other greenhouse gases. The iron and steel industry contribute significantly to global CO2, with 70 % of integrated steel plant emissions arising from the blast furnace. Green alternatives to blast furnaces are still in development, requiring an intermediate stepping-stone solution to begin the decarbonisation journey. Chemical absorption using amine solvents is a proven carbon capture technology, theoretically ideal for flue gas CO2 concentrations and conditions typical of iron and steel making industrial processes. A representative simulation of the Translational Energy Research Centre (TERC) pilot-scale amine capture plant (ACP) was developed in Aspen Plus V11.0 and identified conditions to minimise the specific reboiler duty (SRD) for representative gases of the iron and steel industry. This work predicted operating conditions and trends when using a monoethanolamine (MEA) solvent concentration of 35 wt% across flue gas CO2 concentrations up to 25 mol% CO2. This work established that optimal L/G and solvent/CO2 ratios for MEA absorption systems can be predicted through knowledge of the flue gas CO2 concentration and the desired capture efficiency of the system alone, without consideration of the volumetric gas flow rate of the system. For flue gas CO2 concentrations of 10 to 25 mol%, optimal L/G ratios of 2.5 to 4.6 and solvent/CO2 ratios of 17.1 to 13.5 were identified to achieve 90 % capture efficiency, with the optimal L/G ratio increasing by approximately 0.7 for each 5 mol% increase of CO2 concentration. Optimal lean solvent loadings ranged from 0.245 to 0.294 mol·CO2/mol·MEA, with rich solvent loadings ranging from 0.500 to 0.517 mol·CO2/mol·MEA. Solvent capacities proved instrumental in understanding the relationship between optimal solvent flow rate and flue gas CO2 concentration for different capture efficiencies. Temperature profile assessment of absorbing and stripping columns is crucial to optimise the system, as each column exhibits unique operational behaviours, with additional attention given to the cross-heat exchanger. The results illustrate key parameters and considerations for CO2 capture of the iron and steel industry, providing initial setpoint conditions and guidance for optimisation. The developed simulation model can be calibrated to represent other MEA absorption systems.