Integrating carbon capture into an industrial combined-heat-and-power plant: performance with hourly and seasonal load changes

The present work aims to map the variations in process gas and available excess heat of an integrated steel mill and to investigate the effects of these variations on the performance of a chemical absorption CO2 plant. Two time-scales are considered for the variations: seasonal and hourly changes. Dynamic process simulations are used to investigate the dynamic interactions between the steel mill and the capture unit. This includes the effect that periodic variations in the reboiler heat duty have on the performance of the capture plant and the effect of implementing a control strategy. The mapping of the operation of the steel mill reveals numerous variations on an hourly basis that are important for the design and operation of the capture plant, including decreases in the blast furnace gas (BFG) flow to 0% on approximately 10 occasions per year and variations of +/- 30 MW in the available heat more than 40 times per year. The simulations show that the capture unit responds very differently depending on the season, with a generally slower response during winter operation due to a lower level of circulation of the solvent. The capture unit shows also non-linearity in its response to changes in heat load - the deviation from the steady-state value is more pronounced when the heat is increased than when it is decreased. Thus, the simulation results indicate that implementing CO2 capture with chemical absorption in an integrated steel mill requires flexible operation of the capture plant. Dynamic simulations over a two-week period with historical (hourly) boundaries demonstrate that the capture process can operate in the presence of the steel mill variations. Implementation of a decentralized control strategy increases the amount of captured CO(2 )by 1.2%.