Energetic assessment of CO2 sequestration through slurry carbonation of steel slag: a factorial study

An assessment of the energetic requirements of slurry-phase accelerated carbonation for CO2 sequestration using steelmaking slag was conducted. The results of dedicated lab-scale carbonation experiments in which the CO2 sequestration yield of basic oxygen furnace slag was investigated at different operating conditions were used for the energy requirement calculations. The operating variables of the process and the associated values adopted were total gas pressure, temperature, and CO2 concentration in the gas phase. The energy duties of the slurry-phase carbonation layout were calculated for the different unit operations, which included slag milling, mixing, slurry pumping, heating, CO2 compression, solid/liquid separation, and CO2 capture (when required). The estimated energy requirements were found to lie in the range 980−6300 MJ t−1 CO2 sequestered, where the lower end of the range was associated with the use of diluted CO2. In all cases, the use of a concentrated CO2 flow proved largely energetically unfavorable over the use of diluted gas streams, since the energy duty of the required CO2 capture stage by far overcame the benefits associated with improved sequestration yields at increased CO2 concentrations in the gas phase. The calculated energy requirements were also processed to derive a second-order model accounting for the main effects and interactions between the operating variables of the carbonation process. The model developed is meant to predict the expected energy demand of the carbonation process under different operating conditions and to define the optimal combination of these in terms of the energetic profile of the process itself.