Heat optimisation of a staged gas–solid mineral carbonation process for long-term CO2 storage

Carbonation of magnesium silicates offers an interesting option for CO2 emission mitigation in Finland, a country with large resources of serpentine-type minerals. Wet processes using aqueous solutions show reasonable chemical kinetics combined with poor energy economy. A dry, gas–solid process with slower chemical kinetics (demonstrated previously), but better energy economy could be an alternative. This paper addresses the energy economy of a two- or three-stage gas–solid process for magnesium silicate carbonation. It involves production of reactive magnesium as magnesium oxide or hydroxide in an atmospheric pressure step, followed by carbonation at elevated pressures that allow for reasonable carbonation reaction kinetics under conditions where magnesium carbonate is thermodynamically stable. For a feasible large-scale process the kinetics in the individual reactors must be fast enough, while the heat produced in the carbonation step must be sufficient to compensate for energy inputs to the preceding step(s). Results give reactor temperature combinations that allow for operation at a negative or zero energy input, for given carbonation reactor pressure and degree of carbonation conversion, and other process energy requirements. Softwares used were HSC and Aspen Plus. Also, some results from gas–solid kinetics studies with magnesium oxide-based materials at the pressures considered are included.