CO2 mineral sequestration integrated with water-gas shift reaction

Mineralisation of CO2 using magnesium silicate rock offers a large carbon and storage (CCS) potential with documented advantages compared to underground storage of pure CO2. Work in Finland has resulted in what is referred to as “the ÅA route”, involving stepwise carbonation of serpentinite rock. Magnesium is extracted and converted into magnesium hydroxide (Mg(OH)2), which is carbonated in a pressurised fluidised bed (PFB) reactor at elevated pressure and temperature. The combined operation of a water-shift reaction and carbonation of Mg(OH)2 is addressed in this paper for (coal) gasification syngas and, in more detail, blast furnace top gas. Water produced during the carbonation step can drive the water-gas shift reaction. HSC and Aspen Plus are used for thermodynamic equilibrium product gas and solid products composition analysis. Optimal process conditions appear to be 400–450 °C, at a pressure of 40 bar or higher, for acceptable degrees of conversion. This is partly the result of the water-gas shift reaction equilibrium moving to the CO side at higher temperatures, besides increased calcination of Mg(OH)2 to much less reactive MgO. An energy requirement assessment for blast furnace top gas processing shows that power input requirements may be more than compensated for by waste heat.