CO2 mineral sequestration integrated with water-gas shift reaction

Mineralisation of CO2 using the world’s abundant resources of suitable magnesium-silicate rock offers a large carbon and storage (CCS) potential with documented advantages compared to methods that employ underground CO2 storage. Work in Finland has resulted in what is referred to as “the ÅA route” or “ÅAU process”, which is based on stepwise carbonation of serpentinite rock, containing mainly serpentine (3MgO·2SiO2·2H2O) besides a significant fraction of iron oxides. Magnesium is extracted using ammonium sulphate and converted into magnesium hydroxide (Mg(OH)2), which is carbonated in a pressurised fluidised bed (PFB) reactor at elevated pressure and temperature (~500°C, ~20 bar CO2 pressure).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 (v 5.1.) and Aspen Plus (v.8.2) 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 optimum range partly the result of the water-gas shift reaction equilibrium moving to the CO side at higher temperatures, and the increasing intensity of Mg(OH)2 calcination, giving much less reactive MgO instead of the carbonation of Mg(OH)2 to MgCO3. Further work shall address reaction kinetics supported by experiments.