CO2 mineral sequestration in oil-shale wastes from Estonian power production

In the Republic of Estonia, local low-grade carbonaceous fossil fuel – Estonian oil-shale – is used as a primary energy source. Combustion of oil-shale is characterized by a high specific carbon emission factor (CEF). In Estonia, the power sector is the largest CO2 emitter and is also a source of huge amounts of waste ash. Oil-shale has been burned by pulverized firing (PF) since 1959 and in circulating fluidized-bed combustors (CFBCs) since 2004–2005. Depending on the combustion technology, the ash contains a total of up to 30% free Ca–Mg oxides. In consequence, some amount of emitted CO2 is bound by alkaline transportation water and by the ash during hydraulic transportation and open-air deposition. The goal of this study was to investigate the possibility of improving the extent of CO2 capture using additional chemical and technological means, in particular the treatment of aqueous ash suspensions with model flue gases containing 10–15% CO2.The results indicated that both types of ash (PF and CFBC) could be used as sorbents for CO2 mineral sequestration. The amount of CO2 captured averaged 60–65% of the carbonaceous CO2 and 10–11% of the total CO2 emissions.