CALCULATION OF THE AMOUNT OF ESTONIAN OIL SHALE PRODUCTS FROM COMBUSTION IN REGULAR AND OXY-FUEL MODE IN A CFB BOILER

This paper presents the results of the calculation of the flue gas amount during combustion of oil shale using oxy-fuel technology in a circulated fluidized bed mode. The calculations were performed for different oil shale heating values and different recycled flue gas ratios. Oxy-fuel combustion with flue gas recycling was found to enable the decrease of the extent of carbonate minerals decomposition (ECD), thereby increasing the amount of heat released per 1 kg of fuel. To minimize ECD, the recycled flue gas ratio should be maintained at a level higher than 0.7. This condition allows an increase of the partial pressure of CO2 over the equilibrium state line of calcite decomposition reaction at the bed temperature. The decrease of ECD was observed up to kCO2-min = 0.28. The decrease of CO2 k leads to an additional increase in the amount of heat released during oil shale combustion per 1 kg and, depending on the mean lower heating value, the heat can be increased up to 0.34 MJ/kg.