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

Oxy-fuel combustion is considered as one of the promising carbon capture and storage (CCS) technologies for coal-fired boilers. In oxy-fuel combustion, the combustion gases are oxygen and the recirculating flue gas, and the main components of the combustion gas are O₂, CO₂ and H₂O [1]. The 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 (CFB) mode. The calculations were performed for different oil shale heating values and different recycled flue gas (RFG) 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 k_CO2-min = 0.28. The decrease of k_CO2 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 (LHV), the heat can be increased up to 0.34 MJ/kg. A comparison with the bituminous and anthracite coals revealed that the specific emission of CO₂ per input fuel energy for oil shale is expected to be even smaller compared with those of the considered coals. [ABSTRACT FROM AUTHOR]