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The paper presents analysis of data obtained from tests of oil shale (OS) and peat co-combustion in a full-scale 250 MWth (useful heat output) circulating fluidized bed (CFB) boiler. The tests were conducted at nominal boiler load, with peat thermal input up to 30%. During the experiments, gas analysis was performed and ash samples were collected. The specific consumption of the oil shale and peat blend per useful heat and gross electricity was calculated and other techno-economic characteristics were determined. It was found that the co-combustion of oil shale and wet peat increased the CO emission to the level of 60 mg/Nm³. The NOx concentration increased from 120 to 165 mg/Nm³. The SO2 and HCl emissions remained at a very low level -- below 20 mg/Nm³. A significant ash reduction, approximately 4%, was measured in the case of a 30% peat content. Due to the high peat moisture, the flue gas volume increased 5-10%. As a result of addition of peat, the content of particulate matter (PM) 10/2.5 was also lower than that by conventional oil shale CFB firing. Oil shale and peat co-combustion can be considered as a viable option and near-term solution for reducing the environmental impact of oil shale power production. [ABSTRACT FROM AUTHOR]

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 kCO2-min = 0.28. The decrease of kCO2 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]