Combustion behaviors and pollutant emission characteristics of low calorific oil shale and its semi-coke in a lab-scale fluidized bed combustor

Experiments on co-combustion of oil shale and its semi-coke were conducted in a lab-scale bubbling fluidized bed. Oil shale blend ratios from 0 to 100% at the interval of 25% were separately tested at 800, 850 and 900 °C, to clarify combustion behaviors and pollutant emission characteristics. Results indicated that as oil shale mass fraction increased, the combustion efficiency of samples firstly increased, and then decreased. Positive synergistic relationships between oil shale and its semi-coke were identified. The addition of oil shale could help reducing the SO2 emissions during co-combustion, while the NO emissions showed no significant change. Meanwhile, with temperature rising, the CO concentrations of samples with lower oil shale blend ratios (0, 25% and 50%) slightly decreased, on the contrary, for higher oil shale blend ratios (75% and 100%), the CO concentrations increased, however, the SO2 and NO concentrations got a monotonic increase for all the samples. Hence, from the view point of combustion efficiency and pollutant emission performances, it was recommended that the oil shale blend ratio was 50% and the bed temperature was about 800 °C. Besides, the ultra-low emission of SO2 and NO emitted from the co-combustion of oil shale and semi-coke were able to be achieved by adopting appropriate pollutant control measures.