Co-pyrolysis of oil shale and bituminous coal in a fluidized bed: Properties and distribution of pyrolysates, and reaction mechanisms

The co-pyrolysis of mixed samples of Longkou oil shale (OS) and bituminous coal (BC), using the ash of the mixture as the heat carrier, was investigated in a fluidized bed. The influencing factors were determined, including temperature, particle size, nitrogen flow rate, and heating rate. With the effect of modulating volatile residence time and secondary reaction severity, the basic properties and distribution of pyrolysates were obtained. Among them, temperature was the most critical factor. The yield of pyrolysis oil increased initially and then decreased with rising temperature, reaching a maximum of 20.95 wt.% and the yield of pyrolysis gas from cracking was suppressed to 10.67 wt.% under the optimized conditions of 520 ℃, a particle size of 0.7–1.0 mm, and a nitrogen flow rate of 0.6 L/min. The relative content of alkane in the pyrolysis oil was decreased from 55.90% to 41.33%, while the relative contents of olefins, aromatics, and phenols were increased. At the same time, the yields of CH₄ and H₂ were also increased according to the intensified secondary reactions. The analysis of synergistic effect indicated that the addition of OS diluted the alkali/alkaline earth metals in the system, which effectively inhibited cross-linking and coking, promoted the release of aromatic structures and the yield of phenols in pyrolysis oil increased from 1.27 wt.% to 1.75 wt.%. This study confirmed that secondary cracking during co-pyrolysis was mainly driven by free radical chain reactions, which promoting the carbon of pyrolysis gas and pyrolysis oil lower.