Secondary Catalytic Effect of Circulating Ash on the Primary Volatiles from Slow and Fast Pyrolysis of Coal

Abstract

The lab-scale fixed-bed pyrolyzer by circulating ash as heat carrier was used to study the secondary catalytic effect of circulating ash on the primary volatiles from slow and fast pyrolysis of coal. Different mass ratios of ash to coal were layered in the pyrolyzer. Combined with the simulated distillation analysis, gas chromatograph-mass spectrum (GC-MS), and elemental analysis, the yields and compositions of gas, tar, and semicoke were analyzed. The results show that circulating ash catalyzes the cracking of primary volatiles generated by both slow and fast coal pyrolysis. CO2 is very sensitive to the proportion of circulating ash; it mainly comes from the breaking of −C–O– bonds with low energy in tar. After adding circulating ash, the gas yield increases while the tar quality is improved despite the reduction in tar yield. Circulating ash is beneficial to the cracking of oxygen-containing, nitrogen-containing, and sulfur-containing bonds in asphalt. The components with carbon numbers of ≥26 in tar can be upgraded and then results in the growing yields of ≤C25 components. Circulating ash can increase the tar saturation in the secondary catalytic reaction. This study can provide basic data for the effect of secondary catalytic as well as the heating rate on the coal pyrolysis by circulating ash as solid heat carrier.

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