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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