Heating rate effects on the coking properties evolution for varying rank coals: Insights into volatiles reaction and mass transfer

The comprehensive understanding of coking behavior for different coal species under various pyrolysis reaction environments contributes to the oriented regulation of coke-making process in diverse coke ovens. The heating rate effects on the covalent bonds cleavage and volatiles reaction of coal macromolecules during coking was demonstrated through 13C Nuclear Magnetic Resonance Spectroscopy (13C NMR), Thermogravimetric Analysis (TGA) and Reactive Force Field Molecular Dynamics (ReaxFF MD) techniques. The essential role of heating rate in coking characteristics evolution was investigated based on the recognition of volatiles mass transfer through fluidity, permeability, Mercury Intrusion Porosimetry (MIP), synchrotron radiation Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) techniques. The tests reveal that quick heating inhibits decomposition of carbonyl and carboxyl relating to cleavage of Cal - O prior to 400 °C. More C40 + pyrolyzates convert into C14-C22 pyrolyzates in the initial stage while transform to C23-C40 and C14- pyrolyzates at 300 ∼ 600 °C. The fluidity is enhanced at high heating rates due to the stabilization of three to five rings pyrolytic fragments by H·or CH3· radicals that remained in coal as a result of thermal hysteresis. The amorphous structure in volatiles migrates into semi-coke at high heating rates due to insufficient pyrolysis time and restrictions imposed by the thermoplastic layer characterized by blocked pores with 37 ∼ 50 nm. The transient heating activates aromatic carbon layer rearrangement, resulting in aromatic interlayer spacing minishes and average stacking height and width enlarge. These investigations aid in establishing theoretical framework for effectively controlling the coking process in diverse coke ovens for various blended coals.