Insight Into Upgrading Caking Property of Shenmu Long Flame Coal Using Low-temperature Slow Pyrolysis Treatment

We proposed a low-temperature slow pyrolysis treatment (LTSPT) to improve the caking property of Shenmu long flame coal (SMCY). To reveal the factors affecting the caking property of SMCY, Fourier transform infrared spectroscopy, solid-state ¹³C nuclear magnetic resonance spectroscopy, Raman spectroscopy, and pyrolysis-gas chromatography with mass spectrometric were used to analyze the changes in the chemical properties of the pyrolysis products. The results showed that LTSPT could significantly improve the caking index of SMCY, and it increased with the increase in temperature. LTSPT could decrease the content of oxygen; therefore, the consumption of hydrogen decreased, indicating that the increased hydrogen radicals can be produced, which serve as stabilizers for the aromatic radicals generated from coal pyrolysis. As a result, relatively high-molecular weight aromatic free radicals are inhibited from cross-linking into semi-coke. On the other hand, SMCY with a suitable upgrading degree possessed a suitable content of aromatic hydrocarbons, which are precursors of caking components. The combined effects of the abovementioned two factors led to the increase in caking index.