Herein, the pyrolysis characteristics of low-rank coal under a CO-containing atmosphere was studied via thermogravimetry coupled with mass spectrometry and Fourier transform infrared analysis. Further, the pore structure, carbon chemical structure, and combustion reactivity of the prepared coal chars were characterized via N2/CO2 adsorption, Raman spectroscopy, and thermal analysis, respectively. The CO-containing atmosphere suppressed coal devolatilization at the rapid pyrolysis stage. During coal pyrolysis, this atmosphere reduced CH4 evolution by suppressing the formation of free radicals such as CH3 • and CH2 •; H2 evolution reduced owing to the inhibition of the formation of hydrogen free radicals and the working of the inverse water–gas reaction; the H2O yield was increased through the inverse water–gas reaction but not by the conversion of the hydroxyl group in coal. At 300–700 °C, the disproportionation reaction of CO produced copious CO2 molecules, significantly raising the CO2 emission intensity over the CO2 released during coal pyrolysis. The pore structure of the chars-CO was suppressed via shingling of the carbon particles generated in the disproportionation reaction and the inverse water–gas reaction, which inhibits the release of volatiles in a CO-containing atmosphere. The carbon chemical structure of the chars-CO was ordered by the interaction between the char’s skeleton structure and the newly formed carbon and the contribution of the carbon particles with an ordered structure adhered on the char. The combustion reactivity of chars-CO was not improved by its higher volatile content, because the underdeveloped pore structure and ordered carbon structure degraded the combustion reactivity of chars-CO. Conversely, the pore structure of chars-CO is more developed than that of chars-N2 due to the release of volatiles in the high-temperature segment before the gasification reaction starts so as to improve the gasification reactivity of chars-CO.

No abstract

No abstract

No abstract

Pyrolysis chars have potential as fuels for pulverized coal injection (PCI); however, their proper and efficient utilization requires evaluation of char combustion kinetics. The combustion characteristics of two chars (F-char and M-char) and two pulverized coals (H-PCI and P-PCI) were analyzed herein using thermogravimetric analysis-mass spectrometry. The apparent activation energy (E a ) of the sample under non-isothermal combustion conditions was obtained using the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods, and the reaction mechanism for the fuels was established using the Malek method. Additionally, changes in the microscopic pore structure and carbon chemical structure of the fuels at different stages of combustion were characterized using N 2 adsorption and X-ray diffraction to analyze the relationship between microstructural evolution and E a . The results suggested that E a of the sample first rapidly decreased and then became stabilized during combustion. Compared with pulverized coals, the two chars presented more developed microscopic pore structure, less-ordered carbon chemical structure and lower E a during reaction. During combustion, the stacking height of the aromatic layer first decreased and then increased, whereas the specific surface area first increased and then decreased. The volatile content significantly influenced E a only during the initial stage of combustion. During the middle stage, E a was controlled more by the microscopic pore structure and the carbon chemical structure, and those influences disappeared in the later stage. The transition point of the structures affecting E a occurred at a combustion rate between 52.9% and 72.0%. In general, the microscopic pore structure and the carbon chemical structure influenced kinetic parameters more than the volatile content.