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In this study, the effects of coal blending ratio, pyrolysis temperature, pyrolysis atmosphere and coal particle size on the quality of pyrolyzed char were investigated via a combination of orthogonal experimental design and grey relational analysis. Coal-XG and Coal-LL were pyrolyzed under various conditions to produce chars which were characterized to ascertain their properties such as chemical structure and reactivity. The results indicated that the pyrolysis temperature has the most significant impact on the quality of the char, followed by the pyrolysis atmosphere, coal blending ratio and coal particle size. The increase in pyrolysis temperature not only diminished char yield but also accelerated the consumption of oxygen-containing functional groups and the polycondensation of small aromatic ring structures throughout the reaction process. This led to a reduction in the reactivity of pyrolyzed char and the establishment of a more ordered structure. Meanwhile, the involvement of CO 2 and H 2 O prevented the condensation of small aromatic rings and fostered the generation of additional oxygen-containing functional groups, which resulted in lower yield and higher reactivity of the char under these two atmospheres. Through systematic analysis, only the Raman characteristic parameter I (Gr+VL+Vr) /I D exhibited a strong positive linear correlation with char reactivity, making it a reliable indicator for characterizing the reactivity of char. • The orthogonal design was used to study four response factors. • GRA was used to find optimal conditions and impact ranking of different factors. • Linear regression was applied to relate Raman/FTIR parameters to reactivity. • Blend experiments were conducted with two coking coals. [ABSTRACT FROM AUTHOR]

In this study, the effect of pressure on the pyrolysis characteristics of Naomaohu coal and the physicochemical properties of char during slow pyrolysis is evaluated, and the mechanism of pressure is explored. The results show that the influences of pressure on char yield and physical properties are reflected in both promoting and inhibiting effect, and the latter is more obvious with the increasing temperature. As the pressure increases, the char yield first reduces and then improves, and at 600 °C and 800 °C the minimum yields are in 1.0 MPa and 0.1 MPa, which are 57.48% and 54.04%, respectively. The S BET of char increases first and then decreases. At 800 °C, the S BET of char increases from 7.86 m2/g at 0.1 MPa to 19.81 m2/g at 0.5 MPa and then decreases. The effect of pressure on the chemical properties of char is relatively simple. As the pressure rises, the content of functional groups in char reduces and the degree of graphitization enhances. The TG-DTG curve, XPS, BET, SEM test, experiments on the pressurized micro-fluidized bed reaction analyzer and pressurized pyrolysis-gas chromatography/mass spectrometry show that the pressure mainly affects the pyrolysis process by affecting the secondary reaction of the primary volatiles in the particle and is related to temperature. • The effect of pressure on pyrolysis process has two kinds of promotion and inhibition. • The inflection pressure point from promotion to inhibition is regulated by temperature. • As the pressure increases, the char yield and S BET both rise first and then decrease. • The graphitization degree of char is deepened with pressure. • Pressure mainly affects the pyrolysis process by affecting the secondary reaction of tar. [ABSTRACT FROM AUTHOR]