Study on the Physical, Chemical and Combustion Characteristics of Pyrolysis Semi-coke

Abstract

ABSTRACT Combustion is an effective method for large-scale utilization of pyrolytic semi-coke (SC), a high order carbon-based solid fuel with low volatile content. The combustion characteristics of SC can be deeply understood through the study of physical and chemical properties. Taking SC as the research object and anthracite (YQ) with similar chemical composition as the control, the activation energy (E) of SC and YQ was calculated respectively by using model-free method and model method (16 typical mechanism functions). The pre-exponential factor (A), the change of enthalpy (ΔH), the change of entropy (ΔS), and the change of Gibbs free energy (ΔG) during the reaction were calculated. As a result, the pore inside of the particle is the main part of the pore structure of SC. The total specific surface area, pore-volume, and fractal dimension of SC are all larger than that of YQ. There is a lot of amorphous carbon in both SC and YQ, and the lattice spacing and graphitization degree of SC is smaller than that of YQ, but the average aromatic carbon lateral size and crystallite volume are much larger than that of YQ. The carbon in SC and YQ mainly exists in the form of aromatic carbon and aliphatic carbon, and the relative content of aromatic carbon in SC and YQ is basically the same. For the model method, the E of SC and YQ calculated by the three-dimensional diffusion (Spherical symmetric) mechanism function is the closest to the E obtained by the model-free method. Different from YQ, the main combustion stage of SC is composed of fixed carbon combustion and CaCO3 decomposition, and basically, no NH3 and HCN are generated. The volatile content of SC, the total specific surface area, and the pore volume in the pore are larger than that of YQ, which results in that the ignition temperature of SC is lower than that of YQ. The E and burn-out temperature of SC are higher than that of YQ due to the lower oxygen-containing functional group content, higher aromatic carbon content, fractal dimension and larger crystallite volume. Comprehensive physical, chemical, and combustion characteristics results show that using SC by combustion is more difficult than YQ.