A renew cognition of coking mechanism: Proposing the “Structure Derivation Coking Mechanism”

Abstract

Understanding the coal properties and investigating the coking mechanism is essential to develop fine coal blending coking technology. The traditional coking mechanism explains the phenomenon of thermoplastic and caking properties in the absence of a substantial understanding of chemical reactions during coking process. The evolution of coking properties is recognized at a molecule level and the “Structure Derivation Coking Mechanism” is proposed. A series of chemical reactions occur during coal coking. The macroscopic characteristics depend on the transient spatial structure of the coal matrix, that is, “the properties are determined by structure”. The regulation of heat and mass transfer conditions shows a significant influence on the coal thermal conversion and affects the coking properties and coke performances, that is “environment affects behavior”. The evolution of fluidity and swelling during coking is analyzed and the correlation between coal structural transformation and coke strength is revealed based on the coal structural properties and cleavage and reconstruction of covalent bonds. The breakage of covalent bonds with weak dissociation energy contributes to the development of fluidity while the coal matrix re-solidification is related to the cross-linking and condensation reactions. The coal pyrolysis fragments in the form of molecular chain segments migrate to the pores across the fluidity range, which contributes to the formation of a low permeability zone containing a plastic layer, coal layer and semi-coke layer. Also, the swelling pressure generates because of the restriction of volatiles’ release in the range of low permeability zone. In addition, the rearranged reaction of the carbon matrix occurs, which increases the orientation and order degree of the semi-coke microcrystalline structure. The coke strength is related to the spatial arrangement of sp2 and sp3 carbon atoms. The scientific regulation of heating rate presents a significant superiority in improving the coke strength and realizing energy conservation during the coking process. As a supplement and extension to the traditional coking mechanism, the “Structure Derivation Coking Mechanism” contributes to the theoretical guidance and technical support for the fine development of coal coking industry.

Keywords

• coking mechanism
• coal structure transformation
• coking property
• heat and mass transfer
• coke quality