Properties Of The Plastic Layer Formed During Coal Coking Process And Coking Performance

In chamber coking process,coal forms coke through a plastic layer.The properties of the plastic layer have a significant impact on coke quality.However,there is currently no technology that can realize the in-situ measurement of the properties of the plastic layer when it forms,and it is impossible to study the coking performace of coal based on this.Therefore,in this paper,a new technology for studying the relevance between the various behaviors during coking coal carbonization has been developed.Using this technology,the plastic layer properties and the related carbonization behaviors characteristics during coal coking process are investigated.In addition,the quality,chemical structure,and thermoplasticity of 17 coking coal samples from Mongolia and Shanxi are analyzed.The quality and different structures characteristics of coke formed from these coal samples are studied.The correlation between the quality indexes of coal and the characteristic indexes in coking process of coal with the quality of coke is analyzed,and the coke quality prediction model is established.The main findings are as follows:(1)Compared with Shanxi coal samples,the coal samples from Mongolia have lower metamorphic degree,higher active maceral content and mineral catalytic index MCI,developed aliphatic structure and mostly alicyclic hydrocarbon structure,easy decomposition,high shrinkage degree,and low coking rate.The coke produced from Mongolia coal samples have low particle size,high CRI,low CSR,pore structure is well developed and connected,while the cold state strength index(M40,M10)and carbon microcrystal structure are close to those from Shanxi coke.(2)The plastic layer can be divided into four structural zones with different penetrometer-resistance(PR)characteristics,namely,the increasing,decreasing,constant,and re-rising PR zones.At the PR increasing zone(IZ),the thermoplasticity is low,and softened coal particles fusion and filling the interparticle spaces.At the PR decreasing zone(DZ),the thermoplasticity increases continuously,melting and bubbling behaviors occur,and crystallite begin to form.At the PR constant zone(CZ),the thermoplasticity is highest,bubble expands sufficiently and ruptures,and form condensed aromatic rings.In the PR re-rising zone(Re-rZ),the thermoplasticity decreases rapidly,resolidification and volatiles escaping occur,and form pores and crystallite.The DZ and CZ are the critical zones for thermoplastic development.The CZ and Re-rZ appear to be critical zones for the development of a coke crystallite structure.Some derived parameters(PRmax,YDZ+YCZ,(YDZ+YCZ)/YRe-rZ)may be used as indicators to reflect the impermeability,internal thermoplastic properties,and caking performance of the plastic layer.(3)The coking process of coal inside the coke oven chamber is a process that coal pyrolysis undergoes matters-state evolution inside the plastic layer,that is,the trapped and developed of volatiles drive the thermoplastic evolution of matters-state and the development of carbon crystallite structure in the plastic layer,ultimately forming semicoke and coke with certain pore structure and pore wall characteristics.The comprehensive characteristics of the coking process can be characterized by ? index and ?index.The a named permeability index,which has a significant effect on the development of optical textures,carbon crystallite structure and pore structure of coke.The ? named deformation index,which is the physical factor reflecting the interaction between the expansion of matters in the plastic layer and the shrinkage of coal charge.(4)The traditional thermoplastic indexes of coal samples(a+b,1g MF,G and Ynax)can not be well used to evaluate the quality characteristics of coke formed from coal samples in different regions.The a and ?,as new technical property indexes of coking coal,can be used to study the influence of the coal characteristics during coking process on coke quality.(5)The prediction models of coke quality are established based on a index and ?index,combined with coalification degree(Rmax)and mineral catalytic index MCI.Within the range of experimental samples,the prediction accuracy of the model reached a high level.