Study On Formation Characteristics Of Pyrolysis Products Of The Low Metamorphic Coal

The low metamorphic coal reserves in northern Shaanxi are abundant,and pyrolysis is the main means for the effective utilization of low metamorphic coal.Therefore,it is of great theoretical and practical significance to study the formation characteristics of pyrolysis products for the efficient conversion of low metamorphic coal.In this paper,the low metamorphic coal in northern Shaanxi was used as the raw material.The pyrolysis experiment method was used to study the effect of ash,carbon content,sample selection and the pyrolysis temperature.Combined with TG-FTIR and Py-GC/MS analysis methods,the formation characteristics of the products on pyrolysis process were revealed.And the process kinetics study were carried out.the following conclusions were drawn:（1）The deashing process converts the structure of O-linked with alkali metal into a hydroxyl structure in the coal,and the content of phenolic substances in the liquid product increases,and the growth part is mainly composed of hydroquinone.The new pores are produced after deashing,which is beneficial to the escape of light volatiles.（2）The total yield of gas-liquid products is closely related to the carbon content of coal samples.The C=O structure cracking mostly escapes in the form of oxygen-containing gas（CO,CO₂）,while the hydroxyl group is mostly converted into a liquid product.Alkane release in liquid product tar mostly escapes in the form of long chains;phenols are mainly present in the form of lower phenols;aromatics are mostly released in the form of toluene,meta/p-xylene,naphthalene.（3）CO is mainly caused by cracking and decomposition of weak bonds in carboxyl,aldehyde or ketone structures and cracking of a small number of ether bonds and oxygen-containing heterocycles.CO₂ is mainly produced by the cleavage of anthracene,aldehyde or ketone structure and ether bond structure,and the cleavage of an oxygen-containing heterocyclic or carbonyl functional group in tar.CH₄ is formed by the cleavage of weak methyl bonds and the cleavage of alkanes in methoxy,side chain methyl and tar.H₂ is produced by a combination of very few free hydrogen radicals,as well as dehydropolycondensation,aromatization of solid product structures,and polymerization between gas molecules or small molecule cleavage.（4）TG-FTIR pyrolysis analysis shows that the highest gas absorption peak is between 400-600℃,which is the optimal gas release temperature range.Py-GC/MS analysis found that ZM coal has the most liquid product components at 600℃,and the phenol content is the most,while other coal-like tars have the most component types at400℃,and the best release temperature of alkanes is 300℃.（5）The kinetic pyrolysis process can be described by three consecutive first-order reactions.In the first stage,the release of small molecules of the guest,the weak bond with poor thermal stability and the breakage of the living wave functional group mainly occur,so the required activation energy is relatively small.The second stage is the active wave thermal decomposition stage of coal.At this stage,the decomposition and depolymerization of coal structure macromolecules occur,and a large number of weightless processes generate a large amount of tar and gas.This process requires a lot of energy,so the activation energy is the largest.In the third stage,the semi-coke is further polycondensed into coke.With the secondary degassing reaction,the energy required is relatively small,so the activation energy is low.