Effect Of Pretreatment On The Structure And Pyrolysis Characteristics Of Ordos Lignite

Lignite reserves account for about 13% of the total coal.Due to the characteristics of three highs and one low,it cannot be applied on a large scale under the existing pyrolysis technology.Therefore,it is necessary to explore the pyrolysis characteristics and pyrolysis mechanism of lignite to provide data reference for the design and development of coal technology.In this paper,Ordos lignite was taken as the research object.Firstly,the lignite was pretreated by hydrothermal pretreatment,solvent swelling pretreatment and ion load pretreatment,respectively.Then a fluidized bed is used to pyrolyze the raw coal to determine the optimal pyrolysis temperature.Finally,the pyrolysis experiment of the pretreated coal sample was carried out at this temperature.Pyrolysis products are analyzed for yield and composition by Thermogravimetric analyzer(TG),Fourier transform infrared spectrometer(FT-IR),Gas chromatography-mass spectrometry(GC-MS),X-ray photoelectron spectrometer(XPS),Gas Chromatograph(GC),Karl Fischer water meter,etc.The results are as follows:1.Through hydrothermal pretreatment in the range of 200-300?,it is found that after hydrothermal pretreatment,oxygen-containing functional groups and water-soluble inorganic metals in coal can be decomposed and removed,and aliphatic side chains can be broken.The destruction of the cross-linked bonds of the coal structure causes the pore structure to collapse.And the higher the pretreatment temperature,the stronger these effects.The pyrolysis effect at 200? is the best,the tar yield is the largest,and the content of aliphatic hydrocarbons,monocyclic aromatic hydrocarbons and phenols in the light components increases.The higher the pretreatment temperature,the lower the yield of pyrolysis tar is due to the decrease in the content of small molecules and metal ions,which weaken the stabilization of free radicals and the cracking of macromolecules during the pyrolysis process,respectively.2.In this research,we used n-hexane,methanol,acetone,and tetrahydrofuran to swell the coal at room temperature.The results show that: Non-polar solvents have little effect on coal structure;After the polar solvent treatment,the coal-like aromatic lamella spacing increased,the hydroxyl peaks moved to a low wave number,and the pore structure collapsed.It shows that the hydrogen bond cross-linking between the oxygen-containing functional groups of lignite and the hydroxyl groups is banned by the solvent,which promotes the volume expansion of coal,increases the fluidity of small molecules,and reduces the initial temperature of pyrolysis.The destruction of hydrogen bond crosslinks reduces the pyrolysis water yield of the swollen coal sample,and increases the yield of tar and gas phase.Compared with raw coal,and the contents of phenolic,monocyclic and bicyclic aromatic hydrocarbons components in the light components of tar were significantly increased.3.In this research,we used potassium chloride,calcium chloride,copper chloride,and cobalt chloride to input the load through the impregnation method.It is found that the four ions all reduce the initial temperature of pyrolysis and increase the pyrolysis reactivity of coal,but the degree of influence is different.Potassium is conducive to the increase of pyrolysis gas content,and calcium inhibits the escape of volatiles in the active pyrolysis stage,which increases the semi-coke production.The catalysis of transition metals copper and cobalt reduces the binding energy of oxygen and promotes the conversion of coal to light weight,which increases the yield of tar by 23.9% and 17.8%,respectively,and increases the content of aliphatic hydrocarbons and monocyclic and bicyclic aromatic hydrocarbons.Compared with raw coal,the content of pyrolysis water in ion-loaded coal samples is generally higher.