Study On Pyrolysis Extraction Of Low Rank Coal And Thermal Conversion Of Extracts To Coke

China is rich in low-rank coal resources,accounting for more than 50%of the total.However,due to the characteristics of high water content,easy oxidation,low calorific value,high ash content,fragile and flammable,low-rank coal has not been effectively utilized in a large-scale manner in China.Currently,the efficient and clean utilization of low rank coal has become a research hotspot in the field of coal chemistry,and solvent extraction and upgrading is the key to achieving efficient,clean,classified utilization of low rank coal and improving utilization efficiency.In this thesis,two kinds of low-rank coal（lignite and long-flame coal）are used as raw materials.First,the solubility parameters of coal,single solvent and mixed solvent are simulated and calculated by MS software.Then,wash oil is used as solvent to conduct pyrolytic extraction in a high-pressure reactor.The influence of process conditions on the extraction effect is investigated.The basic properties,chemical structure,fluidity and pyrolysis characteristics of the extract are characterized.Finally,PLM,XRD,Raman SEM and other means have studied the microstructure（mesophase,carbon microcrystalline）changes of the two extracts during thermal conversion and coking,providing data support for the comprehensive utilization of low-rank coal extracts with high added value.The results show that:（1）Using the classic Fuchs model,Given model,Wiser model,Wender model,and Shinn model as model molecules for low-priced coal,through box model construction,structural optimization,and kinetic simulation,their solubility parameters were obtained to be 17.18（J/cm³）^1/2,18.41（J/cm³）^1/2,17.49（J/cm³）^1/2,17.29（J/cm³）^1/2,and 21.49（J/cm³）^1/2,respectively,which are smaller than the 22.46（J/cm³）^1/2of wash oil.（2）The extraction yields of both types of coal increase with the increase of temperature,reaching 76%and 84.33%respectively at 400 ℃.The extract has low aromaticity index(I_ar),high branched chain index（CH₃/CH₂）and rich oxygen functional group structure.The viscous flow activation energies of the two extracts（H-10-400 and C-10-400）are 105.84 k J/mol and 108.26 k J/mol,respectively.The pyrolysis process of the extract has three distinct stages（<240 ℃,240～400 ℃,400～500 ℃）,with activation energies of 44.77 k J/mol,79.97 k J/mol,and 140.78k J/mol for H-10-400,and 55.58 k J/mol,84.21 k J/mol,and 193.03 k J/mol for C-10-400.The corresponding pyrolysis mechanisms for each stage are:random nucleation and subsequent growth model,first-order chemical reaction model,random nucleation and subsequent growth model.（3）The thermal conversion process of the two extracts（H-10-400 and C-10-400）into coke conforms to the liquid phase carbonization theory.The yield of lignite extract at 500 ℃ is 45.55%,while the yield of long flame coal extract at 500 ℃ is50.18%.The mesophase content of lignite extract is 50.16%at 420 ℃ and 4 hours,while that of long flame coal extract is 59.66%at 420 ℃ and 4 hours.The mesophase coke prepared from lignite extract mainly has a sheet-like structure,supplemented by a medium particle mosaic structure and a fine fiber structure,which can be used as the preferred raw material for preparing needle coke.The intermediate coke prepared from long flame coal extract has a completely embedded structure,mainly consisting of fine and medium particle embedded structures,and is the preferred raw material for preparing isotropic coke.With the increase of carbonization temperature,the content of regular graphite microcrystals in the two kinds of mesophase coke increases,the content of amorphous carbon decreases,the microcrystalline structure tends to be more orderly,and the carbon layer stacking is closer to the graphite sheet layer structure.