Simulation Research Of Catalytic Depolymerization Process Of Low Rank Coal

In china's coal resource,low rank coal?lignite,sub-bituminous coal?account for a large proportion,and account for more than 40%of coal.Due to the low rank coal has the characteristic of high oxygen content,high internal moisture and low calorific value,it has no advantages to direct combustion and utilization.Therefore,based on the characteristics of the low rank coal is a large number of aromatic structural units are connected by bridge bonds,it is an important way to achieve the clean and efficient cascade utilization of low rank coal,under proper temperature promote bridge bond fracture,obtain higher value added oil and gas products,and increase the carbon content of solid semi-coke.Compared with the pyrolysis of coal by direct heating depolymerization,the addition of catalysts can help to promote the higher energy bridge breaks,regulate hydrogen radical stability,increase the conversion rate and change the yeild and distribution of products in low rank coal.In the catalytic depolymerization process,the catalyst can be directly involved in the bond breaking and cross-linking reactions of coal macromolecules through the addition of innovative catalysts,which can effectively improve the pyrolysis reaction efficiency under the low catalyst dosage?0.1 wt%?.Due to many complex reactions are involved in the process of catalytic depolymerization process of low rank coal,difference in the reaction mechanism between different catalysts and coal types has intensified the complexity of the process,so in order to further understand the characteristics and the subsequent industrial amplification of the catlaytic depolymerization process,it is necessary to build a macroscopic dynmaic model to describe the change trend,characteristics,make quantitative analysis and prediction of the catalyst depolymerization process.Firstly,the chemical percolation devolatilization?CPD?model was used to quantitaively analyze the raw coal pyrolysis and the catalytic depolymerization process of low rank coal with FeCl₃ and ZnCl₂ catalysts,respectively.Combining with the corresponding catalytic depolymerization experiment was carried out with Shaanxi long-flame coal.Based on the understanding of the mechanism of catalyst action and the results of catalytic depolymerization experiment,the corresponding apparent kinetic parameters were determined.The model quantitatively gives the mass distribution of tar,light gas and semi-coke products in different depolymerization time and temperature.The simulated results showed a good agreement with the experimental data and can better reflect the difference of different stages of pyrolysis process.In this model,the effect of the catalyst on the yield of pyrolysis tar was reflected by the composite rate constant and the crosslinking reaction activation energy,and the tar yield increased with the increase of these two parameters.For the Fe-based catalysts,it can promote the cleavage of side chain resulting in the increase of gas yield.As for the Zn-based catalysts,it can inhibit the crosslink reaction.However,when the activation energy of the crosslink reaction was too higher,the increase of the tar yield was increased slowedown due to the restriction of reaction temperature.Secondly,based on the CPD and FG-DVC model,the light gas functional group model is introduced into the low rank coal depolymerization CPD model.The relative content of functional groups of different precursors related to each component of light gas was obtained by using 2D linear interpolation method combine with the peak of infrared spectrogram of low rank coal was used to obtain the information of related side functional groups.Based on the understanding of the mechanism of catalytic depolymerization of NMA and XJA coal,combining with the results of catalytic depolymerization experiment,the corresponding apparent kinetic parameters of functional group fracture reaction were determined.The specific composition and distribution of light gas in the process of catalytic depolymerization were quantitatively analyzed and predicted,and this work quantitatively predict and analyze the influence of heating rate and pressure on catalytic depolymerization of low rank coals.The results showed that heating rate increased,which will reduces the active time of the catalyst on the coal during the catalytic depolymerization,which is beneficial to increase the yeild of tar and reduce the yeild of light gas.The increase of pressure is not conductive to the limited fragment during catalytic depolymerization,which reduces the probability of combining small molecule radical with limited debris,which will reducing the yeild of tar and can slightly increase the yeild of light gas.