Evolution Of Coke Functional Groups And Pore Structures During Oxygen-enriched Combustion Of Typical Coals

Coal plays an important role in China's energy structure.However,coal has problems such as poor combustion stability,low efficiency,and serious environmental pollution during the combustion process due to the limitation of current technics.In order to achieve an efficient and clean combustion of coal,many scholars at home and abroad have studied the changes in the physical and chemical structure of coal during combustion.However the effects of changes in coal functional groups and pore structures,and the influence of oxygen concentration on combustion in the process of oxygen-enriched combustion have been studied less.Therefore,this subject has conducted an in-depth study of the evolution of coke functional groups and pore structure during the oxygen-rich combustion of coal.Based on the current status of coal-fired power plants in China,three typical coal types with volatile content of 10-30%are selected:Shanxi Wanliu Coal?Wanliu Coal?,Guizhou Guiyang Coal?Guiyang Coal?,Shanxi Luan Coal?Luan Coal?),to analyze the fuel characteristics,Thermogravimetric analysis method was used in combination with combustion kinetics analysis to study the effect of different oxygen concentrations on the ignition,steady burning,and burnout of the coal combustion process.Secondly,coal char samples with different oxygen concentrations and different combustion stages were prepared on a reformed tubular furnace.The functional group structure of coal char was analyzed by Fourier transform infrared spectroscopy?FTIR?to study the change law and the effect of different oxygen concentration on the functional group change.Finally,the pore structure analysis and SEM surface morphology analysis of the prepared char samples were performed by isothermal N2 adsorption method and Scanning Electron Microscopy?SEM?to study the specific surface area of coal char,the change law of pore structure and surface morphology,and the effect of different oxygen concentration on the pore structure change of char in the combustion process.The results showed that the combustion characteristics of coal were improved with the increase of O₂ concentration,but the degree of this improvement was different for different types of coal.It shows that different coals have different sensitivity to oxygen;With the increase of O₂ concentration,the ignition point and the burn-out temperature of coal sample were advanced,but the burn-out temperature of different coals varies in advance,with Wanli coal advanced by 20? and Luan coal and Guiyang coal advanced by 58?.With the increase of O₂ concentration,the apparent activation energy was increased as well.With the progress of the combustion,the relative content of functional groups such as hydroxyl,aliphatic,and aromatic hydrocarbons in the coal char particle functional groups were decreased,while the relative content of ether groups were increased.The coal char functional groups had similar changes in the combustion process with different O₂ concentrations.In the combustion process,the specific surface area and pore volume of the coal had been experienced a process of increasing first and then decreasing.In addition,coal and coke had more continuous pore structures,and similar trends occurred in the combustion.In the early stage of combustion,the pores?2-20nm?had a larger fluctuation,and the general trend was that the medium and large pores were increased.As the O₂ concentration increased,the temperature of maximum specific surface area and pore volume was reached more quickly,and the maximum specific surface area was increased as well.