Experimental Study On Shenhua Coal Carbon/Nitrogen Conversion Characteristics During Pressurized O₂/CO₂ Combustion

At present,global climate change is becoming more and more serious.By 2021,global carbon emissions in energy will reach 33.6 billion tons,up 6%year on year.As the Chinese economy plays an increasingly important role in the world economy,carbon emissions in China also account for about one-third of the world’s total carbon emissions.Among them,the carbon emission of coal-fired power plants is as high as3.539 billion tons,ranking first among all industries in China.The Chinese government has pledged to achieve carbon peaking by 2030 and carbon neutrality by2060.Therefore,it is urgent to realize low-carbon emissions in coal combustion.Pressurized oxy-fuel combustion technology has attracted the extensive attention of scholars in recent years as a new technical means to achieve efficient CO ₂ capture in coal-fired power plants.The Shenhua bituminous coal is taken as the experimental samples in this thesis.The experimental research on the pressurized thermal conversion and carbon/nitrogen conversion characteristics of Shenhua bituminous coal is conducted,providing a theoretical basis for low-carbon and clean utilization in coal-fired power generation.Based on fully referring to the research of horizontal furnace reactors,the experimental system of the pressurized horizontal furnace reactor（Pressurized Horizontal Tube Furnace,PHTF）is designed and built.In this thesis,the main structure,feeding method,gas circuit system,preheating system,and other subsystems of PHTF are described in detail.Finally,the experimental system can realize stable operation under high temperature,high pressure conditions,which provides the basis for the experimental research of this research.The Pressurized Drop Tube Furnace（PDTF）is used to study the formation characteristics of carbon/nitrogen-containing gas-phase products and the evolution laws of physicochemical structure of pyrolysis char samples during the pyrolysis of Shenhua bituminous coal under high pressure,high temperature,and high heating rate.During the experiment,a portable Fourier transform infrared spectrometer（FTIR）flue gas analyzer is used to measure the volatile products in the process of pressurized rapid pyrolysis.Nitrogen adsorption,X-ray photoelectron spectroscopy（XPS）and FTIR and other methods are used to characterize the physicochemical structure of the pressurized pyrolysis char.The formation characteristics of CO/CO₂/CH₄/HCN/NH₃and other light gases during the pressurized pyrolysis of pulverized coal are quantitatively analyzed,and the evolution laws of the carbon/nitrogen-containing functional group structures on the surface of the pressurized pyrolysis char are obtained,and the correlation between physicochemical structure and reactivity of char is clarified.The pressurized O₂/CO₂ devolatilization characteristics and nitrogen migration transformation characteristics of Shenhua bituminous coal under different temperatures,pressures,atmospheres and residence times are studied.The effects of pressure factors（0.3～1.2 MPa）,temperature factors（1073～1273 K）and residence time factors（0.2～0.9 s）on the formation characteristics of gas phase products CO,N₂O and NO are analyzed in three devolatilization atmospheres.The effects of the above factors on the evolution of the physical and chemical structures of residues are analyzed by offline characterization.The results show that the increased devolatilization pressure and the introduction of a CO₂ atmosphere can lead to an increase in the specific surface area of the devolatilization residues and a decrease in the conversion rate of Fuel-N to nitrogen oxides.The increased residence time can lead to the decrease of CO and N₂O emissions,and emissions of NO first decrease and then increase.Combined with the relevant data results of the pressurized pyrolysis process of raw coal and the pressurized devolatilization process of char,the NO formed in the process of pulverized coal pressurized O₂/CO₂ devolatilization mainly comes from the oxidation of Char-N,and N₂O mainly comes from the oxidation of Volatile-N.The oxy-fuel combustion characteristics and N transformation characteristics of pressurized rapid pyrolysis char samples produced by Shenhua bituminous coal are experimentally studied using a Pressurized Horizontal Tube Furnace.The effects of experimental pressure（0.3～1.2 MPa）,temperature（1123～1273 K）,atmosphere（21～40%O₂）,and reaction time on the char samples’combustion weight loss rate are calculated by weighing methods.The influences of various factors on the conversion of carbon/nitrogen are investigated by online detection of gas-phase products during pressurized oxy-fuel combustion of char and offline analysis of the surface physical and chemical structure of combustion residues.The results show that the main nitrogen-containing phase products are NO and N₂during the process of char pressurized oxy-fuel combustion.The increased combustion pressure can accelerate the consumption of Char-N and inhibit its conversion to nitrogen oxides,while the increased combustion temperature and oxygen concentration can both consume Char-N and promote its conversion to NO_x.In summary,the formation characteristics of gas-phase products in the process of pressurized pyrolysis,O₂/CO₂ devolatilization and char samples O₂/CO₂combustion are measured online,and the surface physicochemical structures of above residual char samples are analyzed and characterized in this thesis.The formation characteristics of carbon/nitrogen-containing phase products in the pressurized thermochemical conversion process of pulverized coal/char are quantitatively obtained,and the evolution laws of carbon/nitrogen-containing structures of solid phase products during the above process are semi-quantitatively analyzed.The mechanism of pressure,temperature,atmosphere and residence time on carbon-containing/nitrogen-containing gas-solid products during pressurized oxy-fuel combustion of pulverized coal is revealed,which provides experimental data support for the development of pressurized oxy-fuel combustion technology.