Study On Physicochemical Structure Of Char In Pressurized Thermal Conversion Of Pulverized Coal

In recent years,pressurized oxy-fuel combustion has received increasing attention as a new technology for controlling greenhouse gas emissions.It requires pressurized reaction environment with high temperature and high concentration of carbon dioxide is used to dilute oxidant.Pressurized pyrolysis and pressurized carbon dioxide gasification are the two foundations of this technology.The current domestic understanding of this process is still insufficient.In particular,the chemical structure of solid fuels in thermal conversion.In this paper,the physicochemical structure and reactivity of pressurized rapid pyrolysis char and pressurized fast gasification char of Shenhua bituminous coal were studied.Argon and carbon dioxide were used as a reaction atmosphere at a pressure of 0 MPa to 1.2 MPa,at 800 ° C and 1000 ° C using a pressurized drop tube furnace(PDTF).Focus on the effects of pressure,temperature and gasification atmosphere on char structure and reactivity.The surface pore structure was characterized by nitrogen adsorption,and the fractal dimension of different char was calculated.The functional group of char was measured by Fourier transform infrared spectrometer and the carbon skeleton of char was analyzed by Raman spectroscopy.X-ray photoelectron spectroscopy was used to measure the surface functional groups of char;char reactivity was measured using a microfluidic bed reaction analysis system.The analysis results show that the specific surface area of the pyrolysis char peaks at 0.5 MPa as the pressure increases.At 800 °C,the increased pressure promotes the growth of microbubbles,which causes the pore structure of the char transferring into small size.However,due to the small amount of gas production,the pressure increase does not significantly affect the aggregation of the bubbles.At 1000 °C,the pressure promotes the fusion between the bubbles.The char pores are developed to the macropores,and the pressure increase has a great influence on the coalescence behavior of the bubbles.After 0.5 MPa,the specific surface area decreases but the pore volume expands.At 800 °C,the increased pressure increases the decomposition of volatiles in the char continuously.At 1000 °C,the volatiles begin to decrease with the increase of pressure after 0.8MPa.Both the increased pressure and the high pyrolysis temperature promote the polymerization between aromatic rings,and the char carbon skeleton macromolecule gradually develops toward the stable graphitized structure.The increase in pressure promotes the formation of esters.The correlation between ketones and pressure is not high.Increasing the environmental pressure of the gasification reaction,the number of macropores,mesopores and micropores on the char surface are increased to different extents,resulting in larger specific surface area,making the gasification reaction attack the amorphous structure of char and reducing char reactivity more easily.However,the effect of pressure on the polymerization of aromatic sheets is more significant to the reactivity of char.The increase of carbon dioxide concentration greatly promotes the char specific surface area of the char and forms a certain surface complex on the surface of char;however,the increase of gasification reaction reduces the reactivity of char by the consumption of amorphous structure of char.