Study On Reaction Mechanism And Char Structure Characterization In Pulverized Coal Injection Combustion Process

Blast furnace Pulverized coal injection is one of the most effective technologies to reduce coke consumption in blast furnace.Its main function is to provide heat source for blast furnace ironmaking and produce reducing gas CO.High-grade anthracite is usually used for pulverized coal injection,but with the decrease of anthracite reserves,more and more attention is paid to the injection technology of low-grade pulverized coal or blended coal.In this paper,the thermogravimetric experiment of pulverized coal was carried out by thermal analyzer,and the combustion characteristic index,reaction kinetic characteristics and combustion mechanism of several typical injected pulverized coal were studied.The results show that the combustion process of pulverized coal can be divided into a low-temperature stage,which generates a large amount of gas and devolatilizes,and a high-temperature stage,which is dominated by carbon oxidation.The results of thermal experiment show that with the increase of heating rate,the maximum combustion peak temperature of pulverized coal combustion goes back,and the thermal lag phenomenon appears.The kinetic study of pulverized coal combustion shows that the activation energy and frequency factor of coal will increase by the temperature,but with heating rate going up the activation energy and frequency factor of coal will gradually decrease.By comparing the activation energy of combustion with the pre-exponential factor under different working conditions,it is found that both of them have dynamic compensation effect.The combustion experiment of pulverized coal was carried out by simulating the injection process of blast furnace with high temperature settling furnace system.Studying the law of pore structure and surface morphology during the coal combustion.Results show that the adsorption-desorption curve of coal char presents a typical reverse S-shape,with the relative pressure going up the adsorption capacity of N₂will going up.When the temperature rises,some pore structures are destroyed,the number of pores decreases,and the adsorption capacity decreases.When the particle size increases,more pores are produced after the combustion of large-aperture coal char,and the pore volume and adsorption capacity increase.With the increase of oxygen concentration,the coal char burns violently,volatiles escape and holes are broken,the micropore structure disappears in large numbers,and the adsorption capacity of coal char gradually increases.According to the SEM results of coal char morphology,during the combustion process,the particle surface changes from micropores to macropores,and after macropores appear,the particles begin to collapse into irregular shapes.