The Influence Of The Coke Microstructure On The Reaction Behavior And Performance In The Blast Furnace

New technology applications in blast furnace, such as high PCI, oxygen blast furnace ironmaking technology and injection coke oven gas technology, made the blast furnace coke rate greatly reduced. So that load of mechanical and chemical reactions was increased and put forward higher requirements to coke performance. At the same time, these new technology applications made the gas composition changed significantly. Especially, the influence of H2O content increase on the behavior of coke reactivity and strength should be paid attention. In this paper, several typical coking coals prepared directionally coke with different microstructures. Using optical microscopy, scanning electron microscopy, thermal gravimetric analysis and a variety of physical and chemical properties methods, the microstructure evolution of coke and its influence on strength were carried out under the conditions of CO2 and H2O. It was expected to reveal the microstructure evolution of coke in blast furnace and the law of macroscopic properties and provide a reference for the coke selection and macro performance under the new process.First, using optical microscopy, Raman spectroscopy, mercury and other detection methods, optical texture, pore structure and physical and chemical structure evolution of were studied in the process of solution loss. The results showed that, there was no difference in fine mosaic structure in the reaction with CO2 or H2O, but many large hole in CO2. The solution loss of H2O on coarse-grained structure and flow-type was greater than that in CO2. The destruction of CO2 on coke optical texture was concentrated in certain area. The solution loss reaction in H2O was focused on low optical effect. Under the same reaction rate, average pore diameter decreased and surface area increased with the increasing H2O content in reaction gas. Adding H2O to CO2 can promote the generation of small pore, but the effect was limited. Gasification reaction accelerated aromatic ring cleavage, which increased hydrogen-rich parameter. Gasification capacity of CO2 was lower than H2O. Selectivity for low activation energy was stronger and increased aryl structured extent after reaction. Selectivity of CO2 on disordered structure was stronger, so that the order of coke structure in H2O was lower than that in the CO2 conditions.By thermogravimetric analysis, coke optical texture, size and influence of H2O content on coke gasification reaction were studied. The initial reaction temperature of coke with optically isotropic tissue of fine mosaic structure and fragment-based was low. It can be achieved high reaction rate at lower temperatures and the influence of particle size on the gasification reaction behavior was small. The initial reaction temperature of coke with coarse mosaic, flow type and structure of the main char was high. The gasification reaction rate increases slowly with the temperature increasing and the maximum reaction rate required higher temperatures. Coke gasification reaction behavior was affected largely by particle size. In the condition of CO2 and H2O mixed gas, the optical tissue reaction higher, the smaller the impact of H2O content on the gasification reaction behavior. Compared with CO2, the solution loss effect of H2O in coke gasification with low optical tissue of coarse mosaic, flow-type structure and reactivity of carbon residue was stronger.By Nano indentation method, the mechanical property of micro-coke optical texture was characterized. Combined with the tensile strength of experiments, the effects of reaction conditions, pore structure and temperature on the properties of coke with different microstructure. After the gasification reaction of coke, different optical texture withstand the maximum load and elastic modulus decreased. Compared with CO2, the structure of coarse mosaic and residual carbon increased in H2O, which suppressed the strength reduction of microstructure. The influence of gasification on fine mosaic structure was smallest, followed by residual carbon and coarse mosaic structure. Under the same reaction rate, with the increasing of H2O content in CO2 and H2O mixture, the tensile strength of coke increased. The average pore size increases and the tensile strength decreased. Coke strength had a high sensitivity on hole. The more holes, the higher tensile strength of coke. Compared with in CO2, the strength of coke pore wall was higher in H2O. The resistance to deformation of coke was enhanced. Under high temperature tensile strength of coke was slightly higher than that in normal temperature. The tensile strength decreased with the rising of reaction rate and temperature.In the simulation condition of traditional blast furnace, oxygen blast furnace and injection coke oven gas blast furnace, coke microstructure evolution and its relationships with macroscopic properties were studied. Compared with the traditional blast furnace, reaction rate increased and drum strength decreased under oxygen blast furnace and injection coke oven gas blast furnace. The increase of H2O content promoted the formation of small pore and protected the pore wall of coke, which will suppress pulverization of coke. CO2 and H2O in gases promoted aromatic ring cleavage, which increased the absorption peak intensity of functional groups in the coke. The increasing of graphitization degree at high temperature reduced microstructure strength. In actual blast furnace, the low H2O content did not have much impact on coke strength. It will not have much effect on coke strength. For the influence of CO2 and H2O, comprehensive considerations should be the reaction rate, pore structure, microstructure, etc.