Degradation behaviors of coke under complex solution loss conditions

Solution loss reaction of coke provides reducing agent for ironmaking, which is an important chemical reaction in blast furnace. The coke itself is also degraded by the loss of carbon. In this paper, the degradation behavior of coke under complex conditions including alkali metal enrichment, simulated blast furnace temperature and atmosphere was studied. The pore size and pore wall thickness distribution of coke were measured by a microscope to characterize the structure of coke. The gasification reaction rate of coke matrix was measured by a thermogravimetric analyzer to characterize the matrix reactivity of coke. The results show that a coke has high CRI and low CSR, but it has high matrix reactivity and thick pore wall, which may lead higher strength after solution loss under alkali metal enrichment and simulated blast furnace atmosphere and heating conditions.

Investigation of the Effects of Coke Reactivity and Iron Ore Reducibility on the Gas Utilization Efficiency of Blast Furnace

The use of coke with high reactivity in the ironmaking blast furnace (BF) has yet to be explored, and a thorough understanding is still required to clarify the effect of coke reactivity on the BF gas utilization efficiency. In this paper, a one-dimensional kinetic model of the BF is presented and the accuracy of the model is verified. The model is then applied to analyze the effect of coke reactivity on the gas utilization efficiency of the BF. The results show that, under the operating conditions considered, the height of indirect reduction region and the starting temperature of coke solution loss reaction decrease with the increase of coke reactivity. Moreover, coke reactivity is first, directly proportional to gas utilization efficiency, and then, inversely proportional to it. In addition, high-reactivity coke may not improve gas utilization efficiency in case of high H2 content. Both, lowly and highly reactive coke need to be combined with highly reducible iron ore to maximize the gas utilization efficiency. Nevertheless, only appropriately reactive coke can combine with lowly reducible iron ore to obtain an optimal gas utilization efficiency. Hence, it is necessary to select coke with appropriate reactivity, in accordance with iron-ore reducibility, instead of blindly pursuing high-reactivity coke in actual operation.

Effects of alkali metal on solution loss and coke degradation

To research the effect of alkali metals on the solution-loss rate and coke strength after reaction, potassium and sodium vapors were prepared by a high-temperature thermal-reduction method, and the thermal properties of four industrial cokes that absorbed potassium and sodium vapor were studied. The thermal properties include the traditional thermal-property indices, coke reactive index and coke strength after reaction, and the coke strength after a 25% mass loss, which is obtained by a continuous thermogravimetric test. Results show that because of the different adsorption mode, the catalytic effect of potassium and sodium is different. During the early stages of the solution-loss reaction, the reaction rate of the potassium-rich coke is higher than that of the sodium-rich coke, but the reaction rate decreases rapidly. The reaction rate of the sodium-rich coke in the later stage of the reaction is higher than that of the potassium-rich coke. The coke strength after reaction of the alkali-rich coke is low, mainly because of the high carbon-solution loss. The coke strength after the 25% mass loss of potassium-rich coke was higher than that of the original coke because the solution reaction was closer to the surface reaction.