Tianjun Yang

Zinc Accumulation and Behavior in Tuyere Coke

A case study of zinc oxide, which represents the first report on the occurrence, crystalline features, formation mechanism, and influence of this mineral in tuyere coke, was conducted in this study. A number of zinc oxides, some of which were in hexagonal wurtzite habit, were observed to distribute mainly in coke pores, cracks, surfaces, and around coke minerals. The accumulation of zinc in tuyere coke may enhance the degradation of coke and increase the generation and accumulation of coke fine in a blast furnace, which would cause bad effect on blast furnace operation. Investigations into zinc behavior in tuyere coke can be important for further interpretations of coke degradation in the high temperature zone of a blast furnace.

Influence of Profile of Blast Furnace on Motion and Stress of Burden by 3D-DEM

The objective of the present investigation is to analyze the influence of profile of blast furnace on the burden motion and stress field through 3D-DEM (three-dimensional discrete element method). It is clarified that the decrease of shaft angle speeds up the velocity of burden descending and decreases normal stress between particles or particle and wall. This change is good for the smooth operation of blast furnace. However,-ore and coke would be mixed for the too small shaft angle (75°), which would influence the permeability in blast furnace. Thus, the appropriate shaft angle is around 80°. Decrease of bosh angle prevents the burden descending motion and increases normal stress between particles and bosh wall. Meanwhile, maximum normal stress acting on the wall moves from belly wall to bosh wall in the case of 68° bosh angle, which accelerates abrasion of refractory in bosh by friction force between particles and wall. Although burden descends smoothly in the case of 88° bosh angle, room is not enough for the ascending heated gas flow. Thus, the appropriate bosh angle is about 78°.

Interfaces Between Coke, Slag, and Metal in the Tuyere Level of a Blast Furnace

An in-depth understanding about the reactions in the high-temperature zone of a blast furnace is significant to optimize both the current and future blast furnace process. The interfaces between coke, slag, and metal were observed using scanning electronic microscope with samples obtained from the tuyere level of a blast furnace. Two types of slag phases were identified, one originating from coke ash and the other from the bosh slag. Slag formed by coke ash was seen to cover the coke surface, which may hinder the reaction of coke with both gas and liquid iron. The reduction of FeO from the bosh slag (originated from the primary slag) occurs in the coke/slag interface with the reduced iron forming a metal layer surrounding the coke surface. The reduction of SiO2 occurs both in and outside the coke, and the reduced silicon reacts with iron to form iron silicide if the two species come into contact. Further study is proposed based on the results of this study.

Graphitization of Coke and Its Interaction with Slag in the Hearth of a Blast Furnace

Coke reaction behavior in the blast furnace hearth has yet to be fully understood due to limited access to the high temperature zone. The graphitization of coke and its interaction with slag in the hearth of blast furnace were investigated with samples obtained from the center of the deadman of a blast furnace during its overhaul period. All hearth coke samples from fines to lumps were confirmed to be highly graphitized, and the graphitization of coke in the high temperature zone was convinced to start from the coke surface and lead to the formation of coke fines. It will be essential to perform further comprehensive investigations on graphite formation and its evolution in a coke as well as its multi-effect on blast furnace performance. The porous hearth cokes were found to be filled up with final slag. Further research is required about the capability of coke to fill final slag and the attack of final slag on the hearth bottom refractories since this might be a new degradation mechanism of refractories located in the hearth bottom.

Pulverized Coal Combustion of Nitrogen Free Blast Furnace

The efficiency of coal combustion is an important factor for the blast furnace process. The influence of low xo/xc on coal combustion performance under nitrogen free blast furnace condition was researched through the self-developed pulverized coal burning device. The results show that the coal combustion rate reduces with xo/xc decreasing, and the combustion rate of bituminous coal is higher than that of anthracite. The coal combustion rate ascends with the rise of volatile matter, but when volatile matter of pulverized coal is more than 18%, the combustion rates will not increase correspondingly. Small amount of CaCO3 and CO2 additions can promote coal combustion, and the effect of CaCO3 is more apparent, which can increase the pulverized coal combustion rate by 15%–18% or so.

Comprehensive Evaluation of OxyCup Process for Steelmaking Dust Treatment Based on Calculation of Mass Balance and Heat Balance

Through the mass balance and thermal balance calculation for a typical OxyCup (or OxiCup) furnace process featuring a capacity of 380 kt/a of steel plant residuals, the material flow and thermal flow diagrams were firstly obtained. Then, the performance of the main fuel in the OxyCup process, i. e. coke and carbon dust, was analyzed, and the results indicated that coke was mainly used as the stock column skeleton for the furnace and exothermal agent with a weak reduction ability; whereas carbon dust was mixed in the C-brick to reduce the iron oxide. In addition, the comparison between OxyCup process and traditional blast furnace process indicated that the reduction and melting processes in the OxyCup process were relatively isolated, while in the traditional blast furnace process, they were mixed with each other in the high temperature zone. Moreover, oxidizing atmosphere is necessary in part of the OxyCup furnaces to ensure the complete combustion of part of the coke, while only reducing atmosphere is allowed in traditional blast furnaces. Finally, it was confirmed that oxygen enrichment can make a remarkable increase of the energy income and high temperature blast makes only a small contribution to energy income as the energy from the combustion of carbon takes up nearly 90% of the total income.

Ore blending ratio optimisation for sintering based on iron ore properties and cost

Abstract The iron ore blend for sintering depends to a great extent on ore properties. It is hard to determine the final sinter reducibility from the reducibility and ratio of single iron ores in a mixture. For production cost reduction, optimised blending ratios were designed according to ore prices and properties (microstructure, crystal water decomposition, assimilation ability, liquid phase fluidity), ensuring nearly identical chemical composition as the mixture used in actual sintering. Sinter pot tests were conducted to determine the optimum mix. The results indicate that properties of iron ores vary greatly, which should be considered for the design of ore blending ratio. The total content of the two Australian ores tested should not exceed 45%. The cost of sintering process could be further reduced together with an improvement of economic and technical indices, only by ratio adjustment of present ores.

Damage mechanism of blast furnace tuyere by zinc

ABSTRACT A damaged tuyere from a practical blast furnace was sampled. The microscopic structure was investigated using a metallurgical microscope. The chemical analysis and mapping were investigated by a scanning electron microscope with energy spectrum analysis. Meanwhile, line scanning electron microscope with energy spectrum analysis was applied to investigate the change of content of copper and zinc from hot surface to the interior of copper matrix of the damaged tuyere. The results show that an alloy layer of about 2 mm in thickness appears on the hot surface of the damaged tuyere manufactured from pure copper, and the size of grains increases compared with the new tuyere. The content of zinc in the alloy layer decreases with spreading into the copper matrix. ExpAssoc function fits well with the variation of thermal conductivity of the alloy, and the thermal conductivity decreases with increasing zinc content in the alloy layer.

Damage mechanism of copper stave used in blast furnace

ABSTRACT In order to prolong the life of copper stave, the damage forms and reasons for copper stave were studied through the investigation of 49 blast furnaces. The damage mechanism for copper stave was investigated through thermodynamic calculation, microstructure analysis and scanning electron microscope. The results show that the main reason for the damage of copper stave is mechanical wear owing to the slag layer peel off on the hot face. Thermodynamic calculation results show the hydrogen disease reaction occurs as long as the gas flow is directly contact with copper stave body, and the volume expansion rate of copper stave body is about 183%, a large number of micro pores appear in the microstructure forcing copper stave damage. The oxygen content in copper material is critical to hydrogen disease; the service life of copper stave will be extended by strictly controlling the oxygen content in copper material.

Optimization model coupling both chemical compositions and high-temperature characteristics of sintering materials for sintering burden

We developed a mathematical optimization model coupling chemical compositions and high-temperature characteristics of sintering materials, targeting the best quality and lowest cost. The simplex algorithm was adopted to solve this model. Four kinds of imported iron ores, two kinds of Chinese iron ore concentrates, and two kinds of fluxes were selected to verify both the model and the algorithm. The results confirmed the possibility of considering both chemical compositions and high-temperature characteristics of iron ores in the optimization model. This model provides a technical roadmap to obtain a precise mathematical correlation between the lowest cost and the grade of iron in sinters based on the condition of given raw materials, which can provide a reference to adjust the grade of iron in the sintering process for enterprise.