Search

Present study investigates the premature failure (leakage) of copper (Cu) cooling staves placed at the lower stack region of a Blast Furnace (BF). This failure resulted in an increased frequency of make-up/ reserve water compensation every 10 h instead of average 24hrs. Detailed macro and microstructural analysis were carried out to understand the mechanism of failure in the Cu stave using phenomena observations, dial gauge measurements, metallographic investigation, and chemical analysis. Directional accretion of burden fines and puncture (leakage) profile were observed macroscopically. Puncture occurred from outer surface to inner surface of the channels of the stave. Micrographs of puncture location revealed non-uniform microstructure and grain deformation. Analysis suggested surface wear of the Cu stave due to a combined effect of continuous accretion of burden along with hot gas flow. Wear led to reduction in thickness and subsequent puncture/ leakage took place at the channel locations having a minimum cross-sectional thickness. With the help of this study, a failure mechanism of BF Cu Stave, a process critical component, has been explored. Recommendations such as insert modification, using more wear-resistant material or protective layer and conducting intermittent ultrasonic thickness measurements have been proposed to get an early warning of any untoward damages and process delays. [ABSTRACT FROM AUTHOR]

The blast furnace is the dominant high-temperature reactor in the modern ironmaking industry. Iron oxide in iron ores can be converted to metallic iron through blast furnace smelting, and this high-temperature melting can be used to separate the molten iron from the gangue components. The formation and thickness of the hot-surface slag crust on the copper stave in the high-temperature area of the middle and lower parts of the blast furnace are crucial for the safe operation and long campaign of the blast furnace. To enhance the precision of determining the thickness of the slag crust in this specific region, samples were extracted from the hot surface of the copper cooler situated in the high-temperature area. This extraction was carried out during the maintenance procedure of the blast furnace stockline. Subsequently, the thermal conductivity and melting performance of the slag crust were measured. The slag crust thicknesses corresponding to the various temperature measurement sites of the stave were determined by developing a mathematical model for the heat transfer of the copper stave. The actual slag crust thickness measurement data were acquired while the blast furnace stockline was in operation, and the data were then utilized to corroborate the model's predictions. A blast furnace with an effective volume of 3200 m3 was used to test the model. The average thickness of the hot-surface slag crust was computed for cases that occurred between 2020 and 2022. The data's correlations with the blast furnace's technical and economic indices during the same time period were examined. The findings indicated that the blast furnace's operation indices improved with a thinner slag crust, but there was also a higher chance of damage to the copper stave's internal cooling water pipes. Taking into account the technical and economic indices as well as a long campaign of the blast furnace, 150–200 mm is recommended as the appropriate average slag crust thickness on the surface of the copper stave in the high-temperature section. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The stability and nonlinear dynamic behavior of drilling shaft system in copper stave deep hole drilling were analyzed. The effects of the fluctuation of the cutting force, the mass eccentricity and the hydrodynamic forces of cutting fluid could be taken into consideration in the model of drilling shaft system. Based on the isoparametric finite element method, the variational form of Reynolds equation in hydrodynamic fluid was used to calculate nonlinear hydrodynamic forces and their Jacobian matrices simultaneously. In the stability analysis, a new shooting method for rapidly determining the periodic orbit of the nonlinear drilling shaft system and its period was presented by rebuilding the traditional shooting method and changing the time scale. Through the combination of theories with experiment, the correctness and effectiveness of the above methods are verified by using the Floquet theory. The results show that the mass eccentricity can inhibit the whirling motion of drilling shaft to some extent. [ABSTRACT FROM AUTHOR]

Copper staves have been widely applied in large blast furnaces especially those whose inner volumes exceed 2000 m3 due to high cooling capacity. In the past decade, copper staves suffered severe damages in some blast furnaces, which not only shortened their campaign lives, but also caused huge economic losses. In order to make out this phenomenon, the damage mechanism of copper staves was investigated via analyzing the chemical composition, thermal conductivity, metallographic aspects and microstructure in this paper. As a result, the working state was more likely to damage copper staves instead of their materials. At the beginning, the poor quality of the coke and the large bosh angle promoted the development of edge airflow, which intensified the erosion of refractory materials, resulting in the fall-off of slag crusts and damage of cooling water pipes. After repair, the cooling capacity of copper staves still declined, causing the temperature to rise easily; consequently, hydrogen attack happened when the temperature reached 370 °C, which degraded the performance of copper staves. Therefore, copper staves were worn too quickly to form slag crusts, which finally failed under the hydrogen attack and the scouring of the edge airflow at high temperatures. [ABSTRACT FROM AUTHOR]