Copper Stave Research Articles

Metallurgical insight of premature failure of a Blast Furnace copper stave

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.

Simulation and Validation of Thickness of Slag Crust on the Copper Stave in the High-Temperature Area of Blast Furnace

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.

X‐ray Computed Tomography Characterization of Slag Crust and the Effect of Bubbles and Metallic Iron in Slag on Heat Transfer to Copper Stave

Understanding the heat transfer properties of the slag crust is critical to the safe operation of copper staves. The distribution of metallic iron and bubbles in the slag crust is detected by X‐ray computed tomography. The thermal conductivity of the slag crust is modified based on an effective thermal conductivity model and laser thermal conductivity measurements to predict the effect of metallic iron and bubbles on the heat transfer in the slag crust. The results show that the average volume fractions of metallic iron and air bubbles in the slag crust are 3% and 4.5%, respectively. The measured value is consistent with the trend of the effective thermal conductivity calculation model, and the calculation result of the Maxwell–Eucken effective thermal conductivity model is very accurate. Variations in the volume fraction of metallic iron in the slag crust have a greater effect on the thickness of the slag crust, while variations in the volume fraction of bubbles have a smaller effect on the thickness of the slag crust. It is recommended to keep it between 10 and 30 mm in blast furnace production to help improve the operational life of the copper stave.

Investigation of Formation and Shedding Behavior of Slag Crust in a Large Blast Furnace with Copper Stave: Flow Properties and Crystallization Characteristics

The damage of the copper stave will affect the sustainable production of the blast furnace and is not conducive to improving the economic efficiency of the blast furnace. The formation of a stable slag crust is crucial for the longevity of the copper stave. In this study, the flow properties and crystallization characteristics of the slag crust in a blast furnace with the copper stave running for 10 years without damage in China were analyzed. The phase precipitation during the cooling process was calculated by FactSage software. The phase composition and micromorphology of the slag crust were studied in detail by XRD and SEM–EDS. The results show that the slag phase in the slag crust is a CaO-SiO2-Al2O3-MgO-FeO slag system with high alumina content (33.62 ~ 35.72%) and low magnesium oxide content (2.68 ~ 3.84%). The melting characteristic temperature of the slag crust in the belly and the bosh is between 1127–1303 °C and 1287–1500 °C, respectively, and the characteristic temperature of the cold side of the slag crust is higher than that of the hot side, which was mainly resulted from the tendency of gehlenite and magnesia-aluminum spinel in the slag phase to precipitate during the cooling process. With the increase of the basicity of the slag phase, the precipitation temperature and amount of gehlenite increase, resulting in the characteristic temperature of the slag crust in the bosh significantly higher than that in the belly. The increase of FeO content reduces the initial precipitation temperature of crystals, and the increase of cooling strength is beneficial to the slagging on the copper stave, which provides a theoretical basis for the stable operation of the slag crust on copper stave blast furnace.

Numerical simulation of slag layer and its distribution on hot surface of copper stave based on ANSYS birth-death element technology

The core of the long-life copper stave was to ensure the stability of the slag layer, and the uniform distribution of the slag layer was beneficial to restrict the generation of the overthick slag layer. A novel model for calculating the thickness and distribution of the slag layer in the part of copper stave was established based on the finite element theory through the ANSYS birth-death element technology. The distribution and thickness of the slag layer on the hot surface of copper stave were calculated and analyzed when the gas temperature and slag properties tended to be changed, which was applied to characterize the slag-hanging capability of copper stave with the changes of furnace conditions. It was shown that the thickness of hot surface slag layer in the part of copper stave decreased obviously while the temperature of stave body raised rapidly with increasing gas temperature. When the gas temperature was 1400 °C, the inlaid slag layer was gradually melted, and the maximum temperature of the stave body was closed to 120 °C. The change of gas temperature was very sensitive to the adherent dross capability of copper stave which would be enhanced by the promotion of slag-hanging temperature. However, when the slag-hanging temperature was 1150 °C and the gas temperature was lower than 1250 °C, the overthick slag layer was easily formed on the hot surface of the copper stave, and its stability was poor. The improvement in the thermal conductivity of slag could be conducive to the formation of the uniform and stable slag layer on the hot surface of copper stave, especially in the dovetail groove. When the thermal conductivity of the slag was greater than 1.8 W m−2 °C−1, the inlaid slag layer in the dovetail groove was not melted, although the gas temperature reached 1500 °C.

Optimization Analysis of Mechanical Performance of Copper Stave with Special-shaped Tubes in the Blast Furnace Bosh

Optimization Analysis of Mechanical Performance of Copper Stave with Special-shaped Tubes in the Blast Furnace Bosh

Manufacturing technology and application of cooling stave in blast furnace

The service life of blast furnace (BF) is depending on the cooling equipment of furnace body, cooling stave which is an important cooling equipment for BF has attracted more attention. In the current paper, the classification of BF cooling staves in China was introduced, cast iron stave, cast steel stave, copper stave, and copper-steel composite stave were used on different parts of furnace body. The manufacture of cooling staves was studied, evaporative pattern casting (EPC) was favored due to high automation and environmental protection. The strong combination between steel plate and copper plate of copper-steel composite stave could be ensured under high-speed oblique impact through explosive welding. High density and high thermal conductivity of copper stave could be obtained by efficient rolling technology. The performance and application of BF cooling stave were investigated, the advantages and disadvantages of the various cooling staves were analysed, the thermal resistance between the steel water pipe and the cast iron body accounted for about 80% of the total thermal resistance which would affect the cooling effect of cast iron stave. The significant cost advantage of copper-steel composite stave was found compared with copper stave, test results of copper-steel composite stave in a commercial BF showed that the cooling effect is equivalent to that of the copper stave. The suitable cooling stave in BF should be selected according to the characteristics of the various cooling staves, the heat transfer balance and the stability of the skull on the hot face must be ensured to protect the cooling stave.

Research on the Influence of Furnace Structure on Copper Cooling Stave Life

Abstract In this paper, a blast furnace gas flow distribution model with variable furnace structure was founded based on CFD (computational fluid dynamics) theory, and the gas velocity distribution near the surface of the copper staves in different areas of the BF is calculated under different conditions of variational structure parameters like Bosh angle, shaft angle, and the newly proposed “equivalent Bosh angle.” Based on the calculation, the influence rule of the BF structure on the service life of copper stave and the corresponding operation measures were obtained. The result shows that the increase of the Bosh angle and the decrease of the shaft angle will incur increasing of the gas flow velocity near the surface of the copper staves, which is harmful to the cooling stave life; the variation of the equivalent Bosh angle has a most significant influence on the cooling stave life, and the increase of the equivalent Bosh angle will cause a sharp increase of the gas flow velocity, which will damage the copper staves seriously; adopting long tuyeres and minishing the equivalent Bosh angle will reduce the washing action of the gas flow and ensure the stability of slag hanging to achieve a long service life of copper staves.

Heat transfer and thermal deformation analyses of a copper stave used in the belly and lower shaft area of a blast furnace

This article describes a mathematical model to predict the temperature, thermal deformation and stress in a copper stave with no accretion layer during operation. The effects of gas temperature, cooling water velocity, copper stave thickness and bolt position on temperature, thermal deformation and stress of copper stave are investigated. The results show that a maximum temperature, about 422.5 K (149.5 °C), is found just near the top or bottom of the copper stave hot face. Copper stave deforms into the typical parabolic arc. Decreasing gas temperature can decrease the temperature, thermal deformation and stress, and decreasing the distance between the bolts and top or bottom border of copper stave are available in decreasing the copper stave thermal deformation, therefore improving the copper stave life. Increasing copper stave thickness can increase the temperature and thermal deformation for smaller copper stave thickness, while the thermal deformation in copper stave decreases with copper stave thickness increase for higher copper stave thickness. Water velocity has little effect on temperature and thermal deformation in copper stave, while much effect on the thermal stress around the root of the pipe.

The Process Optimization of Cast Copper Stave Based on ProCAST

According to the structure of cast copper cooling stave, two kinds of different pouring systems were designed, and the casting process numerical simulations were conducted with ProCAST software in order to project the foundry defects. Then adopting the process optimization based on the preliminary simulated results and determined the final casting technique of cast copper cooling stave. The results of trial production show that the cast copper cooling stave basically meets the requirements of technology.

The Research on Creep Deformation and Thermal Stress of Cast Copper Staves

The creep deformation of the cast copper cooling staves was researched based on the steady temperature field by using thermal - mechanical coupling finite element transient analysis method and ABAQUS software. The results show that the creep deformation only under the effect of thermal stress is slight and negligible compared to the deformation generated by thermal expansion. The total tress is not adequate to crack the stave body. Therefore, the cast copper stave can meet the requirements of blast furnace longevity.

Model of Forming-Accretion on Blast Furnace Copper Stave and Industrial Application

Copper staves have been equipped on nearly all of BF (blast furnaces) with volume over than 1000 m3 in China since their introduction from abroad about more than 10 years ago. Because of short application and lack of experience, phenomena of thickened or naked of copper stave happen occasionally which influence production severely. So it is important to study the model of forming-accretion on BF copper stave and realize real-time monitoring of forming-accretion on different copper staves. Therefore, mathematic model of calculating accretion thickness by heat flow of BF is proposed, and the calculated results indicate that accretion thickness could be kept at a reasonable range of around 50 mm by controlling heat flux around 22.0 kW/m2. The monitoring program based on the model was applied to a certain BF in China successfully, and it is found that slip of BF near the inner wall is one of most important reasons that cause fluctuation of accretion thickness. During the period of scheduled maintenance of the certain BF, the thickness of accretion measured through the static pressure holes is in good accordance with the value calculated by the monitoring program, so the results calculated by the monitoring program can be used to guide industrial production.

Conjugate heat transfer analysis of copper staves and sensor bars in a blast furnace for various refractory lining thickness

Lining erosion is the most important factor for determining the campaign life of a blast furnace. To provide information about the heat transfer of the copper stave in the belly of the No. 1 blast furnace at CSC (China Steel Corporation), a conjugate heat transfer model, including the heat transfer of the stave and sensor bar in thermal conduction and radiation transmission from the gas temperature inside the blast furnace and convection heat transfer in cooling pipe, was developed for the steady state process. The simulations focus specifically on the effects of the gas temperature, the geometric thickness of the cooling stave, the slag layer thickness and the material and diameter of the sensor bar. The results show that the refractory lining and the slag shell provide significant protection for the stave body. A copper sensor bar can be used to measure the residual lining thickness of the cooling stave. To estimate a more reasonable stave thickness, several key factors, such as the diameter and material of the sensor bar, were examined in this study. The results can serve as important reference information for blast furnace operation and the prediction of its campaign life.

Quantificational indexes for design and evaluation of copper staves for blast furnaces

The quantificational and normative design is the precondition of improving the design of copper staves for blast furnaces. Based on a 3-dimensional temperature field calculation model, from the view point of heat transfer and long campaigns note with the core of forming accretion, the forming-accretion-ability (FAA) and the rib hot surface maximum temperature difference (ΔT max) as quantificational indexes to direct and evaluate the design of copper staves for blast furnaces were presented. The application of the two indexes in design essentially embodies the new long campaigns in the stage of design. With the application of the two indexes, good results can be obtained. Firstly, it was suggested that the rib height of a copper stave can be reduced to 15 mm, which is a new method and theory for the reduction of copper staves. Secondly, the influence of insert on FAA and ΔT max is decided by the volume of insert. According to this, the principle of design for the hot surface geometry of copper staves was put forward that the ratio of the rib hot surface to the copper stave hot surface (abbreviated as the ratio of rib to stave) must be maintained in the range of 45% to 55%; for the present copper stave with a 35–40 mm thick rib, the ratio of rib to stave in the range of 50% to 55% can optimize the design of copper staves; for the copper stave with a smaller rib thickness, for example 15 mm, the ratio of rib to stave in the range of 45% to 50% can optimize the design of copper staves. It can be summarized that the thicker the rib thickness, the larger is the ratio of rib to stave.

Monitoring Method for Blast Furnace Wall With Copper Staves

Abstract A monitoring method that has been designed for the first time for blast furnace wall with copper staves manufactured in China was introduced. Combining the method of “inverse problem” and the concept “non-inverse problem”, the monitoring program for blast furnace wall with copper staves has been realized, which can be used to calculate online the accretion thickness and temperature of hot surface of copper staves after obtaining the values of thermocouples of copper staves. The accretion state obtained in the actual investigation has proved that the result of the program is correct. The monitoring program shows that the accretion would easily fluctuate when the accretion layer is extremely thick or thin, thereby the stable and smooth operation of the blast furnace is hindered. By maintaining appropriate accretion thickness, both long campaigns and high productivity of the blast furnace can be achieved; furthermore, it can also optimize the operation of blast furnace and maximize its production. Approximately 30–50 mm in thickness of accretion layer is maintained on the wall of Shougang blast furnace 2, which can meet the requirement for obtaining both long campaign and high productivity.