Coupled Thermo-mechanical Analysis About Blast Furnace Staves

BF stave is one of main cooling equipments of the blast furnace. To keep the staves in safety is necessary for BF to attain a long life. The steady slag skull that protects the staves is formed on the surface of the staves in the higher heat load areas such as belly and breast of BF. The thickness and shape of slag skull depended on cooling parameters and process conditions. At the same time, they have influence on the stave state. The mathematic models of steady and unsteady thermal transfer of BF staves made of cast iron, copper and compound copper-steel were established respectively, which were used to analyze stave conduction, slag skull distribution and growing process. The thermal stress of copper-steel compound stave was studied with the method of thermal mechanical coupling. Finite element analyzing software ANSYS was taken to build model, mesh and calculate. The main researches are as follows:A new analysis method of steady thermal transfer was established by simulating slag skull melting through 'Element Birth and Death' of ANSYS, called as 'Slag Skull Melting Iteration'. The problem that the slag skull thickness could not be ascertained presently was solved. The accuracy and practicability of thermal transfer analysis about stave was improved. According to working condition of BF staves, the refractoriness under load was used to describe the adhesion capacity of slag skull. The adhesion temperature was defined as 1100℃. The steady thermal transfer analysis about three kinds of stave with different materials was carried out through the model built in this research. The influence of process condition and cooling parameters on the body temperature, slag skull thickness and heat load was studied.Based on steady thermal transfer analysis, the stimulating method for slag skull recovery was created through 'Element Birth and Death' of ANSYS. For the first time, the unsteady thermal transfer analysis was actualized during slag recovering after dropping off. On the unsteady thermal transfer model, the slag skull recovering process on the surface of copper and copper-steel staves was studied. The growth rhythm of slag skull, as well as varying of stave temperature and heat load was analyzed. The influences of process conditions on the stabilization time taken by slag skull recovering and copper body steadying were also researched.By means of the slag skull melting iteration, the unsteady thermal transfer analysis about cast iron stave in different process conditions was performed. The results showed that gas temperature was the main factor that affected slag skull thickness, heat load and stave temperature. Increasing intensity of cooling had no obvious effect on stave. The safe temperature for cast iron stave was 1280℃. In addition, the safe heat load was 39.6kW/m~2. The standing capacity of stave was improved by increasing the pipe diameter and decreasing gap width. The slag skull dropping off made the stave temperature rise rapidly, which decreased the life of stave. After the stave had been burned out, spraying water on the shell would increase heat loss enormously. Only when gas temperature was lower, there was solid slag filled among the water pipes and the shell.The results showed that slag skull was not distributed uniformly on the surface of copper stave in height through analysis of the steady thermal transfer about copper stave. There was thicker slag skull on the surfaces of copper ribs. In addition, the slag skull thickness was thinner in the front of the inlayed bricks. As gas temperature went up, no uniformity was ascending and the slag skull was easier to drop off. The slag property had larger influence on copper stave temperature, heat load and slag skull thickness. When slag velocity was higher, slag skull thickness increased. If gas temperature changed, the heel would be formed. During slag skull recovery, slag skull growth followed the power function. In the primary stage, slag skull grew more quickly. Subsequently the growing rate decreased. Gas temperature had obvious influence on slag adhering. The stabilization time was 10.5~32.7min. The maximum temperature of copper body was 140℃. The analysis results were consistent to process experience of copper stave.On the foundation of steady and unsteady thermal transfer analysis, coupled thermo-mechanical analysis about copper-steel compound stave was performed to investigate slag adhering capacity and safety. The results showed that slag adhering capacity of copper-steel stave was the same as copper stave. When slag skull was stable, the maximum temperature in the stave is 120℃. There was the maximum equivalent stress 122MPa in the copper body and 87MPa on the interface of copper plate and steel plate. The stabilization time is 17.6~46.4 minutes during slag skull recovery. The maximum temperature in the copper body went up to 166℃. The maximum The copper body and interface equivalent stress rose respectively to 171MPa and 127MPa. Therefore, there would not be plastic deformation in the copper body and separation between copper plate and steel plate. The results from the model were consistent to process experience in test.