Working State Of Jingtang 5500 M~3 Blast Furnace Hearth

Hearth working is the beginning and end of the blast furnace (BF) smelting process. It is very important for the BF stability and smooth operation. The working state of BF hearth directly affects hearth longevity and high efficiency. The reasonable working state is generally characterized by safe lining thickness, no abnormal erosion, stable and reasonable skull, uniform and moderate blast parameters for each tuyere, good deadman permeability, abundant heat and active hearth center, smooth drainage, high quality of cast iron and so on. Hearth longevity is to solve the problem of hearth erosion. The rapid and abnormal erosion is mainly caused by poor hearth design, bad masonry, inapposite material selection, inadequate dry-out process, wrong operation or hostile working state. The deadman status, drainage behavior and tuyere blast distribution are the important components of hearth working state, which influence the longevity and efficiency directly. In addition, the hearth circular uniformity and activity are the concentrated expression of hearth working state. Particularly, it’s more difficult to predict and control the hearth circular uniformity and activity of large-scale or huge-scale BF due to its large hearth diameter than that of small one. At present, the judgment of hearth working state depends mostly on the original monitoring data and operational experience. The establishment and improvement of relative theoretical models and quantitative evaluation indexes will help analyze the hearth working state accurately. It is beneficial for achieving long campaign life and high efficiency. Therefore, this study focuses on the hearth working state of Jingtang 5500 m3 BF. The main innovation points are as follows.(1) The heat transfer model of hearth lining was established and the heat transfer difference between small carbon brick structure and large carbon brick structure was researched. What’s more, the improving measure on large carbon brick structure is put forward. The dynamic iron slag erosion experiment was carried out, and the erosion of liquid slag iron on ceramic cup and carbon bricks were studied. The critical hearth heat flux and dangerous critical hearth heat flux were defined. It was found that the critical heat flux for these BFs were different. Therefore, there was no uniform critical heat flux standard. Moreover, the differences between dangerous critical heat flux of hearth lining and stave were analyzed at different hearth conditions.(2) The floating height of deadman were calculated by deadman force-balance model and some influence factors including iron or slag filling were discussed. The molten iron flow model was built and the effect of floating state and permeability of deadman on hearth bottom temperature, molten iron flow patterns, wall shear stress and erosion position were studied. In addition, the reasons of different erosion profiles were also explained.(3) The two-phase flow model of hearth drainage was established. Furthermore, it was improved with considering interaction between deadman floating state and drainage behavior. The drainage behavior of Jingtang BF was calculated at overlap tapping mode. The reliability of the calculation results was demonstrated by the production data of Jingtang BF. During the drainage process, the influence factors on deadman floating height and drainage phenomena were also discussed.(4) The mathematical model of tuyere blast distribution was established and the tuyere flow resistance concept and formula were put forward. The influence of tuyere length and area on tuyere blast parameters was analyzed. The results show that with increasing tuyere length, the blast parameters of adjusted tuyeres would decrease, whereas the blast parameters of unadjusted tuyeres would increase. The blast volume of adjusted tuyeres would decrease when the tuyere area decreased; however, the blast velocity and kinetic energy would not always increase. In addition, the critical number formula of adjusted tuyere was proposed.(5) The hearth bottom of Jingtang BF was divided into some zones. The hearth circular uniformity index and activity index were built. The results show that in order to maintain the good circular uniformity, the hearth circular uniformity index should be bigger than 0.1. In order to maintain the good hearth activity, the overall activity index should be bigger than 7.