The Research Of Corrosion Mechanism And Longevity Of Hearth In Large Blast Furnace

Under the background of large-scale development of blast furnace in China,the hearth life of large blast furnace became the key to blast furnace longevity,and is becoming restrictive link in large scale blast furnace advantage.Baosteel built the over4000 m³ large scale blast furnace in China at the earliest,and have investigated 5 large scale blast furnace hearthes systematically.Combined with experimental study,numerical simulation research and achievements in the operation of the blast furnace research analyzed the main reasons for the large scale blast furnace hearth damage as well as how to design,operating up to prolong the service life of blast furnace hearth.Since Baosteel No.1 blast furnace(1^st generation)was blown out in 1994,the hearth damage investigations were on-going from then on,the latest blast furnace No.3 and No.4 blast furnace not only conducted wear line survey,but also studied deadman and salamander states,physical and chemical properties,microstructures of hearth residual materials without drilling out residual iron.The researchers concluded that:1)the blast furnace hearth corrosion degree was different in different locations,the most serious corrosion was 1-2 meters under taphole;2)although the solidification layer was continuously deepened,the salamander of the large blast furnace hearth still sat on the bottom of the hearth;3)after corrosion,the carbon brick substrates inside the hearth were permeated by the foreign elements,and the closer to hot side the carbon brick was,the higher the content of foreign elements was.4)There were solidification and crisp layer between the carbon substrate and deadman,iron,the crisp layer may be powdered on the serious corrosion area.The size of solidification and crisp layer were different in hearth various regions.By Baosteel X-ray study and other scholars of carbon brick corrosion resistance experiment results can be seen when the molten iron and carbon brick after contact,the molten iron will permeate into carbon brick through the porosity of carbon brick soon,once high temperature molten iron and carbon brick has had the contact,carbon brick was soon eroded by unsaturated carbon hot metal,molten iron was easy to permeate into carbon brick substrate,it showed that the main reason for the blast furnace carbon brick hearth corrosion may be dissolution of molten iron after carbon brick contacted the molten iron,it also illustrated the other elements found in residual carbon brick of blast furnace.Because of these,the hot side temperature of carbon brick should be reduced to below 1150?,it also formed solidification layer between carbon brick hot side and deadman to isolate the molten iron and carbon brick,avoiding direct contact.There is no method to directly measure the carbon brick hot surface temperature,the method of numerical simulation of quantitative research of carbon brick can research the temperature filed of carbon brick hot side,molten iron flow field and sidewall shear stress field,due to operating blast furnace hearth structure is very complex,the study uses single factor analysis method to study operation,design parameter changes and these influence of the temperature field.From the operation of the blast furnace,the influence of carbon hot side temperature were analyzed thought changing smelting intensity,tap hole depth,tap hole angle,taphole diameter and tapping angle parameters.Smelting intensity,tap hole depth,and tapping angle have the greatest effects on the hot surface,the higher the smelting intensity,shallower tap hole depth is,the smaller the iron angle is,they maybe lead to sidewall temperature rise,shear stress increases,adverse to the longevity of the hearth.From blast furnace longevity operation practice,some methods have been used such as reducing production,blocking off tuyeres and increasing blast kinetic energy,to decrease sidewall temperature.On large blast furnace operation process,the depth of the tap hole must not be less than 3500 mm,minimum tap hole angle as far as possible big,try to arrange the big tapping angle to tap.At the time of sidewall temperature is higher,opposite angle tapping mode was benefit to reduce the sidewall temperature.In terms of design,it can improve the heat transfer efficiency of the whole hearth by improving the heat conductivity of the refractory material,increasing the high thermal conductivity safety wall and eliminating the air gap in the side wall of the hearth.The higher the thermal conductivity of refractory material,can effectively lower the temperature in the hearth sidewall hot side,helps to form a solidification layer,high thermal conductivity in hearth sidewall safety wall can push high temperature to the furnace,but high heat conduction safety wall will be at the expense of the other performance carbon brick,is likely to cause corrosion intensified.Blast furnace hearth in the process of production may produce gas gap,by means of grouting can eliminate the air gap,improve the heat transfer efficiency of sidewall,but in actual production,due to thoughtless on the paste solidification performance,pressure control,irreversible damage may be caused,that is the reason the Baosteel blast furnace No.3 and No.4blast furnace have large difference on longivity.Large blast furnace deadman depth is increasing,and the depth of baosteel blalst furnace deadman increase from 1800 mm to3600 mm,from the perspective of the results of numerical simulation,it is disadvantage with the deadman depth increasing and do not relieve molten iron ring current along the side wall.Many measures have been taken on the operation and long life maintenance to prolong the life of Baosteel blast furnace.Compared with 5 large blast furnaces that have been blown out in Baosteel,the life have big differences,through researching blast furnace performance index,longevity maintenance measures to analyze the main cause of the blast furnace life differences,including smelting intensity choice on the early blow-in,coal ratio,the stability of the blast furnace operation,the blast furnace grouting maintenance,tap hole depth,tapping angle and so on has carried on the detailed analysis.