Development of iron layers on the internal wall of reduction reactors

Refractory bricks are the most common materials used in equipments for carr ying processes at high temperatures, such as the production of steel, cemen t and glass. These bricks are exposed to severe operation conditions, their life determines if an equipment should be stopped for reparation or replac ement of the bricks. One of the phenomena that is present inside reactors o r furnaces with an internal wall covered by refractory material is the form ation of layers. As they growth, they cause disturbs in the product flow or at least decreases the reactor or furnace capacity, and in the worst case it is necessary to stop the equipment for major reparations. This work is c entred in the formation of layers inside the direct reduction reactors. The se layers are formed over the firebrick (Al2O3, SiO2) wall from the Direct Reduced Iron (DRI) that is being processed in the reactor. The aim of this work is to describe the mechanism of formation and growth of these layers. We conducted several test for simulating the formation of layers by the app lication of shear stresses at high temperatures and under a reductive atmos phere to the a DRI pellet-refractory interphase. The amount of DRI adhered to the sample bricks was measured following an experimental design of nine independent variables. Temperature, shear stress and time were identified a s important variables for the mechanism of formation and growth of the laye rs. Confirmation of the importance of these variables was determined by mea ns of a proposal for avoiding the adhesion problem. This proposal consists in a treatment on the surface of the brick that minimizes the adhesion of D RI. The successful treatment of more than 6000 bricks for operating plants proves that our conclusions are correct. (C) 1999 Elsevier Science Limited and Techna S.r.l. All rights reserved.