Anode baking furnaces is an integral part of aluminium industry. In this furnace, anodes are baked to use in electrolytic reduction. Depending on the design either open top or closed top furnaces are employ ed. Till date, alumino-silicate refractories are the choicest material due to low cost, low creep under compression, high resistance to thermal cycle, carbon monoxide disintegration and alkali attack. This paper deals with failure mechanism of such type of refractories. Used samples from a Reid Hammer bake oven have been studied to find out the reasons of failure. The failure has occurred due to thermomechanical, pyro-chemical stresses and alkali attack in reducing condition. Out of different reasons of failure, alkali attack in reducing condition is found to be the prime cause for failure.[Keywords : Alumino-silicate, Alkali attack, Aluminium industry]
IntroductionAnodes are required for pot lining furnaces where alumina is reduced to metallic aluminium. These anodes are made of petroleum coke along with spent anode bonded with pitch which is formulated at high pressure for baking in furnace before use. The anodes are baked at a temperature range of 1150 o -1200 o C. In the electrolytic pot cryolite (NaAlF 6 ) is being added as electrolyte. During the process the anode absorbs alkali oxide and comes in the spent anode. 1 Alumino-silicate refractories with alumina content ranging from 45-50% are generally used in these types of furnace. For getting higher life, the proper selection of refractory is of paramount importance to refractory manufacturers and users. 2 In the present study, attempts have been made to understand the failure mechanism of refractory used in a Reid Hammer bake oven with future action to augment the furnace life.A number of literatures are available on the study of failure mechanism of alumino-silicate refractories in anode baking furnace. However, till now, significant studies have not been carried out to assess the failure due to alkali attack on the refractory. 3 The present study is attempted to understand the mechanism of refractory attack by alkali.
Interdependence of structure and viscosity of blast furnace slag is discussed based on the available literature. Emphasis is given to both, bridging tendency and network breaking/modifying tendency of the constituents. It is clearly pointed out that slag viscosity cannot be explained only by depolymerization through an increase in basicity, despite the fact that an increase in basicity of the slag, in general, lowers the viscosity of the slag by a process of generation of discrete anions containing simple chains and/or rings by causing depolymerization of the 3D silicate network.
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