A study on dissolution kinetics of carbon in liquid iron bath

Abstract

Dissolution of carbon in liquid iron melt is one of the very important reactions in chemical and metal processing industries, as it decides, in many cases, the productivity of a process or quality of the product. As a result, the current investigation was undertaken to study the effect of different physical and chemical characteristics of five types of carbon sources on dissolution kinetics. Bath chemistry being a very important factor in determining the process, two types of iron bearing materials, namely, electrolytic iron and sponge iron were employed for the study. It has been found that though the ash in carbon exhibits significant effect on carbon dissolution, the influence of the volatile matter was not found to be noteworthy. It has also been observed that petroleum coke undergoes maximum dissolution possibly due to its porous structure as well as less amount of inherent impurity. Silicon is found to be a strong promoter of the kinetics whereas the depressing effect of sulphur is not found to be that pronounced. Preliminary results of a mathematical model shows that the dissolution in Tamman furnace takes place under constant heat flux condition.

Introduction

The dissolution of carbon in molten iron bath is one of the important reactions in the chemical and metal processing industries and has assumed special significance in the last two decades in the light of new technological developments around the world. To cite a few practical examples: coal gasification in iron bath involves dissolution of carbon in the liquid iron bath where it reacts with the dissolved oxygen to form carbon monoxide. When oxygen is blown in iron–carbon melt, an exothermic reaction takes place and thus, there is a possibility of using increasing amount of scrap in oxygen steel making. The latest trend in non-conventional iron making route is smelting–reduction process where iron oxide in liquid iron bath gets reduced with the help of dissolved carbon. The success of this process depends greatly depends on the rate of carbon dissolution in liquid iron as it decides the rate of carbon supply for reduction of iron oxide and thus the productivity. In shaft furnaces like blast furnaces and cupola, carbon dissolution from coke takes place where liquid iron droplets are in direct contact with carbon. For many foundry practices, carbon pick up by hot metal is a limiting factor because the machinability depends on the amount of carbon and it should be high for good machining characteristics. On the other hand, carbon dissolution by hot metal should be avoided in certain situations. For example, in the well zone of blast furnace extensive carbon pick up from carbon blocks will lead to break down.

Many investigators [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11] have studied the effect of inherent physical properties of different forms of carbon, bath composition, state-of-bath, etc. on dissolution kinetics. But it has been found that anomalies still exist on many major issues such as the effect of sulphur, carbon structure, role of volatile matter, etc. on the carbon dissolution. In the present investigation, an attempt has been made to reinvestigate some of the controversies employing carbon sample widely varying in chemical composition as well as in structure. Further, a comprehensive mathematical model has been developed involving heat and mass transfer phenomena. Salient aspects of the model have been presented briefly in this paper to perform preliminary analyses for mass transfer coefficient and thermal state-of-bath.