Decarburization of High Carbon Iron with CO-CO2 and H2-H2O Gas Mixtures and Influence of Sulphur on the Decarburization Rate

Decarburization of iron with a high carbon content is one of the main reactions in the coal gasification process using molten iron bath, where O2 or H2O is used as an oxidizing agent. In this process, sulphur accumulation through direct dissolution of coal into the melt may influence the decarburization rate. In the present study, high carbon iron was decarburized by blowing H2-H2O and CO-CO2 gas mixtures on the metal surface in the temperature range between 1673 and 1873 K. Influence of sulphur on the rate of decarburization was also studied. The results were summarized as follows. (1) The following non-dimensional correlation was found in the regime of mass transfer control in the gas phase. (This article is not displayable. Please see full text pdf.) (2) When sulphur was added, a negative deviation from the above relationship was observed. This might be due to the mixed control of mass transfer in the gas phase and the chemical reaction on the iron surface. Much more deviation for CO-CO2 than for H2-H2O was observed. It was attributed to the fact that the apparent rate constant for dissociative chemisorption, kC, of H2O was much greater than that of CO2. The ratio between the rate constants was estimated to be more than ten at about 0.4 mass%S. (3) The rate constant for dissociative chemisorption, kC0, of H2O was found to be 30-80 times as large as that for CO2 on the basis of the sulphur blockage mechanism by chemisorbed sulphur. It was concluded that this difference in the kC0-values may cause the stronger influence on the rate of decarburization with CO-CO2 by the chemisorbed sulphur.