Chemical desulfurization of west Kentucky coal using air and steam

Abstract

This paper presents the results of a detailed study on air-steam desulfurization of high volatile bituminous coal from West Kentucky that contains very fine pyrite (<10 ..mu..m). In this, study, temperature, coal treatment time, and the steam-to-air ratio were found to be important process variables, while particle sizes within the range of 1.4 mm to 150 ..mu..m were found to have no significant effect on desulfurization. An optimum steam-to-air mass ratio was found for maximum desulfurization as a result of two opposing mechanisms. While desulfurization was found to increase with oxygen concentration (which increases as the steam-to-air ratio decreased) at a low steam-to-air ratio, the rate of oxygen diffusion into the reaction sites descreases because of the reduced superficial gas velocity. This study also concludes that the use of steam together with air provides not only the advantage of increasing superficial gas velocity expected of the inert diluting gas but also the advantages of minimizing coal oxidation and improving coal desulfurization in a manner not obtainable with inert diluting gas such as nitrogen. Furthermore, through the air-steam treatment, the pyrite in coal was converted into magnetic iron compounds, iron sulfates, and pyrrhotites at first, and iron oxides (..gamma..-hematite and magnetite)more » in the end. This effect has provided additional desulfurization in subsequent magnetic separation.« less