A study of the volatilisation of coal sulphur during combustion under conditions similar to a blast furnace raceway

Pulverised coal injection (PCI) is used in ironmaking to replace expensive and energy intensive coke with coal, reducing overall costs and greenhouse gas emissions. As the coke making process removes some of the sulphur present in coal, the utilisation of PCI results in the admission of greater levels of sulphur into the blast furnace. The increased sulphur levels could potentially lead to an increase in costs and energy usage related to hot metal sulphur removal processes. In an increasingly volatile market, the ability to make use of higher sulphur coals is also of both financial and logistical relevance. This work aims to produce a more thorough understanding of the transformation of sulphur introduced through PCI into the blast furnace, leading to changes in coal selection, blending, or mitigation efforts. The volatilisation of sulphur from four coals used in PCI was investigated using a drop tube furnace (DTF) to produce conditions similar to a blast furnace raceway. Chars and flue gases were analysed using a range of techniques, including X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, and wet chemistry methods. The coal's burnout was found to be the biggest factor in coal sulphur volatilisation. It was found that a coal's volatile matter content was a key indicator into the volatility of a coal's sulphur content; it influences the rate of a coal's burnout, the availability of hydrogen for the formation of H2S, and the reactivity of the produced chars. Coals with higher volatile matter contents are more likely to volatilise their sulphur component at shorter residence times than coals with lower volatile matter contents. The bonding of volatilised sulphur to nascent char was seen in coals with lower volatile matter contents. The sulphur forms present in the initial coal samples were shown to influence the sulphur forms found in the collected chars.

Automated summary

Pulverised coal injection (PCI) is a method used in ironmaking to reduce costs and greenhouse gas emissions by replacing coke with coal. However, the use of PCI results in higher levels of sulphur in the blast furnace, which can increase costs and energy usage for sulphur removal. This study investigated the volatilisation of sulphur from coals used in PCI and found that the coal's burnout and volatile matter content are important factors affecting sulphur volatilisation. Furthermore, the sulphur forms present in the initial coal samples can influence the sulphur forms found in the collected chars.