Optimisation of blast furnace raceway at high injection rates

The aim of this project was to clarify the raceway behaviour during high coal injection operations and to establish its influence on the whole blast furnace operation. A two-dimensional physical model (coke combustion with cold air) was built to simulate the raceway dynamics. Results show an unsteady raceway, expanding cyclically from a minimal to a maximal size, followed by the massive collapsing of the coke vault. Without coal injection, most relevant parameters on the raceway size are coke grain size and gas flow rate, with opposite effects. Coal injection produces a quick change of the raceway behaviour, which becomes larger. Optical methods were developed to investigate raceway depth (peephole method) and three-dimensional raceway space (lance method) during blast furnace operation. Results show raceway dimensions of 40-110 cm in depth and 40-60 cm in width, with possible change of 30 cm in depth during short periods. These measurements could not be clearly correlated with the blast parameters and with the results of coke core borings performed in parallel at the tuyere level. The influence of many parameters (raceway, bird nest and dead man characteristics, burden distribution) on blast furnace operation has been studied with an upgraded mathematical model. Results contribute to get a better picture of the situation inside the blast furnace, mainly in terms of cohesive zone position and shape. They provide a better understanding of the involved phenomena, of their interactions and of the furnace behaviour in response to an increase of the coal injection rate.