Development of analytical methods for characterizing metallurgical coke and the injectant coal chars, tars and soots formed during blast furnace operation

摘要

Blast furnace operation with coal injection at rates greater than 200 kg coal/tonne of hot metal, a rate less than the theoretical limit, has been often found problematic. The present study aims to gain a better understanding of the fate of injectant coal in the blast furnace by means of characterizing samples extracted from working BFs and pilot-scale rigs. The NMP (1-methyl-2-pyrrolidinone) solvent has been used to extract carbons relevant to BF operation, and comparison of the Size Exclusion Chromatographic patterns of the extracts has indicated that injectant coal is not able to completely combust or even completely pyrolyze during its journey from the tuyere nose through to and out of the “raceway”, and that the secondary reactions e.g. dehydrogenation and repolymerization, of coal tars are closely associated with the formation of the “soot-like” material. This has been confirmed by combined results from analyses using Ultraviolet-fluorescence, FT-IR spectroscopy and Transmission Electron Microscope. In addition, an attempt has been made to use FT-Raman spectroscopy as a relatively rapid technique to characterize various NMP-extracted carbon samples, with the aim to differentiate between carbons from different regions of the blast furnace. Two Raman spectral ratios, i.e.ID/IG ( intensity ratio of D to G band) and IV/IG(intensity ratio of the valley between D and G band to G band), have been found to be suitable parameters to indicate the size of the graphitic crystallites and the overall homogeneity of the carbon structures, respectively. Raman spectroscopy has been found to be able to closely estimate the composition of synthetic carbon mixtures, to indicate the different time-temperature histories that carbons had experienced at tuyere level. Finally, the ID/IG vs. IV/IG mapping has demonstrated its great potential as a reliable method based on Raman spectroscopy to differentiate between various types of carbons.