Minimising environmental emissions by optimised reductant utilisation (MEORU) : final report

The temperature profile at tuyere level is probably the most important parameter for influencing blast furnace performance because it has an effect at every step of physical and chemical reaction. This is seen especially as increased abrasion of coke, caused by carbon graphitisation and silicate reduction in the hottest flame zone, and as alkali attack on the coke in the colder deadman. The Raman analysis technique has proved to be a sensitive method for differentiation of carbon structure within BF dusts, coke and different chars related to BF operation. Results of the Raman analyses indicate that BF dust is a mixture of tuyere carbon (from high temperature zones of the BF) and coke formed by abrasion in the upper BF shaft. For BF dusts, a roughly linear relationship of the FWHM values from Raman analysis to the percentage of tuyere carbon is revealed. This relationship enables the quantification of tuyere carbon within the BF dust. The technique is useful for semi-continuous monitoring of the efficiency of reductant consumption during BF injection. Increasing amounts of tuyere carbon in the BF dust means lower efficiency of reductant consumption. Different injection modes (oil injection; PCI) lead to a characteristic content of tuyere carbon in the BF top gas dust. With oil injection a lower content of tuyere carbon is observed than with PCI. A lower tuyere carbon content with oil injection means improved reductant utilisation compared to PCI operation. However, this advantage is associated with higher costs for the injected reductant. The theoretical maximum decrease of reductant utilisation for PCI operation amounts to 0.6 % of the total carbon input (which is the amount of tuyere carbon in the top gas dust). A realistic assumption is that 50 % of the tuyere carbon emissions may be reduced, which means that 0.3 % of total carbon consumption is potentially saved by optimised injection practice. The new Raman analysis technique would be capable of assisting blast furnace operators in optimising furnace operation conditions by maximising reductant injection rates while maintaining best efficiency of reductant consumption.