Material losses in the blast furnace process arecaused by particles which are blown out by the offgas.In order to reduce these losses, it is important tounderstand the off-gas dust formation. Off-gas dust,as flue dust and sludge, were collected in LKABExperimental Blast Furnace (EBF) and from twoindustrial blast furnaces of SSAB in Lulea andOxelosund. Characterisation of the off-gas dust wasmade using XRD, SEM and LOM. The evaluation ofcharacterisation results focused on fines from carboncontaining particles, although the results includes ironbearing materials and slag formers as well. Thegraphitisation degree of coke in flue dust is comparedwith charged coke. Results from the different blastfurnaces are compared and discussed. The resultsshow that flue dust is mechanically formed wherecarbon containing particles dominates in the fractions>0.075 mm and consists mainly of coke particlesfrom the shaft. Fe-containing particles, as Fe_2O_3, arethe major component of flue dust fractions <0.063mm and originated from the top of the shaft. In theEBF, sludge is mainly made of chemically formedspherical particles <1μm precipitating from theascending gas as the temperature decreases. Theamount of alkali and SiO_2 in sludge increases withhigher PCR and flame temperature, which confirmedthat sub-micron spherical particles in sludge originatefrom the high temperature area around the raceway.In full scale blast furnaces, sludge is more crystallinethan in the EBF. SEM investigations revealed thatsludge is affected by the gas cleaning water andchemicals.
展开▼
