Upgrading of Blast Furnace Sludge and Recycling of the Low-Zinc Fraction via Cold-bonded Briquettes

Abstract

Depending on the operation of the blast furnace (BF), the main outlet of zinc from the furnace is more or less via the BF dust and sludge. As the dust is recycled to the BF, the sludge has to be de-zinced prior to recycling to prevent the accumulation of zinc in the BF. De-zincing and recycling of the low-zinc fraction via sinter have been reported. However, no research concerning recycling of upgraded BF sludge via cold-bonded briquettes has been performed. In the present study, a fine-grained BF sludge with low zinc content, generated by a BF operating on a ferrous burden of 100% pellets, was upgraded using the tornado process. The process simultaneously dried and separated the BF sludge into a high-zinc and a low-zinc fraction. The feasibility of recycling the low-zinc fraction to the BF using cold-bonded briquettes was studied on a laboratory-scale BF shaft simulator. On comparison with a reference briquette, the experiments indicated that 10 wt% of the upgraded BF sludge can be added to the briquette without negatively affecting the reducibility. Higher additions were found to render the briquette less reduced compared to the reference under test conditions corresponding to the central part of the BF. The strength of the briquettes was not compromised with the addition of the upgraded BF sludge, and a decision to study the briquettes in the LKAB experimental blast furnace was made in order to evaluate the behavior under actual BF conditions.

Metallurgical Properties of Vacuum Extrusion Iron‐Rich Dust Briquette and Its Effects on Blast Furnace Soft Melting Zone

“…Severe reduction disintegration reduces the permeability of the blast furnace and elevates the pressure differential within it, adversely affecting blast furnace production. [20,21] Generally, in the upper zone of the blast furnace, burden disintegration occurs within the temperature range of 500-600 °C. Low-temperature reduction disintegration performance was assessed following the international standard ISO 4696.…”

Suitability of Auger Pressing Briquettes for Blast Furnace Use Based on Laboratory Tests

“…A decrease in permeability may cause operational problems and affect the productivity of the BF process [9,10]. The material to be recycled, such as BF sludge [11], can also be moist, which further complicates the detection of fines [9]. Therefore, a suitable agglomeration technique is needed.…”

The production of high value pig iron nuggets from steelmaking by-products – A thermodynamic evaluation

“…Iron rich by-product dusts and sludges are an unavoidable consequence of ironmaking and steelmaking activity. The recycling of these fine dusts is usually simple, reincorporating the material into the process through agglomeration in a sinter plant (Umadevi et al, 2013) or via cold bonded briquetting/pelletization (Andersson et al, 2019); however, dusts recovered from the off-gas dedusting systems in the blast furnace (BF) and basic oxygen steelmaking (BOS) plants at integrated works are often contaminated with zinc. The deleterious effect of zinc on the blast furnace is well known (Besta et al, 2013;Narita et al, 1981) and even relatively low concentrations of zinc (100-120 g Zn per ton of hot metal) in feedstock material can have negative effects on process stability and thus the economics of production.…”