Zinc accumulation during recycling of iron oxide wastes in the blast furnace

Abstract

Byproducts/wastes of iron-and steelmaking processes and steel scrap are the main sources of iron units recycled in the steel plants. Direct recycling of the iron oxide wastes (dusts and sludge) in the blast furnace (BF) is however hampered by its chemistry (.0 . 1%Zn in the charge). Vaporisation, condensation, oxidation and circulation of zinc may collectively lead to the accumulation in the furnace. Very fine particles are deposited on other particles that have high surface areas which diminish BF refractory life and impair the quality of high quality pig iron produced. For effective continuous recycling of iron units, it is necessary to identify their sources, determine their composition and evolve device and appropriate technology for the treatment of zinc bearing units. The present paper analyses the process of zinc accumulation in the BF and derives an algebraic model to determine the extent of the accumulation. On the basis of analysis of zinc base formation, its recirculation in the furnace and other related productive units, a homograph (alignment chart) of zinc accumulation is designed. The paper also outlines the feasible processes of zinc removal from the close-looped system (sinter plant-BF-sinter plant).

Recycling of Blast Furnace Dust in the Iron Ore Sintering Process: Investigation of Coke Breeze Substitution and the Influence on Off-gas Emissions

“…In the BF dust the Zn is present as an oxide. 6,32) In the blast furnace, Zn is volatilised and when the top gas cools down it forms fine ZnO particles. 8) Figure 6 shows an image of a BF dust particle with a large number of small deposits on its surface.…”

“…2,3) The recycling is generally controlled depending on the analysis of the material 4) because the recycled residues also have some effect on sinter quality, strength and productivity. In particular, the concentration of zinc and alkali metals (sodium and potassium) has to be controlled to avoid problems in BF operations 5,6) and similarly the concentration of hydrocarbons must be controlled to avoid problems in the sintering plant gas cleaning system. 7) Therefore, materials which contain harmful components like Na, K, Zn, Pb or oil at higher concentrations cannot be recycled through a sinter plant.…”

“…4) If an up-cycling of zinc happens in a closed-loop system, where the BF dust is recycled to the sinter feed depends on the de-zincing capacity of the sintering process. 6) Recycling of BF dust also increases the sulphur input to the sintering process. The concentration of sulphur in the BF dust is usually in the same range as the sulphur concentration of the coke breeze.…”

Erosion of Carbon Brick by Zinc in Hearth of Blast Furnace

“…The cyclic accumulation of zinc in a BF occurs due to the oxidation of the zinc vapors at low temperatures and their transformation into raw materials. [1][2][3] Zinc vapor condenses into fine particles in the pores of the raw materials and this causes hanging in the BF. Willemite (Zn 2 SiO 4 ) and zinc aluminate (ZnO•Al 2 O 3 ), which are considered as furnace accretions, are formed when zinc oxidizes on the surface of the lining.…”

Avaliação De Rota Híbrida Aplicada À Remoção Seletiva De Zinco Contido Na Lama De Aciaria Ld

“…Caso a lama contendo elevados teores de zinco seja reciclada, o acúmulo desse metal pode contribuir para a formação de uma crosta que impregna a parede refratária do alto-forno, sendo conhecida popularmente no jargão operacional por "cascão", que pode acarretar problemas operacionais, como o aumento no consumo de coque e a diminuição na vida útil dos refratários. (8)(9)(10) Portanto, é imprescindível remover o zinco da lama de aciaria LD, caso se deseje reutilizá-la no processo de produção de aço.…”