Phase Composition and Formation Mechanism of Slag Crust in Blast Furnace

Abstract

Copper stave damage is common problem in blast furnace operations, and the formation of slag crust is beneficial to reduce the damage of copper stave. Therefore, an in-depth understanding of phase composition and formation mechanism of slag crust is helpful to clarify the protection mechanism of copper stave, so as to control the growth of the slag crust and to increase the service life of copper staves. In this study, the slag crust from a copper stave blast furnace was sampled, and the phase composition and structure of the slag crust were characterized in detail through XRD analysis and SEM-EDS. The results indicated that the slag crust presented apparent layer structure as the solid slag layer and viscous layer, which primarily consisted of gehlenite (Ca 2 Al 2 SiO 7), calcium aluminate (CaAl 4 O 7), magnesia-alumina spinel (MgAl 2 O 4), pleonaste (Mg 0.7 Fe 0.23 Al 1.97 O 4), kaliophilite (KAlSiO 4) and metallic iron. In addition, the ternary phase diagram analysis of CaO-SiO 2-Al 2 O 3 showed that the primary crystal phase of the slag is in the gehlenite region, and that the primary crystal region migrates to the calcium aluminate region with the increasing of Al 2 O 3 content, which are beneficial to the slag crust formation. Finally, the formation mechanism of slag crust was proposed.

X‐ray Computed Tomography Characterization of Slag Crust and the Effect of Bubbles and Metallic Iron in Slag on Heat Transfer to Copper Stave

“…The formation of the slag crust is a layered deposition. [ 5 ] When the gas temperature decreases or the cooling intensity of the copper stave increases, the thickness of the slag crust further increases and the enrichment of metallic iron appears on the hot side of the slag crust.…”

“…In previous studies, [8][9][10][11] the thermal conductivity of slag crust was assumed to be the thermal conductivity of slag. However, researchers have determined that the slag crust is a slag-ironmixed phase with porous structure, [5,6] which means that the selection of thermal conductivity of slag crust ignores the influence of metallic iron and bubbles. Currently, seldom literature is referred for slag crust thermal conductivity and the effect of bubbles/ metallic iron on the thermal conductivity of the slag crust.…”

“…Its detailed sampling location and macroscopic characteristics are reported in previous studies. [5,6] 2.2. X-ray Computed Tomograph…”

“…It is often during the medium repair or the end of the first generation of the blast furnace service that the researchers enter the furnace to sample and analyze the slag crust remaining in the copper stave after shutdown and clarify the phase composition and flow properties. [5,6] However, the operating life of a blast furnace is generally more than 10 years, which indicates that the information available on the slag crust heat transfer is still very limited. Ning et al [7] investigated the temperature distribution and heat flux through the copper stave under hanging slag conditions by thermal test.…”

Occurrence State and Behavior of Carbon Brick Brittle in a Large Dissected Blast Furnace Hearth

“…With the progress of low‐carbon and high‐efficiency smelting, researchers have gradually realized the importance of the blast furnace hearth. [ 1–5 ] The residual thickness of carbon bricks on the sidewall in the hearth has been seen as one of the key indicators for predicting the life of the blast furnace. [ 6,7 ] In the actual production process, there is often a sudden increase in the thermocouple temperature.…”