Abstract
Freeze lining is a solidified layer of slag formed on the inner side of a water-cooled pyrometallurgical reactor, which protects the reactor walls from thermal, physical, and chemical attacks. Because of the freeze lining's high thermal resistance, the reactor heat losses strongly depend on the freeze lining thickness. In a batch process such as slag fuming, the conditions change with time, affecting the freeze lining thickness. Determining the freeze lining thickness is challenging as it cannot be measured directly. In this study, a conceptual framework based on the morphology and microstructure of freeze lining and the rheology of the slag is discussed and experimentally evaluated to determine the freeze lining thickness. It was found that the bath/freeze lining interface lies just below critical viscosity temperature. The growth of the freeze lining is primarily controlled by the mechanical and thermal degradation of the crystals forming at the interface. The bath/freeze lining interface temperature for the measured slag lies in the range of 1035–1070°C.
Highlights
Refractories are heat-resistant materials that are physically and chemically stable at high temperatures
Freeze lining is a solidified layer of slag formed on the inner side of a watercooled pyrometallurgical reactor, which protects the reactor walls from thermal, physical, and chemical attacks
Microstructure and composition changes across the freeze lining thickness have been studied to identify the bath/freeze lining interface and compared with the solid fraction measured at the critical viscosity temperature
Summary
Refractories are heat-resistant materials that are physically and chemically stable at high temperatures. Microstructure and composition changes across the freeze lining thickness have been studied to identify the bath/freeze lining interface and compared with the solid fraction measured at the critical viscosity temperature. The viscosity measurements were made in a continuous cooling regime (1°C/min) from 1250°C and at three spindle speeds (90, 60, and 30 rpm) for slag A and 90 rpm for slag B until the temperature at which the spindle reached a set torque limit of 200 mNm. To determine the solid volume fraction of the slags at and near the critical viscosity temperature, the equilibrium quenching tests were carried out in a vertical tube furnace in an argon atmosphere at 1200°C, 1100°C, 1090°C, 1080°C, 1070°C. and 1060 °C. Each image was randomly divided into several smaller sections to obtain the distribution of solid fraction data within an image in contrast to the overall image
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