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Cooling elements in operating furnaces, such as waffle coolers, finger coolers, cooling staves, and plate coolers, are subject to wearing and deterioration over time. Ultrasonic (UT) pulse echo is an efficient nondestructive testing methodology to monitor the thickness and quality of the cooling blocks through periodica] inspections; however, the highly dampening properties of copper and the high temperatures on the hot face of the cooling elements could cause errors in UT thickness measurements. To eliminate potential errors in UT measurements, a study was conducted to determine the correct temperature and velocity distributions and relationship in waffle coolers. In this study, a combination of mathematical modeling and experimental work was used to establish a relationship between the temperature and the speed of ultrasonic waves in copper elements.
INTRODUCTION
In August 2003, Polokwane Smelter experienced a structural failure caused by a water leak from an extensively corroded waffle cooler. In order to avoid similar situations in the future, an extensive effort was undertaken jointly by Hatch NDT and Anglo Platinum Polokwane Research teams aimed at identifying and applying a reliable, continuous monitoring technique for measuring copper thickness variations during furnace operation.
This paper presents a description of the method developed for continuous monitoring of deterioration and wearing of waffle coolers and the experimental verifications of this technique.
PROBLEM DEFINITION
Copper has a high thermal conductivity and is used as the main component in cooling elements in metal- lurgical furnaces, such as finger cool- ers, plate coolers, and waffle coolers. Waffle coolers in pyrometallurgical furnaces are designed to prevent the furnace shell from overheating, thereby prolonging the furnace campaign. The coolers are made of high-quality copper, 99.7% purity, with internal Monel cooling circuits to control the heat flux to the furnace shell from the smelting process.
Chemical reactions and mechanical wearing effects, alone or combined, inside the operating furnace could result in alteration of the geometry of the copper hot face, reducing its intended thermal and structural functionalities. Excessive wearing results in a reduction of the copper thermal mass and could ultimately cause failure of the water-bearing cooling circuits, and thus, failure of the waffle coolers.
In the case of the Polokwane Smelter, because of the reactive nature of the concentrate with the copper, the waffle coolers...