The Potential of Acousto-Ultrasonic Techniques for Inspection of Baked Carbon Anodes

Carl Duchesne,Moez Ben Boubaker,Jayson Tessier,Mario Fafard,Donald Picard,Houshang Alamdari

doi:10.3390/met6070151

Carl Duchesne, Moez Ben Boubaker + Show 4 more

Open Access

https://doi.org/10.3390/met6070151

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Journal: Metals	Publication Date: Jul 4, 2016
Citations: 9	License type: CC BY 4.0

Affiliation: Université Laval, Alcoa (Canada)

Abstract

High quality baked carbon anodes contribute to the optimal performance of aluminum reduction cells. However, the currently decreasing quality and increasing variability of anode raw materials (coke and pitch) make it challenging to manufacture the anodes with consistent overall quality. Intercepting faulty anodes (e.g., presence of cracks and pores) before they are set in reduction cells and deteriorate their performance is therefore important. This is a difficult task, even in modern and well-instrumented anode plants, because lab testing using core samples can only characterize a small proportion of the anode production due to the costly, time-consuming, and destructive nature of the analytical methods. In addition, these results are not necessarily representative of the whole anode block. The objective of this work is to develop a rapid and non-destructive method for quality control of baked anodes using acousto-ultrasonic (AU) techniques. The acoustic responses of anode samples (sliced sections) were analyzed using a combination of temporal features computed from AU signals and principal component analysis (PCA). The AU signals were found sensitive to pores and cracks and were able to discriminate the two types of defects. The results were validated qualitatively by submitting the samples to X-ray Computed Tomography (CT scan).

Highlights

The currently decreasing quality and increasing variability of anode raw materials make it challenging to manufacture the anodes with consistent overall quality
Defective baked carbon anodes decrease the performance of primary aluminum reduction processes by increasing energy and carbon consumption in the electrolysis cells
It is important to detect them before they are set in reduction cells

Summary

Introduction

The currently decreasing quality and increasing variability of anode raw materials (coke and pitch) make it challenging to manufacture the anodes with consistent overall quality. Intercepting faulty anodes before they are set in reduction cells and deteriorate their performance (i.e., energy consumption and efficiency) requires testing all or the majority of the manufactured anodes. Even in modern and well-instrumented anode manufacturing plants, the traditional lab inspection strategy based on core sampling can, at best, evaluate the properties of about 1% of the manufactured anodes due to the costly, time-consuming, and destructive nature of the analytical methods. The core sample properties are typically available after the anode is set in the reduction cells due to the long lab delays. For economical and logistics reasons, it is generally not possible to improve the rate of anode testing by increasing the lab work load.

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Conclusion