Hogne Linga

The Equivalent Temperature Method for Measuring the Baking Level of Anodes

The equivalent temperature is a measure of baking level using a temperature scale (°E) based on heat treatment temperatures.

Interaction Between Anode Aggregate and Binder in the Sessile Drop Wetting Test

Coal Tar Pitch (CTP), recycled butts and Calcined Petroleum Coke (CPC) are the main raw materials used for anode fabrication. Over the last decades, considerable changes in CTP and CPC quality have been observed. Changes in metallurgical coke production technology have affected coal tar quality, and crude oil qualities have changed causing severe changes of CPC properties. This can have consequences for the mixing step during anode production, and the final anode performance. Hydro Aluminium has systematically followed these raw material changes and studied the effect on the interaction between coke and binders by applying a sessile drop measurement wetting test. The results are reviewed in terms of relevance for the anode production process. This article focuses on equipment, routines and sample preparation as they are crucial factors for obtaining reliable and repeatable results during these experiments. Wetting dependence on particle size and butt impurity level was found. Additionally, a method where hot pitch is added to a hot coke substrate is demonstrated.

Effect of Coke Properties on the Bubble Formation at the Anodes During Aluminium Electrolysis in Laboratory Scale

The anodic reaction of aluminium electrolysis cells leads to the formation of CO2 bubbles, which partly screen the anode surface and leads to an increase in the cell voltage. An advantage of these bubbles is that the formation and release contribute to the stirring of the electrolyte, however, the screening of the surface increases the irreversible energy losses. The voltage and current oscillation due to the bubble evolution during electrolysis for different anode materials have been determined in a laboratory cell. The effect of coke sulphur content and grain sizes were investigated. Anodes with finer coke fraction showed lower oscillations than coarser fraction equivalents. Additionally, the influence of current density on the amplitude of the anode potentials was measured. A 64% increase of current density caused an increase of anode potential oscillations from 79 to 170%.

Drilling of Stub Holes in Prebake Anodes

Stub holes may be a troublesome part in the production of anodes. Tension and cracks can be created around the stub hole. Vibrating the stub holes often introduces limitations for the optimisation of the production process.

Evaluating the Crack Resistance of Carbon Anodes: Implementation of a Measurement System for Tensile Strength and Fracture Toughness

Monitoring anode mechanical strength is increasingly important in production and operation of carbon anodes in high amperage cells due to higher crack driving forces. To achieve a better understanding of the directional crack resistance of the anode, a laboratory testing rig has been developed and installed at Hydro Aluminium Primary Metal Technology. The rig consists of a high-precision testing machine and a Hydro-developed measurement system which calculates the Young’s modulus of elasticity, the tensile strength, the fracture strain and the fracture toughness. The equations of the physical parameters are derived from a finite element modelling of the specimen loadings, and are implemented in a Hydro developed laboratory software which computes the values from load-deflection data and transfers the parameters to a database. The paper outlines this method including the sample preparation machine.

Hydro Aluminium's Historical Evolution of Closed Type Anode Baking Furnace Technology

The paper summarizes the historical evolution of the closed anode baking furnace technology from the Riedhammer design to the Hydro Aluminium concept in the Norwegian carbon plants; Ardal and Sunndal over the last 50 years.

Pilot Scale Anodes for Raw Material Evaluation and Process Improvement

Primary and secondary raw materials and carbon plant practices are of critical importance for anode quality. Frequent testing of cokes, pitch and production factors in a full scale plant would be feasible, but might be high risk and expensive. It could also be time consuming as the testing would be subject to the demand of production for priority. For over twenty years, Hydro has run systematic pilot scale tests in Ardal, Norway, and since 2005 the facility has been upgraded with intensive mixers and vacuum vibroforming. Today the pilot production simulates full scale operation, and pilot scale results are successfully implemented in carbon plants. The paper discusses the factors that ensure quality practices for pitch level evaluation, aggregate screening curves and baking level control. Examples are from tests of new material sources, a study of secondary raw materials quality related to carboxy reactivity, and studies of production parameters.