Sponsored by: LMD Aluminum Committee
Program Organizer: Lise Castonguay, Alcan International Ltd., Arvida Research and Development Centre, PO Box 1250, 1955 Mellon Blvd, Jonquière, Québec, Canada, G7S 4K8
Tuesday, PM Room: A7
February 6, 1996 Location: Anaheim Convention Center
Session Chairperson: Mr. Per Stokka, Norsk Hydro a.s., Research Centre Porsgrunn, N-3901, Porsgrunn, Norway
2:00 pm
MODELLING OF PACKING OF PETROLEUM COKE FRACTIONS: Harald Schreiner, Morten Sorlie, Elkem A/S Research, PO Box 40 Vagsbygd, N-4602 Kristiansand, Norway; Per Goltermann, Vagn Johansen, G.M. Idorn Consult, Ramboll A/S, Bredevej 2, DK-2830 VIRUN, Denmark
The dry aggregate of anodes is composed of several petroleum coke fractions made up of particles from > 10mm to sub-micron size. The amount of each fraction in the recipe, and hence the packing of these particles have a determining influence on properties such as dry aggregate density, pitch demand, green paste rheology, green and baked anode density, anode slumping behaviour, permeability and others. A semi-empirical mathematical model originally developed for calculating bulk porosity (bulk density) in concrete mixtures, has been modified for use with paste plant petroleum coke fractions. The paper discusses the model and the necessary modifications to input parameters that make it useful for aluminum smelter paste plants, whether they make prebaked anodes or Söderberg anode paste.
2:30 pm
MASS LOSS, FUME AND POROSITY STUDIES OF PITCH + DUST BINDER MATRIX FOR ANODES: L. P. Lossius, M. Eie, S, Rorvik, H. A. Oye, Institute of Inorganic Chemistry, NTH/Unit, Sem Saelandsv, 12, N-7034 Trondheim, Norway
A commercial coal-tar pitch binder for anodes was mixed with petroleum coke dust, carbon black or graphite to study the effect of binder level, type of filler and analytic parameters on the mass loss and the porosity that developed after controlled heat treatment in a thermobalance. The porosity was determined by a recently developed automatic method of image analysis. The evolving fume was collected during the heat treatment and analysed by gas chromatography to study the effect of these parameters on the quantity and composition of the fume.
2:50 pm
METHODS FOR DETERMINING THE DEGREE OF BAKING IN CARBON ANODES: Colin P. Hughes, Comalco Research Centre, PO Box 316 Thomastown, Victoria, Australia 3074
Anode baking temperature is recognised as a critical factor in determining anode quality and performance. It is difficult and costly to measure directly and an indirect method, the coke Lc technique, is often used. In this technique, baking temperature is estimated from the average crystallite size in the "c" direction (Lc) of a coke sample placed in the anode stubhole. The paper details the results of a large statistically designed experimental program in which coke Lc results are compared to anode properties routinely measured by smelters. Anode thermal conductivity and air and carboxy reactivity were found to correlate well with baking remperature. Real density and a direct anode Lc measurement technique were found to correlate best at high baking temperatures. Recommendations are given on the usefulness and simplicity of traditional anode property measurements for assessing baking temperatures as alternatives to the coke Lc method.
3:10 pm
A 3D MATHEMATICAL MODEL FOR THE HORIZONTAL ANODE BAKING FURNACE: Y. S. Kocaefe, E. Dernedde, D. Kocaefe, Process and Systems Engineering Research Group (GRIPS), Department of Applied Sciences, University of Québec at Chicoutimi, 555 boul. de l'Université, Chicoutimi, Québec, Canada, G7H 2B1; R. Ouellet, Q. Jiao, Noranda Technology Centre, 240 boul. Hymus, Pointe Claire, Québec, Canada, H9R 1G5; W. F. Crowell, Noranda Aluminum Inc., P.O. Box 70, New Madrid, MO 63869
In aluminum industry, carbon anodes are baked in large horizontal or vertical ring furnaces. The anode quality depends strongly on the baking conditions (heating rate, soaking time and final anode temperature). A three-dimensional mathematical model has been developed for a horizontal anode baking furnace to be able to assess the effects of different operational and design parameters on the baking process. The commercial CFD code CFDS-FLOW3D is used to solve the governing differential equations. The model gives the temperature, velocity and concentration distributions in the flue, and the variation of temperature distribution with time in the pit. In this paper, a description of the 3D model for the horizontal anode baking furnace will be given. Some of results from different case studies will also be presented. The results show clearly the importance of flue geometry on the gas flow distribution in the flue and the heat transfer to the anodes.
3:30 pm BREAK
3:50 pm
COKE CALCINATION LEVELS AND ALUMINUM ANODE QUALITY: Christian Dreyer, Bernard Samanos, Aluminium Pechiney, LRF-B.P. 114, 73303 Saint-Jean-de-Maurienne, Cedex, France; Franz Vogt, Calciner Industries, Inc., PO Box 1306, Chalmette, LA 70044
The calcination temperature of petroleum coke for aluminum anode applications has been generally increased by coke suppliers during the past 5 to 10 years. This paper discusses the effects of this trend for both the calciner and the user. High and low sulphur cokes were calcined industrially at different levels and used to manufacture laboratory scale anodes. Anodes were produced with these individual cokes and with blends of these cokes. The influence of anode baking level on the anode properties was investigated. The results are presented and discussed.
4:10 pm
BATH IMPREGNATION OF CARBON ANODES: R. Perruchoud, W. Fischer, R&D Carbon Ltd., PO Box 157, CH-3960 Sierre, Switzerland
The mechanisms of the anode impregnation by bath in the electrolysis pots are reviewed. The rapidity of the penetration of bath in the anodes under different electrolysis conditions was measured in full size pots. In case of a cathodic contact of the anodes or of a cell current interruption, the butts (anode at the end of its service life) pick-up initially 0.2% of Na per minute. An exposition of the anodes to such conditions should therefore not exist otherwise a dramatic deterioration of the anode quality will occur when these butts are recycled.
4:30 pm
KINETIC STUDY OF THE CATALYTIC CARBONIZATION OF COAL TAR PITCH WITH PETROLEUM COKE: Jilai Xue, Harald A. Oye,Institute of Inorganic Chemistry, The Norwegian Institute of Technology N-7034 Trondheim, Norway. Morten Sorlie, Elken a/s Research, PO Box 40 Vagsbygd, N-4602 Kristiansand, Norway
The rate of carbonization has important impacts on the energy consumption and the unit productivity in baking process of prebaked anodes. In the present work the catalysts, such as S, AlCl3, ZnCl2, and FeCp2(CO)4, for pyrolysis or carbonization of pitches were seleted according to the defined criteria, and the kinetic behaviors of the carbonization of coal tar pitch - petroleum coke mixtures with and without catalysts were mainly investigated by thermogravimetric analysis (TGA). It was found that the mass loss over the major range of temperature for releasing of non-coking volatiles was increased with the catalysts, while a high coke yield (to binder pitch) was still possible. The observed kinetic effects of the catalysts will be discussed in connection with the anode baking process.
4:50 pm
A STUDY OF MEANS FOR IMPROVING PREBAKED ANODES AND REDUCING THEIR CONSUMPTION DURING ELECTROLYSIS: S. F. Egorov, H. Post, V. A. Sverdlin, Russia, 198147, St- Petersburg, Malodetskoselsky av, 26-7, HACA Technocentr, St- Petersburg
The modern tendency in the development of aluminum industry is the
construction of high efficiency prebaked smelters. Improving cell efficiency
and increasing anode block size not only modify cell operation but also affect
the anode performance due to higher thermal and mechanical stresses. The
quality of the carbon anodes will affect the cell life and the technical and
economical characteristics of the process. A higher prebaked anode consumption
will affect the total net cost of aluminum, deteriorate the cell process and
the environmental conditions in the potrooms. The objective of this paper is to
present means of reducing prebaked anode consumption by improving anode
quality. Results of laboratory and pilot plant experiments with various
impregnating materials and an inhibiting substance are reported. The former are
used to block anode pores and the latter reduces anode consumption during
electrolysis.
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