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
Wednesday, PM Room: A7
February 7, 1996 Location: Anaheim Convention Center
Session Chairperson: Dr. Bénédicte Allard, Carbone Savoie, 30, rue Louis Jouvet, B.P. 16, F-69631, Vénissieux Cedex, France
2:00 pm
RESIN BINDERS IN RAMMING PASTE: K. Kvam, H. A. Oye, Institute of Inorganic Chemistry, Norwegian Institute of Technology, University of Trondheim, N-7034 Trondheim, Norway; J. A. Johansen, R. Ugland, Elkem a/s Carbon , PO Box 40 Vaagsbygd, N-4602 Kristiansand, Norway
Resin bonded carbon refractories avoid the emission of PAH associated with tar based binders. Five prototype resin binders were tested and compared with two reference binders, one tar and one resin based. The binders were tested in the laboratory as well as in actual operation. For the optimum formulation, the mechanical strength was reasonably high and the baking shrinkage was low. Even if resin binders have a glassy structure, the sodium resistance was satisfactory. The viscosity of the resin binder can be adjusted to provide the desired range of temperature of use for the ramming paste.
2:30 pm
OPTIMIZATION OF ANTHRACITE CALCINATION PROCESS IN A VERTICAL ELECTRIC ARC FURNACE: Jean Perron, Alcan International Ltd., PO Box 1250, 1955 Mellon Blvd, Jonquière, Québec, Canada, G7S 4K8; Jean-François Bouvette, Alcan Smelters and Chemicals, Centre des Produits Cathodiques, PO Box 1500, Jonquière, Québec, Canada, G7S 4L2; Marc Dupuis, Génisim, 3111 Alger Street, Jonquière, Québec, Canada, G7S 2M9
Anthracite used for cathode block manufacturing must be calcined prior its use to eliminate volatile matter and reduce its electrical resistivity. Anthracite calcination in vertical electric arc furnaces is widely used in the industry. It is well known that this technology leads to a radial temperature gradient in the furnace which results in non-homogeneous calcined anthracite properties. Also, operation experience has shown that production of calcination furnaces can be difficult to stabilize if process changes occur, which may lead to variable quality of the calcined material. To optimize the calcination process, an improved control strategy and a mathematical model of Elkem-type electric arc furnace were developed. Using these, it was successfully demonstrated that temperature gradient in the furnace can be reduced and that furnace productivity can be substantially increased.
2:50 pm
INTERFACIAL OXIDATIVE PROCESSES OF CARBON ELECTRODES AND LINERS AT LOW OXYGEN POTENTIALS - AN EXPERIMENTAL METHOD: B. J. James, M. M. Hyland, B. J. Welch, Department of Chemical and Materials Engineering, The University of Aukland, Private Bag 92019, Auckland, New Zealand; J. R. Mittag, SGL Carbon GmbH, Griesheim, D-65933, Frankfurt, Germany
Oxidative reactions of carbon are frequently characterised by an ignition temperature determined for example, by thermogravimetric analysis. However, the heterogeneous nature of carbon materials makes this method insensitive. Ignition in furnace liners is complicated by select oxidation. An experimental apparatus has been designed using a low thermal mass furnace in which samples may be heated in an atmosphere with controlled low oxygen partial pressures, similar to those that might exist in the cathode cavity of a reduction cell. Product gases are led to a mass spectrometer for sensitive detection of oxides; a combined thermogravimetric apparatus is then used in order to perform a continuous materials balance. Results show slow reaction occurs well before accepted ignition temperature, the rate displaying a time/temperature interdependence. After a certain temperature the oxygen partial pressure appears to become the limiting factor (e.g. 650deg.C for a fully graphitic sample). This paper presents description of the method and apparatus used with results and comparison with reported ignition temperatures.
3:10 pm
AUTOGENOUS GRINDING FOR BATH SCRAPS RECYCLING: André Pinoncely and Philippe Podda, FCB Mineral Processing and Carbon Plant Division, B.P. 24 - 69702 Givors Cedex, France
In the early 80's, FCB designed an original process for the recycling of bath scraps in aluminium smelters, using a single stage fully air-swept autogenous mill. Since then, the 9 industrial references confirmed and even exceeded the expectation in terms of dust-free and easy to run operation, high recovery ratio of bath among the metallic scraps, and low maintenance cost. Problems encountered on conventional processes belong to the old days and new projects tend to give an increasing importance to classification and storage of crushed products, autogenous grinding being already recognised as the most suitable, simple and reliable process route. Present paper describes this original process and draws up the overall performances of ten years of experience.
3:30 pm BREAK
3:50 pm
AN IMPROVED APPROACH TO THE CONSTRUCTION OF AIR CLEANING ARRANGEMENTS FOR CARBON ANODE PLANTS: L. L. Basov, S. F. Egorov, G. N. Kuz'min, H. Post, V. A. Sverdlin, Russia; 198147, St- Petersburg, Malodetskoselsky av, 26-7, HACA Technocentr, St- Petersburg
Carbon anodes for aluminum production are fabricated with coal-tar pitch.
When pitch is heated to 200[[ordmasculine]]C, volatiles mainly composed of
polynuclear aromatic hydrocarbons (PAH) are emitted. Central ventilation with a
scrubber at the exit is the usual way of cleaning the air of the working
environment. The existing air-cleaning systems are massive, technically
complicated, metal consuming and their efficiency is poor. The duct arrangement
from the working area to the scrubber cannot guarantee the required reduction
of PAH concentration in the working areas and any failure of the system
necessitates interruption of the anode production. An improved concept of air
cleaning system which includes the same local equipment based on a
plasmachemical method is proposed. Experience has shown that air-cleaning
efficiency is improved and energy consumption is reduced. This new concept has
the following advantages: simplicity, small size and weight and high
reliability. Modules can be installed at the source of gas emission with
individual air intake system. Due to the high cleaning efficiency of the
system, air can be recirculated in working areas or emitted directly to the
atmosphere.
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