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Session Chairpersons: Alton T. Tabereaux, Reynolds Metals Company, Manufacturing Technology Laboratory, 3326 East 2nd Street, Muscle Shoals, AL; Peter Polyakov, Light Metals Department, Non-ferrous Metals Academy, Krasnoyarsk sabochiy St. 95, 660025, Krasnoyarsk, Russia
IMPLEMENTATION OF POINT FEEDING IN THE SØDERBERG LINES AT HYDRO ALUMINUM KARMØY: Knut Arne Paulsen, Willy K. Rolland, Asbjørn Larsen, Hydro Aluminum a.s, Karmøy Plants, N-4265 Håvik, Norway; Marvin Bugge, Norsk Hydro a.s, Research Centre, N-3901 Porsgrunn, Norway
A concept for point feeding of alumina to Søderberg cells has been developed at Hydro Aluminum Karmøy. During 1996 and early 1997 the bar breaker equipment on all 340 cells will be replaced by point feeders. Alumina is fed by means of a fluidized feeder and mechanically forced into the bath. The lifetime of the equipment is comparable to that of the cathode life. The concept has proved to stabilize the operation of the cell. Furthermore, the stability improves the current efficiency and also allows the amperage to be increased. Implementation of point feeding includes revised operational procedures and new target values for the operational parameters and also affects the organization. The anode effect frequency has been reduced in several steps during the development period. Today, the anode effect frequency is about one tenth of the corresponding value for the previous bar breaker cells resulting in reduction of perfluorocarbon emissions.
A UNIQUE, ECONOMIC SØDERBERG TO PREBAKE CONVERSION FOR THE RUSSIAN ALUMINIUM INDUSTRY: S. Tsymbolov, G. Necheav, Nadvoitsky Aluminium Smelter, Zavodskaya Street, 1, Nadvoitsy, 186430, Karelia, Russia; Lee E. Swartling, Kaiser Aluminum Technical Services, Inc. 6177 Sunol Boulevard, Pleasanton, CA 94566; G. Volfson, All-Russian Aluminium & Magnesium Institute, 86 Sredny Prospect, St. Petersburg, 199026, Russia
The majority of Russian aluminum smelting technology is Søderberg, historically associated with non-competitive performance and ecological problems. After conversion to conventional prebake cell technology was found economically unjustifiable, the Nadvoitsky Aluminium Smelter, Karelia, Russia commissioned the All-Russia Aluminium and Magnesium Institute and Kaiser Aluminum Technical Services Inc. to design a unique prebake technology cell with world class performance which could be economically retrofitted into the existing facility. This multi-national team utilizing state of the art modeling and process control technology, successfully designed and implemented a twelve pot test section at Nadvoitsy. Cell performance measured over twelve months has consistently exceeded minimum design indices and paces world class cell performance. Measurements of magnetic field, heat flow, and voltage distribution compare closely with predicted values. Design features, including a novel six anode superstructure, design methodology, test protocol, construction and operation practices, and cell performance data are presented in this paper.
BATH TEMPERATURE MEASUREMENTS WITH THERMOCOUPLES: Paul Verstreken, Heraeus Electro-Nite Int. N.V., Grote Baan 27a, 3530-Houthalen, Belgium
After a brief introduction into the physical principles of thermoelectricity an overview of commonly used thermocouples is given. The construction of thermocouple sensors and assemblies is discussed. An overview of calibration procedures is given. Errors can arise from the materials (thermocouple wires and sheathing) used, and the way the actual measurement is performed. Reasons for drifting are discussed. There is a relation between the thermal properties (thermal mass and heat conductivity) of the sheathing material, the measuring procedure and the obtained accuracy of the temperature measurement. From this, recommendations on how to improve the quality of bath temperature readings, are made.
3:15 pm BREAK
A NEW INSTRUMENT FOR FAST TEMPERATURE MEASUREMENT IN ALUMINIUM REDUCTION CELLS: Fucang Xu, Jie Li, Huazhang Wang, Yexiang Liu, Department of Metallurgy, Central South University of Technology, Changsha, Hunan 410083, China
A new instrument, with a single-chip microcomputer as its core and based on a new method named Dynamic Temperature Measurement, has been developed for fast temperature measurement in aluminium reduction cells. When a cold thermocouple is inserted into hot electrolyte, the instrument measures the thermocouple output curve and meantime identifies the parameters of a time series-analysis model which is used to describe the temperature-time curve. Until the convergence of the identification is verified, the instrument predicts the temperature of the electrolyte from the obtained information. In the way, the temperature can be indicated before the thermocouple output reaches its balance point, with the measurement process lasting only some 50 seconds and measurement accuracy reaching ±2°C, a range acceptable for industrial measurement.
A DEVICE FOR CONTINUOUS ALUMINA FEED INTO AN ALUMINIUM ELECTRIC CELL: A.I. Begunov, E.V. Kudryavtseva, State Technical University, Lermontov Str. 83, Irkutsk, Russia
A new device is suggested here to cover the cell and feed alumina into it. The covering is designed having such thermal resistance that no crust develops on the electrolyte surface. Alumina is fed from the intermediate hopper, which is one piece with the covering plate, into the electrolyte through the narrow slot, the width of which ranges from 0.8 to 1.2 mm. The alumina feed rate is determined by its bulk properties ("sandy", "mealy", "moist"), the width and length of the slot and the intermediate hopper wall flare angle. The cold model of the device yielded the dependencies of alumina slot spead on the parameters mentioned above. The device has no crust-breaking appliances or volumetric dosers. Dosage is effected only to gravity feed of raw materials through a slot of predetermined cross-section. Because of that, low operation costs and high reliability of the suggested device are expected.
VISUALISATION OF TAPPING OPERATIONS: Marcus Walker, Comalco Research Centre, P.O. Box 316, Thomastown, Australia 3074
The removal of molten aluminium from Hall- Heroult cells is known a "tapping". This operation causes process disturbances including entrainment of electrolyte and sludge in the tapped metal as well as producing localised wear of the cathode. This paper describes the use of a full scale physical model for determining the optimal tapping conditions to reduce both bath entrainment and cathode erosion for various cell operating strategies. Flow visualisation and numerical modelling has shown that the flow towards the tapping pipe is predominantly radial, however under and inside the pipe, the flow swirls intensely. Under certain conditions the swirling flow induces a vortex at the bath metal interface through which bath can be entrained in the flow. The swirling action was also seen to produce a region of locally high velocities on the cathode surface which enhances erosion of the cathode through a number of possible mechanisms.
A NEW CONCEPT OF RESOLVING LADLE CLEANING AT SLOVALCO BY TECHMO: F. Zannini, F. Marchetti, R. Balasso, J. Ifju, Techmo Car SpA, Via R. Colpi 15/17, 35010 Limena (PD), Italy
Techmo has elaborated a new concept of resolving the problem of ladle cleaning based on standard features of the new aluminium smelter implemented by Hydro Aluminium's technology at SLOVALCO a.s. A thorough design work has resulted in a piece of equipment with new arrangement and orientation in good agreement with the tapping system and work organization of the plant. Some optimization was fulfilled in order to meet the requirements of the new plant in possible best manner.
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