Plastic and nonmetallic article shaping or treating: processes – Furnace lining formation or repair
Patent
1980-07-07
1982-06-15
Pavelko, Thomas P.
Plastic and nonmetallic article shaping or treating: processes
Furnace lining formation or repair
F27D 116
Patent
active
043350640
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for making the packing for electrometallurgical furnaces and, in particular, for cells for the production of aluminum by electrolysis of alumina dissolved in molten cryolite.
A cell for the production of aluminum is formed by a metal box, the length of which currently ranges from 5 to 8 meters and the width from 2 to 4 meters. The bottom of the box is first packed to a thickness on the order of 18 to 42 centimeters with electrically and thermally insulating refractory materials and is resistant to possible infiltration by aluminum and fluorinated products. The assembly of "cathode blocks" which constitutes the cathode of the electrolysis cell and which will be located directly in contact with the sheet of liquid aluminum produced by the cell is then arranged. Next, the joints have to be produced between the cathode blocks and then the lateral packing of the cell, that is to say the space between the lateral walls of the box and the cathode blocks has to be filled with a substance which is resistant to the chemical action of the aluminum and of the fluorinated bath at a temperature in the area of 1000.degree. C.
This packing has to possess a certain number of other qualities, in particular high mechanical strength as it has to withstand high stresses, dimensional stability during baking, the ability to receive a reinforcement such as a conventional concrete, high resistance to oxidation and to erosion by the electrolysis bath and the metal.
This packing operation is also known as "lining" or "luting" because it is usually carried out using "lining paste" or "lute", that is to say a mixture based on pitch and coke which is positioned while hot and tamped.
The care taken in the production of this "lining" and the quality of the products used determine to a very large extent the service life of an electrolysis cell, as infiltration of metal and molten cryolite through imperfect or fissured joints make it unserviceable after a short time.
The process forming the object of the invention is based on the use, for the lining operation, of a product composed of a non-carbonaceous binder and an aggregate of which at least a proportion is constituted by a carbonaceous product.
Up until now it has been maintained that only carbonaceous products could be used in contact with the electrolyte and the liquid aluminum with the exception, however, of special products such as boron nitride which is too expensive for industrial use.
Now it has surprisingly been found that it is possible to use lining products which are not completely carbonaceous and, in particular, concretes composed of hydraulically or chemically setting cement and a charge (generally known as aggregate), all or a part of which is constituted carbonaceously, such as anthracite, anode or cathode waste, or material recovered, for example, from the dismantling of unused cells. It has been observed that the proportion of carbonaceous material in the aggregate must be at least 5% to obtain the desired properties.
In view of the temperature to which the concrete will be brought and the need for its porosity to be as low as possible, it is preferable to use, for making it up, a cement having a low water retention capacity, that is to say in practice a cement having a low CaO content as this element is largely responsible for the reduction in the refractoriness and the water retention.
In particular, the chemically setting cement forming the subject of French Pat. No. 2,359,090 in the name of the Societe Europeenne de Produits Refractaires is eminently suitable. It is characterized by a mixture of from 25 to 30% by weight of an aluminous cement selected from among the cements based on calcium mono-aluminate and di-aluminate, from 35 to 40% by weight of vitreous silica in particles of from 0.01 to 0.1 micrometers and from 35 to 45% of an inert charge in particles of from 1 to 100 micrometers. In addition this cement contains less than 15%, and even less than 10% of CaO.
Other types of cement having small lime content are als
REFERENCES:
patent: 3717602 (1973-02-01), Koch
patent: 4052288 (1977-10-01), Sala
patent: 4111711 (1978-09-01), Kiehl
patent: 4174972 (1979-11-01), Drouzy
Hudault Gerard
Sulmont Benoit
Aluminium Pechiney
Pavelko Thomas P.
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