Title of Invention

DEVICE FOR ELECTROLYTIC PRODUCTION OF ALUMINIUM

Abstract

. A device for electrelytlc production of aluminium (St) Abstract' comprising an electrolytic cell equipped with a Seidenberg anode. The anode is equipped with an anode casing (1) inertial contact bolts (3/ far helpingly the anode and for conducting operating current to the anode. The top of the anode casing isbeuipped with at least one cover (4; having opening s'Cl l) for the contact bolts (3) and at least one off-gas opening (24) is regulated in such a way that a sufficient diminished pressure is provided on the top of the anode that surrounding air will flow through air gaps (22) arranged between the cover (4), and each of the contact belts (3), The amount of air is such that gas from the top of the anode does not escape through the air gaps (22) and the temperature of the top of the anode casing is maintained below a predetermined value. PRICE: THIRTY RUPEES

Full Text

The present invention relates to a device for electrolytic production of aluminium in an electrolytic cell equipped with a S0derberg anode. The Soderberg anode which is used in electrolytic production cells for aluminium comprises a permanent anode casing, made from cast iron or steel, surrounding the selfbaking carbon anode. Unbaked carbonaceous electrode paste is charged at intervals to the top of the anode and the unbaked electrode paste is baked to a solid carbon anode by means of the heat generated by the current supply to the anode and by means of heat from the molten electrolytic bath. Thus, a main feature of the Soderberganode is that the baked anode is moved relative to the permanent anode casing. Each electrolytic cell is normally equipped with one Soderberganode. The S0derberganode is suspended by a large number of vertically arranged contact bolts normally made from steel, which are also used for conducting the electrical operating current to the anode. The lower ends of the contact bolts are baked into the anode. The contact bolts follow the downward movement of the anode until the lower ends reach a predetermined distance from the lower end of the anode. The contact bolts are then pulled out of the anode and placed in a higher position. By keeping the tip position of the contact bolts at different height positions in the anode, there will always be a sufficient number of bolts having with such tip positions that a sufficient holding force is maintained and a good current connection between the bolts and the anode is ensured. The unbaked electrode paste which is charged to the top of the anode evolves gases and volatile organic compounds during the baking process. Some of the gases and volatile compounds, such as for example polyaromatic hydrocarbon compounds (PAH), are harmful to health and it is therefore desirable to prevent these gases from escaping to the surroundings. In the past, attempts have been made to reduce the escape of gases from the top of the anode by using electrode pastes which have the lowest possible content of volatile matter and by keeping the temperature at the top of the anode as low as possible. Even if the emission of gases from the top of the anode by these means has been reduced in recent years, it is not possible using known technology to reduce the emission of harmful gases from the anode top to an acceptably low level. From Norwegian Patent No. 172250 it is known to close the top of a Soderberganode by means of at least one cover having openings for the contact bolts. The annular gaps between the contact bolts and the openings in the cover are sealed by means of sealing elements and the gases which evolve during the baking of the electrode paste are collected and combusted. According to the Norwegian patent the cover comprises central cover plates having openings for the contact bolts and side cover plates arranged outside the central cover plates, the side cover plates being rotatably arranged. The annular gaps between the central cover plates and the contact bolts in this reference are sealed by means of sealing elements which are arranged in a gas tight manner about each of the contact bolts and which are freely floating on the central cover plates. In order to make it easier to replace damaged central cover plates, the central cover plates are made in sections with each section having openings for at least two and preferably four contact bolts. The arrangement according to Norwegian Patent No. 172250 has been found in practice to have the disadvantage that the cooling of the top of the anode which is achievable is insufficientresulting in too high a temperature at the top of the anode. This adversely affects the softening and the baking of the anode paste, as too high a proportion of the binder in the unbaked anode paste which is charged to the top of the anode, is volatized and is therefore sucked off, together with the gases evolved during baking. It is an object of the present invention to provide a method and an arrangement for closing and cooling of the top of the anode which makes it possible to maintain the temperature of the top of the anode at a predetermined value during operation of the electrolytic cell. According to one aspect of the invention, there is provided a method for closing and cooling of the top of a S0derberganode for use in connection with electrolytic production of aluminium, the anode being equipped with an anode casing and vertical contact bolts for holding and for conducting operating current to the anode and in which the top of the anode casing is equipped with at least one cover having openings for the contact bolts and at least one off-gas opening, the method comprising regulating the amount of gas removed from the top of the anode through the off-gas opening in such a way that a sufficient diminished pressure is provided at the top of the anode so that: surrounding air will flow through air gaps arranged between the cover and each of the contact bolts in such an amount that gas from the top of the anode does not escape through the air gaps, and the top of the anode is maintained below a predetermined temperature. According to another aspect of the present invention, there is provided an arrangement for closing and cooling of the top of a Sederberganode used in connection electrolytic production of aluminium, the anode being equipped with an anode casing and vertical contact bolts for holding and for conducting operating current to the anode and in which the top of the anode casing is closed by means of at least one cover having openings for the contact bolts and at least one opening for charging anode paste and at least one off-gas opening for continuously withdrawing gas from the top of the anode, the arrangement defining air gaps of between 1 and 10 mm between each of the contact bolts and the openings in the cover, in order to allow a regulated flow of air into the air gaps for cooling of the top of the anode and to prevent leakages of gases from the top of the anode through the air gaps. The invention also extends to a Soderberganode for use in connection with electrolytic production of aluminium, the anode comprising an anode casing; vertical contact bolts for holding and for conducting operating current to the anode; at least one cover closing the top of the anode casing, the cover having openings for the contact bolts, at least one opening for charging anode paste and at least one off-gas opening for continuously withdrawing gas from the top of the anode; and the openings in the cover defining between them air gaps of between 1 and 10 mm, thereby allowing a regulated flow of air into the air gaps in order to cool the top of the anode and to prevent leakages of gases from the top of the anode through the air gaps. Preferably, the air gaps between the cover and each of the contact bolts are between 2 and 4 mm. According to a preferred embodiment according to the present invention, elements freely floating on the cover are arranged about each contact bolt and the air gaps are arranged between the elements and the contact bolts. By regulating the amount of gas sucked out through the gas outlet opening in the cover, the amount of air flowing in through the air gaps between each contact bolt and the element will be sufficient to keep the temperature on the anode top below a preset value. The invention may be carried into practice in various ways and one embodiment will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a vertical section through a part of a Saderberganode for an electrolytic cell for the production of aluminium; Figure 2 is a vertical section through the top of a S0derberganode for an electrolytic cell for the production of aluminium; Figure 3 is an enlarged view of the area A in Figure 2 in a first position; Figure 4 is an enlarged view of the area A in Figure 2 in a second position; and Figure 5 is a section along line I-I in Figure 3. Figures 1 and 2 show a S0derberganode for electrolytic cells for the production of aluminium. The anode comprises a casing 1 made from iron or steel. Into the anode casing a carbon containing anode paste 2 is charged. The carbon containing paste 2 is baked to a solid carbon anode by means of the heat which evolves during current supply to the anode and the heat from the electrolytic bath. The baked anode is consumed during the electrolytic process. The carbon anode is held by a plurality of vertical contact bolts 3 which also serve as current conductors to the anode. As can be seen from the Figures, the contact bolts 3 are arranged in four rows in the longitudinal direction of the anode. The contact bolts 3 are suspended from the current conducting beams in a conventional way (now shown in the drawings). The top of the anode is equipped with covers 4 connected to a central beam 5 arranged along the longitudinal axis of the anode, and two outer beams 6, 7 arranged on the outside of the rows of contact bolts. The beams 5-7 are suspended upon the short sides of the anode casing and preferably also on at least one transverse beam 8. As show in Figure 2, the outer beams 6, 7 are connected to the transverse beam 8 by means of bolt connections 9, 10. The covers 4 have openings 11 for the contact bolts 3. Between the outer beams 6, 7 and the longitudinal sides of the anode casing there are arranged rotatable side covers 12, 13. In the embodiment shown in Figure 2, the side covers 12, 13 are suspended by pipes or rods 14, 15 rotatably connected to the top of the anode casing 1. The side covers 12, 13 can thereby be moved from a closed position (shown for the side cover designated 13) to an open position (shown for the side cover designated 12) by means of for example a pneumatic cylinder 16. When the side covers 12, 13 are in the open position, anode paste 2 can be charged to the top of the anode and the top of the anode can be inspected visually. In order to ensure a good seal between the side covers 12, 13 and the outer beams 6, 7, flexible sealing sheets 17, 18 are preferably arranged along the side covers 12, 13. These sealing sheets ensure a good seal between the outer beams 6, 7 and the side covers 12, 13 when the side covers 12, 13 are in the closed position. About each of the contact bolts 3, elements 20 are arranged which float on the cover 4. The elements 20 are shown in detail in Figures 3-5. As shown, each element comprises a ringshaped member 21 having a central opening with a diameter between 1 and 5 mm larger than the diameter of the contact bolts 3. Gaps 22 are thus formed between the ringshaped members 21 and the corresponding contact bolts 3. Each ringshaped member 21 is equipped with two horizontal brackets 23 each having an opening 24. By means of a bolt 25 extending through the opening 24 in the bracket 23 and through a corresponding opening 26 in the cover 4 and the flats 27, 28 located respectively above the brackets 23 and below the cover 24, each elements 2 0 is connected to the cover 4 in such a way that the elements 20 are allowed to move freely in the horizontal direction, but are prevented from being lifted vertically. In Figure 3, the contact bolt 3 is shown centrally arranged in the opening 11 in the cover 4, while the contact bolt 3 in Figure 4 is shown in a position where the contact bolt 3, due to horizontal forces, has moved the element 20 horizontally on the cover 4. During operation of the electrolytic cell, gases evolved at the top of the anode are removed through a gas outlet opening 29 in the cover 4. The amount of gas removed through the gas outlet opening 2 9 is regulated by air which flows through the air gaps 22 in such an amount that the gases from the anode top are themselves prevented from escaping through the air gaps 22. Furthermore, the amount of gas which is removed through the gas outlet 2 9 is regulated in such a way that the amount of air flowing in through the air gaps 22 is sufficient to cool the top of the anode to a predetermined temperature. By means of the present invention a simple and reliable way is provided to seal the top of the anode against the atmosphere while at the same time maintaining the temperature at the top of the anode at a predetermined value. CLAIMS: 1. A device for electrolytic production of aluminum comprising an electrolytic cell equipped with a Seidenberg anode, the anode comprising an anode casing; vertical contact bolts for holding and for conducting operating current to the anode; at least one cover closing the top of the anode casing, the cover having openings for the contact bolts, at least one opening for charging anode paste and at least one off-gas opening for continuously withdrawing gas from the top of the anode; and the openings in the cover defining between them air gaps of between 1 and 10 mm, thereby allowing a regulated flow of air into the air gaps in order to cool the top of the anode and to prevent leakages of gases fix)m the top of the anode through the air gaps. 2. The device as claimed in claim 1, wherein the air gaps between the cover and each of the contact bolts are between 2 and 4 mm. 3. The device as claimed in claim 1 or claim 2, wherein elements freely floating on the cover are arranged about each contact bolt and the air gaps are arranged between the elements and the contact bolts. 4. A device for electrolytic production of aluminium, substantially as hereinabove described and illustrated with reference to the accompanying drawings.

Documents:

205-mas-95-abstract.pdf

205-mas-95-claims.pdf

205-mas-95-correspondence-others.pdf

205-mas-95-correspondence-po.pdf

205-mas-95-description-complete.pdf

205-mas-95-drawings.pdf

205-mas-95-form-1.pdf

205-mas-95-form-26.pdf

205-mas-95-form-4.pdf

205-mas-95-other-document.pdf