GB2179727A

GB2179727A - Baking electrode

Info

Publication number: GB2179727A
Application number: GB08620241A
Authority: GB
Inventors: Erik Q Dahl; Arnfinn Vatland; Olaf T Vegge
Original assignee: Elkem ASA
Current assignee: Elkem ASA
Priority date: 1985-08-22
Filing date: 1986-08-20
Publication date: 1987-03-11
Also published as: FI82309B; IS1349B6; PT83207A; NL187331B; TR22597A; NO853320L; AU582008B2; IN168474B; CA1289311C; FI863158A0; PT83207B; YU144586A; FI863158A; JPH0247679B2; YU44926B; FI82309C; NL187331C; IT8621427A1; CH671667A5; PL261089A1

Abstract

The present invention relates to a baking furnace for continuous production of elongated carbon bodies having uniform cross section, the baking furnace being intended to be moved continuously or substantially continuously in relation to a casing containing unbaked carbonaceous electrode paste with a speed which corresponds to a preset baking speed for the carbon body. The baking furnace comprises an outer steel shell (5) and a refractory lining (6) arranged on the inside of the shell (5), said refractory lining (6) defining a combustion chamber (7). A cooling chamber (16) is arranged between the upper part (15) of the refractory lining (6) and the casing (3). Above the cooling chamber (16) there is provided gas sealing means (23). An off-gas channel (11) is arranged below the refractory lining (16). <IMAGE>

Description

SPECIFICATION Baking electrodes The present invention relates to a baking furnace for continuous production of elongated carbon bodies with a substantially uniform cross section such as for example carbon electrodes for use in electric smelting furnaces, lining blocks, and anode and cathode elements of electrolytic cells for production of aluminium. The elongated carbon bodies may have any cross section, e.g. circular or rectangular. The invention also relates to a method for production of such elongate carbon bodies.

It is known to produce elongated solid carbon bodies by continuously baking a carbonaceous electrode paste comprising a carbon material and a carbonaceous binder. The unbaked electrode paste is charged into a casing having a cross section corresponding to the cross section of the carbon body to be produced, and the casing continuously or substantially continuously lowered down through a baking furnace to which baking furnace heat energy is supplied. It is further known to use a perforated casing whereby the gases which evolve in the electrode paste on heating, flow from the electrode and into the baking furnace where they are burned.

It has been observed that the gases which evolve during the heating of the electrode paste and flow into the baking furnace through the perforations in the casing have a tendency to condense in the upper part of the baking furnace where the cold electrode casing containing cold electrode paste enters into the baking furnace. This condensate, which consists of a large number of different hydrocarbon fractions, will eventually be carbonised in the upper part of the baking furnace and a layer of hard carbonised material will slowly build up. After some time, it may completely fill up the annulus between the baking furnace and the electrode casing, with the result that after operation of the furnace for some weeks it will not be possible to move the casing and thereby the electrode body relative to the baking furnace.The growth in this layer of hard carbonised material in the upper part of the baking furnace must therefore more or less continuously be monitored and at a certain time the baking process stopped and the baking furnace dismantled in order to remove the layer of carbonised material. During removal of the layer of carbonised material, the baking zone in the carbon body is cooled, whereby an inconsistency is produced in the elongated carbon body.

If the baking furnace is operating in direct connection with an electric smelting furnace for production of a carbon electrode which is directly used in the smelting furnace, the operation of the smelting furnace has to be shut down during the removal of the layer of carbonised material in the baking furnace. This will result in loss of production from the smelting furnace and in addition there will be a high risk of electrode breakage when the part of the electrode containing the above mentioned inconsistency enters into the smelting furnace.

It is an object of the present invention to provide a method and baking furnace which prevents or at least substantially reduces, the build up of hard, carbonised material in the upper part of the baking furnace.

It is a further object of the present invention to provide an efficient gas seal between the electrode casing and the upper part of the baking furnace in order to prevent or substantially reduce gas leakages from the baking furnace to the environment.

According to one aspect of the present invention a baking furnace for substantially continuous production of an elongated carbon body, comprising a furnace, chamber and an inlet port for entry therein of a casing for the said body cooling means at or adjacent the inlet port, and gas sealing means between the cooling means and the casing.

According to a further aspect of the invention a baking furnace for continuous production of elongated carbon bodies, said baking furnace being intended to be moved continuously or substantially continuously in relation to a casing containing unbaked carbonaceous electrode paste with a speed which corresponds to the required baking speed for the carbon body, in which that the baking furnace comprises an outer shell and a refractory lining arranged, said refractory lining defining a combustion chamber, a cooling chamber arranged between the upper part of the refractory lining and the casing, gas sealing means arranged above the cooling chamber and an off-gas channel arranged below the refractory lining.The invention in this form may therefor relate to a baking furnace for continuous production of elgonated carbon bodies having a substantially uniform cross section, wherein the baking furnace continuously or substantially continuously is moved relatively to the carbon body with a speed which corresponds to a preset baking speed for the carbon body.

According to yet a further aspect of the invention, a method of substantially continuous production of an elongate carbon body in which a carbon based paste is charged into a casing for the body, the casing being moved through an inlet port into a baking furnace chamber, gases evolved from said paste into the furnace chamber being retained in a cooling zone at or adjacent the inlet port by gas sealing means, and there condensed.

The baking furnace may comprise an outer shell made from steel and a refractory lining arranged on the inside of the shell which defines a combustion chamber about the carbon body which is being produced. A cooling chamber may be arranged between the upper part of the refractory lining and the carbon body which is being produced, the lower part of the cooling chamber extending into the combustion chamber and the upper part of the cooling chamber extending above the refractory lining of the combustion chamber. In the lower part of the combustion chamber there may be arranged a channel for the off-gases from the combustion chamber.

The cooling chamber preferably has internal channels for circulation of a cooling medium.

Above the cooling chamber there is arranged a guide ring for guiding the carbon body through the baking furnace and a gas sealing to prevent gas leakages from the combustion chamber. The gas sealing preferably comprises a flexible gasket arranged between vertically arranged lower flanges which are affixed to a plate on the top of the cooling chamber and vertically arranged upper flanges which are affixed to another plate and where the distance betwen the upper and lower flanges and thereby the tightening of the gasket against the carbon body, can be adjusted by means of a plurality of bolts.

A baking furnace embodying the present invention will now be further described by way of example, with reference to the accompanying drawings, in which Figure 1 shows a vertical section through a baking furnace according to the present invention; and Figure 2 shows an enlarged view of a part of Fig. 1.

In Fig. 1 there is shown a baking furnace 1 for production of elongated carbon bodies 2.

The baking furnace is arranged about a casing 3 for the carbon body 2. The casing 3 has a cross section which corresponds to the cross section of the carbon body.

Unbaked carbonaceous electrode paste 4 which consists of a carbon material and a carbonaceous binder is charged into the casing 3. By heating of the electrode paste 4 in the baking furnace 1, the electrode paste is baked into a solid carbon body 2. The casing 3 is preferably perforated (not shown) in order to allow gases which evolve during the heating of the electrode paste to flow through the perforations and into the baking furnace.

The baking furnace 1 comprises an outer shell 5 and a refractory lining 6 defining a combustion chamber 7. The combustion chamber 7 is heated to the necessary baking temperature by means of at least one burner 8 for solid, liquid or gaseous fuel. The burner or burners 8 are preferably tangentially arranged in relation to the combustion chamber 7. The burner 8 has supply pipes 9 and 10 for fuel and combustion air. Below the refractory lining 6 there is arranged a channel 11 for off-gases from the baking furnace 1. The off-gas is sucked out from the channel 11 through an off-gas pipe 12. In the off-gas pipe 12 there is arranged a valve 13 for regulating the volume of off-gas from the baking furnace.

The channel 11 has a central opening with a diameter slightly greater than the diameter of the baked carbon body 2. Between the channel 11 and the casing 3 for the carbon body 2 there will therefore be a slot 14. When the baking furnace 1 is in operation, environmental air is sucked in through the slot 14 and thereby provides a seal so that gases from the combustion chamber 8 will not escape through the slot 14.

In the upper part 15 of the refractory lining 6 of the baking furnace 1, there is provided an opening for the casing 3. This opening has a somewhat greater cross section than the cross section of the casing 3. In the annular slot between the upper part 15 of the refractory lining 6 and the casing 3 there is arranged a cooling chamber 16 for circulation of a cooling medium. The cooling chamber 16 has supply pipe 17 and return pipe 18 for the cooling medium which preferably is water. The cooling chamber 16 may be divided into sections and each section may be provided with internal walls (not shown) in order to ensure a proper flow of cooling medium through the cooling chamber 16.

The cooling chamber 16 is arranged in such a way that its lower end is at about the same level as the lower end of the upper part 15 of the refractory lining 6 as shown on Fig. 1.

The cooling chamber 16 extends upwardly to a level at least above the upper end of the upper part 15 of the refractory lining 6.

The cooling chamber 16 is affixed to the outer shell 5 via an annular plate 20 which is secured to the shell 5 by means of bolts 21.

If the baking furnace 1 is used for baking a carbon electrode in direct connection with an electric smelting furnace, electric insulation 25 is preferably inserted between the shell 5 on the baking furnace 1 and the annular plate 20.

Above the cooling chamber 16 there is secured a guide ring 22 made from rod iron or the like. The purpose of guide ring 22 is to guide the casing relatively to the baking furnace. In the area above the guide ring 22 there is arranged gas sealing means 23 for preventing gas leakages between the casing 3 and the baking furnace 1.

The gas sealing means 23 is shown in enlarged scale on Fig. 2. The gas sealing means 23 comprises a lower annular plate 24 which is secured to the cooling chamber 16. To the plate 24 there is affixed two annular vertically running flanges 26 and 27. Between the flanges 26 and 27 there is provided a flexible gasket 28 made of a material having a high melting point. The upper end of the gasket 28 is arranged between annular vertical flanges 29 and 30 which are connected to a second annular plate 31. The second annular plate 31 is affixed to the flange 26 by means of a plurality of threaded bolts 32 having handles 33. By adjusting the distance between the first plate 24 and the second plate 31 by operating the handles 33, the flexible gasket 28 is tightened or loosened. The gasket 28 can be adjusted locally about the circumference of the casing 3 by operations of the handles 33.

In operation the baking furnace 1 is continuously or substantially continuously moved relative to the casing 3 with a speed corresponding to the preset baking speed for the carbon body 2. When the casing 3 with the unbaked electrode paste 4 enters into the baking furnace 1, the electrode paste is heated and the electrode paste then becomes liquid, whereafter the paste is baked into a solid carbon body.

During the baking, carbonaceous gases evolve in the electrode paste. These gases flow into the baking furnace 1 through perforations in the casing 3 and most of the gases are immediately burned by the combustion air which is supplied to the baking furnace.

A part of the gases will, however, condense on the cooling area 19 and on the lower vertical part of the cooling chamber 16 where the temperature is kept below 400"C by the cooling medium circulating the cooling chamber.

As the temperature in the baking chamber is in the interval between 700 and 1300"C, the part of the gases which come into contact with the cooling area 19 will condense. The temperature in the area of the cooling chamber 16 is, however, so low that the condensed gases will not be carbonised. The condensed gases will therefore drop down into the combustion chamber where they immediately will be combusted. The cooling chamber further provides that the gases in the annulus between the casing 3 and the cooling chamber is kept at a lower temperature. The gasket 28 is thereby protected against high temperature exposure. The lifetime for the gasket 28 will thereby be increased.

By the present invention it is thereby provided a baking furnace which can be operated for very long periods without operation difficulties due to build ups of layers of carbonised material. Further, a very good gas seal between the carbon body and the baking furnace is obtained, thereby minimizing the possibility for leakage of hazardous gases from the baking furnace to the environment.

Claims

1. A baking furnace for substantially continuous production of an elongated carbon body, comprising a furnace chamber and an inlet port for entry therein of a casing for the said body, cooling means at or adjacent the inlet port, and gas sealing means between the cooling means and the casing.

2. A furnace as claimed in Claim 1, in which the casing is disposed substantially vertically, the cooling chamber substantially surrounds the casing above the furnace chamber and the gas sealing means substantially surround the casing above the cooling chamber.

3. A baking furnace for continuous production of elongated carbon bodies, said baking furnace being intended to be moved continuously or sustantially continuously in relation to a casing containing unbaked carbonaceous electrode paste with a speed which corresponds to the required baking speed for the carbon body, in which that the baking furnace comprises an outer shell and a refractory lining arranged, said refractory lining defining a combustion chamber, a cooling chamber arranged between the upper part of the refractory lining and the casing, gas sealing means arranged above the cooling chamber and an off-gas channel arranged below the refractory lining.

4. A furnace as claimed in any of the preceding claims, in which that the lower end of the cooling chamber is situated at substantially the same level as the lower end of the upper part of the refractory lining.

5. A furnace as claimed in any of the preceding claims, in which a guide ring for guiding the casing is arranged above the cooling chamber.

6. A furnace as claimed in any of the preceding claims, in which the gas sealing means comprises a flexible gasket arranged between flanges and such that the distance between the flanges can be adjusted.

7. A furnace as claimed in Claim 6, in which that the distance between the flanges is adjustable by means of a plurality of bolts.

8. A furnace as claimed in any of the preceding claims having at least one burner for solid, liquid or gaseous fuel.

9. A furnace as claimed in Claim 8, in which the burner is substantially tangentially arranged relative to the combustion chamber.

10. A furnace as claimed in any of the preceding claims having at least one pipe for supply of combustion air to the combustion chamber.

11. A baking furnace for substantially continuous production of an elongated carbon body, substantially as described herein with reference to the accompanying drawings.

12. A method of substantially continuous production of an elongate carbon body in which a carbon based paste is charged into a casing for the body, the casing being moved through an inlet port into a baking furnace chamber, gases evolved from said paste into the furnace chamber being retained in a cooling zone at or adjacent the inlet port by gas sealing means, and there condensed.

13. A method as claimed in Claim 12, in which the condensed gases are returned to the furnace chamber for combustion.

14. A method of continuous production of an elongate carbon body substantially as de scribed herein with reference to the accompanying drawings.