CN1005285B - Bakeout furnace for electrode bar - Google Patents

Abstract

The invention relates to a baking furnace for the continuous production of elongated carbon rods of constant cross-section. The baking oven is moved continuously or substantially continuously relative to a housing containing the unbaked carbon electrode paste at a speed compatible with the predetermined baking speed of the carbon rods. The baking furnace includes an outer steel furnace shell (5) and a refractory lining (6) installed inside the furnace shell (5). The lining (6) defines the combustion chamber (7). A cooling chamber (16) is installed between the upper part of the refractory lining (6) and the casing (3). A gas sealing device (23) is installed above the cooling chamber. Exhaust gas passages (11) are installed below the refractory lining (6).

Description

Electrode bar baking oven

The present invention relates to a baking oven for the continuous production of elongated carbon rods having substantially uniform cross-section, such as carbon electrodes, pads for use in electric smelting furnaces, anode and cathode elements for use in electrolysis cells for aluminium products, and the like. The cross section of the slender carbon rod can be round, rectangular or other various shapes.

A method for producing an elongated carbon rod is known in which an unbaked carbonaceous electrode paste containing a carbon raw material and a carbonaceous binder is continuously baked to form a solid carbon rod. First, unbaked electrode paste is filled into a shell having a cross section corresponding to that of a carbon rod to be produced. The housing is then passed continuously or substantially continuously downwardly through a roaster oven which is heated by the heat energy of the roaster oven. It is also known to use a porous shell, whereby the gas generated when the electrode paste is heated flows from the electrodes into the oven and is burned off.

It can be seen that the gases generated when the electrode paste is heated, after flowing into the oven through the housing apertures, have a tendency to condense at the upper portion of the oven at the point where the cold electrode housing containing the cold electrode paste enters the oven. These condensates, which consist of a large number of various hydrocarbon fractions, are finally carbonized in the upper part of the roaster oven, slowly building up a layer of hard carbides, which after a while completely fills the annular space between the roaster oven and the electrode housing. As a result, it is impossible to move the housing and thus the electrode relative to the oven after several weeks of operation of the oven. Therefore, it is necessary to constantly observe the growth of the hard carbide layer in the upper part of the baking oven, and to stop the baking process at a certain time, disassemble the baking oven, and remove the carbide layer. During the removal of the carbide layer, the baked area of the carbon rod is cooled down, resulting in non-uniformity of the elongated carbon rod.

If the roaster furnace is directly connected to an electric cold hearth furnace for producing carbon electrodes for direct use in the smelting furnace, the operation of the furnace must be stopped during the removal of the carbide layer from the roaster furnace. Resulting in a reduced production capacity of the smelting furnace and, in addition, there is a great risk of breakage of the electrodes when the electrode parts containing the above-mentioned irregularities enter the smelting furnace.

An object of the present invention is to provide a baking oven which can prevent hard carbide from being accumulated on an upper portion of the baking oven.

Another object of the invention is: an effective gas seal is provided between the electrode housing and the upper portion of the roaster oven to prevent gas from escaping from the roaster oven to the ambient environment.

Accordingly, the present invention relates to a baking oven for continuously producing an elongated carbon rod having a substantially constant cross-section, which oven is continuously or substantially continuously movable relative to the carbon rod at a speed adapted to a predetermined baking speed of the carbon rod.

According to the invention, the baking oven comprises an outer shell of steel and a lining mounted inside the shell. The furnace lining defines a combustion chamber therein, which surrounds the carbon rods being produced. A cooling chamber is provided between the upper part of the refractory lining and the shell. The cooling chamber has a bottom portion extending into the combustion chamber and an upper portion extending above the refractory lining of the combustion chamber, and is provided with a gas sealing device. A channel is arranged in the bottom of the combustion chamber for the exhaust gases of the combustion chamber to exit.

The cooling chamber preferably has internal passages for circulating a cooling medium. The upper surface of the cooling chamber is provided with a guide ring for guiding the carbon rod when the carbon rod passes through the baking oven, and a gas sealing device for preventing gas from leaking out of the combustion chamber. The gas seal preferably comprises a flexible gasket mounted between a lower vertical flange connected to one plate at the top of the cooling chamber and an upper vertical flange connected to the other plate. The distance between the upper flange and the lower flange can be adjusted by a plurality of bolts, so that the degree of the lining ring clinging to the carbon rod can be adjusted.

Other embodiments of the invention will become apparent from the description below and from the claims.

The oven of the present invention will now be further described with reference to the accompanying drawings, in which preferred embodiments of the invention are shown.

Fig. 1 is a vertical sectional view of a baking oven of the present invention.

Fig. 2 is a partially enlarged sectional view of fig. 1.

Fig. 1 shows a baking oven 1 for producing elongated carbon rods 2. The baking oven is arranged around the housing 3 of the carbon rod body 2. The cross section of the shell 3 is adapted to the cross section of the carbon rod.

The unbaked carbonaceous electrode paste 4 is composed of a carbonaceous material and a carbonaceous binder, and is filled in the casing 3. The electrode paste 4 is baked in a baking oven 1 to be baked into a solid carbon rod 2. The casing 3 is preferably porous (not shown) so that gas emitted when the electrode paste is heated can flow into the oven through the perforations.

The roaster 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 desired roasting temperature by means of at least one burner 8, burning solid, liquid or gaseous fuel or the like. The arrangement of the single or multiple burners 8 is preferably tangential to the combustion chamber 7. The burner 8 has a fuel supply pipe 9 and a combustion air supply pipe 10. A channel 11 is provided below the refractory lining 6 for the discharge of flue gases from the roaster oven 1, the flue gases being extracted from the channel 11 through an exhaust gas duct 12. A valve 13 is provided in the exhaust gas pipe 12 to regulate the amount of exhaust gas discharged from the interior of the oven.

The channel 11 has a central hole with a diameter slightly larger than the diameter of the carbon rod 2 to be baked. Thus, there is a gap 14 between the channel 11 and the housing 3 of the carbon rod 2. When the roaster oven 1 is in operation, ambient air is drawn into the gap 14, creating a seal so that gases within the combustion chamber 7 do not escape through the gap 14.

In the upper part 15 of the refractory lining 6 of the roaster furnace 1, an opening is made through which the housing 3 passes. The cross-sectional dimension of the orifice is slightly larger than the cross-sectional dimension of the housing 3. In the annular groove between the upper part 15 of the refractory lining 6 and the shell 3, a cooling chamber 16 is provided, in which a cooling medium circulates. The cooling chamber 16 is provided with a supply pipe 17 and a discharge 18 for the cooling medium. The cooling medium is preferably water. The cooling chamber 16 may be segmented, each segment being provided with internal walls (not shown) to ensure a proper flow of the cooling medium in the cooling chamber 16.

The cooling chamber 16 is arranged with its bottom end at about the same level as the bottom end of the upper part 15 of the refractory lining 6, as shown in fig. 1. The cooling chamber 16 projects upwards at a height at least above the upper end of the upper part 15 of the refractory lining 6.

The cooling chamber 16 is placed on the housing 5 by means of an annular plate 20, which annular plate 20 is fastened to the housing 5 by means of bolts 21.

If the roaster 1 for roasting carbon electrode rods is directly coupled to the electric smelting furnace, it is preferable to insert an insulating plate 25 between the outer casing 5 of the roaster 1 and the ring plate 20.

Above the cooling chamber 16, a guide ring 22 made of round iron or the like is installed. The purpose of the guide ring is to guide the housing relative to the roaster oven. The upper part of the guide ring 22 is provided with a gas-tight device 23 for preventing gas from leaking out between the housing 3 and the oven 1.

Fig. 2 shows the air-tight device 23 in an enlarged manner. The air-tight means 23 comprise a bottom annular plate 24 which can be fixed to the cooling chamber 16. The plate 24 is connected to two vertical annular flanges 26 and 27. Between the flanges 26 and 27 is provided a flexible collar 28 of refractory material. The upper end of the collar 28 is mounted between two vertical annular flanges 29 and 30, the flanges 29 and 30 being connected to a second annular plate 31. A second annular plate 31 is secured to the flange 26 by a plurality of bolts 32 with handles 33. The flexible collar 28 can be tightened or loosened by rotating the handle 33 to adjust the distance between the first annular plate 24 and the second annular plate 31. Turning the handle 33 allows partial adjustment of the collar 28 over the outer circumference of the housing 3.

During construction, the baking oven 1 is continuously or substantially continuously moved relative to the housing 3 at a relative speed corresponding to a predetermined baking speed of the carbon rod 2. When the casing 3 containing the unbaked electrode paste 4 is introduced into the baking oven 1, the electrode paste is heated to become liquid, and then dried to become a solid carbon rod.

During baking, the electrode paste emits carbon-containing gas. These gases flow into the oven through the perforations in the housing 3, and most of the gases are rapidly burned by the combustion air fed into the oven.

However, in the cooling zone 19 at the bottom of the vertical part of the cooling chamber 16, the temperature of this zone is kept below 400 ℃ due to the circulation of the cooling medium in the cooling chamber, and a part of the gas is condensed there. The temperature of the oven chamber is in the range of 700 ℃ to 1300 ℃, so that a portion of the gas in contact with the cooling zone 19 condenses. Since the temperature of the region near the cooling chamber 16 is low, the condensed gas is not combined with carbon. The condensed gas then drips down into the combustion chamber and is immediately combusted. The cooling chamber also keeps the gas in the annular space between the housing 3 and the cooling chamber at a low temperature. The liner 28 is thus protected from exposure to high temperatures, thereby increasing the useful life of the liner.

Accordingly, the present invention provides a baking oven which is long in service life and does not cause a trouble due to a deposition layer of a carbonized material during operation. In addition, a good gas seal can be obtained between the carbon rod and the baking oven, so that the possibility of harmful gas leakage from the baking oven to the surrounding environment is greatly reduced.

Claims (6)

1. A baking furnace for the continuous production of elongated carbon rods of uniform cross-section, the baking furnace being moved continuously or substantially continuously relative to a housing containing unbaked carbon electrode paste at a speed adapted to a predetermined baking speed of the carbon rods, the baking furnace comprising an outer steel shell and a refractory lining mounted within the shell, the refractory lining defining a combustion chamber, the invention being characterized in that a cooling chamber (16) is provided between an upper portion (15) of the refractory lining (6) and the housing (3), a gas sealing device (23) being provided above the cooling chamber (16), and an exhaust gas channel (11) being provided at a lower portion of the refractory lining (6). 2. A baking oven according to claim 1, characterised in that the bottom end (19) of the cooling chamber (16) is located at the same vertical level as the bottom end of the upper portion (15) of the refractory lining (6). 3. The baking oven according to claim 1, characterized in that a guide ring (22) for guiding the shell (3) is installed on the upper side of the cooling chamber (16). 4. The baking oven according to claim 1, characterized in that the gas sealing device (23) includes a flexible liner (28), a first connecting plate (24) and a second connecting plate (31); the first connecting plate has two spaced-apart lower annular flanges (26, 27) extending vertically upward; the second connecting plate has two spaced-apart upper annular flanges (29, 30) extending vertically downward; the lower end of the flexible liner (28) is mounted between the two lower vertical annular flanges, and the upper end thereof is mounted between the two upper vertical annular flanges, and the distance between the first connecting plate and the second connecting plate is adjustable. 5. A baking oven according to claim 4, characterized in that the distance between the upper flange (29, 30) and the lower flange (26, 27) is adjusted by means of bolts (32). 6. A baking oven according to claim 1, characterised in that the baking oven has at least one burner (8) arranged tangentially to the combustion chamber (7) for burning solid, liquid or gaseous fuel.