ES2929591T3 - Tunnel kiln for heat treatment of products, method for operating such a tunnel kiln and use of such a tunnel kiln - Google Patents

Abstract

The invention relates to a tunnel kiln for the heat treatment of products, to a method for operating said tunnel kiln and to the use of said tunnel kiln. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Tunnel kiln for heat treatment of products, method for operating such a tunnel kiln and use of such a tunnel kiln

The invention relates to a tunnel kiln for the heat treatment of products, to a method for operating such a tunnel kiln and to the use of such a tunnel kiln.

A tunnel kiln which is also called a continuous kiln is a type of continuous kiln, ie an industrial kiln that is continuously loaded with products to be heat treated in the kiln. For this, a tunnel kiln has a tunnel-shaped kiln chamber, through which the products to be heat treated are continuously moved, being subjected to heat during this. The tunnel-shaped furnace chamber extends from a first end, where the products are introduced into the furnace chamber, to a second, opposite end, where the products are again forced out of the furnace chamber after their heat treatment in the furnace chamber. Tunnel kilns are generally operated on the countercurrent principle. In this case, at the second end, which is also called the kiln outlet, fresh air is introduced into the kiln chamber, then it is passed through the kiln chamber and at the first end, which is also called kiln inlet, it is again evacuated from the kiln chamber. In the central area of the oven chamber, which is also called the cooking zone, means for heating the oven chamber are arranged, usually in the form of gas burners. The fresh air introduced into the furnace chamber at the second end is therefore initially relatively cold, it is heated in the firing zone, this hot fuel gas is then led to the first end of the furnace chamber and there is evacuated from the furnace. Therefore, the products conveyed through the furnace chamber are first preheated by the heated flue gases, are heat treated in the combustion chamber by the hot gases, and then before leaving the furnace chamber, They are indirectly cooled by a heat exchanger. For this reason, these three zones in the furnace chamber of a tunnel kiln are also called heating zone, holding zone and cooling zone. In order to reduce temperature losses at the furnace inlet and the furnace outlet, it is known to configure the furnace inlet and the furnace outlet in such a way that they can be closed by closing devices, for example in the form of locks.

For transporting the products through the oven chamber, rail-guided oven cars are known. These kiln cars are usually moved by means of traction cables or other types of mechanical drive means.

In principle, these types of tunnel furnaces have proven to be accredited for the heat treatment of products. However, the heat treatment of products in powder form in this type of tunnel kilns is challenging. The fact is that due to the gas flows of the flue gases occurring in the furnace chamber in known tunnel furnaces, undesirable swirling of the powdery products can occur.

US 2008/0116621 A1 describes a tunnel kiln in the form of a debarking kiln with gas burners. GB 886524 A discloses a tunnel kiln using pulse burners to apply heat to the kiln chamber. Documents US 2010/0127418 A1 and WO 2007/111045 A1 describe roller kilns with electric heating elements.

The invention has the object of providing a tunnel furnace for the heat treatment of products, which can advantageously also be used, in particular, for the heat treatment of powdered products. In particular, the invention has the object of providing a tunnel kiln for the heat treatment of powdered products, in which swirling of the powdered products can be avoided during the heat treatment in the tunnel kiln.

Furthermore, the object of the invention is to provide a method for operating such a tunnel oven.

In order to achieve the objectives described above, a tunnel oven is made available for the heat treatment of products, which includes the following characteristics:

A tunnel-shaped furnace chamber extending from a first end to a second end of the furnace chamber, the furnace chamber being bounded on the upper side by a furnace roof and laterally by furnace walls;

kiln cars that can be moved from the first end to the second end along a conveying direction through the kiln chamber and on which products to be heat-treated in the kiln chamber can be transported;

auxiliary combustion means for receiving the products, the auxiliary combustion means being arranged on the kiln cars;

gas outlets, through which the gas located in the furnace chamber can be evacuated from the furnace chamber;

gas inlets, through which gas can be introduced into the furnace chamber; Y

means for heating the furnace chamber; being able to be evacuated from the furnace chamber, through the gas outlets, the gas located in the zone of the furnace roof; gas can be introduced into the furnace chamber through the gas inlets in the area of the furnace walls; and the auxiliary combustion means being arranged on the kiln cars under the formation of at least one vertical gap between the auxiliary combustion means;

and the additional features according to claim 1.

The provision of the tunnel kiln according to the invention is based in particular on the knowledge according to the invention that swirling of powdered products is caused in particular by horizontal flows of gases located in the chamber. kiln in the area of the powder to be heat treated in the tunnel kiln. According to the invention it was also recognized that these horizontal gas flows are caused in particular by the gas flow along the longitudinal axis of the furnace chamber, i.e. along the conveying direction of the carriages. furnace in tunnel furnaces operated according to the countercurrent principle, which are customary according to the state of the art. A basic idea of the invention is therefore to avoid, as far as possible, horizontal gas flows in the oven chamber, especially in the area of the products to be fired. In this sense, a central idea of the invention is to generate a substantially vertical upward flow of gas in the area of the products to be cooked. In particular, this also means a departure from the usual countercurrent principle in the operation of the tunnel furnace according to the invention. In order to enable a vertically upwards directed gas flow during operation of the tunnel kiln according to the invention, gas inlets and outlets of the tunnel kiln according to the invention are provided. These gas outlets or inlets, specifically arranged in accordance with the invention, allow a substantially vertically upward oriented flow of combustion gases in the furnace chamber. In addition, these gas inlets and outlets are synergistically complemented by the specific arrangement of the auxiliary combustion means, which are arranged on the kiln cars under the formation of a vertical gap between the auxiliary combustion means. According to the invention it has been found that by forming such vertical gaps between the combustion aids, a vertical upward gas flow can be generated or supported in the furnace chamber.

The tunnel furnace according to the invention is used in particular for the heat treatment of products in powder form. The tunnel furnace according to the invention has proven to be particularly advantageous for the heat treatment of products in the form of cathode material, in particular such cathode material in powder form. In particular, the tunnel furnace according to the invention has turned out for the synthesis of such powdered cathode material.

The tunnel furnace chamber according to the invention can be configured substantially in accordance with the state of the art. In this connection, the furnace roof can be configured as known from the prior art, preferably as a flat or vaulted ceiling, but preferably as a vaulted ceiling. Preferably, the furnace roof can be made of refractory bricks, in particular ceramic refractory bricks, particularly preferably AhO ³ -based bricks, in particular stones with an Al ² O ³ content of at least 97% by mass, so that more preferably at least 99% by mass, based on the mass of the stones.

The gas outlets in the furnace roof can be provided, in particular, in the form of openings in the furnace roof. Preferably, several gas outlets are provided, preferably distributed over the furnace roof, particularly preferably evenly distributed over the furnace roof, in particular over the length of the furnace. In this way a very uniform, upwardly oriented vertical flow of the gases in the furnace chamber can be achieved. According to a preferred embodiment, the gas outlets are arranged in the center of the furnace roof. If the furnace roof is configured as a vault, the outlets are preferably arranged at the top of the vault, in which case the top of the vault preferably runs in the center of the furnace roof.

The gas outlets preferably open into gas lines through which the gas that can be discharged from the gas outlets can be led.

Preferably, one or more blowers are provided, by means of which the gas that can be exhausted from the gas outlets can be withdrawn and transmitted in particular through the gas lines. Said blowers are preferably totally or partially outside the furnace chamber. If the blowers are arranged partly outside the furnace chamber, the blowers can have a socket that can also extend into the furnace chamber, into which the gas outlets open, for example. Preferably, the gas lines for conducting the exhaustable gas from the gas outlets extend in each case to at least one of these blowers.

The furnace walls preferably run vertically and are preferably made of refractory brick masonry, in particular ceramic refractory bricks. Preferably, the furnace walls can consist of refractory bricks, in particular ceramic refractory bricks, particularly preferably A^O ³ -based bricks, in particular bricks with an A^O ³ content of at least 97 % by mass, more preferably at least 99% by mass, based on the mass of the bricks.

The gas inlets are preferably provided in the form of openings in the furnace walls. Preferably, several gas inlets are provided, preferably distributed over the furnace walls, particularly preferably evenly distributed over the furnace walls. In this way, the gas can be introduced very evenly into the furnace chamber via the gas inlets, whereby swirling of powdery products that are to be heat-treated in the furnace chamber can be avoided. Preferably, the gas inlets are arranged at a distance from one another along the conveying direction, particularly preferably evenly distributed over the length of the furnace. In this way, the gas can be introduced into the furnace chamber particularly evenly along the length of the furnace, which in turn prevents swirling of the powdery products in the furnace chamber.

If both the gas outlets and the gas inlets are provided evenly along the length of the furnace, in particular evenly along the length of the furnace, a particularly uniform, oriented gas flow can be generated. vertically upwards in the furnace chamber.

According to one embodiment, the flow section of the gas inlets is adjustable. This has the particular advantage that the flow volume and the flow distribution of the gas that can be introduced into the furnace chamber via these gas inlets can be adjusted.

According to a preferred embodiment, the gas inlets are arranged in such a way that gas can be fed into the furnace chamber below the combustion aids via the gas inlets. This has the particular advantage that the gas introduced into the furnace chamber via these gas inlets does not cause any swirling of powdery products in the furnace chamber. In order to be able to introduce the gas into the furnace chamber below the auxiliary combustion means, the gas inlets are preferably arranged at the lower end of the furnace walls, i.e. in the area of the furnace walls, adjacent to the oven floor. Preferably, the gas can be introduced horizontally into the furnace chamber through these gas inlets, so that direct exposure of the powdered products to the gas introduced into the furnace chamber from these gas inlets can be avoided, avoiding thus the swirling of these products.

According to one embodiment, it can be provided that the gas can be introduced into the furnace chamber via the gas inlets exclusively below the combustion aids.

It is provided that gas can be introduced into the furnace chamber via gas inlets at different heights, ie at different (vertical) heights of the furnace chamber. For this, the gas inlets can be arranged at different heights on the furnace walls. A particular advantage of this embodiment is that the gas can be introduced into the furnace chamber evenly over the height of the furnace chamber, whereby the gas can be introduced into the furnace chamber very evenly and thus Therefore, swirling of the powdered products in the furnace chamber can be avoided. In this embodiment, it is also possible that the gas can be introduced into the furnace chamber via gas inlets in the area or at the level of the products to be treated in the furnace chamber. In order, however, to be able to prevent swirling of the powdered products in the baking chamber, provision may be made in this embodiment that gas can be introduced into the baking chamber via the openings in this embodiment as well. gas inlets located below the auxiliary combustion means, in which case, as regards these gas inlets, through which gas can be introduced into the furnace chamber below the auxiliary combustion means, the gas can be introduced into the oven chamber at a higher velocity than through the other gas inlets, in particular those additional gas inlets through which gas can be introduced into the oven chamber at the height of the products to be they must be treated in the furnace chamber.

If gas can be fed into the furnace chamber below the combustion aids via the gas inlets, this gas can then flow vertically upwards and, in particular, also flow upwards through the gas inlets. vertical gaps formed between the auxiliary combustion means, up to the furnace roof, where the gas is evacuated from the furnace chamber through the gas outlets. In this way, the products located in the auxiliary combustion means are substantially exposed to heat by the vertically upwardly oriented combustion gases. In particular, it can be provided that the gas can be introduced into the furnace chamber below all the combustion aids via the gas inlets. This has the particular advantage that all combustion aids can be supplied with gas from below, which can then flow vertically upwards between all combustion aids, so that all combustion aids, i.e. , over the entire width of the furnace chamber, can be uniformly supplied with gas, in particular by a gas flow directed vertically upwards.

Another advantage of the gas that can be introduced into the furnace chamber below the auxiliary combustion means is, in particular, that the products located in the auxiliary combustion means can be heat treated very advantageously, since, in particular , the heat losses of the products arranged in the lower combustion aids can also be compensated.

If, as explained above, additional gas inlets are provided at the height of the combustion aids, these can be provided, in particular, to supply gas to the combustion aids adjacent to the furnace wall.

In general, the gas inlets and gas outlets can be arranged in such a way that the gas can be guided through the furnace chamber under the formation of an upward flow, in particular a vertically upward flow.

Furthermore, the gas inlets and gas outlets can be arranged, as explained above, so that the gas can be guided through the furnace chamber avoiding a horizontally oriented flow.

In particular, as explained above, the gas inlets and gas outlets can thus be arranged in such a way that the gas can be guided through the furnace chamber avoiding a gas flow according to the countercurrent principle.

In this connection, as explained above, the gas inlets and the gas outlets can be arranged in such a way that the gas can be guided through the furnace chamber avoiding a flow of gas in the direction of transport.

The gas inlets are preferably connected to gas lines which open into the gas inlets and through which gas can be led which can be introduced into the furnace chamber via the gas inlets. According to a particularly preferred embodiment, it is provided that the gas outlets open into the gas lines described above, through which this gas can in turn be led to the gas inlets. Thus, the gas can be looped through the tunnel furnace. This gas recirculation can be supported by means of the blowers, as explained above. A particular advantage of using blowers in this context is that they can also contribute to a homogenization of the furnace gases drawn from the furnace chamber.

Of course, not all gases withdrawn from the furnace chamber through the gas outlets have to be reintroduced into the furnace chamber through the gas inlets and be recirculated accordingly. Rather, as is known from the prior art, a part of the exhaust gases from the furnace chamber can be continuously withdrawn from the furnace as exhaust gas and in addition fresh gas can be continuously introduced into the furnace. For this, the gas conduction means known from the prior art can be provided.

For the heat treatment of the products in the furnace chamber, ie for bringing these products to the temperature in the furnace chamber, the tunnel furnace according to the invention has means for heating the furnace chamber. These means are devices for heating the furnace chamber with thermal energy. The means for heating the furnace chamber are electric heating elements. It is that, according to the invention, it was found that unwanted horizontal gas flows here can be caused to some extent by gas burners, while electric heating elements do not cause gas flows in the horizontal direction in the cooking chamber. oven, or these are negligible. According to a preferred embodiment, the tunnel kiln according to the invention has only such electric heating elements for heating the kiln chamber. Electric heating elements are the so-called resistance heating elements that heat up due to their resistance when electric current is passed through. Electric heating elements are provided in the form of ceramic heating elements, in particular non-oxide ceramic heating elements, in particular SiC (silicon carbide) or SiN (silicon nitride) ceramic heating elements with particular preference. Preferably, it is provided that heat can be applied to the furnace chamber by the electric heating elements mainly by means of convection and less by means of radiation. The advantage of applying convective heat in the oven chamber is, in particular, that the products located in the oven chamber can be exposed to heat more evenly, since substantially no shielding effects occur. In this connection, it is preferably provided that in order to heat the furnace chamber by means of the electric heating elements, the gas located in the furnace chamber can be heated by the heating elements. Particularly preferably, it can be provided that the gas that can be introduced into the furnace chamber via the gas inlets can be heated by the heating elements. It is provided that the gas that can be introduced into the furnace chamber through the gas inlets can be heated by the heating elements prior to the introduction of the gas into the furnace chamber. In this sense, the gas that can be introduced into the furnace chamber is first heated by the heating elements and then is introduced into the furnace chamber through the gas inlets. Provision can be made for this to first guide the gas past the heating elements so that it heats up and is then introduced into the furnace chamber via the gas inlets. According to a particularly preferred embodiment, it can be provided that the gas is first passed in front of the heating elements via the above-mentioned gas lines, so that the gas is heated up, and that it is then introduced into the furnace chamber through the gas inlets. According to a variant of this idea of the invention, it can be provided that the gas is evacuated from the furnace chamber via the gas outlets, that it is then led past the heating elements so that the gas is heated by them and that, then the gas is introduced into the furnace chamber through the gas inlets. In this case, as explained above, the gas can be led through gas lines from the gas outlets to the heating elements and then to the gas inlets. Furthermore, the gas flow can be supported by blowers, as explained above.

By means of the heated gas introduced into the furnace chamber via the gas inlets, the furnace chamber can be heated to a desired temperature. In particular, the furnace chamber is heated to the desired temperature for the heat treatment of the products located in the auxiliary combustion means. The tunnel furnace according to the invention is also particularly suitable for the heat treatment of products at high temperatures, in particular also at least 300 °C or at least 700 °C. In particular, the furnace chamber can be heated to a temperature in the range from 300 to 1,200 °C, in the range from 700 to 1,200 °C, in the range from 300 to 1,000 °C and particularly preferably in the range from 700 to 1,000 °C. If the tunnel furnace according to the invention is used for the heat treatment of products in the form of cathode material, in particular for the synthesis of powdered cathode material, provision can be made for the furnace chamber to be heated to a temperature in the range from 1,000 to 1,200 °C.

According to a particularly preferred embodiment, provision is made for a gas distribution space to be provided below the combustion aids. This gas distribution space serves, in particular, to distribute the fuel gas evenly below the combustion means, so that the homogenized gas can then rise out of the gas distribution space vertically between the combustion means. In this way, the products located in the auxiliary combustion means can be subjected in a very homogeneous way to fuel gas and, therefore, to heat. To form such a gas distribution space below the auxiliary combustion means, the auxiliary combustion means can preferably lie on bases located at a distance from each other, the bases preferably lying on the kiln cars. The supports can preferably be ceramic bricks, in particular refractory ceramic bricks. The gas distribution space is preferably made between the upper side of the kiln cars and the auxiliary combustion means.

Particularly preferably, gas can be introduced into this gas distribution space via the gas inlets. Particularly preferably, the gas can be introduced into the gas distribution chamber via the gas inlets described above, through which the gas can be introduced into the furnace chamber below the auxiliary combustion means. .

The combustion aids are arranged on the kiln cars under the formation of at least one vertical gap between the combustion aids. Through these vertical gaps between the combustion aids, gases can flow vertically upwards to the furnace roof. Particularly preferably, at least one of the at least one vertical gap between the combustion aids runs in the direction of transport. Preferably, several of the vertical gaps run in the direction of transport. According to the invention, it was found that by means of such gaps between the combustion aids running vertically in the conveying direction, not only can a vertically oriented flow of gases be generated upwards in the furnace chamber, but at the same time time, a flow of gases in the furnace chamber in the conveying direction can be suppressed particularly effectively.

In order to form vertical gaps between the combustion aids, the combustion aids can be arranged horizontally at a distance from one another on the kiln cars. Particularly preferably, the combustion aids are arranged on the kiln carriages at a distance from each other transversely to the direction of transport, with the formation of at least one vertical gap between the combustion aids, thus forming at least one gap between the combustion aids in the direction of transport.

Cumulatively, vertical gaps can also be formed transversely to the direction of transport between the combustion aids, for which the combustion aids can be arranged on the kiln cars at a distance from one another along the direction of transport under the formation of at least one vertical gap between the auxiliary combustion means.

According to a particularly preferred embodiment, stackable combustion aids are provided, in particular combustion aids that can be stacked on top of one another, particularly preferably combustion aids that can be stacked vertically on one another. According to a particularly preferred embodiment, the combustion aids are provided in the form of cassettes, ie in the form of "boxes", in particular with a rectangular outer contour (in plan view from above). In particular, if the combustion aids are in the form of such cassettes, especially with a rectangular outer contour, the combustion aids can be arranged particularly easily and effectively side by side on the kiln cars, in such a way that gaps of vertical path can be formed between the auxiliary combustion means.

For the transport of the products through the furnace chamber, the products are received by means combustion aids. If the products are present in the form of powder products, the powders are received in the combustion aids, ie, in the case of cassette or box-shaped combustion aids, they are received in the cassettes or boxes respectively.

The combustion aids preferably consist of graphite or ceramic, for example an oxide ceramic or a non-oxidic ceramic, particularly preferably a non-oxidic ceramic, in particular a nitride or carbide non-oxidic ceramic, particularly preferably made of SiC, in particular of silicate- or ceramic-bonded SiC.

In order to make it possible for the products received in the combustion aids to be exposed to the hot gases from the furnace, even in the case of combustion aids stacked vertically one on top of the other, it can preferably be provided that the combustion aids are stacked vertically one above the other so that a passage is formed between the vertically adjacent combustion aids. If the combustion aids are configured in the form of cassettes, it can be provided, for example, that these cassettes each have closed walls in their lower region, so that powders can be safely accommodated in the cassettes, and that the walls of the cassettes have perforations, holes or other openings in their upper area, through which combustion gases can flow between vertically adjacent cassettes.

The kiln cars can be configured according to the state of the art. In this regard, the kiln cars can be moved around the kiln chamber, for example, on rails. For the movement of the kiln cars, these can be mobile, for example, by traction cables or similar mechanical drive means. Kiln cars may have a substantially rectangular outer contour (in plan view from above).

The kiln cars each have an upper side, on which the combustion aids can be arranged. Preferably, the combustion aids can be placed on the upper side of the kiln cars. Preferably, the upper side of the oven trolleys is designed as a flat surface, preferably with a rectangular outer contour.

Preferably, the upper sides of the kiln cars delimit the kiln chamber on the lower side, thus forming the kiln floor.

Preferably, the tunnel furnace is sealed in a gas-tight manner. For this, it can preferably be provided that the tunnel furnace is formed on its outside by a gas-tight jacket, preferably a gas-tight steel casing. Particularly preferably, the gas-tight steel casing also encloses the kiln carriages located in the kiln chamber. In this way, the gas-tight steel casing encloses in particular also the furnace roof, the furnace walls and the furnace carriages. Preferably, the gas-tight steel casing runs below the oven trolleys, so that these are also enclosed in a gas-tight manner.

To seal the tunnel furnace in a gas-tight manner at the first end of the furnace chamber, i.e. at the furnace inlet, and at the second end of the furnace chamber, i.e. at the furnace outlet, Closing means may be provided by means of which the furnace chamber can be closed in a gas-tight manner, but which allows the entry or exit of furnace cars into or from the furnace chamber. For this, locks can preferably be provided at the first end and at the second end. By means of corresponding locks respectively at the first end and the second end of the kiln chamber, the kiln cars can be brought into or out of the kiln chamber, while at the same time the kiln chamber remains permanently sealed. algae.

The particular advantage of such a gas-tight tunnel furnace is that a desired furnace atmosphere can be established.

In particular, it is preferred that an oxidizing furnace atmosphere prevail in the furnace chamber or that the tunnel furnace according to the invention is operated with an oxidizing furnace atmosphere. However, it can also be provided to operate the tunnel furnace with a reducing furnace atmosphere, for example, if graphite combustion auxiliaries are provided.

Preferably, the proportion of oxygen gas in the furnace atmosphere is greater than 95% by volume. However, it is also possible to operate the furnace with an air atmosphere, ie with an oxygen gas percentage of approximately 21% by volume. If the tunnel kiln is operated with a reducing kiln atmosphere, the kiln can, for example, be operated with nitrogen as process gas and, for example, with a residual oxygen content of less than 100ppm.

A particular advantage of the tunnel furnace according to the invention consists in particular also in the fact that virtually any length (in the conveying direction), in particular also with a length of more than 50 m. According to a preferred embodiment, it is provided that the tunnel furnace has a length of at least 120 m, in particular at least 150 m. In this regard, the tunnel kiln may, for example, have a length in the range of 50 to 250 m. Preferably, the tunnel kiln has a length within the range of 120 to 250 m, more preferably within the range of 150 to 250 m, and most preferably within the range of 150 to 200 m.

Another object of the invention is a procedure for operating a tunnel kiln, which comprises the following steps:

The provision of a tunnel oven according to the invention; according to one of claims 1 to 11; the displacement of the kiln cars through the kiln chamber along the direction of transport;

the evacuation of gas located in the furnace chamber through the gas outlets;

the introduction of gas into the furnace chamber through the gas inlets; Y

heating of the furnace chamber through heating elements.

Furthermore, the method according to the invention can comprise the measures described here for the operation of the tunnel furnace according to the invention. Another object of the invention is the use of a tunnel furnace according to the invention according to one of claims 1 to 11 for heat treatment of products in powder form. Preferably, the use is made with the proviso that the tunnel furnace is used for the heat treatment of products in the form of powdered cathode material, in particular for the synthesis of powdered cathode material.

Otherwise, the use can be made under the conditions described here for operating the tunnel kiln according to the invention.

Further features of the invention are derived from the claims, the figures as well as the respective description of the figures.

All features of the oven according to the invention can be combined with each other at will, individually or in combination.

An exemplary embodiment of the invention is explained in more detail by the following description of the figures.

Show:

1 a cross-sectional view of an exemplary embodiment of a tunnel kiln according to the invention perpendicular to the longitudinal axis of the tunnel kiln;

2 is a fragmentary cross-sectional view of the tunnel furnace according to FIG. 1 parallel to the longitudinal axis; Y

3 a cross-sectional view of the tunnel furnace according to FIG. 1 parallel to the longitudinal axis.

The illustrations in the figures are very schematized with respect to the configuration and dimensioning of the tunnel kiln.

1 shows a cross-sectional view of the tunnel kiln perpendicular to the direction of transport or the longitudinal axis of the tunnel kiln, in which the tunnel kiln is designated as a whole by the reference sign 1. 1, the conveying direction and the longitudinal axis of the tunnel furnace 1 run perpendicular to the plane of the drawing. The longitudinal axis is designated L in FIGS. 2 and 3, the conveying direction running along the longitudinal axis L to the right in FIGS. 2 and 3. The tunnel kiln 1 comprises a tunnel-shaped kiln chamber 2 extending perpendicular to the drawing plane from a first end (in front of the drawing plane) to a second end (behind the drawing plane) of the furnace chamber 2, the furnace chamber 2 being bounded on its upper side by a furnace roof 3 and laterally by a first furnace wall 4, in FIG. 1 the left, and a second furnace wall 5, in FIG. 1 the right. The tunnel kiln 1 also comprises kiln cars 6 which can be moved through the kiln chamber 2 by means of wheels 7 on rails 8 along the transport direction, i.e. perpendicular to the drawing plane in figure 1 and to the left. right in Figures 2 and 3. Auxiliary combustion means 9 are arranged on the kiln carriages 6 for accommodating products.

The roof of kiln 3 is made of refractory ceramic brick masonry. In the center of the furnace roof 3, gas outlets 10 are arranged at uniform distances from each other in the form of openings through the furnace roof 3, of which one gas outlet 10 can be seen in the figures. The gas outlets 10 are arranged at uniform distances from each other along the conveying direction on the furnace roof 3. The outlets gas tubes 10 lead to a blower 12 driven by a motor 11.

The walls of the kilns 4, 5 running vertically are made of refractory ceramic brick masonry. Gas inlets 17, 18, 19 are provided in the side walls 4, 5 in the form of openings that pass through the furnace walls 4, 5. The gas inlets 17, 18, 19 are arranged at different heights in the furnace walls. 4, 5, at uniform distances from each other in the direction of transport along the length of the furnace. In each case on the side walls 4, 5 opposite lower gas inlets 17 are arranged, gas inlets 18 arranged above these and gas inlets 19 arranged above these in turn on the side walls 4, 5. The gas inlets 17 are arranged in such a way that gas can be introduced into the furnace chamber 2 through these below the auxiliary combustion means 9. As explained in more detail below, gas can be introduced, through these lower gas inlets 17, into a gas distribution space 20 formed below the combustion aids 9, which is indicated by the arrows P1. Via the gas inlets 17, 18, 19 gas can be introduced horizontally into the furnace chamber 2 in each case, it being possible for gas to be introduced into the furnace chamber 2 through the lower gas inlets 17 at a higher speed than through of the gas inlets 18, 19 arranged above.

The refractory ceramic bricks for the kiln roof 6 and kiln walls 4, 5 are high-alumina bricks with an A^O ³ content greater than 99% by mass, based on the mass of the bricks.

The tunnel furnace 1 is formed on its outer side by a steel casing 27, which seals the tunnel furnace 1 in a gas-tight manner. The steel casing 27 has a substantially rectangular outline with a top 27.1 running horizontally, a bottom 27.2 running horizontally and two walls 27.3, 27.4 running vertically respectively. Below the ceiling 27.1 of the steel shell 27, a suspended ceiling 16 of refractory ceramic bricks is suspended from the ceiling 27.1 and extends above the furnace ceiling 3 at a distance therefrom. In this way, above the furnace ceiling 3, a free space 13 is created between the furnace ceiling 3 and the suspended ceiling 16.

The two walls 27.3, 27.4 of the steel jacket 27 are lined on the inside with a lining of refractory bricks 14, 15, which extends to the side walls 4, 5 at the level of the side walls 4, 5. The refractory brick lining 14, 15 has openings 28 running at a distance from each other between the walls 27.3, 27.4 and the side walls 4, 5. The gas inlets 17, 18, 19 extend respectively through the side walls 4 , 5 from the furnace chamber 2 to within these openings 28.

The free space 13 and the openings 28 together form gas conduits through which gas can be conducted.

The exhaust gas lines 31 pass through the suspended ceiling 16 and open at one end in the free space 13 and at the other end in the valves 33 in the ceiling 27.1.

Furthermore, fresh gas lines 32 extend through the linings 14, 15, opening at one end into the openings 28 and at their other end into the valves 34 in the walls 27.3, 27.4.

The vertically arranged electric heating elements 21 extend from the suspended ceiling 16 through the free space 13 and the openings 28. The electric heating elements 21 are SiC ceramic heating elements.

The oven cars 6 are configured substantially in accordance with the state of the art. In this regard, the kiln cars 6 can be moved along the transport direction by means of wheels 7 on rails 8, thus they can be moved by traction cables (not shown). The oven cars 6 have a substantially rectangular outer contour (in plan view from above). The upper side 22 of the oven trolleys 6 is configured as a flat surface and delimits the oven chamber 2 on the underside. To one side, the kiln cars 6 are separated from the foundations 24 of the linings 14, 15 of the tunnel kiln 1 via a labyrinth closure 23.

The upper side 22 of the kiln cars 6 serves as a support for the combustion aids 9. In this case, the combustion aids 9 are placed on the kiln cars 6 through supports 25 in the form of refractory ceramic bricks. at a distance from the upper side 22 of the oven cars. In this way, between the kiln carriage 6 and the auxiliary combustion means 9, the gas distribution chamber 20 is formed.

The combustion aids 9 consist of ceramic-bonded SiC cassettes that can be stacked vertically on top of one another. The combustion aids 9 have a rectangular cross-sectional outline (in plan view from above). In their lower region, the combustion aids 9 have closed walls and in their upper region they have openings, so that a passage is left between the vertically adjacent combustion aids 9 .

In the exemplary embodiment, each of eight lifting aids are stacked one on top of the other. combustion 9. The stacks are arranged in rows in the direction of transportation on kiln cars 6. In this case, three of these rows are arranged side by side transversely to the direction of transportation, so that between the rows Adjacent stacks of combustion aids 9 stacked one on top of the other each have a vertical gap 26 between the combustion aids 9.

A powdery cathode material is respectively arranged in the combustion means 9 .

At the first end, in figure 3 the left, of the furnace chamber 2, the tunnel furnace 1 has an entrance lock 29 and at the second end, in figure 3 the right, of the furnace chamber 2 presents an exit lock 30 for gas-tight closing of the furnace chamber 2 according to the state of the art. The entrance lock 29 and the exit lock 30 make it possible for kiln cars 6 to enter and exit the kiln chamber 2, while the kiln chamber 2 can, however, be closed gas-tight at the same time.

The transport furnace 1 has a length of approximately 150 m in the transport direction.

In practical application, the tunnel kiln 1 shown in the figures is operated as follows: The kiln cars 6 are introduced into the kiln chamber 2 through the inlet lock 29, then they are moved from continuously through the furnace chamber 2 in the direction of transport along the longitudinal axis L and, after running through the furnace, exit the furnace chamber 2 again through the outlet lock 30 located in the second end of furnace chamber 2.

The gas located in the furnace chamber 2 is evacuated from the furnace chamber 2 through the gas outlets 10. This discharge of gas from the furnace chamber 2 through the gas outlets 10 is assisted by the blower 12 driven by the motor 11, which, after the evacuation of the gases from the furnace through the gas outlets 10, transports them first to the free space 13 (indicated by the arrows P3), then to the ceramic heating elements 21 and along of these, through the openings 28 and finally through the gas inlets 17, 18, 19 back into the furnace chamber 2. Passing along the ceramic heating elements 21, the gas from the furnace is heated , so that the correspondingly heated gas is then fed back into the furnace chamber 2 via the gas inlets 17, 18, 19, which is indicated by the arrows P1.

During this, the heated gas is introduced into the gas distribution space 20 via the lower gas inlets 17 and is led through the gas inlets 18, 19 arranged above in the direction towards the respective outer media rows. combustion aids 9 stacked on top of each other, which are respectively adjacent to the side walls 4, 5. In the gas distribution chamber 20, the introduced gas is distributed and then flows vertically upwards through the interstices 26 formed between the auxiliary combustion means 9 (indicated by the arrows P2) up to the zone of the furnace roof 3, where it again leaves the furnace chamber 2 through the gas outlets 10. The gas introduced in the furnace chamber 2 through the gas inlets 18, 19 it flows vertically upwards between the outer stacks of combustion aids 9 and the side walls 4, 5 to the area of the furnace roof 3, where it leaves the furnace chamber 2 likewise through the gas outlets 10. Thus, the gas circulates continuously in a loop.

This enables the flue gases to flow substantially vertically upwards into the furnace chamber 2. A flow of flue gases in the horizontal direction and above all in the direction of transport can be practically completely avoided.

Parts of the fuel gas circulated in the circuit can be withdrawn as exhaust gas. For this, the fuel gas can be withdrawn from the free space 13 via the exhaust gas ducts 31, be evacuated from the furnace 1 by opening the valves 33 and be fed to an exhaust gas treatment. In addition, fresh gas can be supplied to the fuel gas. For this purpose, by opening the valves 34 via the fresh gas lines 32, fresh gas, for example air or oxygen, can be introduced into the flue gas circuit in the area of the openings 28.

Tunnel kiln 1 is operated in an oxidizing kiln atmosphere, the oxygen concentration in kiln chamber 2 being greater than 95% by volume.

The ceramic heating elements 21 heat the furnace chamber in such a way that the temperature in the furnace chamber 2 is approximately 1,100 °C. In this way, the powdered cathode material located in the auxiliary combustion means 9 can be synthesized.

Due to the flow conditions in the furnace chamber 2 described above, no swirling of the powdered cathode material occurs.

List of reference signs

1 tunnel oven

2 Furnace chamber

3 Furnace roof

4 Left side wall of the furnace chamber

5 Furnace chamber right side wall

6 Kiln trolley

7 wheels

8 rails

9 Auxiliary Combustion Media

10 gas outlet

11 engine

12 blower

13 Free space

14, 15 Lateral lining of the steel jacket

16 Steel jacket roof cladding

17, 18, 19 Gas inlets

20 Gas distribution space

21 Ceramic heating elements

22 Upper side of oven racks

23 Labyrinth closure

24 Side cladding foundations

25 Supports

26 Interstices

27 Steel jacket

27.1 to 4 Wall parts of the steel jacket

28 openings

29 entrance lock

30 Exit lock

31 Exhaust gas ducts

32 Fresh gas lines

33 Exhaust gas duct valves

34 Fresh gas line valves

P1 to P3 Gas flows

Claims (13)

1. Tunnel furnace for heat treatment of products, comprising the following characteristics: 1.1 A tunnel-shaped furnace chamber (2) extending from a first end to a second end of the furnace chamber (2), the furnace chamber (2) being bounded on the upper side by a furnace roof (3) and laterally by oven walls (4, 5); 1.2 kiln cars (6) that can be moved through the kiln chamber (2) from the first end to the second end along a transport direction and on which products to be treated can be transported with heat in the oven chamber (2); 1.3 auxiliary combustion means (9) to receive the products, the auxiliary combustion means (9) being arranged on the kiln cars (6); 1.4 gas outlets (10), through which the gas located in the furnace chamber (2) can be evacuated from the furnace chamber (2); 1.5 gas inlets (17, 18, 19), through which gas can be introduced into the furnace chamber (2); and 1.6 means (21) for heating the furnace chamber (2); where 1.7 through the gas outlets (10), the gas located in the area of the furnace roof (3) can be evacuated from the furnace chamber (3); 1.8 through the gas inlets (17, 18, 19), gas can be introduced into the furnace chamber (4, 5) in the area of the furnace walls (4, 5); where 1.9 the auxiliary combustion means (9) are arranged on the kiln cars (6) under the formation of at least one vertical gap 26 between the auxiliary combustion means (9); where 1.10 the means (21) for heating the oven chamber (2) are electric heating elements; where 1.11 the gas that can be introduced into the furnace chamber (2) through the gas inlets (17, 18, 19) can be heated by the heating elements before the introduction of the gas into the furnace chamber ( 2); and where 1.12 in which, through the gas inlets (17, 18, 19) gas can be introduced into the furnace chamber (2) at different heights. Tunnel kiln according to claim 1, in which gas can be introduced into the kiln chamber (2) via the gas inlets (17, 18, 19) below the combustion aids ( 9). Tunnel kiln according to at least one of the preceding claims, in which the gas inlets (17, 18, 19) and the gas outlets (10) are arranged in such a way that the gas can be guided through through the furnace chamber (2) with the formation of an upwardly directed gas flow. Tunnel kiln according to at least one of the preceding claims, in which the gas inlets (17, 18, 19) and the gas outlets (10) are arranged in such a way that the gas can be guided through through the furnace chamber (2) avoiding a horizontally directed gas flow. Tunnel kiln according to at least one of the preceding claims, in which the gas inlets (17, 18, 19) and the gas outlets (10) are arranged in such a way that the gas can be guided through through the furnace chamber (2) avoiding a flow of gas according to the countercurrent principle. Tunnel kiln according to at least one of the preceding claims, in which the gas inlets (17, 18, 19) and the gas outlets (10) are arranged in such a way that the gas can be guided through through the furnace chamber (2) avoiding a flow of gas in the direction of transport. Tunnel kiln according to at least one of the preceding claims, in which a gas distribution space (20) is realized below the combustion aids (9). Tunnel kiln according to claim 8, in which gas can be fed into the gas distribution space (20) via the gas inlets (17, 18, 19). Tunnel kiln according to at least one of the preceding claims, in which at least one of the at least one gap (26) between the combustion aids (9) runs in the conveying direction. Tunnel kiln according to at least one of the preceding claims, with combustion aids (9) in the form of stackable combustion aids. Tunnel furnace according to at least one of the preceding claims, which is sealed in a gas-tight manner. 12. Procedure for operating a tunnel kiln, comprising the following steps: 12.1 Provision of a tunnel oven (1) according to at least one of the claims previous; 12.2 the displacement of the kiln cars (6) along the direction of transport through the kiln chamber (2); 12.3 the evacuation of the gas located in the furnace chamber (2), through the gas outlets (10); 12.4 the introduction of gas into the furnace chamber (2), through the gas inlets (17, 18, 19); Y 12.5 heating the furnace chamber (2) through the means (21) for heating the furnace chamber (2). Use of a tunnel furnace according to at least one of claims 1 to 11 for heat treatment of products in powder form.