EP0247100B1 - Device and process for the thermal treatment of formed bodies - Google Patents

Abstract

A device for thermally treating preforms includes two parallel oven channels (10, 12) which work in opposite directions and cross at least a heating zone, (30, 36), a baking zone (32, 38) and a cooling zone (34, 35). An outlet (50) leads from one of the oven channels (10, 12) into a baking chamber (54) from which a feeding device (55) opens into either of the oven channels (10, 12).

Description

The invention relates to a device for the heat treatment of moldings with two mutually parallel furnace channels, through which the material to be burned is guided in opposite directions, each with at least one heating zone, combustion zone and cooling zone, and a corresponding method for heat treatment.

A device of the type mentioned is known from DE-OS-3 042 708. In the tunnel kiln described there, the heat removed from one zone of one kiln channel can be used in a zone of the other kiln channel, for which purpose ventilation means are provided which carry out gas transport in countercurrent to the product streams.

A similar arrangement is also known from DE-OS-3 023 228, the material moving in two opposite directions through the furnace chamber being acted upon and flowed through by a circulating cross-flow of the furnace gases in order to bring about a heat exchange between the material flows.

The known ovens are intended for firing porcelain (DE-OS-3 042 708) or blast furnace coke (DE-PS-3 023 228).

The known systems are unsuitable for the heat treatment of materials containing a large amount of pyrolyzable substances, in particular moldings, since the pyrolyzable substances released during the heat treatment are only conducted in a cycle and thus increase the pollutant load in the furnace atmosphere.

Substances are known which in some cases release considerable amounts of such pyrolyzable substances during the fire. For example, carbon electrodes that are impregnated with tar or pitch and / or mixed with crushed coke, graphite or soot under vacuum, release significant amounts of pyrolyzable substances (e.g. tar and / or pitch vapors) during the fire, which represent a considerable burden on the furnace atmosphere .

The pyrolysis products are often not in thermal equilibrium, so that, for example, secondary fission products, such as retort coke and especially soot, are formed on the hot furnace walls, which increasingly lead to a cross-sectional taper.

It is known to avoid the deposition and precipitation of carbonaceous substances by burning the volatile pyrolysis products.

On the part of the applicant it has already been proposed for a pyroprocess in a chamber furnace to supply oxygen to the circulated flue gas, in such a way that the fuel is burned below a chamber temperature of 600 ° C by supplying a stoichiometric amount of air and above a chamber temperature of 600 ° C by special An additional amount of air is blown into the chamber.

A correspondingly set up furnace or the corresponding method have significantly reduced the risk of explosion, but the method as such is not easy to master, so that new possibilities are sought to optimize the pyroprocess. It is also important to be able to carry out a complete fire with the least possible energy and with a high safety standard, and to enable continuous heat treatment in a continuous furnace.

The invention is based on the knowledge that an optimization of the pyroprocess can be achieved in that the flue gases loaded with the pyrolyzable substances are withdrawn from the furnace channel of a continuous furnace, burned in a separate room with energy generation without ongoing burner support, and the burnt flue gases cleaned in this way then be returned to the furnace channel at another location.

The invention is further based on the knowledge that it prevents adherence or build-up, for example on the furnace walls, and that utilization of the heat generated during the combustion of the flue gases can be optimized by the fact that the flammable gases emerging from the fuel and from the flue gas are recorded, fed to the shortest possible route to combustion and then returned to the furnace duct as useful heat in the same short way. It has been shown that the entire furnace without a burner can only be heated by "self-combustion" of the flue gases with an appropriate supply of oxygen. The flue gases have a significant proportion of combustible constituents (binding agents) in a combustible material such as carbon electrodes, which can not only be made harmless by burning, but is sufficient to provide the energy necessary for the heat treatment of the material itself.

To this end, the invention proposes a tunnel kiln with the features of claim 1 and a method for the heat treatment of moldings containing pyrolyzable substances with the features of claim 21. Preferred embodiments are disclosed in dependent claims 2 to 20 and 22.

A tunnel kiln is known from DE-OS-2 001 148, in which kiln gases are drawn off and also burned in a combustion chamber located outside the kiln channel. The "external" combustion takes place there, however, by means of a fuel-fed burner and only serves to avoid direct contact of the burner flame with the sensitive material (pottery).

With the invention, on the one hand, combustion of the pyrolyzable substances is simple Tem ways outside the furnace channel can be achieved, on the other hand, the heat gained as useful heat can be supplied in an equally short way to the furnace channel, from which the gases have been removed, and / or the adjacent furnace channel. As a result, the control of the pyroprocess in the individual furnace channels is made significantly easier by excluding any risk of explosion, in addition to the considerable energy savings. An auxiliary burner is only required to ignite when starting the furnace. Then the flue gas, to which oxygen is added, burns itself. The external energy requirement is practically zero. Appropriate regulation / control of the supply devices (oxygen, flue gas) enables optimal combustion and supply of the useful heat to be carried out in individual furnace sections.

The guidance of the flue gases is facilitated in that at least one blower and / or at least one suction device are provided in the area of the extraction device and / or feed device. Under certain circumstances, however, the injector effect of the combustion chamber, for example, is also sufficient to achieve a gas flow.

In an advantageous embodiment of the invention, it is proposed to design the space for the combustion of the flue gases as an enlarged duct. The extraction device and / or feed device can open into the channel from the ceiling area of an oven duct, as proposed by a further embodiment of the invention.

As already mentioned, the object on which the invention is based is solved particularly advantageously in all its parts when the feed device (s) opens into the furnace channel at a short distance from the extraction device in order to keep the distances as short as possible.

It is advantageous to introduce the fresh air into the combustion chamber directly next to the point where the flue gases also flow. The spontaneous combustion works best then.

For reasons of further combustion optimization, the invention proposes in an advantageous embodiment to lead the fresh air supply line at least partially inside the walls or the ceiling of the oven according to the invention, which are inevitably very hot, in particular in the area of the combustion zone, and preheating the fresh air supplied from the outside enable. Again, fans can be provided to support the air flow.

The extraction and feed devices are preferably arranged within the respective firing zones of the two furnace channels, and preferably here at least at the beginning, since particularly large quantities of the combustible substances mentioned are released and can be used in this area.

A further optimization can be achieved in that the combustion chamber is arranged parallel to and between the two furnace channels, which further shortens the transport distances.

In a tunnel kiln according to the invention with two kiln channels parallel to one another but operated in opposite directions, according to a further advantageous embodiment of the invention, it is possible, in particular, to arrange two devices of the aforementioned type arranged essentially in mirror-inverted fashion one behind the other in the longitudinal direction of the tunnel kiln, with the extraction device in one furnace duct, in the second case the extraction device is provided in the other furnace duct.

This enables the combustible gases to be extracted and the useful heat obtained during the combustion to be extracted over the entire extent of the combustion zones of the two furnace channels, as will be explained in more detail below with reference to the exemplary embodiment.

A further generation of energy can be achieved by providing an additional fresh air supply line which runs along at least a partial section of the walls / ceiling of one or both furnace ducts and opens into the area of the preheating zone of a furnace duct. Similar to that described above using the fresh air supply line to the combustion chamber, the storage heat present in the furnace masonry, for example, is also used here to enable air to preheat the material without its own heating units / burners. In this case, the fresh air supply device can be guided, for example, around the cooling zone of one furnace duct and open into the preheating zone of the other furnace duct adjacent to the cooling zone.

An advantageous embodiment of the invention proposes that an extraction device opens from the preheating zone of one and / or 'other furnace duct into a space separate from the furnace ducts, preferably a duct, in which at least one heating device, preferably a burner, is arranged. The flue gases introduced here, which contain only a small proportion of combustible substances, can be subjected to a combustion before they are discharged from the room / duct into a chimney via an exhaust device.

This additional combustion chamber also serves for the post-combustion of the flue gases which circulate in the combustion zone of the two furnace channels through the device described above. It is clear that the extraction, combustion and recirculation of the flue gases described above cannot always be recirculated in the combustion zone, rather a relief device must be provided in order to be able to discharge a partial gas stream from the furnace channel or channels. In an advantage Adherent embodiment of the invention is provided so that a relief line from the zone of the furnace, in which the inventive device described above is arranged, opens into this additional (afterburning) chamber in the area of the preheating zone, so that the gases burn there again and then can be discharged to the outside via the chimney.

To even out the furnace atmosphere over the cross section, it is finally also proposed to preferably arrange circulation fans in the ceiling region of the furnace ducts.

Although the invention has been described above with reference to a tunnel kiln with two kiln channels which are arranged in parallel and run in opposite directions, the arrangement according to the invention of a fume cupboard / combustion chamber / recirculation device can also be provided in a conventional continuous kiln with one kiln channel, in which case several such devices may then be arranged one behind the other The longitudinal direction of the furnace must be arranged in order to achieve an optimization, while according to the invention the burned flue gases can be supplied to the furnace channels lying next to one another over short distances.

• Figur 1: eine Aufsicht auf einen erfindungsgemäßen Tunnelofen mit zwei zueinander parallelen Ofenkanälen
• Figur 2: einen Querschnitt entlang der Linie A - B
• Figur 3: einen Querschnitt entlang der Linie C - D
• Figur 4: einen Querschnitt entlang der Linie E - F

The invention is explained in more detail below using an exemplary embodiment. The drawing shows in

• Figure 1: a plan view of a tunnel kiln according to the invention with two mutually parallel furnace channels
• Figure 2 shows a cross section along the line A - B
• Figure 3: a cross section along the line C - D
• Figure 4: a cross section along the line E - F

The tunnel furnace according to the invention shown in Figure 1 shows two mutually parallel furnace channels 10, 12; which are separated by a wall 14 running between them. As particularly shown in Figures 2 to 4, the furnace channels 10, 12 are otherwise closed by side walls 16, 18 or a common ceiling 20 and the floor 22.

1 shows pairs of rails 24 on the outside, on which, for example, tunnel kiln cars 26 are guided for transport through the kiln channels 10, 12. While the direction of transport of the wagons 26 and thus of the material 28 to be burned takes place from left to right in the direction of arrow A in the top furnace duct 10 as viewed in FIG. 1, the direction of transport of the wagons 26 through the furnace duct 12 is exactly the opposite (arrow B) 1, the furnace duct 10 is divided from left to right into a preheating zone 30, an adjoining combustion zone 32 and two adjoining cooling zone sections 34, 35, while the furnace duct 12 shows a corresponding structure in the opposite direction (preheating zone 36 , Combustion zone 38, cooling zone sections 40, 41)

As can be seen in particular from the sectional view according to FIG. 4, a fresh air supply line 42 runs from the outside through the side wall 18 over the ceiling area 20 and the wall 14 around the furnace channel 12, which after a short section is slightly above the floor 22 in the area of the wall 14 runs upwards again, to open there after a kink 44 in the ceiling area 20 of the furnace duct 10. On the outside, a fan 46 is provided at the entrance to the wall 18, which ensures that the fresh air is transported through the line 42 into the furnace duct 10, the air heating up along the path inside the walls / ceiling.

This arrangement is arranged approximately in the middle (seen in the transport direction) of the preheating zone 30 or the cooling zone 41. The two zones 30, 41 are otherwise separated from the subsequent combustion zone 32 or upstream cooling zone 40 by locks 48 known from the prior art. The locks 48 (shown only schematically by arrows in FIG. 1) can, for example, be slides which can be moved into the furnace duct 10, 12 and which allow the cross section of the furnace duct 10, 12 to be tapered in accordance with the size of the furnace carriage 26 carried out in each case. Such locks 48 are also arranged on the input and output sides and between the combustion zone 32 and the cooling zone 34 and the two cooling zones 34, 35. The same also applies to the locks 48 in the region of the furnace duct 12.

The sectional view A - B (FIG. 2) shows the design of the tunnel oven according to the invention directly behind the lock 48 between the preheating zone 30 and the combustion zone 32 of the furnace duct 10 or directly in front of the lock 48 between the cooling zone 40 and the cooling zone 41 of the furnace duct 12.

A suction line 50 extends from the ceiling area 20 of the combustion zone 32 of the furnace duct 10, in the course of which a fan 52 (suction device) is arranged. The suction line 50 opens into a combustion chamber 54 via a duct piece 50 running parallel to and in the furnace wall 14, which, as can also be seen in FIG. 1, is designed as an enlarged duct in the region of the wall 14 between the furnace ducts 10, 12 in the ceiling region 20 . The combustion chamber 54 extends from the mouth area of the suction line 50 to the locks 48 '.

In the immediate vicinity of the mouth of the suction line 50 into the combustion chamber 54, a fresh air supply line 56 opens out, which, as can be seen in particular in FIG. 1, from there in the direction of the wall 18 and then after an angle of 90 ° parallel to the furnace channels 10, 12 runs and approximately in Area of line C - D leads upwards from ceiling 20 into the open.

From there, fresh air can be sucked in, which is heated along the path through the (hot) furnace ceiling and transported into the combustion chamber 54 by a fan 60 arranged in the region of the bend 58. In this way, oxygen is led into the combustion chamber 54. A supply line 55 extends from the end of the combustion chamber 54 (at 48 ′) and transports previously burned flue gases in the direction of the opposite end of the furnace. This transport can in turn be supported by fans. Branches 62, 63, 64, 65 run at a distance from one another in the area of the ceiling 20 from the supply line 55, which branches open into the furnace duct 10 (branches 63, 65) or the furnace duct 12 (branches 62, 64).

In this way, flue gas, which contains combustible components and is extracted from the furnace duct 10 via the suction line 50, is conveyed into the combustion chamber 54, where, without a burner, the flue gases containing the combustible components self-combust, while the hot gases thus burned then subsequently pass through the line 55 and the branches 62, 63, 64, 65 are returned to the firing zones 32, 38 cleaned at the same time.

It is particularly advantageous to arrange the suction device at the beginning of the firing zone (viewed in the direction of transport) of a furnace duct, since in this area in particular large amounts of pyrolyzable substances are released when carbon moldings are burned (for example electrodes impregnated with pitch), and here the proportion of combustible materials is particularly high, namely - as it turned out in the development of the invention - is so high that combustion is possible without any burner support. Only when the furnace is "started up" is the flue gas initially ignited via a start (auxiliary) burner (not shown), while only a sufficient amount of oxygen has to be provided via line 56 for further combustion. The oxygen supply can preferably be regulated as a function of the atmosphere and the desired temperature, for example via throttle valves (not shown). In the region of the branch 62, a relief line 66 is provided in this embodiment, which at the end of the combustion zone 38 of the furnace duct 12 ensures that the flue gases are discharged from the furnace duct and, after a distance, essentially parallel to the combustion chamber 54, opens into an afterburning chamber 68, which is largely aligned in front of the combustion chamber 54 (viewed in the transport direction of the furnace duct 10). The afterburning chamber 68 runs as a duct until just before the end face of the wall 14 in the region of the entrance of the furnace duct 10 or the outlet of the furnace duct 12. A line 70 opens at the end diagonally opposite the inlet of the relief line 66, the other end of which line ends in the surface of the ceiling 20 of the furnace channel 10 opens.

A fan arranged along the line 70 ensures that the exhaust air drawn off from the preheating zone 30 is led into the afterburning chamber 68, where a heating device, preferably a burner (not shown), is arranged, which ensures afterburning of the exhaust gases. The flue gas cleaned in this way can be discharged to the outside via a chimney 74 emerging from the afterburning chamber 68 (FIG. 4)

Circulation fans 76 are also arranged along the furnace channels 10, 12 at a distance from one another in the ceiling area, which ensure that the flue gases in the furnace channels 10, 12 are evened out. In particular, Figure 3 shows the corresponding arrangement. This figure also shows once again the feed line 55, along which the cleaned flue gases are guided after their combustion, and the branch 65, via which the cleaned flue gas reaches a section of the combustion zone 32 of the furnace duct 10.

FIG. 1 shows that the arrangement described above is reversed in a mirror-inverted manner in the right half of the tunnel furnace according to the invention in FIG. 1, that is to say that the afterburning chamber 78 runs in front of the combustion chamber 80 or the feed line 81, which ends at a distance from the feed line 55. Due to the arrangement according to the invention, it is not necessary to guide the burned flue gases along the entire combustion zone in order to then guide them through the corresponding branches into the combustion chamber; rather, the embodiment shown depicts a split in order to shorten the transport routes of the flue gas and thus to make the facility more effective overall.

A different division over the length of the furnace is also possible.

With the tunnel furnace according to the invention, the pyro process can be guided independently of burners fired with oil, gas or coal. Apart from the minimum energies during the initial ignition, the furnace is only heated with the energy obtained from the flue gases.

Claims (22)

1. A tunnel kiln for heat treating green bodies (28) containing pyrolysable substances, comprising two kiln channels (10, 12) arranged in mutually parallel relationship and operated in opposite directions, each kiln channel having at least one heating section (30, 36), firing section (32, 38), and cooling section (34, 35; 40, 41 ),
characterized by the following features:

a) from at least one of said kiln channels (10, 12) extends an offtake means (50) for the flue gas to a chamber (54) separated from said kiln channels (10, 12),

b) said chamber (54) is designed as a combustion chamber for the flue gases without burner support,

c) from said combustion chamber (54) extends supply means (55) for the burned flue gases,

d) said supply means (55) is connected to said one and/or said other kiln channel (10, 12) in distant relationship with respect to said offtake means (50).

2. A tunnel kiln as claimed in claim 1,
characterized in
that a fresh air supply line (56) is connected to said combustion chamber (54).

3. A tunnel kiln as claimed in claim 2,
characterized in
that said fresh air supply line (56) is connected, in the admission region of the flue gases to be burned, to said combustion chamber (54).

4. A tunnel kiln as claimed in claims 2 or 3,
characterized in
that said fresh air supply line (56) extends along at least a partial section of the walls/ceiling (18, 20, 14) of one of said kiln channels (12), preferably in the region of said firing section (38) and that at least one ventilating means (60) is provided along the way.

5. A tunnel kiln as claimed in any of claims 1 to 4,
characterized in
that a support burner is arranged in said combustion chamber (54) for initially igniting the admitted flue gases.

6. A tunnel kiln as claimed in any of claims 1 to 5,
characterized in
that in the region of said offtake means (50) and/or said supply means (55) at least one fan and/or at least one suction means (52) are provided.

7. A tunnel kiln as claimed in any of claims 1 to 6,
characterized in
that said offtake and/or said supply means (50, 55) are formed as channels.

8. A tunnel kiln as claimed in any of claims 1 to 7,
characterized in
that said offtake means (50) and/or said supply means (55) extend from said ceiling region (20) of one of said kiln channels (10) and run into it, respectively.

9. A tunnel kiln as claimed in any of claims 1 to 8,
characterized in
that said supply means (55) runs into (63, 65; 62, 64) said kiln channel (10, 12) in short distance with respect to said offtake means (50).

10. A tunnel kiln as claimed in any of claims 1 to 9,
charactarized in
that said offtake means (50) and/or said supply means (55) extend from said respective firing section (32, 38) of said two kiln channels (10, 12).

11. A tunnel kiln as claimed in any of claims 1 to 10,
characterized in
that said chamber (54) is arranged in parallel relationship with respect to said kiln channels (10, 12) and between said kiln channels.

12. A tunnel kiln as claimed in any of claims 1 to 11,
characterized in
that at least two mutually separate combustion chambers (54, 80) are arranged with their respective offtake and supply means (50, 55, 81) arranged one after the other and in mirror-inverted fashion.

13. A tunnel kiln as claimed in any of claims 1 to 12,

characterized in
that a further fresh air supply means (42) extending along at least a partial section of the wall/ceiling (18, 20, 14) of said kiln channel or both kiln channels (12, 10) runs into said kiln channel (10) in the region of the preheating section (30) of said kiln channel (10).

14. A tunnel kiln as claimed in claim 13,

characterized in
that said fresh air supply means (42) is guided around said cooling section (41) of said kiln channel (12) and runs into said preheating section (30), which is annexed to said cooling section (41) of said other kiln channel (10).

15. A tunnel kiln as claimed in any of claims 1 to 14,
characterized in
that from said preheating section (30) of one and/or said other kiln channel (10) an offtake means (70) runs into a chamber (68), preferably a channel, which is separated from said kiln channels (10, 12), where in said chamber (68) at least one heating means, preferably a burner, is disposed and where, in a distance with respect to the mouth of said offtake means (70), a chimney (74) extends from said chamber/channel (68).

16. A tunnel kiln as claimed in claim 15,
characterized in
that in the region of said offtake means (70) at least one fan (72) and/or at least one suction means are provided.

17. A tunnel kiln as claimed in any of claims 13 to 16,
characterized in
that a further offtake line (66) from said firing section (38) of said kiln channel (12) runs into said chamber (68).

18. A tunnel kiln as claimed in claim 17,
characterized in
that along the path of the kiln channel at least one circulating fan (76) is arranged, preferably in the region of said ceiling (20)

19. A tunnel kiln as claimed in any of claims 1 to 18,
characterized in
that said individual kiln sections (30, 32, 34, 35; 36, 38, 40, 41) are mutually separated by locks (48) which are mowable into said kiln channel (10, 12).

20. A tunnel kiln as claimed in any of claims 1 to 19,
characterized in
that the design is mirror-inverted with respect to a plane in the middle of the longitudinal extension.

21. A method for heat treating of green bodies (28) containing pyrolysable substances in a tunnel kiln having two mutually parallel kiln channels (10, 12) operated in opposite directions,
characterized in
that the combustible flue gas is taken off from said kiln channel (10, 12) and burned in a chamber (54), separated from said kiln channel (10, 12), self-acting with supply of oxygen and that the flue gas thus burned and purified is subsequently supplied from said chamber (54) to said one or other kiln channel (10, 12).

22. A method as claimed in claim 21,
. characterized in
that the flue gas having been taken off is ignited, at the start of the heat treatment, by a startup burner and that the combustion of the flue gas is afterwards continued in a self- supporting manner.

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