EP2257752A2

EP2257752A2 - Industrial furnace and method for operating an industrial furnace

Info

Publication number: EP2257752A2
Application number: EP09727908A
Authority: EP
Inventors: Manfred Husslein
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-04-01
Filing date: 2009-03-26
Publication date: 2010-12-08
Also published as: DE102008020449A1; WO2009121326A3; WO2009121326A2

Abstract

The invention relates to an industrial furnace comprising a heatable interior chamber (1), a housing (2) enclosing the interior chamber (1), an insulating layer (3) which is at least partially lining the inner side of the housing (2), and thermal input means (4) for introducing thermal energy into the interior chamber (1). With respect to an energy-efficient operation, said industrial furnace is characterized by an insulating sleeve (7), which at least partially surrounds the housing (2) and is located at a distance from the housing wall, wherein a convection chamber (8) is formed between the housing wall and the insulating sleeve (2), and/or by a pre-heating and/or tempering furnace (10) in which the waste heat of the interior chamber (1) can be used. The invention further relates to a method for operating an industrial furnace.

Description

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Industrial furnace and method for operating a

INDUSTRIAL FURNACE

The present invention relates to an industrial furnace having a heatable interior, a housing surrounding the interior, with an insulating layer at least partially lining the inside of the housing, and heat input means for introducing heat energy into the interior. Furthermore, the invention relates to a method for operating an industrial furnace, in particular for bridging downtime.

Devices of the type mentioned are known in various embodiments from industrial use. For example, industrial furnaces are used for firing bricks and porcelain. Furthermore, such industrial furnaces are widely used for the treatment of metallic workpieces, for example in order to convert them into the forgettable state, for heating before quenching in a cold fluid (hardening) or for so-called tempering for a specific change in the microstructure of the metal.

Today known industrial furnaces have a wide temperature range, depending on the purpose and depending on the batch to be treated temperatures of a few hundred to about 1000 ⁰ C driven. For heating such ovens gas burners are preferably used, which may have an efficiency of about 60% to more than 80%.

Although modern industrial furnaces generally have a highly efficient insulating layer on the inside of the housing, it is not possible to prevent the outside of the housing from becoming excessively hot during operation. In general, however, it is necessary, during operation, in terms of working conditions and occupational safety for the operating personnel, to limit the outside temperature of the furnace to a maximum of approximately 60 ^° C. Therefore, the insulation layer in systems according to the prior art is dimensioned so that during operation, the outside temperature reaches at most about 45 ° C to about 60 ⁰ C. The exiting through the housing wall heat flow is absorbed by the ambient air. However, this cooling by the ambient air already causes about 2/3 of the total heat loss of the system. Further, in prior art systems, the exhaust of the heat input means (gas burner) is rapidly mixed with large amounts of fresh air to lower the temperature of the exhaust stream. As a result, a cheaper piping can be used, and the heat input into the building is also reduced. On the other hand, the heat losses of the entire system are again increased disadvantageously.

The present invention is therefore based on the object, a generic industrial furnace in such a way and further, that an energy-efficient operation is realized.

This object is initially achieved with the characterizing features of claim 1. Thereafter, an industrial furnace mentioned above is configured and further developed such that a housing surrounding the housing at least partially and spaced from the housing wall is provided, wherein a convection space is formed between the housing wall and the insulating jacket.

In accordance with the invention, a greatly improved insulation of the furnace is achieved by the additional insulating. The convection space formed between the original housing wall and the insulating sleeve can be filled with air. The convection chamber acts as an additional insulating layer and significantly reduces the heat flow exiting the housing wall.

In accordance with the invention, the original housing wall may have a significantly higher outside temperature than if no insulating cover were present. Thus, the housing wall can now, for example, a temperature of at most 16O ⁰ C (corresponding to the first tempering stage in steels, so that in low-carbon steels no change, the crystalline structure occurs) or even above, without the outer surface of the insulating sleeve according to the invention a Temperature above the targeted 6O ⁰ C assumes.

In addition, it has been recognized according to the invention that a heat reservoir is created by the convection space, which is used for a further energetic use. be fed. The air of the convection space can serve in many ways to recover energy and thus to a significant improvement in the overall efficiency.

The furnace according to the invention can be configured as a rotary hearth, ring hearth or pusher furnace. The preferred shape and thus also the design of the insulating cover provided according to the invention depends on the purpose, the batch size, the batch material and the temperature and the residence time of the batch in the oven.

In the context of the invention, it is possible to convert already built, older industrial furnaces and to provide with an insulating sheath. This means that already existing plants can be optimized in terms of energy.

The insulating layer of the industrial furnace may consist of a refractory lining and / or mineral wool. Again, the choice of the material of the insulating layer depends on the operating conditions of the furnace.

In a preferred embodiment, the heat input means comprise at least one gas burner, possibly with a jet pipe. With a plurality of gas burners distributed over the interior, a high heat input with compact heat input means can be realized.

With regard to a further improved usability of waste heat from the interior, a development is preferred in which the exhaust system, in particular the exhaust pipes for the heat input means and / or exhaust manifolds, is guided substantially through the convection space. Thus, the hot exhaust gases can be used to heat the inventively created convection space. As a side effect, an insulation of the exhaust gas pipes can be omitted, since they are not laid on the outside of the furnace. In addition, it can be dispensed with mixing of the exhaust gas stream with fresh air with the aim of cooling the gas stream. Thus, the heat energy of the exhaust gas stream in the convection space according to the invention "captured" and can be recovered energetically in many ways. - A -

For this purpose, an embodiment is particularly preferred in which the convection air can be fed to a device in which the heat energy is usable, and in particular is convertible into electrical energy. This can be accomplished, for example, by providing at least one air channel which leads out of the convection chamber and by means of which the heated convection air can be fed to a further energy-producing treatment. Alternatively or additionally, a circuit for the convection air can be provided. The convection air can, for example, be used directly or indirectly as a heating medium, for example for space heating or as an energy supplier for a heating medium cycle. In a particularly preferred manner, electrical energy can also be obtained from the convection air. Since the convection air is at a comparatively low temperature level, the implementation of an ORC (Organic Rankine Cycle) process is particularly preferred. Suitable ORC systems are known to the person skilled in the art.

A preferred development of the industrial furnace additionally has a system for carrying out an ORC cycle in which the heat energy of the convection air and / or the heated charge can be used. Accordingly, in addition to the convection air already mentioned, the waste heat in the furnace of heated workpieces or batches can also be used in a very general sense. For example. Metallic workpieces are heated in industrial ovens to then return the heat energy in the intended manner again. This is done in hardening shops by rapid cooling in an oil bath, in drop forging, for example, but by slow cooling (via radiation and convection) in a so-called. Cooling conveyor. The heat emitted in this case could now be taken from the hardener bath or the cooling conveyor or any other means provided for receiving heat energy from workpieces and supplied to the ORC system. Particularly interesting is the use of waste heat, if it is available at a high temperature level. Thus, processes are known in which workpieces are quenched in Härterbad only 16O ⁰ C. The waste heat of the oil bath used for this purpose can be fed directly to an ORC system.

Another industrial furnace within the scope of the invention is indicated by the features of claim 9. Thereafter, a generic industrial furnace is so designed and developed that a preheating and / or tempering furnace is provided in which the waste heat of the interior is available.

In accordance with the invention, a preheating and / or tempering furnace is positioned directly or indirectly at the actual main furnace, wherein the waste heat from the interior of the industrial furnace can be transferred in a suitable manner to the preheating and / or tempering furnace. In this case, heat transfer can take place in a variety of ways. For example. burner exhaust gases and / or gas from the interior can be passed directly into the preheating and / or tempering furnace according to the invention. Furthermore, the aforementioned gas streams can also be used for indirect heating of the additional furnace. Particularly advantageous is a combination of a preheating and / or tempering furnace and a convection space produced in accordance with the invention around the main or high-temperature furnace.

In the proposed preheating and / or tempering furnace, any workpieces can be preheated before being placed in the main furnace. If a higher temperature is reached in the additional furnace, it can even serve for tempering metallic workpieces. In both ways, an optimal use of the waste heat of the industrial furnace is realized without it being released useless into the environment.

With regard to advantageous embodiments of the latter industrial furnace according to the invention, reference is first expressly made to the already mentioned developments. Accordingly, with regard to a preheating and / or tempering furnace according to the invention further developments prove to be particularly advantageous in which the main or high-temperature furnace is designed as Drehherd-, Ringherd- or pusher and / or an insulating layer of a refractory lining and / or Mineral wool and / or a Wärmeeintragmittel from at least one gas burner, possibly with a jet pipe having.

The preheating and / or tempering furnace according to the invention can also be designed as a ring hearth or piercing furnace. If the main furnace is formed as a rotary hearth furnace or annular hearth furnace, proves to be designed as a ring hearth additional or Low temperature oven as particularly advantageous. However, if the main furnace is a pusher furnace, it is particularly advantageous to also design the preheating and / or tempering furnace as a pusher furnace, which can be operated countercurrently in an energetically particularly optimal manner.

In a particularly preferred embodiment of the inventive concept, the preheating and / or tempering furnace above the interior of the main furnace - if necessary, offset obliquely - arranged. In this embodiment, natural convection is utilized in the case of air or gas streams. Thus, an escaping from the interior of the main furnace or heated by the main furnace gas flow inevitably rises, where he - as suggested here - automatically enter the preheating and / or tempering furnace or can heat this indirectly. Moreover, if the preheating and / or tempering furnace is arranged obliquely offset with respect to the main furnace, the transition region between the main furnace and the additional furnace can be formed as a gap, as a result of which additionally a chimney effect occurs which promotes natural convection. If both furnaces are designed as ring or rotary hearth furnaces, each furnace can have a different radius, so that an annular, gap-like connecting region results between the two furnaces.

As already indicated, in view of an effective use of the waste heat of the main furnace, an embodiment is preferred in which the waste heat of the interior through heat-transfer contact between the interior and the preheating and / or tempering furnace and / or by the direct or heat-transferring exchange of air and / or gases between the interior and the preheating and / or tempering furnace is transferable.

In a particularly preferred embodiment, the industrial furnace having a preheating and / or tempering furnace is further characterized by an insulating sleeve at least partially surrounding and spaced from the housing wall, wherein a convection space is formed between the housing wall and the insulating sleeve. In other words, a particularly advantageous industrial furnace according to the invention can be formed by providing on the one hand an additional preheating and / or tempering furnace in which the waste heat of the interior space is used, and on the other hand at least partially surrounding the housing of the furnace Insulating is provided, whereby a convection space is formed around the interior of the main furnace. Although a combination of these two aspects of the invention is particularly preferred, however, the invention is not limited to this combination; rather, each of the named groups of features is in itself within the scope of the invention and can be realized alone. With regard to the insulating sleeve according to the invention, in order to avoid repetition, reference should be made to the aforementioned advantages and embodiments according to the invention, to which reference is made without restriction as regards this embodiment.

Thus, it is particularly preferred that the exhaust system, in particular the exhaust gas lines and / or exhaust manifolds, are also guided substantially through the convection space.

In this case, an embodiment in which the preheating and / or tempering furnace can be fed with convection air from the convection space proves particularly effective. Thus, both an optimal insulation of the industrial furnace as well as an effective use of the waste heat of the interior are combined.

Alternatively or additionally, the preheating and / or tempering furnace can be fed with exhaust gas from the heat input means and / or with gas diverted from the interior, in particular endogas, and / or with exhaust gas generated from the flaring off of endogas. The furnace atmosphere usually consists of a protective and carrier gas, which is referred to as endogas. This means a gas mixture enriched with natural gas and / or propane, which is continuously fed into the interior. In order to ensure the circulation of the furnace atmosphere and / or to remove spent gas, this must be diverted back from the interior. The branched off, hot gas can be used directly and / or after a thermal utilization in order to operate the preheating and / or tempering furnace according to the invention. Accordingly, the exhaust gas of the heat input directly (flue gas flow is passed through the auxiliary furnace) or indirectly (heat transfer) in preheating and / or tempering furnace usable. With regard to a particularly effective use of the aforementioned gas flows, an embodiment is proposed, in which between the interior and the preheating and / or tempering furnace and / or between the convection and the preheating and / or tempering furnace and / or between the exhaust system and the Preheating and / or tempering furnace one or more air or gas ducts are provided, which optionally have a conveying means for the convection air, in particular a fan. Through the use of a fan or a blower, the corresponding gas flow can be further amplified or precisely regulated.

With regard to a particularly uniform operation and an accurate and insensitive temperature control, a development is preferred in the Luftbzw. Gas flows from the interior and / or the convection space and / or the exhaust system before being fed into the preheating and / or tempering furnace are miscible and / or heat between the air or gas streams is transferable.

Both the convection air from the convection chamber as well as from the preheating and / or tempering gas escaping gas and / or one or more of the above gas streams can be supplied to a device in which the heat energy is usable, and in particular convertible into electrical energy. Such a device preferably consists of an already mentioned ORC system. Thus, the waste heat of the interior is usable not only in an additional furnace, but also for the production of electrical energy.

With regard to a particularly energy-efficient operation, a system for carrying out an ORC cycle process can additionally be provided in connection with a preheating and / or tempering furnace. In this system, the heat energy of air or gas streams from the interior and / or the convection and / or the exhaust system and / or the heated batch could be used. Reference may be made to the above statements regarding an optional ORC system.

In view of a particularly variable mode of operation may be provided between the interior and the preheating and / or tempering furnace lock for the exchange of batches. This makes preheated workpieces particularly easy easy, fast and without excessive loss of heat energy from the preheat furnace in the interior of the main furnace bring. Furthermore, it is avoided that workpieces are exposed to the oxygen during the transition. Optionally, the lock can be designed so that it can be acted upon by a specific gas atmosphere, for example a nitrogen atmosphere.

With regard to a method for operating an industrial furnace, the above-indicated object is achieved with the features of claim 20. Thereafter, a suitable method for operating an industrial furnace, in particular for bridging downtimes, is proposed, with batches being reloaded from the interior into the preheating and / or tempering furnace.

If an industrial oven is not used in 24-hour and weekend operation, it may still be necessary to keep the oven at or near operating temperature around the clock, depending on the batch type and operating purpose. However, this results in a high energy demand and high heat losses. The inventive method proposes to reload batches from the interior of the main furnace in a preheating and / or tempering furnace. Thereafter, the temperature of the main furnace can be shut down, the main furnace can possibly even be switched off completely. This mode of operation is particularly suitable if the stove is not used at the weekend. Possibly. Until the end of the shift not yet machined workpieces can be given in accordance with the invention in the preheating furnace and kept there in an energy-saving manner at a desired temperature. For this purpose, it is particularly preferred that a lock for the exchange of batches is provided between the interior of the main furnace and the preheating and / or tempering furnace.

The inventive method proves to be particularly advantageous in connection with the use of an industrial furnace as a carburizing furnace. When carburizing or inserting steel grades that are not curable due to a low carbon content, so far enriched with carbon that hardening is possible. For this purpose, the steel to be carburized is brought into contact with a carbon-containing atmosphere in the industrial furnace. A preferred operating temperature for the carburizing process is about 920 ^° C. Hardening-operated carburizing furnaces are typically run empty for the weekend and exposed to a nitrogen atmosphere. A considerable production time is lost. If workpieces are still present in the carburizing furnaces during the lowering of the furnace temperature, the carbon present in the workpiece can further diffuse into the workpiece, whereby a low-carbon layer undesirably forms on the surface of the workpiece. A sudden drop in temperature in the carburizing to interrupt the diffusion process would be desirable, but fails due to the large heat capacity of the furnace.

With the method according to the invention, however, this problem is overcome. If the carburizing furnace (main furnace) go into standstill operation, the grates are transferred with the workpieces from the main furnace in the auxiliary furnace. The temperature of the additional furnace can be about 400 ⁰ C, while - as already mentioned - the temperature of the carburizing furnace can be about 920 ⁰ C. This ensures that the surface layer of the workpieces is abruptly cooled within about one minute, which freezes the diffusion process. Optionally, the additional furnace can be acted upon in the meantime with a nitrogen atmosphere. Furthermore, with regard to an efficient mode of operation, it is possible to selectively introduce the workpieces from the main furnace only into the hot zone of the additional furnace.

Preferably, a lock is provided between the main and the additional furnace, which may be beauschlagbar with a nitrogen atmosphere.

As soon as the main furnace is discharged, it can - as usual - be exposed to a nitrogen atmosphere during standstill operation. The temperature can now be shut down for energy saving reasons. If the main furnace has colder and warmer zones, grates may remain in the colder zone while the grates have been transferred from the hot zone to the hot zone of the additional furnace.

If the production is to be resumed, the hot zone of the additional furnace up to the limit of the diffusion temperature, for example. Up to 860 ⁰ C, increased. These can be provided in the additional furnace gas burner. Parallel to the main oven can already on the operating temperature, for example. Be brought about 920 ⁰ C.

Once the main furnace is at the desired operating temperature and the additional furnace has a temperature of about 800 ⁰ C, the main furnace can be charged again with the usual for carburizing rich hydrocarbon atmosphere. Thereafter, the intermediately stored in the additional furnace workpieces from the interrupted carburizing process can be reloaded into the main furnace. The edge layer of the workpieces is heated up to the optimum diffusion temperature within a very short time.

With the proposed method, undesired and non-controllable diffusion processes in the workpieces, in particular during a service interruption of the main furnace, are effectively prevented. The intermediate storage in the additional furnace saves a large amount of primary energy. The workpieces are cooled within a very short time starting from the diffusion temperature and, conversely, heated again to diffusion temperature. As a result, a business interruption can be bridged without a concomitant deterioration in product quality.

The aforementioned method proves to be advantageous not only in the scheduled night and / or weekend operation, but also in other planned or unforeseen production interruptions, for example. In case of defects or maintenance of the industrial furnace.

There are now various possibilities for designing and developing the teaching of the present invention in an advantageous manner. For this purpose, on the one hand to refer to the subordinate claims and on the other hand to the following explanation of a preferred embodiment of the invention with reference to the drawings. In conjunction with the explanation of the preferred embodiment of the invention with reference to the drawing, generally preferred embodiments and developments of the teaching are explained. In the drawing shows Figure 1 is a side sectional view of an annular furnace designed as an industrial furnace according to the invention with a convection space and arranged at the upper outer edge preheating and / or tempering furnace, and

Fig. 2 is a sectional view of the industrial furnace according to FIG

Section A-A of FIG. 1.

Fig. 1 shows a side sectional view of a preferred embodiment of an industrial furnace according to the invention. The industrial furnace is designed as a ring hearth furnace. Accordingly, the furnace has an inner space 1, which has an annular base. The interior 1 is surrounded by the wall of a housing 2. In this case, the housing 2 is lined on the inside with an insulating layer 3. This consists of a refractory lining and / or mineral wool. For the dissipation of heat energy into the interior 1, the furnace has a plurality of heat input means 4, which are configured in the form of gas burners 5, which each have a jet pipe 6.

In accordance with the invention, the industrial furnace has a spaced from the wall of the housing 2 insulating sleeve 7, which may be made of sheet steel. As a result, a convection space 8 is formed between the housing wall and the insulating sleeve 7, which can be flowed through by air or other gases, in particular in the ascending direction. The air flowing through the convection chamber 8 absorbs the waste heat of the interior 1, which can then be used in an energetically meaningful way. Furthermore, the insulation of the industrial furnace is considerably improved by the formation of the convection space 8, so that the wall of the housing 2 can have a significantly higher temperature than an embodiment without an insulating jacket 7.

Also in the convection chamber 8 are the exhaust pipes 9, which collect the flue gas of the gas burner 5 and dissipate. As a result, the heat energy of the exhaust gas of the gas burner 5 is used, since this energy can be initially held in the convection 8. In a further inventive manner, another annular hearth furnace is constructed on the actual industrial furnace (main or high-temperature furnace), namely a preheating and / or tempering furnace 10 (additional or low-temperature furnace). The preheating furnace 10 in this case has a base area, which is designed concentrically in comparison to the main furnace, but with a larger radius. In addition, the usable space of the preheating furnace 10 is spaced from the interior 1 both upwardly and outwardly. By the offset of the preheating furnace 10 in the vertical direction, the phenomenon of natural convection is particularly effectively taken into account. In this case, the air entering the convection chamber 8 of the main furnace can heat and pass through the gap-like passage between the convection chamber 8 and the work space of the preheating furnace 10 through the formation of a chimney effect in the preheating furnace 10. The opening between Konvektionsraum 8 and the useful space of the preheating furnace 10 may be formed as a circumferential gap. However, it can also be distributed over the circumference several air or gas channels are provided.

With the preheating and / or tempering furnace 10 according to the invention, the advantages obtained by the convection space 8 can be optimized in a particularly effective manner. However, the invention is not limited to a combination of these two measures, because the sole application of one of the measures already provides advantages of the invention.

It is also possible, in addition to the convection air from the convection chamber 8, which also absorbs the energy from the exhaust pipes 9 in addition to the waste heat of the interior 1, the burner exhaust gases and / or endogas from the interior 1 directly or indirectly (in heat-transmitting contact ) to supply the preheating furnace 10, and thus to increase the heat input into the preheating furnace 10 considerably.

Used gas from the working space of the preheating furnace 10 can then be fed to an ORC plant for power generation. This is of course also possible with endogas from the interior 1 and / or with exhaust gases of the gas burner 5 and makes sense. Both in the main furnace and in the preheating furnace 10, a rotary ring 11 is in each case arranged, on which a plurality of gratings 12 arranged one above the other are placed. On the grates 12, each batch to be heated 13 is arranged.

Fig. 2 shows a top sectional view of the embodiment shown in Fig. 1 of the industrial furnace according to the invention according to the local section A-A. Accordingly, only the main or high-temperature furnace is shown in this illustration, but not the preheating furnace according to the invention. This figure first illustrates the construction of the industrial furnace as a ring hearth. Accordingly, the interior 1 circumscribes an annular base area. At the outer and the inner edge of the inner space 1, a plurality of gas burners 5 are arranged in pairs. Inwardly and outwardly, the interior 1 is bounded in each case by an insulating layer 3, which lines the inside of the housing 2.

In accordance with the invention, a further insulating sleeve 7 is now provided both on the inside and on the outside, whereby in each case a convection space 8 in the form of a cylinder jacket is formed.

The internals of the industrial furnace (not shown), which receive the batches to be heated (not shown), rotate during operation. Furthermore, the gas burners 5 are seen over the entire interior 1 unevenly distributed, so that - depending on the load - in the interior also results in a non-uniform temperature distribution. Therefore, it is provided to direct the air from the convection chamber 8 of the main furnace from hot zones in otherwise colder zones of the preheating furnace, so that a kind of countercurrent effect with each maximum temperature difference in the heat transfer is adjustable.

The illustrated ring hearth furnace is loaded and unloaded at 6 o'clock. Therefore, a clockwise turning ring results in a colder zone between 6 and 12 o'clock, whereas between 12 and 6 o'clock the heat in the interior 1 is stronger. Accordingly, the convection air is collected from the hot zone at 3 o'clock and directed by means of a targeted gas flow guide 14 between 6 and 12 o'clock in the overlying preheating oven, which is shown schematically here. The manifolds for the Gas flow guide 14 run in the convection space 8, so that no heat loss occurs.

As compensation for the withdrawn convection air, it is possible to supply the zones of the preheating furnace located between 12 and 6 o'clock the exhaust gases of the gas burner 5 from the zone between 6 and 12 o'clock, so that a uniform heating of the preheating furnace can be achieved.

With regard to further advantageous embodiments of the industrial furnace according to the invention, reference is made to avoid repetition to the general part of the specification and to the appended claims.

Finally, it should be noted that the above-discussed embodiment of the industrial furnace according to the invention only serves to discuss the claimed teaching, but this does not limit the embodiment.

LIST OF REFERENCE NUMBERS

1 interior

2 housings

3 insulating layer

4 heat input means

5 gas burners

6 jet pipe

7 insulating cover

8 convection room

9 exhaust pipe

10 preheating and / or tempering furnace

11 rotary ring

12 rust

13 batch

14 gas flow guide

Claims

Patent claims

1. Industrial furnace with a heated interior (1), a housing (1) surrounding the housing (2), with an inside of the housing (2) at least partially lining insulating layer (3), and with heat input means (4) for introducing heat energy in the interior (1), characterized by a housing (2) at least partially surrounding and spaced from the housing wall insulating sheath (7), wherein between the housing wall and the insulating sheath (7) a convection space (8) is formed.

2. Industrial furnace according to claim 1, characterized in that the furnace is designed as a rotary hearth, ring hearth or pusher furnace.

3. Industrial furnace according to claim 1 or 2, characterized by an insulating layer (3) made of a refractory lining and / or mineral wool.

4. Industrial furnace according to one of claims 1 to 3, characterized in that the heat input means (4) at least one gas burner (5), optionally with a jet pipe (6).

5. Industrial furnace according to one of claims 1 to 4, characterized in that the exhaust system, in particular the exhaust pipes (9) for the heat input means (4) and / or exhaust manifolds, is guided substantially through the convection chamber (8).

6. Industrial furnace according to one of claims 1 to 5, characterized in that the convection chamber (8) has at least one derivative for the convection air, and in particular one or more air channels, which optionally have a conveying means for the convection air, in particular a fan ,

7. Industrial furnace according to one of claims 1 to 6, characterized in that the convection air of a device can be fed, in which the heat energy is available, and in particular into electrical energy is convertible.

8. Industrial furnace according to one of claims 1 to 7, characterized in that a plant for carrying out an ORC cycle is provided, in which the heat energy of the convection air and / or the heated charge (13) is available.

9. Industrial furnace with a heated interior (1), the interior (1) surrounding housing (2), with an inside of the housing (2) at least partially lining insulating layer (3), and with heat input means (4) for introducing heat energy in the interior (1), characterized in that a preheating and / or tempering furnace (10) is provided, in which the waste heat of the interior (1) is usable.

10. Industrial furnace according to claim 9, characterized in that the preheating and / or tempering furnace (10) is designed as a ring hearth or piercing furnace.

11. Industrial furnace according to claim 9 or 10, characterized in that the preheating and / or tempering furnace (10) above the interior (1) - optionally offset obliquely - is arranged.

12. Industrial furnace according to one of claims 9 to 11, characterized in that the waste heat of the interior (1) by heat transfer contact between the interior (1) and the preheating and / or tempering furnace (10) and / or by the immediate or Heat transferring exchange of air and / or gases between the interior (1) and the preheating and / or tempering furnace (10) is transferable.

13. Industrial furnace according to one of claims 9 to 12, characterized by a housing (2) at least partially surrounding and spaced from the housing wall insulating sheath (7), wherein between the housing wall and the insulating sheath (7) a convection space (8) is formed.

14. Industrial furnace according to claim 13, characterized in that the preheating and / or tempering furnace (10) can be fed with convection air from the convection chamber (8).

15. Industrial furnace according to one of claims 9 to 14, characterized in that the preheating and / or tempering furnace (1) with exhaust gas of the heat input means (4) and / or from the interior (1) branched off gas, esp. Endogas, and / or can be fed with exhaust gas generated from the flaring of endogas.

16. Industrial furnace according to one of claims 9 to 15, characterized in that between the interior (1) and the preheating and / or tempering furnace (10) and / or between the convection chamber (8) and the preheating and / or tempering furnace ( 10) and / or between the exhaust system and the preheating and / or tempering furnace (10) one or more air or gas channels are provided, which optionally have a conveying means for the convection air, in particular a fan.

17. Industrial furnace according to one of claims 9 to 16, characterized in that air or gas flows from the interior (1) and / or the convection chamber (8) and / or the exhaust system before being fed into the preheating and / or tempering furnace (10) are miscible and / or heat between the air and gas streams is transferable.

18. Industrial furnace according to one of claims 9 to 17, characterized in that a plant for carrying out an ORC cycle is provided, in which the heat energy of air or gas streams from the interior (1) and / or the convection space (8). and / or the exhaust system and / or the heated charge (13) is usable.

19. Industrial furnace according to one of claims 9 to 18, characterized in that between the interior (1) and the preheating and / or tempering furnace (10) a lock for the exchange of batches (13) is provided.

20. A method for operating an industrial furnace, in particular an industrial furnace according to one of claims 9 to 19, and in particular for bridging downtimes, characterized in that batches (13) from the interior (1) in the preheating and / or tempering furnace (10) be reloaded.