TUNNEL RUNNING

Description

1. Technical area

[0001] The present invention relates to a tunnel oven for the industrial production of baked goods. In particular, the present invention relates to a tunnel oven in which the baked goods pass through the tunnel oven on a conveyor belt in a specific conveying direction. Such tunnel ovens are used in particular for baking baked goods in tins of tin-bundled tins, such as toast. 2. State of the art

[0002] In tunnel ovens, baked goods are baked by passing through the tunnel oven from one side to the other. Accordingly, they are also referred to as continuous-flow ovens. Such tunnel ovens are generally suitable for very high baking outputs and are dimensioned accordingly. They often have oven widths of 2 to 4 m and oven lengths of 10 to 60 m. Accordingly, such tunnel ovens are also referred to as large-scale tunnel ovens or industrial tunnel ovens. The disadvantage of tunnel ovens is their high space requirements, particularly their great length in the direction of passage. Furthermore, the capital investment for a continuous-flow oven is comparatively high.

[0003] Tunnel kilns can be designed for batch (step-by-step) or continuous operation. Due to their high capacities, loading of the tunnel kiln's conveyor belt is often automated.

[0004] The heat input to the baked goods is crucial for the baking result. Various solutions for this are known in the state of the art.

[0005] DE 10 2018 208 959 A1 discloses a conveyor oven for continuous baking operation, which has at least two stacked baking chambers. The conveyor oven has a thermal oil tube heat exchanger in each of the baking chambers for the top and bottom heat. A recirculation system allows for oven heating via radiation from the thermal oil heat exchanger to be combined with the advantages of convective heat transfer.

[0006] From the publication DE 10 2016 223 041 A1, a continuous-flow oven is known that has a first air-permeable heating element below a conveyor belt and a second air-permeable heating element above the conveyor belt. The heating elements can be designed as thermal oil-heated heating plates with through-openings. Furthermore, air guiding devices with adjustable air passage openings are provided to direct air flow to the two heating elements.

[0007] From EP 2 870 876 B1, a continuous-flow oven is known in which a heating register is arranged beneath a conveyor belt. The heating register consists of a flat arrangement of pipes through which thermal oil flows. Air flows through the heating register from below, which then hits the conveyor belt and the baked goods from below. An air guide device is also provided in a subchamber of the register to direct the air flow to the heating register's pipes.

[0008] From the document EP 3 358 975 B1 and the document DE 10 2015 219 267 A1 a continuous baking oven with combined heat transfer and at least three or two baking zones is known, in which each of the baking zones has at least one means for convection heating of the underside and the top side of the baked goods and additionally a heat exchanger plate for radiant heating of the top side and / or underside of the baked goods.

[0009] US Pat. No. 4,960,100 A discloses a tunnel oven for catering applications, in which slot-shaped nozzles for supplying hot air are arranged beneath a conveyor belt. Exhaust air is discharged between the nozzles and reheated by a burner to be fed back into the oven chamber as a top and bottom heat supply air stream.

[0010] Further prior art can be found in WO2014053745A.

[0011] Although the state of the art offers a wide range of options for heating a tunnel oven, there is a need to further improve the efficiency of the tunnel oven and the baking result, particularly for baked products in boxes or molds, such as toast bread. 3. Summary of the invention

[0012] The above-mentioned object is achieved by a continuous baking oven according to claim 1.

[0013] In particular, the object is achieved by a tunnel oven for the industrial production of baked goods; comprising a baking chamber with an air-permeable, continuously circulating conveyor belt, which is designed to convey baked goods or baked products in a conveying direction through the baking chamber; a plurality of bottom heat air outlet nozzles, which are arranged below the conveyor belt and directed towards the underside of the conveyor belt, wherein the bottom heat air outlet nozzles generate a bottom heat supply air flow directed directly towards the underside of the conveyor belt; a plurality of bottom heat air inlets, which are distributed over a surface below the conveyor belt in order to discharge bottom heat exhaust air below the conveyor belt; wherein the bottom heat exhaust air is extracted by means of a fan and fed in as the bottom heat supply air flow, heated by thermal oil, so that a bottom heat convection cycle is generated.

[0014] A multitude of bottom-heat air outlet nozzles generates a bottom-heat air flow directed directly toward the underside of the conveyor belt, ensuring optimal heat input to the baked goods, especially those in trays, molds, and tray stacks. The direct bottom-heat air flow allows for precise control of the heat input, enabling a very even and high heat input to the baked goods. The direct bottom-heat air flow can reach a flow velocity of up to 20 m / s in the nozzle gap. The directed bottom-heat air flow also convectively heats the side walls of trays, molds, and tray stacks, ensuring even heating of the baked goods.

[0015] The simultaneous supply of the directed bottom heat supply air flow and the flat extraction of the bottom heat exhaust air from below the conveyor belt, i.e. below the baked goods, results in vertical turbulence of the convection flow, which greatly increases the heat transfer of the convection flow to the baked goods compared to laminar flow. The flat extraction of the bottom heat exhaust air via the numerous bottom heat air inlets achieves a consistently high vertical turbulence across the entire oven surface, so that the convective heat input of the bottom heat is uniform despite the very large oven width and length. In addition, the simultaneous supply and extraction of the convection air below the conveyor belt and the bottom heat convection circuit allow the bottom heat of the tunnel oven to be regulated independently of any top heat convection that may be present, which is particularly advantageous given the very high heat input from bottom heat convection.In this case, the bottom heat and the top heat barely influence each other. In particular, the tunnel oven can be operated in such a way that the baked goods experience minimal convection on the top, thus preventing excessive drying on the top. In addition, the heat input can be regulated via an optional top heat convection system, essentially unaffected by the heat input from the bottom heat.

[0016] Furthermore, thanks to the simultaneous supply of directed bottom heat airflow and the surface extraction of bottom heat exhaust air from below the conveyor belt, even sheet products can be baked on an industrial scale. For baked goods on sheet trays, the airtight sheet essentially separates the air space below the tray from the air space above it. In particular, the large number of bottom heat air inlets distributed across the entire baking area allows for large air volumes to be used for sheet products, achieving high but even heat input to the baked goods. Flow through the entire baking chamber from bottom to top or from top to bottom is not necessary.

[0017] By heating the bottom heat supply air flow with thermal oil, a consistently high temperature of the bottom heat supply air flow is achieved, even when heat demand is very high. Using thermal oil as a heat transfer medium, the heat generation site can be separated from the tunnel kiln and provided, for example, as a separate thermal oil heating center. This reduces the space required by the tunnel kiln itself and optimizes heat generation.

[0018] Preferably, the bottom-heat air outlet nozzles are linear, at least in sections, and / or extend substantially across the entire width of the conveyor belt. This ensures uniform airflow and heating of the baked goods across the entire width of the conveyor belt.

[0019] Preferably, the bottom heat air outlet nozzles and the bottom heat air inlets are arranged essentially at the same level below the conveyor belt. This further promotes the most even extraction of the bottom heat exhaust air across the entire surface of the baking chamber, ensuring the heat transfer to the baked goods is as even as possible, even with large baking chamber widths and lengths.

[0020] The tunnel oven further comprises at least one thermal oil-to-air heat exchanger located outside the baking chamber, which is configured to heat the bottom heat exhaust air extracted via the bottom heat air inlets and supply it to the bottom heat air outlet nozzles as bottom heat supply air. The thermal oil-to-air heat exchanger located outside the baking chamber allows the bottom heat supply air to be precisely heated without introducing an additional, undefined heat input into the baking chamber, as is the case with heat exchanger tubes inside the baking chamber.

[0021] Preferably, the tunnel kiln further comprises a plurality of channel-like bottom heat air outlet ducts arranged below the conveyor belt and transversely to the conveying direction for supplying supply air to the bottom heat air outlet nozzles; and / or a plurality of channel-like bottom heat air extraction ducts arranged below the conveyor belt and transversely to the conveying direction for removing exhaust air from the bottom heat air inlets.

[0022] Preferably, the bottom heat air outlet ducts and the bottom heat air extraction ducts are arranged alternately in the conveying direction. This ensures even heating of the baked goods through bottom heat convection.

[0023] Preferably, the bottom heat air outlet ducts have a trapezoidal cross-section that narrows from bottom to top; and / or the bottom heat air extraction ducts have a trapezoidal cross-section that widens from bottom to top; and / or two adjacent bottom heat air outlet and bottom heat air extraction ducts each have a common, inclined partition wall. These cross-sections optimize the directed supply and surface extraction of the bottom heat convection flow.

[0024] The baking chamber is heated by convection underneath the baked goods. Convection heat input is very effective, eliminating the need for additional heat input via radiation.

[0025] The tunnel oven preferably further comprises a plurality of top heat air outlet nozzles arranged above the conveyor belt in the upper region of the baking chamber and directed toward the top of the conveyor belt, wherein the top heat air outlet nozzles generate a top heat supply air flow directed directly toward the top of the conveyor belt; and a plurality of top heat air inlets distributed over a surface above the conveyor belt to discharge top heat exhaust air over a surface above the conveyor belt; wherein the top heat exhaust air is mechanically extracted and fed as the top heat supply air flow, thus creating a top heat convection circuit. Optionally, the tunnel oven can also comprise convection heating for the top heat. This is particularly advantageous when baked goods, such as toast bread, are baked in closed baking tins or closed tins.The heat input to the baked goods can then be further increased using a top heat convection circuit. The heat input from top heat convection is essentially independent of the heat input from bottom heat due to the supply and discharge of top heat convection air above the conveyor belt and thus above the baked goods. Simulations have shown that, due to the type of air flow and the separate convection circuits, the air currents from the bottom heat barely mix with those from the top heat, thus barely affecting the heat input from the convection to the bottom or top of the baked goods. This means that top and bottom heat convection can be controlled essentially independently of each other.

[0026] The tunnel oven preferably further comprises a plurality of top heat thermal oil heating tubes arranged in the upper region of the baking chamber. In addition to or as an alternative to top heat convection, the baked goods can also be heated by means of thermal radiation arranged in the upper region of the baking chamber. Although the heat input to the baked goods through thermal radiation using thermal oil heating tubes is not as effective as heat input through convection, the drying out of the baked goods is less with thermal radiation, so that the finished baked goods have more moisture. This makes it particularly advantageous to bake tray products with a high heat input and, at the same time, less drying out. The tray prevents the baked goods from drying out from below, but they are unprotected at the top, so it is advantageous to bake in the top heat with a higher proportion of radiation.When baking sheet goods, the tray advantageously separates the strong convection of the bottom heat from the area of ​​the top heat, in which only a low level of convection occurs.

[0027] Preferably, the top heat thermal oil heating tubes are circulated from bottom to top by top heat exhaust air. The exhaust air from the top heat heats up and becomes available as top heat supply air, which is blown directly onto the baked goods from above via the top heat air outlet nozzles.

[0028] The bottom heat and / or thermal oil heating tubes are preferably designed as finned tubes or smooth tubes. The fins of the finned tubes increase their surface area and ensure better heat transfer to the convection air flowing through them. Smooth tubes, on the other hand, provide better heat dissipation through radiation than finned tubes.

[0029] Preferably, the top heat air outlet nozzles are linear, at least in sections, and / or extend substantially across the entire width of the conveyor belt. This allows the top heat convection to be directed linearly onto the baked goods, heating them as effectively and evenly as possible.

[0030] Preferably, the tunnel kiln further comprises a thermal oil boiler configured to heat thermal oil for the at least one thermal oil-air heat exchanger and / or configured to heat the plurality of top heat thermal oil heating tubes.

[0031] Preferably, the width of the conveyor belt is a maximum of 4 m, preferably 2 - 4 m, particularly preferably 3 - 4 m and in particular 2 m, 2.5 m, 3 m, 3.5 m, 4 m.

[0032] The length of the tunnel kiln is preferably a maximum of 50 m, preferably 10 to 30 m, particularly preferably 10 to 20 m. 4. Short description of the characters

[0033] Preferred embodiments of the present invention are illustrated below with reference to the accompanying figures. Herein: Fig. 1 is a schematic cross-sectional view of a first embodiment of a tunnel kiln with heating by bottom heat convection; Fig. 2 is a schematic horizontal partial sectional view from above of the embodiment of the Fig. 1 ; Fig. 3 a schematic cross-sectional view of a detail of the embodiment of the Fig. 1 ; Fig. 4 a schematic three-dimensional sectional view of bottom heat air outlet ducts and bottom heat air extraction ducts of the embodiment of the Fig. 1 Fig. 5 a schematic cross-sectional view of a bottom heat air outlet duct of the embodiment of Fig. 1; Fig. 6 is a schematic cross-sectional view of a second embodiment of a tunnel oven with heating by bottom heat convection, top heat convection, and top heat radiation; Fig. 7 is a schematic cross-sectional view of a non-inventive embodiment of a tunnel oven with heating by bottom heat convection, bottom heat radiation, top heat convection, and top heat radiation; Fig. 8 is a diagram of the heat flux densities at a baked product in the shape of a box as a function of the nozzle outlet velocity of the bottom heat convection; and Fig. 9 is a diagram of the heat flux densities at a baked product in the shape of a box as a function of the nozzle outlet velocity of the top heat convection. 5. Detailed description of preferred embodiments

[0034] In the following, preferred embodiments of the present invention will be described in detail with reference to the accompanying figures.

[0035] The Fig. 1 to 5show a first embodiment of a tunnel oven 1, in which the baking chamber 10 is heated essentially by bottom-heat convection. The tunnel oven 1 has an air-permeable conveyor belt 20, on which the baked goods 2 to be baked are conveyed through the baking chamber 10 in the conveying direction F. The length of the tunnel oven 1 is preferably a maximum of 50 m, preferably 10 to 30 m, particularly preferably 10 to 20 m.

[0036] The conveyor belt 20 is endlessly rotating and has an upper run that moves in the conveying direction F and a lower run that moves opposite to the conveying direction F, and which is not shown for simplification purposes. When the conveyor belt 20 is mentioned below, reference is made to the upper run on which the baked goods 2 are deposited.

[0037] The baked goods 2 can lie freely on the conveyor belt 20 or, as is preferred, be arranged in trays, boxes, or sets of boxes. The boxes or sets of boxes can be closed with a lid, as is the case, for example, for baking toast.

[0038] As in Fig. 1 As shown, the baked goods 2 can also be baked as so-called sheet goods on baking trays 3.

[0039] Preferably, the width of the conveyor belt 20 is a maximum of 4 m, preferably 2 - 4 m, particularly preferably 3 - 4 m and in particular 2 m, 2.5 m, 3 m, 3.5 m, 4 m.

[0040] A plurality of bottom-heat air outlet ducts 32 are arranged beneath the conveyor belt 20. These outlet ducts preferably have a trapezoidal cross-section that narrows from bottom to top. Alternating between these ducts are a plurality of bottom-heat air extraction ducts 42, which preferably have a trapezoidal cross-section that widens from bottom to top. Preferably, two adjacent bottom-heat air outlet and bottom-heat air extraction ducts 32, 42 each have a common, inclined partition wall 26. This allows the bottom-heat air outlet and bottom-heat air extraction ducts 32, 42 to be manufactured, particularly from sheet metal, in a material-saving manner.

[0041] The bottom heat air outlet channels 32 each form bottom heat air outlet nozzles 30, 80 on the top side, which are arranged below the conveyor belt 20 and directed toward the underside of the conveyor belt 20. Thus, the bottom heat air outlet nozzles 30, 80 can generate a bottom heat supply air flow 12 directed directly toward the underside of the conveyor belt 20.

[0042] As in Fig. 2 As can be seen, the bottom heat air outlet nozzles 30 are linear and extend essentially across the entire width of the conveyor belt 20. Thus, the baked goods are blown from below in a linear fashion with a strong, directed air flow 12. The speed of the air flow 12 in the nozzle gap of the bottom heat air outlet nozzles 30 can be up to 20 m / s. As shown in Fig. 5 As can be seen, the width b D of the nozzle gap is preferably 5 mm to 15 mm, particularly preferably 8 mm.

[0043] The bottom heat air extraction ducts 42 each have bottom heat air inlets 40 on their upper side, which are distributed flatly below the conveyor belt 20 in order to discharge bottom heat exhaust air 14 below the conveyor belt 20. As in Fig. 2 and Fig. 4 As can be seen, the bottom heat air inlets 40 can consist of a series of individual openings. However, other configurations of the bottom heat air inlets 40 are also possible.

[0044] As in Fig. 2 As shown, the bottom heat exhaust air 14 is mechanically extracted from the baking chamber 10 by a fan 110 and fed back into the baking chamber 10 as bottom heat supply air flow 12, creating a bottom heat convection circuit 13. The positive pressure in the bottom heat air outlet ducts 32 is symbolized by a "+" sign, and the negative pressure in the bottom heat air inlet ducts 42 is symbolized by a "-" sign.

[0045] The bottom heat convection circuit 13 contains a thermal oil-to-air heat exchanger 100, which heats the bottom heat exhaust air 14 to the desired inlet temperature. The thermal oil-to-air heat exchanger 100 is heated by thermal oil, which is heated by a boiler (not shown).

[0046] By blowing the bottom heat supply air flow 12 from below onto the baked goods 12 and the surface suction of the bottom heat exhaust air 14 also from below the baked goods 12, a bottom heat vertical turbulence 16 is created, as it is greatly simplified in Fig. 3 As shown in the right-hand section of the Fig. 3As shown, the bottom heat vertical turbulence 16 can also extend into the area between parts of the baked product 2, i.e. between the molds, trays or parts of tray assemblies, and heat their side walls. However, a complete flow through the baking chamber 10 into the area of ​​the top heat is neither necessary nor desired. The bottom heat vertical turbulence 16 causes a strong heat transfer between the convection air 12, 16 and the baked product 12. This turbulent heat transfer is significantly higher than with a purely laminar flow of the convection air 12, 16 along the baked product 12. Accordingly, the tunnel oven 1 can either be made shorter than comparable tunnel ovens, or the throughput through the tunnel oven 1 can be increased.

[0047] Since the bottom heat vertical turbulence 16 essentially only influences the bottom heat, the top heat of the tunnel kiln can be designed as required.

[0048] In the first embodiment of the Fig. 1 No top heat is provided, and the baking chamber is heated essentially exclusively by the bottom heat vertical turbulence 16. This has the advantage of a high heat input through bottom heat convection onto the baking tins, boxes, or baking trays 3, without the baked goods drying out excessively.

[0049] Fig. 6 shows a second embodiment of the tunnel kiln 1, which with respect to the bottom heat of the first embodiment of Fig. 1 and which additionally has a heating of the baking chamber 1 with top heat.

[0050] For this purpose, a plurality of top heat air outlet nozzles 60 are arranged above the baked goods 2, i.e., in the upper area of ​​the baking chamber 10, and are directed toward the top of the conveyor belt 20. These top heat air outlet nozzles 60 generate a top heat supply air flow 64 directed directly toward the top of the conveyor belt 20.

[0051] Furthermore, the second embodiment of the tunnel kiln 1 has a plurality of top heat air inlets 66, which are distributed over a large area above the conveyor belt 20 in order to discharge top heat exhaust air 54 over a large area above the conveyor belt 20. This top heat exhaust air 54 is mechanically extracted, for example, by means of a fan (not shown), and supplied as the top heat supply air flow 64.

[0052] This creates a top heat convection cycle in which the top heat air is essentially circulated, creating a top heat vertical turbulence that essentially heats the top surfaces of the baked goods 2 by convection. The corresponding pressure differences of the top heat convection are also symbolized by "+" and "-" signs.

[0053] The top heat system optionally further comprises a plurality of top heat thermal oil heating tubes 50, which are also arranged in the upper area of ​​the baking chamber 10. These top heat thermal oil heating tubes 50, on the one hand, emit heat radiation from above onto the baked goods 2 and, on the other hand, heat the top heat exhaust air 54, which flows through the top heat thermal oil heating tubes 50 from bottom to top. The space between the top heat thermal oil heating tubes 50 forms the top heat air inlets 66. Above the top heat thermal oil heating tubes 50 are top heat air extraction ducts 52, which lead into the top heat fan. From the fan, the top heat supply air is directed to the top heat air outlet nozzles 60 via top heat supply air distributors 62.

[0054] The top-heat thermal oil heating tubes 50 are preferably designed as smooth tubes to improve heat input via radiation. This is particularly advantageous when baking in the top-heat oven is to be carried out predominantly with radiant heat rather than with pre-baked products, for example, to prevent excessive drying of the baked goods.

[0055] If, however, heating the top heat convection air is the primary objective, the top heat thermal oil heating tubes 50 can also be designed as finned tubes to increase their surface area. This increases the heat transfer to the top heat exhaust air 54 flowing through and also radiates heat onto the baked goods 2.

[0056] As an alternative to the top heat thermal oil heating pipes 50, the top heat can also be designed purely as convection, wherein the top heat exhaust air 54 is either not additionally heated at all or wherein the top heat exhaust air 54 is heated similarly to the bottom heat by a thermal oil-air heat exchanger located outside the baking chamber.

[0057] Fig. 7 shows a non-inventive embodiment of the tunnel kiln 1, which with respect to the top heat of the second embodiment of Fig. 6 and which has a bottom heat which is structurally the top heat of the second embodiment of Fig. 6 , only with reversed flow directions. In the third embodiment, the baked goods 2 are heated by means of bottom heat convection and bottom heat radiation in addition to the top heat.

[0058] In this embodiment of the tunnel kiln 1, a plurality of bottom-heat thermal oil heating tubes 74 are arranged below the conveyor belt 20. Bottom-heat exhaust air 76 flows through these tubes from top to bottom. The bottom-heat thermal oil heating tubes 74 therefore form bottom-heat air inlets 70 between them. The bottom-heat thermal oil heating tubes 74 are preferably designed as smooth tubes to optimize the emitted heat radiation. However, they can also be designed as finned tubes to increase their surface area.

[0059] Between the bottom heat thermal oil heating tubes 74, bottom heat air outlet nozzles 80 are arranged, generating a bottom heat supply air flow 12 directed directly toward the underside of the conveyor belt 20. These bottom heat air outlet nozzles 80 are preferably linear and extend transversely across substantially the entire width of the conveyor belt 20. The bottom heat exhaust air 76 is mechanically extracted through bottom heat air inlets 70 between the bottom heat thermal oil heating tubes 74 by means of a fan (not shown), which is symbolized by the "-" sign. The bottom heat thermal oil heating tubes 74 heat the bottom heat exhaust air 76. Below the bottom heat thermal oil heating tubes 74 are bottom heat exhaust air collectors 72, which open into the bottom heat fan. From the fan, the bottom heat supply air 12 is directed via bottom heat supply air distributors 84 to bottom heat air outlet ducts 82, which open into the bottom heat air outlet nozzles 80.

[0060] The bottom heat air outlet nozzles 80 are arranged below the conveyor belt 20 according to the first and second embodiments and directed toward the underside of the conveyor belt 20, generating a bottom heat supply air flow 12 directed directly toward the underside of the conveyor belt 20. The bottom heat supply air flow 12 and the extraction of the bottom heat exhaust air 14 also create a bottom heat vertical turbulence in this embodiment, which provides the majority of the heat input to the baked goods 2. In addition, the bottom heat thermal oil heating tubes 74 radiate upwards and heat the underside of the baked goods 2 through thermal radiation.

[0061] Because the convection air supply and exhaust for the top and bottom heat are separated, individual control of the convection of the top and bottom heat is possible. For example, the air flow rate, air velocity, and air temperature for the top and bottom heat can be adjusted individually, for example, to provide a significantly higher convection heat input through the bottom heat than through the top heat. This can improve the baking result.

[0062] The Figures 8 and 9 show diagrams of the heat flux density of a baked product baked in a loaf pan as a function of the nozzle outlet velocities of the bottom heat and top heat convection. The diagrams were created as part of flow simulations of an exemplary tunnel oven 1 according to the embodiment of the Fig. 6 created.

[0063] The graph 201 shows the heat flux density on the underside of the baked product 2, the graph 202 shows the heat flux density on the top side of the baked product 2 and the graph 203 shows the heat flux density on the side surfaces of the baked product 2.

[0064] In the diagram of the Fig. 8 the nozzle outlet velocity of the top heat convection is kept constant at 12 m / s and the nozzle outlet velocity of the bottom heat convection is varied from 4.5 m / s to 18 m / s. Graph 201 shows that the heat flux density on the underside of the baked product increases with the nozzle outlet velocity of the bottom heat convection from approximately 6.2 kW / m 2< to approximately 11.2 kW / m 2<. On the side surfaces, the heat flux density increases from approximately 2.4 kW / m 2< to 5.8 kW / m 2<, as shown in graph 203. Graph 202, on the other hand, shows that the heat flux density for the top side of the baked product is virtually constant (minimal increase from 5.9 kW / m 2< to 6.4 kW / m 2<).

[0065] In the diagram of the Fig. 9The nozzle outlet velocity of the bottom heat convection is now kept constant at 9 m / s, and the nozzle outlet velocity of the top heat convection is varied from 12 m / s to 18 m / s. Graph 202 shows that the heat flux density on the top side of the baked product increases with the nozzle outlet velocity of the bottom heat convection from approximately 6.1 kW / m 2< to approximately 7.6 kW / m 2<. Graph 203 shows that the heat flux density on the side surfaces is virtually constant (minimal drop from 3.7 kW / m 2< to 3.4 kW / m 2<). Graph 201 shows that the heat flux density remains constant at approximately 8.3 kW / m 2<.

[0066] The flow simulations of the diagrams of the Figures 8 and 9show that the special air flow with a separation of bottom heat and top heat vertical turbulence allows independent control of bottom heat convection and top heat convection, even at very high nozzle outlet velocities and the associated very high heat flux densities on the baked goods. List of reference symbols

[0067] 1Tunnel oven 2Baked goods 3Baking tray 10Baking chamber 12Bottom heat supply air flow 13Bottom heat convection circuit 16Bottom heat vertical turbulence 14Bottom heat exhaust air 20Conveyor belt 26Partition wall 30, 80Bottom heat air outlet nozzles 32, 82Bottom heat air outlet ducts 40, 70Bottom heat air inlets 42, 72Bottom heat air extraction ducts 50Top heat thermal oil heating pipes 52Top heat air extraction ducts 54Top heat exhaust air 60Top heat air outlet nozzles 62Top heat supply air distributor 64Top heat supply air flow 66Top heat air inlets 74Bottom heat thermal oil heating pipes 84Bottom heat supply air distributor 100Thermal oil-air heat exchanger 110Fan 201Graph for heat flux density at the bottom of the baked product 202Graph for heat flux density at the top of the baked product 203Graph for heat flux density at the side surfaces of the baked product

Claims

1. Tunnel oven (1) for the industrial production of baked goods; comprising a. a baking chamber (10) with an air-permeable, endlessly circulating conveyor belt (20), which is configured to convey baked goods (2) in a conveying direction (F) through the baking chamber (10); b. a plurality of bottom-heat air outlet nozzles (30), which are arranged below the conveyor belt (20) and are directed towards the underside of the conveyor belt (20), wherein the bottom-heat air outlet nozzles (30) generate a bottom-heat inlet air flow (12) directed directly towards the underside of the conveyor belt (20); c. a plurality of bottom-heat air inlets (40), which are distributed in a planar manner below the conveyor belt (20), to discharge bottom-heat exhaust air (14) below the conveyor belt (20); wherein d. the bottom-heat exhaust air (14) is sucked off by means of a fan (110) and is supplied heated by thermo oil as the bottom-heat inlet air flow (12), so that a bottom-heat convection circuit (13) is generated, and e. the tunnel oven (1) further comprises at least one thermo oil-air heat exchanger (100) arranged outside the baking chamber (10), which is configured to heat the bottom-heat exhaust air (14) sucked off via the bottom-heat air inlets (40) and to supply it to the bottom-heat air outlet nozzles (30) as bottom-heat inlet air (12).

2. Tunnel oven according to claim 1, wherein the bottom-heat air outlet nozzles (30) are formed to be linear at least in sections and / or extend substantially over the entire width of the conveyor belt (20).

3. Tunnel oven according to one of claims 1 or 2, wherein the bottom-heat air outlet nozzles (30) and the bottom-heat air inlets (40) are arranged substantially on the same plane below the conveyor belt (20).

4. Tunnel oven according to one of claims 1 to 3, further comprising - a plurality of bottom-heat air outlet channels (32) formed in a channel-like manner, which are arranged below the conveyor belt (20) and transversely to the conveying direction (F), for supplying inlet air (12) to the bottom-heat air outlet nozzles (30); and / or - a plurality of bottom-heat air suction channels (42) formed in a channel-like manner, which are arranged below the conveyor belt (20) and transversely to the conveying direction (F), for discharging exhaust air (14) from the bottom-heat air inlets (40).

5. Tunnel oven according to claim 4, wherein the bottom-heat air outlet channels (32) and the bottom-heat air suction channels (42) are arranged in an alternating manner in the conveying direction (F).

6. Tunnel oven according to one of claims 4 or 5, wherein - the bottom-heat air outlet channels (32) have a trapezoidal cross section, which narrows from bottom to top; and / or - the bottom-heat air suction channels (42) have a trapezoidal cross section, which widens from bottom to top; and / or - two adjacent bottom-heat air outlet and bottom-heat air suction channels (32, 42) each have a common intermediate wall (26) arranged in an inclined manner.

7. Tunnel oven according to one of claims 1 to 6, wherein the baking chamber (10) below the baked goods (2) is heated substantially by means of convection.

8. Tunnel oven according to one of claims 1 to 7, further comprising: - a plurality of top-heat air outlet nozzles (60), which are arranged above the conveyor belt (20) in the upper region of the baking chamber (10), and are directed towards the upper side of the conveyor belt (20), wherein the top-heat air outlet nozzles (60) generate a top-heat inlet air flow (64) directed directly towards the upper side of the conveyor belt (20); and - a plurality of top-heat air inlets (66), which are distributed in a planar manner above the conveyor belt (20), to discharge top-heat exhaust air (54) in a planar manner above the conveyor belt (20); wherein - the top-heat exhaust air (54) is mechanically sucked off and supplied as the top-heat inlet air flow (64), so that a top-heat convection circuit is generated.

9. Tunnel oven according to one of claims 1 to 8, further comprising a plurality of top-heat thermo-oil heating tubes (50), which are arranged in the upper region of the baking chamber (10).

10. Tunnel oven according to claims 8 and 9, wherein top-heat exhaust air (54) flows through the top-heat thermo-oil heating tubes (50) from bottom to top.

11. Tunnel oven according to one of claims 8-10, wherein the top-heat air outlet nozzles (60) are formed to be linear at least in sections and / or extend substantially over the entire width of the conveyor belt (20).

12. Tunnel oven according to one of claims 1 to 11, further comprising a thermo-oil heating boiler, configured to heat thermo oil for the at least one thermo-oil-air heat exchanger (100) and / or configured to heat the plurality of top-heat thermo-oil heating tubes (50).

13. Tunnel oven according to one of claims 1 to 12, wherein - the width of the conveyor belt (20) is at least 2 m and / or at most 4 m, preferably 3 to 4 m, and in particular 2 m, 2.5 m, 3 m, 3.5 m, 4 m and / or - the length of the tunnel oven (1) is at least 10 m and / or at most 50 m, preferably 10 to 30 m, particularly preferably 10 to 20 m.