Tunnel oven

Abstract

Tunnel oven (1) for the industrial production of baked goods; comprising a. a baking chamber (10) with an air-permeable, continuously circulating conveyor belt (20) which is set up for conveying baked goods (2) in a conveying direction (F) through the baking chamber (10); b. a plurality of under-heat air outlet nozzles (30, 80) arranged below the conveyor belt (20) and directed towards the underside of the conveyor belt (20), wherein the under-heat air outlet nozzles (30, 80) generate an under-heat supply air flow (12) directed directly towards the underside of the conveyor belt (20); c. a plurality of under-heat air inlets (40, 70) distributed over a surface below the conveyor belt (20) to discharge under-heat exhaust air (14) below the conveyor belt (20), resulting in vertical turbulence (16) of the convection flow; wherein d. the bottom heat exhaust air (14) is extracted by means of a blower (110) and heated by thermal oil as the bottom heat supply air flow (12) is supplied, so that a bottom heat convection circuit (13) is generated.

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 especially for baking baked goods in trays or trays, such as toast bread. 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 operation (i.e., in stages) or continuous operation. Due to their high capacity, the loading of the tunnel kiln's conveyor belt is often automated.

[0004] The heat input to the food being baked is crucial for the baking result. Various solutions for this are known in the prior art.

[0005] German patent application DE 10 2018 208 959 A1 discloses a continuous baking oven for continuous operation, which has at least two baking chambers arranged one above the other. The continuous oven has a thermal oil tube heat exchanger in each baking chamber for top and bottom heating. A convection fan allows the oven chamber heating via radiant heat from the thermal oil heat exchanger to be combined with the advantages of convective heat transfer.

[0006] German patent application DE 10 2016 223 041 A1 discloses a continuous oven which 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 guide devices with adjustable air passage openings are provided to direct the airflow to the two heating elements.

[0007] EP 2 870 876 B1 discloses a continuous-flow oven 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 publication EP 3 358 957 B1, a continuous oven with combined heat transfer and at least three 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 of the baked goods and additionally a heat exchanger plate for radiant heating of the top and / or underside of the baked goods.

[0009] 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

[0010] The above-mentioned problem is solved by a continuous oven according to claim 1.

[0011] 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.

[0012] A multitude of bottom-heat air outlet nozzles generate a direct flow of heated air directed towards the underside of the conveyor belt, ensuring optimal heat transfer to the baked goods, especially those in trays, molds, and tray sets. This direct airflow allows for precise control of the heat input, resulting in a very uniform and high level of heat transfer to the baked goods. The direct airflow can reach a flow velocity of up to 20 m / s in the nozzle gap. This directed airflow also convectively heats the side walls of trays, molds, and tray sets, ensuring even heating of the baked goods.

[0013] 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 system, the bottom and 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 their upper surface, thus preventing excessive drying. Furthermore, the heat input via optional top convection can be regulated essentially independently of the bottom heat input.

[0014] Furthermore, by simultaneously supplying directed bottom heat air and extracting bottom heat exhaust air from below the conveyor belt, even sheet metal goods can be baked on an industrial scale. With baked goods on trays, the airtight tray essentially separates the air space below the tray from the air space above it. However, thanks to the numerous, evenly distributed bottom heat air inlets, high air volumes can still be used for sheet metal goods to achieve high but uniform heat input. Airflow through the entire baking chamber from bottom to top or top to bottom is not necessary.

[0015] 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.

[0016] Preferably, the bottom heating air outlet nozzles are designed to be linear, at least in sections, and / or extend substantially across the entire width of the conveyor belt. This ensures a uniform airflow and heating of the baked goods across the entire width of the conveyor belt.

[0017] 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.

[0018] Preferably, the tunnel oven further comprises at least one thermal oil-to-air heat exchanger arranged 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 arranged 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 in the baking chamber.

[0019] Preferably, the tunnel kiln further comprises a plurality of channel-like lower heat air outlet channels, arranged below the conveyor belt and transversely to the conveying direction, for supplying air to the lower heat air outlet nozzles; and / or a plurality of channel-like lower heat air extraction channels, arranged below the conveyor belt and transversely to the conveying direction, for removing exhaust air from the lower heat air inlets.

[0020] Preferably, the bottom heat air outlet channels and the bottom heat air extraction channels are arranged alternately in the conveying direction. This ensures even heating of the baked goods by bottom heat convection.

[0021] 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. These cross-sections optimize the directed supply and area-wide extraction of the bottom heat convection flow.

[0022] Preferably, the baking chamber below the baked goods is heated primarily by convection. Convection heat input is very effective, so additional heat input via radiation is unnecessary.

[0023] As an alternative to pure convection, the tunnel oven preferably also features a large number of bottom-heat thermal oil heating tubes arranged below the conveyor belt. While the heat input to the baked goods via thermal oil heating tubes is not as effective as heat input via convection, it does add to the convection heat.

[0024] Preferably, the bottom heating thermal oil heating tubes are permeated from top to bottom with bottom heating exhaust air, with bottom heating air inlets forming between the bottom heating thermal oil heating tubes. Since the bottom heating thermal oil heating tubes are permeated from top to bottom with bottom heating exhaust air, this air heats up and is available as bottom heating supply air, which is blown directly onto the baked goods from below via the bottom heating air outlet nozzles in a defined manner and preferably at a high flow velocity.

[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] Preferably, the tunnel oven also features a large number of top-heat thermal oil heating tubes arranged in the upper part of the baking chamber. In addition to or as an alternative to top-heat convection, the baked goods can also be heated by radiant heat via top-heat thermal oil heating tubes located in the upper part of the baking chamber. While heat input to the baked goods via radiant heat from thermal oil heating tubes is not as efficient as heat input via convection, radiant heat results in less drying of the baked goods, thus preserving the moisture content of the finished baked goods. This is particularly advantageous for baking sheet goods with high heat input and simultaneously low drying. The sheet metal prevents the baked goods from drying out from below, but the top is unprotected, making it beneficial to bake with a higher proportion of radiant heat in the top-heat setting.When baking sheet goods, the sheet continues to advantageously separate the strong convection of the bottom heat from the area of ​​the top heat, in which only a slight 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 and / or bottom 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 especially 2 m, 2.5 m, 3 m, 3.5 m, 4 m.

[0032] Preferably the length of the tunnel kiln is a maximum of 50 m, preferably 10 to 30 m, and 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. These figures show: Fig. 1 a schematic cross-sectional view of a first embodiment of a tunnel furnace with heating by bottom heat convection; Fig. 2 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 the Fig. 1; Fig. 6 a schematic cross-sectional view of a second embodiment of a tunnel kiln with heating by bottom heat convection, top heat convection and top heat radiation; Fig. 7 a schematic cross-sectional view of a third embodiment of a tunnel furnace with heating by bottom heat convection, bottom heat radiation, top heat convection and top heat radiation; Fig. 8 a diagram of the heat flux densities of a baked product in a loaf shape as a function of the nozzle outlet velocity of the bottom heat convection; and Fig. 9 a diagram of the heat flux densities of a baked product in a box shape 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. Figures 1 to 5 show 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 product 2 to be baked is conveyed through the baking chamber 10 in the conveying direction F. Preferably, the length of the tunnel oven 1 is a maximum of 50 m, more preferably 10 to 30 m, and 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. As shown in 1, 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 especially 2 m, 2.5 m, 3 m, 3.5 m, 4 m.

[0040] Below the conveyor belt 20, a plurality of under-heat air outlet ducts 32 are arranged, preferably having a trapezoidal cross-section that narrows from bottom to top. Alternating between these are a plurality of under-heat air extraction ducts 42, preferably having a trapezoidal cross-section that widens from bottom to top. Preferably, two adjacent under-heat air outlet and under-heat air extraction ducts 32, 42 each share a common, inclined partition 26. This allows the under-heat air outlet and under-heat air extraction ducts 32, 42 to be manufactured 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. As can be seen in Figure 2, the bottom heat air outlet nozzles 30 are linear and extend essentially across the entire width of the conveyor belt 20. This ensures that the baked goods are blown from below with a strong, directed airflow 12 in a linear pattern. The speed of the airflow 12 in the nozzle gap of the bottom heat air outlet nozzles 30 can reach up to 20 m / s. As shown in Figure 2, the bottom heat air outlet nozzles 30 are linear and extend essentially across the entire width of the conveyor belt 20. Fig. 5, the width b D The nozzle gap is preferably 5 mm to 15 mm, particularly preferably 8 mm.

[0043] The under-heat air extraction ducts 42 each have under-heat air inlets 40 on their upper side, which are distributed over a surface area below the conveyor belt 20 in order to discharge under-heat exhaust air 14 below the conveyor belt 20. As in Fig. 2 and Fig. As can be seen in Figure 4, 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. As shown in Figure 2, the bottom heat exhaust air 14 is mechanically extracted from the baking chamber 10 by means of a blower 110 and returned to the baking chamber 10 as bottom heat supply air flow 12, thus creating a bottom heat convection circuit 13. The overpressure in the bottom heat air outlet ducts 32 is symbolized by a "+" sign, the underpressure in the bottom heat air inlet ducts 42 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 2 and the surface suction of the bottom heat exhaust air 14 also from below the baked goods 2, a bottom heat vertical turbulence 16 is created, as it is shown in a very simplified manner in Fig. 3 is shown. As in the right-hand section of the Fig. 3, 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, including 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 2. This turbulent heat transfer is significantly higher than with a purely laminar flow of the convection air 12, 16 along the baked product 2. 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 bottom vertical turbulence 16. This has the advantage of a high heat input through bottom convection onto the baking tins, boxes, or baking trays 3, without the baked goods drying out excessively.

[0049] Fig. Figure 6 shows a second embodiment of the tunnel furnace 1, which differs from the first embodiment in terms of the bottom heat. Fig. 1 corresponds to and additionally features heating of the baking chamber 1 with top heat.

[0050] For this purpose, a multitude 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 towards the top of the conveyor belt 20. These top-heat air outlet nozzles 60 generate a top-heat supply air flow 64 directed directly towards the top of the conveyor belt 20.

[0051] Furthermore, the second embodiment of the tunnel oven 1 has a plurality of top-heat air inlets 66, which are distributed over a surface above the conveyor belt 20 in order to discharge top-heat exhaust air 54 over a surface above the conveyor belt 20. This top-heat exhaust air 54 is mechanically extracted, for example, by means of a blower (not shown) and supplied as top-heat supply air 64. This creates a top-heat convection circuit in which the top-heat air is essentially circulated and a top-heat vertical turbulence is generated, which essentially heats the upper surfaces of the baked goods 2 by convection. The corresponding pressure differences of the top-heat convection are also symbolized by "+" and "-" signs.

[0052] The top heating element optionally features a large number of top heating thermal oil heating tubes 50, which are also located in the upper area of ​​the baking chamber 10.

[0053] These top-heat thermal oil heating tubes 50 emit heat radiation from above onto the baked goods 2 and simultaneously 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 blower. From the blower, the top-heat supply air is directed via top-heat supply air distributors 62 to the top-heat air outlet nozzles 60.

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

[0055] If, however, the primary focus is on heating the convection air from the top heat source, 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 flowing top heat exhaust air 54 and also emits heat radiation onto the baked goods 2.

[0056] As an alternative to the top heat thermal oil heating tubes 50, the top heat can also be implemented purely as convection, whereby the top heat exhaust air 54 is either not heated additionally at all or whereby 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. Figure 7 shows a third embodiment of the tunnel furnace 1, which differs from the second embodiment with respect to the top heat. Fig. 6 corresponds and has a bottom heat that 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 in addition to top heat by means of bottom convection and bottom radiation.

[0058] In this third embodiment of the tunnel furnace 1, a plurality of bottom-heat thermal oil heating tubes 74 are arranged below the conveyor belt 20. These tubes are supplied with bottom-heat exhaust air 76 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 underfloor heating thermal oil heating tubes 74, underfloor heating air outlet nozzles 80 are arranged, generating a underfloor heating supply air flow 12 directed towards the underside of the conveyor belt 20. Preferably, these underfloor heating air outlet nozzles 80 are linear and extend transversely across substantially the entire width of the conveyor belt 20. The underfloor heating exhaust air 76 is mechanically extracted through underfloor heating air inlets 70 between the underfloor heating thermal oil heating tubes 74 by means of a blower (not shown), symbolized by the hyphen. In this process, the underfloor heating thermal oil heating tubes 74 heat the underfloor heating exhaust air 76. Below the underfloor heating thermal oil heating tubes 74 are underfloor heating exhaust air collectors 72, which open into the underfloor heating blower. The blower directs the lower heat supply air 12 via lower heat supply air distributor 84 to lower heat air outlet channels 82, which open into the lower heat air outlet nozzles 80.

[0060] The bottom heat air outlet nozzles 80 are arranged below the conveyor belt 20, as in the first and second embodiments, and directed towards the underside of the conveyor belt 20, generating a bottom heat supply air flow 12 directed directly towards the underside of the conveyor belt 20. In this third embodiment as well, the bottom heat supply air flow 12 and the extraction of the bottom heat exhaust air 14 create bottom heat vertical turbulence, which accounts for 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 by thermal radiation.

[0061] Because the supply and extraction of convection air for the top and bottom heating elements are separate, individual control of the convection between them is possible. For example, the airflow, air velocity, and air temperature for the top and bottom heating elements can be adjusted independently to provide significantly higher convection heat input from the bottom than from the top. This improves baking results.

[0062] The Fig. 8 and Fig. Figure 9 shows diagrams of the heat flux densities at a baked good baked in a loaf pan, as a function of the nozzle outflow velocities of the bottom and top heat convection. The diagrams were obtained as part of flow simulations of an exemplary tunnel oven 1 according to the embodiment of the Fig. 6 created.

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

[0064] In the diagram of the Fig. In Figure 8, the nozzle outflow velocity for top heat convection is kept constant at 12 m / s, while the nozzle outflow velocity for 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 goods is approximately 6.2 kW / m² with a nozzle outflow velocity of bottom heat convection. 2 to about 11.2 kW / m 2 increases. The heat flux density increases on the side surfaces from approximately 2.4 kW / m². 2 to 5.8 kW / m 2 as can be seen in Graph 203. Graph 202, on the other hand, shows that the heat flux density for the top of the baked goods is virtually constant (minimal increase of 5.9 kW / m²). 2 to 6.4 kW / m 2 ).

[0065] In the diagram of the Fig. 9, the nozzle outlet velocity of the bottom heat convection is 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 goods is increased with the nozzle outlet velocity of the bottom heat convection of approximately 6.1 kW / m 2 approximately 7.6 kW / m² 2 increases. Graph 203 shows that the heat flux density at the side surfaces is virtually constant (minimal drop of 3.7 kW / m²). 2 to 3.4 kW / m 2 Graph 201 shows that the heat flux density remains constant at approximately 8.3 kW / m². 2 remains.

[0066] The flow simulations of the diagrams of Fig. 8 and Fig.9 show that due to the special air flow with a separation of bottom heat and top heat vertical turbulence, independent control of bottom heat convection and top heat convection is possible, even at very high nozzle outlet velocities and the associated very high heat flux densities on the baked goods. List of reference symbols 1 tunnel kiln 2 Baked goods 3 baking trays 10 Baking chamber 12 Bottom heat supply air flow 13 Bottom heat convection circuit 16 Bottom heat vertical turbulence 14 Bottom heat exhaust 20 Conveyor belt 26 Partition wall 30, 80 bottom heat air outlet nozzles 32, 82 bottom heat air outlet channels 40, 70 bottom heat air inlets 42, 72 bottom heat air extraction ducts 50 top-heat thermal oil heating pipes 52 top heat air extraction ducts 54 Top heat exhaust 60 top heat air outlet nozzles 62 Top heat air supply distributors 64 Top heat supply air flow 66 top heat air inlets 74 bottom heat thermal oil heating pipes 84 Bottom heat air supply distributors 100 thermal oil-air heat exchangers 110 blowers 201 Graph for heat flux density at the bottom of the baked goods 202 Graph for heat flux density at the top of the baked goods 203 Graph for heat flux density on side surfaces of baked goods

Claims

[1] Tunnel oven (1) for the industrial production of baked goods; comprising a baking chamber (10) with an air-permeable, endlessly circulating conveyor belt (20) which is designed 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, 80) arranged below the conveyor belt (20) and directed towards the underside of the conveyor belt (20), the bottom heat air outlet nozzles (30, 80) generating a bottom heat supply air flow (12) directed directly towards the underside of the conveyor belt (20); c. a plurality of bottom heat air inlets (40, 70) distributed over a surface below the conveyor belt (20) for discharging bottom heat exhaust air (14) below the conveyor belt (20), so that a vertical turbulence (16) of the convection flow is produced; wherein d. the bottom heat exhaust air (14) is extracted by means of a fan (110) and heated by thermal oil as the bottom heat supply air flow (12), so that a bottom heat convection circuit (13) is generated. [2] Tunnel kiln according to claim 1, wherein the bottom heat air outlet nozzles (30, 80) are at least partially linear and / or extend substantially over the entire width of the conveyor belt (20). [3] Tunnel kiln according to one of claims 1 or 2, wherein the bottom heat air outlet nozzles (30, 80) and the bottom heat air inlets (40, 70) are arranged substantially on the same level below the conveyor belt (20). [4] Tunnel oven according to one of claims 1 to 3, further comprising at least one thermal oil-air heat exchanger (100) arranged outside the baking chamber (10), which is designed to heat the bottom heat exhaust air (14) extracted via the bottom heat air inlets (40, 70) and to supply it to the bottom heat air outlet nozzles (30, 80) as bottom heat supply air (12). [5] Tunnel kiln according to one of claims 1 to 4, further comprising - a plurality of channel-like bottom heat air outlet channels (32, 82) arranged below the conveyor belt (20) and transversely to the conveying direction (F) for supplying supply air (12) to the bottom heat air outlet nozzles (30, 80); and / or - a plurality of channel-like bottom heat air extraction channels (42, 72) arranged below the conveyor belt (20) and transversely to the conveying direction (F) for removing exhaust air (14) from the bottom heat air inlets (40, 70). [6] Tunnel kiln according to claim 5, wherein the bottom heat air outlet channels (32) and the bottom heat air extraction channels (42) are arranged alternately in the conveying direction (F). [7] Tunnel kiln according to one of claims 5 or 6, wherein - the bottom heat air outlet ducts (32) have a trapezoidal cross-section which narrows from bottom to top; and / or - the bottom heat air extraction ducts (42) have a trapezoidal cross-section which widens from bottom to top; and / or - two adjacent bottom heat air outlet and bottom heat air extraction ducts (32, 42) each have a common, inclined partition wall (26). [8] Tunnel oven according to one of claims 1 to 7, wherein the baking chamber (10) below the baked goods (2) is heated substantially by convection. [9] Tunnel kiln according to one of claims 1 to 7, further comprising a plurality of bottom heat thermal oil heating tubes (74) arranged below the conveyor belt (20), wherein the bottom heat thermal oil heating tubes (74) are flowed through from top to bottom with bottom heat exhaust air (14) and bottom heat air inlets (70) are formed between the bottom heat thermal oil heating tubes (74). [10] Tunnel kiln according to one of claims 1 to 9; further comprising: - a plurality of top heat air outlet nozzles (60) arranged above the conveyor belt (20) in the upper region of the baking chamber (10) and directed towards the top side of the conveyor belt (20), wherein the top heat air outlet nozzles (60) generate a top heat supply air flow (64) directed directly towards the top side of the conveyor belt (20); and - a plurality of top heat air inlets (66) distributed over a surface above the conveyor belt (20) in order to discharge top heat exhaust air (54) over a surface above the conveyor belt (20); wherein - the top heat exhaust air (54) is mechanically extracted and supplied as the top heat supply air flow (64), so that a top heat convection circuit is created. [11] Tunnel oven according to one of claims 1 to 10, further comprising a plurality of top heat thermal oil heating tubes (50) arranged in the upper region of the baking chamber (10). [12] Tunnel kiln according to claims 10 and 11, wherein the top heat thermal oil heating pipes (50) are flowed through from bottom to top with top heat exhaust air (54). [13] Tunnel kiln according to one of claims 10 to 12, wherein the top heat air outlet nozzles (60) are at least partially linear and / or extend substantially over the entire width of the conveyor belt (20). [14] Tunnel kiln according to one of claims 1 to 13, further comprising a thermal oil boiler, arranged to heat thermal oil for the at least one thermal oil-air heat exchanger (100) and / or arranged to heat the plurality of top heat and / or bottom heat thermal oil heating tubes (50, 74). [15] Tunnel kiln according to one of claims 1 to 14, wherein - the width of the conveyor belt (20) is at least 2 m and / or a maximum of 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 kiln (1) is at least 10 m and / or a maximum of 50 m, preferably 10 to 30 m, particularly preferably 10 to 20 m.

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