TUNNEL OVEN

Abstract

Tunnel oven for the industrial production of baked goods; having a baking chamber with an air-permeable, endlessly circulating conveyor belt, which is set up for conveying baked goods in a conveying direction through the baking chamber; a plurality of bottom-heat air outlet nozzles, which are arranged below the conveyor belt and are directed towards the underside of the conveyor belt, wherein the bottom-heat air outlet nozzles generate a bottom-heat inlet air flow directed directly towards the underside of the conveyor belt; a plurality of bottom-heat air inlets, which are distributed in a planar manner below the conveyor belt, in order to discharge bottom-heat exhaust air below the conveyor belt; wherein the bottom-heat exhaust air is sucked off by means of a fan and is supplied heated by thermo oil as the bottom-heat inlet air flow, so that a bottom-heat convection circuit is generated.

Claims

1. Tunnel oven for the industrial production of baked goods; having a. a baking chamber with an air-permeable, endlessly circulating conveyor belt, which is configured to convey baked goods in a conveying direction through the baking chamber; b. a plurality of bottom-heat air outlet nozzles, which are arranged below the conveyor belt and are directed towards the underside of the conveyor belt, wherein the bottom-heat air outlet nozzles generate a bottom-heat inlet air flow directed directly towards the underside of the conveyor belt; c. a plurality of bottom-heat air inlets, which are distributed in a planar manner below the conveyor belt, to discharge bottom-heat exhaust air below the conveyor belt; wherein d. the bottom-heat exhaust air is sucked off by means of a fan and is supplied heated by thermo oil as the bottom-heat inlet air flow, so that a bottom-heat convection circuit is generated.

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

3. Tunnel oven according to claim 1, wherein the bottom-heat air outlet nozzles and the bottom-heat air inlets are arranged substantially on the same plane below the conveyor belt.

4. Tunnel oven according to claim 1, further comprising at least one thermo oil-air heat exchanger arranged outside the baking chamber, which is configured to heat the bottom-heat exhaust air sucked off via the bottom-heat air inlets and to supply it to the bottom-heat air outlet nozzles as bottom-heat inlet air.

5. Tunnel oven according to claim 1, further having a plurality of bottom-heat air outlet channels formed in a channel-like manner, which are arranged below the conveyor belt and transversely to the conveying direction, for supplying inlet air to the bottom-heat air outlet nozzles; and/or a plurality of bottom-heat air suction channels formed in a channel-like manner, which are arranged below the conveyor belt and transversely to the conveying direction, for discharging exhaust air from the bottom-heat air inlets.

6. Tunnel oven according to claim 5, wherein the bottom-heat air outlet channels and the bottom-heat air suction channels are arranged in an alternating manner in the conveying direction.

7. Tunnel oven according to claim 5, wherein the bottom-heat air outlet channels have a trapezoidal cross section, which narrows from bottom to top; and/or the bottom-heat air suction channels 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 each have a common intermediate wall arranged in an inclined manner.

8. Tunnel oven according to claim 1, wherein the baking chamber below the baked goods is heated substantially by means of convection.

9. Tunnel oven according to claim 1, furthermore having a plurality of bottom-heat thermo-oil heating tubes, which are arranged below the conveyor belt, wherein the bottom-heat thermo-oil heating tubes are flowed through from top to bottom with bottom-heat exhaust air, and wherein between the bottom-heat thermo-oil heating tubes bottom-heat air inlets are formed.

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

11. Tunnel oven according to claim 1, further having a plurality of top-heat thermo-oil heating tubes, which are arranged in the upper region of the baking chamber.

12. Tunnel oven according to claim 10, wherein top-heat exhaust air flows through the top-heat thermo-oil heating tubes from bottom to top.

13. Tunnel oven according to claim 10, wherein the top-heat air outlet nozzles are designed to be linear at least in sections and/or extend substantially over the entire width of the conveyor belt.

14. Tunnel oven according to claim 1, further having a thermo-oil heating boiler, configured to heat thermo oil for the at least one thermo-oil-air heat exchanger and/or configured to heat the plurality of top-heat and/or bottom-heat thermo-oil heating tubes.

15. Tunnel oven according to claim 1, wherein the width of the conveyor belt 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 is at least 10 m and/or at most 50 m, preferably 10 to 30 m, particularly preferably 10 to 20 m.

Description

4. BRIEF DESCRIPTION OF THE FIGURES

[0034] In the following, preferred embodiments of the present invention are illustrated by means of the attached figures. In the figures:

[0035] FIG. 1 a schematic cross-sectional view of a first embodiment of a tunnel oven with heating by bottom-heat convection;

[0036] FIG. 2 a schematic horizontal partial sectional view from above of the embodiment of FIG. 1;

[0037] FIG. 3 a schematic cross-sectional view of a detail of the embodiment of FIG. 1;

[0038] FIG. 4 a schematic three-dimensional sectional view of bottom-heat air outlet channels and bottom-heat air suction channels of the embodiment of FIG. 1

[0039] FIG. 5 a schematic cross-sectional view of a bottom-heat air outlet channel of the embodiment of FIG. 1;

[0040] FIG. 6 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;

[0041] FIG. 7 a schematic cross-sectional view of a third embodiment of a tunnel oven with heating by bottom-heat convection, bottom-heat radiation, top-heat convection and top-heat radiation;

[0042] FIG. 8 a diagram of the heat flow densities at a baked goods in box form in dependence on the nozzle outflow velocity of the bottom-heat convection; and

[0043] FIG. 9 a diagram of the heat flow densities at a baked goods in box form in dependence on the nozzle outflow velocity of the top-heat convection.

5. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0044] In the following, preferred embodiments of the present invention are described in detail with reference to the attached figures.

[0045] FIGS. 1 to 5 show a first embodiment of a tunnel oven 1, in which the heating of the baking chamber 10 takes place substantially 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 in the conveying direction F through the baking chamber 10. Preferably, the length of the tunnel oven 1 is at most 50 m, preferably 10 to 30 m, particularly preferably 10 to 20 m.

[0046] The conveyor belt 20 is endlessly circulating and has an upper run, which moves in the conveying direction F, and a lower run, which moves counter to the conveying direction F, and which is not shown for simplification purposes. When the conveyor belt 20 is mentioned in the following, reference is made to the upper run, on which the baked goods 2 are deposited.

[0047] The baked goods 2 can lie freely on the conveyor belt 20 or, which is preferred, can be arranged in moulds, boxes or box assemblies. The boxes or box assemblies can be closed with a lid, as is the case, for example, for baking toasted bread.

[0048] As shown in FIG. 1, the baked goods 2 can also be baked as so-called sheet metal goods on baking sheets 3.

[0049] Preferably, the width of the conveyor belt 20 is at most 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.

[0050] A plurality of bottom-heat air outlet channels 32, which preferably have a trapezoidal cross section, which narrows from bottom to top, are arranged below the conveyor belt 20. A plurality of bottom-heat air suction channels 42, which preferably have a trapezoidal cross section, which widens from bottom to top, are arranged in an alternating manner in between. Preferably, 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. Thus, the bottom-heat air outlet and bottom-heat air suction channels 32, 42 can be produced in a material-saving manner in particular from sheet metal.

[0051] The bottom-heat air outlet channels 32 each form on the upper side bottom-heat air outlet nozzles 30, 80, which are arranged below the conveyor belt 20 and are directed towards the underside of the conveyor belt 20. Thus, the bottom-heat air outlet nozzles 30, 80 can generate a bottom-heat inlet air flow 12 directed directly towards the underside of the conveyor belt 20.

[0052] As can be seen in FIG. 2, the bottom-heat air outlet nozzles 30 are designed to be linear and extend substantially over the entire width of the conveyor belt 20. Thus, the baked goods are blown in a linear manner from below with a strong, directed air flow 12. The velocity 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 can be seen in FIG. 5, the width b.sub.D of the nozzle gap is preferably 5 mm to 15 mm, particularly preferably 8 mm.

[0053] The bottom-heat air suction channels 42 each have on their upper side 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. As can be seen in FIG. 2 and FIG. 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 likewise possible.

[0054] As illustrated in FIG. 2, the bottom-heat exhaust air 14 is mechanically sucked off from the baking chamber 10 by means of a fan 110 and supplied again as bottom-heat inlet air flow 12 to the baking chamber 10, so that a bottom-heat convection circuit 13 is generated. The positive pressure in the bottom-heat air outlet channels 32 is symbolized by a “+” sign, the negative pressure in the bottom-heat air inlet channels 42 by a “−” sign.

[0055] In the bottom-heat convection circuit 13 there is a thermo-oil-air heat exchanger 100, which heats the bottom-heat exhaust air 14 to the desired blow-in temperature. The thermo-oil-air heat exchanger 100 is heated by means of thermo oil, which is heated by a heating boiler (not illustrated).

[0056] As a result of the blowing in of the bottom-heat inlet air flow 12 from below onto the baked goods 12 and the planar suction of the bottom-heat exhaust air 14 likewise from below the baked goods 12, a bottom-heat vertical turbulence 16 is generated, as is illustrated in a greatly simplified manner in FIG. 3. As illustrated in the right-hand region of FIG. 3, the bottom-heat vertical turbulence 16 can also extend into the region between parts of the baked goods 2, i.e. between the moulds, boxes or parts of box assemblies, and can heat the side walls thereof. A complete flow through the baking chamber 10 also into the region of the top heat is however neither necessary nor desired. The bottom-heat vertical turbulence 16 in this case brings about a strong heat transfer between the convection air 12, 16 and the baked goods 12. This turbulent heat transfer is substantially higher than in the case of a purely laminar flow of the convection air 12, 16 along the baked goods 12. Correspondingly, either the tunnel oven 1 can be designed to be shorter than comparable tunnel ovens, or the throughput through the tunnel oven 1 can be increased.

[0057] By virtue of the fact that the bottom-heat vertical turbulence 16 substantially only influences the bottom heat, the top heat of the tunnel oven can be configured as required.

[0058] In the first embodiment of FIG. 1, no top heat is provided, and the baking chamber is heated substantially exclusively by the bottom-heat vertical turbulence 16. This has the advantage of a high heat input by bottom-heat convection onto the baking moulds, boxes or baking sheets 3, without the baked goods drying out excessively.

[0059] FIG. 6 shows a second embodiment of the tunnel oven 1, which corresponds in respect of the bottom heat to the first embodiment of FIG. 1 and which additionally has a heating of the baking chamber 1 with top heat.

[0060] For this purpose, a plurality of top-heat air outlet nozzles 60, which are directed towards the upper side of the conveyor belt 20, are arranged above the baked goods 2, i.e. in the upper region of the baking chamber 10. These 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.

[0061] Furthermore, the second embodiment of the tunnel oven 1 has 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. The top-heat exhaust air 54 is mechanically sucked off, for example, by means of a fan (not illustrated) and supplied as the top-heat inlet air flow 64. Here, a top-heat convection circuit is generated, in which the top-heat air is guided substantially in a circle and a top-heat vertical turbulence is generated, which substantially heats the upper sides of the baked goods 2 by convection. The corresponding pressure differences of the top-heat convection are likewise symbolized by “+” and “−” signs.

[0062] The top heat further optionally has a plurality of top-heat thermo-oil heating tubes 50, which are likewise arranged in the upper region of the baking chamber 10. These top-heat thermo-oil heating tubes 50 emit a thermal radiation onto the baked goods 2 from above, on the one hand, and on the other hand they heat the top-heat exhaust air 54, which flows through the top-heat thermo-oil heating tubes 50 from bottom to top. Here, the space between the top-heat thermo-oil heating tubes 50 forms the top-heat air inlets 66. Above the top-heat thermo-oil heating tubes 50 there are top-heat air suction channels 52, which open into the fan of the top heat. The top-heat inlet air is guided from the fan via top-heat inlet air distributors 62 to the top-heat air outlet nozzles 60.

[0063] The top-heat thermo-oil heating tubes 50 are preferably formed as smooth tubes, in order to improve the heat input via radiation. This is advantageous in particular when baking in the top heat predominantly with radiant heat and less with convection, for instance in order to prevent excessive drying out of the baked goods.

[0064] If, on the other hand, a heating of the top-heat convection air is in the foreground, the top-heat thermo-oil heating tubes 50 can also be formed as ribbed tubes, in order to enlarge the surface thereof. Thus, the heat transfer onto the top-heat exhaust air 54 flowing through is increased and thermal radiation is also emitted onto the baked goods 2.

[0065] Alternatively to the top-heat thermo-oil heating tubes 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 thermo-oil-air heat exchanger, which is located outside the baking chamber.

[0066] FIG. 7 shows a third embodiment of the tunnel oven 1, which corresponds in respect of the top heat to the second embodiment of FIG. 6 and which has a bottom heat which structurally corresponds to the top heat of the second embodiment of FIG. 6, merely with reversed flow directions. In the third embodiment, the baked goods 2 are heated in addition to the top heat by means of a bottom-heat convection and a bottom-heat radiation.

[0067] In this third embodiment of the tunnel oven 1, a plurality of bottom-heat thermo-oil heating tubes 74 are arranged below the conveyor belt 20. These are flowed through from top to bottom with bottom-heat exhaust air 76. The bottom-heat thermo-oil heating tubes 74 therefore form between them bottom-heat air inlets 70. The bottom-heat thermo-oil heating tubes 74 are preferably formed as smooth tubes in order to optimize the emitted thermal radiation. However, they can likewise be formed as ribbed tubes in order to enlarge the surface thereof.

[0068] Between the bottom-heat thermo-oil heating tubes 74, bottom-heat air outlet nozzles 80 are arranged, which generate a bottom-heat inlet air flow 12 directed directly towards the underside of the conveyor belt 20. Preferably, these bottom-heat air outlet nozzles 80 are designed to be linear and extend transversely over substantially the entire width of the conveyor belt 20. The bottom-heat exhaust air 76 is mechanically sucked off by bottom-heat air inlets 70 between the bottom-heat thermo-oil heating tubes 74 by means of a fan (not illustrated), which is symbolized by the “−” sign. Here, the bottom-heat thermo-oil heating tubes 74 heat the bottom-heat exhaust air 76. Below the bottom-heat thermo-oil heating tubes 74 there are bottom-heat exhaust air collectors 72, which open into the fan of the bottom heat. From the fan, the bottom-heat inlet air 12 is guided via bottom-heat inlet air distributors 84 to bottom-heat air outlet channels 82, which open into the bottom-heat air outlet nozzles 80.

[0069] Corresponding to the first and second embodiment, the bottom-heat air outlet nozzles 80 are arranged below the conveyor belt 20 and are directed towards the underside of the conveyor belt 20, wherein they generate a bottom-heat inlet air flow 12 directed directly towards the underside of the conveyor belt 20. By means of the bottom-heat inlet air flow 12 and the suction of the bottom-heat exhaust air 14, a bottom-heat vertical turbulence also arises in this third embodiment, which brings about the main part of the heat input onto the baked goods 2. In addition, the bottom-heat thermo-oil heating tubes 74 radiate upwards and heat the underside of the baked goods 2 by thermal radiation.

[0070] By virtue of the fact that the supply and suction of the convection air for the top heat and the bottom heat are separated from one another, an individual regulation of the convection of the bottom and top heat is possible. Thus, for example, the air throughput, the air speed and the air temperature for bottom and top heat can be set individually from one another, in order, for example, to provide a substantially higher convection heat input by the bottom heat than by the top heat. The baking result can thus be improved.

[0071] The FIGS. 8 and 9 show diagrams of the heat flow densities at a baked goods, which is baked in a box form, in dependence on the nozzle outflow velocities of the bottom-heat and top-heat convection. The diagrams were created within the scope of flow simulations of an exemplary tunnel oven 1 according to the embodiment of FIG. 6.

[0072] The graph 201 shows the heat flow density onto the underside of the baked goods 2, the graph 202 shows the heat flow density onto the upper side of the baked goods 2 and the graph 203 shows the heat flow density onto the side surfaces of the baked goods 2.

[0073] In the diagram of FIG. 8, the nozzle outflow velocity of the top-heat convection is kept constant at 12 m/s and the nozzle outflow velocity of the bottom-heat convection is varied from 4.5 m/s to 18 m/s. It can be seen from the graph 201 that the heat flow density onto the underside of the baked goods increases with the nozzle outflow velocity of the bottom-heat convection from approximately 6.2 kW/m.sup.2to approximately 11.2 kW/m.sup.2. At the side surfaces, the heat flow density increases from approximately 2.4 kW/m.sup.2 to 5.8 kW/m.sup.2, as can be seen in graph 203. Graph 202, on the other hand, shows that for the upper side of the baked goods, the heat flow density is quasi constant (minimum increase from 5.9 kW/m.sup.2 to 6.4 kW/m.sup.2).

[0074] In the diagram of FIG. 9, the nozzle outflow velocity of the bottom-heat convection is now kept constant at 9 m/s and the nozzle outflow velocity of the top-heat convection is varied from 12 m/s to 18 m/s. It can be seen from the graph 202 that the heat flow density onto the upper side of the baked goods increases with the nozzle outflow velocity of the bottom-heat convection from approximately 6.1 kW/m.sup.2 to approximately 7.6 kW/m.sup.2. Graph 203 shows that the heat flow density at the side surfaces is quasi constant (minimum decrease from 3.7 kW/m.sup.2 to 3.4 kW/m.sup.2). At graph 201, it can be seen that the heat flow density remains constant at approximately 8.3 kW/m.sup.2.

[0075] The flow simulations of the diagrams of the FIGS. 8 and 9 show that an independent regulation of bottom-heat convection and top-heat convection is possible by means of the particular air guidance with a separation of bottom-heat and top-heat vertical turbulence, even at very high nozzle outflow velocities and associated very high heat flow densities at the baked goods.

THE LIST OF REFERENCE NUMBERS

[0076] 1 Tunnel oven

[0077] 2 Baked goods/baked good

[0078] 3 Baking sheet

[0079] 10 Baking chamber

[0080] 12 Bottom-heat inlet air flow

[0081] 13 Bottom-heat convection circuit

[0082] 16 Bottom-heat vertical turbulence

[0083] 14 Bottom-heat exhaust air

[0084] 20 Conveyor belt

[0085] 26 Intermediate wall

[0086] 30, 80 Bottom-heat air outlet nozzles

[0087] 32, 82 Bottom-heat air outlet channels

[0088] 40, 70 Bottom-heat air inlets

[0089] 42, 72 Bottom-heat air suction channels

[0090] 50 Top-heat thermo-oil heating tubes

[0091] 52 Top-heat air suction channels

[0092] 54 Top-heat exhaust air

[0093] 60 Top-heat air outlet nozzles

[0094] 62 Top-heat inlet air distributors

[0095] 64 Top-heat inlet air flow

[0096] 66 Top-heat air inlets

[0097] 74 Bottom-heat thermo-oil heating tubes

[0098] 84 Bottom-heat inlet air distributors

[0099] 100 Thermo-oil-air heat exchanger

[0100] 110 fan

[0101] 201 Graph for heat flow density at underside of the baked goods

[0102] 202 Graph for heat flow density at upper side of the baked goods

[0103] 203 Graph for heat flow density at side surfaces of the baked goods