OVEN WITH IMPROVED DRAG

Abstract

The present invention relates to an oven comprising: a first chamber and a second chambers, which are separated by separation means conveyor means for guiding products from the inlet through these chambers to the outlet, temperature control means for controlling the temperature and/or humidity in each chamber individually using a fluid, respectively, and a passage in the separation means through which the conveyor means are directed from the first chamber to the second chamber.

Claims

1. A method for operating an oven comprising: cooking a product in a first chamber and in second chamber with a heated fluid, transporting the product with a conveyor means from an inlet through the first chamber and the second chamber to an outlet, the conveyor means are at least partially arranged in a helical path, wherein the oven comprises a separation means to separate the first chamber and the second chamber, the conveyor means pass through the separation means, and wherein a pressure difference is established or reduced between the fluid in the first chamber and the fluid in the second chamber in a vicinity of the separation means.

2. The method according to claim 1, wherein the pressure difference is established between both sides of a passage in the separation means.

3. The method according to claim 1, wherein one circulation means is provided per chamber, which recirculates the heated fluid in each of the chambers at a certain flow rate, and wherein the flow rate of the recirculation is at least temporarily different in at least one of the two chambers in order to establish or reduce the pressure difference between the two chambers.

4. The method according to claim 1, wherein: i) a fluid is injected into at least one of the chambers, and/or ii) a fluid is sucked into at least one of the chambers and then heated, and/or iii) a density difference between the fluids in the two chambers is established, and/or iv) an exhaust-gas is sucked out of at least one of the chambers in order to establish or reduce the pressure difference between the two chambers.

5. The method according to claim 1, wherein a drag is induced between the chambers, and wherein an amount of the drag is controlled by the pressure difference.

6. The method according to claim 1, wherein fresh air is dragged into one of the chambers.

7. The method according to claim 6, wherein the fresh air is dragged into the chamber with a higher recirculation rate, and an amount of the fresh air is adjusted by adjusting a difference between a recirculation rate in the chambers.

8. The method according to claim 1, wherein a dew-point of the fluid in the chambers is adjusted by controlling a pressure difference or by adjusting a circulation rate in the chambers.

9. The method according to claim 8, wherein the dew-point of the chamber with the higher recirculation rate is lower.

10. The method according to claim 8, wherein the dew-point of the chamber with the lower recirculation rate is higher.

11. The method according to claim 1, wherein the chamber furthest downstream relative to a product flow direction has the highest recirculation rate.

12. The method according to claim 1, wherein a drag is in counter-flow to a transport direction of the product.

13. The method according to claim 1, wherein the oven comprises an exhaust fluid stream.

14. The method according to claim 13, wherein the exhaust fluid stream is utilized to pre-heat the product.

15. A method for controlling an oven comprising: cooking products in a first chamber and in a second chamber with a heated fluid, transporting the products with a conveyor means from an inlet through the chambers to an outlet the conveyor means are at least partially arranged in a helical path, wherein the oven comprises a separation means to separate the first chamber and the second chamber, the conveyor means pass through the separation means, and wherein a pressure difference between the fluid in the first chamber and the fluid in the second chamber in the vicinity of the separation means is controlled.

16. The method according to claim 15, wherein a recirculation rate of gas in one of the chambers is controlled.

17. The method according to claim 15, wherein energy consumption of the cooking operation is optimized.

18. The method according to claim 15, wherein steam consumption is optimized.

19. An oven comprising: a first chamber and a second chamber, and at least one heater to heat a fluid which cooks a product, conveyor means for transporting the product from an inlet through the chambers to an outlet, the conveyor means are at least partially arranged in a helical path, separation means to separate the first chamber and the second chamber the conveyor means pass through the separation means, wherein the oven comprises means to establish a pressure difference between the fluid in the first chamber the fluid in the second chamber in a vicinity of the separation means.

20. The oven according to claim 19, wherein the oven comprises means to measure: i) a flowrate of a drag between the first chamber and the second chamber, and/or ii) pressure in each chamber, and wherein a signal of the measurement is utilized to control a means, which circulates a fluid in the respective chamber and/or the inlet of fresh gas and/or steam.

Description

[0041] FIGS. 1-3 show an embodiment of the inventive method.

[0042] FIGS. 1-3 show the oven in which the inventive method is utilized. The oven 1 comprises a first chamber 13 and a second chamber 14. The chambers are divided by means of a separation means 17, for example a metal wall, preferable an insulated separation means, which is sealed against the housing 2 of the oven. The oven comprises conveyor means 4, which transport the products to be cooked through the oven. The conveyor means 4 are here utilized by a helical transport belt in each chamber 13, 14. Therefore, here a rotatable drum 3 is arranged in each of these chambers, around which the conveyor belt 4 is guided along the helical paths. The endless conveyor belt enters the oven 1 via the inlet 15 in the housing 2, preferably by a straight conveyor belt section and leaves the oven 1 via the outlet 16 in the housing, likewise preferably by means of a straight section. The two helical sections are preferably connected by the straight conveyor belt section, which lies here at the top. The belt is preferably permeable to the process fluid, e.g. air and steam. The separation means 17 comprise a passage 18 for the belt section between the two helical paths. The conveyor means are preferably operated continuously.

[0043] The fluid in the oven, preferably a mixture of air and vapor, is heated by heating means, which are overall denoted by 7, which are here arranged in the top of the housing. There is preferably one heating means per chamber, which, more preferably can be controlled individually. These heating means 7 each comprise a recirculation means, here at least one fan 6. Here, there are two recirculation means per chamber 13, 14, even though the person skilled in the art understands that one recirculation means per chamber may be sufficient. The recirculation means in at least one chamber, preferably in both chambers whose fluid flow rate can be adjusted individually. The fluid, is sucked up by the fans 6 from each chamber 13, 14 and forced back into the same chamber, 13, 14 from which it has been taken. The fluid here flows past the heating elements 7 and is then recycled into the respective chamber 13, 14. Prior to the reintroduction of the fluid into the respective chamber, the fluid flow may be distributed according to a desired pattern by distribution means 9, for example a holed plate. The pressure 10 upstream from the distribution means is higher than the pressure 11 downstream from the distribution means 9. The moisture/dew-point temperature of the fluid in the chamber can be adjusted by a water bath 12 provided in one or both chambers and/or by the addition of steam. In the two chambers 13, 14 different dry-bulb temperature- and/or humidity/dew-point temperature conditions can be set.

[0044] Reference is now particularly made to FIG. 3. The product enters the oven in the first chamber 13 passes from the first to the second chamber 14 and then leaves the oven via the outlet. The product flow is indicated with reference sign 20. The first chamber 13 preferably has a higher dew-point temperature than chamber 14. The dry-bulb temperatures can be equal or different in both chambers.

[0045] According to the present invention, the pressure P1 of the fluid adjacent to the separation means in chamber 14 is different from the pressure P2 of the fluid adjacent to the separation means in chamber 13. In the present case P2 is larger than P1. Due to this pressure difference, there is a fluid flow 19 from chamber 14 to chamber 13. In the present case, this pressure difference is achieved by a difference in the recirculation rate, e.g. average speed of the fluid in chamber 13 and 14, i.e. the recirculation means 6 in each chamber 13, 14 are set such, that the flow rate of the recirculation flow, preferably its average velocity, is adjusted differently in the chambers 13 and 14. The recirculation rate can be higher or lower in chamber 14 than in chamber 13. Due to the pressure difference, fresh air is only drawn into chamber 14, for example via outlet 16 or an opening provided for fresh air intake. Additionally, and/or preferably, the drag 19 between the two chambers via opening 18 is directed from the second chamber 14 to the first chamber 13, i.e. in counter-flow to the product. Normally, an exhaust fluid is produced in the oven, this exhaust fluid is vented to the ambient preferably in the vicinity of the inlet 15 and/or further upstream as explained later on. No or essentially no fresh air is dragged into chamber 13. Hence the dew-point temperature in chamber 14 is lower than in chamber 13. Exhaust fluid can also vented to the ambient at the outlet as depicted by arrow 22. In order to reduce the energy consumption of the inventive method, the exhaust fluid at the inlet of the oven can be utilized to transfer heat to the product in a preheating zone 21, upstream from the oven 1. This preheating preferably takes place in a separate pre-heating zone, preferably with no recirculation. The exhaust fluid flows, preferably in counter flow to the product and is then vented to the ambient as depicted by arrow 22 at the inlet of preheating zone 21.

[0046] The pressure difference can also be accomplished by injecting a fluid, for example air and/or steam under pressure into at least one chamber. The pressure differential can also be accomplished by sucking a fluid, preferably air, in and heat it up. This steam and/or air can also be utilized to adjust the dew-point temperature in the respective chamber.

[0047] Alternatively, or additionally, the pressure difference can be accomplished by sucking an exhaust-gas-stream out of one at least one chamber.

[0048] Since no or little fresh air is drawn into chamber 13, no extra air needs to be heated up and the addition of vapor/steam to this chamber can be reduced. A moisture difference between the two chambers can be maintained more easily. The drag is in a direction as desired. And the exhaust is at least mainly removed from the oven at the inlet or upstream from the inlet. All this can be achieved by a difference in the magnitude of the recirculation flow in the respective chambers 13, 14.

[0049] The invention is now further explained by an example. Reference is made to the oven as described according to FIGS. 1-3, particularly FIG. 3. The dry bulb temperature is identical in both chambers. A product enters the product at the entrance of zone 1, wherein the preheating zone is not necessarily existent. The speed of the gas in zone 1 and zone 2 is initially identical. A certain dew-point-temperature difference establishes, wherein the dew-point in zone 1 is significantly higher than in zone two. The static pressure in zone 1 is lower than in zone 2. This results in a drag from zone 2 to zone 1 and hence may result in an intake of fresh air e.g. through the product exit 20. In order to reduce this drag and/or in order to reduce the dew-point temperature difference between the two zones, the speed of the gas in zone two is decreased, which results in a reduction of pressure differential and consequently in a reduction of the drag between the two zones. By changing the speed of the gas in the respective zones, for example by changing the rpm of the fan, it is even possible to reverse the drag.

[0050] Alternatively, or additionally, steam or fresh air can be injected in one or both chambers to increase or decrease the pressure difference, while the speed of the gas is maintained constant to influence the drag between the two zones.

[0051] By these means it is possible to change a recipe slightly for example to improve the energy efficiency of the cooking process.

REFERENCE SIGNS

[0052] 1 Oven [0053] 2 Housing [0054] 3 Drum [0055] 4 Conveyor means, Helical transport belt [0056] 5 Exhaust chimney [0057] 6 Circulation means, circulation fans [0058] 7 Heating element, heating means [0059] 8 Air guide [0060] 9 Distribution means, holes plate [0061] 10 Higher pressure [0062] 11 Lower pressure [0063] 12 Water bath [0064] 13 First chamber [0065] 14 Second chamber [0066] 15 Intel [0067] 16 Outlet [0068] 17 Separation means [0069] 18 Opening, passage [0070] 19 Drag [0071] 20 Product flow [0072] 21 Preheating zone [0073] 22 Exhaust-fluid [0074] P1-P2 Pressure difference