DRYING INSTALLATION

Abstract

A drying installation for the continuous drying of a moving web material is provided. The installation includes radiating or heating elements, burning the gas. The installation includes a gas flow circulation system configured to suction combustion products generated by the radiating or heating elements. The gas flow circulation system also includes an extraction pipe configured for the evacuation from the installation of at least part of the combustion products suctioned by the gas flow circulation system. The installation also includes a device for treating carbon monoxide and optionally nitrogen oxides, the treatment device-including an oxidation and optionally reduction catalyst and being mounted on or downstream of said extraction pipe in order to treat the carbon monoxide and optionally the nitrogen oxides contained in the combustion products. The installation includes a regulation means configured to regulate the temperature of the catalyst at a temperature greater than or equal to 130° C.

Claims

1. A drying installation intended for the continuous drying of a moving web material, the installation comprising: radiating or heating elements, burning the gas, a gas flow circulation system configured to suction combustion products generated by the radiating or heating elements, in which the gas flow circulation system also includes an extraction pipe configured for the evacuation from the installation, of at least part of the combustion products suctioned by the gas flow circulation system, wherein the installation also includes a device for treating the combustion products the treatment device including an oxidation catalyst for oxidizing the carbon monoxide and being mounted on or downstream of said extraction pipe in order to treat the carbon monoxide contained in the combustion products, and wherein the installation also includes a regulation means configured to regulate the temperature of the catalyst at a temperature greater than or equal to 130° C.

2. The installation according to claim 1, wherein the regulation means is configured to heat the catalyst to a temperature greater than or equal to 130° C. and/or wherein the regulation means is configured to maintain the catalyst at a temperature greater than or equal to 130° C.

3. The installation according to claim 1, wherein the regulation means includes a heating element, such as an electric element and/or a heat exchanger, configured to supply heat to the catalyst.

4. The installation according to claim 1, wherein the regulation means includes at least one carbon monoxide, mounted upstream and/or downstream of the catalyst and configured to measure the amount of carbon monoxide contained in the combustion products upstream and/or downstream of the catalyst.

5. The installation according to claim 4, wherein the regulation means is configured to maintain the catalyst at a temperature greater than or equal to 130° C. when the amount of carbon monoxide contained in the combustion products upstream of the catalyst, is greater than a defined threshold.

6. The installation according to claim 4, wherein the installation also includes means for adding fresh air to the gas supplying the radiating or heating elements, and wherein the regulation means includes control means configured to reduce the amount of fresh air added to the gas supplying the radiating or heating elements when the amount of carbon monoxide contained in the combustion products upstream of the catalyst, is below a defined threshold.

7. The installation according to claim 1, wherein the regulation means is configured to regulate the temperature of the combustion products entering the catalyst.

8. The installation according to the preceding claim 7, wherein the installation also includes means for adding fresh air to the combustion products and/or to the gas supplying the radiating or heating elements, and wherein the regulation means includes a temperature sensor mounted in the extraction pipe, upstream of the catalyst, and control means controlling the amount of fresh air added to the combustion products and/or to the gas supplying the radiating or heating elements.

9. The installation according to claim 8, wherein the means for adding fresh air include a controlled valve mounted on the extraction pipe, and configured to adjust the amount of fresh air mixed with the combustion products.

10. The installation according to claim 8, wherein the means for adding fresh air include a cooling air inlet in the installation.

11. The installation according to claim 1, wherein the catalyst includes a metallic or ceramic support in the form of a honeycomb, with at least one portion coated with one or more precious metals.

12. The installation according to claim 1, also including a device for unclogging the catalyst.

13. The installation according to claim 12, wherein the device for unclogging the catalyst is a device for circulating a pressurized fluid through the catalyst.

14. The installation according to claim 1, wherein the catalyst is also a reduction catalyst configured to reduce the nitrogen oxides of the combustion products.

15. The installation according to claim 4, wherein the regulation means also includes at least one nitrogen oxide sensor, mounted upstream and/or downstream of the catalyst and configured to measure the amount of nitrogen oxides contained in the combustion products upstream and/or downstream of the catalyst.

16. The installation according to claim 5, wherein the regulation means is also configured to maintain the catalyst at a temperature greater than or equal to 130° C. when the amount of nitrogen oxides, contained in the combustion products upstream of the catalyst, is greater than a defined threshold.

17. The installation according to claim 10, wherein the cooling air inlet is close to the radiating or heating elements.

18. The installation according to claim 11, wherein the catalyst includes an injector of a reducing agent.

19. The installation according to claim 18, wherein the reducing agent is ammonia.

20. The installation according to claim 13, wherein the device for unclogging the catalyst is a device for circulating a compressed air through the catalyst.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG. 1 shows a schematic view of a drying installation with a treatment device, according to the invention.

DESCRIPTION OF EMBODIMENTS

[0052] FIG. 1 schematically illustrates an example of a drying installation 1 for the continuous drying of a moving web material 2 according to the invention. The web material 2 moves in the direction indicated by the arrow 4 through the drying installation 1.

[0053] The exemplary drying installation 1 preferably comprises several gas radiation emitters 6 supplied with gas such as a premix of gas and air, installed along the line of movement of the web material 2, and a gas flow circulation system, or mass transfer system, 8 mounted downstream, in the direction of movement of the web material 2, of the emitters 6 and configured to allow the circulation of a gas flow, for example by natural or forced convection.

[0054] Conventionally, the gas flow circulation system 8 comprises suction nozzles 10 and an extraction pipe 12 to suction the hot air, or combustion products, at the moving web material 2. The extraction pipe 12 is provided for the evacuation from the drying installation 1 of the combustion products suctioned via a central fan 14 from the drying installation 1 and from one or more extraction pipes 16. The combustion products can thus be discharged outside, into the atmosphere, for example via a chimney, but can also, at least in part, be reused in another system. Thus, the combustion products leaving the treatment device as described below, can be rerouted in the drying installation itself, for example towards a heat exchanger, or else towards another installation, for example an air dryer.

[0055] The gas flow circulation system 8 can also comprise suction nozzles for the suction of hot gases from the moving web material towards a suction duct. The gas flow circulation system 8 can also comprise blow nozzles for blowing, for example, at least part of the hot gas suctioned into a blow pipe towards the moving web material, the blow pipe being in fluid communication with the suction pipe, in particular via a fan. Such suction nozzles, and optionally blowing nozzles, in combination with the corresponding pipes, allow to re-circulate the hot air present on the surface of the moving web material 2 during drying, so as to increase the proportion of water vapor in the air before it is evacuated from the installation 1.

[0056] In order to limit the impact of the gases emitted by the installation 1, the latter also includes a combustion product treatment device 18 mounted on the extraction pipe 16, for example downstream of the central fan 14. The treatment device 18 is intended to limit in particular the content of carbon monoxide and optionally nitrogen oxides present in the combustion products discharged by the installation 1, before their discharge into the open air.

[0057] For this purpose, the treatment device 18 may comprise an oxidation and optionally reduction catalyst 20, mounted on the extraction pipe 16 and allowing to react the carbon monoxide with an oxidizing compound, for example oxygen in the air, to transform it into carbon dioxide, and optionally to react the nitrogen oxides with a reducing compound, for example ammonia or urea injected into the catalyst 20. The catalyst 20 can thus be disposed, in a conventional manner, on a support having a high active or contact surface. The catalyst 20, present on the surface of the support, allows the implementation thereon of the reaction of oxidation of carbon monoxide into carbon dioxide and/or reduction of nitrogen oxides into dinitrogen. The support may in particular be a metal or ceramic support, and have a honeycomb geometry. The catalyst can itself comprise an oxidation catalyst with precious metals and/or a reduction catalyst associated with a means for injecting a reducing agent such as ammonia or urea. For example, the catalyst 20 can comprise a first portion with a reduction catalyst, associated with a means for injecting a reducing agent, and a second portion with an oxidation catalyst. Preferably, the catalyst includes a reduction catalyst, part of which is coated with precious metals to oxidize the carbon monoxide.

[0058] However, in order to allow high efficiency of the catalyst 20 during the various operating phases of the drying installation 1, the treatment device 18 also comprises means 22 for regulating the temperature of the catalyst 20. The regulation means 22 is configured to allow the catalyst 20 to be in its range of nominal operating temperatures, for example at a temperature greater than or equal to 130° C., preferably greater than or equal to 150° C., and more preferably greater than or equal to 200° C. Alternatively, or in addition, the regulation means 22 can be configured to allow the catalyst 20 to be at a temperature greater than or equal to 300° C., or even 400° C., so as to increase its efficiency or so as to obtain a similar efficiency with a catalyst less rich in precious metal but operating at a lower temperature.

[0059] To this end, the regulation means 22 can be configured to allow a rapid modification of the temperature of the catalyst 20 when the latter is outside of said nominal temperature range, and/or else to allow maintaining the temperature of the catalyst 20 when the latter is within said nominal temperature range.

[0060] For example, the regulation means 22 can be configured to heat the catalyst 20 to a temperature greater than or equal to 130° C., preferably greater than or equal to 150° C., and more preferably greater than or equal to 200° C. or even 300° C. or 400° C., and/or to maintain the oxidation catalyst at a temperature greater than or equal to 130° C., preferably greater than or equal to 150° C., and more preferably greater than or equal to 200° C., or even 300° C. or 400° C.

[0061] Thus, the regulation means 22 can comprise a heating element 24, such as an electric element and/or a heat exchanger, for example mounted within or in contact with the catalyst support 20, in order to heat the latter when its temperature is too low, in particular during the start-up phases of the installation 1. The heating element 24 is thus used temporarily, in order to bring the catalyst into its nominal operating conditions until it can remain therein independently. Moreover, the heat exchanger can be advantageously used to recover the calories released elsewhere in the installation and to supply them to the catalyst in order to heat it without thereby increasing the energy consumption of the installation.

[0062] The regulation means 22 can also regulate the temperature of the combustion products supplying the catalyst 20, so that they have a temperature comprised in the range of nominal temperatures of the catalyst 20, so as to put or maintain the catalyst 20 in its range of nominal temperatures.

[0063] In order to modify the temperature of the combustion products routed by the extraction pipe 16 and supplying the catalyst 20, the regulation means 22 may comprise a control means 26 configured to add fresh air to the combustion products, either before the combustion of the gas by the emitters 6, or between the combustion and the suction by the gas flow circulation system 8, or after the suction by the gas flow circulation system 8.

[0064] Thus, the control means 26 can increase or decrease the amount of fresh air mixed with the gas supplying the emitters 6, before their combustion, so as to obtain less or more hot combustion products. Similarly, when the amount of carbon monoxide in the combustion products supplying the treatment device 18 is less than a defined threshold, the control means 26 can also reduce the amount of fresh air supplying the emitters 6, since the combustion is already complete.

[0065] Alternatively, or in addition, the control means 26 can increase or decrease the amount of fresh cooling air introduced into the installation 1 between the gas emitters 6 and the gas flow circulation system 8. Such cooling air, by mixing with the combustion products before the suction by the gas flow circulation system 8, allows to obtain a modification of the temperature of the gases routed by the extraction pipe 16 to the catalyst 20.

[0066] Finally, alternatively or in addition to the embodiments described above, the control means 26 can also be configured to add fresh air or not to the combustion products, at the extraction pipe 16 supplying the catalyst 20. For example, the treatment device 18 may comprise a controlled valve 28 for adding fresh air which is mounted on the extraction pipe 16, upstream of the catalyst 20. The controlled valve 28 is connected to a fresh air inlet and allows, according to the control given by the control means 26, to add or not, or to modify an amount of fresh air added to the combustion products, so as to change the temperature thereof.

[0067] In order to determine the control of the controlled valve, or of the fresh air supplies of the emitters 6 or of the cooling means of the installation 1, the treatment device 18 may include one or more temperature sensors, one or more carbon monoxide sensors and/or one or more nitrogen oxide sensors (not shown), mounted at different points of the installation 1, for example upstream, on or downstream of the catalyst 20 but also at the extraction pipe 16. The control means 26 can then determine a control from the information supplied by this or these sensors.

[0068] The control means 26 can also directly control the power of the radiating or heating elements 2, for example individually or else globally. Thus, the control means 26 can regulate the temperature of the catalyst by modifying the power or the number of the radiating or heating elements 6 operating in the installation 1, or else the distribution of the radiating or heating elements 6 operating in the installation 1. Likewise, the frequency or the circulation paths of the gas flows in the circulation system 8 can be modified by the control means in order to obtain the temperature desired for the combustion products entering the catalyst 20.

[0069] Finally, and in order to limit the phenomena of clogging of the catalyst 20, in particular of the channels of the support, the treatment device 18 can comprise an unclogging device 30. The unclogging device 30 can for example be a device for circulating a pressurized fluid, for example compressed air, through the catalyst and be mounted upstream or downstream of the catalyst 20. By creating a significant pressure difference between the inlet and the outlet of the catalyst 20, the unclogging device 30 can then reduce or break the plugs likely to have formed in the channels of the support, and evacuate them outside the catalyst 20.

[0070] The use of the unclogging device 30 can in particular be controlled according to the operating time of the catalyst 20, for example with an unclogging procedure provided for every 20, 30 or 50 hours of operation of the catalyst 20. Alternatively, the unclogging 30 can be controlled according to the evolution of the pressure drop between the inlet and the outlet of the catalyst 20, for example when such a pressure drop exceeds a defined threshold or else increases, for a defined time, by a defined value.

[0071] Thus, thanks to the invention, it becomes possible to treat effectively and over the long term, the combustion products discharged by a drying installation of a moving web material. In particular, the treatment device is configured to operate as long as possible in its nominal area, including during transient periods, in particular start-up. Likewise, prolonged operation is ensured thanks to the unclogging device which allows to maintain the catalyst's capacity to treat the combustion products routed by the extraction pipe.