Temperature control device for surface-treated items such as vehicle parts

Abstract

Temperature control device (10) for surface-treated objects such as vehicle parts, comprising a) a temperature control chamber (16) in which a surface-treated object can be temperature controlled, b) a high-boiling-point exhaust air stream (26) containing high-boiling organic compounds from the temperature control chamber (16), c) a combustion device (30) for thermal post-treatment of the high-boiling-point exhaust air stream (26), characterized in that d) a device (32) for pyrolysis of the high-boiling-point exhaust air stream is provided.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe invention relates to a temperature control device for surface-treated articles such as vehicle parts, having a temperature control chamber in which a surface-treated article can be temperature-controlled, a high-boiler exhaust air stream comprising high-boiling organic compounds from the temperature control chamber, and a combustion device for thermal aftertreatment of the high-boiler exhaust air stream.The invention further relates to a method for tempering a surface-treated object with such a tempering device.2. Description of the Prior ArtThe invention will be described below with priority to vehicle parts such as vehicle bodies as surface-treated articles. However, the invention also relates to temperature control devices for other objects, which have to be temperature controlled in a production process. The term "tempering" is understood here to mean the bringing about a temperature change of an object. This can be a temperature increase or a temperature decrease. Thus, in particular, an evaporation process falls under such a temperature change process. In an evaporation process, an object releases solvent directly after the painting process at, for example, slightly elevated room temperature.Exhaust air is understood to mean exhaust air taken from the temperature control space, which is laden with organic compounds, for example, on account of a temperature control process taking place in the temperature control space.In the automotive industry, after a painting operation or another surface treatment operation such as, for example, the application of adhesives, the vehicle bodies or vehicle parts treated in this way are often heated in order to remove moisture from vehicle bodies or to dry the coating of such a vehicle body or to stabilize and cure the coating applied to the object.In this case, in some cases considerable amounts of the organic compounds mentioned at the beginning pass into the ambient air. These organic compounds can be emitted from the painted object to the ambient air, for example, during an evaporation process after a painting process or during a drying process following the painting process. They generally have different boiling points. Some of the organic compounds boil below a temperature of 200° C. and thus represent solvents or solvents in the narrow sense. This part is referred to here as low boiler and is often already liberated at room temperature.A further portion of the organic compounds only boil in the region of this temperature of 200° C., for example between 150° C. and 220° C., or above. This part is often not released until drying processes at the corresponding temperature and is referred to here as high boiler.This high boiler fraction in the high boiler exhaust air stream can lead to problems in the further guidance of the air stream. If the temperature of the high boiler exhaust air stream falls below the boiling point of the pollutants contained in the high boiler fraction, the organic compounds condense and accumulate in an undesired manner within the air conduits. For this reason, solutions exist such that the low boiler exhaust air stream and the high boiler exhaust air stream are treated separately. Specifically, the low boiler exhaust air stream can be fed to a regenerative post-combustion plant and the energy fraction contained therein can thus be at least partially recovered. At the same time, this can meet the air maintenance regulations. On the other hand, the high boiler exhaust air stream is not accessible to regenerative after-combustion due to the aforementioned problems and cannot be mixed with the low boiler exhaust air stream either. When the two air streams are mixed, the temperature of the high boiler exhaust air stream would fall below the boiling point of the high boiling organic compounds and the high boiler fractions present would condense, as already indicated. Consequently, the high boiler exhaust air stream has to be supplied to a thermal post-combustion with higher energy expenditure. A particular disadvantage of this solution is that two separate exhaust air processing installations have to be provided for the two different exhaust air streams, which disadvantageously increases the design outlay, the maintenance outlay and thus also the financial outlay of the entire temperature control device.SUMMARY OF THE INVENTIONIt is an object of the invention to specify a temperature control device of the type mentioned at the beginning, in which the problems mentioned above are alleviated and in particular only one combustion device is required for the after-treatment of the exhaust air streams.The object is achieved by a temperature control device having the features according to independent claim 1.The temperature control device according to the invention for surface-treated articles such as vehicle parts has a temperature control chamber in which a surface-treated article can be temperature-controlled, a high-boiler exhaust air stream comprising high-boiling organic compounds from the temperature control chamber and a combustion device for the thermal aftertreatment of the high-boiler exhaust air stream.According to the invention, a device for pyrolysis of the high boiler exhaust air stream is provided for such a temperature control device. By means of pyrolysis of the high boiler exhaust air stream, chemical bonds are broken up in the organic constituents contained in the exhaust air stream and larger molecules are thus split into smaller ones. In this case, substantially no combustion or gasification processes, i.e. no oxidation reactions, take place. As a result of the splitting of the molecular compounds, the molecular mass is reduced and the boiling point of the compounds present falls within a desired range which allows a mixture of the high boiler exhaust air stream after pyrolysis with the low boiler exhaust air fraction without undesired condensation processes. It is then consequently possible to feed both exhaust air streams to a common combustion device. Both exhaust air streams, i.e. the low boiler exhaust air stream and the high boiler exhaust air stream, can in each case also comprise small proportions of the other proportion. For example, the high boiler exhaust air stream may have between 5% and 15% of low boiler fractions. Conversely, between 5% and 15% of high-boiling components can be present in the low-boiling effluent stream.In a preferred embodiment of the temperature control device, it is provided that the pyrolysis device is arranged between the temperature control chamber and the combustion device. Thus, after the high boiler exhaust air has been removed from the temperature control chamber, a pyrolysis treatment and subsequently an introduction into the combustion device can take place.The high boiler exhaust air stream which can be fed to the pyrolysis apparatus preferably comprises organic compounds having a boiling point in a range around 200° C., that is to say, for example, in a range from 150° C. to 200° C. These organic compounds are preferably released when coatings such as paint systems are dried, if they are dried at a significantly elevated air temperature in a range of 200° C., i.e. for example at a temperature of 150° C.-220° C.In this context, it may be provided that the high boiler exhaust air stream is taken from the temperature control chamber at a temperature C which is in a range from 150° C. to 200° C.In contrast, in one embodiment, it may be provided that the low-boiler exhaust air stream with low-boiling organic compounds has a boiling point below 200° C., wherein the low-boiler exhaust air stream can be fed to the combustion device for thermal aftertreatment, in particular for regenerative thermal aftertreatment. The low boiler exhaust air stream may have a temperature of 40° C. -60° C., for example.In a preferred embodiment, it can be provided that the high boiler exhaust air stream and the low boiler exhaust air stream can be removed from the temperature control chamber at different process stages. Thus, for example, the low boiler exhaust air stream can be removed in an evaporation zone and the high boiler exhaust air stream can be removed in a drying zone.In an advantageous embodiment, the combustion device is designed as regenerative thermal afterburning.In a further development of the invention, it is provided that the pyrolysis device has a preheating region and a reaction region. In this case, it can be provided, for example, that the preheating region serves for preheating the high boiler exhaust air stream provided for pyrolysis. The preheating region can be heatable, for example, by means of heat of the reaction region. This has the advantage that the energy used for pyrolysis can be used as waste heat for preheating the high boiler exhaust air stream.A specific embodiment of such a pyrolysis device may have a longitudinal axis along which the high boiler exhaust air stream flows during pyrolysis, and wherein the pyrolysis device has an air duct which is designed such that the high boiler exhaust air stream can flow into the pyrolysis device tangentially to this longitudinal axis. The tangential inflow of the high boiler exhaust air stream can take place in particular in the preheating region. In the case of tangential inflow, particularly good heat transfer can take place between the preheating region and the high boiler exhaust air stream.In an advantageous development of the invention, it can be provided that the preheating region is designed at least in sections as a hollow cylinder. In this case, the high boiler exhaust air stream can be guided within the hollow cylinder, more precisely within the wall of the hollow cylinder. This shape enables a particularly good heat transfer between the inner surfaces of the preheating region and the high boiler exhaust air stream.In one embodiment, the reaction region can be arranged at least partially within the hollow cylinder. For example, the reaction region can be arranged within the passage of the hollow cylinder and thus enclosed by the preheating region. This causes additional thermal insulation and thus contributes to energy efficiency.In an advantageous development of the invention, provision can be made for a displacement body to be arranged within the reaction space in order to influence the flow velocity. By means of the flow speed, the amount of heat which is transferred between the reaction region and the preheater region can be influenced.In a concrete embodiment of the invention, it can be provided that the reaction region can be heated by means of a burner. The burner can be designed, for example, as a gas lance and can bring about heating of the high boiler exhaust air by at least 50° C., preferably by 80° C., particularly preferably by 100° C.-150° C.The object is also achieved by a method for tempering a surface-treated object with a tempering device as described above.BRIEF DESCRIPTION OF THE DRAWINGSExemplary embodiments of the invention are explained in more detail below with reference to the drawings. In these show: FIG. 1 shows a schematic illustration of the general structure of a temperature control device according to the invention; FIG. 2 shows a schematic illustration of a longitudinal section of a pyrolysis apparatus according to the invention for a temperature control device according to FIG. 1 ; FIG. 3 shows a schematic cross section of a first embodiment of the pyrolysis device of FIG. 2 ; and FIG. 4 shows a schematic cross section of a second alternative embodiment of the pyrolysis device of FIG. 2.DESCRIPTION OF PREFERRED EMBODIMENTSFIG. 1 shows a schematic illustration of a temperature control device 10. The dryer 12 comprises a tempering chamber 16, in which surface-treated articles can be tempered. The objects to be temperature-controlled can be, for example, vehicle bodies, vehicle components, rims or the like.In the exemplary embodiment shown in FIG. 1, the temperature control chamber 16 comprises an evaporation zone 18 and a drying zone 20. While the article remains in the evaporation zone 18, the surface of the article is brought to a similar temperature. Accordingly, the article gives organic compounds having a boiling point of 60°C or lower. These organic compounds are enriched in the exhaust air of the evaporation zone 18 and leave the evaporation zone 18 as low-boiler exhaust air 22 via an evaporation zone exhaust air line 24.In the drying zone 20, an object to be temperature-controlled is brought, for example, to a temperature of 200° C. Accordingly, the surface of the article heats up and organic compounds having a boiling point of 200° C., i.e. high boilers, accumulate in the ambient air of the surface-treated article. Exhaust air which is taken from the drying zone 20 is correspondingly laden with high boilers and leaves the temperature control space 16 as high boiler exhaust air 26 via a drying zone exhaust air line 28.The above-mentioned temperatures are to be understood merely as exemplary embodiments. For example, the evaporation zone 18 could also be charged with a room temperature of 30° C. and the drying zone 20 with a temperature significantly above 200° C., for example 250° C. or 300° C.The exhaust air lines 24, 28 can each also be a plurality of exhaust air lines.The evaporation zone exhaust air line 24 connects the temperature control chamber 16 to a regenerative thermal post-combustion device 30, also referred to as RMV. The RMV 30 can be designed, for example, such that ceramic bodies are subjected to alternating flow with the exhaust air 26 and with clean air already cleaned via a rotating air distribution system. In this way, the clean air heats the ceramic bodies, which then release the stored heat to the exhaust air 24. A burner is provided to achieve the necessary temperature.As already explained, it is not possible to mix the high boiler exhaust air stream 26 with the low boiler exhaust air stream 20, since, in the case of the temperature of the high boiler exhaust air stream 26 then being reduced, the organic compounds contained therein would condense and, for example, would precipitate on inner walls of the pipeline. In addition, the undesired high boiler material can settle in the interior of the heat exchanger of the regenerative post-combustion device and can significantly influence the function there. The flow can be almost completely blocked and a fire load can be generated by the deposition processes.According to the invention, therefore, the high boiler exhaust air stream 26 is fed via the dry zone exhaust air line 28 to a pyrolysis device 32. The waste air stream 34 pyrolysed in this way can then be fed to the RMV 30 together with the low boiler waste air stream 22.FIG. 2 shows a schematic illustration of a longitudinal section of the pyrolysis device 32 of FIG. 1 The pyrolysis device 32 has a substantially cylindrical housing 35 which extends along a longitudinal axis A. The housing 35 has an exhaust air feed line 36, via which the high boiler exhaust air 26 enters the pyrolysis device 32 at one end of the housing 35. At the same end, a process gas discharge line 37 is provided in the housing 35, via which the pyrolyzed exhaust air stream 34 leaves the pyrolysis device 32 again.The housing 35 is provided on its outer side with a thermal insulation 38 and has in the inner region a reaction tube 43 arranged along the longitudinal axis A. After the high boiler exhaust air 26 enters via the exhaust air feed line 36, the high boiler exhaust air 26 is located in a hollow cylindrical preheating region 40, which surrounds an outflow region 42 of the reaction tube 43 as a preheating region annular gap 41 to a certain extent.Heat is transferred via the annular gap 41 from the outflow region 42 lying in the interior of the reaction tube 43 into the preheating region 40 surrounding the reaction tube 43, so that this region can be referred to as heat exchanger region 44.This heat exchanger region 44 is adjoined along the longitudinal axis A by a combustion chamber region 46 having a reaction region 50 and a burner 56.The reaction region annular gap 48 is located between the reaction tube 43 and the housing 35 and adjoins the preheating region 40. The reaction region annular gap 48 surrounds the actual reaction region 50 located in the interior of the reaction tube 43. the reaction region annular gap 48 has a heat shield 52 which surrounds the outer side of the reaction tube 43 and thus the reaction region 50 located in the interior of the reaction tube 43. The heat shield 52 serves to assist in maintaining the reaction temperature prevailing in the reaction region 50. An inflow path 54 connects the reaction region annular gap 48 to the reaction region 50 located in the interior of the reaction tube 43 and leads past in the immediate vicinity of a burner 56. The burner 56 is likewise arranged along the longitudinal axis A and can, for example, project at least partially into the reaction tube 43. The burner 56 can be designed as a surface burner or as a gas lance, for example, with a power of 40-100 kW. Natural gas, for example, can be provided as the fuel.The reaction region 50 extends in the interior of the reaction tube 43 along the longitudinal axis A. The reaction region 50 is adjoined by the already mentioned outflow region 42. While the reaction region 50 is surrounded by a heat shield 52, as already mentioned, there is the possibility of transferring heat between the outflow region 42 and the preheating region 40. This allows recuperation of the heat generated by the burner 56 by transferring a part thereof to the incoming exhaust air 26.In the outflow region 42, a displacement body 58 is arranged inside the reaction tube 43. In the present exemplary embodiment, the displacement body 58--as with the exception of the exhaust air feed line 36 the entire pyrolysis device 32--is designed rotationally symmetrical and can be attached, for example, in a suspended or braced manner. The displacement body 58 serves to influence the flow velocity in the preheating region 40 and thus also to influence the heat transfer from the outflow region 42 into the preheating region 40.The process gas discharge line 37 adjoins the outflow region 42.During operation, the high boiler exhaust air 26 enters the preheating region annular gap 41 of the preheating region 40 via the exhaust air feed line 36, which is formed here as an inlet connector 39, by way of example. Because of the configuration of the preheating region 40 as a hollow cylinder or annular gap, the exhaust air 26 laden with high boilers is twisted, which leads to intensive surface contact of the exhaust air 26 with the outer surface of the reaction tube 43. In this case, the exhaust air 34 located in the reaction tube 43, in particular in the outflow region 42, and already pyrolyzed, releases part of its heat to the high-boiler exhaust air 26 which has flowed in and heats the latter by, for example, approximately 100° C. This means that a high-boiler exhaust air 26 which flows in at 200° C. has heated to, for example, 300° C. after flowing through the preheating region 40 and enters the reaction region annular gap 48 at this temperature. After it has a heat shield 52 compared to the reaction region 52, for example an air gap of the order of magnitude of 50 to 100 mm, the high-boiler exhaust air 26 heats up only slightly, for example by 20° C., until it enters the reaction region 50 via the inflow path 54.The burner 56 ensures, via an inflow of a hot combustion gas, a heating of the high-boiler exhaust air 26 by 100° C. to 150° C., so that the exhaust air 26 is heated from the temperature prevailing at the entry from, for example, 350° C. to, for example, 470 ° C. As explained at the beginning, pyrolysis of the high boiler fractions takes place in the exhaust air 26, so that the high boiler fraction is reduced to <5%, for example.In the reaction region 50 inside the reaction tube 43, an average temperature of about 450° C. results. After the process gas has overflowed from the reaction region 50 into the outflow region 42, the temperature of the process gas decreases to about 350° C.The process gas remains in the reaction region 50 for approximately 1 second and flows, for example, at a speed of 50 m / s. The residence time of the process gas in the reaction region 50 and the heat transfer within the heat exchanger region 44 can be influenced via the design of the displacer 58.FIGS. 3 and 4 show a section along the line III-III of FIG. 2, FIG. 3 shows a first embodiment of the pyrolysis device 32, in which the inlet connection piece 39 is arranged radially with respect to the longitudinal axis A. Figure 4 shows a second alternative embodiment of a pyrolysis apparatus 32'. Identical or comparable features were provided with an apostrophe.The alternative pyrolysis device 32 differs from the pyrolysis device 32 of FIGS. 2 and 3 in that an inlet connection piece 39' is provided, which is arranged tangentially to the longitudinal axis A. This facilitates the swirling of the high boiler exhaust air 26 flowing in via the inlet connection 39' within the preheating region annular gap 41' and thus improves the heat transfer between the preheating region 40' and the outflow region 42'.

Claims

Temperature control device (10) for surface-treated articles such as vehicle parts, having a) a temperature control chamber (16) in which a surface-treated article can be temperature-controlled, b) a high-boiler exhaust-air stream (26) having high-boiling organic compounds from the temperature control chamber (16), c) a combustion device (30) for the thermal aftertreatment of the high-boiler exhaust-air stream (26), characterized in that d) a device (32) for pyrolysis of the high-boiler exhaust-air stream is provided.Temperature control device according to claim 1, wherein the pyrolysis device (32) is arranged between the temperature control chamber (16) and the combustion device (30).Temperature control device according to one of the preceding claims, wherein the high-boiler exhaust air stream (26) which can be fed to the pyrolysis device (32) comprises organic compounds having a boiling point equal to or above 150°.Temperature control device according to claim 3, wherein the high boiler exhaust air stream (26) is taken from the temperature control chamber (16) at a temperature above 200°C.Temperature control device according to one of the preceding claims, having a low-boiler exhaust air stream (22) with low-boiling organic compounds having a boiling point below 200°C, it being possible for the low-boiler exhaust air stream (22) to be fed to the combustion device (30) for thermal aftertreatment.Temperature control device according to claim 5, wherein the high boiler exhaust air stream (26) and the low boiler exhaust air stream (22) can be removed from the temperature control chamber (16) at different process stages.Temperature control device according to one of the preceding claims, wherein the combustion device (30) is regenerative thermal afterburning.Temperature control device according to one of the preceding claims, wherein the pyrolysis device (32) has a preheating region (40) and a reaction region (50).Temperature control device according to claim 8, wherein the pyrolysis device (32') has a longitudinal axis (A) along which the high boiler exhaust air stream (26) flows during pyrolysis, and wherein the pyrolysis device (32) has an air duct (36') which is designed such that the high boiler exhaust air stream (26) can flow into the pyrolysis device (32) tangentially to this longitudinal axis (A).Temperature control device according to either of Claims 8 and 9, wherein the preheating region (40) is designed at least in sections as a hollow cylinder.Temperature control device according to claim 10, wherein the reaction region (50) is arranged at least partially within the hollow cylinder.Temperature control device according to one of claims 8 to 11, wherein a displacement body (58) for influencing the flow speed of the high boiler exhaust air stream (26) is arranged within the reaction space.Temperature control device according to one of claims 8 to 12, wherein the reaction region can be heated by means of a burner (56).Temperature control device according to claim 13, wherein the burner (56) is designed for heating the high boiler exhaust gas stream (26) by at least 50 K.Method for tempering a surface-treated object with a tempering device according to one of the preceding claims.

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