Patent Publication Number: US-9410741-B2

Title: Device for controlling the temperature of objects

Description:
RELATED APPLICATIONS 
     This application is a national phase of International Patent Application No. PCT/EP2012/004677, filed Nov. 10, 2012, which claims the filing benefit of German Patent Application No. 10 2011 119 436.7, filed Nov. 25, 2011, the contents of both of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a device for controlling the temperature of objects, in particular for drying coated motor vehicle bodies, having 
     a) a temperature-controlling tunnel which is accommodated in a housing and defines at least one tunnel portion which comprises at least one air outlet and at least one air inlet; 
     wherein 
     b) there is associated with the tunnel portion a heater assembly in which a hot primary gas can be generated by means of a burner unit; 
     c) the hot primary gas can be conducted into a heat exchanger of the heater assembly, in which tunnel air can be heated by hot primary gas, which tunnel air can be fed to the tunnel portion again in a circuit via the at least one air inlet as a circulating air stream. 
     BACKGROUND OF THE INVENTION 
     The invention is described below using the example of motor vehicle bodies as objects, but the invention relates also to devices for other objects whose temperature must be controlled in a production process. When the term “temperature control” is used here, it means the inducement of a specific temperature of the object that the object does not initially possess. It can be a temperature increase or a temperature reduction. “Temperature-controlled air” is understood as meaning air that has the required temperature for controlling the temperature of the object. 
     A frequent case of the temperature control, namely the heating, of motor vehicle bodies in the automotive industry is the operation of drying wet motor vehicle bodies or of drying the coating of a motor vehicle body, whether that be a paint or an adhesive or the like. Wet objects other than motor vehicle bodies or the coating of other objects can correspondingly be dried. The detailed description of the invention which is given below is made using the example of such a drier for motor vehicle bodies. 
     When the term “drying” is used here, it means any operations in which the coating of the motor vehicle body, in particular a paint, can be made to cure, whether that be by the expulsion of solvents or by the crosslinking of the coating substance. 
     Devices of the type mentioned at the beginning that are known on the market are used for drying freshly painted motor vehicle bodies and are heated, inter alia, by extracting air from tunnel portions that are short compared with the overall length of the drying tunnel, heating it in a heater assembly by means of a heat exchanger, and feeding it to the corresponding tunnel portion again in a circuit. 
     In the drying of freshly painted motor vehicle bodies, the air removed from the tunnel portion is loaded mainly with solvent, which is released in the drying operation. This air additionally contains coating constituents which are released during the drying of the motor vehicle body; nevertheless, for the sake of simplicity, reference will be made only to waste air below. 
     In known devices, the burner air necessary for operating the burner unit is removed from the surroundings via a separate air compressor fan. Accordingly, the burner air must be heated from ambient temperature to the burner temperature and is removed from the surroundings as clean air, which is contaminated during use and can optionally be purified before being returned to the surroundings. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a device of the type mentioned at the beginning which offers an alternative to known devices and in particular has a better energy balance. 
     The object may be achieved in a device of the type mentioned at the beginning in that 
     d) a burner supply device is provided, by means of which waste air from the tunnel portion can be fed to the burner unit of the heater assembly as a burner air stream for generating the primary gas to the burner unit. 
     According to the invention, therefore, waste air from the tunnel portion is used to generate the hot primary gas flow by means of which the circulating air is heated. Unlike known burner units, clean ambient air is thus not used as burner air; instead, already contaminated waste air from the temperature-controlling tunnel is used for that purpose. This waste air is already hotter than the ambient air and therefore does not have to be heated in the burner unit to the same extent as fresh ambient air. The overall energy balance of the device is thereby improved. 
     It is particularly advantageous if the heater assembly is so configured that the burner air is guided to the burner unit after the burner air has flowed through the heat exchanger and been heated therein. In this manner, the burner air is at a high temperature when it reaches the burner unit, so that the heating of the burner air that is necessary there is again reduced. 
     It is an advantage if the heater assembly comprises a distributor device by means of which tunnel air from the tunnel portion can be divided into the circulating air stream and the burner air stream. 
     It is particularly efficient if the distributor device is arranged downstream of the heat exchanger, so that the tunnel air heated therein is divided into the circulating air stream and the burner air stream. 
     If the volume flows of the circulating air stream and of the burner air stream are adjustable by means of the distributor device, the device can be adapted in a simple manner to different objects whose temperature is to be controlled. To that end, for example, a regulating valve can be present in the flow path. 
     It is particularly advantageous if the burner unit is a thermal after-burning device. In this case, the after-burning, and thus the disposal of the solvent-containing waste air, is accordingly integrated into the heater assembly and only part of the air removed from the tunnel portion is fed back into the tunnel portion again as circulating air. 
     It has been found to be particularly successful if the burner unit is a gas burner, in particular a planar burner. 
     It is advantageous if means are provided by which the burner air can be divided into primary air and secondary air, the primary air being mixed directly with the burnable gas. The secondary air can then be used for other measures. 
     It is particularly advantageous if secondary air is mixed by means of flue gas recycling with flue gases generated by the burner unit, and a secondary air/flue gas mixture so obtained is fed to the combustion gases of primary air and burnable gas. In this manner, the amount of oxygen available for combustion can be adjusted via the flue gas admixture. This will be discussed in greater detail below. 
     It is to be understood that the aspects and objects of the present invention described above may be combinable and that other advantages and aspects of the present invention will become apparent upon reading the following description of the drawings and detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the invention will be described in greater detail below with reference to the drawings, in which: 
         FIG. 1  shows a schematic representation of a drier with a thermal after-burning device and a plurality of heater assemblies; 
         FIG. 2  shows a more detailed view of a heater assembly; 
         FIG. 3  shows schematically a section of the heater assembly in the region of a gas burner present there. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. 
     In  FIG. 1 , a drier  10  is shown schematically as an example of a device for controlling the temperature of objects. The drier  10  comprises a heat-insulated drier housing  12  in which a drying tunnel  14  is accommodated as the temperature-controlling tunnel, through which motor vehicle bodies (not shown) are conveyed continuously. To that end, the drier  10  comprises a conveyor system known per se for the motor vehicle bodies, which is likewise not shown for the sake of clarity. 
     Heated air is fed to the drying tunnel  14  in order to dry the motor vehicle bodies, or a coating applied thereto. When the term “drying” is used here, it means any operations in which the coating of the motor vehicle body, in particular a paint, can be made to cure, whether that be by the expulsion of solvents or by the crosslinking of the coating substance. 
     The drier  10  comprises a thermal after-burning device  16  and a waste air heat exchanger  18  arranged downstream thereof, as well as a plurality of heater assemblies  20  of identical construction, which will be discussed in greater detail below. 
     The thermal after-burning device  16  is a gas burner to which waste air from the drying tunnel  14  is fed via a waste air line  22  by means of a waste air fan  24 . In the after-burning device  16 , burnable gas is added to the waste air from the drying tunnel  14 , and the waste air/gas mixture so obtained is burnt, whereby the noxious substances contained in the waste air are rendered harmless. 
     The waste air treated and freed of noxious substances by heating in the thermal after-burning device  16  then passes into the waste air heat exchanger  18 , in which fresh air fed to the waste air heat exchanger  18  by means of a fresh air fan  26  is heated by the heated waste air. This heated fresh air is then conveyed from the waste air heat exchanger  18  via fresh air feed lines  28  into the drying tunnel  14 , preferably via the inlet and outlet region thereof. The waste air that has flowed through the waste air heat exchanger  18  is discharged via the top. 
     The temperature necessary for drying is maintained in the drying tunnel  14  by the heater assemblies  20 , which are arranged in the form of compact gas burner units along the drying tunnel  14  and form a burner system. Associated with each heater assembly  20  is a tunnel portion T defined by the drying tunnel  14 , the drying tunnel  14  having a plurality of such tunnel portions T. In the present exemplary embodiment, six tunnel portions T 1  to T 6  and six associated heater assemblies  20  are shown by way of example. The tunnel portions T 1  to T 6  are not structurally separate from one another in the present exemplary embodiment. 
     Tunnel air is fed to each of the heater assemblies  20  through an air outlet of the associated tunnel portion T, which air outlet is in the form of an outlet line  30 . The outlet line  30  merges into a useful air line  32 , in which a conveyor fan  34  is arranged. 
     The useful air line  32  in turn leads through a heat exchanger coil  36  of a heat exchanger  38  to a distributor device  40 , which divides the useful air stream coming from the useful air line  32  into a circulating air stream and a waste air stream, after the useful air has passed through the heat exchanger  38 . 
     The circulating air is blown into the associated tunnel portion T of the drying tunnel  14  again through an air outlet in the form of an inlet line  42 . The waste air serves as burner air for a burner unit in the form of a gas burner  44 , to which the waste air is fed as the burner air stream via a burner air line  46 . A planar burner, as is known per se, has been found to be suitable in practice as the gas burner  44 . 
     The distributor device  40  and the burner air line  46  thus form a burner supply device via which waste air from the associated tunnel portion is fed to the gas burner  44  as the burner air stream in order to generate the hot primary gas. 
     The required burnable gas is fed to the gas burner  44  from a burnable gas source  48  via a burnable gas line  50 . The volume flow of the burnable gas can be adjusted by means of a valve  52  that is arranged in the burnable gas line  50 . In the gas burner  44 , the solvents in the waste air are burnt as far as possible, hot combustion gases forming as primary gas. These hot combustion gases are fed via a feed line  54  to the heat exchanger  38 , where they heat the solvent-containing useful air flowing through its heat exchanger coil  36 , the useful air at the temperature achieved therein consequently flowing into the gas burner  44  as solvent-containing burner air. 
     After flowing through the heat exchanger coil  36  of the heat exchanger  38 , the hot combustion gases of the gas burner  44  are discharged via a waste gas line  56 , which is connected as a collecting line to the heat exchanger coils  36  of all the heater assemblies  20  and merges at a junction into a waste air line  58 , via which the waste gases, like the waste gases of the after-burning device  16 , are discharged via the top. 
     The primary gas of the gas burner  44  accordingly heats in the heat exchanger  38  both circulating air, which is fed to the associated tunnel portion T again in a circuit via the air inlet line  42 , and waste air, which is fed to the gas burner  44  as burner air. 
     The distributor device  40  of a heater assembly  20  can be adjustable so that it is possible to adjust the volume flows that are fed as circulating air into the drying tunnel  14  again and as burner air to the gas burner  44 . The proportion of tunnel air branched off as burner air is of the order of magnitude of about 1% of the tunnel air that flows from the tunnel portion T of the associated heater assembly  20  into the outlet line  30 . 
     As can be seen in  FIG. 2 , the distributor device  40  can be formed, for example, by arranging an inlet opening  60  of the burner air line  46  in the inlet line  42  leading to the drying tunnel  14  so that part of the useful air coming from the heat exchanger  38  through the useful air line  32  flows into the burner air line  46 , while the other part enters the inlet line  32  and, via the inlet line  32 , the drying tunnel  14 . 
     As is likewise shown in  FIG. 2 , the heat exchanger coil  36  of the heat exchanger  38  can be in the form of a tube bundle  62  through which there flow the hot combustion gases of the gas burner  44 , the combustion chamber of which is designated  64 . In the representation according to  FIG. 2 , the hot combustion gases from the combustion chamber  38  enter the individual tubes of the tube bundle  62 , which are not provided individually with a reference numeral, behind the plane of the drawing, flow through the tubes in front of the plane of the drawing and there enter the waste gas line  56  via, a collecting line  66 . 
     The guiding of air and gas in the gas burner  44  is shown schematically in  FIG. 3 , where  68  designates a gas nozzle which is fed with burnable gas via the burnable gas line  50 , which is indicated in  FIG. 3  by an arrow, and blows it into the combustion chamber  64 . 
     The burner air passes via the burner air line  46  first into a combustion chamber pre-space  70 , from where it flows via a swirl plate  72  into a mixing zone  74  of the gas burner  44 , which surrounds the delivery opening of the gas nozzle  68 . By means of the swirl plate  72 , the burner air is swirled before it enters the mixing zone  74 , as a result of which swirls and turbulences are purposively generated in order to assist with the mixing of the burner air and the burnable gas. To that end, the swirl plate  72  can include, for example, flow channels or paddle elements, by means of which the burner air is swirled as it flows through the swirl plate  72 . 
     The mixing zone  74  in turn comprises a cylindrical core region  76  around the gas nozzle  68  and an annular space  78  which surrounds the core region  76  coaxially, to which end a cylindrical inner wall  80  and a cylindrical outer wall  82  are present in the mixing zone  74 . The burner air which has flowed through the swirl plate  70  is divided by the inner wall  80 . Part of the burner air thus passes as primary air into the core region  76 , while the other part flows as secondary air into the annular space  78 . 
     The annular space  78  additionally communicates with the combustion chamber  64  of the gas burner  44  via an annular gap  84 . Overall, flue gas recycling in the form of an annular nozzle  86  is formed in the annular space  78  according to the Venturi principle. The flowing secondary air creates a suction effect at the annular gap  84 , which causes flue gas to be drawn from the combustion chamber  64  of the gas burner  44  into the annular space  78 , where the flue gas mixes with the secondary gas coming from the swirl plate  70 . 
     By the removal of waste air from the drying tunnel  14  via the outlet lines  30  and division into a useful air stream and a burner air stream, part of the air circulated in the drying tunnel  14  is accordingly heated considerably in the gas burners  44  of the heater assemblies  20  on combustion. As a result, neutralisation of the noxious substances which have accumulated in the waste air is already ensured in the heater assemblies  20 . The gas burner  44  is accordingly a thermal after-burning device. 
     Because the burner air is heated by the heat exchanger  38  before it reaches the gas burner  44 , burnable gas can be saved at the respective gas burner  44 . This saving can amount to up to 15%, relative to gas burners whose burner air is not heated or is heated to a lesser degree. On account of the warmer burner air, the flame temperature increases, resulting in an improvement in the efficiency of the gas burner  44 . Although this is generally at the expense of higher values in terms of nitrogen oxides NO x , these can be reduced again by measures known from the prior art. 
     Alternatively to the known measures, the reduction in the nitrogen oxides NO is achieved in the gas burner  44  by the division of the mixing zone  74  into the core region  76  and the annular space  78  with the flue gas recycling  86 . The oxygen content in the secondary air/flue gas mixture which forms in the annular space  78  is lower than the oxygen content of the secondary air prior to mixing. In addition, the secondary air is heated and the recycled flue gas is cooled by the flue gas recycling; the secondary air/flue gas mixture has a corresponding mean temperature. 
     Combustion in the core region  76  first takes place substoichiometrically, so that, for example, not all the carbon monoxide CO that is initially produced oxidises to carbon dioxide CO 2  with the oxygen O 2  supplied by the primary air, and carbon monoxide CO is still present in the combustion gases that form. 
     The secondary air/flue gas mixture having a reduced oxygen content passes, after flowing through the annular space  78 , into the edge region of the core region  76 , where it mixes with the combustion gases formed in the core region  76  from primary air and burnable gas. The secondary air/flue gas mixture serves as the oxygen donor for the carbon monoxide CO that is still present, which is now oxidised completely to CO 2  at a relatively low temperature, only small amounts of nitrogen monoxide NO being formed, so that only small amounts of nitrogen oxides NO x  are consequently also produced. Overall, with this burner configuration, excellent values in terms of carbon monoxide CO and nitrogen oxides NO are achieved with an oxygen content of not more than 3%. 
     Because a portion of the waste air removed from the drying tunnel  14  is used as combustion air for the gas burners  44 , the proportion of tunnel air that must be fed as waste air to the after-burning device  16  is reduced by the corresponding proportion. As a result, the contribution made by after-burning is lower and the gas consumption for the after-burning device can be reduced overall. 
     Overall, the proportion of waste gases discharged to the atmosphere via the top is also reduced. 
     It is to be understood that additional embodiments of the present invention described herein may be contemplated by one of ordinary skill in the art and that the scope of the present invention is not limited to the embodiments disclosed. While specific embodiments of the present invention have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying claims.