EP4643072A1

EP4643072A1 - Oven for air drying with energy saving

Info

Publication number: EP4643072A1
Application number: EP23840712.6A
Authority: EP
Inventors: Luigi Franzoni
Original assignee: Cefla SCARL
Current assignee: Cefla SCARL
Priority date: 2022-12-29
Filing date: 2023-12-22
Publication date: 2025-11-05
Also published as: WO2024141506A1

Abstract

Tunnel oven for drying/flashing off and cooling paints/glues on pieces comprising: • - at least a drying tunnel chamber; • - at least a cooling tunnel chamber optionally comprising a heat exchanger; said drying tunnel chamber and cooling tunnel chamber comprising: • a. at least a conveying system • b. at least an air treatment group comprising: • - an inlet for recirculated air • - an inlet for outer air • - optionally a filter for flows of outer air and/or recirculating air or their mix; • - optionally a heat exchanger • - a fan supplying said flows of air or their mix into the drying or cooling chamber • optionally an exhaust fan exhausting a flow of drying or cooling fluid; • at least one heat pump comprising: an evaporator, a compressor, a condenser, an expansion valve and a refrigerant fluid, said evaporator and condenser transferring thermal energy between the refrigerant fluid therein and a further gas or fluid; said drying and cooling chamber being connected to said heat pump.

Description

OVEN FOR AIR DRYING WITH ENERGY SAVING

[0001] The present invention relates to apparatuses and a method for drying pieces, preferably having the shape of panels or components. In particular, the invention relates to an oven comprising at least two distinct chambers arranged in series, a first chamber for drying pieces, and a second chamber for cooling said pieces, for drying painted pieces made of sundry materials (wood and its derivatives, fibre cement, glass, plastics, etc.), wherein a heat pump is advantageously employed, in order to bring the drying fluid and the cooling fluid in the drying chamber and in the cooling chamber, respectively, to the desired temperature, making a more efficient use of the energy at play. The present invention is described in two distinct embodiments, which nonetheless make use of the same inventive concept. In the first embodiment, the oven is in the form of a tunnel oven, while in the second embodiment the oven is in the form of a vertical multilevel oven. In the following, said apparatuses are defined as oven, tunnel, tunnel oven or vertical oven.

[0002] The present invention is part of the group of inventions trying to improve the energy performance of plants and to prevent waste, with a view to an improved ecologic sustainability.

[0003] In said ovens, the drying fluid is mainly air, but also other gases might be used, e.g. inert gases.

[0004] In the first embodiment in the form of tunnel ovens, with mainly flat panel, a panel wherein two of its three dimensions are markedly bigger than its third dimension is meant. Typically, the measures of such panels range 100x300x2 mm to 1600x3500x300 mm. Such ovens can also dry continuous sheets of materials having their third dimension (thickness) smaller than their other two dimensions, thanks to the feature of these ovens of allowing a continuous passage of pieces (one-level tunnels as described in the following). [0005] In the second embodiment in the form of vertical multilevel ovens, said pieces can reach lengths of over 6 metres, with a typical width of 1300- 1600 mm and a typical thickness of 5-300 mm.

[0006] It also might be necessary drying components, e.g. automotive components, which can be provided with non-planar shapes, but which are dried on supporting frames. The assembly of frame and components supported by said frame reaches dimensions similar to the above-quoted ones. Nonetheless, the process is applicable also to bigger components provided with three similar dimensions, like car bodyworks, car bumpers, windows, which can be provided with dimensions bigger than those described in the preceding paragraph.

[0007] It is worth mentioning that drying means the step wherein the applied paint passes from its liquid to its solid phase, while in cooling the solidified paint and the piece on which it is applied are brought from the drying temperature to a temperature near to room temperature.

[0008] It is known in the art that drying temperature and speed affect the final result: when the drying temperature is too high and/or the drying speed is too fast, paint cracks or aesthetical defects can form in the paint layer covering a panel. For this reason, in the art it is known to perform a process known as flashing off, wherein the process temperature is low, about 15-35°C.

[0009] Flashing off has the aim of removing most of the solvent, while paint is still fresh; flashing off is performed at temperatures near to room temperature (15-35°C) in order to prevent the curing of just the surface of the paint while the underlying paint is still soft, which could lead to surface defects of the applied painting layer. The actual temperature of the environment wherein the oven is installed sometimes requires to heat the flash off chamber.

[0010] When drying, higher temperatures are used, typically 40-100°C, in order to complete the drying of solvents and accelerate the polymerization of paint, and therefore paint hardening. From the point of view of process time, drying is the longest step.

[0011] After drying, generally pieces are cooled down, in order to make them suitable for handling by human operators during the manual unloading of the finished piece from the production line, and/or prevent damages connected to a possible thermoplasticity of the paint, which might be softer at higher temperatures, even after its drying. Typically, the cooling down occurs at room temperature, too.

[0012] It is worth mentioning that the temperature of the environment can vary widely according to the geographical location of the plant and to the season of the year. The environmental air used for cooling can be taken from outside the production line or from the environment wherein the plant is installed. This means starting from environmental air having a temperature ranging -20°C to +40°C. Therefore, heating or cooling the air provided to the cooling chamber might be necessary, in order to bring it to the required 10- 30°C. In the known art, sometimes a chiller must be provided in order to obtain the cooling fluid at the desired temperature.

[0013] Concerning the first embodiment in the form of tunnel ovens, in the art two main types of ovens are known:

- One-level tunnels wherein the pieces to be dried are conveyed along a plane on the same level as the working plane of the production line, therefore on one level only; pieces follow a linear path.

- Multi-level tunnels wherein the pieces to be dried are arranged on a plurality of superimposed levels, each level provided with its own conveying system; the conveying systems are arranged in a mobile pack moving upwards and downwards in the vertical direction, that takes a position according to a FIFO logic at the working level of the productive line in order to load and unload pieces, so as to increase the drying time with a limited footprint. The pieces to be dried travel in parallel inside a tunnel. In this way, the pieces to be dried follow a linear path, different from the typical meandering or ring path of vertical multilevel ovens, but stay for a longer drying time with respect to one-level tunnels, one-level and multi-level tunnels being provided with the same length.

[0014] In the art, it is known providing at least two tunnels arranged in series, the first providing the drying of the painted pieces and the second providing the cooling of the painted and dried pieces. Said tunnels can be one-level or multi-level tunnels, as described in the preceding paragraph.

[0015] In the art, it is known providing one or more drying tunnels and one or more cooling tunnels arranged in line.

[0016] Concerning the second embodiment in the form of vertical multilevel ovens, vertical ovens for drying pieces are well known in the art, being e.g. described in the utility model IT221807 of the same applicant, or in EP2609021B1 of Haenel or in GB2078651 of Lienhard. In such documents there are described vertical ovens for drying pieces, with trays moved by chain lifting systems that can be motorized, i.e. suitable for being moved by or housing suitable motorizing means fixed to the frame of the oven, in order to obtain the automatic loading and unloading of the pieces.

[0017] Typically, vertical ovens with trays comprise a plurality of superimposed trays arranged in a plurality of adjacent stacks contained in chambers, along which the trays are shifted through lifting chains. When a tray reaches the top of an ascending stack (i.e. in which the chain moves trays toward the top), it is shifted on the top of a descending stack (in which the chain moves the trays toward the bottom) through suitable devices for horizontal shifting. Through similar devices, at the end of the last descending stack, the trays are shifted to the base of the first ascending stack to be collected by the relative lifting chain. In this way, each tray of the oven follows a complete meandering or ring path through the oven, during which the panels, arranged on the trays, dry, and often cool down.

[0018] Obviously, said vertical chambers are separated, but for the small space needed to shift a tray from a chamber to the following one.

[0019] The loading and unloading of the panels on trays occur thanks to the fact that the trays are moved through a motorizable conveying system, which allows to automatically load and unload the panels, without the need to extract the tray from the oven.

[0020] The shape of vertical ovens, having a plurality of superimposed trays, allows a good storing capability with a limited footprint, allowing a dwell time inside the oven itself that can vary from some ten minutes to over a couple of hours, according to production line speed and dimensions of the oven itself.

[0021] In their simplest embodiment, vertical ovens comprise two chambers; nonetheless other embodiments are known, comprising a plurality of chambers, typically a multiple of a pair of chambers, i.e. e.g. from two to six chambers. Such ovens are e.g. described in MI97A000463 Elmag and IT 1309018 CEFLA. In such ovens, the trays typically follow a meandering path, and the loading and unloading of the pieces can occur from the same chamber or from two different chambers, as appropriate. Another well-known embodiment comprises three chambers and two stacks, wherein the central chamber is empty.

[0022] Typically, flashing off is performed with low air flows, both in supply and in exhaust of the total air flow, so as not to disturb the distension of paint. During drying the airflows are important and typically are recirculated (70- 80%) taking the rest percentage of air from the environment, heating the air for drying pieces before sending it on pieces and exhausting a percentage of air from the oven that is analogous to that taken from the environment.

[0023] In consequence of the above-described working of the oven, oven chambers need independent air inlets and outlets. This entails at the exhaust of each chamber, and in particular of the drying chambers, a dispersion of energy under the shape of heat, because hot air is dispersed outside the oven, and the need to warm up the replenishing airflow taken from the environment in order to compensate for the exhaust airflow.

[0024] This is true even for the flashing off chamber, even if to a lesser extent, given the lower working temperature and the typically low flashing off airflow.

[0025] In a known embodiment of vertical ovens, the flashing off occurs in the first chamber/s, the drying in the central chamber/s, and the cooling down in the last chamber/s.

[0026] E.g., while 8,000 m³/h of air might be employed for drying and cooling down in each chamber, typically for flashing off just one quarter to a half of that quantity is used.

[0027] For painting the surfaces of different materials, the most used industrial processes make use of products applied in their liquid phase containing solvents or water, which in a subsequent step must be evaporated: this requires relatively long drying times. Moreover, the vapours of said solvents might be dangerous for operators’ health, and must be removed or absorbed in special systems. The process requires a high energy consumption, in that the pieces to be dried are normally heated in order to cause the evaporation of solvents and the process of polymerization of the applied products, and even cooled in order to allow the handling of the pieces at their egress from the oven.

[0028] The drying process is a polluting process, in that the organic solvents contained in paints are evaporated through heat, and organic molecules may be dispersed in the environment. The class of the Volatile Organic Compounds (VOCs) comprises different chemical compounds whose molecules contain different functional groups: such compounds overall have different physical and chemical behaviours, but share a high volatility, that is characteristic e.g. of the common organic solvents, like paint thinners or alcohols. If the solvent is water, in order to increase its evaporation often substances are added, which in turn can release VOCs.

[0029] In the known art, due to the water and/or VOCs removed by the air used in the drying process, it is necessary to disperse a portion of the drying air outside the oven, in order to prevent the progressive increment of their concentration, which might limit the drying capacity of the oven, and could even reach dangerous concentrations possibly leading to explosions.

[0030] Ovens for drying panels are well known in the art; normally, such ovens use hot air that is heated through water heat exchangers, steam, electric heaters or other means. All these systems are provided with an efficiency lower than 1 : in the face of 1 kWh consumed, in the best of hypotheses the energy available for heating the air needed for drying paint is about 0.85 kWh. In the case of electric heaters, the efficiency is even lower, in that it is linked to the efficiency of the electric energy production and distribution chain: typically, efficiencies around 40% are reached.

[0031] Heat pumps are known in the art: a heat pump is a thermal device that can extract and transfer thermal energy using different forms of energy, generally mechanical energy.

[0032] Typically, the working of a heat pump is the following: the compressor of a heat pump suctions a gaseous refrigerant compressing it in the high-pressure area of the circuit. The compressed gaseous refrigerant, that is heated through the increase in pressure, is pushed into a first heat exchanger (condenser), wherein it releases heat to the environment to be heated, environment that has a temperature lower than the temperature of the gaseous refrigerant itself; said gaseous refrigerant cools down, until it condenses in liquid form. The liquid is pushed through a reversing valve that separates the high-pressure portion from the low-pressure portion of the heat pump circuit. When the liquid, now at low pressure and cooled down through the reduction in pressure, reaches a second heat exchanger (evaporator), it absorbs heat from the environment from which thermal energy is taken, environment that has a temperature higher than the temperature of the liquid itself; said liquid passes to its gaseous form to be suctioned by the heat pump compressor again, restarting the cycle.

[0033] When comparing the performances of heat pumps, the term efficiency is avoided, as by definition it is always lower than 1. Preferably, the term performance is used, which is expressed as a Coefficient Of Performance (COP), which is the ratio between supplied energy (provided heat) and consumed energy (generally electric energy, required by the compressor), usually indicated in technical physics as coefficient of effectiveness. A value of 3 for the COP means that for each kWh of consumed electric energy the heat pump transfers 3 kWh of thermal energy from or to the interested source. [0034] CN107843113A of Guangxi Xuteng Ind. describes a kiln for the production of ceramics. In said kiln, the recirculation of air is provided through a system of fans 3, defined as heat pump in the sense that such fans transfer heat from an area to another area in the oven; nonetheless, they are not provided with the elements characteristic of a heat pump. Moreover, the high temperatures required for firing ceramics entail the need of a heating system for the kiln.

[0035] CN214440639U of Jiangsu Yutong Drying Equipment describes an oven for drying paint working in a closed circuit, without exhausting heat outside, which can be recovered through a heat pump. Said oven can recover organic solvents and humidity evaporated from paint. Said oven comprises a heat pump that is used for energy saving, but which does not recover energy from the air exhausted in the environment, as there is no air exhausted in the environment.

[0036] WO2019140862A1 of Guangzhou Hengxinchuangzhan Tech, describes an energy-saving tunnel oven provided with a heat pump, wherein the exhaust recovers energy through a heat exchanger and not through the heat pump, which is used only as a supplementary system for heating or cooling. [0037] CN109569989A of University Tongji describes a drying system for coating lithium batteries, wherein a heat pump recovers energy from the environment, while an air/air exchanger placed downstream the heat pump further heats the air pre-heated by the heat pump.

[0038] EP3767215B1 of Wienerberger AG describes a dryer and a kiln for producing ceramics, wherein exhaust gases are recovered, and through an absorption heat pump, having a different cycle from a compressor heat pump, a heating fluid is produced and sent to the dryer. The air exhausted from the oven, through an intermediate heat exchanger, heats water that is sent to the evaporator of the heat pump; in the heat pump, through the absorption process, water with a higher temperature is produced in the circuit of the condenser, which is sent to heat exchangers placed in the kiln in order to produce hot air in the kiln. The temperatures at play are quite high: the kiln works at 750- 1200°C, while the dryer works at 80-120°C, which require to use other energy sources in addition to the heat pump, in order to obtain the high temperatures required for firing ceramics. In this document, the heat pump is an absorption heat pump which, differently from compressor heat pumps, works without the use of a compressor, exploiting the available high temperatures in order to increase the temperature of the refrigerant fluid and of the absorbing fluid of the heat pump.

[0039] WO2017158550A1 of the same applicant describes the functioning of vertical multilevel ovens, which typically comprise a plurality of trays superimposed in a plurality of adjacent vertical stacks contained inside transit vertical chambers, along which said trays are translated through lifting chain provided so that said trays follow a closed meandering path.

[0040] CN210725526U of Yancheng Tianyue Xiafeng Electronic Tech describes a system for drying circuit boards which does not take and does not exhaust air from/into the environment. The closed system for recirculating air has the aim of condensing the substances evaporated during the baking of circuit boards and heating the recirculated air again.

[0041] US4173924A of Schwitzer Industrial Corporation describes a paint spray booth for painting cars comprising a heat pump. Said heat pump is used for conditioning the air taken from the environment, heating or cooling air according to the season working of said booth, so as to always have air having constant temperature (62-75°F) and humidity inside said spray booth. Said temperatures are significantly lower than drying temperatures, while the heat pump plays the role of a conditioning group with inversion of the cycle between summer (when it cools) and winter (when it heats).

[0042] EP3117906A1 of Zachodniopomorski Univ. Tech. W Szczecinie describes a spray booth with heat recovery comprising a heat pump, which further comprises heat exchangers and heating systems.

[0043] CN109682206A of Fujian Ronghua Science and Tech CO LTD describes a furnace body for polymerizing lithium iron phosphate in the field of battery production. The heating and cooling system comprises an air heat pump. In this case, the furnace environment is filled with an inert gas for a process with hot gas wherein there is not recirculation, but replacement of the oxygen in the drying chamber with pre-heated nitrogen through a heat pump, keeping the furnace closed at its ingress and egress. Once the furnace is opened, the gas must be replaced. The furnace works in batch, not in a continuous way. There is no hint of the use of a heat pump also for the cooling, and the heat pump is simply used as a replacement of electric heaters.

[0044] The ovens for drying panels and/or components presently on the market do not provide the recovery of the heat accumulated by the pieces to be dried and successively cooled, which is dispersed during their cooling.

[0045] In the known art, hot air produced through an air/water exchanger, an electric battery, etc. is used to transfer heat to the painted pieces and to the paint itself in order to dry it. This air, in order to save energy, is generally recirculated by the oven to the heat exchanger through a fan. Only a limited portion of exhaust air is discharged outside said oven. Indicatively, if between oven and heat exchanger 12,000 m³/h of air circulate, about 1/5 is exhausted outside the oven in order to remove the drying products (solvents, water, VOCs). The pieces to be dried, which are heated through the drying process, are successively cooled, generally using environmental air.

[0046] In a tunnel oven or in a vertical multilevel oven according to the known art, the use of the supplied energy (100%) can be schematized as follows: a. about 2% for supplying the conveying system for pieces; b. about 8% for supplying the fans providing the circulation of air in the oven (taking air from environment, exhausting air into environment, and recirculation of air inside said oven); c. about 90% for heating the air used for drying/flashing off pieces and where necessary for cooling the air needed for cooling pieces, if required according to the temperature of the environment.

[0047] The portion c, i.e. the energy supplied for heating, is largely predominant with respect to the portions a and b, that in the following will not be considered.

[0048] The portion c of energy carries out different tasks in the oven: i. Heating paint in order to evaporate solvents and activate the chemical reaction of paint crosslinking; ii. Heating pieces; iii. Heating the inside of the oven, compensating, when fully operational, for heat dispersions both of the walls and of piece inlet and outlet; iv. Heating the air that is reinserted into the oven in order to compensate for the hot air containing solvents that is exhausted outside the oven.

[0049] The first effect is desired, the second and third effects are not desired, but are inherent and inevitable to the functioning of the oven. In the field of application of the present invention, in terms of energy the fourth effect is analogous to the sum of the first three effects, when the oven is fully operational.

[0050] In the ovens according to the present invention, which are ovens preferably working in continuous, and therefore communicating with the environment through piece inlet and outlet, heat dispersion due to the air exhausted in the environment and to the ingress and egress of pieces is very high. In fact, said ovens need to work under a light depression with respect to the outside environment, in order to prevent the leakage of VOCs and heat into the working environment; this entails the exhaust of a hot air flow in order to allow the entry of environment air having a cooler temperature through the inlet and outlet of pieces. Moreover, the need of removing VOCs from the inside of the oven must be considered, in order to prevent potentially explosive concentrations or inhibiting paint drying; therefore, the oven needs to exhaust hot air, exhausting with it also an important quantity of thermal energy.

[0051] Aim of the present invention is providing a process performed by at least two one-level or multi-level tunnels arranged in line or by at least two vertical chambers of a vertical multilevel oven arranged one after the other for drying and subsequently cooling chemical compounds applied on pieces, allowing a more efficient and therefore cheaper management of the energy, than the ovens presently on the market.

[0052] This object is achieved by apparatuses and a method having the features of the independent claims. Advantageous embodiments and refinements are specified in claims dependent thereon.

[0053] The present invention provides ovens wherein the energy used by the tunnel oven or vertical multilevel oven for flashing off and drying pieces is the energy (portion c) supplied to the compressor of the heat pump. Obviously supplying energy for the conveying of pieces (portion a) and the working of fans (portion b) remains necessary, but such energy is not different in the ovens according to the present invention in comparison with known art ovens. [0054] Advantageously, the heat pump provides thermal energy to the oven in an alternative way with respect to other heat sources.

[0055] In the present invention, the consequence of the fourth effect, i.e. the need to exhaust hot air into the environment, is exploited to recover thermal energy, optimizing the working of the process and making it very efficient from the energy point of view.

[0056] In the field of application of the present invention, recovering and reusing the energy otherwise exhausted outside, increasing it with the contribution of energy by the compressor, makes the system very efficient.

[0057] The oven is progressively heated by the heat pump, that thanks to the contribution of energy of the compressor, transfers into the oven a quantity of thermal energy that is larger than the thermal energy recovered from the air exhausted from the oven. This energy is initially provided by the compressor only, which starts to heat the air circulating in the oven; initially, said air is at the temperature of the environment. Progressively the exhaust air heats up; the thermal energy provided by the compressor sums up with the thermal energy recovered by the exhausted air, increasing the oven temperature up to reaching and maintaining the oven working temperature. The system provides the energy needed for drying paint, for heating pieces and for compensating for the heat dispersions of the oven itself, consuming only the electrical energy needed for supplying the compressor of the heat pump.

[0058] Advantageously, concerning cooling, the air exhausted from the cooling area, after having been cooled down in the heat exchange with the evaporator of the heat pump, can be re-inserted in the cooling area again.

[0059] In an embodiment, when switched on, the oven that is at the temperature of the environment, is empty, i.e. does not contain pieces to be dried. Once the desired working temperature is reached thanks to the action of the compressor recovering thermal energy from the environment, the painted pieces are inserted into the oven and the paint covering the pieces can start to be dried, and successively the pieces are cooled down.

[0060] In an alternative embodiment, painted pieces are already inside the oven that is at the temperature of the environment when the oven is switched on. The pieces remain still in the oven (in other words, the conveying system is inactive) until the oven reaches the desired drying temperature, thanks to the action of the compressor that recovers thermal energy from the environment. Once the desired working temperature is reached, the conveying system is started and just painted pieces start to be moved in ingress to the oven to be dried and successively cooled down.

[0061] In both cases, when the hot pieces enter into the cooling area, the energy available for drying increases, too. [0062] In its first embodiment with at least two tunnel ovens arranged in series, the first for drying and the second for cooling pieces, the apparatus according to the present invention comprises:

- at least a conveying system, lying on a plane (one-level tunnel) or on a plurality of planes (multi-level tunnel), of painted pieces inside said oven;

- one or more drying chambers (in the form of tunnel), wherein the evaporation of the paint solvent applied to the piece occurs;

- one or more cooling chambers (in the form of tunnel) wherein the cooling of pieces occurs;

- at least one heat pump.

[0063] In its second embodiment in the form of vertical multilevel ovens provided with at least two vertical chambers, the first being a drying chamber and the second a cooling chamber belonging to at least one vertical multilevel oven, a heat pump is used for heating up and optionally cooling down the different vertical chambers so as to perform the desired drying and cooling cycle of pieces.

[0064] According to the present invention, there must be provided at least a drying chamber and at least a cooling chamber.

[0065] In an embodiment, said drying chamber and said cooling chamber belong to the same vertical oven.

[0066] In an embodiment, said drying chamber and said cooling chamber belong to two distinct vertical ovens, the first oven intended for drying and the second oven intended for cooling.

[0067] In an embodiment, said heat pump is functionally placed so as to recover heat from the exhaust/s of the cooling chamber/s and to transfer said heat to the drying chamber/s through a heat pump. It is worth mentioning that just one heat pump may be provided, serving all the drying and cooling chambers of the vertical oven, optionally even the flashing off chamber/s. In an alternative embodiment, there are provided a plurality of heat pumps. [0068] In a more specific embodiment, there are provided different variants: in the preferred embodiment shown in Figures 7-14, the vertical oven comprises four chambers and four stacks. In other embodiments, the oven is provided with a multiple of two chambers and two stacks (e.g., two chambers and two stacks, or six chambers and six stacks). Alternatively, the vertical oven is provided with three chambers and two stacks, wherein the central chamber is empty.

[0069] According to a further feature, the tunnel oven or vertical multilevel oven is provided in combination with a control unit executing a control program, having a man-machine interface for the input of commands or data, and for visualizing information about the thermal treatment process, which control unit controls the tray transfer devices according to the known art.

[0070] It is worth mentioning that in the present invention there are provided heat transfers between two, optionally three, fluids:

1) a first fluid circulating inside the heat pump, that is a refrigerant fluid chosen from the manufacturer of the heat pump (a heat pump is a commercial object that is bought and added to the plant);

2) a second fluid, that is the drying fluid and/or the cooling fluid circulating inside the oven, in most cases air, but possibly an inert gas;

3) an optional third intermediate fluid for transferring the heat released by the condenser of the heat pump to the drying fluid through heat transfer between said intermediate fluid and said drying fluid and/or for transferring the heat from the drying fluid to the evaporator with a different circuit; said intermediate fluid is preferably water, with which thermal exchanges occur in the air/water, water/water, water/air embodiments. The first term refers to the evaporator of the heat pump and the second term to the condenser. Said water is employed as means for transmitting heat from the first to the second fluid and vice versa.

[0071] In the heat pump, both the condenser and the evaporator transfer heat with - the cooling fluid and/or drying fluid;

- the environmental air to be introduced as an addition to the drying fluid or cooling fluid re-entered in the oven;

- optionally the intermediate fluid, generally water, when present.

[0072] According to the present invention, a hot fluid, preferably hot air, is used, produced preferably through an exchanger supplied with hot water by the heat pump, in order to transfer heat to the painted pieces and to the paint itself to dry it. In order to save energy, this drying fluid is generally partially recirculated from the chamber to the heat exchanger through a fan, like in the known art.

[0073] According to the present invention, a cooling fluid is used, preferably air, in order to remove heat from painted and dried pieces, i.e. to cool them down. According to the temperature of the environment, cooling or heating the environmental air might be necessary, as explained above.

[0074] In an embodiment, the heat pump can advantageously produce a hotter fluid used in the drying chamber, and a cooler fluid used in the cooling chamber.

[0075] In an embodiment, the exhaust cooling fluid and/or drying fluid flow exhausted outside the oven is opportunely mixed with air coming from the environment having the temperature of the environment, so as to allow the working of the heat pump in a more ideal temperature range (heat pumps work better with small temperature differences between evaporator and condenser), and, at the same time, the recovery of energy even from the environmental air, increasing the performance of the oven.

[0076] Heat pumps allow to heat water up to 70-80°C, which is a temperature generally sufficient to allow the drying of a wide variety of paints, both solvent-based paints and water-based paints. In the known art, traditionally there is provided a water heater that it is used to warm the drying fluid (typically air), that enters into contact with the pieces during the drying process. Said water is the intermediate fluid, that can be convenient in some conditions (see further).

[0077] Nonetheless, according to the present invention, it is possible to dispense with the generation of hot water, used as an intermediate fluid for the cooling/heating of the cooling fluid and/or the drying fluid, proceeding directly to the cooling/heating of the cooling fluid and/or the drying fluid, by using a direct heat exchanger.

[0078] With reference to the structure of heat pumps, in their most general form and as previously indicated, heat pumps comprise a refrigerant fluid that is circulated between an evaporator and a condenser, which works according to a thermal cycle configured so that, in the present application, condenser and evaporator release and collect, respectively, thermal energy into and from the cooling fluid and/or the drying fluid. By configuring evaporator and condenser as heat exchangers, they can work so as to recover heat from, and release heat to, a cooling fluid and/or a drying fluid or an intermediate fluid with which they enter into thermal contact, thanks to their configuration as heat exchangers.

[0079] According to the present invention, the heat removed from the pieces by the cooling fluid during the cooling step is exploited by the heat pump, so as to recover said heat in order to heat the drying fluid according to the typical process of heat pumps.

[0080] In an embodiment (air/water), the heat transfer occurs through the condenser and the evaporator of the heat pump, wherein the evaporator exchanges directly with the exhaust cooling fluid recovering heat, while the condenser transfers heat with the intermediate fluid (water), releasing heat to the same. The heat recovered from the cooling fluid is sent to the drying chamber. This embodiment allows to obtain an accurate adjustment of the temperature of the drying fluid, thanks to the presence of the intermediate fluid, which is provided with a significant thermal inertia. Moreover, such solution is suitable also for providing a retrofit for ovens already installed in a production line, typically already provided with water heat exchanger supplied by a water heater.

[0081] In an embodiment (air/air), the heat transfer occurs between the condenser and the evaporator of the heat pump, respectively: the condenser heats directly the drying fluid of the oven, while the evaporator recovers directly the heat from the cooling fluid that crossed the cooling chamber, at its exhaust, through an air heat exchanger. This embodiment is the most efficient from the thermodynamic point of view, in that there are not provided intermediate fluids for heat transfer, but it is more complex from the point of view of the configuration of the heat pump, which must be integrated in the oven and is of wider dimensions.

[0082] In an embodiment (water/water), the heat transfer occurs between the condenser and the evaporator of the heat pump, two fluids and a circuit for each of them (water), that successively supply oven heat exchangers with one of said fluids, that is water. The heat of the cooling fluid is recovered and sent to the drying chamber. In this embodiment, the solution is less efficient from the energy point of view, but from the plant point of view is more flexible for positioning and use. This embodiment is particularly convenient in the case of just one heat pump connected to a plurality of drying tunnels and cooling tunnels, even placed at a distance from each other, and allows to obtain a cold intermediate fluid circulating in the air treatment group of cooling chamber/s, increasing the performance of the cooling.

[0083] In a further embodiment (water/air), the heat transfer occurs between the condenser and the evaporator of the heat pump, respectively; the condenser directly heats the drying fluid of the oven and the evaporator recovers the heat of the cooling fluid at the exhaust through a water exchanger. [0084] In the first embodiment with at least two tunnel ovens placed in series, in a preferred embodiment, the oven is supplied with the pieces to be dried in a continuous way.

[0085] In the first embodiment with at least two tunnel ovens placed in series, in an embodiment, the oven is supplied in a discontinuous way. In an embodiment, the oven is provided with mobile shutters in ingress and egress, that are opened/closed in order to allow the ingress/egress of painted pieces, so as to form an intermittently closed chamber, capable to maintain the desired temperature inside the drying tunnel.

[0086] In an alternative (not shown) embodiment, even the air recirculated inside the oven can pass through the condenser of the heat pump.

[0087] According to the method of the present invention in both the embodiments in the form of tunnel ovens or vertical multilevel ovens, said heat pump is placed downstream the air exhaust of the cooling chamber into the environment of the oven, so as to recover the heat that normally is released outside the cooling chamber. In an embodiment, the method comprises mixing the exhaust cooling fluid exhausted from the cooling chamber with a suitable quantity of drying fluid exhausted by the drying chamber. This allows to bring the mix of said two fluids successively coming into contact with the heat pump to a temperature allowing the best thermal performance of the oven according to the present invention.

[0088] In an embodiment of both tunnel ovens and vertical multilevel ovens, the method comprises mixing the cooling fluid exhausted from the cooling chamber with a suitable quantity of environmental air. This allows to bring the mix resulting from said two fluids, that comes into contact with the heat pump, at a temperature allowing the best thermal performance of the oven according to the present invention.

[0089] In another embodiment, both in the tunnel ovens and in the vertical multilevel ovens, in the cooling area the whole or a part of the air exhausted in the cooling area itself, after having been cooled in the heat exchange with the evaporator of the heat pump, can be recirculated and be re-inserted in the cooling chamber. This embodiment is particularly advantageous when the temperature of the environment is higher than the temperature of the cooling fluid.

[0090] The first advantage of the present invention consists in recovering the heat removed from the pieces during their cooling to heat up the drying fluid, while according to the known art said heat is simply dispersed in the environment.

[0091] The second advantage of the present invention, in some of the embodiments, consists in the possibility of using the heat pump in order to heat the drying fluid and to cool down the cooling fluid.

[0092] A third advantage of the present invention consists in the reduction of the energy consumption connected to drying and cooling operations, with the possibility of replacing the traditional gas boiler with a heat pump working with electric energy.

[0093] A fourth advantage of the present invention consists in that, when energy comes from renewable sources, the performance of the system is about thrice that of traditional systems (gas boiler).

[0094] The two above-quoted advantage translate into a fifth advantage: lack of impact from the point of view of greenhouse gases.

[0095] A sixth advantage is that, according to the known art, there must be provided a boiler for generating hot water, and sometimes a chiller for producing cold water, which hot and cold water must be supplied to the points of use through piping and pumps. With the present invention, the plant can be markedly simplified, in that the heat pump can be installed directly on a drying chamber and cooling chamber or a group of adjacent drying and cooling chambers with a simplified dedicated plant, requiring only electrical supply.

[0096] A seventh advantage is a better upgradability of the system with respect to a traditional boiler and/or chiller that, once its thermal capacity is exceeded, e.g. because other drying and/or cooling chambers were added to the plant, would require the replacement of the boiler or of the chiller. With the present invention, adding a heat pump is sufficient.

[0097] Further advantages and properties of the present invention are disclosed in the following description, in which exemplary embodiments of the present invention are explained in detail on the basis of the drawings: Figure 1 First embodiment, two tunnels placed in series according to the known art, lateral view;

Figure 2 First embodiment, two tunnels placed in series according to the present invention, air/water embodiment, lateral view;

Figure 3 First embodiment, two tunnels placed in series according to the present invention, air/air embodiment, lateral view;

Figure 4 First embodiment, two tunnels placed in series according to the present invention, water/water embodiment, lateral view;

Figure 5 First embodiment, two tunnels placed in series according to the present invention, air/water embodiment, recovering heat also from the drying tunnel, lateral view;

Figure 6 First embodiment, two tunnels placed in series according to the present invention, water/water embodiment, recovering heat also from the drying tunnel, lateral view.

Figure 7 Second embodiment, known art vertical oven provided with four chambers and four stacks, axonometric view;

Figure 8 Second embodiment, known art vertical oven provided with four chambers and four stacks, axonometric view;

Figures 9A, 9B Second embodiment, drying chamber and cooling chamber according to known art, longitudinal section;

Figure 10 Second embodiment, drying chamber and cooling chamber according to the present invention, longitudinal section, air/water embodiment;

Figure 11 Second embodiment, drying chamber and cooling chamber according to the present invention, longitudinal section, air/air embodiment;

Figure 12 Second embodiment, drying chamber and cooling chamber according to the present invention, longitudinal section, water/water embodiment;

Figure 13 Second embodiment, drying chamber and cooling chamber with recovery of the drying exhaust according to the present invention, longitudinal section, air/water embodiment;

Figure 14 Second embodiment, drying chamber and cooling chamber with recovery of the drying exhaust according to the present invention, longitudinal section, second water/water embodiment.

[0098] Although not shown in the Figures, in practice the ovens according to the known art and the ovens according to the present invention are typically part of a painting line comprising a plurality of apparatuses of different kind placed in series. E.g., upstream the oven there will be placed at least an apparatus capable of painting said pieces with a painting product. Said painting can be performed e.g. through a spraying machine, or a curtain coater or a roller apparatus, etc. The painting line might comprise a plurality of apparatuses applying the painting product and a plurality of ovens placed in series. Downstream the oven there can be placed a storage or an apparatus capable of sorting and/or package said pieces. All this is well known in the art.

[0099] The shown embodiments are meant as examples of the different and various possibilities of plant configuration, and in particular of the drying and cooling ovens according to the present invention, as well as of its possible multiple operating modes. Nothing in this specification should be considered as limiting the scope of the present invention, in that the wide variety of embodiments does not allow a detailed, specific description of the present invention, while the embodiments are determined by the requirements of treatment of the products to be dried, of their shape and dimension features, and of the geographical location of the plant.

[0100] In the Description hereunder, Figures 1-6 show the first embodiment of the present invention, i.e. tunnel ovens, while Figures 7-14 show the second embodiment, i.e. vertical multilevel ovens. It is worth noting that in Figures 1-6 the drying chamber 6 and the cooling chamber 66 take the shape of a tunnel, while in Figures 7-14 the drying chamber 6 and the cooling chamber 6’ take the shape of a vertical chamber containing a stack of trays and adjacent to at least another vertical chamber. From the point of view of the drying process, the aim of the tunnel or of the vertical chamber is the same: maintaining pieces to be dried at the desired temperature for a pre-defined time.

[0101] Concerning the first embodiment with at least two tunnel ovens arranged in series, it is also worth mentioning that Figures show just one drying tunnel and one cooling tunnel arranged in series. Actually, according to the desired processing, one or more drying tunnels or one or more cooling tunnels might be arranged in series (e.g., two drying tunnels and one cooling tunnel). Moreover, Figures 1-6 show always one-level drying and cooling tunnels, but nothing prevents providing multi-level tunnels instead. E.g., a typical configuration is a multi-level drying tunnel followed by a one-level cooling tunnel.

[0102] Figure 1 shows a lateral view of a one-level oven 1 comprising a one- level drying tunnel chamber 6 and a one-level cooling tunnel chamber 66 arranged in series according to the known art. Each tunnel chamber 6, 66 comprises at least a device 3, 3’ for conveying painted pieces 2 to be dried. Said pieces 2 are preferably painted mainly flat panels of sundry materials (wood and derivatives, fibre cement, glass, plastics, etc.) or painted materials in the form of a continuous sheet wherein one dimension (thickness) is much smaller than the other two; typically, the measures of panels range 100x300x2 mm to 1600x3500x300 mm. Optionally, the pieces might be three- dimensional pieces (having three comparable dimensions) supported, or not supported, by a supporting frame, or even material in a continuous sheet.

[0103] In the oven 1 according to the known art, pieces 2 to be dried are conveyed by at least a known conveying system 3, 3’, preferably in the form of a conveying band or a plurality of rollers. Said pieces 2 are conveyed inside a drying tunnel 6 and successively inside a cooling tunnel 66. The bold black arrows show the conveying direction of the pieces 2 to be dried, while the small black arrows show the flowing direction of drying fluid and of cooling fluid.

[0104] In a known way, in the drying tunnel chamber 6 the hot air used for drying pieces 2, symbolized by small black arrows, circulates in the opposed direction with respect to the supplying direction of pieces 2, symbolized by the bold black arrow. This allows to gradually increase the temperature of said pieces 2, so as to increase the thermal efficiency of the oven. In a known way, in the cooling tunnel chamber 66, the cooling fluid is shown as small black arrows perpendicular to the pieces, in that said fluid is distributed through air curtains (air curtains are sometimes used also for drying tunnel chambers 6). [0105] In the known art, in the drying tunnel chamber 6 a fan 4 blows a drying fluid, e.g. hot air, through a diffuser 5 inside said tunnel chamber 6. Said drying air, that released its heat to the drying pieces 2, is suctioned by an inlet 7 placed at the piece ingress of the drying tunnel 6: a first portion (20-30%) of said air is suctioned by an exhaust fan 8 adjustable in its flow and is exhausted outside (indicated by an arrow 9), in order to remove at least a portion of the solvents of the paint. Said air is typically exhausted outside the oven, and therefore its heat is dispersed in the environment.

[0106] A second portion 12 of the drying air (80-70%) is recirculated through a recirculating channel 10 inside an air treatment group 30 providing recirculation, comprising an inlet for recirculating air 12 and an inlet for air 11 coming from the environment; both are typically provided with an adjustable shutter.

[0107] The sum of the environmental air flow 11 and recirculated air 12 is filtered through a filter 13 and heated through a heat exchanger 14 before reinserting it in the oven through said fan 4. In many cases said heat exchanger 14 is an exchanger using water as working intermediate fluid.

[0108] In the known art, in the cooling tunnel chamber 66 a fan 4’ blows a cooling fluid, e.g. environmental air, through a diffuser 5’ inside said cooling tunnel chamber 66. Said air, that removed the heat released by cooling pieces 2, is suctioned through a fan 8’ that can be adjusted according to season and the temperature of the environment and exhausted outside (indicated by arrow 9’) in order to remove at least a part of the heat released by pieces. The upwards small black arrows represent the flow of hot air suctioned in some areas of the cooling tunnel through the inlet 31’ and the fan 8’. Said air 9’ is typically exhausted outside the plant, and therefore the heat associated to it is dispersed in the environment.

[0109] A portion of the cooling air (0-60%) is recirculated through said inlet 31 ’ inside an air treatment 30’ providing recirculation, comprising an inlet 31 ’ for recirculated air and an inlet for air 11’ coming from the environment; both are typically provided with an adjustable shutter.

[0110] The sum of air flows coming from environment 11’ and recirculated 12’ is filtered through a filter 13’, and optionally cooled down through a heat exchanger 14’ before re-inserting it in the oven through said fan 4’. In many cases, said heat exchanger 14’ is an exchanger using cool water as intermediate fluid.

[0111] In a known way, the oven 1 according to the known art comprises said air treatment groups 30, 30’, in their turn comprising, respectively: an inlet for recirculated air 12, 12’; an inlet for air 11, 11’ coming from the environment; optionally a filter 13, 13’ for filtering the flows of air 11, 11’ and/or 12, 12’ or their mix; optionally a heat exchanger 14, 27’ that can use or not an intermediate fluid; a fan 4, 4’ supplying said flows of air 11, 11’ and/or 12, 12’ and their mix into the drying tunnel chamber 6 or the cooling tunnel chamber 66. It is worth mentioning that in the art it is known providing air treatment groups 30, 30’ showing variations with respect to the above-described composition, without affecting the presented concepts. E.g., the above-described functions can be performed through components arranged in the oven without being aggregated in an air treatment group 30, 30’ that can be identified as a unit. E.g., the fan 4, 4’ might be arranged upstream the filter 13, 13’, and/or the heat exchanger 14, 27’.

[0112] Figure 2 shows an oven 300 provided with a heat pump 15 according to the present invention; this preferred embodiment realizes an air/water exchange.

[0113] Said heat pump, overall indicated with 15, comprises in a known way an evaporator 16, a condenser 18, a compressor 17, an expansion valve 19.

[0114] In said oven 300, which works analogously to the oven 1 according to the known art, the cooling fluid flow 9’, e.g. air, discharged from the exhaust fan 8’, is conveyed through a closed circuit to the heat pump 15, in particular to the evaporator 16, that is configured as a heat exchanger between said cooling fluid and the refrigerant gas of the heat pump. Inside said evaporator 16, the exhaust air flow 9’ releases heat to the refrigerant fluid of the heat pump, being exhausted outside the plant as air flow 23 at a lower temperature than the temperature of the exhaust air flow 9’ at its ingress.

[0115] The refrigerant fluid, that is the working fluid inside the circuit of the heat pump 15, according to its normal cycle, is brought to a higher pressure by the compressor 17, so increasing its temperature. This heat is released from the condenser 18 of the heat pump configured as heat exchanger to an intermediate fluid, preferably hot water, circulating in a circuit 20 by means of a pump 21. Said hot water supplies the heat exchanger 14 of the drying tunnel of the oven 300, while the refrigerant fluid outputting from the condenser of the heat pump through the expansion valve 19 is brought to the evaporator 16 again, at a lower pressure and temperature. Therefore, the heat otherwise dispersed at the exhaust of the cooling tunnel 66 is advantageously employed to heat the drying fluid through the heat pump 15, the circuit 20 and the heat exchanger 14 of the drying tunnel 6 of the oven 300.

[0116] The above-described air-water exchange is the preferred embodiment, but different thermal exchanges can be realized in alternative embodiments.

[0117] Figure 3 shows an alternative embodiment of an air/air oven 301, wherein the cooling fluid flow 9’, preferably air, releases its heat directly to the evaporator 16, while an air flow 24 (corresponding to the air flow 11 of Figures 1 and 2) coming from the environment is heated passing through the condenser 18 configured as a heat exchanger, before entering into the air treatment group 30 through an air duct 25 and mixed with the recirculated air flow 12, dispensing with the hot water circuit 20, the heat exchanger 14 and the recirculating pump 21 according to the embodiment shown in Figure 2. Therefore, the heat otherwise dispersed at the exhaust of the cooling tunnel 66 is advantageously employed to heat the drying fluid of the drying tunnel 6 of the oven 301. This embodiment has the least requirements from the plant point of view.

[0118] Figure 4 shows an alternative embodiment of a water/water oven 302, wherein there is provided an exchange intermediate fluid, e.g. water, that is circulated in heat exchangers 14 and 27’ through pumps 26’ and 21, wherein the cooling fluid flows 9’ and 12’ released from the cooling tunnel release their heat to the intermediate fluid, i.e. water, in the heat exchanger 27’. Said intermediate fluid releases heat to the evaporator 16 configured as a heat exchanger and connected through a closed circuit 28’ with a recirculation pump 26’, while the condenser 18 is the heat exchanger with an intermediate fluid, e.g. water, to which releases the heat of the refrigerant fluid of the heat pump 15, heat that is transferred to the heat exchanger 14. In its turn, the heat exchanger 14 transfers heat to the mix of environmental air 11 taken from the environment and recirculation fluid 12, i.e. to the portion of drying fluid intended to be re-inserted in the oven through the air treatment group 30 passing in the heat exchanger 14 of said treatment group 30. Therefore, the heat otherwise dispersed at the exhaust 9’ of the cooling tunnel 66 is advantageously employed to heat the drying fluid of the drying tunnel 6 of the oven 302. Moreover, it allows to cool the mix of airflows 9’ and 12’ before reinserting them in the cooling tunnel. In this configuration, the fan 8’ might be superfluous in that all the airflow could occur through airflow 12’, but is nonetheless shown because it might be useful for obtaining the aeraulic balance of the cooling tunnel.

[0119] The embodiment of a water/air oven is not represented for simplicity’s sake; here the heat transfer occurs between the condenser and the evaporator of the heat pump, respectively. The condenser directly heats the drying fluid, preferably air, taken from the environment; to it, after having been in thermal contact with the condenser for heating, the portion of drying fluid that crossed the drying tunnel, and was not exhausted from it (recirculated air) is mixed. The evaporator recovers heat from said portion of cooling fluid; this occurs in an indirect way, as the heat of the portion of cooling fluid exhausted from the oven used in order to heat said intermediate fluid, e.g. water, through a water heat exchanger, while said heated water coming out from the heat exchanger is used as intermediate fluid to transfer heat to the refrigerant fluid of the heat pump through the evaporator configured as heat exchanger.

[0120] Indicatively, the temperature of the air used for drying pieces 2 is about 60-70°C; the temperature of cooling exhaust air 9’ coming from the fan 8’ is about 10°C higher than the temperature of the environment, unless a chiller is provided.

[0121] In two even more performing embodiments, the heat pump 15 is supplied, in addition to the cooling fluid, with the exhaust portion of the drying fluid 9 of the drying tunnel 6, too, further increasing the recovered energy.

[0122] In Figure 5 an oven 303 is shown, comprising an air/water system recovering heat from the drying exhaust, by mixing the exhaust air 9 of the drying tunnel 6 with the exhaust flow 9’ of the cooling tunnel 66 before channelling them to the evaporator 16, and exhausting their mix as airflow 23 at a temperature lower than their ingress temperature.

[0123] In Figure 6 an oven 304 is shown, comprising a water/water system recovering heat from the drying exhaust, too, using two intermediate fluids, through the heat exchanger 27, the water circuit 28 and the pump 26, and from the cooling tunnel through the heat exchanger 27’, the circuit 28’ and the pump 26’, the two intermediate fluids being sent to the evaporator 16 in order to release heat.

[0124] In this case, too, the energy of the drying fluid can be recovered by providing air/air and water/air systems that are not shown in Figures for simplicity’s sake, but that work according to the already described principles [0125] According to the method of the present invention, said heat pump 15 is placed so as to recover the heat of cooling tunnel 66 of the oven 300, 301, or 302, optionally with the interposition of one or more heat exchangers working with an intermediate fluid, so as to recover the heat normally released outside the cooling tunnel through the cooling fluid before it is exhausted outside. Said heat is instead used to heat the drying fluid.

[0126] In an even more performing embodiment 303, 304, to the heat recovered from the cooling fluid, the heat recovered from the portion of drying fluid exhausted from the drying tunnel is added.

[0127] In an embodiment applicable to the ovens 300, 301, 303 according to the present invention, the method comprises the mixing of the exhaust air 9’ exhausted from the cooling tunnel, with a suitable quantity of air at the temperature of the environment (indicatively 15°C or higher according to the season) through a flow 22 of environmental air taken upstream the evaporator 16. This allows to bring the air coming into contact with the heat pump to a temperature allowing the best thermal performance of the oven according to the present invention. The energy contribution of the air flow 22 is useful for increasing the total energy transmitted through the heat pump to the condenser 18. E.g., when air 22 is taken from environment, having a temperature of 20°C, and the evaporator 16 is working at a temperature of the refrigerant fluid of 10°C, the difference of temperature between the two fluids allows a transmission of energy proportional to the flow of the fluid 22 coming from the environment.

[0128] Concerning the second embodiment, providing at least a drying vertical chamber and a cooling vertical chamber placed in series with respect to the conveying of pieces and belonging to at least one vertical multilevel oven, providing vertical ovens with different numbers of chambers and stacks, generally in an even number (two chambers and two stacks, six chambers and six stacks, etc.) is known in the art. Such vertical ovens are not shown in the Figures, but they are well known and their working is comparable to that of the four chambers/four stack oven shown in Figures 7-14. Another typical embodiment is the three chambers, two stack vertical oven.

[0129] Figure 7 shows a typical oven 61 having four chambers 71, 72, 73, 74 and four stacks 81, 82, 83, 84 according to the known art. When a tray 3 reaches the top of an ascending stack 71 or 73, it is shifted on the top of a descending stack 72 or 74 through suitable devices for horizontal shifting. Through similar devices, at the end of the descending stack 72, 74, the trays 3 are shifted to the base of the ascending stack 73, 71 to be collected by the relative lifting chain. In this way, each tray follows a complete meandering path through the oven, as shown by the arrows, during which the panels, arranged on the trays, dry.

[0130] Figure 8 shows again an oven 61 according to the known art, comprising the said plurality of trays 3, which following the path shown in Figure 1, perform a drying cycle. The small arrows in Figure 2 show the direction of the drying fluid (typically air).

[0131] Preferably, in the first chamber 71 the flashing off of (not shown) pieces, supported by trays 3, occurs; in the two central chambers 72 and 73 the drying of pieces occurs; while in the last chamber 74 the cooling off of the pieces occurs, before their egress from the oven. [0132] Figure 9A shows a longitudinal section of the drying chamber 72 of the oven 61 according to the known art. In the drying chambers 72, 73 there is provided a known air treatment group 30 that, through an inlet, takes air 11 from the environment, while it recirculates air 12 taken from the chamber itself through a recirculating channel 10. Said drying fluid, typically air, is filtered through a filter 13, heated by a heat exchanger 14 and sent by a fan 4 in a distribution channel 5 sending it among the trays 3 on pieces 2, according to the path indicated by the small white arrows.

[0133] Figure 9B shows a longitudinal section of the cooling chamber 74 of the oven 61 according to the known art. In the cooling chamber 74 there is provided a known air treatment group 30’ that, through an inlet, takes air 11’ from the environment, while it optionally recirculates air taken from the oven itself through an optional recirculating channel 10’. Said cooling fluid, typically air, is filtered through a filter 13’, possibly cooled by a heat exchanger 27’ and sent by a fan 4’ into a distribution channel 5’ distributing it among the trays 3 on pieces 2, according to the path indicated by the small black arrows. Said cooling fluid flow is taken from the suction channel 7’ thanks to a fan 8’ or to the depression generated by the fan 4’ through the channel 10’ itself. Therefore, said fan 8’ can be optional, but is shown in order to ease the understanding of the system. In fact, in the known art, there may be provided a different configuration of the air treatment group 30’, allowing to generate an air flow 9’ thanks to the pressure generated by the fan 4’, without need of said fan 8’. From the exhaust outlet, a percentage of air 9’ (typically 100-40%) is exhausted, in order to allow air renewal for cooling the pieces 2.

[0134] In a known way, the oven 61 according to the known art comprises said air treatment groups 30, 30’, in their turn comprising, respectively:

- an inlet for recirculated air 12, 12’;

- an inlet for air 11, 11’ coming from the environment;

- optionally a filter 13, 13’ for filtering the flows of air 11, 11’ and/or 12, 12’ or their mix;

- optionally a heat exchanger 14, 27’ that can use or not an intermediate fluid;

- a fan 4, 4’ supplying said flow of air 11, 11’ and/or 12, 12’ or their mix into the drying chamber 6 or the cooling chamber 6’.

[0135] It is worth mentioning that in the art it is known providing air treatment groups 30, 30’ showing variations with respect to the above-described composition, without affecting the presented concepts. E.g., the abovedescribed functions can be performed through components arranged in the oven without being aggregated in an air treatment group 30, 30’ that can be identified as a unit. E.g., the fan 4, 4’ might be arranged upstream the filter 13, 13’, and/or the heat exchanger 14, 27’.

[0136] The above description refers to the working of the known art oven 61. [0137] Figure 10 shows an oven 400 according to the present invention.

[0138] The oven 400 comprises a system for treating air schematized as a unit 30, which provides air recirculation, comprising an inlet for recirculated air 12 and an inlet for air 11 coming from the environment; both inlets are typically provided with a shutter.

[0139] The mix of the airflows of recirculated air 12 coming from channel 10 and of the replenishment air 11 is filtered through a filter 13 and heated through a heat exchanger 14 before being reintroduced in the oven through the fan 4. In many cases, said heat exchanger 14 is a heat exchanger using water as intermediate working fluid.

[0140] According to an embodiment of the present invention, to the oven according to the known art, at least a heat pump 15 is added, so as to recover the heat otherwise dispersed in the environment by the exhaust airflow 9.

[0141] Said heat pump, overall indicated with 15, comprises in a known way an evaporator 16, a condenser 18, a compressor 17, an expansion valve 19.

[0142] In particular, in Figure 10 an oven 400 according to the present invention is shown in its first air/water embodiment, wherein the drying fluid exhaust flow 9’ of the cooling chamber 74 coming from the fan 8’, is conveyed through a closed air duct to the heat pump 15 to release its heat to the evaporator 16; optionally air 22 taken from the environment may be added, so exhausting air 23 with a temperature lower than that of the air entering into the heat pump 15. According to the cycle of the heat pump 15, the refrigerant fluid of the heat pump heated by the heat released by the exhaust air 9 to the evaporator 16 of the pump, through the compressor 17 of the heat pump, is brought to a higher pressure and temperature, and through the condenser 18 acting as a heat exchanger, releases heat to an intermediate fluid (preferably water) in a circuit 20, that by means of a pump 21 brings the heated intermediate fluid to the heat exchanger 14 of the drying chamber 72, so recovering a good portion of the heat otherwise dispersed. Through the expansion valve 19, the refrigerant fluid cooled off in the condenser 18 is brought back to a lower pressure and sent to the evaporator 16 again.

[0143] The above-described air-water exchange is the preferred embodiment, but different thermal exchanges can be realized in alternative embodiments.

[0144] Figure 11 shows an alternative embodiment of an air/air oven 401, wherein the cooling fluid exhaust flow 9’ of the cooling chamber 74, preferably air, releases its heat directly to the evaporator 16, while an air flow 24 coming from the environment is heated passing through the condenser 18 configured as a heat exchanger, before entering into the air treatment group 30 through an air duct 25 and mixed with an air flow 12, dispensing with the hot water circuit 20, the heat exchanger 14 and the recirculating pump 21 according to the embodiments shown in the preceding Figures. This embodiment has the least requirements from the plant point of view.

[0145] Figure 12 shows an alternative embodiment of a water/water oven 402, wherein there is provided an exchange intermediate fluid, e.g. water, circulating in two different circuits 20 and 28’ through pumps 21 and 26’ in heat exchangers 14 and 27’, wherein the recirculated cooling fluid flow 12’ released from the cooling chamber 74 releases its heat to the intermediate fluid, i.e. water, in the heat exchanger 27’ . Said intermediate fluid releases the heat to the evaporator 16 configured as a heat exchanger and through the pump 17 of the heat pump transfers heat to the condenser 18 in its turn working as heat exchanger connected to circuit 20 for an intermediate fluid, e.g. water, that through the pump 21 circulates the intermediate fluid toward the heat exchanger 14 to heat the drying fluid inside the drying chamber 72.

[0146] The water/air embodiment is not shown for simplicity’s sake; here the heat transfer occurs between the condenser and the evaporator of the heat pump, respectively. The condenser directly heats the drying fluid, preferably air, taken from the environment; to it, after having been in thermal contact with the condenser for heating, the portion of drying fluid that crossed the drying chamber, and was not exhausted from it (recirculated air) is mixed. The evaporator recovers heat from said portion of cooling fluid exhausted from the cooling chamber; this occurs in an indirect way, as the heat subtracted from the pieces from the cooling fluid exhausted is used to heat said intermediate fluid, e.g. water, through a heat exchanger, while said heated water coming out from the heat exchanger is used as intermediate fluid to transfer heat to the refrigerant fluid of the heat pump through the evaporator configured as heat exchanger.

[0147] Indicatively, the temperature of the air used for drying pieces 2 is about 60-70°C; the temperature of cooling exhaust air 9’ coming from the fan 8’ is about 10°C higher than the temperature of the environment, unless a chiller is provided.

[0148] In two even more performing embodiments, the heat pump 15 is supplied, in addition to the cooling fluid 9’ exhausted from the cooling chamber 74, with the exhaust portion of the drying fluid 9 of the drying chamber 72 too, further increasing the recovered energy.

[0149] In Figure 13 an oven 403 is shown, comprising an air/water system recovering heat from the drying exhaust, by mixing the exhaust air 9 of the drying chamber 72 with the exhaust flow 9’ of the cooling chamber 74 before channelling them to the evaporator 16, and exhausting their mix as airflow 23 at a temperature lower than their ingress temperature.

[0150] In Figure 14, an oven 404 is shown, comprising a water/water system recovering heat from the drying exhaust of the drying chamber 72, too, using two intermediate fluids through two circuits, the first circuit comprising the heat exchanger 27, the circuit 28 and the pump 26, and the second circuit comprising the cooling chamber 74 the heat exchanger 27’, the circuit 28’ and the pump 26’, the two intermediate fluids being sent to the evaporator 16 in order to release heat.

[0151] In this case, too, the energy of the drying fluid of the drying chamber 72 can be recovered by providing air/air and water/air systems that are not shown in Figures for simplicity’s sake, but that work according to the already described principles.

[0152] According to the method of the present invention, said heat pump 15 is placed so as to recover the heat of cooling chamber 74 of the oven 400, 401, or 402, optionally with the interposition of one or more heat exchangers working with an intermediate fluid, so as to recover the heat normally released outside the cooling chamber 74 through the cooling fluid before it is exhausted outside. Said heat is instead used to heat up the drying fluid of the drying chamber 72.

[0153] In an even more performing embodiment 403, 404, to the heat recovered from the cooling fluid, the heat recovered from the portion of drying fluid exhausted from the drying chamber is added.

[0154] In an embodiment applicable to the ovens 400, 401, 403 according to the present invention, the method comprises the mixing of the exhaust air 9’ exhausted from the cooling chamber, with a suitable quantity of air at the temperature of the environment (indicatively 15°C or higher according to the season) through a flow 22 of environmental air taken upstream the evaporator. This allows to bring the air coming into contact with the heat pump to a temperature allowing the best thermal performance of the oven according to the present invention. The energy contribution of the air flow 22 is useful for increasing the total energy transmitted through the heat pump to the condenser 18. E.g., when air 22 is taken from environment, having a temperature of 20°C, and the evaporator 16 is working at a temperature of the refrigerant fluid of 10°C, the difference of temperature between the two fluids allows a transmission of energy proportional to the flow of the fluid 22 coming from the environment.

1 tunnel oven according to the known art

2 pieces

3 conveying system

4 recirculating fan

5 diffuser

6 drying chamber

7 inlet

8 exhaust fan

9 exhaust air flow

10 recirculating channel

11 replenishing air flow

12 recirculated air flow

13 filter

14 heat exchanger

15 heat pump

16 heat pump evaporator

17 heat pump compressor

18 heat pump condenser

19 heat pump expansion valve

20 intermediate fluid circuit

21 recirculating pump

22 air from the environment

23 cooler discharged air

24 replenishment air flow

25 air duct

26 recirculating pump

27 heat exchanger

28 intermediate fluid circuit

30 air treatment group

31 inlet 61 four chambers, four stacks oven according to known art

71, 72, 73, 74 chambers

81, 82, 83, 84 trays stacks

66 cooling tunnel 300 first embodiment, air/water embodiment

301 first embodiment, air/air embodiment

302 first embodiment, water/water embodiment

303 first embodiment, air/water embodiment with heat recovery from drying tunnel exhaust 304 first embodiment, water/water embodiment with heat recovery from drying tunnel exhaust

400 second embodiment, air/water embodiment

401 second embodiment, air/air embodiment

402 second embodiment, water/water embodiment 403 second embodiment, air/water embodiment with heat recovery from drying chamber exhaust

404 second embodiment, water/water embodiment with heat recovery from drying chamber exhaust

Claims

1) One-level or multi-level tunnel oven (300, 301, 302, 303, 304) for drying/flashing off and cooling superficial treatments like paints or glues applied on pieces (2) comprising in series in this order: at least a drying chamber (6) in the form of a tunnel; at least a cooling chamber (66) in the form of a tunnel; said cooling tunnel (66) optionally comprising a heat exchanger for cooling; said drying tunnel chamber (6) and said cooling tunnel chamber (66) comprising: a. at least a conveying system (3 and/or 3’) for said pieces; b. at least an air treatment group (30, 30’), in its turn comprising:

- an inlet for recirculated air (12, 12’);

- an inlet for air (11, 11 ’) coming from the environment;

- optionally a filter (13, 13’) for filtering the flows of air (11, 11’) coming from the environment and/or recirculating air (12, 12’) or their mix;

- optionally a heat exchanger (14, 27’) that can use or not an intermediate fluid;

- a fan (4, 4’) supplying said flows of air (11, 11’ and/or 12, 12’) or their mix into the drying chamber (6) or the cooling chamber (66); c. optionally an exhaust fan (8, 8’) exhausting a flow (9) of drying fluid or of cooling fluid (9’); d. at least one heat pump (15) comprising: an evaporator (16), a compressor (17), a condenser (18), an expansion valve (19), and a refrigerant fluid, which evaporator (16) and which condenser (18) are configured to transfer thermal energy between the refrigerant fluid of said heat pump and a further gas or liquid fluid; said drying chamber (6) and cooling chamber (66) being functionally connected to at least one said heat pump (15), wherein the drying fluid and the cooling fluid comprise:

- a first portion of air (9, 9’) that is exhausted in the environment;

- optionally a second portion of air (12, 12’) that is recirculated inside the chambers (6, 66), respectively; characterized in that said cooling fluid (9’) is placed in a condition of direct thermal heat transfer, or indirect thermal heat transfer through an intermediate fluid for thermal transfer, with the refrigerant fluid of said heat pump (15) in order to recover its thermal energy before dispersing said cooling fluid in the environment, said thermal energy being recovered through the heat pump in order to heat the drying fluid circulating in the drying tunnel (6).

2) Vertical multilevel oven (400, 401, 402, 403, 404) for drying/flashing off superficial treatments applied on pieces (2) to be dried, transiting inside chambers having the form of vertical chambers (71, 72, 73, 74), said oven comprising in series in this order with respect to the conveying direction of pieces:

- at least a drying vertical chamber (72), and

- at least a cooling chamber (74), optionally comprising at least a heat exchanger (27’) for cooling; said drying vertical chamber (72) and cooling vertical chamber (74) comprising: a. a conveying system of said pieces in the shape of trays (3) for supporting said pieces arranged in at least two stacks (81, 82, 83, 84), said stacks arranged in respective vertical chambers (71, 72, 73, 74), wherein in two adjacent chambers the stacks of trays circulate in opposed directions through suitable vertical and horizontal conveying devices, so that each tray (3) follows a closed meandering path; b. an air treatment group (30, 30’), in its turn comprising:

- an inlet for recirculated air (12, 12’); - an inlet for air (11, 11 ’) coming from the environment;

- a fan 4, 4’ supplying said flows of air (11, 11’ or 12, 12’) or their mix into the drying chamber (72) or the cooling chamber (74); c. optionally an exhaust fan (8, 8’), exhausting a flow (9’) of drying fluid or of cooling fluid (9’); d. at least a heat pump (15) comprising: an evaporator (16), a compressor (17), a condenser (18), an expansion valve (19), and a refrigerant fluid, which evaporator (16) and which condenser (18) are configured to transfer thermal energy between the refrigerant fluid of said heat pump and a further gas or liquid fluid; said drying chamber (72) and cooling chamber (74) being functionally connected to at least one said heat pump (15), wherein the drying fluid and the cooling fluid comprise:

- a first portion of air (9, 9’) that is exhausted in the environment;

- optionally a second portion (12, 12’) of air that is recirculated inside the chambers (72, 74), respectively; optionally said drying fluid (9) and cooling fluid (9’) exchanging thermal energy through the contact with an intermediate fluid, characterized in that said cooling fluid (9’) is placed in a condition of direct thermal heat transfer, or indirect thermal heat transfer through an intermediate fluid for thermal transfer, with the refrigerant fluid of said heat pump (15) in order to recover its thermal energy before dispersing said cooling fluid in the environment, said thermal energy being recovered through the heat pump in order to heat up the drying fluid circulating in the drying chamber (72).

3) One-level or multi-level tunnel oven (303, 304) according to claim 1 or vertical multilevel oven (403, 404) according to claim 2 for drying/flashing off and cooling superficial treatments like paints or glues applied on pieces (2), wherein at least a part of the drying fluid (9) circulating in said drying chamber (6, 72) is channelled directly to the evaporator (16) of the heat pump (15), or indirectly through an air/water heat exchanger (27) and a circuit (28), in order to recover its thermal energy.

4) One-level or multi-level tunnel oven (300, 301, 303) according to claim 1 or 3 or vertical multilevel oven (400, 401, 403) according to claim 2 or 3 for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2), wherein the exhaust cooling fluid (9’) exhausted from the oven is opportunely mixed with environmental air (22) before being exhausted, said mix being placed in a condition of heat transfer at the evaporator (16) configured as a direct or indirect heat exchanger between said mix and the refrigerant fluid of said heat pump, allowing the evaporator (16) of the heat pump to have a higher energy content to be transmitted to the condenser (18) through the process of the heat pump, so increasing the performance of the system.

5) One-level or multi-level tunnel oven (300, 301, 302, 303, 304) according to claim 1 or vertical multilevel oven (400, 401, 402, 403, 404) according to claim 2 for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2), wherein the air treatment group (30, 30’) and/or the heat pump (15) is/are connected to the environment so as to take an airflow (11, 11’, 24) and to reintegrate in this way the flow of drying fluid and/or cooling fluid (9, 9’).

6) One-level or multi-level tunnel oven (302, 304) according to claim 1 or vertical multilevel oven (402, 404) according to claim 2 for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2), wherein an intermediate fluid is used, and wherein the heat pump (15) takes heat from the exhaust flow (9’) of the cooling fluid through the thermal contact with the refrigerant fluid inside the evaporator (16) configured as heat exchanger between said exhaust flow (9’) and said refrigerant fluid of the heat pump, while the condenser (18) is configured as heat exchanger between the refrigerant fluid of the heat pump (15) and said intermediate fluid, preferably water, circulating in a circuit (20) by means of a pump (21) to heat the recirculation air (12) of the drying chamber through a heat exchanger (14); optionally a flow of replenishment air (11) being taken from the environment.

7) One-level or multi-level tunnel oven (301) according to one or more of claim 1, 4 or vertical multilevel oven (401) according to one or more of claim 2, 4 for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2), wherein said heat pump (15) takes heat from the exhaust flow (9’) of the cooling fluid through thermal contact with the refrigerant fluid inside the evaporator (16) configured as heat exchanger between said exhaust flow (9’) and said refrigerant fluid of the heat pump, while the condenser (18) is configured as heat exchanger between the refrigerant fluid of the heat pump and said drying fluid; a flow of replenishment fluid (24), preferably air, being taken from the environment.

8) One-level or multi-level tunnel oven (302) according to claim 1 or vertical multilevel oven (402) according to claim 2 for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2), wherein an intermediate fluid is used, and wherein the evaporator (16) is configured as heat exchanger between the refrigerant fluid of the heat pump and said intermediate fluid, preferably water, and is connected with a circuit (28’) containing an intermediate fluid through a water/air heat exchanger (27’) inside said air treatment group (30’) optionally connected with an inlet to the exhaust fan (8’) for transferring heat from the mix of the exhaust fluid (9’) of cooling fluid and recirculated cooling fluid (12’) to said intermediate fluid so as to cool said cooling fluids before inserting them into the cooling chamber (66, 74), while the condenser (18) is configured as heat exchanger between the refrigerant fluid of the heat pump (15) and said intermediate fluid, preferably water, circulating in a circuit (20) by means of a pump (21); optionally a flow of replenishment air (11) being taken from the environment in order to heat the drying fluid through the water/air heat exchanger (14).

9) One-level or multi-level tunnel oven (300, 301, 302, 303, 304) for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2) according to one or more of the claims 1, 3-8, said oven being supplied with pieces (2) in a continuous way; or alternatively in a discontinuous way, preferably being provided with mobile shutters in ingress and egress, that are opened/closed in order to allow the ingress/egress of painted pieces, so as to form an intermittently closed chamber.

10) Vertical multilevel oven (400, 401, 402, 403, 404) according to one or more of claims 2-8 for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2), wherein said drying chamber (72) and said cooling chamber (74) belong to two distinct vertical ovens, the first oven intended for drying and the second oven intended for cooling; said two distinct vertical multilevel ovens being connected either to one same heat pump (15) or to at least two heat pumps.

11) Method for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2) performed through an oven comprising: a. at least a drying chamber provided with a suitable conveying system (3) of said pieces (2) allowing the ingress and the egress of said pieces from said chamber after drying the just painted pieces, with a predetermined time of permanence of said pieces in said drying chamber; b. at least a cooling chamber provided with a suitable conveying system (3’) of said pieces (2) allowing the ingress and the egress of said pieces from said chamber after cooling the dried pieces, with a predetermined time of permanence of said pieces in said cooling chamber; c. a set of fanning elements overall ensuring:

- the introduction into the drying chamber and into the cooling chambers of an air flow taken from the environment outside said oven;

- the circulation of the drying fluid inside the drying chamber and of the cooling fluid inside the cooling chamber;

- the recirculation of a first portion the drying fluid inside the drying chamber and of a first portion of the cooling fluid inside the cooling chamber;

- the exhausting of a second portion of the drying fluid and of a second portion of cooling fluid into the environment outside said oven; d. at least a heat pump (15) comprising: an evaporator (16), a compressor (17), a condenser (18), an expansion valve (19), and a refrigerant fluid, which evaporator (16) and which condenser (18) are configured to transfer thermal energy between the refrigerant fluid of said heat pump and a further gas or liquid fluid; wherein said first portion (9, 9’) of air is exhausted in the environment outside said oven; - said second portion is optionally recirculated in the respective drying chambers and/or cooling chambers, characterized in that the cooling fluid (9’) exhausted from said cooling chamber is placed in a condition of direct thermal heat transfer, or indirect thermal heat transfer through an intermediate fluid for thermal transfer, with the refrigerant fluid of said heat pump (15) in correspondence of the evaporator (16) in order to recover its thermal energy and use it through a direct, or an indirect thermal exchange by an intermediate fluid, with the refrigerant fluid of the heat pump (15) in condenser (18), for heating the drying fluid circulating inside said drying chamber.

12) Method for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2) according to claim 11 performed through a one-level or multi-level tunnel oven (303, 304) or through a vertical multilevel oven (403, 404), wherein at least a part the exhaust drying fluid (9) exhausted from the drying chamber (6) is placed in a direct or indirect thermal transfer condition with the refrigerant fluid of the heat pump in correspondence of the evaporator (16) before being exhausted allowing the heat pump to transfer a higher energy content to said condenser (18) through the process of the heat pump.

13) Method for drying/flashing off and cooling superficial treatments like paints or glue applied on said pieces (2) according to claim 11 or 12 performed through a one-level or multi-level tunnel oven (302, 304) or through a vertical multilevel oven (402, 404), wherein, when the temperature of the environment is higher than that of the cooling fluid (9’, 12’), the whole or a part of the air exhausted from the cooling area is reinserted into the cooling area again.

14) Method for drying/flashing off superficial treatments like paints or glue applied on said pieces (2) according to one or more of claims 11-13, wherein the one-level or multi-level tunnel oven (300, 301, 302, 303, 304) or the vertical multilevel oven (400, 401, 402, 403, 404) works empty, i.e. without pieces (2), until when the compressor (17) of the heat pump (15) brings said oven to the desired temperature; only then just painted pieces (2) are inserted into the oven and the flashing off/drying cycle starts.

15) Method for drying/flashing off superficial treatments like paints or glue applied on said pieces (2) according to one or more of claims 11-13, wherein the one-level or multi-level tunnel oven (300, 301, 302, 303, 304) or the vertical multilevel oven (400, 401, 402, 403, 404) contains pieces (2) at temperature of the environment; said pieces remain still inside said oven until when the compressor (17) of the heat pump (15) brings said oven to the desired temperature; only then just painted pieces (2) are moved into the oven and the flashing off/drying cycle starts.