EP4643071A2 - Oven for air drying with energy saving - Google Patents

Abstract

One-level or multi-level tunnel oven (100, 101, 102, 103) for drying/flashing off through a drying fluid superficial treatment like paints or glues applied on pieces (2) transiting through a drying chamber (6) having the shape of a tunnel, said oven comprising: a. a conveying system (3) of said pieces (2): b. an air treatment group (30), in its turn comprising: - an inlet for recirculated air (12); - an inlet for air (11) coming from the environment; - optionally a filter (13) for filtering said flows of air (11 and/or 12) or their mix (11 and 12); - optionally a heat exchanger (14) that can use or not an intermediate fluid; a fan (4) supplying said air flows (11 and/or 12) or their mix into the drying chamber (6); c. optionally an exhaust fan (8); 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) being functionally connected to said at least one heat pump (15), wherein the drying fluid comprises: a first portion of exhaust drying fluid (9) that is exhausted in the environment; optionally a second portion of drying fluid (12) that is recirculated inside said oven (100, 101, 102, 103); optionally said drying fluid being heated through the contact with an intermediate fluid, characterized in that said first portion (9) of drying fluid 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 first portion of drying fluid in the environment; and in that the energy employed for the process of drying/flashing off of paint is the energy needed to supply the compressor (17) of the heat pump (15).

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 ovens 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 in the drying chamber 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. The first embodiment is in the form of tunnel ovens, while the second embodiment is in the form of vertical multilevel ovens.

[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 with a tunnel oven, 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 materials having the form of a continuous sheet having always its 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 with vertical multilevel oven, said pieces can reach lengths of over 6 metres, with a typical width of 1300-1600 mm and a 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] 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.

[0008] 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, often substances are added in order to increase its evaporation, which in turn can release VOCs.

[0009] 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. [0010] 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.

[0011] 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.

[0012] 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 that of the gaseous refrigerant; 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 of 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 fluid; said liquid passes to its gaseous form to be suctioned by the heat pump compressor again, re-starting the cycle.

[0013] 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.

[0014] 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 occur 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. On the other hand, in the drying process the temperatures range typically 40-100°C.

[0015] 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 temperature of the environment wherein the oven is installed sometimes requires to heat the environment air sent into the flash off chamber.

[0016] 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.

[0017] 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 to 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.

[0018] Typically, flashing off is performed with low air flows, so as not to disturb the distension of paint, both in supply and in exhaust of the total air flow. During drying the airflows are important and typically are recirculated (70-80%), taking the rest percentage of air flow from the environment, heating the air for drying pieces before sending it on the pieces and exhausting a percentage of air coming from the oven that is analogous to the quantity withdrawn from the environment.

[0019] CN214440639U of Jiangsu Yutong Drying Equipment describes an oven for drying paint working in a closed circuit, without emitting 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 that does not recover energy from the air exhausted from the oven, as there is no air exhausted in the environment.

[0020] 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).

[0021] 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. These temperatures require the use of 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.

[0022] CN109569989A of University Tongji describes a drying system for coating lithium batteries, wherein a heat pump recovers energy from the environment only, while an air/air exchanger placed downstream the heat pump further heats the air pre-heated by the heat pump.

[0023] CN204902530U of Hefei Taoneng Environment Science & Technology describes a system for recovering energy from a drying environment comprising an air heater in the main channel. Downstream the heat pump there is a heat exchanger. The heat pump is used in order to preheat the air coming from the environment, but does not recover heat generated by the oven itself.

[0024] 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 of heating the recirculated air again.

[0025] EP3430337A1 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.

[0026] 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 for electric heaters.

[0027] Concerning the first embodiment in the form of tunnel ovens, providing two main types of ovens is known in the art:

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; the 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 system is 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, as opposed to the typical meandering or ring path of vertical 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.

[0028] Concerning the second embodiment in the form of vertical multilevel ovens for drying pieces, said 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 to be moved by or to house suitable motorizing means fixed to the frame of the oven in order to obtain the automatic loading and unloading of the pieces.

[0029] Typically, vertical ovens 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 the 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.

[0030] Obviously, said vertical chambers are separated, but for the small space needed to shift a tray from a chamber to the following one.

[0031] The loading and unloading of the panels on the 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.

[0032] 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 that can vary from some ten minutes to over a couple of hours, according to production line speed and dimensions of the oven itself.

[0033] 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.

[0034] 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.

[0035] This is true also for the flashing off chamber, even if to a lesser extent, given the lower working temperature and the typically low flash off airflow.

[0036] 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.

[0037] In a known embodiment of vertical ovens, the flashing off occurs in the lower portion of the first chamber, the drying in the higher portion of the first chamber and of the following chamber (second or third chamber if the central chamber is empty), and the cooling down in the lower portion of said chamber.

[0038] 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.

[0039] 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, which is dispersed during their cooling.

[0040] In the known art, hot air produced through an air/water exchanger, an electric heater, 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 continuously 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 discharged 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.

[0041] 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, discharging air into environment, and recirculation of air inside said oven); c. about 90% for heating the air used for flashing off/drying pieces.

[0042] 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.

[0043] 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 in the oven in order to compensate for the hot air containing solvents that is exhausted outside the oven.

[0044] 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.

[0045] 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.

[0046] Aim of the present invention is providing an oven for drying chemical compounds applied on pieces, allowing a more efficient and therefore cheaper management of the energy, than the ovens presently on the market.

[0047] 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.

[0048] The present invention provides ovens wherein the energy used by the tunnel oven or vertical multilevel oven for flashing off and drying pieces (portion c) is the energy 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.

[0049] The heat pump provides thermal energy to the oven in alternative way with respect to other heat sources.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] In an embodiment, when switched on, the oven that is at temperature of the environment, is empty, i.e. does not contain painted 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 loaded into the oven and the paint covering them can start to be dried.

[0054] 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 painted 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. [0055] In its first embodiment in the form of tunnel ovens, shown in the Figures 1-5, 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 (tunnel), wherein the evaporation of the paint solvent applied to the piece occurs; at least one heat pump.

[0056] In the first embodiment in the form of a tunnel oven, in a preferred embodiment, the oven is supplied with the pieces to be dried in a continuous way.

[0057] In an alternative embodiment, the tunnel oven is supplied in a discontinuous way. In an embodiment, the oven is provided with mobile shutters at 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. [0058] In its second embodiment in the form of vertical multilevel ovens, the apparatus according to the present invention comprises a heat pump for adjusting the temperature in the different chambers of the vertical oven.

[0059] In an embodiment, said heat pump is functionally placed so as to recover heat from the exhaust/s of the chamber/s and to transfer said heat to the drying chamber/s. It is worth mentioning that just one heat pump may be provided, serving all the drying chambers of the vertical oven, optionally even the flashing off chamber/s.

[0060] In a more specific embodiment, there are provided different variants: in the preferred embodiment shown in Figures 6-12, the vertical oven comprises four chambers and four stacks. In other not shown 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.

[0061] According to a further feature, the tunnel 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.

[0062] 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 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 released from the exhausted drying fluid to the evaporator; 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.

[0063] In the heat pump, both the condenser and the evaporator transfer heat with

- the drying fluid and/or

- the environmental air to be introduced as an addition to the drying fluid re-entered in the oven optionally with the intermediate fluid, generally water, when present. [0064] According to the present invention, a hot fluid, preferably hot air, is used, produced preferably through an exchanger supplied with hot water produced 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 tunnel to the heat exchanger through a fan, like in the known art. The exhaust airflow discharged outside the oven is forced through a heat pump, optionally with the interposition of an intermediate fluid and exchangers, in order to recover the thermal energy otherwise dispersed in the environment.

[0065] In an embodiment, the exhaust drying fluid flow exhausted outside the oven is suitably mixed with air coming from the environment having the environment temperature, so as to allow the working of the heat pump in a more suitable 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 environmental air, increasing the performance of the oven.

[0066] The heat pump allows 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 heat the drying fluid (typically air), that enters into contact with the pieces during the drying process. Said water is an intermediate fluid, that can be convenient in some conditions (see further).

[0067] Nonetheless, according to the present invention, it is possible to dispense with the generation of hot water, used as an intermediate fluid for the heating of the drying fluid, proceeding directly to the heating of the drying fluid, by using a direct heat exchanger.

[0068] 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 drying fluid. By configuring evaporator and condenser as heat exchangers, they can work so as to take heat from, and release heat to, a drying fluid or an intermediate fluid with which they enter into thermal contact, thanks to their configuration as heat exchangers.

[0069] 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 drying fluid taking heat, while the condenser transfers heat with the intermediate fluid (water), releasing heat to the same. This is the preferred embodiment, in that 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 even for providing a retrofit for ovens already installed in a production line, typically already provided with water heat exchanger supplied by the water heater.

[0070] 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 at the exhaust of the oven the evaporator recovers directly the heat from the drying fluid that crossed the oven, 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 the 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.

[0071 ] 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 supplied with one of said fluids, that is water. 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 ovens, even placed at a distance from each other.

[0072] 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 at the exhaust through a water exchanger.

[0073] According to the method of the present invention, said heat pump is placed downstream the air intake from environment and of the air exhaust of the oven, so as to recover the heat that normally is released outside the oven with the hot air extracted from the oven, which indicatively is the 20-30% of the air flow circulating in the oven.

[0074] In an embodiment, the method comprises mixing the exhaust drying fluid exhausted from the oven with a suitable quantity of air at the temperature of the environment (indicatively equal to or higher than 15°C according to the season). This allows to bring the mix of said two fluids that successively comes into contact with the heat pump to a temperature allowing the best thermal performance of the oven according to the present invention.

[0075] A first advantage of the present invention consists in the reduction of the energy consumption connected to drying operations, with the possibility of replacing the traditional gas boiler with a heat pump working with electric energy.

[0076] A second advantage of the present invention consists in that, when energy comes from renewable sources, the performance of the system is about thrice the one of the traditional systems (gas boiler).

[0077] The two above-quoted advantages translate into a third advantage: lack of impact from the point of view of greenhouse gases.

[0078] A fourth advantage is that, according to the known art, there must be provided a boiler for generating hot water, which water must be supplied to the points of use through circuits and pumps. With the present invention, the plant can be markedly simplified, in that the heat pump can be installed directly on an oven or a group of adjacent ovens with a simplified dedicated plant, requiring only electrical supply.

[0079] A fifth advantage is a better upgradability of the system with respect to a traditional boiler: once the thermal capacity of said boiler is exceeded, e.g. because other ovens were added to the plant, the replacement of the boiler itself would be required. With the present invention, adding a heat pump is sufficient.

[0080] A sixth advantage is the greater freedom of choice in the drying conditions, in that by recovering a more significant portion of the heat of the drying fluid, a bigger quantity than the traditional 30% of drying fluid can be expelled from the oven. This percentage is normally limited by the need of not dispersing too much heat. The possibility to increase this percentage can be useful for performing drying cycles wherein the concentration of evaporated water and solvents needs be decreased.

[0081] 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, tunnel oven according to the known art, lateral view;

Figure 2 First embodiment, tunnel oven according to the present invention, air/water embodiment, lateral view;

Figure 3 First embodiment, tunnel oven according to the present invention, air/air embodiment, lateral view;

Figure 4 First embodiment, tunnel oven according to the present invention, water/water embodiment, lateral view;

Figure 5 First embodiment, tunnel oven according to the present invention, water/air embodiment, lateral view;

Figure 6 Second embodiment, known art vertical oven provided with four chambers and four stacks, axonometric view;

Figure 7 Second embodiment, known art vertical oven provided with four chambers and four stacks, axonometric view; Figure 8 Second embodiment, vertical oven drying chamber according to known art, longitudinal section;

Figure 9 Second embodiment, vertical oven drying chamber according to the present invention, longitudinal section, air/water embodiment;

Figure 10 Second embodiment, vertical oven drying chamber according to the present invention, longitudinal section, air/air embodiment;

Figure 11 Second embodiment, vertical oven drying chamber according to the present invention, longitudinal section, water/water embodiment;

Figure 12 Second embodiment, vertical oven drying chamber according to the present invention, longitudinal section, water/air embodiment.

[0082] Although not shown in the Figures, in practice the oven according to the known art and the oven 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 sorting and/or packaging said pieces. All this is well known in the art.

[0083] The shown embodiments are meant as examples of the different and various possibilities of plant configuration, and in particular of the oven 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 and by their shape and dimension features.

[0084] In the Description hereunder, Figures 1-5 show the first embodiment of the present invention, i.e. a tunnel oven, while Figures 6-12 show the second embodiment, i.e. a vertical multilevel oven. It is worth noting that in Figures 1-5 the drying chamber 6 takes the shape of a tunnel, while in Figures 6-12 the drying chamber 6 takes 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.

[0085] It is worth precising that the present Figures 1-5 and Description focus on one-level tunnel ovens; nonetheless, the concepts described here are easily applicable to multi-level tunnel ovens.

[0086] Figure 1 shows a lateral view of an oven 1 according to the known art. Said oven comprises at least a device 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 by a supporting frame.

[0087] In the oven 1 according to the known art, pieces 2 to be dried are conveyed by at least a known conveying system 3, preferably in the form of a conveying band or a plurality of rollers. Said pieces 2 are conveyed inside a drying tunnel 6. The bold black arrow shows the conveying direction of the pieces 2 to be dried, while the small white arrows show the flowing direction of the drying air.

[0088] In a known way, the hot air used for drying pieces 2, shown as small white arrows, circulates in the opposed direction with respect to the supplying direction of pieces 2, shown as bold black arrow. This allows to gradually increase the temperature of said pieces 2, so as to increase the thermal efficiency of the oven.

[0089] In the known art, a fan 4 placed at the egress of the pieces of the drying chamber 6 blows a drying fluid, e.g. hot air, through a diffuser 5 inside said tunnel 6. Said drying fluid, that released its heat to the drying pieces 2, is suctioned by an inlet 7 placed at the piece’s ingress of the drying chamber 6: a first portion 9 (20-30%) of said drying fluid is suctioned by an exhaust flow- adjustable fan 8 and is discharged outside, in order to remove at least a portion of the solvents of the paint. Said drying fluid is typically discharged outside the oven, and therefore its heat is dispersed in the environment.

[0090] A second portion 12 of the drying fluid (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.

[0091] The sum of the outside 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.

[0092] In a known way, the oven 1 according to the known art comprises said air treatment group 30, in its turn comprising: an inlet for recirculated air 12; an inlet for air 11 coming from the environment; optionally a filter 13 for filtering the flow of air 11 and /or 12; optionally a heat exchanger 14 that can use or not an intermediate fluid; a fan 4 supplying said air flows 11 and/or 12 or their mix into the drying chamber 6. It is worth mentioning that in the art it is known providing air treatment groups 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 that can be identified as a unit. E.g., the fan 4 might be arranged upstream the filter 13, and/or the heat exchanger 14.

[0093] Figure 2 shows an oven 100 provided with a heat pump 15 according to the present invention; this preferred embodiment realizes an air/water exchange.

[0094] 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.

[0095] In said oven 100, which works analogously to the oven 1 according to the known art, the drying fluid flow 9, e.g. air, exhausted from the exhaust fan 8, typically 20-30% of the drying fluid circulating in the oven 100, 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 drying 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, having a lower temperature than the temperature of the exhaust air flow 9 at its arrival in the exhaust.

[0096] 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 oven 100, 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. [0097] The above-described air-water thermal exchange is the preferred embodiment, but different thermal exchanges can be realized in alternative embodiments.

[0098] Figure 3 shows an alternative embodiment of an air/air oven 101, wherein the exhaust drying 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 a recirculated air flow 12, so dispensing with the hot water circuit 20, the heat exchanger 14 and the recirculating pump 21 according to the embodiments shown in Figures 1 and 2. This embodiment has the least requirements from the plant point of view.

[0099] Figure 4 shows an alternative embodiment of a water/water oven 102, wherein there is provided an exchange intermediate fluid, e.g. water, that is circulated in heat exchangers 14 and 27 through pumps 21 and 26, wherein the drying fluid flow 9 exhausted from the oven 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 connected through a closed circuit with a recirculation pump 26 to the heat exchanger 27, 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 air 11 taken from the environment and to the portion 12 of drying fluid intended to be re-inserted in the oven through the air treatment group 30 in the heat exchanger of said treatment group 30.

[0100] Figure 5 shows a still different embodiment of a water/air oven 103, wherein the heat transfer occurs between the condenser 18 and the evaporator 16 of the heat pump, respectively. The condenser 18 directly heats the drying fluid 24, preferably air, taken from the environment; to it, after having been in thermal contact with the condenser for heating, the portion 12 of drying fluid is mixed; said portion is kept to be recirculated in the oven; the mix of the two flows is re-inserted in the oven after having passed through the air treatment group 30.

[0101] The evaporator 16 recovers heat from said portion of drying fluid; this occurs in an indirect way, as the heat of the portion of drying fluid 9 exhausted from the oven used in order to heat said intermediate fluid, e.g. water, through a heat exchanger 27, while said heated water coming out from the heat exchanger 27 is used as intermediate fluid to transfer heat to the refrigerant fluid of the heat pump through the evaporator 16 configured as heat exchanger. Said air is heated through a thermal exchange with the refrigerant fluid of the heat pump in the condenser 18, configured as heat exchanger.

[0102] According to the method of the present invention, said heat pump 15 is placed downstream the air intake from environment and the exhaust air exhausted into the environment of the oven 100, 101, 102, 103, optionally with the interposition of one or more electric heaters working with an intermediate fluid, so as to recover the heat normally released outside the oven with the drying fluid flow 9 exhausted from the oven, indicatively 20-30% of the drying fluid flow circulating in the oven.

[0103] Figures 6-12 and the Description hereunder refer to the second embodiment of the present invention, i.e. vertical multilevel ovens.

[0104] In the art, 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. 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 the Figures. Another typical embodiment is the three chambers, two stack vertical oven. [0105] Figure 6 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 entire oven, as shown by the arrows, during which the panels, arranged on the trays, dry.

[0106] Again, Figure 7 shows 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).

[0107] 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.

[0108] Figure 8 shows a lateral view of the oven 61 according to the known art, wherein a longitudinal section of the drying chamber 72 is visible. In the drying chambers 72, 73 there is provided a known air treatment 30 that, through an inlet, takes air 11 from the environment, while it recirculates air 12 taken from the oven itself through an air duct 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 black arrows.

[0109] Said drying fluid flow is taken from the suction channel 7 thanks to a fan 8 or to the depression generated by the fan 4 itself; said airflow is then recirculated in a channel 10. The fan 8 can be optional, but is shown in order to ease the understanding of the present invention. Actually, in the known art, there may be a different configuration of the air treatment group 30, allowing to generate the airflow 9 thanks to the pressure generated by the fan 4, without need of the fan 8. From the exhaust outlet a percentage of air 9 (typically 20- 30%) is expelled, in order to allow air renewal for removing residual solvents. [0110] In a known way, the oven 1 according to the known art comprises said air treatment group 30, in its turn comprising:

- an inlet for recirculated air 12;

- an inlet for air 11 coming from the environment;

- optionally a filter 13 for filtering the flow of air 11 and /or 12;

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

- a fan 4 supplying said air flows 11 and/or 12 or their mix into the drying chamber 6.

[0111] It is worth mentioning that in the art it is known providing air treatment groups 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 that can be identified as a unit. E.g., the fan 4 might be arranged upstream the filter 13, and/or the heat exchanger 14.

[0112] The above description refers to the working of the known art oven 61.

[0113] Figure 9 shows an oven 200 according to the present invention.

[0114] The oven 200 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.

[0115] The mixing 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. Said recirculation unit 30 is well known in the art; while there are provided some variants of it, they do not affect the concepts of the present Description.

[0116] According to the first 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.

[0117] 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.

[0118] In particular, in Figure 9 an oven 200 according to the present invention is shown in an air/water embodiment, wherein the drying fluid exhaust flow 9 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 higher pressure and temperature, and through the condenser 18 acting as a heat exchanger, releases the heat to an intermediate fluid (preferably water) 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.

[0119] The above-described air- water exchange is the preferred embodiment, but different thermal exchanges can be realized in alternative embodiments.

[0120] Figure 10 shows an alternative embodiment of an air/air oven 201, wherein the drying fluid exhaust 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 8, 9 and 10) 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 Figures 9 and 11. This embodiment has the least requirements from the plant point of view. [0121] Figure 11 shows an alternative embodiment of a water/water oven 202, wherein there is provided an exchange intermediate fluid, e.g. water, that is circulated in heat exchangers 14 and 27 through pumps 21 and 26, wherein the exhaust drying fluid flow 9 released from the oven 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 connected through a closed circuit 28 with a recirculation pump 26 to the heat exchanger 27, while the condenser 18 works as heat exchanger with an intermediate fluid, e.g. water, to which releases the heat of the refrigerant fluid of the heat pump 15, heat transferred to the heat exchanger 14. In its turn, the heat exchanger 14 transfers heat to the mix of environment air 11 taken from the environment and to the portion 12 of drying fluid intended to be re-inserted in the oven through the air treatment group 30 passing into the heat exchanger 14 of said treatment group 30.

[0122] Figure 12 shows a still different embodiment of a water/air oven 203, wherein the heat transfer occurs between the condenser 18 and the evaporator 16 of the heat pump, respectively. The condenser 18 directly heats the drying fluid 24, preferably drying air, taken from the environment (replenishment air); after having come into contact with the condenser 18 for heating, the portion of drying fluid 12 that crossed the oven and that was not exhausted from the oven (recirculation air) is mixed with it. The air flow taken from the environment and heated in the thermal exchange through the condenser 18, mixed with the drying fluid 12 that is not exhausted to be recirculated in the air duct 10 is reinserted in the oven after passing through the air treatment unit 30. The evaporator 16 recovers heat from the exhausted portion 9 of the drying fluid, and this occurs indirectly, as the heat of the portion of drying fluid exhausted from the oven is used to heat said intermediate fluid, e.g. water, through a water heat exchanger 27. Said heated water outcoming from the heat exchanger 27 is used as intermediate fluid to transfer heat to the refrigerant fluid of the heat pump thanks to the evaporator 16 configured as a heat exchanger.

[0123] In an alternative (not shown) embodiment of both tunnel ovens and vertical multilevel ovens, even the air 12 recirculated inside the oven can pass through the condenser 18 of the heat pump.

[0124] In both the embodiments in the form of tunnel ovens and vertical multilevel ovens, indicatively the temperature of the air used for drying pieces 2 is about 60-70°C; the temperature of exhaust air 9 coming from the fan 8 is about 10°C lower. The temperature of the mix of the air 22 coming from environment and of the exhaust air 9 of the oven must be higher than the temperature of the fluid circulating in the evaporator 16, in order to obtain an efficient heat exchange. The air treatment group 30 brings back air to the process temperature, i.e. 60-70°C.

[0125] According to the method of the present invention, said heat pump 15 is placed downstream the air intake from environment and the air exhaust into the environment of the oven 200, 201, 202, 203, optionally with the interposition of one or more heat exchangers working with an intermediate fluid, so as to recover the heat normally exhausted outside the oven with the drying fluid exhaust flow 9 extracted from the oven, indicatively 20-30% of the drying fluid flow circulating in the oven.

[0126] In an embodiment applicable to the air/water ovens 100, 200, and to the air/air ovens 101, 201 according to the present invention, and as shown in the previous embodiments, the method comprises the mixing of the exhaust hot air 9 exhausted from the oven with a suitable quantity of air 22 at the temperature of the environment (indicatively 15°C or higher according to the season) through an inlet. This allows to bring the air coming into contact with the heat pump at 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

61 four chambers, four stacks oven according to known art 71, 72, 73, 74 chambers

81, 82, 83, 84 stacks

100 first embodiment, air/water embodiment

101 first embodiment, air/air embodiment

102 first embodiment, water/water embodiment

103 first embodiment, water/air embodiment

200 second embodiment, air/water embodiment

201 second embodiment, air/air embodiment

202 second embodiment, water/water embodiment

203 second embodiment, water/air embodiment

Claims

1) One-level or multi-level tunnel oven (100, 101, 102, 103) for drying/flashing off through a drying fluid superficial treatment like paints or glues applied on pieces (2) transiting through a drying chamber (6) having the shape of a tunnel, said oven comprising: a. a conveying system (3) of said pieces (2): b. an air treatment group (30), in its turn comprising: an inlet for recirculated air (12); an inlet for air (11) coming from the environment; optionally a filter (13) for filtering said flows of air (11 and/or 12) or their mix (11 and 12); optionally a heat exchanger (14) that can use or not an intermediate fluid; a fan (4) supplying said air flows (11 and/or 12) or their mix into the drying chamber (6); c. optionally an exhaust fan (8); 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) being functionally connected to said at least one heat pump (15), wherein the drying fluid comprises: a first portion of exhaust drying fluid (9) that is exhausted in the environment; optionally a second portion of drying fluid (12) that is recirculated inside said oven (100, 101, 102, 103); optionally said drying fluid being heated through the contact with an intermediate fluid, characterized in that said first portion (9) of drying fluid 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 first portion of drying fluid in the environment; and in that the energy employed for the process of drying/flashing off of paint is the energy needed to supply the compressor (17) of the heat pump (15).

2) Vertical multilevel oven (200, 201, 202, 203) for drying/flashing off superficial treatments applied on pieces (2) to be dried which transit inside drying chambers (6) having the shape of vertical chambers (71, 72, 73, 74), said oven 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, wherein in at least a portion of said chamber (71, 72, 73, 74) a heating of said pieces (2) occurs; b. an air treatment group (30) in its turn comprising: an inlet for recirculated air (12); an inlet for air (11) coming from the environment; optionally a filter (13) for filtering the flow of air (11 and/or 12) or their mix (11 and 12); optionally a heat exchanger (14) that can use or not an intermediate fluid; a fan (4) supplying said air flows (11 and/or 12) or their mix into the drying chamber (6); c. optionally an exhaust fan (8); d. at least one heat pump (15), in its turn 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/s being functionally connected to said at least one heat pump (15), wherein the drying fluid comprises: a first portion of exhaust drying fluid (9) coming from at least a vertical drying chamber (72, 73) that is exhausted in the environment; optionally a second portion of drying fluid (10) coming from at least a vertical drying chamber (72, 73) that is recirculated inside said oven (200, 201, 202, 203); optionally said drying fluid being heated through the contact with an intermediate fluid, characterized in that said first portion (9) of drying fluid 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 first portion of drying fluid in the environment; and in that the energy employed for the process of drying/flashing off of paint is the energy needed to supply the compressor (17) of the heat pump (15).

3) One-level or multi-level tunnel oven (100, 101) according to claim 1 or vertical multilevel oven (200, 201) according to claim 2 for drying/flashing off superficial treatments like paints or glue applied on said pieces (2), wherein the exhaust drying fluid (9) exhausted from the oven is suitably mixed with external air (22), said mix being placed in a condition of heat transfer at the evaporator (16) configured as a direct heat exchanger between said mix and the refrigerant fluid of said heat pump, allowing the evaporator (16) of the heat pump to collect a higher energy content to transfer to the condenser (18) through the process of the heat pump, so increasing the performance of the system before that mix is exhausted in the environment.

4) One-level or multi-level tunnel oven (101, 103) according to claim 1 or 3 or vertical multilevel oven (201, 203) according to claim 2 or 3 for drying/flashing off superficial treatments like paints or glue applied on said pieces (2), wherein the heat pump (15) is connected to the environment so as to take an airflow (24) and to reintegrate in this way the flow of drying fluid (23) discharged from said exhaust fan (8).

5) One-level or multi-level tunnel oven (100) according to one or more of claims 1, 3 or vertical multilevel oven (200) according to one or more of claims 2-3 for drying/flashing off superficial treatments like paints or glue applied on said pieces (2), wherein an intermediate fluid is used, preferably water, and wherein the heat pump (15) takes heat from the exhaust flow (9) through the thermal contact with the refrigerant fluid of the heat pump (15) with 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 circulating in a circuit (20) by means of a pump (21) to heat the mix of recirculation air (12) and a flow of replenishment air (11) taken from the environment through a heat exchanger (14).

6) One-level or multi-level tunnel oven (101) according to one or more of claims 1, 3 or vertical multilevel oven (201) according to one or more of claim 2, 3 for drying/flashing off superficial treatments like paints or glue applied on said pieces (2), wherein said heat pump (15) recovers heat from the exhaust flow (9) through thermal contact with the refrigerant fluid of the heat pump with 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) being taken from the environment, optionally said flow (24) being mixed with the recirculating flow (12) downstream said condenser (18).

7) One-level or multi-level tunnel oven (102) according to claim 1 or vertical multilevel oven (202) according to claims 2 for drying/flashing off superficial treatments like paints or glue applied on said pieces (2), wherein an intermediate fluid is used, preferably water, and wherein the evaporator (16) is configured as heat exchanger between the refrigerant fluid of the heat pump and said intermediate fluid, and is connected with a water circuit (28) through an air/water heat exchanger (27) connected with an inlet to the exhaust fan (8) for transferring heat from the exhaust fluid (9) to said intermediate fluid, while the condenser (18) is configured as heat exchanger between the refrigerant fluid of the heat pump (15) and said intermediate fluid, circulating in a circuit (20) by means of a pump (21); optionally a flow of replenishment air (11) being taken from the environment.

8) One-level or multi-level tunnel oven (103) according to claim 1 or 4 or vertical multilevel oven (203) according to claim 2 or 4 for drying/flashing off superficial treatments like paints or glue applied on said pieces (2), wherein an intermediate fluid is used, preferably water, and wherein the evaporator (16) is configured as heat exchanger between the refrigerant fluid of the heat pump and an intermediate fluid, preferably water, and is connected with a water circuit (28) to an air/water heat exchanger (27) placed at the exhaust fan (8) for transferring heat from the exhaust flow (9) to said intermediate fluid, while said 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) being taken from the environment, optionally said flow (24) being mixed with the recirculating flow (12) downstream said condenser (18).

9) One-level or multi-level tunnel oven (100, 101, 102, 103) for drying/flashing off superficial treatments like paints or glue applied on said pieces (2) according to one or more of claims 1, 3-8, said oven being supplied with pieces (2) in a continuous way; or alternatively being supplied 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 (200, 201, 202, 203) for drying/flashing off superficial treatments applied on pieces (2) according to one or more of claims 2-8, comprising a plurality of independent heat pumps each working on a chamber of the same oven, or just one heat pump managing all the thermal exchanges of all the chambers of said oven.

11) Vertical multilevel oven (200, 201, 202, 203) for drying/flashing off superficial treatments applied on pieces (2) according to one or more of claims 2-8 or 10, wherein a portion of thermal energy is spent for flashing off and a portion of energy is spent for drying through the separation in two dedicated heat exchangers of said condenser (18).

12) Method for drying/flashing off 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 the pieces after the drying of the just painted pieces, with a predetermined time of permanence of said pieces in said drying chamber: b. a set of fanning elements overall ensuring: the introduction into the oven of an air flow taken from the environment outside said oven;

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

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

- the exhausting of a second portion of drying fluid into the environment outside said oven; c. at least one heat pump (15), in its turn 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 the drying fluid comprises: said first portion of exhaust drying fluid (9) that is exhausted in the environment; optionally said second portion of drying fluid (12) that is recirculated inside said drying chamber; characterized in that the energy employed by the oven for the process of drying/flashing off paint on pieces (2) is the energy needed for the working of the compressor (17) of the heat pump (15); and in that said first portion (9) of drying fluid 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) and in correspondence of the evaporator (16) in order to recover its thermal energy.

13) Method for drying/flashing off superficial treatments like paints or glue applied on said pieces (2) according to claim 12, wherein the exhaust drying fluid (9) discharged from the oven is opportunely mixed with air (22) coming from the environment, and said mix is placed in a 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 through the process of the heat pump to said condenser (18).

14) Method for drying/flashing off superficial treatments like paints or glue applied on said pieces (2) according to claim 12 or 13, wherein the one- level or multi-level tunnel oven (100, 101, 102, 103) or the vertical multilevel oven (200, 201, 202, 203) works empty, i.e. without painted pieces (2), until when the compressor (17) of the heat pump (15) brings said oven to the desired temperature; only then said 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 claim 12 or 13, wherein the one- level or multi-level tunnel oven (100, 101, 102, 103) or the vertical multilevel oven (200, 201, 202, 203) contains painted pieces (2) at the temperature of the environment; said painted 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 the just painted pieces (2) are moved into the oven and the flashing off/drying cycle starts.