Yankee drying cylinder for paper production

Abstract

Yankee dryer cylinder (1) for paper production comprising a body comprising a metal cylinder (2) having a circular cross-section and two side heads (3) on which two respective coaxial pins (4) arranged along an axis of rotation (x-x) of the Yankee are formed or mounted, said body being configured to rotate about said axis of rotation (x-x) at a predetermined angular velocity. Inside the body there is arranged a stationary electromagnetic induction heating system comprising one or more inductors (H; hN), the one or more inductors (H; hN) interacts electromagnetically with the cylinder (2) to generate an induced current in the same cylinder, said one or more inductors (H; hN) is arranged in the vicinity of the radially innermost surface of the cylinder (2).

Description

[0001] manual

[0002] The invention relates to a Yankee dryer for producing paper.

[0003] As is known, toilet paper is generally produced using a fiber suspension containing cellulose fibers, usually called pulp. In continuous machines, the pulp is introduced onto a mesh drainage support. At this stage, the formation of the paper web takes place, i.e. the fibers overlap and produce bonds, which will form the paper web once the water has been removed. The removal of water takes place gradually by the actions of drainage, absorption, pressing and evaporation until a paper roll with a residual moisture of about 5% is obtained. According to the combined production scheme, the water present in the fiber suspension is filtered out by a forming cloth, after which the paper web formed passes through a press section, where further water is removed, and then the paper web passes through a cylinder usually called a "Yankee" that is heated from the inside by the introduction of high-pressure steam. The heat transferred to the paper web through the outer surface of the Yankee and the combined action of the hot air blown in the hood arranged around the Yankee itself and the absorption of water ultimately determine the achievement of the desired degree of dryness. The paper web can be detached from the Yankee by means of a creping doctor and rolled up in the form of a reel. In alternative systems, the detachment of the paper web from the Yankee can take place in different known ways. The term "tissue" generally refers to low-weight paper products intended for hygienic and cleaning purposes, such as toilet paper, kitchen paper or hand towel rolls, handkerchiefs, napkins, and the like.

[0004] The present invention relates to a Yankee dryer whose surface in contact with the paper is heated, thereby avoiding the use of steam.

[0005] According to the invention, this result is achieved by adopting the concept of realizing a Yankee dryer for producing hygiene paper having the features indicated in claim 1. Other characteristics of the invention are the subject of the dependent claims.

[0006] The present invention provides a construction for a Yankee dryer having an electromagnetic induction system inside it and a cylinder made of any conductive material (such as carbon steel or cast iron) suitable for utilizing the thermal effect associated with electromagnetic induction. There are two corresponding end caps at both ends of the cylinder.

[0007] According to the invention, the Yankee shell can also be multi-layered, the main layer corresponding to the radial inner surface of the cylindrical shell (the layer on which the electromagnetic field acts) being made of an electrically conductive material. In this case, the shell layers adjacent to the main layer are heated by thermal conduction by contact with the material of the main layer.

[0008] Preferably, the induction system placed inside the Yankee is static, ie it does not rotate with the Yankee and is supported by an axis passing through two pins formed on the end of the Yankee.

[0009] The inner surface of the Yankee, i.e. the inner surface of the cylinder, is free of circumferential grooves. These grooves are usually present in Yankees heated by steam and perform the dual function of increasing the convective exchange surface with the internal steam (which is not used according to the invention) and collecting condensed steam (which is not formed according to the invention because the steam is not used).

[0010] According to the invention, the electromagnetic induction system comprises a single inductor or a plurality of inductors which are located at a radial distance from the inner surface of the cylinder, preferably at a distance between 30 cm and 1 mm, and are not in contact with the inner surface of the cylinder. More preferably, the radial distance is between 5 cm and 2 mm, and still more preferably between 2 cm and 5 mm. In this context, the term radial distance means the radial distance between the inner conductive cylindrical surface of the Yankee and the point of the induction system closest to it.

[0011] Inductors can be manufactured in a variety of ways.

[0012] The inductor is configured to heat the metallic inner surface of the cylinder. The heating is obtained by generating an alternating electromagnetic field through the inductor, the frequency and amplitude of which vary according to the power to be transmitted. The time-varying electromagnetic field generates induced currents in the metallic material of the cylinder, which induced currents generate local overheating due to the Joule effect. In this way, the heat required for drying the paper is generated. The heat generated on the inner surface of the Yankee is diffused through the thickness of the cylinder by conduction until it reaches the outer surface in contact with the paper web being dried. Part of the heat will diffuse inside the cylinder itself by radiation and convection. However, since the internal volume of the Yankee is essentially closed, the heat diffused inside will not be dissipated, but will cause an increase in the temperature of the air contained inside it. In this way, a corresponding part of the thermal energy will not be dissipated to the external environment, except for the part transmitted to the outside through the end. In any case, similarly to what happens in the case of a Steam Yankee dryer, the head can be suitably insulated by systems known per se so as to limit to a minimum the portion of thermal energy transferred to the external environment, so that the greatest portion of thermal energy is transferred to the paper web being dried.

[0013] The electrical power to be converted into thermal power for drying the paper web is of the same order of magnitude as the thermal power provided by steam in conventional systems. In fact, the thermal power does not depend on the source, but on the way it must be used. The function of the Yankee is to provide heat to the paper so as to raise the dryness of the paper web attached to it from a minimum value (usually in the range of 25%-50%) when the paper comes into contact with the outer surface of the cylinder to a maximum value (usually in the range of 55%-99%) when the paper leaves the Yankee. Therefore, the thermal energy required for the correct operation of the Yankee will depend on the programmed production parameters, for example on: paper weight, web width, input dryness and output dryness from the Yankee, Yankee rotation speed and input web temperature. These parameters make it possible to calculate the exact amount and enthalpy of water that must be removed from the paper web. In general, the power required to evaporate the water contained in the paper web to achieve the required dryness varies between about 2MW and 15MW, depending on the production rate, the temperature of the web entering the Yankee and various other parameters (grammage, degree of creping, etc.).

[0014] According to a particular embodiment of the invention, the Yankee may have an outer cylindrical surface with an outer layer harder than the base metal to increase its wear resistance (due to the presence of paper and of a doctor blade for removing and / or creping the dried web and / or cleaning the surface upstream of the web attachment area). For example, the outer layer may be produced by metal deposition, or by electroplating deposition (by melt deposition) or by surface treatment (for example by laser hardening).

[0015] Among the advantages provided by the present invention, the following ones may be particularly mentioned.

[0016] Decarbonization: In a conventional Yankee dryer, steam is usually produced in a boiler burning fossil fuels. Steam generation represents a large amount of energy for running a paper mill. More and more national and international regulations, in addition to the need to reduce the impact of the greenhouse effect on the climate, also require limiting and, as far as possible, eliminating the production of carbon dioxide, one of the main greenhouse gases. According to the invention, the electrification of the production of thermal energy to be used for drying paper in a Yankee makes it possible to reduce (or even eliminate) the production of carbon dioxide required for the operation of this Yankee, since the required electrical energy can be produced using renewable energy sources without the use of fossil fuels. Assuming the use of electricity generated exclusively from renewable energy sources, it can be estimated that the potential reduction in CO2 emissions is between 2500 tons / year and 25000 tons / year, depending on the productivity of the machine.

[0017] Another advantage of the invention relates to the simplification and greater controllability of the system: in a conventional Yankee dryer, heat is introduced by using steam as a fluid carrier. The steam condenses after heat exchange with the paper web being dried, so that at the Yankee outlet there is a two-phase fluid consisting of condensed water and steam (introduced in excess to precisely maintain the driving force required to extract the condensed water, in order to avoid overflowing inside the cylinder). The steam must have a sufficiently high temperature to allow the paper to be dried while maintaining a high production rate (the heat exchanged will be a function of the gradient between the steam temperature and the paper web temperature). Therefore, the steam pressure must be kept above a minimum value that depends on the process balance. In order to produce paper at speeds even higher than 2000 mpm, modern, higher performance machines require internal steam temperatures exceeding 150-160°C, with peaks approaching 190°C. As saturated steam, these temperatures require pressures inside the Yankee of up to 10 bars. All this requires the construction of a steam generation, treatment and transportation plant, which is completed by a series of components and pipes that have a great impact on the complexity of the paper production plant. In particular, the following components are present in most applications: steam generating boilers, transmission piping, thermocompressors (which use high-pressure steam to increase the pressure of the exhaust steam in the cycle to regenerate it and keep it in the cycle itself), safety systems (safety valves and regulating valves), heat recovery systems, condensate separators, etc. In addition, systems must be built inside the Yankee that allow the continuous removal of the condensate itself. These systems usually consist of multiple sleeves immersed in the grooves (in the case of a grooved Yankee): the steam introduced into the cylinder is excessive relative to the steam required to transfer heat to the paper; the only way out for the pressurized excess steam is to be discharged through the sleeve openings connected to the headers distributed circumferentially inside the cylindrical surface of the Yankee, and then discharged from these headers into the headers coaxial with the Yankee itself. The effect of the excess steam causes the condensate accumulated at the bottom of the grooves after the heat has been transferred to the paper to be forced back through the sleeves themselves. In this way, the condensate is continuously removed from the inside of the Yankee with the steam flow, avoiding overflow. In the case of non-grooved Yankees (usually used in applications with poor performance or for specific types of paper to be produced, such as MG paper), the condensate extraction system involves the use of large collecting scoops that rotate with the Yankee: in this case, given the lower rotation speed of these systems, the condensate tends to accumulate on the lower part of the cylinder. As the scoops (the number depends on the diameter of the cylinder) rotate, they pass from the lower part, collect the condensate and direct it to a central collector through a specific path that uses gravity and condensate removal pipes.

[0018] All these systems serve the correct flow of steam and condensate to be able to transfer the required heat. Each individual component requires inspection and maintenance to keep the system efficient and avoid corrosion / erosion phenomena. The steam circuit requires constant quality control of the flowing substance. For example, it is necessary to keep the PH level within pre-established limits and it is necessary to constantly guarantee the absence of free oxygen in the circuit to prevent corrosion phenomena that can cause damage not only to the components of this circuit, but also to the Yankee itself. Therefore, it is necessary to constantly monitor the operating conditions and check the quality of the steam by using specific chemicals.

[0019] According to the present invention, by avoiding the use of steam as a heat transfer fluid, all of these problems are eliminated and the resources required to keep these systems efficient are maintained.

[0020] The use of induction heaters makes it possible to eliminate the use of steam and all the components, systems and technical problems associated with the use of steam.

[0021] The need to use pressurized steam (up to 10 bar) inside a conventional Yankee dryer also leads to a series of structural complexities. Due to the large amount of pressurized steam contained inside the Yankee (diameter even exceeding 7 m and width exceeding 5.6 m), the resultant forces to which the inner surface of the Yankee is subjected are significant (a circular head with an inner diameter of 6.6 m exposed to steam at a pressure of 10 bar is subjected to a resultant thrust equal to about 14,000 tons). Furthermore, the use of pressurized steam means that the design of the Yankee must comply with the strict rules imposed by national and international pressure vessel regulations in order to avoid catastrophic accidents such as the explosion of the Yankee. Therefore, the structure itself and the connection system of the various structural components require care and a very high level of control in order to absolutely guarantee the structural reliability of the cylinder throughout its entire working life, which greatly increases the cost of the materials used and the necessary construction and control procedures, which are repeated periodically during the life of the product.

[0022] Usually, the surface of the Yankee, before contact with the paper to be attached, is sprayed with substances whose function is to promote the attachment of the paper, to facilitate its detachment after drying, to give specific properties to the attached paper and to protect the outer cylindrical surface of the Yankee. This is usually called an organic coating, the chemical composition of which can vary greatly depending on the product, the condition of the Yankee surface and the recipe used by the paper mill. Some of the chemicals contained in the coating (e.g., the epichlorohydrin polyaminoamide resins that can be used in the attachment component) require the generation of crosslinking bonds promoted by high temperatures in order to function correctly. This aspect also has an impact on the size of the Yankee and the machine configuration, in fact, it is necessary to ensure the crosslinking of the coating before contact with the paper, which leads to the coating spray bar (or, more simply, the coating bar) being placed at a certain distance from the point of contact with the paper (depending on the type of coating and the rotation speed of the Yankee). The surface between the coating rod and the point of contact with the paper is developed along an arc that is not actually used: the purpose of the Yankee is to transfer thermal energy to the paper for drying, which can only occur in the area where the paper is attached to the Yankee; if a part of the Yankee cannot receive the paper because the coating distributed on it is not "ready" to ensure correct adhesion, then, under conditions of equal performance, the Yankee must have a larger diameter to compensate for the unused area (the development of the wrapping of the paper around the Yankee and therefore the diameter of the Yankee depends on the overall performance of the machine and of the Yankee and on the basis weight of the paper). On the other hand, the use of an induction system placed inside the Yankee and not rotating with it allows the intensity of the thermal power to be adjusted, also according to the section involved, by adopting a modular design. In this way, it is possible to control the temperature of the section dedicated to the crosslinking of the coating. By optimizing the crosslinking process, it is possible to reduce the space dedicated to the crosslinking process. Reducing the space required for crosslinking allows reducing the Yankee diameter under conditions of equal performance.

[0023] Another potential advantage relates to greater energy efficiency: current systems provide for the generation of thermal power outside the Yankee (steam is generated in boilers outside the Yankee and is thus brought to the interior of the Yankee via pipes and regulating components). On the contrary, the system object of the invention provides for the generation of thermal energy directly in the metal coating of the Yankee, i.e. corresponding to the exchange zone where the paper is dried, due to the Joule effect caused by the induced current. This allows to reduce all the losses caused by the high-temperature transport of fluids from remote areas inside the Yankee. This fact enables the thermodynamic paths to be significantly shortened, improving the overall efficiency, if associated with a source of electricity production from renewable energy sources (i.e. without the need to generate the heat transfer fluid for electricity generation by combustion).

[0024] In the drawings which are provided as examples and are not to be understood in a limiting sense:

[0025] - Figure 1 A paper machine equipped with a Yankee dryer according to the invention is shown;

[0026] - Figure 2 represents a schematic vertical cross-sectional view showing some components of a Yankee dryer according to the invention;

[0027] - Figure 3 represents a possible operating configuration of a Yankee dryer according to the invention;

[0028] - Figure 4 represents another possible operating configuration of the Yankee dryer according to the invention;

[0029] - Figure 5A shows a schematic longitudinal cross-sectional view of a Yankee according to the present invention;

[0030] - Figure 5B express Figure 5A A zoomed in view of the Yankee cylinder and highlights the magnetic field lines that intercept the Yankee cylinder;

[0031] - Figure 6-8 Three different views showing possible embodiments of an inductor for a Yankee dryer according to the invention;

[0032] - Figure 9-12 Four different views showing another possible embodiment of an inductor for a Yankee dryer according to the invention;

[0033] - Figure 13-15 Three different views showing possible embodiments of an inductor group for a Yankee dryer according to the invention;

[0034] - Figure 16-20 Five different views of further possible embodiments of an inductor group for a Yankee dryer according to the invention are shown.

[0035] Reduced to its basic structure and with reference to the accompanying drawings, the Yankee dryer (1) according to the invention is a body comprising a metal cylinder (2) of circular cross section and two end heads (3) on which two corresponding coaxial pins (4) arranged along the axis of rotation (xx) of the Yankee are formed or mounted. A transmission (5) acts on the pins (4) and controls the speed of rotation of the Yankee about the axis (xx) via the transmission (5). The outer surface of the cylinder (2) forms a heat exchange surface with the paper web produced upstream of the Yankee in order to reduce its moisture content, i.e. increase its dryness. The paper web can be produced in a machine for producing toilet paper or MG paper by a method known per se to a person skilled in the art, the machine comprising, for example, a forming zone (A) in which the paper web is formed starting from a fiber suspension of a predetermined composition; a drainage zone (B) of the paper web downstream of the forming zone (A), along which the water content of the paper web gradually decreases; and a drying zone (C) downstream of the drainage zone (B), in which a Yankee (1) is installed.

[0036] exist Figure 1 In the drawings, the arrow "MD" indicates the machine direction of the paper web.

[0037] Downstream of the Yankee (1), a section (D) may be arranged for collecting the web in the form of reels (R1, R2).

[0038] In the inlet section of the drying zone (C) there is a press (6) which presses the paper web on the Yankee (1) with a predetermined pressure. For example, the press (6) can consist of a shoe press, a blind roll or a suction roll.

[0039] The section (B) may eventually integrate systems for reducing the water content of the web based on a number of concepts (vacuum application using suction boxes or suction rolls in order to induce drainage, pressing zones, means for providing thermal energy, means based on the removal of water from the web by capillary action, forced blowing of hot air through the web, etc.). All these systems, even in combination with one another, are known per se. The hood (7) may be arranged on the Yankee (1).

[0040] In the drying section (C), from the entry point (P1) to the exit point (P2), the paper web is in contact with the outer surface of the cylinder of the Yankee (1), the contact portion having an angular extension (a) greater than 180°. Figure 2 In the embodiment of the invention, the web is indicated by the reference numeral "S". At the exit point (P2), a creping blade (8) may be arranged for detaching the web from the Yankee (1), and downstream of the creping blade (8) with respect to the direction of rotation (1C) of the Yankee there is a cleaning blade (80). In an alternative configuration, even without using a blade, the web may be detached from the Yankee by using a support belt which collects the web at its end passing from the Yankee surface.

[0041] The paper web (F) is transferred from the forming zone (A) to the drying zone (C) by the wire (9), and in the pressing zone formed by the press (6) in cooperation with the Yankee (1), the paper web (F) is also associated with the wire (4).

[0042] exist Figure 3 In the schematic diagram of the press (6) is a shoe press and the wire (9) is a felt. The same schematic diagram shows a suction roll (SR) onto which the wire (9) is guided upstream of the press (6).

[0043] exist Figure 4 In the schematic diagram of , the press (6) is associated with a further press (60) which is arranged downstream with respect to the direction of rotation (1C) of the Yankee. In this configuration, the wire (9) is associated with the paper web both in the pressing zone defined by the press (6) and by the further press (60) cooperating with the Yankee (1). For example, the additional press (60) consists of a blind hole press.

[0044] The linear pressure corresponding to the Yankee applied by the press (6) is preferably between 60 kN / m and 200 kN / m, more preferably between 90 kN / m and 150 kN / m, even more preferably between 90 kN / m and 120 kN / m. Figure 4 In a configuration of the type shown, the linear pressure exerted by the additional press ( 60 ) at the Yankee is preferably between 90 kN / m and 120 kN / m.

[0045] For example, the Yankee (1) has an outer diameter comprised between 2.00 m and 7.500 m and an axial length comprised between 3.00 m and 7.400 m.

[0046] Inside the Yankee (1) there is a fixed electromagnetic induction heating system consisting of one or more inductors (H; HN) positioned and configured to generate an alternating electromagnetic field of predetermined frequency and amplitude according to the thermal power to be generated. In the case of installing a plurality of inductors (HN) distributed in the axial direction and fed individually or in groups, it is possible to carry out a partial control of the thermal power generated in the cylinder in the axial direction. In this way, it is possible to compensate for any non-uniformity in the transverse moisture distribution of the paper being dried by increasing the electrical induction, by acting on solenoids that act on the zones corresponding to the bands of paper with greater moisture. The time-varying electromagnetic field generated by the inductors induces the generation of electric currents in the metallic material of the Yankee cylinder and the cylinder itself is heated due to the Joule effect. The heat thus generated is used to dry the paper web (F). The induction heating system makes it possible to produce a uniform thermal imprint on the surface of the Yankee cylinder (2), i.e. a uniform heat distribution along the generatrix defining the cylindrical surface of the cylinder.

[0047] The electromagnetic induction heating system extends axially along the inner surface of the Yankee cylinder (2), i.e. parallel to the axis (xx) of the Yankee, but is preferably shorter than the cylinder so that a free space (10) is left in front of each end (3). In this way, the electromagnetic interaction with the cylinder (2) extends only or almost only over the central zone (20) of the cylinder (2). Thus, the energy transfer to the lateral parts of the cylinder not in contact with the paper web (F) is reduced.

[0048] Preferably, the radial distance between the radially outermost side of the electromagnetic induction system and the inner surface of the cylinder (2) is comprised between 20 cm and 1 mm, more preferably, the radial distance is comprised between 5 cm and 2 mm, even more preferably between 2 cm and 5 mm.

[0049] exist Figure 5A , Figure 6 , Figure 7 and Figure 8In the schematic diagram of , there is a single inductor (H) in the form of a solenoid that is developed around the (xx) axis of the Yankee. The solenoid is formed by turns of a coil that are concentric with the axis (xx).

[0050] 5 , the inductor (H) extends axially inside the Yankee (1) for a length (LH) that is shorter than the length (L2) of the cylinder (2). The terminal (HT) of the inductor (H) may pass through one of the pins (4).

[0051] exist Figure 9-12 In the schematic diagram of , there is a single toroidal inductor (H) developed parallel to the axis (xx) of the Yankee. The toroidal inductor is formed by a coil parallel to the inner surface of the cylinder (2). Also in this case, preferably, the radial distance between the radial outer side of the inductor (H) and the inner surface of the housing (2) is between 20 cm and 1 mm, more preferably, the radial distance is between 5 cm and 2 mm, even more preferably between 2 cm and 5 mm. Also in this case, the terminal (HT) of the inductor (H) can pass through one of the pins (4).

[0052] exist Figure 13-15 In the schematic diagram of , there are a plurality of inductors (HN), each of which consists of a solenoid developed around the axis of the Yankee and formed by coil turns concentric with said axis. In this example, the inductors (HN) are arranged side by side in the axial direction. Also in this case, the terminal (HT) of the inductor (HN) can pass through one of the pins (4).

[0053] exist Figure 16-20 In the schematic diagram of , more inductors (HN) are provided, each inductor being formed by a solenoid consisting of turns of a coil wound around a respective radial axis (RHN). In this case, the inductors (HN) are arranged circumferentially around the axis of the Yankee. Also in this case, the terminals (HT) of the inductors (HN) can pass through one of the pins (4). In the figures, the reference numeral "HP" indicates a core of ferromagnetic material, which can optionally be used to realize the inductors (HN).

[0054] By using Figure 13-15 The multiple inductors (HN) arranged in the schematic diagram can also control the thermal power transmitted to the cylinder (2) in the axial direction of the Yankee in different ways to produce an axially variable heat distribution.

[0055] By using Figure 16-20 The multiple inductors (HN) arranged in the schematic diagram of FIG. 1 also make it possible to control the thermal power transmitted to the cylinder (2) in a different manner in the circumferential direction so as to change the heat transfer in the circumferential direction.

[0056] Preferably, the inductor consists of one or more solenoids which are geometrically configured so that the generated electromagnetic field is intercepted only or almost only by the cylindrical barrel (2) of the Yankee, thereby minimizing the projection of the electromagnetic field lines towards the end head (3) without the paper web coming into contact with the end head (3).

[0057] In effect, the Yankee cylinder forms the armature in "near field" geometry.

[0058] In this way, in addition to directing the electromagnetic energy toward the barrel with greater spatial accuracy, reducing startup transients, the projection of the electromagnetic field toward the tip is reduced, which also helps to increase operator safety at the Yankee installation site.

[0059] Therefore, the substantial absence of an electromagnetic field outside the volume affected by the presence of the cylinder makes it possible to limit the amount of energy transmitted by the electromagnetic field to the tip, thereby reducing the amount of energy dissipated in the environment and not effectively directed to the dried web.

[0060] In other words, using the near field to sense the cylinder allows as many electromagnetic field lines as possible to be intercepted by the cylinder, thereby reducing leakage of the electromagnetic field from the volume circumferentially bounded by the cylinder and simplifying the realization of the tip.

[0061] From a construction point of view, preferably in accordance with the present invention, the following condition should be satisfied: S ≤ Pd, where "S" is the radial distance of the inductor from the inner surface of the Yankee cylinder, "d" is the diameter of the conductor forming the coil turns (HS), and "P" is the pitch between the coil turns of the inductor (or a single inductor). It is noted that, in general, all other conditions being equal, turns that are more spaced apart from each other will mean a lower spatial density of the local field, and therefore a lower temperature generated on the cylinder, compared to turns wound with a smaller winding pitch (i.e., closer coil turns).

[0062] More preferably, according to the present invention, S and the difference Pd have the same order of magnitude and have substantially the same value, i.e., the following conditions are satisfied: wherein S, d and P have the meanings indicated above.

[0063] Thus, according to the invention, a geometrical configuration of an inductor system (understood as a single solenoid or a plurality of solenoids) is achieved in which the distance between the turns of the coils of the inductor system and the inner surface of the armature consisting of a Yankee cylinder is approximately equal to or smaller than the pitch between the coils (HS) minus said diameter (d).

[0064] In this way, the magnetic field of the individual coils intercepts the barrel material which is limitedly affected by the magnetic field of the adjacent coil turns. It is therefore possible to more effectively concentrate the magnetic field effect of the individual coil turns. Furthermore, given that once the induced magnetic field has been generated in the metallic material of the barrel, the magnetic field generated is reduced (Faraday cage effect), it is easier to prevent electromagnetic induction from extending to the head, thereby reducing the amount of energy that should be dissipated in the external environment.

[0065] Reference Figure 9-12 In the example shown, the inductor (H) has a side (HM) radially closer to the cylinder (2) and a side (HW) radially further away from the cylinder (2), and the side (HM) radially closest to the cylinder (2) is at a given radial distance from the inner surface of the cylinder (2), and in this case, the inductor is formed by coil turns (HS) consisting of a conductor of a predetermined diameter and spaced apart at a pitch of a predetermined value (P). This case is characterized in that the radial distance of the side (HM) from the inner surface of the cylinder (2) has a value less than or equal to the difference between the pitch (P) and the diameter (d). The same applies if, instead of a single inductor (H), there are several inductors constructed in this way and aligned along the axis of the Yankee.

[0066] From the description provided above, it is apparent that the Yankee dryer for producing paper according to the present invention is a main body, which includes a metal cylinder (2) with a circular cross-section and two side heads (3), on which two corresponding coaxial pins (4) arranged along the rotation axis (xx) of the Yankee are formed or mounted, and the main body is configured to rotate around the rotation axis (xx) at a predetermined angular velocity, wherein a fixed electromagnetic induction heating system is arranged inside the main body, and the electromagnetic induction heating system includes one or more inductors (H; HN), which electromagnetically interact with the cylinder (2) to generate an induced current in the same cylinder, and the one or more inductors (H; HN) are arranged near the radially innermost surface of the cylinder (2).

[0067] According to the above description, it is also obvious that the Yankee dryer according to the present invention may also have one or more of the following features, and these features may also be combined:

[0068] The Yankee dryer has an external diameter comprised between 2.00 m and 7.500 m, and the cylinder (2) has an axial length comprised between 3.00 m and 7.400 m.

[0069] The electromagnetic induction heating system extends axially along the inner surface of the cylinder (2), ie parallel to the Yankee axis (xx), but is shorter than the cylinder (2), leaving a free space (10) in front of each of the end pieces (3).

[0070] - The radial distance (S) between the radially outermost side of the electromagnetic induction system and the inner surface of the cylinder (2) is comprised between 20 cm and 1 mm, more preferably between 5 cm and 2 mm, even more preferably between 2 cm and 5 mm.

[0071] - said electromagnetic induction system comprises a single inductor (H) in the form of a solenoid developed around a Yankee axis (xx), the solenoid being formed by a coil concentric with said axis (xx).

[0072] The electromagnetic induction system comprises a single toroidal inductor (H) formed by a coil developed parallel to the Yankee axis (xx).

[0073] The electromagnetic induction system comprises a plurality of inductors (HN), each consisting of a solenoid developed around a Yankee axis and formed by a coil concentric with said axis.

[0074] The electromagnetic induction system comprises a plurality of inductors (HN) placed side by side in the axial direction.

[0075] The electromagnetic induction system comprises a plurality of inductors (HN), each inductor being formed by a solenoid consisting of a coil wound around a respective radial axis (RHN).

[0076] The electromagnetic induction system comprises a plurality of inductors (HN) arranged circumferentially around the axis of the Yankee.

[0077] - an inductor (H) or an inductor (HN) at a radial distance (S) from the inner surface of the cylinder (2), these inductors being formed by a coil (HS) consisting of a conductor having a predetermined diameter (d), the coils being spaced apart at a pitch of a predetermined value (P), characterised in that the value of the radial distance (S) is less than or equal to the difference between the pitch (P) and the diameter (d).

[0078] - one or more inductors having a side (HM) radially closer to the cylinder (2) and a side (HW) radially further away from the cylinder (2), wherein the side (HM) radially closest to the cylinder (2) is at a radial distance (S) from the inner surface of the cylinder (2), the inductor being formed by a coil (HS) consisting of a conductor of a predetermined diameter (d) and spaced from each other at a pitch of a predetermined value (P), and the value of the radial distance (S) being less than or equal to the difference between the pitch (P) and the diameter (d).

[0079] In practice, with respect to the various elements described and illustrated, the implementation details may in any case vary in an equivalent manner without thereby departing from the scope of the solution adopted and thus remaining within the scope of protection conferred by this patent according to the accompanying claims.

Claims

1. A Yankee dryer (1) for paper production, the Yankee dryer (1) comprising a main body, the main body comprising a metal cylinder (2) with a circular cross section and two side heads (3), on which two corresponding coaxial pins (4) arranged along the rotation axis (xx) of the Yankee are formed or mounted, the main body being configured to rotate around the rotation axis (xx) at a predetermined angular velocity, characterized in that: A fixed electromagnetic induction heating system is arranged inside the main body, and the electromagnetic induction heating system includes one or more inductors (H; HN). The one or more inductors (H; HN) interact electromagnetically with the cylinder (2) to generate an induced current in the cylinder, and the one or more inductors (H; HN) are arranged near the radial innermost surface of the cylinder (2).

2. The Yankee dryer according to claim 1, characterized in that: The Yankee dryer has an outer diameter comprised between 2.00 m and 7.500 m, and the cylinder (2) has an axial length comprised between 3.00 m and 7.400 m.

3. The Yankee dryer according to claim 1, characterized in that: The electromagnetic induction heating system extends axially along the inner surface of the cylinder (2), that is, parallel to the axis (xx) of the Yankee, but the electromagnetic induction heating system is shorter than the cylinder (2), thereby leaving a free space (10) in front of each of the end heads (3).

4. The Yankee dryer according to claim 1, characterized in that: The radial distance (S) between the radial outermost side of the electromagnetic induction system and the inner surface of the cylinder (2) is between 20 cm and 1 mm, more preferably between 5 cm and 2 mm, even more preferably between 2 cm and 5 mm.

5. The Yankee dryer according to claim 1, characterized in that: The electromagnetic induction system comprises a single inductor (H) in the form of a solenoid developed around the axis (xx) of the Yankee, the solenoid being formed by a coil concentric with the axis (xx).

6. The Yankee dryer according to claim 1, characterized in that: The electromagnetic induction system comprises a single toroidal inductor (H) formed by a coil developed parallel to the axis (xx) of the Yankee.

7. The Yankee dryer according to claim 1, characterized in that: The electromagnetic induction system comprises a plurality of inductors (HN), each consisting of a solenoid developed around the axis of the Yankee and formed by a coil concentric with the axis.

8. The Yankee dryer according to claim 1, characterized in that: The electromagnetic induction system includes a plurality of inductors (HN) arranged side by side in an axial direction.

9. The Yankee dryer according to claim 1, characterized in that: The electromagnetic induction system comprises a plurality of inductors (HN), each inductor being formed by a solenoid consisting of a coil wound around a respective radial axis (RHN).

10. The Yankee dryer according to claim 1, characterized in that: The electromagnetic induction system comprises a plurality of inductors (HN) arranged circumferentially around the axis of the Yankee.

11. The Yankee dryer according to claims 5-8, wherein: The inductor (H) or the inductor (HN) is at a radial distance (S) from the inner surface of the cylinder (2), these inductors are formed by a coil (HS), the coil (HS) is composed of a conductor with a predetermined diameter (d), and the coils (HS) are spaced apart at a pitch of a predetermined value (P), characterized in that the value of the radial distance (S) is less than or equal to the difference between the pitch (P) and the diameter (d).

12. The Yankee dryer according to claims 5-8, wherein: The inductor (H) or the inductor (HN) has a side (HM) radially closer to the cylinder (2) and a side (HW) radially farther from the cylinder (2), wherein the side (HM) radially closest to the cylinder (2) is at a radial distance (S) from the inner surface of the cylinder (2), the inductor is formed by a coil (HS), the coil (HS) is composed of a conductor of a predetermined diameter (d) and is spaced apart from each other at a pitch of a predetermined value (P), characterized in that the value of the radial distance (S) is less than or equal to the difference between the pitch (P) and the diameter (d).

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