Scope of the invention
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The present invention refers to the technical field relating to burner devices for heating a flow of gas, generally air.
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Preferably, said burner device can be used in the paper production sector, in particular to dry the cellulose mixture in a plant for producing paper.
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In particular, the invention refers to a burner device that provides for the use of electrical resistors and gas burners placed in parallel to each other.
A brief outline of the prior art
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The process for producing paper, for example in tape form, has been well known for some time.
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In this process, plants are used in which the tape under processing, constituted by a water-rich cellulose mixture, must be dried to obtain the finished product.
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Drying takes place by passing the water-rich tape (percentage of water typically in the range between 50% - 60%) on a heated roll called in technical jargon Yankee dryer roll or Yankee cylinder. The roll (or cylinder as the case may be) is heated as it contains a steam passage inside it and, in this way, the heated tape dries as its water content evaporates.
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In addition to the heat released by the Yankee dryer roll, a hood arranged above said Yankee dryer roll is also used in combination in order to at least partially cover said roll. The hood is connected to a burner (also called a burner device) which is in line burner and therefore heats a flow of air that is projected through the hood on the tape arranged on the single layer. The burner therefore heats a flow of air that, through the hood, hits the tape that passes over the Yankee dryer roll.
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In this way, the tape under processing undergoes drying thanks to the combined effect of the steam-fed Yankee dryer roll and the flow of hot air ejected from the hood through the burner device.
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The liquid that is progressively dried generates a "flue", that is, a hot flow of air and steam (hot fumes), with high temperatures, even above 400 °C. It is also generally known to recover these hot fumes generally fed at least in part to the plant for energy savings and an increase in efficiency.
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There are many drying plants that commonly use burner devices used to send a flow of hot air towards the Yankee dryer roll.
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For example, European publication
EP4 089 230 in the name of the same Applicant is known, in which recovery steam is produced using two separator tanks connected in succession to each other and with a heat exchanger interposed between them.
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The Mevas Srl's solution therefore comprises the usual in line burner device 116 that feeds the hood and with the hood recovering the flue, as described above.
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A further solution, specifically for the burner device, concerns the
Italian application 102022000025203 of 07-12-2022 on behalf of Fives ITAS S.p.A.
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This solution describes, in a burner device, the combined use of classic gas burners together with electrical resistors.
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In the preferred configuration of the invention, the electrical resistors are arranged upstream of the classic gas burners with respect to the direction of forward motion of the airflow, so that the air first intercepts the electrical resistors to preheat, and then completes the heating immediately after intercepting the burners placed downstream.
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This solution therefore has the advantage of allowing a saving in the use of the gas burners with a consequent reduction in carbon dioxide.
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However, in all the configurations described, both the classic gas burner and the electrical resistors are placed in the same chamber and concentrically or in series, such that there is a single airflow that hits both of the aforementioned components in series.
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In particular, a solution is described in which the electrical resistor pack is placed upstream of the subsequent classic burner and in series.
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This solution causes several technical problems.
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One of these concerns the interruption of the process due to possible clogging of the electrical resistors due to paper residues.
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The airflow, in fact, is loaded with microparticles of paper since the plant operates in a paper production environment and the material under processing is cellulose. The passage of airflow loaded with paper particles through the resistors causes a combustion effect of the paper particles. If, however, they do not burn completely, it can result in a flow clogging effect which therefore greatly reduces the flow rate, even being able to block the entire process. Upstream clogging of the resistors implies a lack of downstream flow supply to the burners.
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In addition, the arrangement in series is not flexible as it does not allow to adjust the amounts of airflows that it is wished to pass through the classic heater and through the electrical resistors. As there is an arrangement in series, there is a single flow that is preheated by meeting the electrical resistors and then completes the process by intercepting the gas heater.
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The series configuration means that the burner and resistor pressure drops are added together. In fact, the pressure drop due to the resistors influences the further pressure drop due to the next burner.
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In the series configuration, moreover, there is generally a working condition with constant airflow rate to be heated and variable temperature. This means that, in the case of partial powers, there is a surface temperature of the resistor below the clogging limit temperature.
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The problem related to clogging set forth above, in the series plant configuration, is even accentuated in the operating condition with the electrical resistor switched off and the burner on. All the air passing through the resistor meets the cold filaments creating an exponential clogging effect.
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In the opposite configuration to the one mentioned above, i.e. with the burner off and high load resistor, the burner in the rear section is hit by very hot air that decreases its structural life over time. Generally, the in-line burners for industrial processes are in fact made of refractory materials (therefore for high temperature) only in the front part on the flame front.
Summary of the invention
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It is therefore an object of the present invention to provide a new burner device that solves the aforementioned technical drawbacks.
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In particular, it is the object of the present invention to provide a burner device that allows reducing the problem of possible clogging of electrical resistors, optimizing the flexibility of the device and therefore also optimizing the possibility of being able to use an electrical source, when for example it is available in large quantities, for example because it is derived from renewable sources, thus reducing CO2 production.
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It is also an object of the present invention a solution that allows to better adjust the heating of the flow while minimizing pressure losses.
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These and other purposes are achieved with the present burner device, preferably for a plant for producing paper, in accordance with claim 1.
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Such a burner device (or heating device as the case may be) is therefore preferably suitable for performing the drying (or for drying as the case may be) a tape of paper material (for example a cellulose mixture) in a paper production process.
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Preferably, said burner device is therefore usable for drying paper material, preferably in the form of a tape, in a plant for producing paper.
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Preferably, the burner device is an in-line burner, that is, it heats a flow of air that passes through it and which is then used to perform the drying.
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In all the aforementioned cases, said burner device comprises:
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A main conduit along which, in use, an airflow, to be heated can be sent;
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One or more burners adapted to generate a flame and one or more electrically heating elements arranged inside said main conduit;
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In this way the heating of the gaseous flow, for example air, is carried out.
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Preferably, but not necessarily, the burners may be classical gas burners in which the gas, which is mixed with air, generates the flame.
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Generally, these gas burners are also referred to as heaters.
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Advantageously, the electrically heating elements heat the flow intercepted by them as they heat up through the passage of electric current, thereby heating the flow that laps them.
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Advantageously, in a preferred configuration of the invention these electrically heating elements are simple electrical resistors which, as mentioned, heat up during the passage of electric current (generally this is referred to as the Joule effect).
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Advantageously, in all the aforementioned cases, said one or more electrically heating elements (for example electrical resistors as mentioned) and said one or more burners are arranged in such a way as to be, in use, intercepted (or in any case in such a way as to intercept the) by the airflow sent along said main conduit;
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In this way, advantageously, the incoming airflow along the main conduit intercepts both the burners (for example the gas heaters) and the electrically heating elements (for example the electrical resistors) hence heating up to a predetermined temperature and hence a flow heated to a predetermined temperature exiting the main conduit.
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Now, in accordance with the invention, we have that:
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Said one or more electrically heating elements are arranged in parallel to said one or more burners.
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In this way these two elements can work independently of each other, such that the obstruction of one does not cause the blockage of the other as happens in the series or concentric arrangement.
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In particular, this configuration solves the problem of possible clogging of the electrically heating elements, especially in use in the plant for producing paper.
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In fact, in the plants for producing paper, the paper residues present in the flow may not be burned by the heat of the resistors causing clogging. In accordance with the proposed parallel solution, even in case of clogging, the electrically heating elements and the burners work independently (they are in fact placed side by side) such that an obstruction of the electrically heating elements does not cause an interruption or reduction of flow for the burners.
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In addition, the parallel configuration means that burner and resistor pressure drops do not add up as in the series solution.
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With the same electrical power available, in the parallel configuration with respect to the series one, there is the advantage of being able to have the resistors work at fixed temperature and variable air flow rate. Setting the filament temperature above the deposition temperature of the paper powder solves clogging problems.
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In addition, the parallel solution greatly increases the durability of the burner component when the latter, for reasons of energy opportunity, should be switched off for long periods.
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The parallel arrangement may therefore provide for side arrangements, including arrangements side by side or one above and the other below but always parallel to each other.
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Advantageously, in a preferred configuration of the invention, at least the main conduit portion which comprises said one or more electrically heating elements and said one or more burners comprises or forms two different through-chambers independent of each other.
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In this way one can have a fluidic insulation between the two chambers that work independently.
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Advantageously, therefore, in this way the incoming flow can partly access one chamber and partly access the other chamber by passing through the through-chambers to head towards the exit.
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Furthermore, always in accordance with a preferred configuration of the invention, in one of said two chambers one or more burners are placed while in the other chamber one or more electrically heating elements are arranged.
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Thanks to this preferred solution, further advantages can be obtained.
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The arrangement in parallel, through two mutually distinct chambers, allows to precisely adjust the amount of flow that one wishes to pass from one chamber or from the other so that one can precisely make the most of the possible availability of electricity in the event that it is available in quantities, for example through renewable sources.
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This adjustment is important, in order to maintain high temperatures on the elements of the electrical resistors in order to avoid deposits of paper material that lead to the consequent clogging.
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Advantageously, said two chambers are fluid-tight (or fluidifies, as the case may be).
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In this way, advantageously, the gaseous flow (for example air) circulating in one chamber cannot therefore pass into the other adjacent chamber.
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This allows to precisely control the amount of flow to be heated through the electrically heating elements compared to the amount of flow to be heated with the burners.
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Advantageously, said two chambers are parallel to each other.
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As mentioned, the electrically heating elements may be electrical resistors.
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According to an advantageous aspect of the invention, within each chamber at least one barring element (for example a shutter) can be provided movable between a position obstructing the passage of flow and a position in which it fully releases said passage of flow.
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Advantageously, said barring elements are movable in a plurality of intermediate positions comprised between said barring position and said position in which the passage is fully released.
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In this way, it is advantageously possible to precisely adjust a total or partial passage of flow depending on the selected position (intermediate, fully closed, fully open).
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According to a possible constructive solution, advantageously, the main conduit can for example comprise a dividing partition arranged inside the main conduit in such a way that it creates two distinct chambers in which the passage of flow from one chamber to the other is prevented.
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For example, advantageously, said dividing partition may extend for a longitudinal length portion of said main conduit.
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In this way, advantageously, a single conduit can be obtained in an initial portion of the main conduit upstream of the dividing partition and a single conduit in a final portion of the main conduit downstream of said dividing partition, along the direction of forward motion of the flow.
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In accordance with this solution, advantageously, the initial portion of the conduit has an inlet opening of the airflow to be heated and the final portion of the conduit has an outlet opening for the heated flow coming from at least one of said two distinct chambers.
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In this way, the incoming flow splits into predetermined percentages in the two chambers and then reunites in the final outflow portion.
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Advantageously, the electrical resistors are placed to form a barrier that affects the entire cross section of the chamber where they are placed in such a way as to form a barring wall for the flow that passes through them passing in the free space between the resistors.
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A first temperature sensor (M) to measure an outlet temperature and a second temperature sensor (M') arranged in the chamber (31) where the electrically heating elements reside are also provided.
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A controller is therefore provided that adjusts the gas flows entering the two chambers (31, 32) and/or the powers in order to have a preset temperature value in the chamber containing the electrically heating elements and/or at the downstream outlet.
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In particular, the temperature in the chamber containing the electrically heating elements is such as to allow all paper residues to be burned, avoiding clogging, for example above 400 °C, for example about 500 °C.
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Advantageously, there is therefore a controller connected to a first temperature sensor (M) arranged downstream of the main conduit.
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Advantageously, the controller is further connected to a second temperature sensor (M') arranged to detect the temperature in the through-chamber (31) containing the electrically heating elements (15).
In this way the two sensors detect the measured temperatures and the controller adjusts the flows entering the through-chambers and/or the electrical powers to be fed to the electrically heating elements and/or the powers to be fed to the burners in such a way as to maintain the temperatures in exit and/or in the chamber containing the electrically heating elements at a value which can be preset.
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According to a preferred form of invention there is provided at least one temperature sensor (M') to measure a temperature in the chamber (31) where the electrically heating elements reside.
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A controller is therefore provided that adjusts the flow of gas entering the through-chamber (31) where said temperature sensor (M') and/or the powers to be fed to the electrically heating elements arranged in said through-chamber (31) are provided in order to have a preset temperature value in the chamber containing the electrically heating elements.
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Another object of the present invention is a plant for producing paper comprising at least one Yankee dryer roll on which a tape of paper material to be dried transits or is arranged in use.
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The plant also comprises a hood arranged above said Yankee dryer roll and through which a flow of drying air is sent to the tape under processing.
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In accordance with the invention, the plant comprises a burner device in accordance with one or more of the above characteristics, for heating the airflow to be sent to the hood.
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All the above advantages are therefore obtained.
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It is also an object of the present invention to use a burner device, in accordance with one or more of the above characteristics, in a plant for producing paper.
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In particular, advantageously, such use is indicated in order to generate a hot airflow to be sent along a path towards the outer surface of a Yankee dryer roll for drying a cellulose tape arranged or transiting in use on said Yankee dryer roll.
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A further object of the present invention is a method for drying a tape under processing constituted by a cellulose mixture in a plant for producing paper.
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The method, in accordance with the invention, provides for transit of the tape on the surface of a Yankee dryer roll and sending of a flow of hot air on the surface of the Yankee dryer roll for drying the tape arranged thereon.
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In accordance with the method, the airflow is heated through a device in accordance with one or more of the above characteristics.
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In particular, advantageously, the following steps can be highlighted:
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Detection of the temperatures downstream (in exit from the conduit) and inside the chamber 31 containing the electrically heating elements;
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Adjustment of the flows and/or powers as a function of the measured temperatures.
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In particular, the temperature in the chamber 31 and/or that downstream of the outlet can be set to a predetermined value.
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Advantageously, an adjustment of the barring elements can take place to adjust the percentage of airflow to be sent along the chamber containing the electrically heating elements and along the chamber containing said one or more burners;
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Subsequently sending airflow along the main conduit once the electrically heating elements and the burners have been activated.
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A method for heating an airflow through a device in accordance with one or more of the above features is also an object of the present invention.
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Advantageously, said method envisages the steps of:
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Adjusting the barring elements for adjusting the percentage of airflow to be sent along the chamber containing the electrically heating elements and along the chamber containing said one or more burners;
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Subsequently sending airflow along the main conduit once the electrically heating elements and the burners have been activated.
Brief description of the drawings
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Further features and advantages of the present burner device, in accordance with the invention, will become clearer with the following description of some of its embodiments, made by way of non-limiting example, with reference to the accompanying drawings, in which:
- figure 1 shows a solution schematization;
- figure 1A shows a detailed diagram in relation to the burner device installed inside a plant portion, preferably a plant for producing paper;
- figure 2 shows an example of a plant for producing paper in which this type of device can preferably be used, for example a plant in accordance with publication EP4089230 in the name of the same Applicant;
- figure 3 schematizes the arrangement of the electrical resistors in the specific chamber where they are arranged.
Description of some preferred embodiments
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The present invention concerns a burner device usable in various contexts, including for example in the plants for producing paper where it is necessary to generate and send a flow of hot gas, generally heated air, to be sent on the cellulose tape under processing to cause it to dry and obtain the finished product, i.e. the paper.
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In accordance with the invention, as better detailed below, the combination of electrically heating elements, for example an electrical resistor pack, and one or more burners (for example a burner pack), for example the classic gas burners also called heaters, are used.
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The electrical resistor pack is placed in parallel with respect to the burner or the burner pack so that it turns out that a pack of the one is placed next to the other at a certain distance.
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Furthermore, preferably and advantageously, these elements can be arranged in two distinct channels, i.e. the resistor pack in a channel fluidically isolated (i.e. fluid-tight) from the other channel that receives the burner pack.
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Figure 2 schematizes a plant for producing paper in which such a burner device can advantageously be applied.
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The plant for producing paper described in figure 2 is a non-limiting example, being obviously understood that the present burner device is perfectly usable in any plant for producing paper.
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The present burner device can obviously also be used in other applications in sectors other than the paper sector where a hot flow is necessary.
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In the specific case of a plant for producing paper, the tape under processing, constituted by a water-rich cellulose mixture, must be dried to obtain the finished product.
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Drying takes place by passing the water-rich tape (percentage of water well above 60%) on a heated roll called a Yankee dryer roll in technical jargon. The roll is heated as it contains a steam passage therein and, in this way, the heated tape dries as its water content evaporates.
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Figure 2 shows, therefore, the Yankee dryer roll (also called Yankee Roll) 112.
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In addition to the heat released by the Yankee dryer roll, a hood 114 arranged above said Yankee dryer roll and connected to a in-line burner 1 is also used in combination.
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The burner heats the airflow which, through the hood, hits the tape that passes on the Yankee dryer roll.
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In this way, the tape under processing undergoes drying thanks to the combined effect of the Yankee dryer roll and the flow of hot air ejected from the hood through the burner.
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These plants may then have any energy recovery systems, not a specific object of the present invention.
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In particular, the liquid that is progressively dried generates a "flue" that is a hot flow of steam and liquid particles that rises from the tape and with high temperatures, even above 400 °C. The recovery of these hot flows may allow them to be re-introduced into the plant in order to reuse them, for example, to heat the Yankee dryer roll or feed the line of the burner.
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With reference to figure 2, the Yankee dryer roll 112 wrapped at least in part by the hood 114 placed above it is therefore highlighted.
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The hood 114 is arranged on the roll 112 in such a way as to wrap it at least in part.
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The fumes ("the flue") rising upwards and collected by the hood can be sent in part through a first line 126' to a fan 128 that forces these fumes towards the burner device 1, thus already having a first partial recovery.
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The burner device 1 feeds the hood with the flow of hot drying air that is sent on the surface of the Yankee dryer roll on which the cellulose material tape (essentially paper tape) to be dried passes.
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Going into more detail of the burner device 1, this is schematically represented in figure 1.
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The burner device 1 develops, through a special conduit 10, according to a main longitudinal direction (X) indicated in figure 1 through the arrow X.
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The development therefore starts from an inlet zone of the gas flow to be heated, generally air, and in figure 1 this zone is indicated as "Upstream".
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The flow moves along the conduit 10 from upstream to downstream, hence from an inlet opening of the conduit towards an outlet opening of the conduit itself.
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Figure 1 shows, therefore, with the designation (In) the opening of entry to the conduit 10 and with the designation (Ex) the exit.
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In the conduit, therefore, three zones can be distinguished:
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An inlet zone 11 (also called initial portion 11) facing upstream and comprising said inlet opening (In);
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An outlet zone 12 (also called end portion 12) facing downstream and comprising said outlet opening (Ex);
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A central connecting zone 13 (also called the intermediate portion) that connects the inlet zone with the outlet zone.
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Figure 1 shows how the inlet zone 11 is connected to a fan 21 that forces the gaseous flow, for example air, along the conduit 10 feeding it to the inlet 11.
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Further hot gaseous flow recovered from the flue can be pushed into the conduit 10 through the inlet 11 by means of a further auxiliary fan 21' (see in this regard figure 1A).
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Inside the conduit 10, as shown in figure 1 and figure 1A, one or more burners, for example gas burners in the preferred form, are arranged to form a burner pack 16 and one or more electrically heating elements 15, for example one or more electrical resistors to form an electrical resistor pack 15.
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The electrically heating elements, for example electrical resistors, are powered by electric current such that the circulating current generates, as is well known, a heating. In particular, the electrical resistor heats up thus transferring the heat to the flow that laps it.
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The electrical resistor pack 15, arranged in the conduit 10, is therefore hit by the gaseous flow (generally air) pushed by the fan 21, hence heating the air that enters the inlet with a certain temperature T1 and exits the conduit at a temperature T2 greater than T1.
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In the same way, the burner pack 16 arranged in the conduit 10 is therefore hit by the gaseous flow (generally air) pushed by the fan 21, hence heating the air that enters the inlet with a certain temperature T1 and exits the conduit at a temperature T2 greater than T1.
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The temperature T2 is obviously the result of heating due to the contribution of the burner pack and of the electrical resistor pack.
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The temperature T2 is therefore a function of the current adjustment in the resistor and function of the flame in the burners.
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In accordance with the invention, as schematized in figure 1 and 1A, the electrical resistor pack 15 and the burner pack 16 are arranged in parallel, thus at a certain distance from each other.
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The parallel arrangement therefore indicates that the burner pack 16 can be placed next to or above or below the resistor pack 15.
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Figure 1A clearly schematizes this arrangement.
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Figure 1A therefore shows the fuel that is fed to the burners which, through fuel (gas generally) and air produce the flame. In the same way, the electric resistors are electrically powered with a potential difference to generate circulating electric current.
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The parallel arrangement therefore makes it possible to optimise the heating process by allowing the two envisaged packs (electric and gas) to operate independently, avoiding the obstruction of one of them hindering the operation of the other like in the concentric or series arrangement.
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Advantageously, again with reference to figure 1 or 1A, it is possible to make the connecting part 13 containing said elements (15, 16) in such a way as to form two distinct through-chambers separated from each other and therefore not in fluidic communication with each other.
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Fluidic communication means a communication of fluid, for example gas.
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In particular, the schematization of figure 1A shows a dividing wall 30 also highlighted in figure 1.
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The dividing wall can have any shape but, in any case, it generates the formation of two through-chambers.
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So the intermediate portion 13 is as if it comprises inside it or conforms two independent conduits fluidly isolated from each other. The resistor pack is arranged in one conduit and the burner pack in the other.
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The wall 30, as schematized in figure 1A, prevents the passage of the introduced air to be heated from one chamber to the other such that two independent conduits are formed in each of which a certain percentage of the air introduced into the conduit penetrates.
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In other words, the air introduced in entry partly goes into the conduit 31 containing the electric resistor pack 15 and partly into the other conduit 32 containing the burner pack 16.
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The flow circulating in the conduit 31 cannot pass in the conduit 32 (and vice versa) because of the dividing wall 30.
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Still in accordance with the invention, the schematization of figure 1 shows the barring elements 21 which, for example, can be placed at the entry and/or exit of said chambers 31 and 32.
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These barring elements can be in the form of automatically movable shutters, for example with a motion controllable by an outer control system, such that an operator can close or open them or partially open them.
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In this way it is possible to adjust the degree of opening of these barring elements, thus controlling the amount of flow (as said, generally air) that can penetrate the two chambers escaping from them.
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It is thus possible to selectively adjust the amount of flow to be heated by means of the electrical system and the one that can be heated by means of burners, thus also inducing an operation in which the flow circulating in the chamber 32 containing the burner pack 16 is equal to zero, thus diverting all the flow towards the through-chamber 31 or vice versa.
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Figure 3 finally shows, schematically, an arrangement of the electrical resistors 15 that are arranged to form a barrier of the opening to which they are applied, such that the flow obviously passes in the interspace between the coils.
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The resistors, generally coil-like, can therefore be connected to one wall side of the chamber and extend for almost the entire width of the chamber towards the opposite wall and for the entire height, thus forming a transverse barrier that therefore heats the entire flow-through section.
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Coming back briefly to figure 1, a first temperature sensor is shown, indicated as M, which is used to detect the downstream exit temperature so that, in feedback, the power of the resistors and/or burners and/or the relative flows that hit them can be adjusted in order to obtain the desired exit temperature.
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In this regard, there is therefore a temperature controller (also called a controller) that can modulate the amount of electric current or voltage to be fed to the resistors, the flame power of the burners and the flow fed to both to obtain the desired value downstream.
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That said, there is also a further temperature sensor (therefore a second temperature sensor) indicated with the wording (M') which is instead arranged at the chamber 31 having the electrical resistors. Said second temperature sensor makes it possible to detect an ambient temperature in the specific chamber 31 such that the temperature set in said chamber is at the preset value, for example about 500 °C. For example, temperatures can be set from 400 °C upwards. Regardless of the temperature, monitoring is used to know what the heat is produced by the resistors and the consequent temperature in chamber 31 where arranged, ensuring that the temperature is such that all the paper residues can be burned well, thus avoiding clogging of the resistors. The example temperature of 500 °C is considered as optimal. It follows that, if the second sensor (M') measures a temperature lower than that preset by the control panel (for example lower than 500 °C), an adjustment takes place automatically (through the controller) that brings the temperature back to the set value. The setting can operate depending on the conditions detected, such as the usable amount of current if this is available, hence feeding more the resistors and/or modulating the flow in entry to the chamber relative to the electrical resistors 15. For example, in the event of low current availability, there is a reduction in the flow in entry to the chamber 31 containing the electrical resistors. The controller is therefore programmed to perform these operations through temperature detection made by means of the sensors (M, M').
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In other words, by means of the second temperature sensor (M') the temperature in the electrical resistor chamber 31 can be measured in real time in order to modulate the use of current to be fed to the resistors and/or the flow in order to maintain a preset temperature, for example of 500 °C, in order not to clog the electrical resistors with paper residues.
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The first downstream sensor (M) detects the exit temperature such that, if this is not at the preset value, the controller intervenes by adjusting flows and/or powers always in compliance with the preset temperature condition in the chamber 31.
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In this way there is no risk of clogging with a precise exit temperature.
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As therefore shown in figure 1 from the arrow direction of the flows, an airflow, pushed by the fan 21, is pushed along the conduit 10. It is divided into a portion that passes through the chamber 31 containing the electrical resistor pack 15 and a portion that passes through the chamber 32 containing the burner pack 16. The portion of flow that passes through the burner pack 16 is heated as a function of the heat produced by them while the flow that passes through the electrical resistor pack 15 is heated as a function of the current circulating in them and therefore of the heat of overheating of their filaments of which they are made.
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The two flows in exit from the two said chambers mix in the outlet portion 12 of the conduit in order to exit from the outlet (Ex).
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The outflow can be directed, for example, towards the hood in the case of plants for producing paper.