Apparatus for producing a web-shaped paper material

Abstract

This document describes an apparatus for producing web-shaped paper material, comprising forming equipment for dispensing paper material slurry onto a supporting canvas and dewatering equipment for dewatering the paper material slurry to form web-shaped paper material. The dewatering equipment includes a first rotating perforated cylindrical member and a second rotating rotating perforated cylindrical member, and a heating system for generating and delivering hot process air to at least one of the first and second rotating rotating perforated cylindrical members. The first rotating perforated cylindrical member operates under relative pressure conditions, and hot process air is blown from inside the first rotating perforated cylindrical member toward the web-shaped paper material conveyed by the supporting canvas. The second perforated cylindrical member operates under relative vacuum conditions, and hot process air is drawn from the web-shaped paper material conveyed by the supporting canvas through the second rotating perforated cylindrical member. A recovery loop recovers the hot process air drawn from the second rotating perforated cylindrical member and delivers this hot process air to the first rotating perforated cylindrical member.

Description

Technical Field

[0001] The present invention generally relates to apparatus for producing web-like paper materials, and particularly to apparatus of the so-called TAD (an acronym for "Through Air Drying") type for producing high-quality tissue paper. Background Technology

[0002] As is well known, in general papermaking processes, especially in the production of tissue paper, a step of drying the treated product by evaporation to remove its residual moisture is necessary. The product to be dewatered, typically consisting of cellulose-based pulp diluted with water, is initially prepared in suitable forming equipment and thus delivered to subsequent drying and dewatering equipment after an intermediate pressing step. At the inlet of the drying and dewatering equipment, the pulp forming the paper to be treated contains a lower dry fraction content that can be between about 24% and 28%. In other words, after the pressing step, the pulp may still contain up to 75% or more water. Therefore, the vacuum extraction step cannot remove all the water from the pulp fibers, and this water must be removed by evaporation.

[0003] The final product, typically but not entirely composed of tissue paper, requires a dry fraction content far exceeding the aforementioned values, usually between approximately 94% and 98%. Therefore, it is evident that most of the residual moisture needs to be removed from the fibrous pulp through evaporation during the drying step to obtain a sufficiently dry, continuous sheet. Following the drying and dewatering steps via evaporation, the paper is stored in rolls for subsequent processing (the so-called "conversion" step) and finally packaged for transport and final retail.

[0004] Among the equipment used for producing web-like paper materials, the known type of equipment called TAD (an acronym for "by air drying") is well-known and particularly valued. TAD technology uses a jet of hot air that passes through the cellulose pulp before it is wound around a conventional Yankee dryer. Essentially, by transferring sensitive heat, the air allows the water retained by the paper material fibers and the water chemically bound to the cellulose fibers to evaporate.

[0005] In the TAD process, the paper fiber pulp is supported by a continuously moving support belt, which typically comprises a canvas that can withstand temperatures up to 200°C to 250°C. The canvas, and therefore the paper fiber pulp, follows the rotating surface of a perforated cylindrical section, allowing for the exchange of hot air with the paper fiber pulp.

[0006] Therefore, TAD technology allows for the production of high-quality tissue paper because it is a drying technique that applies very slight impact mechanical action to the paper material fiber pulp, thus avoiding the strong effects of conventional suction presses and / or blind holes. The end result is paper with greater volumetric strength, softness, and absorbency compared to paper manufactured using conventional techniques, thereby allowing for lower fiber consumption.

[0007] The TAD type equipment currently offers two operating types of paper fiber pulp drying equipment, which is essentially connected to two corresponding types of perforated cylinders. In fact, these perforated cylinders can operate under relative pressure conditions (so-called "Vertiflow type") or under relative vacuum conditions (so-called "Inflow type"). For each type of perforated cylinder, the winding of the paper fiber pulp to be dried can be carried out on two or more cylinders.

[0008] For example, US 3303576 A discloses an apparatus for producing web-like paper material, wherein the perforated drying cylinder operates under relative pressure conditions. Alternatively, FR 2733522A1 discloses an apparatus for producing web-like paper material, wherein the perforated drying cylinder operates under relative vacuum conditions. Other known types of apparatus for producing web-like paper material are disclosed in US 2003 / 019601 A1 and US 2018 / 073195 A1.

[0009] TAD-type equipment, which includes perforated cylindrical sections operating under relative pressure (“vertical flow type”), suffers from limitations in certain drying capabilities due to the difficulty in maintaining the paper material fiber pulp adhered to the surface of each section by tensioning the canvas. Conversely, TAD-type equipment, which includes perforated cylindrical sections operating under relative pressure, has a simpler structural design because these sections are subjected to lower mechanical stresses.

[0010] TAD-type equipment, which includes perforated cylindrical elements (“inflow type”) operating under relative vacuum conditions, has a greater specific evaporation capacity; however, this depends on the capacity of the recirculation fan installed in these devices. Conversely, TAD-type equipment, which includes perforated cylindrical elements operating under relative vacuum conditions, requires a more robust mechanical structure because each cylindrical element is subjected to very high mechanical stresses under operating conditions.

[0011] Regardless of the type of equipment, each perforated cylindrical component is equipped with a corresponding extraction hood and process air recirculation loop, which includes one or more recirculation fans, one or more air-heated burners, and one or more extraction fans for extracting hot and humid air (the so-called "flue gas"). In addition to removing air that permeates from the machine room through the contact seals, the extraction fans must also remove water vapor generated due to the drying of the paper material fiber pulp. Considering the amount of air permeated, the heat loss occurring under these conditions is significant, even though the extraction temperature is approximately 100°C or slightly higher.

[0012] It should be observed that when two or more perforated tubular sections are used in a TAD-type device, the average unit evaporation of the paper material fiber pulp decreases significantly from the first tubular section to the last. Furthermore, it should be observed that in TAD-type devices comprising perforated tubular sections operating under relative pressure conditions (“vertical flow type”), the canvas supporting and maintaining the paper material fiber pulp (wet-formed) to be dried and adhering to each perforated dewatering tubular section is particularly under mechanical stress because it must support the thrust of the air passing through from the inside of the perforated tubular section toward the outside.

[0013] Conversely, in TAD-type equipment that includes a perforated cylindrical element (“inflow type”) operating under relative vacuum conditions, the canvas is subjected to low mechanical stress, while the perforated cylindrical element is subjected to high mechanical stress because the perforated cylindrical element must support the entire thrust of the air passing through it from the outside of the perforated cylindrical element toward the inside of the perforated cylindrical element. Summary of the Invention

[0014] Therefore, the object of the present invention is to provide an apparatus for producing web-shaped paper materials, particularly a so-called TAD-type apparatus, which overcomes the aforementioned deficiencies of the prior art in an extremely simple, cost-effective, and particularly practical manner.

[0015] In detail, the object of the present invention is to provide a TAD-type device for producing web-shaped paper materials that is easier to manufacture than similar TAD-type devices according to the prior art.

[0016] Another object of the present invention is to provide a TAD-type device for producing web-type paper materials that is simpler to construct than similar TAD-type devices according to the prior art, yet capable of producing high-quality web-type paper materials.

[0017] Another object of the present invention is to provide a TAD-type device for producing web-shaped paper materials that allows for energy savings compared to similar TAD-type devices according to the prior art.

[0018] These objectives of the invention are achieved by providing apparatus for producing web-shaped paper materials as described in embodiments of the invention. Further features of the invention are summarized by preferred embodiments thereof, which are an integral part of this application. Attached Figure Description

[0019] The features and advantages of the apparatus for producing web-shaped paper materials according to the invention will become more apparent from the following exemplary and non-limiting description with reference to the accompanying drawings, in which:

[0020] Figure 1 This is a schematic diagram of the main components of an apparatus for producing web-shaped paper materials according to the present invention;

[0021] Figure 2 It is used for production Figure 1 A detailed schematic diagram of the desiccating equipment in the fabrication of web-shaped paper materials;

[0022] Figure 3 yes Figure 2 A partial cross-sectional view of the first drying unit of the dehydration equipment; and

[0023] Figure 4 yes Figure 2 A partial cross-sectional view of the second drying unit of the dehydration equipment. Detailed Implementation

[0024] Referring to the accompanying drawings, a preferred embodiment of an apparatus for producing web-shaped paper material according to the present invention is shown. The apparatus is generally indicated by reference numeral 10. Figure 1 As shown in the schematic diagram, the device 10 first includes at least one continuous support belt 14, 16, which is movable by a plurality of rollers 18, 20.

[0025] The apparatus 10 also includes at least one forming device 12 for forming a web of paper material 200. This forming device 12 further includes at least one means 22 for dispensing the paper material slurry 100. The dispensing means 22 is designed to deposit the paper material slurry 100 onto support belts 14, 16, which must subsequently be dried. The paper material slurry 100 can be any known type in the art, and may include cellulose fibers and / or any other materials suitable for manufacturing the web of paper material 200; the paper material slurry preferably, but not exclusively, includes tissue paper.

[0026] Downstream of the forming equipment 12, at least one dewatering device 24 is provided, which is designed to at least partially dewater the paper pulp 100 conveyed by the support belts 14, 16 to form a web of paper material 200A. In the embodiment of the device 10 shown in the figure, a first support belt 14 belonging to the forming equipment 12 and a second support belt 16 belonging to the dewatering device 24 are provided. The configuration of the support belts 14, 16 can be modified as needed in any case, while maintaining the technical function of first supporting and conveying the paper pulp 100 and then supporting and conveying the web of paper material 200 throughout the device 10. Preferably, each support belt 14, 16 may comprise a fabric with a plain weave, and each support belt 14, 16 is made of a material that can withstand temperatures up to 200°C to 250°C.

[0027] The dewatering equipment 24 includes at least one first device for drying paper pulp 100. The first device includes a first rotating perforated cylindrical member 26, on which the paper pulp 100, conveyed by a support belt 16, is dynamically adhered. Specifically, the first rotating perforated cylindrical member 26 is a cylindrical member having an annular base with a predetermined diameter D1.

[0028] The dewatering equipment 24 also includes at least one second device for drying the paper pulp 100. The second device includes a second rotating perforated cylindrical member 28, on which the paper pulp 100, conveyed by the support belt 16, is dynamically adhered. This second rotating perforated cylindrical member is also a cylindrical member having an annular base with a predetermined diameter D2. Therefore, the second rotating perforated cylindrical member 28 is positioned downstream of the first rotating perforated cylindrical member 26.

[0029] The dehydration equipment 24 also includes heating systems 30, 32, 34, 36, 38, and 40, which are designed to generate hot process air and deliver it to at least one of a first rotating perforated cylindrical member 26 and a second rotating perforated cylindrical member 28. Specifically, the heating system may sequentially include, relative to the first rotating perforated cylindrical member 26, one or more combustion air fans 34, one or more process air heating burners 30, and one or more pumps 40 for supplying heated process air to the first rotating perforated cylindrical member 26. Similarly, relative to the second rotating perforated cylindrical member 28, the heating system may sequentially include one or more combustion air fans 36, one or more process air heating burners 32, one or more process air fans 38 to move the heated process air and one or more extraction fans 54.

[0030] The dewatering equipment 24 may also include an additional rotary heating cylinder 52, also known as a "Yanke dryer," in a manner known per se. The Yanke dryer 52 is positioned downstream of the second rotary perforated cylinder 28, and the paper pulp 100 is dynamically adhered to the entire surface of the Yanke dryer 52 for final drying of the paper pulp.

[0031] The first rotary perforated cylindrical member 26 is a cylindrical member operating under relative pressure conditions (“vertical flow type”), such that hot process air is blown from the interior of the first rotary perforated cylindrical member 26 toward the paper material pulp 100 conveyed by the support belt 16, and the paper material pulp 100 is at least partially wrapped around the surface of the first rotary perforated cylindrical member 26. The second rotary perforated cylindrical member 28 is a cylindrical member operating under relative vacuum conditions (“inflow type”), such that hot process air is drawn from the paper material pulp 100 conveyed by the support belt 16 through the second rotary perforated cylindrical member 28, the paper material pulp 100 being at least partially wrapped around such a second rotary perforated cylindrical member 28.

[0032] Advantageously, the diameter D1 of the first rotary perforated cylindrical member 26 is smaller or larger than the diameter D2 of the second rotary perforated cylindrical member 28. The second rotary perforated cylindrical member 28, having low specific evaporation, can operate at high temperatures (up to 200°C and above), thereby making it possible to extract flue gas at temperatures suitable for cascaded blowing of the flue gas onto the first rotary perforated cylindrical member 26.

[0033] According to the invention, the dewatering equipment 24 is actually provided with at least one recovery loop 42, which is designed to recover the hot process air (exhaust gas) drawn in from the second rotating perforated cylindrical member 28 and deliver this hot process air to the first rotating perforated cylindrical member 26. This allows hot process air, other than the hot process air directly generated by the components 30, 34, 40 of the heating system connected to the first rotating perforated cylindrical member 26, to be blown onto the paper pulp 100.

[0034] Based on a preferred but non-limiting configuration of device 10, the diameter D1 of the first rotary perforated cylindrical member 26 may include between about 2 m and about 2.2 m, which corresponds to a diameter D1 of about 7 feet in imperial units. The diameter D2 of the second rotary perforated cylindrical member 28 may alternatively include between about 2 m and about 7.5 m, which corresponds to a preferred diameter D2 ranging from a minimum of 7 feet (equal to about 2.13 m) to above 7 feet.

[0035] A first rotating perforated cylinder 26, with a small diameter approximately equal to about 7 feet, allows operation under conditions of low tension on the canvas of the support belt 16, low lateral airflow velocity, high unit evaporation rate of the paper pulp 100, and air flow at low temperatures (typically equal to about 85°C to about 90°C) and high counts (typically equal to about 200 to about 350 grams of vapor per kilogram of dry air). Alternatively, a second rotating perforated cylinder 28, with a large diameter (on the order of approximately 24 feet, 18 feet, or 14 feet), allows air to be extracted from the paper pulp 100 at high temperatures, and the airflow velocity is sufficient to fully or partially meet the blowing requirements of the first rotating perforated cylinder 26, resulting in an integral or nearly integral cascade due to the recovery loop 42. The balance of the blowing velocity, blowing temperature, extraction velocity, and extraction count of the first rotating perforated cylinder 26 and the second rotating perforated cylinder 28 is managed by computerized algorithms related to the drying process.

[0036] Still based on Figure 2 In a preferred, but not limiting, configuration of the illustrated device 10, heating systems 30, 34, and 40 are designed to generate hot process air and deliver it from bottom to top (or vice versa) to the first rotating perforated cylindrical member 26 via at least one first conveyor 44 positioned below it. A recovery circuit 42 recovers the hot process air drawn in by the second rotating perforated cylindrical member 28; this circuit can also be designed to deliver the hot process air from bottom to top to the first rotating perforated cylindrical member 26 via the first conveyor 44. Alternatively, hot process air is extracted from the first rotating perforated cylindrical member 26 via at least one extractor 46 positioned above it.

[0037] In such Figure 2 In a preferred but non-limiting configuration of the illustrated device 10, the heating systems 32, 36, 38 are designed to generate hot process air and deliver it from bottom to top through at least one second conveyor 48 positioned below the second rotating perforated cylindrical member 28. However, it cannot be ruled out that the hot process air in the second rotating perforated cylindrical member 28 can be delivered in a different manner, such as from top to bottom, and that the outflow of such hot process air from the second rotating perforated cylindrical member 28 can be performed by a side head or by both side heads of the second rotating perforated cylindrical member.

[0038] Preferably, one or more energy recovery devices can be provided on the extraction circuit 50, and these devices can be located downstream of the extractor 46 to extract hot process air from the first rotating perforated cylindrical member 26. Furthermore, the hot process air extracted by the first rotating perforated cylindrical member 26 can also be conveyed to the forming equipment 12 located upstream of the dewatering equipment 24 to be used as air for heating the paper pulp 100 by means of one or more dispensing devices.

[0039] Preferably, the temperature range of the hot process air blown by the first rotating perforated cylindrical member 26 can include between about 80°C and about 250°C. The temperature range of the hot process air drawn in by the second rotating perforated cylindrical member 28 can include between about 100°C and about 230°C.

[0040] Preferably, the blowing count value of the first rotating perforated cylindrical member 26 can be in the range of 100 grams of steam per kilogram of dry air to 350 grams of steam per kilogram of dry air. For the second rotating perforated cylindrical member 28, the value can be in the range of 70 grams of steam per kilogram of dry air to 200 grams of steam per kilogram of dry air.

[0041] like Figure 3 As shown, in the step of dynamically adhering the support belt 16 and the paper material slurry 100 supported by the support belt to the first rotary perforated cylindrical member 26, the paper material slurry 100 adheres to the surface of the first rotary perforated cylindrical member 26, while the support belt 16 is on the outside and wrapped around the paper material slurry 100. This configuration allows the paper material slurry 100 to remain attached to the support belt 16 when the first rotary perforated cylindrical member 26 is in the blowing mode.

[0042] Conversely, the same applies, such as Figure 4 As shown, in the step of dynamically adhering the support belt 16 and the paper material slurry 100 supported by the support belt to the second rotary perforated cylindrical member 28, the support belt 16 adheres to the surface of the second rotary perforated cylindrical member 28, while the paper material slurry 100 is located on the outside. This configuration allows the paper material slurry 100 to not penetrate into the holes of the second rotary perforated cylindrical member 28 when the second rotary perforated cylindrical member 28 is in the suction mode.

[0043] In the dewatering apparatus 24 of device 10, it is also possible to replace the first rotating perforated cylindrical member 26 with a capillary absorption-specific roller, which can provide similar or higher performance than the first rotating perforated cylindrical member 26, but does not use traversing air. In this case, the capillary absorption roller operates in parallel with the second rotating perforated cylindrical member 28.

[0044] The heating system of the dehydration equipment 24 can be used as follows Figure 2The fuel-driven burners 32 and 34 shown are obtained via a heat exchange cell (which uses steam, heat transfer oil, or other fluids). It is also possible to use exhaust gas from a cogeneration unit (turbine or internal combustion engine) added to the mains as the heating fluid.

[0045] Therefore, it has been observed that the apparatus for producing web-shaped paper materials according to the present invention achieves the above-mentioned objectives, and in particular gains the following advantages:

[0046] - The high-cost first rotary perforated cylindrical member 26 (so-called "vertical flow type") still has a small diameter, thus reducing costs;

[0047] - The second rotating perforated cylindrical member 28 (so-called "inflow type") with low unit evaporation capacity operates at high temperatures (up to 200°C and above), making the extracted flue gas usable at temperatures for stepwise blowing onto the first rotating perforated cylindrical member 26.

[0048] - The management of the drying cycle is controlled by PLC or DCS to optimize the drying cycle, thereby optimizing the quality of the paper produced and reducing certain costs.

[0049] The apparatus conceived in this way for producing the web-shaped paper material of the present invention is readily subject to various modifications and variations in any case, all falling within the same inventive concept; furthermore, all details can be replaced with technically equivalent elements. Essentially, the materials used, as well as the shape and size, may vary depending on technical requirements.

[0050] Therefore, the scope of protection of this invention is defined by the appended claims.

Claims

1. An apparatus (10) for producing web-shaped paper material (200), the apparatus (10) comprising: - At least one continuous support belt (14, 16), at least one of said support belts (14, 16) being movable by a plurality of rollers (18, 20); - At least one forming device (12), the at least one forming device (12) being used to form the web-shaped paper material (200), the forming device (12) including at least one dispensing device (22) for dispensing paper material slurry (100), the at least one dispensing device (22) being designed to deposit the paper material slurry (100) onto at least one of the support belts (14, 16); - At least one dewatering device (24), said dewatering device (24) being disposed downstream of at least one of said forming devices (12) and designed to at least partially dry the paper material pulp (100) conveyed by at least one of said support belts (14, 16) to form the web paper material (200), said dewatering device (24) comprising: - At least one first drying device, the at least one first drying device comprising a first rotating perforated cylindrical member (26), wherein the paper material pulp (100) conveyed by at least one of the support belts (14, 16) dynamically adheres to the surface of the first rotating perforated cylindrical member (26), the first rotating perforated cylindrical member (26) being an annular cylindrical member having a predetermined diameter (D1), - At least one second drying device, the at least one second drying device comprising a second rotating perforated cylindrical member (28), wherein the paper material pulp (100) conveyed by at least one of the support belts (14, 16) dynamically adheres to the surface of the second rotating perforated cylindrical member (28), the second rotating perforated cylindrical member (28) being an annular cylindrical member having a predetermined diameter (D2), and the second rotating perforated cylindrical member (28) being disposed downstream of the first rotating perforated cylindrical member (26), and - A heating system designed to generate hot process air and deliver the hot process air to at least one of the first rotary perforated cylindrical member (26) and the second rotary perforated cylindrical member (28). The device (10) is characterized in that the first rotary perforated cylindrical member (26) is a cylindrical member operating under relative pressure conditions, and wherein, when the heating system delivers hot process air to the first rotary perforated cylindrical member (26), the hot process air is blown from the interior of the first rotary perforated cylindrical member (26) toward the paper material pulp (100) conveyed by at least one of the support belts (14, 16), wherein the second rotary perforated cylindrical member (28) is a cylindrical member operating under relative vacuum conditions, and wherein, when the heating system delivers hot process air to the second rotary perforated cylindrical member (28), the hot process air is blown from the paper material pulp (100) conveyed by at least one of the support belts (14, 16) The pulp (100) is drawn through the second rotating perforated cylinder (28), and the dewatering equipment (24) includes at least one recovery loop (42), at least one of the recovery loops (42) being designed to recover the hot process air drawn from the second rotating perforated cylinder (28) and deliver the recovered hot process air to the first rotating perforated cylinder (26), such that: when the heating system delivers the hot process air to the first rotating perforated cylinder (26), the recovered hot process air can also be blown onto the paper pulp (100) in addition to the hot process air directly generated by the components (30, 34, 40) of the heating system connected to the first rotating perforated cylinder (26).

2. The device (10) according to claim 1, characterized in that, The diameter (D1) of the first rotating perforated cylindrical member (26) is less than or equal to the diameter (D2) of the second rotating perforated cylindrical member (28).

3. The device (10) according to claim 2, characterized in that, The diameter (D1) of the first rotating perforated cylindrical member (26) is between 2 m and 2.2 m.

4. The device (10) according to claim 2, characterized in that, The diameter (D2) of the second rotating perforated cylindrical member (28) is between 2 m and 7.5 m.

5. The device (10) according to claim 1, characterized in that, The components (30, 34, 40) of the heating system are designed to generate hot process air and deliver the hot process air from bottom to top to the first rotating perforated cylindrical member (26) via at least one first conveyor (44) located below the first rotating perforated cylindrical member (26).

6. The device (10) according to claim 5, characterized in that, The recovery loop (42) for recovering the hot process air drawn in by the second rotating perforated cylindrical member (28) is designed to deliver the hot process air from bottom to top through the first conveyor (44) to the first rotating perforated cylindrical member (26).

7. The device (10) according to claim 1, characterized in that, Other components (32, 36, 38) of the heating system are designed to generate hot process air and deliver the hot process air from bottom to top to the second rotating perforated cylindrical member (28) via at least one second conveyor (48) located below the second rotating perforated cylindrical member (28).

8. The device (10) according to claim 1, characterized in that, The support bands (14, 16) comprise a fabric with a plain weave and are made of a material that can withstand temperatures up to 200 °C to 250 °C.

9. The device (10) according to claim 1, characterized in that, The first rotating perforated cylindrical member (26) is designed to blow the hot process air at a temperature between 80 °C and 250 °C, while the second rotating perforated cylindrical member (28) is designed to draw the hot process air at a temperature between 100 °C and 230 °C.

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