Patent Application
20220267958
This application claims priority of Italian Patent Application No. 102021000003974 filed on Feb. 22, 2021.
The present invention generally relates to a plant for the production of web-like paper material and, in particular, a plant of the so-called TAD (acronym for “Through Air Drying”) type for the production of high-quality tissue paper.
As known, in the paper production process in general, and in the tissue paper production process in particular, a step for drying the product being processed by evaporation must be carried out in order to extract the surplus water content thereof. The product to be desiccated, usually consisting of a fibrous slurry based on cellulose and diluted with water, is initially prepared in an appropriate forming equipment and it is therefore delivered to a subsequent drying and desiccating equipment after an intermediate pressing step. At the inlet of the drying and desiccating equipment, the slurry which forms the paper sheet being processed contains a low dry part content, which can be equal to about 24%-28%. In other words, after the pressing step the slurry may still contain up to 75% and more of water. Therefore, the step for extracting under vacuum is not capable of eliminating all the water from the fibres of the slurry, which must therefore be removed by evaporation.
The finished product, typically but not exclusively consisting of tissue paper, requires a dry part content well higher than the values reported above, that is typically equal to about 94%-98%. Therefore, there clearly arises the need to extract from the fibrous slurry, in the drying step by evaporation, most of the residual water content thereof, in order to obtain a sufficiently dry continuous paper sheet. After the drying and desiccation step by evaporation, the paper sheet is stored in reels in order to be subsequently processed (so-called “converting” step) and, lastly, packaged for shipment and final retail sale.
Among plants for the production of web-like paper material of the known type plants of the so-called TAD (acronym for “Through Air Drying”) are known and particularly valued. The TAD technology uses a hot air jet which traverses the fibrous slurry before the latter is wound on a conventional yankee dryer. Basically, by transferring sensitive heat, the air allows the evaporation both of the water retained by the fibres of the paper material and of the water chemically bound to the fibre of the cellulose.
In the TAD process, the paper material fibrous slurry is supported and accompanied by a continuous and mobile support belt, typically consisting of a canvas, of the type resistant to temperatures up to 200-250° C. The canvas, and therefore also the paper material fibrous slurry follows the rotary surface of a perforated cylinder which allows the exchange of hot air with the paper material fibrous slurry.
Therefore, the TAD technology allows to produce high-quality tissue paper, given that it is a drying technology which imparts a very slight impact mechanical action on the paper material fibrous slurry, avoiding the strong action of the conventional suctioning presses and/or blind holes. The final result is a paper sheet with greater voluminosity, softness and absorption capacity with respect to the ones manufactured with the conventional technologies, allowing a lower specific consumption of fibre.
TAD-type plants currently provide for two types of operation for the paper material fibrous slurry drying equipment, substantially linked to two corresponding types of perforated cylinder. As a matter of fact, this perforated cylinder 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 material fibrous slurry being dried may be carried out on two or more cylinders.
For example, document U.S. Pat. No. 3,303,576 A discloses a plant for the production of web-like paper material according to the preamble of claim 1, wherein the perforated drying cylinders operate under relative pressure conditions. A plant for the production of web-like paper material wherein the perforated drying cylinders operate under relative vacuum conditions is instead disclosed in document FR 2733522 A1. Further plants of the known type for the production of web-like paper material are disclosed in documents US 2003/019601 A1 and US 2018/073195 A1.
TAD-type plants comprising perforated cylinders which operate under relative pressure conditions (“Vertiflow Type”) reveal drawbacks in terms of specific drying capacity, due to the difficulty in maintaining the paper material fibrous slurry adhered onto the surface of each cylinder by tensioning the canvas. On the contrary, TAD-type plants comprising perforated cylinders which operate under relative pressure conditions have simpler structural features, given that these perforated cylinders which operate under relative pressure conditions are subjected to low mechanical stress.
TAD-type plants comprising perforated cylinders which operate under relative vacuum conditions (“Inflow Type”) have a greater specific evaporating capacity, which however depends on the capacity of the recirculation fan with which these plants are provided. On the contrary, TAD-type plants comprising perforated cylinders which operate under relative vacuum conditions require a more robust mechanical construction given that under operating conditions each cylinder is subjected to very high mechanical stresses.
Irrespective of the type of plant, each perforated cylinder is then provided with a respective extractor hood and with a process air circulation circuit comprising one or more recirculation fans, one or more air heating burners and one or more extraction fans for the extraction of hot and humid air (the so called “fume”). The extraction fan must eliminate the water vapour produced by the drying of the paper material fibrous slurry, besides eliminating the air infiltration coming from the machine room through the contact sealings. Considering the amount of infiltrated air, despite the extraction temperatures being around 100° C. or slightly higher, the heat loss that occurs is significant in this case.
It should be observed that when using two or more perforated cylinders in a TAD-type plant the average specific evaporate of the paper material fibrous slurry decreases significantly moving from the first to the last cylinder. Furthermore, it should be observed that in TAD-type plants comprising perforated cylinders which operate under relative pressure conditions (“Vertiflow Type”) the canvas—which supports the paper material fibrous slurry (wet-formed) being dried and which keeps this paper material fibrous slurry adhered to each perforated desiccator cylinder—is particularly mechanically stressed given that must support the thrust of the traversing air which—from the internal of the perforated cylinder—must pass through towards the external.
On the contrary, in TAD-type plants comprising perforated cylinders which operate under relative vacuum conditions (“Inflow Type”) the canvas is subjected to low mechanical stress, while the perforated cylinder is subjected to high mechanical stress, given that it must support the entire thrust of the traversing air from the external toward the internal of the perforated cylinder.
Therefore, an object of the present invention is to provide a plant for the production of web-like paper material, in particular a so-called TAD-type plant, which is capable of overcoming the aforementioned drawbacks of the prior art in an extremely simple, cost-effective and particularly functional manner.
In detail, an object of the present invention is to provide a TAD-type plant for the production of web-like paper material that is simpler to manufacture with respect to similar TAD-type plants according to the prior art.
Another object of the present invention is to provide a TAD-type plant for the production of web-like paper material that, despite being simpler to construct with is respect to similar TAD-type plants according to the prior art, is capable of manufacturing a high-quality web-like paper material.
A further object of the present invention is to provide a TAD-type plant for the production of web-like paper material that allows to save energy with respect to similar TAD-type plants according to the prior art.
These objects according to the present invention are achieved by providing a plant for the production of web-like paper material as described in claim 1. Further features of the invention are outlined by the dependent claims, which are an integral part of the present description.
The features and advantages of a plant for the production web-like paper material according to the present invention will be more apparent from following exemplifying and non-limiting description, with reference to the attached schematic drawings, wherein:
With reference to the figures, a preferred embodiment of the plant for the production of web-like paper material according to the present invention is shown. The plant is indicated as a whole with reference numeral 10. As shown in the schematic view of
The plant 10 further comprises at least one forming equipment 12 for forming the web-like paper material 200. This forming equipment 12 in turn comprises at least one device 22 for dispensing a paper material slurry 100. The dispensing device 22 is designed to deposit—on the support belt 14, 16—the paper material slurry 100 which must be subsequently dried. The paper material slurry 100 may be of any known type at the state of the art and it may comprise cellulose fibres and/or any other material suitable for manufacturing the web-like paper material 200, which preferably but not exclusively consists of tissue paper.
At least one desiccating equipment 24, which is designed to at least partially desiccate the paper material slurry 100 conveyed by the support belt 14, 16, in order to form the web-like paper material 200A is provided for downstream of the forming equipment 12. In the embodiment of the plant 10 shown in the figures there are provided for a first support belt 14, belonging to the forming equipment 12, and a second support belt 16, belonging to the desiccating equipment 24. The configuration of the support belt 14, 16 may in any case be modified depending on the needs, while maintaining the technical function of supporting and conveying the paper material slurry 100 first and then the web-like paper material 200 within the entire plant 10. Preferably, each support belt 14, 16 may consist of a fabric with plain weave, made of a material resistant to temperatures up to 200-250° C.
The desiccating equipment 24 comprises at least one first device for drying the paper material slurry 100, which consists of a first rotary perforated cylinder 26 on whose surface the paper material slurry 100 conveyed by the support belt 16 is dynamically adhered. In detail, the first rotary perforated cylinder 26 is a cylinder with a circular base with predefined diameter D1.
The desiccating equipment 24 further comprises at least one second device for drying the paper material slurry 100, which consists of a second rotary perforated cylinder 28 on whose surface the paper material slurry 100 conveyed by the support belt 16 is dynamically adhered. Also this second rotary perforated cylinder 28 is a cylinder with a circular base with predefined diameter D2. This second rotary perforated cylinder 28 is therefore arranged downstream of the first rotary perforated cylinder 26.
The desiccating equipment 24 further comprises a heating system 30, 32, 34, 36, 38, 40, which is designed to generate hot process air and to deliver such hot process air to at least one of such first rotary perforated cylinder 26 and such second rotary perforated cylinder 28. In particular, the heating system may comprise, sequentially and with reference to the first rotary perforated cylinder 26, one or more comburent air e fans 34, one or more process air heating burners 30 and one or more pumps 40 for supplying the heated process air to the first rotary perforated cylinder 26. Similarly, with reference to the second rotary perforated cylinder 28, the heating system may sequentially comprise one or more comburent 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.
The desiccating equipment 24 may also comprise, in a per se known manner, a further rotary heating cylinder 52, also referred to as “yankee dryer”. This yankee dryer 52, on whose surface the paper material slurry 100 is dynamically adhered for the final desiccation thereof, is arranged downstream of the second rotary perforated cylinder 28.
The first rotary perforated cylinder 26 is a cylinder operating under relative pressure conditions (“Vertiflow Type”), so that the hot process air is blown from inside the first rotary perforated cylinder 26 towards the paper material slurry 100 conveyed by the support belt 16 and which is at least partially wound on the surface of such first rotary perforated cylinder 26. The second rotary perforated cylinder 28 is instead a cylinder operating under relative vacuum conditions (“Inflow Type”), so that, through the second rotary perforated cylinder 28, the hot process air is suctioned from the paper material slurry 100 conveyed by the support belt 16 and which is at least partially wound on such second rotary perforated cylinder 28.
Advantageously, the diameter D1 of the first rotary perforated cylinder 26 is smaller or larger than the diameter D2 of the second rotary perforated cylinder 28. Having low specific evaporation, the second rotary perforated cylinder 28 may operate at high temperature (up to 200° C. and above), making extraction fume available at a temperature useful for blowing on the first rotary perforated cylinder 26 in cascade fashion.
According to the invention, the desiccating equipment 24 is actually provided with at least one recovery circuit 42 which is designed for the recovery of the hot process air (extraction fume) suctioned from the second rotary perforated cylinder 28 and to deliver such hot process air to the first rotary perforated cylinder 26. This allows the hot process air to be blown onto the paper material slurry 100 additionally to the hot process air generated directly by the components 30, 34, 40 of the heating system which are connected to the first rotary perforated cylinder 26.
Based on a preferred but non-limiting configuration of the plant 10, the is diameter D1 of the first rotary perforated cylinder 26 may be comprised between about 2 m and about 2.2 m, which correspond to a diameter D1 of about 7 feet in the imperial units system. The diameter D2 of the second rotary perforated cylinder 28 may instead be comprised between about 2 m and about 7.5 m, which correspond to preferred diameters D2 from a minimum of 7 feet (equal to about 2.13 m) and above.
A first rotary perforated cylinder 26 with small diameter, approximately equal to about 7 feet, allows to operate with low tension on the canvas of the support belt 16, with low traversing air flow rate and with high specific evaporation of the paper material slurry 100, as well as with air outflow at low temperature (typically equal to about 85-90° C.) and high count (typically equal to about 200-350 grams of vapour per kilogram of dry air). A second rotary perforated cylinder 28 with large diameter, approximately in the order of 24 feet, 18 feet or 14 feet, instead allows to extract—from the paper material slurry 100—air at high temperature and with flow rate sufficient to entirely or partly meet the blowing demand of the first rotary perforated cylinder 26, thanks to the recovery circuit 42, creating an integral or almost integral cascade. The balancing of the blowing air flow rates, of the blowing temperatures, of the extraction flow rates and of the count of the extractions respectively of the first rotary perforated cylinder 26 and of the second rotary perforated cylinder 28 is managed by means of a computerised algorithm linked with the drying process.
Still based on a preferred but non-limiting configuration of the plant 10, shown in
In the preferred but non-limiting configuration of the plant 10, shown in
Preferably, one or more energy recovery devices may be provided for on the extraction circuit 50, arranged downstream of the extractor 46, to extract the hot process air from the first rotary perforated cylinder 26. In addition, the hot process air extracted by the first rotary perforated cylinder 26 may also be delivered to the forming equipment 12, arranged upstream of the desiccating equipment 24, so as to be used as air for heating the paper material slurry 100 by means of one or more distribution devices.
Preferably, the blowing temperature range of the hot process air by the first rotary perforated cylinder 26 may be comprised between about 80° C. and about 250° C. The temperature range for suctioning the hot process air by the second rotary perforated cylinder 28 may instead be comprised between about 100° C. and about 230° C.
Still preferably, the blowing count value for the first rotary perforated cylinder 26 may range from 100 grams of vapour per kilogram of dry air to 350 grams of vapour per kilogram of dry air. This value may instead range from 70 grams of vapour per kilogram of dry air to 200 grams of vapour per kilogram of dry air for the second rotary perforated cylinder 28.
As shown in
Vice versa, as shown in
In the desiccating equipment 24 of the plant 10 there may also be provided for possibility of replacing the first rotary perforated cylinder 26 with a capillary absorption special roller, which may offer performance similar to or higher than that of such first rotary perforated cylinder 26, but without using traversed air. In this case, the capillary absorption roller would operate parallel to the second rotary perforated cylinder 28.
The heating system of the desiccating equipment 24 may be obtained both by means of fuel powered burners 32, 34, as shown in
Therefore, it has been observed that the plant for the production of web-like paper material according to the present invention attains the objects outlined above, in particular obtaining the following advantages:
The plant for the production of web-like paper material of the present invention thus conceived is in any case susceptible to various modifications and variants, all falling within the same inventive concept; furthermore, all details can be replaced by technically equivalent elements. Basically, the materials used as well as the shapes and dimensions may vary according to the technical needs.
Therefore, the scope of protection the invention is defined by the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102021000003974 | Feb 2021 | IT | national |
