Facility for producing web-shaped paper material

Abstract

This application describes a facility for producing web-shaped paper material, which includes a system for generating steam at three or more pressure levels using emissions from a Yankee hood. The system allows for the recovery of energy supplied by the emissions of the Yankee hood. A first heat exchanger delivers the mixed-phase effluent into a first pressurized tank, where the steam is separated from the water. The steam is introduced from the first pressurized tank into the line for the paper drying process, while the water, at a temperature in equilibrium with the steam, is transported into a second pressurized tank, which has a lower pressure than the first tank. Finally, the residual water is introduced into a third pressurized tank, which has a lower pressure than the second pressurized tank, which collects the condensate from the Yankee cylinder together with the blow-off steam, so that the blow-off steam is recompressed to the working pressure of the facility and reintroduced into the facility.

Description

Technical Field

[0001] The present invention generally relates to a facility for producing web-shaped paper material, and particularly to a system for generating steam in a facility for producing web-shaped paper material, the system comprising at least one highly efficient extraction hood. Background Technology

[0002] As is well known, in typical paper production processes, especially in tissue paper production, a drying step by evaporation is necessary to remove excess water from the product. The product to be dewatered, typically composed of cellulose-based cellulose pulp diluted with water, is initially prepared in appropriate forming equipment and thus conveyed to subsequent drying and dewatering equipment after an intermediate vacuum extraction step. At the inlet of the drying and dewatering equipment, the pulp forming the paper to be treated contains a low dry fraction content, which can be between approximately 24% and 28%. In other words, after the vacuum extraction 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 significantly higher than the aforementioned values, usually between approximately 94% and 98%. Therefore, it is evident that a large portion of the residual water content needs to be removed from the fiber pulp through evaporation during the drying step to obtain a sufficiently dry, continuous sheet of paper. After the drying and dehydration steps via evaporation, the sheet of paper is stored in rolls for subsequent processing (the so-called "conversion" step) and finally packaged for transport and final retail.

[0004] The most common drying and dewatering equipment in paper production facilities, particularly toilet paper production facilities, consists of two separate drying units. Even when both units operate simultaneously on the web-shaped paper material being processed, this material remains in a fibrous pulp state awaiting drying. The first drying unit comprises one or more high-efficiency "Yanke" hoods that blow hot air, typically at a temperature between 350°C and 650°C, onto the fibrous pulp being processed. Simultaneously, the fibrous pulp being processed comes into contact with the side surface of at least one steam-heated cylinder, typically with a diameter between about 1.5 m and about 6 m. This cylinder, commonly referred to as a "Yanke," generally includes a pressure vessel containing process steam at a pressure typically between about 4 bar G and about 10 bar G.

[0005] Generally, in paper production facilities of the types described above, only a portion of the hot, humid air, often referred to as "mist," is partially recycled and subsequently extracted by the processed pulp through a Yankee hood. In other words, a portion of the mist, consisting of dehydrated air and evaporated water, is drawn in by one or more fans and then reintroduced into the drying and dehydration equipment after appropriate heating. The remaining mist extracted by the Yankee hood is typically disposed of into the atmosphere, resulting in the dissipation of a significant amount of potentially useful energy.

[0006] Prior art document IT MI 20090364 A1 discloses a facility for producing web-shaped paper material. However, the facility for producing web-shaped paper material described in prior art document IT MI 20090364 A1 does not provide any heat exchange equipment as a variable flow rate throttle, which is designed to handle a large amount of humidified air, the amount of which varies with the amount of steam to be generated at a predetermined pressure value.

[0007] Prior art document DE 102010041231 A1 discloses a facility for producing web-shaped paper material, wherein the heat exchange device for collecting heat energy from mist is of the air-water type, rather than the air / water-steam type. Therefore, no system is provided for simultaneously generating steam with two or more pressure levels.

[0008] Finally, prior art document EP 2775030 A1 discloses a facility for producing web-shaped paper material, in which a flue-tube boiler is used to collect the thermal energy of mist. In this case, no system is provided for simultaneously generating steam with two or more pressure levels. Summary of the Invention

[0009] Therefore, the object of the present invention is to provide a system for generating steam in a facility for producing web-shaped paper materials, which overcomes the above-mentioned disadvantages of the prior art in an extremely simple, cost-effective and particularly practical manner.

[0010] In detail, the object of the present invention is to provide a system for generating steam in a facility for producing web-like paper materials, which is capable of recovering all or at least most of the energy contained in the mist, thereby directly reusing this energy in the corresponding drying and dehydration equipment.

[0011] Another object of the present invention is to provide a system for generating steam in a facility for producing web-shaped paper materials, which allows for a heat recovery rate of mist to be increased by more than 50% compared to facilities for producing web-shaped paper materials according to the prior art.

[0012] These objectives according to the invention are achieved by providing a system for generating steam in a facility for producing web-shaped paper materials, as described in the invention. Further features of the invention are outlined by specific embodiments that form part of this description. Attached Figure Description

[0013] The features and advantages of the system for generating steam in a facility for producing web-shaped paper materials according to the invention will become more apparent from the following exemplary and non-limiting description illustrated in the accompanying drawings, in which only... Figure 1 The diagram illustrates a portion of drying and dehydration equipment, and a preferred embodiment of a system for generating steam in a facility for producing web-shaped paper materials according to the invention. Detailed Implementation

[0014] Reference Figure 1 In fact, what is shown is a preferred embodiment of the system for generating steam in a facility for producing web-shaped paper material according to the invention. The facility is generally indicated by reference numeral 10, and includes, in a manner known per se, drying and dewatering equipment designed to dewater the paper material pulp, thereby converting the pulp into web-shaped paper material. This paper material pulp is produced using any type of forming equipment known, and therefore, such forming equipment will not be described further below.

[0015] In detail, the drying and dehydration equipment of facility 10 includes a first drying unit, which in turn includes at least one rotary drying cylinder 12 supplied with pressurized steam. The paper material pulp dynamically adheres to the side surfaces of the drying cylinder 12. Therefore, the drying cylinder 12 is a so-called "Yanke" type, and is supplied with live steam at a predetermined operating pressure, preferably between about 4 bar G and about 10 bar G. Through condensation on the inner side surfaces of the Yanke cylinder 12, the steam transfers heat to the outer side surfaces of the Yanke cylinder 12, i.e., the surfaces to which the dried paper material pulp adheres.

[0016] The drying and dehydration equipment of facility 10 also includes a second drying unit, which in turn includes at least one Yankee shroud 14, 16 that at least partially surrounds the Yankee cylinder 12. Figure 1In the illustrated embodiment, the Yankee hood comprises a first half-hood 14 and a second half-hood 16, which are only examples of their kind. Both the first and second half-hoods are capable of blowing dry air at a relatively high temperature onto the paper material pulp surrounding the side surface of the Yankee cylinder 12 and drawing in the humid, hot air released from the paper material pulp. Preferably, the Yankee hoods 14 and 16 can be designed to blow dry air at a temperature between about 350°C and about 650°C and a speed between about 100 m / s and about 150 m / s.

[0017] The drying and dehydration equipment of facility 10 further includes: at least one hydraulic discharge circuit 18, designed to discharge humidified air exiting from Yankee shrouds 14, 16; and at least one hydraulic supply circuit 20, designed to supply steam into Yankee cylinder 12. The humidified air exits from Yankee shrouds 14, 16 at a first predetermined temperature, preferably between about 250°C and about 400°C.

[0018] According to the invention, facility 10 includes a system for generating steam, which in turn includes at least one first heat exchanger 22 of an air / water-steam type, positioned along a hydraulic circuit 18 for discharging humidified air exiting from Yankee shrouds 14, 16. This first heat exchanger 22 is designed to receive humidified air at the aforementioned first predetermined temperature value as a first-stage fluid, which is extracted by Yankee shrouds 14, 16. After heat exchange with a second-stage fluid, the first heat exchanger 22 discharges humidified air at a second predetermined temperature value, which is lower than the first predetermined temperature value. Preferably, the second predetermined temperature value is equal to approximately 220°C. Also preferably, the second-stage fluid of the first heat exchanger 22 may include a second-stage condensate, which enters the first heat exchanger 22 at a temperature of approximately 200°C and a pressure of approximately 16 bar G, and exits the first heat exchanger 22 at a temperature of approximately 200°C as a water / steam mixture.

[0019] The system for generating steam in facility 10 then includes at least one second heat exchanger 24 of the air-water type, functioning as a variable-flow economizer, arranged in series with respect to the first heat exchanger 22. The second heat exchanger 24 is designed to receive variable-flow humidified air at a second predetermined temperature as a first-stage fluid. After heat exchange with the second-stage fluid, the second heat exchanger 24 discharges humidified air at a third predetermined temperature, which is lower than the second predetermined temperature. Preferably, the third predetermined temperature is equal to approximately 180°C. Also preferably, the second-stage fluid of the second heat exchanger 24 may include a second-stage condensate that enters the second heat exchanger 24 at a temperature of approximately 150°C and exits the second heat exchanger 24 at a temperature of approximately 200°C.

[0020] Multiple separators 26, 28, and 30 are connected to a first heat exchanger 22 and / or a second heat exchanger 24. These separators 26, 28, and 30 are designed to separate steam from water supplied to them as a water / steam mixture and originating from at least one of the first heat exchanger 22 and the second heat exchanger 24. Therefore, steam from at least one of the separators 26, 28, and 30 is supplied to the hydraulic supply circuit 20 of the Yankee cylinder 12 via suitable steam supply devices 32, 34, 36, 38, and 50.

[0021] According to the present invention, such as Figure 1 As shown, the multiple separation tanks 26, 28, and 30 of the system for generating steam include:

[0022] At least one first pressurized tank 26 is hydraulically connected to the first heat exchanger 22 via a first hydraulic connection circuit 40, and the at least one first pressurized tank is capable of delivering steam at a first predetermined pressure value;

[0023] At least one second pressurized tank 28, which is hydraulically connected to the first pressurized tank 26 via a second hydraulic connector 42, and which is capable of delivering steam at a second predetermined pressure value, which is less than a first predetermined pressure value; and

[0024] At least one third pressurizing tank 30 is hydraulically connected to the second pressurizing tank 28 via a third hydraulic connection circuit 44, and the at least one third pressurizing tank is capable of delivering steam at a third predetermined pressure value, which is less than the second predetermined pressure value.

[0025] The first pressurized tank 26 is designed to separate steam from water supplied to it as a water / steam mixture and originating from the first heat exchanger 22. The second pressurized tank 28 is designed to separate flash vapor from the condensate of the first pressurized tank 26. Finally, the third pressurized tank 30 is designed to separate residual flash vapor from the condensate of the second pressurized tank 28. Both the first pressurized tank 26 and the second pressurized tank 28 may be equipped with corresponding valves 52 and 54 for automatic adjustment of the fill level.

[0026] The third pressurization tank 30 may be provided with a fourth hydraulic circuit 46 for connection to the Yanke cylinder 12, such that the third pressurization tank is designed to collect condensate from the Yanke cylinder 12. The third pressurization tank 30 may also be operatively connected to at least one hot press 48, which is designed to draw in blown steam and flash steam from the third pressurization tank 30, thereby increasing the pressure of the steam, and sending the steam to the Yanke cylinder 12 for use via a corresponding hydraulic supply circuit 20.

[0027] Therefore, the second heat exchanger 24 is designed to handle a large volume of humid air, the amount of which varies with the amount of steam generated by the second pressurized tank 28 at a second predetermined pressure. The water level in the second pressurized tank 28 is then kept constant, automatically reaching a level close to the overflow level toward the third pressurized tank 30. The blown steam and flash steam from the third pressurized tank 30 are drawn in by the hot press 48 and then delivered to the Yankee cylinder 12 for condensation.

[0028] The second heat exchanger 24 also serves a dual purpose. Its first function is to preheat the make-up water used by the first heat exchanger 22, which generates high-pressure steam for the first pressurized tank 26. However, the second primary function of the second heat exchanger 24 is to collect heat energy to heat significantly more water (two to three times the amount needed), which is then released as flash steam onto the second pressurized tank 28 and onto the third pressurized tank 30, which is connected in a cascade, thus generating steam at two correspondingly lower pressure values. Since this mist can be released into the atmosphere at a significantly lower temperature, for example, compared to the facility shown in prior art document IT MI 20090364A1, this system for generating steam allows for a more efficient use of the heat content of the mist from the Yankee hoods 14 and 16.

[0029] Preferably, the steam supply devices 32, 34, 36, 38, and 50 are designed to supply steam from separators 26, 28, and 30 to the hydraulic supply circuit 20 of the Yanke cylinder 12. The steam supply devices 32, 34, 36, 38, and 50 include: at least one first automatic motor-driven valve 32 for conveying steam from the first pressurization tank 26; and a first hydraulic connector 34 for connecting the first automatic motor-driven valve 32 to the hydraulic supply circuit 20 of the Yanke cylinder 12. The steam supply devices 32, 34, 36, 38, and 50 may further include: at least one second automatic motor-driven valve 36 for conveying steam from the second pressurization tank 28; and a second hydraulic connector 38 for connecting the second automatic motor-driven valve 36 to the hydraulic supply circuit 20 of the Yanke cylinder 12.

[0030] The steam supply units 32, 34, 36, 38, and 50 may also include one or more circulation pumps 50 for supplying steam from at least one of the separators 26, 28, and 30 to the hydraulic supply circuit 20 of the Yanke cylinder 12. Each circulation pump 50 is equipped with a pressure control device.

[0031] Specifically, at least one of the circulating pumps 50 is installed at a third pressurized tank 30, which collects the condensate generated by the Yankee cylinder 12 via a fourth hydraulic connection circuit 46. Preferably, the circulating pump 50 operates at high temperature and high flow prevalence, and it serves as a water circulator for supplying the air-to-water type second heat exchanger 24, i.e., a throttling device. This water is then returned in cascade and in the initial quantity to the initial tank containing it, without any generated steam.

[0032] Therefore, the steam generation system of facility 10 described so far utilizes the exhaust mist from Yankee hoods 14, 16 to generate steam at three or more predetermined pressure values. Two heat exchangers 22, 24 are used to generate steam useful for the process of drying the paper material pulp surrounding the Yankee cylinder 12; these two heat exchangers 22, 24 are arranged counter-currently relative to the passages of the mist drawn by Yankee hoods 14, 16. Therefore, the steam generation system of facility 10 operates as follows.

[0033] High-pressure steam generated by the first air / water-steam type heat exchanger 22 is separated from water in the first pressurization tank 26. This steam is then introduced into the hydraulic supply circuit 20 of the Yankee cylinder 12 via the first hydraulic connection 34 and the first automatic motor-driven valve 32, thereby being added to the main steam flow from the boiler 56.

[0034] Excess water, which is in thermal equilibrium with the steam, is transferred from the first pressurized tank 26 to the second pressurized tank 28. In the second pressurized tank 28, the water releases flash steam, which is also used in the process of drying the slurry before being introduced into the hydraulic supply circuit 20 of the Yanke cylinder 12 via the second hydraulic connection 38 and the valve 36 driven by the second automatic motor.

[0035] The second predetermined pressure value of the flash steam supplied by the second pressurization tank 28 is less than the first predetermined pressure value of the steam supplied by the first pressurization tank 26. Furthermore, this second predetermined pressure value is very close to the operating pressure value of the Yankee cylinder 12, allowing the flash steam to be used directly during the drying of web-shaped paper materials with appropriate adjustments. Preferably, in fact, the second predetermined pressure value of the flash steam supplied by the second pressurization tank 28 is smaller than the first predetermined pressure value of the steam supplied by the first pressurization tank 26 by an amount between about 4 bar G and about 8 bar G. Even more preferably, the second predetermined pressure value of the flash steam supplied by the second pressurization tank 28 is approximately equal to the operating pressure value of the Yankee cylinder 12.

[0036] Finally, the residual water is transferred from the second pressurization tank 28 to the third pressurization tank 30, which is the initial pressurization tank. The flash vapor, now reduced to a very small amount, is drawn from the third pressurization tank 30 by a hot press 48, which uses the energy of high-pressure steam circulating in the hydraulic supply circuit 20 of the Yanke cylinder 12 to recompress the flash vapor along with the blown steam used to extract the condensate from the Yanke cylinder 12, thereby increasing the pressure of these steams to the operating pressure value of the Yanke cylinder 12. Preferably, the third predetermined pressure value of the flash vapor delivered from the third pressurization tank 30 is therefore about 1 bar G smaller than the predetermined pressure value of the flash vapor delivered from the second pressurization tank 26.

[0037] Since the temperature measurable in the third pressurized tank 30 is approximately 30°C to 40°C lower than the temperature measurable in the first pressurized tank 24, the steam generation system of the facility 10 according to the invention allows the temperature of the mist from the Yankee hoods 14 and 16 to be reduced by several degrees Celsius, the reduction being equal to the aforementioned temperature difference between the first pressurized tank 24 and the third pressurized tank 30. This system for generating recovered steam is managed in a pressure cascade manner by controlling the automatic motor-driven valves 32 and 36 for steam delivery and by controlling the rotational speed of the circulating pump 50, such that the pressure level of the generated steam can be adjusted over a wide range of values.

[0038] Therefore, it has been shown that the system for generating steam in a facility for producing web-like paper material according to the invention can achieve the objectives outlined above. In fact, the logic of such a system for generating steam—which produces steam with at least three different pressure levels—allows the heat recovery rate of the mist in the Yankee hood to be increased by up to 50% relative to facilities for producing web-like paper material according to the prior art.

[0039] The steam generation system of the present invention, conceived in this way, can be modified and varied in any case, all of which fall within the same inventive concept; furthermore, all details can be replaced by technically equivalent elements. Essentially, the materials used, as well as the shape and size, can be varied according to technical requirements.

[0040] Therefore, the scope of protection of this invention is defined by the appended claims.

Claims

1. A facility (10) for producing web-shaped paper material from paper material pulp to be dewatered, said facility (10) comprising: A first drying apparatus comprising at least one rotating Yankee cylinder (12) supplied with pressurized steam, wherein the paper material pulp dynamically adheres to the side surface of the Yankee cylinder (12); The second drying device includes at least one Yankee hood (14, 16) that at least partially surrounds the Yankee cylinder (12) and is capable of blowing hot, dry air at a higher temperature onto the paper pulp material surrounding the side surface of the Yankee cylinder (12) and of sucking up hot, humid air released from the paper pulp material. At least one hydraulic discharge circuit (18) is designed to discharge humid air at a first predetermined temperature value exiting from the at least one Yankee hood (14, 16); At least one hydraulic supply circuit (20) is configured to supply the pressurized steam at a predetermined working pressure into at least one of the Yankee cylinders (12); and A steam generation system, wherein the steam generation system further includes: At least one first heat exchanger (22) of the air / water-steam type, the first heat exchanger (22) being positioned along the hydraulic discharge circuit (18), and the first heat exchanger (22) being designed to: receive the humid air at a first predetermined temperature value as a first-stage fluid, and discharge the humid air at a second predetermined temperature value, which is less than the first predetermined temperature value, after heat exchange with a second-stage fluid of the first heat exchanger (22); A plurality of separation tanks (26, 28, 30) are hydraulically connected to the first heat exchanger (22), and the plurality of separation tanks (26, 28, 30) are designed to separate steam from water supplied as a water / steam mixture to the plurality of separation tanks (26, 28, 30) and originating from the first heat exchanger (22); and Steam supply devices (32, 34, 36, 38, 50) are designed to supply steam from at least one of the plurality of separation tanks (26, 28, 30) to the hydraulic supply circuit (20). The facility (10) is characterized in that it includes at least one second heat exchanger (24) of the air-water type, which serves as a variable flow throttle, the second heat exchanger (24) being arranged in series with the first heat exchanger (22), and the second heat exchanger (24) being designed to: receive the variable humidified air at a second predetermined temperature value as a first-stage fluid, and discharge the humidified air at a third predetermined temperature value, which is lower than the second predetermined temperature value, after heat exchange with the second-stage fluid, wherein the plurality of separation tanks (26, 28, 30) include: At least one first pressure tank (26) is hydraulically connected to the first heat exchanger (22) via a first hydraulic connection circuit (40), and the first pressure tank (26) is capable of delivering steam at a first predetermined pressure value; At least one second pressure tank (28) is hydraulically connected to the first pressure tank (26) via a second hydraulic connection circuit (42), and the second pressure tank (28) is capable of delivering steam at a second predetermined pressure value, wherein the second predetermined pressure value is less than the first predetermined pressure value; and At least one third pressure tank (30) is hydraulically connected to the second pressure tank (28) via a third hydraulic connection circuit (44), and the third pressure tank (30) is capable of delivering steam at a third predetermined pressure value, wherein the third predetermined pressure value is less than the second predetermined pressure value.

2. The facility (10) according to claim 1, characterized in that, The second predetermined pressure value is smaller than the first predetermined pressure value by an amount between 4 bar G and 8 bar G.

3. The facility (10) according to claim 1, characterized in that, The second predetermined pressure value is approximately equal to the working pressure value of the Yanke cylinder (12).

4. The facility (10) according to claim 3, characterized in that, The working pressure value of the Yanke cylinder (12) is between 4 bar G and 10 bar G.

5. The facility (10) according to claim 1, characterized in that, The third predetermined pressure value is 1 bar less than the second predetermined pressure value.

6. The facility (10) according to claim 1, characterized in that, The third pressurized tank (30) is provided with a fourth hydraulic circuit (46) for connection to the Yanke cylinder (12), such that the third pressurized tank (30) is designed to collect condensate from the Yanke cylinder (12).

7. The facility (10) according to claim 1, characterized in that, The third pressurizing tank (30) is operatively connected to at least one hot press (48) which is designed to draw out the blown steam and flash steam from the third pressurizing tank (30) to increase the pressure of the blown steam and flash steam, and deliver the blown steam and flash steam to the Yanke cylinder (12) for use via the hydraulic supply circuit (20).

8. The facility (10) according to any one of claims 1 to 7, characterized in that, The steam supply device (32, 34, 36, 38, 50) includes: at least one first automatic motor drive valve (32) for supplying steam from the first pressurized tank (26); and a first hydraulic connector (34) for connecting the first automatic motor drive valve (32) to the hydraulic supply circuit (20).

9. The facility (10) according to any one of claims 1 to 7, characterized in that, The steam supply device (32, 34, 36, 38, 50) further includes: at least one second automatic motor-driven valve (36) for supplying steam from the second pressurized tank (28); and a second hydraulic connector (38) for connecting the second automatic motor-driven valve (36) to the hydraulic supply circuit (20).

10. The facility (10) according to any one of claims 1 to 7, characterized in that, The steam supply device (32, 34, 36, 38, 50) includes one or more circulation pumps (50) for supplying steam from at least one of the plurality of separation tanks (26, 28, 30) to the hydraulic supply circuit (20), and the circulation pumps (50) are provided with pressure control devices.

11. The facility (10) according to claim 10, characterized in that, At least one of the circulating pumps (50) is installed at the third pressurized tank (30) and is designed to supply water to the second heat exchanger (24).

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