Methods for desteaming process exhaust air

Abstract

Method for removing process exhaust air (4) from a plant for the production or processing of a fibrous web, in particular a pulp, paper or cardboard web, wherein the plant comprises a drying section in which the fibrous web is at least partially dried by contact drying, wherein a first exhaust air (1) is generated and wherein the plant comprises a second source which generates a second exhaust air (2) which is mixed with the first exhaust air (1), wherein the second exhaust air (2) has a higher temperature and a lower relative humidity than the first exhaust air (1), characterized in that the first exhaust air (1) and the second exhaust air (2) are either at least partially mixed together before being released into the environment and a static mixer (13) is used for mixing, and / or the first exhaust air (1) and the second exhaust air (2) are at least partially mixed together after being released into the environment.

Description

[0001] The invention relates to methods for removing steam from process exhaust air of a plant for the production or processing of a fibrous web according to the preamble of claim 1.

[0002] During the production of fibrous webs such as paper or pulp webs, a large amount of very humid exhaust air is generated, particularly during the drying process. If this air is released directly into the environment, a visible fog can form under suitable climatic conditions.

[0003] This fog can fall as precipitation in the immediate vicinity of the facility and, especially in winter, can lead to slippery paths. Furthermore, low-hanging fog banks can impair visibility for road traffic.

[0004] Therefore, legal frameworks often require operators to ensure that no visible plumes of water vapor are emitted from the plants.

[0005] To prevent such a water vapor plume, the ERCS - Type 04 product from Scheuch GmbH in Austria (www.scheuch.com) is known from the state of the art. In this system, cold ambient air is preheated via a heat exchanger and then mixed with the moist exhaust air.

[0006] Document DE 43 04 244 A1 deals with the exhaust air from papermaking and US 8 721 771 B2 deals with the treatment of moist exhaust air.

[0007] One disadvantage of the current state of the art is that the technical effort required for steam removal is considerable, as a separate heat exchanger and a blower system with suitable control must be provided.

[0008] Since a considerable amount of outside air also needs to be supplied, this de-emissioning also increases the energy consumption of the system.

[0009] Finally, the cooling of the process air leads to condensation inside the exhaust system, which can, among other things, result in increased corrosion.

[0010] The object of the present invention is therefore to propose a simple and cost-effective method that effectively prevents fog formation.

[0011] It is further an object of the invention to propose a method that requires no additional energy expenditure and / or structural measures, or only minimal additional expenditure.

[0012] The problem is completely solved by a method according to the characterizing feature of claim 1.

[0013] Advantageous embodiments are described in the dependent claims.

[0014] The problem is solved by a method for removing process exhaust air from a plant for the production or processing of a fibrous web, in particular a pulp, paper, or cardboard web, wherein the plant comprises a drying section in which the fibrous web is at least partially dried by contact drying, generating a first exhaust air, and wherein the plant comprises a second source that generates a second exhaust air, which is mixed with the first exhaust air. According to the invention, it is provided that the second exhaust air has a higher temperature and a lower humidity than the first exhaust air.

[0015] In the production of fibrous webs, such as paper webs, the fiber material is mixed with a large quantity of water to form a suspension. This suspension is then applied to a support, such as a screen, to create the fiber web. Such suspensions often consist of 99% or more water. During the process, this water is removed from the fiber web. While a large portion of the water can be removed mechanically, for example by suction and wringing, another portion must be removed thermally by drying. For this purpose, the fiber web is typically passed over heated cylinders or similar devices in a drying section, where it is dried by contact drying. The water escapes from the web into the ambient air of the drying section. This highly humid air is collected and—possibly after several treatment stages—constitutes the first exhaust air.

[0016] This first exhaust air has an extremely high moisture content, at comparatively moderate temperatures.

[0017] The temperature of the initial exhaust air can be below 90°C, particularly below 80°C, preferably between 60°C and 70°C. It is desirable for the operator to keep the temperature of the initial exhaust air low, as higher exhaust air temperatures necessitate an increase in the temperature of the supply air, leading to higher energy costs.

[0018] The temperature of the first exhaust air is typically chosen to be just low enough to prevent unwanted condensation. A unique characteristic of fiber web production plants is that numerous additional exhaust air streams are generated during manufacturing and processing. The applicant has discovered that some of these can be used to effectively suppress fog formation in the first exhaust air. This requires that the second exhaust air stream has both a higher temperature and a lower relative humidity than the first.

[0019] In advantageous configurations, the second exhaust air can comprise the exhaust air from one or more infrared dryers. These are used, for example, for non-contact drying of painted membranes. The resulting exhaust air is very hot (generally hotter than 120°C) and has low relative humidity.

[0020] Alternatively or additionally, the second exhaust air can also be exhaust air from a gas turbine or a boiler. Since a large amount of electrical energy and steam is required to operate a plant such as a paper machine, suitable power plants are usually located in the immediate vicinity of the machine, making their exhaust air usable as a second exhaust air source.

[0021] In advantageous embodiments, it may also be provided that the first exhaust air and / or the second exhaust air itself can already represent a mixture of several exhaust air streams.

[0022] The process according to the invention can be advantageous for plants for the production of all types of paper and pulp webs. In particular, it is also advantageous for plants for the production of packaging papers; for the production of coated papers and specialty papers.

[0023] In advantageous embodiments of the process, it can be provided that so much of the second exhaust air is mixed with the first exhaust air that the dew point of the process exhaust air is below the ambient temperature of the plant, in particular at least 5° below the ambient temperature of the plant.

[0024] It can be advantageous to measure the temperature in the first exhaust air and / or the second exhaust air and / or in the process exhaust air.

[0025] Alternatively or additionally, it can be advantageous to measure the humidity in the first exhaust air and / or the second exhaust air and / or in the process exhaust air.

[0026] Preferably, the process exhaust air can be released into the environment at a height of more than 40m, in particular 60m or more above the ground.

[0027] In preferred embodiments, it may be provided that the first exhaust air and the second exhaust air are at least partially mixed together before being released into the environment.

[0028] It may be planned that the first exhaust air and the second exhaust air are discharged via a common chimney. At least partial mixing can occur within the chimney or even in front of it.

[0029] In particular, it can be advantageous if the mixing is carried out using a static mixer. This eliminates the need for additional energy to be expended for the mixing process.

[0030] However, it may also be provided that the first exhaust air and the second exhaust air are at least partially mixed together after being released into the environment.

[0031] The first exhaust air and the second exhaust air can be discharged via separate chimneys.

[0032] For mixing after release into the environment, it can be advantageous if the outlets of the two chimneys are close together. In particular, it can be advantageous if the centers of the respective chimneys are less than 20m apart, especially less than 10m or less than 5m.

[0033] Furthermore, it is advantageous if the outlet of both chimneys is at the same height, or if the outlet height differs by less than 2m.

[0034] This is advantageous because it allows the two exhaust air streams to mix before significant fog has formed from the first exhaust air.

[0035] Tests conducted by the applicant have shown that such a suitable arrangement of chimneys can prevent or sufficiently reduce fog formation.

[0036] Further advantageous features of the invention are explained using exemplary embodiments with reference to the drawings. Fig. 1 Schematic representation of a steam removal device known from the prior art Fig. 2 Schematic representation of a fume extraction device for carrying out one aspect of the present invention. Fig. 3 Schematic representation of a fume extraction device for carrying out a further aspect of the present invention.

[0037] In Fig. Figure 1 shows a device known from the prior art. The moist first exhaust air 1 is to be discharged via the outlet 9 of a chimney. To prevent steam formation, cold ambient air 3 is used. This is passed through a heat exchanger 10, where it is warmed by the first exhaust air 1. The warmed ambient air 3 and the cooled first exhaust air 1 are mixed at a mixing point 5 and then released into the environment as process exhaust air 4 via a chimney.

[0038] In this type of exhaust gas removal, however, the moist first exhaust air 1 is cooled in the heat exchanger, causing some of the moisture contained in the first exhaust air 1 to condense. This condensate, which may also contain various other dissolved components of the exhaust air 1, must be collected and discharged separately, resulting in additional construction work. Furthermore, there is an increased risk of corrosion to the piping system and the heat exchanger. Additional measures, such as a flushing system, are also necessary to prevent this corrosion.

[0039] Furthermore, the system requires... Fig. 1. A fan 12 is used to supply ambient air 3. This fan 12 typically includes a control unit with which the required air volume can be adjusted. The more ambient air is needed for de-icing, the more energy is required to supply this ambient air 3.

[0040] At the in Fig. The problems present in the prior art do not arise with the device shown in Figure 2, which allows the de-steaming to be carried out according to one aspect of the invention.

[0041] The first exhaust air 1 consists entirely or partially of the exhaust air from a drying section of a plant for the production or processing of a fibrous web. This air is typically very humid and usually has temperatures between 60°C and 80°C. Upon contact with cold ambient air 3, this exhaust air 1 poses a high risk of fog formation.

[0042] To reduce or prevent this fog formation, a second exhaust air 2 is used in addition to the moist first exhaust air 1. This second exhaust air 2 has a higher temperature and lower relative humidity than the first exhaust air 1. Such exhaust air 2 is frequently generated at various points during the production or processing of a fiber web, for example, during line drying using non-contact IR dryers, or in a power plant located near the plant to supply it with electricity. The first exhaust air 1 is mixed with the second exhaust air 2 at a mixing point 5. To improve the quality of the mixing, as described in Fig. Figure 2 shows a mixer 13, preferably a static mixer 13, being installed. The process exhaust air 4 mixed in this way is then directed via a chimney 7 to an outlet 9 and released into the environment.

[0043] The chimney 7, or its outlet 9, advantageously has a height of more than 40m, for example 60m above the ground.

[0044] If required, the system can measure the temperature of the first exhaust air stream (1), the second exhaust air stream (2), and / or the process exhaust air stream (2). Alternatively or additionally, the (relative) humidity can also be measured in these exhaust air streams. These measurements can be used both to control the process and to store data for documentation purposes, allowing the operator, for example, to demonstrate compliance with legal requirements.

[0045] Since the second exhaust air 2 is hotter and drier than the first exhaust air 1, there is no risk of condensation when they mix. Likewise, this process does not require a fan, as in the prior art, and therefore no additional energy is needed. Because both exhaust air streams must be discharged anyway, only minimal additional structural modifications are required for fume extraction. The heat exchanger 10 required in the prior art is therefore unnecessary.

[0046] The comparison of Fig. 1 and Fig. Figure 2 shows the significantly simpler construction method with which de-steaming according to one aspect of the invention is possible.

[0047] Fig.Figure 3 shows an embodiment according to a further aspect of the invention. In this embodiment, the first exhaust air 1 and the second exhaust air 2 are each directed via a separate chimney 7 to an outlet 9 and released into the environment. The mixing point 5 is located downstream of the outlet 9, in its immediate vicinity. It is advantageous if the chimneys 9 are close to one another. In particular, it can be advantageous if the centers of the respective chimneys 9 are less than 20 m apart, especially less than 10 m or less than 5 m apart.

[0048] Furthermore, it is advantageous if the outlet 9 of both chimneys is at the same height, or if the outlet height differs by less than 2m.

[0049] This is advantageous because it allows the two exhaust air streams to mix before significant fog has formed from the first exhaust air stream. Thus, the first exhaust air stream (1) and the second exhaust air stream (2) can be mixed before significant fog has formed from the first exhaust air stream (1).

[0050] Tests conducted by the applicant have shown that such a suitable arrangement of the chimneys 9 can prevent or sufficiently reduce fog formation. Reference sign 1. First exhaust air 2 second exhaust air 3 Ambient air 4 Process exhaust air 5 Mixing point 7 Fireplace 9 Outlet 10 heat exchangers 12 fans 13 static mixers

Claims

[1] Method for removing process exhaust air (4) from a plant for the production or processing of a fibrous web, in particular a pulp, paper or board web, wherein the plant comprises a drying section in which the fibrous web is at least partially dried by contact drying, wherein a first exhaust air (1) is generated and wherein the plant comprises a second source which generates a second exhaust air (2) which is mixed with the first exhaust air (1), wherein the second exhaust air (2) has a higher temperature and a lower relative humidity than the first exhaust air (1), characterized by , that the first exhaust air (1) and the second exhaust air (2) are either at least partially mixed together before being released into the environment and a static mixer (13) is used for mixing, and / or the first exhaust air (1) and the second exhaust air (2) are at least partially mixed together after being released into the environment. [2] Method according to claim 1, characterized by , that so much of the second exhaust air (2) is mixed with the first exhaust air (1) that the dew point of the process exhaust air (4) is below the ambient temperature of the plant, in particular at least 5 ° [C] below the ambient temperature of the plant. [3] Method according to any one of the preceding claims, characterized by that the temperature is measured in the first exhaust air (1) and / or the second exhaust air (2) and / or in the process exhaust air (4). [4] Method according to any one of the preceding claims, characterized by that the humidity is measured in the first exhaust air (1) and / or the second exhaust air (2) and / or in the process exhaust air (4). [5] Method according to any one of the preceding claims, characterized by , that the second exhaust air (2) is wholly or partly the exhaust air of a turbine, a boiler or an IR dryer of the fiber web. [6] Method according to any one of the preceding claims, characterized by , that the process exhaust air (4) is released into the environment at a height of more than 40m, in particular 60m or more above the ground.

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