Method for treating exhaust air from a paper, cardboard and / or tissue manufacturing machine, and a plant set up for carrying out such a method

Abstract

The invention relates to a method for treating exhaust air from a paper, cardboard and / or tissue manufacturing machine (2), comprising the steps of: a) supplying the exhaust air, containing odorants and water vapor, exiting a dryer hood (7) of a drying station (5) of the manufacturing machine (2) into at least one scrubber (3) operated with cooling and washing water, b) removing at least some of the odorants contained in the exhaust air and condensing at least some of the water vapor contained in the exhaust air by bringing the exhaust air into contact with the cooling and washing water of the scrubber (3), and c) discharging the cooling and washing water heated by contact with the exhaust air from the scrubber (3) and supplying this heated cooling and washing water to a heat exchanger of a heat pump evaporator (8) of a heat pump (4) for evaporation of the heat pump working medium.Furthermore, the invention relates to a system (1) for carrying out such a process.

Description

[0001] Process for the treatment of exhaust air from a paper, board and / or tissue manufacturing machine and plant designed to carry out such a process

[0002] The present invention relates to a method for treating exhaust air from a paper, board, and / or tissue production machine. Furthermore, the present invention relates to a system configured to carry out such a method.

[0003] Paper, board, and / or tissue manufacturing machines of the type mentioned above are generally known in the prior art. They typically comprise several stations arranged one after the other in a production line, including a drying station whose main function is to thermally remove any water present between, on, and in the fibers of the fiber web produced in the preceding stations that cannot be removed mechanically. For this purpose, the fiber web to be dried is normally passed over a cylinder whose wall is heated with superheated steam. The fiber web absorbs the heat from the cylinder, which in turn evaporates the water contained in the fiber web. The condensate produced when the cylinder is heated by superheated steam is collected, superheated again, and then fed back into the cylinder.The exhaust air, which contains odorous substances and water vapor after the water has evaporated, is discharged through a dryer hood of the drying station. This exhaust air is very hot and humid. Accordingly, plumes of steam are created when the exhaust air is released into the ambient air, which is undesirable. Furthermore, the exhaust air is very odorous, which is also undesirable and can lead to licensing issues with the production machine. Furthermore, the humid exhaust air removes water from the process, which is not resource-efficient.

[0004] In order to at least partially solve the problems mentioned above, it has already been proposed to recover the waste heat contained in the exhaust air and use it, for example, to preheat the fresh air, to heat the water, to heat the machine hall or to supply district heating.

[0005] Based on this prior art, it is therefore an object of the present invention to provide an alternative method of the type mentioned at the outset and a plant for carrying out such a method.

[0006] To achieve this object, the present invention provides a method for treating exhaust air from a paper, board or tissue manufacturing machine, comprising the steps: a) feeding the exhaust air containing odorous substances and water vapor from a dryer hood of a drying station of the production machine into at least one washer operated with cooling and washing water, b) removing at least part of the odorous substances contained in the exhaust air and condensing at least part of the water vapor contained in the exhaust air by bringing the exhaust air into contact with the cooling and washing water of the scrubber, c) Discharging the cooling and washing water heated by contact with the exhaust air from the scrubber and feeding this heated cooling and washing water into a heat exchanger of a heat pump evaporator of a heat pump for evaporating the heat pump working medium.

[0007] By bringing the exhaust air coming from the dryer hood in step b), which contains odorous substances and water vapor, into contact with the cooling and wash water of the washer, the odorous substances contained in the exhaust air are absorbed by the cooling and wash water, thereby significantly reducing the odor pollution when the exhaust air is released into the environment. Furthermore, the exhaust air is cooled by the cooling and wash water, which significantly reduces vapor formation. The cooling and wash water, in turn, absorbs heat from the exhaust air and feeds this heat into the heat exchanger of a heat pump evaporator in step c). The heat released in the heat exchanger is then used to evaporate the heat pump's working fluid. Accordingly, the waste heat contained in the exhaust air is recovered here.

[0008] According to one embodiment of the method according to the invention, after step c) has been carried out, the cooling and washing water cooled in the heat exchanger of the heat pump evaporator is at least partially fed back into the scrubber, thereby conserving resources.

[0009] Preferably, after performing step c), a portion of the cooling and wash water cooled in the heat exchanger of the heat pump evaporator is separated from the cooling and wash water stream and fed to a water treatment facility, for example, a sewage treatment plant. Here, the odorous substances contained in the cooling and wash water can be removed.

[0010] According to one embodiment of the present invention, a condensate stream is removed from the drying station of the production machine, fed to a heat exchanger of a heat pump condenser of the heat pump, evaporated by heat exchange with the heat pump working fluid, and returned in the evaporated state to the drying station of the production machine. In this way, the waste heat extracted from the exhaust air is returned to the production process.

[0011] Furthermore, to achieve the object mentioned above, the present invention provides a plant comprising a paper, board, fiber web or tissue manufacturing machine with a drying station having at least one dryer hood, at least one washer and a heat pump with a heat pump evaporator, a heat pump compressor, a heat pump condenser and a heat pump throttle, wherein the plant is designed to carry out a method according to the invention.

[0012] Further features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. Fig. 1 is a schematic view of a plant according to a first embodiment of the present invention and Fig. 2 a schematic view of a system according to a second embodiment of the present invention.

[0013] The same reference numbers refer to the same or similar components.

[0014] Fig. 1 shows a plant 1 according to an embodiment of the present invention, which has as main components a paper, board or tissue manufacturing machine 2, a washer 3 and a heat pump 4.

[0015] The production machine 2 comprises a series of stations arranged one behind the other in the manner of a production line, including a drying station 5 with at least one cylinder 6 and at least one dryer hood 7. The heat pump 3 comprises, in a known manner, a heat pump evaporator 8, a heat pump compressor 9, a heat pump condenser 10, and a heat pump throttle 11. The cylinder 6 of the drying station 5 of the production machine 2 and the heat exchanger of the heat pump condenser 10 are connected to one another via a steam supply line 12 and a condensate return line 13. Furthermore, an exhaust air supply line 14 leads from the dryer hood 7 to the scrubber 3, and an exhaust air outlet line 15 leads out of the scrubber 3. The scrubber 3 is supplied with cooling and washing water via a cooling and washing water supply line 16, which leaves the scrubber 3 again via a cooling and washing water outlet line 17.The cooling and washing water outlet line 17 is connected to the heat exchanger of the heat pump evaporator 8. The same applies to the cooling and washing water supply line 16. A discharge line 18 branches off from the cooling and washing water supply line 16, which leads to a water treatment facility 19, for example, a sewage treatment plant or the like. Furthermore, treated water and / or fresh water can be fed back into the cooling and washing water supply line 16 via a supply line 20 or discharged via a drain line 21.

[0016] In addition, a fresh water supply line 22 is provided through which fresh water can be supplied to the supply line 20. The heat pump evaporator 8, the heat pump compressor 9, the heat pump condenser 10, and the heat pump throttle 11 are also connected to one another in a known manner via lines 23, 24, 25, and 26, through which a suitable heat exchange medium can be circulated.

[0017] During operation of system 1, superheated steam is supplied to cylinder 6 of drying station 5 of production machine 2 via steam supply line 12. This heats the surface of cylinder 6, over which a fiber web 25, still containing residual moisture and produced in the preceding stations of production machine 2, is passed. Contact with the hot cylinder 6 causes the water contained in the fiber web 27 to evaporate. The steam that cools as cylinder 6 heats is conveyed as condensate via condensate return line 13 to the heat exchanger of heat pump condenser 10.

[0018] The exhaust air generated in the drying station 5, containing odorous substances and water vapor, is guided to the scrubber 3 via the dryer hood 7 and the exhaust air supply line 14. In the scrubber 3, at least some of the odorous substances contained in the exhaust air are removed and at least some of the water vapor contained in the exhaust air is condensed by bringing the exhaust air into contact within the scrubber 3 with the cooling and washing water of the scrubber 3, which is supplied to the scrubber 3 via the cooling and washing water supply line 16. The exhaust air, cleaned of odorous substances and cooled, is then discharged from the scrubber 3 via the exhaust air outlet line 15. The cooling and washing water, heated by contact with the exhaust air, is discharged from the scrubber 3 via the cooling and washing water outlet line 17 and fed to the heat exchanger of the heat pump evaporator 8.The cooling and washing water transfers heat energy to the heat pump medium in the heat exchanger of the heat pump evaporator 8, which is then evaporated accordingly. The cooled cooling and washing water then leaves the heat exchanger of the heat pump evaporator 8 via the cooling and washing water supply line 16 and is directed back toward the scrubber 3. A partial flow can be diverted via the discharge line 18 and fed to a water treatment system. Treated cooling and washing water and / or fresh water can then be fed back into the cooling and washing water circuit via the supply line 20.

[0019] The heat pump medium evaporated in the heat pump evaporator 8 is fed via line 23 to the heat pump compressor 9, compressed in the heat pump compressor 9, then fed via line 24 to the heat exchanger of the heat pump condenser 10, where it is condensed. The heat is transferred to the condensate coming from the cylinder 6 of the drying station 5 of the production machine 2, which in turn evaporates and is fed back to the cylinder 6 via the steam supply line 12. The heat pump medium condensed in the heat pump condenser 10 is then fed via line 25 to the heat pump throttle 11 and via line 26 to the heat exchanger of the heat pump evaporator 8, where it is evaporated again.

[0020] The Fig. Annex 1 shown in Figure 2 differs from the one shown in Fig. 1, several scrubbers 3 are provided.

[0021] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.

[0022] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

Claims

[1] A method for treating exhaust air from a paper, board and / or tissue manufacturing machine (2), comprising the steps of: d) feeding the exhaust air containing odorous substances and water vapor emerging from a dryer hood (7) of a drying station (5) of the production machine (2) into at least one washer (3) operated with cooling and washing water, e) removing at least part of the odorous substances contained in the exhaust air and condensing at least part of the water vapor contained in the exhaust air by bringing the exhaust air into contact with the cooling and washing water of the scrubber (3), f) Discharging the cooling and washing water heated by contact with the exhaust air from the scrubber (3) and feeding this heated cooling and washing water into a heat exchanger of a heat pump evaporator (8) of a heat pump (4) for evaporating the heat pump working medium. [2] Method according to claim 1, characterized bythat after carrying out step c), the cooling and washing water cooled in the heat exchanger of the heat pump evaporator (8) is at least partially fed back into the scrubber (3). [3] Method according to claim 2, characterized by that after carrying out step c), a part of the cooling and washing water cooled in the heat exchanger of the heat pump evaporator (8) is separated from the cooling and washing water flow and fed to a water treatment plant. [4] Method according to one of the preceding claims, characterized by that a condensate stream is discharged from the drying station (5) of the production machine (2), fed to a heat exchanger of a heat pump condenser (10) of the heat pump (4), evaporated by heat exchange with the heat pump working medium and, in the evaporated state, fed back into the drying station (5) of the production machine (2). [5] Plant (1) comprising a paper, board, fiber web or tissue manufacturing machine (2) with a drying station (5) having at least one dryer hood (7), at least one washer (3) and a heat pump (4) with a heat pump evaporator (8), a heat pump compressor (9), a heat pump condenser (10) and a heat pump throttle (11), characterized by that the system (1) is designed to carry out a method according to one of the preceding claims.

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