Method for treating exhaust air of a paper, board and / or tissue production machine and system designed to carry out a method of this type

Abstract

The invention relates to a method for treating exhaust air of a paper, board and / or tissue production machine (2), the method comprising the steps of: a) feeding the exhaust air, which exits from a dryer hood (7) of a drying station (5) of the production machine (2) and contains odorous substances and water vapor, into at least one scrubber (3) operated with cooling and scrubbing water, b) removing at least some of the odorous substances 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 scrubbing water of the scrubber (3), and c) removing from the scrubber (3) the cooling and scrubbing water heated by the contact with the exhaust air and feeding said heated cooling and scrubbing water into a heat exchanger of a heat-pump evaporator (8) of a heat pump (4) in order to evaporate the heat-pump working medium. The invention also relates to a system (1) for carrying out a method of this type.

Description

[0001] Description

[0002] 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

[0003] The present invention relates to a method for treating exhaust air from a paper, board, and / or tissue manufacturing machine. Furthermore, the present invention relates to a system configured to carry out such a method.

[0004] Paper, board and / or tissue manufacturing machines of the type mentioned at the beginning are basically known in the prior art. They normally have a number of stations arranged one after the other like a production line, including a drying station whose main function is to thermally remove water present between, on and in the fibers of the fiber web produced in the previous stations, which water cannot be removed mechanically. For this purpose, the fiber web to be dried is normally guided 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 to the cylinder.The exhaust air, which contains odorous substances and water vapor after the water has evaporated, is removed through a dryer hood from the drying station. This exhaust air is very hot and humid. Accordingly, vapor clouds 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.

[0005] In order to at least partially overcome the problems mentioned above, it has already been proposed to recover the waste heat contained in the exhaust air and to use it, for example, to preheat the fresh air, to heat the water, to heat the machine hall or to supply district heating.

[0006] 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.

[0007] To achieve this object, the present invention provides a method for treating exhaust air from a paper, board or tissue manufacturing machine, which method comprises the steps of: a) feeding the exhaust air containing odorous substances and water vapor emerging from a dryer hood of a drying station of the manufacturing machine into at least one washer operated with cooling and washing water, b) removing at least some of the odorous substances 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 washer, c) discharging the cooling and washing water heated by contact with the exhaust air from the washer 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.

[0008] By bringing the exhaust air coming from the dryer hood in step b) into contact with the cooling and washing water of the washer, the odorous substances contained in the exhaust air are absorbed by the cooling and washing water, whereby a significant reduction in the odor pollution when the exhaust air is released into the environment can be achieved.

[0009] Secondly, the exhaust air is cooled by the cooling and scrubbing water, which significantly reduces vapor formation. The cooling and scrubbing water, in turn, absorbs heat from the exhaust air and, in step c), feeds this heat into the heat exchanger of a heat pump evaporator. 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.

[0010] 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.

[0011] 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.

[0012] 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 medium, 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.

[0013] Furthermore, to achieve the object mentioned at the outset, the present invention provides a system comprising a paper, cardboard, 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 system is set up to carry out a method according to the invention.

[0014] Further features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings.

[0015] Figure 1 is a schematic view of a system according to a first embodiment of the present invention and

[0016] Figure 2 shows a schematic view of a system according to a second embodiment of the present invention. Like reference numerals refer to like or similar components.

[0017] Figure 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.

[0018] 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 has, 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 fed 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. In this case, a discharge line 18 branches off from the cooling and washing water supply line 16 and leads to a water treatment facility 19, for example, to 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 drained off via a drain line 21. In addition, a fresh water supply line 22 is provided, via which fresh water can be fed 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.

[0019] During operation of the system 1, superheated steam is supplied to the cylinder 6 of the drying station 5 of the production machine 2 via the steam supply line 12. In this way, the surface of the cylinder 6 is heated, over which a fiber web 25, produced in the preceding stations of the production machine 2 and still containing residual moisture, is passed. Contact with the hot cylinder 6 causes the water contained in the fiber web 27 to evaporate. The steam that cools when the cylinder 6 is heated is conducted as condensate via the condensate return line 13 to the heat exchanger of the heat pump condenser 10.

[0020] The exhaust air generated in the drying station 5, containing odorous substances and water vapor, is conducted via the dryer hood 7 and the exhaust air supply line 14 to the scrubber 3. In the scrubber 3, at least some of the odorous substances contained in the exhaust air is removed and at least some of the water vapor contained in the exhaust air is condensed by bringing the exhaust air within the scrubber 3 into contact with the cooling and washing water from the scrubber 3, which is supplied to the scrubber 3 via the cooling and washing water supply line 16. The exhaust air, which has been 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 releases heat energy in the heat exchanger of the heat pump evaporator 8 to the heat pump medium, 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 branched off 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.

[0021] 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 being 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.

[0022] The system 1 shown in Figure 2 differs from the system shown in Figure 1 in that several scrubbers 3 are provided. Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by a person skilled in the art without departing from the scope of the invention.

[0023] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identity are included.

Claims

Patent 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 manufacturing machine (2) into at least one scrubber (3) operated with cooling and washing water, e) removing at least some of the odorous substances 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), 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 in that 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 in 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 stream and fed to a water treatment plant.

4. Method according to one of the preceding claims, characterized in 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, is fed back into the drying station (5) of the production machine (2).

5. Plant (1) comprising a paper, cardboard, 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 in that the plant (1) is set up to carry out a method according to one of the preceding claims.

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