Operating a drying section of a paper machine

Abstract

The invention relates to a method for operating a drying section (1) of a paper machine. In the method, the melting point of deposits (11) on at least one paper web contact surface (9) is determined, which paper web contact surface is in contact with a paper web (5) travelling through the drying section (1); and the temperature in at least one area of the drying section (1) is controlled or regulated on the basis of the determined at least one melting point.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for operating a drying section of a paper machine. BACKGROUND

[0002] Waste paper is an important raw material for manufacturing paper. In order to pre-treat the waste paper for manufacturing paper, the waste paper is broken into fibres and interfering substances contained in the waste paper are removed, and if necessary, additives are added. In order to break into fibres, the waste paper is usually digested in a beater to form a fibre suspension. In the material pre-treatment, interfering substances, for example, consisting of plastics, metals, glass or ash, are separated from the utilizable fibres of the waste paper. The pre-treated fibre suspension is conveyed to a paper machine for manufacturing paper.

[0003] However, not all interfering substances contained in the waste paper can be separated from the utilizable fibres of the waste paper in the material pre-treatment. Furthermore, in order to reduce fibre loss in the separation of the fibres and interfering substances of the waste paper, the interfering substances are usually removed only limitedly as a compromise in the material pre-treatment. Thus, interfering substances, such as starch, adhesives or ash, can adhere to the fibres. In some cases, in the narrow water circuit of the paper manufacturing, the interfering substances can first be detached from the fibres, but then again be joined with the fibres. In any case, the interfering substances reach the paper machine.

[0004] Some of the interfering substances remain in the manufactured paper and can reduce the quality of the paper. Another part of the interfering substances is deposited adherently on the paper web contact surfaces, which are in contact with the paper web running through the drying section in the drying section of the paper machine. Such paper web contact surfaces are, in particular, the surface of the drying cylinder, via which the paper web is guided in the drying section. These deposits can be carried away by the paper web and cause the paper web to break, which in turn can cause paper production to be stopped and / or impair the quality of the produced paper.

[0005] In order to counteract such deposits, for example, a scraper is placed on the surface of the drying cylinder in order to scrape the deposits from the surface and convey them to a receptacle. However, the deposits often accumulate on such a scraper instead of falling into the receptacle. In this case, the scraper has to be replaced. SUMMARY

[0006] The object of the invention is to reduce the deposits of interfering substances on the paper web contact surfaces in the drying section of a paper machine.

[0007] According to the invention, this object is achieved by the method having the features of claim 1 and the drying section having the features of claim 12.

[0008] Advantageous design solutions of the invention are the subject of the dependent claims.

[0009] In the method according to the application for operating a drying section of a paper machine, the melting point of deposits on at least one paper web contact surface is determined, which paper web contact surface is in contact with a paper web travelling through the drying section in the drying section, and the temperature in at least one region of the drying section is controlled or regulated in accordance with the determined at least one melting point.

[0010] The application is based on the insight that deposits are formed at paper web contact surfaces in a drying section of a paper machine, in particular by interfering substances contained in a paper web travelling through the drying section, which interfering substances melt in the drying section due to the elevated temperature and then adhere to the paper web contact surfaces. The method according to the application therefore provides that the melting point of deposits on at least one paper web contact surface is determined. Knowing the melting point makes it possible to control or regulate the temperature in the drying section in accordance with the determined melting point, so that the melting of interfering substances in the drying section and thus the deposits on the paper web contact surfaces of the drying section can be reduced.

[0011] In an embodiment of the method according to the application, the melting point of deposits on at least one paper web contact surface is determined repeatedly. This embodiment of the method according to the application takes into account that the composition of waste paper, from which a fibre suspension is produced which is fed to the paper machine, can change. The interfering substances contained in the paper web travelling through the drying section therefore also change. Determining the melting point of deposits on paper web contact surfaces in the drying section repeatedly makes it possible to adapt the control and regulation of the temperature in the drying section to the changing interfering substances and in particular to the changing melting points of these interfering substances.

[0012] In a further embodiment of the method according to the application, the melting point of deposits on at least one paper web contact surface is determined, which paper web contact surface is arranged in an entry region of the drying section, in which entry region the paper web travels into the drying section. This embodiment of the method according to the application takes into account that the paper web will be subjected to a particularly great temperature increase in the entry region of the drying section and that the interfering substances in the paper web therefore melt in particular in the entry region of the drying section.

[0013] In a further embodiment of the method according to the application, the melting point of deposits on a paper web contact surface is determined, which paper web contact surface is arranged in a region of the drying section in which the temperature of the paper web increases within the drying section. This embodiment of the method according to the application takes into account that the temperature increase of the paper web within the drying section can also cause interfering substances in the paper web to melt.

[0014] In a further embodiment of the method according to the application, the melting point of the deposits on at least one paper web contact surface is determined, which is the surface of the drying cylinder. The drying cylinder in the drying section is heated, usually with steam, in order to dry the paper web. Thus, the temperature of the paper web at the drying cylinder will increase, which can cause the interfering substances in the paper web to melt when the surface of the drying cylinder is contacted and the molten interfering substances to deposit on the surface. Thus, in the method according to the application the melting point of the deposits at the surface of the drying cylinder is preferably determined.

[0015] In a further embodiment of the method according to the application, the melting point of the deposits is determined using dynamic differential scanning calorimetry (DSC). Alternatively or additionally, the melting point of the deposits is determined using differential thermal analysis (DTA). Dynamic differential scanning calorimetry and differential thermal analysis are known methods for the thermal analysis of a sample, using which the heat absorbed or released or the temperature change of a sample is determined when the sample is heated or cooled compared to a reference vessel or reference substance, in particular when the sample undergoes a phase change. In particular, the temperature at which the sample begins to undergo a phase change can be determined by these methods. Thus, these methods are also suitable for determining the melting point of the deposits on the paper web contact surface in the drying section.

[0016] In a further embodiment of the method according to the application, the temperature in at least one region of the drying section is controlled or regulated such that the temperature of the paper web in this region does not exceed the determined melting point of the deposits. This embodiment of the method according to the application is intended to prevent the interfering substances in the paper web from melting at least in one region of the drying section, the means being to keep the temperature in this region below the melting temperature of these interfering substances.

[0017] In a further embodiment of the method according to the application, a temperature function of the temperature in at least one region of the drying section in relation to the melting point of the deposits on at least one paper web contact surface is predefined for this region, and the temperature in this region is controlled or regulated in accordance with this temperature function. For example, the temperature in at least one region of the drying section is set or regulated to a value which is the function value of the predefined temperature function for this region at a point defined by the determined at least one melting point.

[0018] In other words, the above-mentioned design of the method according to the application provides that the temperature in at least one region of the drying section is controlled or regulated in accordance with a pre-given temperature function, which pre-gives the temperature in this region depending on the melting point of the deposits on at least one paper web contact surface. The temperature function is determined, for example, by means of a mathematical model, experimental investigations and / or empirical values. Furthermore, the temperature function can also be generated and improved by means of machine learning. The temperature function is stored, for example, in a memory unit of a control or regulation unit, which is provided for controlling or regulating the temperature in at least one region of the drying section.

[0019] In a further design of the method according to the application, the temperature in at least one region of the drying section is controlled or regulated by means of the heating of the drying cylinders of the drying section. This design of the method according to the application makes use of the fact that the drying section has drying cylinders which can be heated for drying the paper web, wherein the drying cylinders are usually heated with steam. The temperature in the drying section is therefore, inter alia, influenced by the heating variations of the drying cylinders.

[0020] The drying section of the paper machine according to the application comprises a measuring assembly, which is provided for determining the melting point of the deposits on at least one paper web contact surface, which is in contact with the paper web running through the drying section in the drying section, and a control or regulation unit, which is provided for controlling or regulating the temperature in at least one region of the drying section depending on the determined melting point.

[0021] The measuring assembly and the control or regulation unit enable the method according to the application for operating a drying section to be carried out with the above-mentioned advantages. BRIEF DESCRIPTION OF DRAWINGS

[0022] The above-mentioned features, characteristics and advantages of the application, as well as the forms and ways in which they are implemented, will become more apparent and more clear from the following description of embodiments, which is further explained with reference to the accompanying drawings.

[0023] Here, the only drawing Figure 1 A section of a drying section 1 of a paper machine according to the application is shown schematically. DETAILED DESCRIPTION

[0024] Here, the only drawing Figure 1 A section of a drying section 1 of a paper machine according to the application is shown schematically. The drying section 1 has a plurality of drying cylinders 3, only one of which is shown in the drawing. A paper web 5 is guided over the drying cylinders 3. In order to dry the paper web 5, the drying cylinders 3 can each be heated by a heater 7. The heater 7 is, for example, configured as a steam heater, by means of which steam can be fed to the drying cylinders 3.

[0025] In the drying section 1, deposits 11 can form on the paper web contact face 9, which is in contact with the paper web 5, which deposits are formed, inter alia, by the melting of interfering substances contained in the paper web 5 and adhere to the paper web contact face 9. Such a paper web contact face 9 is, inter alia, the surface of the drying cylinder 3.

[0026] The drying section 1 comprises a measuring assembly 13, which is provided for determining the melting point of the deposits on at least one paper web contact face 9, which is the surface of the drying cylinder 3. Furthermore, the drying section 1 comprises a control or regulating unit 15, which is provided for controlling or regulating the temperature in at least one region of the drying section 1 as a function of the determined melting point. Here, the heater 7 of at least one drying cylinder 3 is controlled or regulated by the control or regulating unit 15.

[0027] In the embodiment shown, a scraper 17 is placed on the surface of the drying cylinder 3, from which the deposits 11 are scraped off the surface of the drying cylinder 3 and are transported to a receptacle 19. A sample of such deposits 11 is transported from the receptacle 19 to the measuring assembly 13 by means of a transport line 21, for example by means of a cannula. The melting point of the deposits 11 is determined by the measuring assembly 13. The melting point of the deposits 11 is determined, for example, by the measuring assembly 13 by means of dynamic differential scanning calorimetry or differential thermal analysis. The determined melting point is transmitted to the control or regulating unit 15.

[0028] In order to control or regulate the temperature in a region of the drying section 1, a temperature function is predefined, which relates the temperature to the melting point of the deposits 11 on at least one paper web contact face 9. The control or regulating unit 15 then sets or regulates the temperature in the region of the drying section 1 to a value, which is the function value of the predefined temperature function at the point defined by the determined at least one melting point. Here, the temperature is controlled or regulated, for example, such that it does not exceed the determined melting point.

[0029] Although the application has been further shown and described in detail by preferred embodiments, the application is not limited to the disclosed embodiments and other variants can be derived therefrom by the person skilled in the art without departing from the scope of protection of the application.

Claims

1. A method for operating a drying section (1) of a paper machine, wherein, - Determine the melting point of at least one deposit (11) on a paper web contact surface (9) in the drying section (1) where the paper web contact surface contacts a paper web (5) traveling through the drying section (1); as well as - The temperature in at least one region of the drying section (1) is controlled or adjusted according to at least one determined melting point. In this process, the temperature in at least one region of the drying section (1) is controlled or adjusted such that the temperature of the paper web (5) in that region does not exceed the desired melting point of the deposit (11).

2. The method according to claim 1, wherein, The melting point of the deposit (11) on at least one paper web contact surface (9) is repeatedly determined.

3. The method according to claim 1 or 2, wherein, Determine the melting point of a deposit (11) on at least one paper web contact surface (9) arranged in the inlet region of the drying section (1) in which the paper web (5) enters the drying section (1).

4. The method according to claim 1 or 2, wherein, Determine the melting point of the deposit (11) on the paper web contact surface (9), which is arranged in a region of the drying section (1), in which the temperature of the paper web (5) in the drying section (1) is increased.

5. The method according to claim 1 or 2, wherein, Determine the melting point of the deposit (11) on at least one paper web contact surface (9), which is the surface of the drying cylinder (3).

6. The method according to claim 1 or 2, wherein, The melting point of sediment (11) was determined by dynamic differential scanning calorimetry.

7. The method according to claim 1 or 2, wherein, Differential thermal analysis was used to determine the melting point of sediment (11).

8. The method according to claim 1 or 2, wherein, For at least one region of the drying section (1), a temperature function relating to the melting point of at least one deposit (11) on the paper web contact surface (9) is given in advance, and the temperature in the region is controlled or adjusted based on the temperature function.

9. The method according to claim 8, wherein, The temperature in at least one region of the drying section (1) is set or adjusted to a value that is a function value of a pre-given temperature function of the region at a location defined by at least one obtained melting point.

10. The method according to claim 1 or 2, wherein, The temperature in at least one region of the drying section (1) is controlled or regulated by the heater (7) of at least one drying cylinder (3) of the drying section (1).

11. A drying section (1) of a papermaking machine, said drying section (1) comprising: - A measuring component (13) is configured to determine the melting point of a deposit (11) on at least one paper web contact surface (9) in the drying section (1) where the paper web contact surface contacts a paper web (5) traveling through the drying section (1); as well as - A control or adjustment unit (15) is configured to control or adjust the temperature in at least one region of the drying section (1) according to the desired melting point.

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