OPERATING A DRY BATCH OF A PAPER MACHINE

Description

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

[0002] Waste paper is an important raw material in paper production. To prepare waste paper for paper production, it is fiberized, and any impurities contained in the waste paper are removed. If necessary, additives are added. For fiberization, the waste paper is usually broken down into a fiber suspension in a pulper. Impurities such as plastic, metal, glass, or ash are separated from the usable fibers of the waste paper during stock preparation. The processed fiber suspension is fed into a paper machine for paper production.

[0003] For example, DE 1194692 A discloses a temperature control device for the drying cylinders of a paper machine with controls assigned to several individual cylinders or groups of cylinders. For example, WO 2012055897 A1 describes a method and device for detecting deposits on the surfaces of moving machine parts in paper machines.

[0004] However, not all of the contaminants contained in waste paper can be separated from the usable fibers of the waste paper during stock preparation. Furthermore, limited removal of contaminants is often accepted during stock preparation in order to reduce fiber loss during the separation of fibers from contaminants in the waste paper. As a result, contaminants such as starch, binders, or ash remain attached to the fibers. In some cases, contaminants are initially released from the fibers in the tight water cycle of paper production, but later recombine with the fibers. In any case, contaminants reach the paper machine.

[0005] Some of these contaminants remain in the produced paper and can reduce its quality. Other contaminants adhere to paper web contact surfaces that are in contact with a paper web passing through the drying section of a paper machine. Such paper web contact surfaces include, in particular, the surfaces of drying cylinders over which the paper web is guided in the drying section. These deposits can be carried along by the paper web and cause paper web breaks, which in turn lead to paper production downtimes and / or impair the quality of the produced paper.

[0006] To combat such deposits, scrapers are placed on the surfaces of drying cylinders, for example, to scrape deposits from the surfaces and convey them to collection containers. However, it often happens that deposits build up on such scrapers instead of falling into a collection container. In this case, the scrapers must be replaced.

[0007] The invention is based on the object of reducing deposits of contaminants on paper web contact surfaces in the drying section of a paper machine.

[0008] The object is achieved according to the invention by a method having the features of claim 1 and by a drying section having the features of claim 12.

[0009] Advantageous embodiments of the invention are the subject of the subclaims.

[0010] In the method according to the invention for operating a drying section of a paper machine, a melting point of a deposit on at least one paper web contact surface which is in contact with a paper web passing through the drying section in the drying section is determined, and a temperature in at least one region of the drying section is controlled or regulated as a function of the at least one determined melting point.

[0011] The invention is based on the finding that deposits on paper web contact surfaces in a drying section of a paper machine form, in particular, because impurities contained in a paper web passing through the drying section melt due to the elevated temperature in the drying section and subsequently adhere to paper web contact surfaces. Therefore, the method according to the invention provides for determining a melting point of a deposit on at least one paper web contact surface. Knowledge of the melting point makes it possible to control or regulate a temperature in the drying section depending on the determined melting point, so that melting of impurities in the drying section and thus deposits on paper web contact surfaces in the drying section can be reduced.

[0012] In one embodiment of the method according to the invention, the melting point of a deposit on at least one paper web contact surface is repeatedly determined. This embodiment of the method according to the invention takes into account that the composition of the waste paper from which the fiber suspension is produced and fed to the paper machine can change. Therefore, the contaminants contained in the paper web passing through the dryer section can also change. Repeated determination of the melting points of deposits on paper web contact surfaces in the dryer section enables the temperature control or regulation in the dryer section to be adapted to changing contaminants and, in particular, to changing melting points of these contaminants.

[0013] In a further embodiment of the method according to the invention, the melting point of a deposit is determined on at least one paper web contact surface located in an entrance area of ​​the drying section, where the paper web enters the drying section. This embodiment of the method according to the invention takes into account that the paper web is exposed to a particularly large temperature increase in the entrance area of ​​the drying section and therefore impurities in the paper web melt, particularly in the entrance area of ​​the drying section.

[0014] In a further embodiment of the method according to the invention, the melting point of a deposit on a paper web contact surface is determined. The deposit is located in a region of the drying section where the temperature of the paper web is increased within the drying section. This embodiment of the method according to the invention takes into account that temperature increases of the paper web within the drying section can also lead to the melting of contaminants in the paper web.

[0015] In a further embodiment of the method according to the invention, the melting point of a deposit on at least one paper web contact surface, which is a surface of a drying cylinder, is determined. Drying cylinders in the drying section are heated (usually with steam) to dry the paper web. Therefore, the temperature of the paper web is increased at a drying cylinder, which can lead to the melting of contaminants in the paper web upon contact with the surface of the drying cylinder and to deposits of molten contaminants on the surface. Therefore, the method according to the invention preferably determines the melting points of deposits on the surfaces of drying cylinders.

[0016] In a further embodiment of the method according to the invention, the melting point of a deposit is determined using differential scanning calorimetry (DSC). Alternatively or additionally, the melting point of a deposit is determined using differential thermal analysis (DTA). Differential scanning calorimetry and differential thermal analysis are known methods for the thermal analysis of samples. They are used to determine the amount of heat absorbed or released by the sample or the temperature changes when the sample is heated or cooled compared to a reference container or a reference substance, in particular during a phase transition of the sample. In particular, these methods can be used to determine the temperature at which a phase transition of the sample occurs.Therefore, these methods are also suitable for determining the melting point of a deposit on a paper web contact surface in the drying section.

[0017] In a further embodiment of the method according to the invention, a 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 a deposit. This embodiment of the method according to the invention aims to prevent the melting of contaminants in the paper web in at least one region of the drying section by keeping the temperature in this region below the melting point of these contaminants.

[0018] In a further embodiment of the method according to the invention, a temperature function is specified for at least one region of the drying section, depending on the melting point of a deposit on at least one paper web contact surface, and a temperature in this region is controlled or regulated based on the temperature function. For example, a temperature in at least one region of the drying section is set or regulated to a value that is the function value of the temperature function specified for this region at the point defined by the at least one determined melting point.

[0019] In other words, the aforementioned embodiment of the method according to the invention provides for the temperature in at least one region of the drying section to be controlled or regulated based on a predetermined temperature function that specifies a temperature in this region as a function of a melting point of a deposit on at least one paper web contact surface. The temperature function is determined, for example, by a mathematical model, experimental investigations, and / or empirical values. Furthermore, the temperature function can also be generated and improved by machine learning. The temperature function is stored, for example, in a memory unit of a control or regulating unit that is configured to control or regulate a temperature in at least one region of the drying section.

[0020] In a further embodiment of the method according to the invention, a temperature in at least one region of the drying section is controlled or regulated by heating the drying cylinders of the drying section. This embodiment of the method according to the invention takes advantage of the fact that a drying section has heatable drying cylinders for drying a paper web, with the drying cylinders generally being heated with steam. Therefore, temperatures in the drying section can be influenced, in particular, by changing the heating of the drying cylinders.

[0021] A drying section of a paper machine according to the invention comprises a measuring arrangement which is designed to determine a melting point of a deposit on at least one paper web contact surface which is in contact with a paper web passing through the drying section in the drying section, and a control or regulating unit which is designed to control or regulate a temperature in at least one region of the drying section as a function of the determined melting point.

[0022] The measuring arrangement and the control or regulating unit enable the implementation of the method according to the invention for operating the drying section with the above-mentioned advantages.

[0023] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of embodiments, which are explained in more detail in connection with the drawings.

[0024] The single figure schematically shows a section of a drying section 1 of a paper machine according to the invention. The drying section 1 has several drying cylinders 3, only one of which is shown in the figure. A paper web 5 is guided over the drying cylinders 3. The drying cylinders 3 can each be heated by a heater 7 to dry the paper web 5. For example, the heaters 7 are designed as steam heaters, through which steam can be supplied to the drying cylinders 3.

[0025] In the dryer section 1, deposits 11 can form on paper web contact surfaces 9 that are in contact with the paper web 5. These deposits are caused in particular by the melting of contaminants contained in the paper web 5 and stick to the paper web contact surfaces 9. Such paper web contact surfaces 9 are in particular the surfaces of drying cylinders 3.

[0026] The dryer section 1 comprises a measuring arrangement 13 configured to determine a melting point of a deposit on at least one paper web contact surface 9, which is a surface of a drying cylinder 3. Furthermore, the dryer section 1 comprises a control or regulating unit 15 configured to control or regulate a temperature in at least one region of the dryer section 1 depending on the determined melting point. The control or regulating unit 15 controls or regulates the heating system 7 of at least one drying cylinder 3.

[0027] In the illustrated embodiment, a scraper 17 is placed on the surface of a drying cylinder 3, by which deposits 11 are scraped off the surface of the drying cylinder 3 and fed to a collecting container 19. A sample of such a deposit 11 is fed from the collecting container 19 to the measuring arrangement 13 via a supply line 21, for example, via a hose. The melting point of the deposit 11 is determined by the measuring arrangement 13. For example, the melting point of the deposit 11 is determined by the measuring arrangement 13 using dynamic differential calorimetry or differential thermal analysis. The determined melting point is transmitted to the control or regulating unit 15.

[0028] To control or regulate the temperature in a region of the drying section 1, for example, a temperature function is specified for the temperature as a function of the melting point of a deposit 11 on at least one paper web contact surface 9. The control or regulation unit 15 then sets or regulates the temperature in the region of the drying section 1 to a value that is the function value of the specified temperature function at the location defined by the at least one determined melting point. For example, the temperature is controlled or regulated such that it does not exceed a determined melting point.

[0029] Although the invention has been illustrated and described in detail by means of preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

1. Method for operating a dryer section (1) of a paper machine, wherein - a melting point of a deposit (11) is determined on at least one paper web contact surface (9) which in the dryer section (1) is in contact with a paper web (5) running through the dryer section (1); and - a temperature in at least one region of the dryer section (1) is controlled in an open or closed loop as a function of the at least one determined melting point.

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

3. Method according to Claim 1 or 2, wherein the melting point of a deposit (11) is determined on at least one paper web contact surface (9) which is arranged in an entry region of the dryer section (1) in which the paper web (5) enters the dryer section (1) .

4. Method according to one of the preceding claims, wherein the melting point of a deposit (11) is determined on a paper web contact surface (9) which is arranged in a region of the dryer section (1) in which the temperature of the paper web (5) within the dryer section (1) is increased.

5. Method according to one of the preceding claims, wherein the melting point of a deposit (11) is determined on at least one paper web contact surface (9) which is a surface of a drying cylinder (3).

6. Method according to one of the preceding claims, wherein the melting point of a deposit (11) is determined using a dynamic differential calorimetry.

7. Method according to one of the preceding claims, wherein the melting point of a deposit (11) is determined using a differential thermal analysis.

8. Method according to one of the preceding claims, wherein a temperature in at least one region of the dryer section (1) is controlled in an open or closed loop in such a manner that the temperature of the paper web (5) in this region does not exceed the determined melting point of a deposit (11).

9. Method according to one of the preceding claims, wherein for at least one region of the dryer section (1) a temperature function for a temperature is specified as a function of the melting point of a deposit (11) on at least one paper web contact surface (9), and a temperature in this region is controlled in an open or closed loop by means of the temperature function.

10. Method according to Claim 9, wherein a temperature in at least one region of the dryer section (1) is set or controlled in a closed loop to a value which is the functional value of the temperature function specified for this region at the point defined by the at least one determined melting point.

11. Method according to one of the preceding claims, wherein a temperature in at least one region of the dryer section (1) is controlled in an open or closed loop by heating (7) at least one drying cylinder (3) of the dryer section (1).

12. Dryer section (1) of a paper machine, the dryer section (1) comprising - a measuring assembly (13) which is designed to determine a melting point of a deposit (11) on at least one paper web contact surface (9) which in the dryer section (1) is in contact with a paper web (5) running through the dryer section (1); and - an open-loop or closed-loop control unit (15) which is specified to control in an open or closed loop a temperature in at least one region of the dryer section (1) as a function of the melting point determined.