Method and machine for producing a material web with an optimised heating process

Abstract

The invention relates to a method and a machine (1) suitable for producing a material web (2), comprising at least one steam-heated drying cylinder (56), at least one steam pressure control valve (61), at least one steam and condensate system (50), and at least one open-loop and closed-loop control device (60), wherein the at least one steam-heated drying cylinder (56) is heated by the steam and condensate system (50) via the at least one steam pressure control valve (61), and wherein the at least one open-loop and closed-loop control device (60) controls a required steam pressure of the at least one steam-heated drying cylinder (56) via the steam pressure control valve (61). According to the invention, during a heating process (H1, H2) of the at least one steam-heated drying cylinder (56) from a starting temperature (T1, T2) to an operating temperature (T6), at least one heating curve (67) of the at least one steam-heated drying cylinder (56) is included as a preferably exponential steam pressure function over time in such a way that the steam pressure is used as a controlled variable for controlling during heating.

Description

[0001] Method and machine for producing a material web with an optimized heating process

[0002] The invention relates to a method for producing a material web, preferably a paper, cardboard or tissue web, in a machine comprising at least one steam-heated drying cylinder, at least one steam pressure regulating valve, at least one steam and condensate system, and at least one control and regulating device, wherein the at least one steam-heated drying cylinder is heated via the at least one steam pressure regulating valve with the steam and condensate system, and wherein the at least one control and regulating device regulates a required steam pressure of the at least one steam-heated drying cylinder via the steam pressure regulating valve.

[0003] The invention also relates to a machine for producing a material web, preferably a paper, cardboard or tissue web, particularly suitable for carrying out the method according to the invention, comprising at least one steam-heated drying cylinder for drying the material web, and at least one steam and condensate system for supplying the at least one steam-heated drying cylinder, and at least one steam pressure control valve arranged between the steam-heated drying cylinder and the steam and condensate system, wherein the at least one steam-heated drying cylinder, the at least one steam pressure control valve and the at least one steam and condensate system are connectable, and wherein at least one control and regulating device is designed such that the required steam pressure of the at least one steam-heated drying cylinder is controllable.

[0004] Devices of this type are known. For example, document WO2016 / 083 170 A1 discloses a machine for producing a material web, preferably a sack kraft paper web. Drying sections are typically arranged in different drying groups with different configurations of steam-heated drying cylinders. A single drying cylinder is connected either via its own steam pressure control valve or several drying cylinders are connected, for example, in so-called heating groups, and the several drying cylinders are controlled via a common steam pressure control valve.

[0005] To date, the control of the steam-heated drying cylinders has been carried out solely via a set steam pressure by the control and regulation system, with the steam being provided via at least one assigned steam and condensate system at a specific pressure and temperature.

[0006] Heating steam-heated drying cylinders to operating temperature may seem trivial at first glance, but when starting or ramping up a machine to produce a material web to operating temperature, increased stress on the mechanical components, for example on seams, is to be expected due to the thermal heating from a colder temperature to a warmer temperature. This is particularly evident in steam-heated drying cylinders, which can reach component temperatures of more than 100°C up to 250°C when drying a material web, especially paper, tissue, or board. Depending on the prevailing starting temperature, the drying cylinder is heated over several hours, preferably two to three hours, until an operating temperature is reached.

[0007] The heating process of the steam-heated drying cylinders is controlled by the control and regulation system using a simple ramp function for the degree of opening of the steam pressure control valves over time; the ramp function can be adjusted empirically.

[0008] Despite advanced digital and fully automated control and regulation systems, the heating processes are still largely controlled and regulated manually by operators to avoid overloads caused by excessively rapid heating. Operators laboriously measure temperatures on the drying cylinders using mobile temperature measuring devices and then manually enable the heating process in the control and regulation system for the next increase in steam pressure via the ramp function. This procedure poses a risk to operators, who must be close to the starting machine for the measurement, and also requires a significant amount of time for the heating process.

[0009] In some machines, a temperature measuring device is omitted in order to avoid the risk of operator interaction, but the empirically determined ramp function must be provided with higher safety factors or more time, which leads to longer heating processes.

[0010] During normal operation of a machine for producing a material web, the heating process of the steam-heated drying cylinders to operating temperature only accounts for a small portion of the time required. However, the duration of the heating process is particularly detrimental if the heating process is interrupted due to a fault and / or if the machine is shut down. Once the fault has been rectified, a new heating process is activated in the control and regulation device after the shutdown. In this case, the process is restarted due to a lack of reliable steam pressure values. This often results in a significant amount of time being wasted during the downtime, during which the machine cannot provide production.

[0011] The inventor has recognized that in the known processes the maximum permissible temperature gradients are very often exceeded despite all precautions and that the heating process therefore has a significant influence on the service life of the drying cylinders.

[0012] The object of the invention is to provide an improved method and an improved machine for time- and load-optimized heating of steam-heated drying cylinders. This object is achieved according to the invention by an embodiment according to the independent claims. Further advantageous embodiments of the present invention can be found in the subclaims.

[0013] The method according to the invention is characterized in that during a heating process of the at least one steam-heated drying cylinder from a starting temperature to an operating temperature, at least one heating curve of the at least one steam-heated drying cylinder is included as a, preferably exponential, steam pressure function over time, such that during heating to the steam pressure is controlled as a controlled variable.

[0014] Advantageously, a calculated and empirically or simulatively calibrated steam pressure curve can enable fully automatic control during the heating process, which is free from manual interaction by the operating personnel and can be shortened in time compared to a purely stored ramp function of the opening degrees of the at least one steam pressure control valve.

[0015] At the same time, the maximum permissible temperature gradient of the at least one steam-heated drying cylinder is advantageously undershot during the heating process via a steam pressure curve over time.

[0016] In an alternative embodiment, the method is characterized in that at the start of the heating process a1 ) a time elapsed since the start of the heating process is counted, and a2) based on the elapsed time, the vapor pressure p(t) is regulated to a vapor pressure calculated in the heating curve.

[0017] In an alternative embodiment, the method is characterized in that, when the machine is at a standstill, b1) a steam pressure p(t6) set in the control and regulation device is recorded and converted into an operating temperature. In an alternative embodiment, the method is characterized in that, when the heating process is interrupted before an operating temperature is reached, b2) a steam pressure p(t5) set in the control and regulation device is converted into a pre-operating temperature.

[0018] In an alternative embodiment, the method is characterized in that at least one cooling curve is stored over time in the control and regulating device, and that when the machine is at a standstill or the heating process is interrupted c) a time elapsed since the start of the standstill is counted, and d) depending on the time elapsed, a cooling temperature reached is calculated from the cooling curve, and e) when a new heating process begins, the cooling temperature reached is converted into a cooling vapor pressure p(t2), and f) the heating process is continued with the cooling vapor pressure p(t2) and the heating curve in a time-dependent manner.

[0019] Advantageously, by converting between a stored heating curve and cooling curve as a function of a past time, a reliable statement can be made about the prevailing boundary conditions in the steam-heated drying cylinder, which enables a resumption of the H2 heating process at a higher steam pressure or higher temperature and thus enables and shortens the required heating time within the maximum permissible temperature gradients.

[0020] In an alternative embodiment, the method is characterized in that a lapsed time of up to a maximum of 24 hours, preferably 12 hours, after the start of a standstill or an interruption of the heating process is recorded, and a cooling temperature reached is determined mathematically. The machine according to the invention is characterized in that the control and regulating device for a heating process of the at least one steam-heated drying cylinder from a starting temperature to an operating temperature comprises at least one heating curve over time, and in that the heating curve is a, preferably exponential, steam pressure function over time, and in that the heating curve is calculated from a maximum permissible temperature gradient of the at least one steam-heated drying cylinder, and the control and regulating device regulates the heating process solely via the corresponding steam pressure and time.

[0021] In an alternative embodiment, the machine is characterized in that the control and regulating device comprises at least one time counter and at least one cooling curve for the at least one steam-heated drying cylinder.

[0022] In an alternative embodiment, the machine is characterized in that the control and regulating device comprises an initial control curve upstream of the heating curve, such that the initial control curve is used first during a heating process from a cold start temperature, and that the initial control curve is a ramp function such that the ramp function limits an opening gradient of the at least one steam pressure control valve to less than or equal to 2% / min, preferably less than or equal to 1% / min, and that the ramp function is limited for a duration of less than or equal to 10 min, preferably less than or equal to 5 min, from the start of the heating process.

[0023] In an alternative embodiment, the machine is characterized in that the at least one steam-heated drying cylinder is free of a temperature measuring device.

[0024] A "heat-up curve" refers to a steam pressure curve plotted against time, which was determined taking into account the physical relationships between pressure and temperature for the steam used and a maximum permissible temperature gradient of the drying cylinders in use. The heat-up curve makes it possible to implement a relationship between temperature and the steam pressure to be controlled in the control and regulation device.

[0025] The mathematically determined steam pressure curve p(t) enables a time-optimized heating process of the steam-heated drying cylinders to be controlled.

[0026] The term “cooling curve” refers to the change in temperature of a steam-heated drying cylinder over time, which was determined empirically or by simulation in combination with Newton’s cooling law and is stored in the control and regulation device as a controlled variable.

[0027] The invention expressly extends to embodiments which are not given by combinations of features from explicit references to the claims, with which the disclosed features of the invention can be combined with one another - as far as this is technically reasonable.

[0028] Corresponding elements of the exemplary embodiments in the figures are provided with the same reference numerals. The functions of such elements in the individual figures correspond to one another unless otherwise stated and unless contradictory. A repeated description is therefore omitted.

[0029] It should also be noted that the differing features of the illustrated embodiments can be interchanged and combined with one another. The invention is therefore not limited to the combinations of features shown in the illustrated embodiments.

[0030] Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings. The invention is explained below with reference to the figures. The figures show in detail:

[0031] Fig. 1 A simplified, schematic side view of a machine for producing a material web;

[0032] Fig. 2 A simplified, schematic diagram of a heating curve stored in the control and regulation system over time p(t);

[0033] Fig. 3 A simplified, schematic diagram of a cooling curve of the drying cylinders stored in the control and regulation system over time T(t).

[0034] The arrow with reference number 16 indicates the running direction 16 or the main movement direction or x-direction of the produced material web 2 in the machine 1.

[0035] Figure 1 shows an exemplary embodiment of a machine 1 for producing a material web 2 in a simplified representation. The machine 1 shown is suitable for producing a material web 2.

[0036] Typically, a fiber suspension is fed into the forming section 3, which in this case is designed as a fourdrinier wire, through a headbox, where it is dewatered and a material web 2 is formed. This is followed in the running direction 16 by a press section 4. In the illustrated embodiment, it comprises, for example, two stand-alone press nips, both of which are designed as press nips with an extended press gap, in this case two shoe press nips.

[0037] The material web 2 is then dried in at least one drying section 5. In the illustrated embodiment, the machine 1 comprises a pre-dryer section 51 and an after-dryer section 52 in which the material web 2 is dried. In the illustrated embodiment, the machine 1 comprises a further, optional material web processing device 18, which is arranged between the pre-dryer section 51 and the after-dryer section 52. The pre-dryer section 51 further comprises at least one drying group 54, 55, which is usually initially designed as a single-row drying group 54. In the single-row drying group 54, the material web 2 is alternately guided around drying cylinders 56, preferably steam-heated drying cylinders 56, and deflection rollers 57. In the illustrated embodiment, the pre-dryer section 51 is designed with two single-row drying groups 54 and subsequently two double-row drying groups 55.In the two two-row dryer groups 55, the material web 2 is alternately guided around drying cylinders 56. The material web 2 runs in a meandering shape around heated drying cylinders 56, preferably steam-heated drying cylinders 56, and around deflection rollers 57 and comes into direct contact with the steam-heated drying cylinders 56. The pre-dryer section 51 is further enclosed by a hood 58. In the downstream after-dryer section 52, the material web 2 is dried to the desired final dry content. In this example, the after-dryer section 52, like the pre-dryer section 51, is enclosed by a hood 58 in order to reduce heat losses. In this example, the after-dryer section 52 comprises exclusively two-row dryer groups 55, whereby the first four upper drying cylinders 56 of the after-dryer section 52 are not wrapped by a dryer fabric.

[0038] As a result, the material web 2 is not covered in the area of ​​the upper drying cylinders and enables the optional use of at least one impingement flow dryer 59, preferably two impingement flow dryers 59, to increase the drying performance during the production of the material web 2.

[0039] After the after-drying section 52, the material web 2 is wound up in a winding unit 10 onto a preferably one-piece winding core 11.

[0040] Furthermore, the machine 1 comprises at least one heating system 50, preferably a steam and condensate system 50, shown here in simplified form, for heating the drying cylinders 56, preferably the steam-heated drying cylinder 56. The at least one heating system 50, preferably a steam and condensate system 50, can be connected to at least one steam-heated drying cylinder 56 via at least one steam pressure control valve 61, so that the necessary heating power can be transferred to the steam-heated drying cylinder 56.

[0041] Furthermore, the machine 1 comprises at least one control and regulating device 60, shown here in simplified form.

[0042] The control and regulation device 60 comprises at least one stored heating curve 67 of a steam-heated drying cylinder 56 and at least one stored cooling curve 65 of a steam-heated drying cylinder 56 and at least one time counter (timer (t)) 63, which registers the elapsed time t from the start of a heating process and / or from the start of a standstill or a cooling process until the end of the heating process or the renewed start of a heating process in a cooling process.

[0043] Furthermore, the control and regulation device 60 is suitable for controlling two logics of heating processes H1, H2 to an operating temperature T6 of the drying cylinders 56. Heating process H1 is a heating process H1 starting from a cold start temperature T1 or ambient temperature T1. Heating process H2 is a heating process H2 starting from a warm start temperature T2, which can be between the cold start temperature T1 and the operating temperature T6.

[0044] The control and regulation device 60 comprises at least one stored heating curve 67, preferably a steam pressure curve 67, for a heating process H1 from a cold start temperature T1. Alternatively, a further control curve 69 with a limitation of an opening gradient of the steam pressure control valve 61 can be stored in the heating process H1 from a cold start temperature T1, wherein the control curve 69 advantageously represents a limitation only in the initial phase of a few minutes in order to ensure gentle heating if the components of the drying cylinders 56 have disadvantageously cooled further below the ambient temperature T1. Furthermore, the control and regulation device 60 comprises the known at least one heating curve 67 and at least one cooling curve 67, as well as at least one time counter 63, for a heating process H2 starting from a warm start temperature T2.

[0045] Figure 2 shows a simplified, schematic diagram of a heating curve 67 stored in the control and regulation device 60 over time t. The heating curve 67 contains a vapor pressure curve p(t) over time t, which can be calculated using a conversion formula between a vapor pressure p and a corresponding temperature value T for the heating temperature, which can also be done in the other direction.

[0046] As an example, various temperature values ​​T1 to T6 are entered, which can be converted and equated with a corresponding vapor pressure.

[0047] The temperature values ​​T1 and T2 represent starting temperatures from which a heating process H1, H2 and H4 of the at least one steam-heated drying cylinder 56 can be started.

[0048] The temperature value T6 represents the operating temperature T6 of the at least one steam-heated drying cylinder 56 aimed for by the heating process.

[0049] The starting temperature T1 is a so-called cold start temperature, which can be set after a longer standstill of the drying cylinders 56 and can usually correspond to the prevailing ambient temperature T1.

[0050] The starting temperature T2 is a so-called warm-start temperature, which can be established after a short standstill of the drying cylinder 56 and can typically correspond between the prevailing ambient temperature T1 and the operating temperature T6. In the event of an interruption of the heating processes H1 and H2 before reaching the operating temperature T6, a pre-operating temperature T5 is shown, which can result in the interrupted heating processes H3 and H4 shown.

[0051] Figure 3 shows a simplified, schematic diagram of a cooling curve 65 stored in the control and regulating device 60 over time t of a steam-heated drying cylinder 56. The cooling curve 65 contains a temperature profile T(t) over time t, which can be determined empirically or mathematically.

[0052] The temperatures T1 to T6 shown correspond to the temperatures in Figure 2.

[0053] Furthermore, three cooling processes K1, K2 and K3 are shown, which in the case of the cooling processes K1 and K2 start from the operating temperature T6 during a standstill and in the case of the cooling process K3 start from a pre-operating temperature T5, which can occur when a heating process is interrupted.

[0054] The combination of Figure 2 and Figure 3 allows for a representation of the various possible sequences of a heating and cooling process. A normal case would be a heating process H1 from a cold start temperature T1 to T6, which ends after reaching temperature T6. Normal operation at operating temperature T6, followed by a standstill. If standstill is activated in the control and regulation device 60, the time counter 63 begins to run from time t6 as the zero point. Using the stored cooling curve 65, a corresponding cooling temperature T2 can be assigned to each time, which transitions to a heating process H2 from the time of a restart. Using the calculated cooling temperature T2, a corresponding vapor pressure value p2 is determined, from which the heating is restarted. List of reference symbols

[0055] 1 machine

[0056] 2 material web

[0057] 3 Forming section

[0058] 4 Press section

[0059] 5 Drying section

[0060] 10 Rolling up

[0061] 11 winding core

[0062] 16 Running direction

[0063] 18 Material web processing device

[0064] 50 Heating system, preferably steam and condensate system,

[0065] 51 Pre-drying section

[0066] 52 night drying section

[0067] 54 single-row dryer group

[0068] 55 two-row dryer group

[0069] 56 drying cylinders, preferably steam-heated drying cylinders

[0070] 57 deflection rollers

[0071] 58 hood

[0072] 59 impingement dryers

[0073] 60 Control and regulation device

[0074] 61 Steam pressure control valve

[0075] 63 time counters, timers

[0076] 65 Cooling curve T(t)

[0077] 67 Heating curve p(t)

[0078] 69 Volume flow curve V(t)

[0079] K1 Cooling process from an operating temperature to an ambient temperature

[0080] K2 Cooling process from an operating temperature to a cooling temperature

[0081] K3 Cooling process from a pre-operating temperature to a cooling temperature

[0082] H1 Heating process during a cold start

[0083] H2 Heating process during a warm start H3 Interrupted heating process during a cold start

[0084] H4 Interrupted heating process during a cold start

[0085] T1 starting temperature, cold start temperature, ambient temperature

[0086] T2 starting temperature, first warm start temperature T6 > T5 > T2 > T1 T5 starting temperature, second warm start temperature T6 > T5 > T2 > T1

[0087] T6 operating temperature

Claims

Patent claims 1. A method for producing a material web (2), preferably a paper, cardboard or tissue web, in a machine (1), comprising at least one steam-heated drying cylinder (56), and at least one steam pressure control valve (61), and at least one steam and condensate system (50), and at least one control and regulating device (60), wherein the at least one steam-heated drying cylinder (56) is heated via the at least one steam pressure control valve (61) with the steam and condensate system (50), and wherein the at least one control and regulating device (60) regulates a required steam pressure of the at least one steam-heated drying cylinder (56) via the steam pressure control valve (61), characterized in that during a heating process (H1, H2) of the at least one steam-heated drying cylinder (56) from a starting temperature (T1, T2) to an operating temperature (T6), at least one heating curve (67) of the at least one steam-heated drying cylinder (56) as,preferably exponential, steam pressure function over time, such that when heating up to the steam pressure is controlled as a controlled variable., 2. Method according to claim 1, characterized in that at the start of the heating process (H1, H2) a1) a time elapsed (t) since the start of the heating process (H1, H2) is counted, and a2) based on the time elapsed (t) the steam pressure is regulated to a steam pressure p(t) calculated in the heating curve (67).

3. Method according to claim 1 or 2, characterized in that when the machine (1) b1) is at a standstill, a steam pressure p(t6) set in the control and regulating device is registered and converted into an operating temperature (T6).

4. Method according to one of the preceding claims, characterized in that when the heating process (H1, H2) is interrupted before an operating temperature (T6) is reached, b2) a steam pressure p(t5) set in the control and regulating device is converted into a pre-operating temperature (T5).

5. Method according to one of the preceding claims, characterized in that at least one cooling curve (65) is stored over time in the control and regulating device (60), and that when the machine (1) is at a standstill or the heating process (H1, H2) is interrupted c) a time elapsed (t2) is counted since the start of the standstill, and d) as a function of the time elapsed (t2), an achieved cooling temperature (T2) is calculated from the cooling curve (65), and e) at the start of a new heating process (H2), the achieved cooling temperature (T2) is converted into a cooling vapor pressure p(t2), and f) the heating process (H2) is continued with the cooling vapor pressure p(t2) and the heating curve (67) in a time-dependent manner.

6. Method according to one of the preceding claims, characterized in that a time elapsed (t2) up to a maximum of 24 hours, preferably 12 hours, after the start of a standstill or an interruption of the heating process is registered and a cooling temperature (T2) reached is determined mathematically.

7. Machine (1) for producing a material web (2), preferably a paper, cardboard or tissue web, particularly suitable for carrying out the method according to claim 1, comprising at least one steam-heated drying cylinder (56) for drying the material web (2), and at least one steam and condensate system (50) for supplying the at least one steam-heated drying cylinder (56), and at least one steam pressure control valve (61) arranged between the steam-heated drying cylinder (56) and the steam and condensate system (50), wherein the at least one steam-heated drying cylinder (56), the at least one steam pressure control valve (61) and the at least one steam and condensate system (50) are connectable, and wherein at least one control and regulating device (60) is designed such that the required steam pressure of the at least one steam-heated drying cylinder (56) is controllable, characterized in that,the control and regulating device (60) for a heating process (H1, H2) of the at least one steam-heated drying cylinder (56) from a starting temperature (T1, T2) to an operating temperature (T6) comprises at least one heating curve (67) over time, and the heating curve (67) is a, preferably exponential, steam pressure function (67) over time, and the heating curve (67) is calculated from a maximum permissible temperature gradient of the at least one steam-heated drying cylinder (56), and the control and regulating device (60) regulates the heating process (H1, H2) solely via the corresponding steam pressure and time.

8. Machine (1) according to claim 7, characterized in that the control and regulating device (60) comprises at least one time counter (63) and at least one cooling curve (65) for the at least one steam-heated drying cylinder (56).

9. Machine (1) according to claim 7, characterized in that the control and regulating device (60) comprises an initial control curve (69) upstream of the heating curve (67), such that in a heating process (H1) from a cold start temperature (T1), the initial control curve (69) is used first, and in that the initial control curve (69) is a ramp function, such that the ramp function limits an opening gradient of the at least one steam pressure control valve (61) to less than or equal to 2% / min, preferably less than or equal to 1% / min, and in that the ramp function is limited for a duration of less than or equal to 10 min, preferably less than or equal to 5 min, from the start of the heating process (H1).

10. Machine (1) according to claim 7, characterized in that the at least one steam-heated drying cylinder (56) is free of a temperature measuring device.

Images