Energy optimized steam blow box

Abstract

The invention relates to a steam application system (1) and a method for the efficient operation of the steam application system (1) for the efficient heating of a paper, cardboard or fibrous web (2) by means of steam condensation, comprising a steam blow box (3) which includes a plurality of application zones (4) which are connected to a steam line (9) by means of application valves (8), wherein the steam application system (1) includes a control device (6) which is configured to control the amount of steam applied to each application zone (4), wherein the application valves (8) include a device for detecting the valve position, and the steam line (9) includes a pressure measurement (7), and wherein the control device (6) is configured to calculate the amount of steam applied from the valve position and the measured value of the steam measurement (7).

Description

[0001] The invention relates to a steam application system for the efficient heating of a paper, board, or fibrous web by means of steam condensation, comprising a steam blower box comprising a plurality of application zones connected to a steam line via application valves. Furthermore, the invention relates to a method for applying steam to a paper, board, or fibrous web using a steam application system.

[0002] Steam blow boxes are known from the state of the art for heating the paper web in paper production. WO 2021 20 92 32 A1 shows a particularly compact steam blow box in which steam flow measurement and steam conditioning are already integrated into the steam blow box. However, steam flow measurement is always complex and error-prone. In practice, steam blow boxes are still not operated effectively to ensure that steam that does not condense on the paper web does not escape into the environment as mist. Finding the ideal operating point requires extensive manual testing, for which, in practice, there is often not enough time due to changing boundary conditions.

[0003] The object of the invention is to provide an efficient steam application system for achieving efficient steaming of the paper web and preventing unused steam from escaping into the environment and condensing on the paper, cardboard, or fiber web. Furthermore, in an advantageous embodiment of the invention, steam quantity measurement can be dispensed with, thereby obtaining a particularly efficient and cost-effective steam application system using calculations, and providing a method for operating it efficiently. This should enable more efficient automatic control of the steam quantity.

[0004] The 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.

[0005] Furthermore, the object is achieved according to the invention, wherein the steam application system comprises a control device which is designed to control the application quantity of the steam for each application zone, wherein the application valves comprise a device for detecting the valve position, and the steam line comprises a pressure measurement and wherein the control device is designed to calculate the application quantity from the valve position and the measured value of the pressure measurement.

[0006] In order to regulate the application quantity, it is necessary to determine information on the steam throughput. In the prior art, flow measurements are used for this purpose, which require a defined pre- and post-flow length of a steam line. These flow measurements are particularly susceptible to measurement errors, which makes precise and therefore efficient dosing of the application quantity difficult. In this invention, flow measurements on the steam line are therefore dispensed with. Instead, the application valves comprise a measuring device for detecting and transmitting the exact valve position. The measuring device can be implemented as a position sensor or can comprise a calculation of the position which is carried out by detecting the steps of a stepper motor. In the case of hydraulic or pneumatic valves, the position of the valves can also be determined by measuring the pressure of the control medium.In order to determine and regulate the application quantity for each application zone, a characteristic curve for the application valves is stored in the control system. This curve represents the application quantity as a function of the steam pressure in the steam supply line and the ambient pressure. Furthermore, the pressure measurement can advantageously also include a temperature measurement, so that the temperature can also be taken into account when calculating the application quantities (the pressure measurement is then temperature-compensated). The characteristic curve can also include specific geometric information of the application chamber and achieve a high level of accuracy for use in the steam blow box. The application valves are advantageously already integrated into the steam blow box and located between the steam line and the application zone.The application zones advantageously comprise a larger number of application nozzles or application openings, in particular between 10 and 200 application openings per application zone, through which the steam reaches the paper, cardboard or fiber web.

[0007] Also advantageous is a steam application system, wherein the control device comprises a speed value of the paper, cardboard or fiber web and controls the application quantity of steam in correlation with the speed value.

[0008] To calculate and control the application rate per area of ​​the paper, board, or fiber web, a speed value is advantageous. The speed is the production speed and / or the speed at which the paper, board, or fiber web moves past the steam blower box. The speed value is preferably transmitted digitally from the machine control system to the control device.

[0009] Also advantageous is a steam application system, wherein the control device comprises a grade value of the paper, cardboard or fiber web, and controls the application quantity of steam in correlation with the grade value.

[0010] The grade value is preferably transmitted digitally from the machine control system and / or a production planning system to the control device. The grade value is a sum value of various quality values ​​and / or production settings of the paper, board, or fibrous web. The grade value includes a basis weight value and / or values ​​relating to the material composition of the paper, board, or fibrous web. Settings in a forming section and / or a press section of the machine used to produce the paper, board, or fibrous web can also optionally be included in the grade value. The amount of steam to be applied can also be selected specifically for the grade and automatically adjusted accordingly using the control device.

[0011] Also advantageous is a steam application system, wherein the steam application system comprises a measuring system, wherein the measuring system determines quality values ​​of the paper, board or fiber web as profile values ​​over the cross machine direction (CD) and transmits them to the control device, and wherein the control device controls the application quantity in correlation with the profile values ​​for each application zone.

[0012] The quality values ​​of the paper, board, or fiber web are measured as a profile across the width of the web. This is advantageously determined using a measuring frame and traversing sensors in a quality control system (QCS), which is part of the steam application system. Control of the steam application system using a control device and measured values ​​from the QCS is advantageous because the application rate can then be adjusted across the cross-machine direction (CD), and the quality values ​​can be compensated and / or improved. Fluctuations in the raw material and / or machine parameters can lead to different quality values ​​across the width of the paper, board, or fiber web. Targeted, increased heating using steam in individual application zones can achieve an improvement in quality values ​​in these areas, for example, by improving drying or dewatering.

[0013] Also advantageous is a steam application system, wherein the steam application system comprises a measuring system, wherein the measuring system determines a moisture value and / or basis weight value of the paper, board or fiber web as profile values ​​over the cross machine direction (CD) and transmits them to the control device, wherein the control device controls the application quantity in correlation with the profile values ​​for each application zone.

[0014] The steam application system can directly influence the moisture content of the paper, board, or fiber web, as the increased temperature caused by steam application enables improved dewatering and / or drying. Therefore, the moisture content is a beneficial input variable for the steam application system's control device. The basis weight is also measured by the measuring system or QCS and advantageously transmitted to the control device, as the amount of steam applied has a different effect depending on the basis weight of the paper, board, or fiber web. The higher the basis weight, the higher the amount of steam applied can be controlled.

[0015] Also advantageous is a steam application system, wherein the steam application system comprises a temperature sensor, wherein the control device is designed to control the application quantity in correlation with the measured value of the temperature sensor.

[0016] The temperature of the paper, cardboard, or fiber web, as well as the ambient temperature, have a direct influence on the effectiveness of steam application. The higher the web temperature, the lower the condensation rate of the applied steam. Other process temperatures can also be advantageously taken into account in the control system, as they influence the product quality or quality parameters. The temperature sensor can be designed as a contact sensor or infrared sensor, or it can include an indirect measured value that is transmitted to the control device by calculation or measurement, for example, from a process control system.

[0017] A steam application system is also advantageous, wherein the steam line has a cross-sectional area of ​​100 - 3000 cm 2< over its length in the cross-machine direction (CD), in particular a cross-sectional area of ​​200 - 1000 cm 2< .

[0018] Control of the application zones by means of application valves is only possible if a uniform steam pressure is applied to all application valves. A correspondingly large dimensioning of the steam line is advantageous for this. Only when the line has a sufficient cross-sectional area can a sufficient steam supply to all application valves be ensured across the entire web width in the cross-machine direction (CD). The steam line is particularly advantageously dimensioned if the cross-sectional area is between 250 - 1000 cm² and the length of the steam line is between 3 and 13 m. A further advantageous method for applying steam to a paper, cardboard, or fibrous web using a steam application system comprising 10 - 200 application zones, each application zone being connected to an application valve, characterized in that the following method steps are carried out: Determining the valve position for each application valve and transmitting the values ​​to a control device. Measuring the steam pressure in the steam line and transmitting the measured values ​​to a control device. Calculating the application quantity for each application zone in the control device using the measured values ​​mentioned above. Controlling the application quantity for each application zone by adjusting the application valves.

[0019] The method for controlling the application rate of steam for each application zone advantageously does not require any additional steam quantity measurements. This is an advantage both in terms of investment costs and for the accuracy of the control, as measurement errors resulting from steam quantity measurements are avoided. Instead of quantity measurement and / or volume measurement in the steam line, this method uses only a pressure value and a precisely determined valve position to determine and / or control the application rate. Furthermore, control via valve position requires a pressure measurement in the steam line, with the pressure measurement advantageously arranged downstream of a steam quantity valve that regulates the amount of steam flowing into the steam line. The pressure measurement advantageously also includes a temperature measurement to enable temperature compensation of the pressure measurement.

[0020] A further advantageous method is one in which, in a further method step, temperature values, type values ​​and / or speed values ​​are transmitted to the control device and are taken into account for the control of the application quantity.

[0021] The transmission of temperatures, grade values, and / or speed values ​​is preferably carried out from the control system of the machine used to produce the paper, board, or fiber web. Typically, a distributed control system (DCS) is used, which transmits various measured values ​​to the control device of the steam application system via digital signal transmission. The measured values ​​are determined in the DCS from various sensors and / or calculations.

[0022] A method is also advantageous, wherein the steam application system comprises a measuring system, wherein the measuring system transmits a profile value of a quality value of the paper-board or fiber web to the control device, wherein the target value for the control of the application quantity for each application zone is carried out taking into account the profile value.

[0023] Irregularities across the web width can arise during the paper, board, or fiber web manufacturing process. These are detected by a quality measurement and control system (QCS) and transmitted as profile information to the control device of the steam application system.

[0024] A method is also advantageous in which the quality values ​​include the moisture content and / or the basis weight of the paper, cardboard or fiber web.

[0025] From the profile values ​​determined in the QCS, the basis weight and moisture content of the paper, board or fiber web are particularly important in order to efficiently control the amount of steam applied.

[0026] A method is also advantageous in which a condensation potential of the paper, cardboard or fiber web is calculated in the control device, wherein the condensation potential is taken into account for the control of the application quantity.

[0027] The amount of steam applied that condenses on the paper, board, or fiber web depends on various factors. The moisture content, the basis weight, and the speed of the paper, board, or fiber web are the quality values ​​most relevant for condensation. The condensation of steam causes the paper, board, or fiber web to heat up, whereby the web has a condensation potential that varies depending on time and location. By taking the condensation potential into account, the optimal amount of steam applied to the paper, board, or fiber web in the application zones of the steam application system can always be calculated under changing production conditions. This can prevent unused steam from escaping from the steam application system into the environment and causing fog.On the other hand, if the application quantity is too small, the advantageous heating cannot be sufficiently utilized if the condensation potential is not fully exploited.

[0028] The invention is explained below with reference to a figure.

[0029] The Figure 1shows a schematic, not to scale, isometric overview of a steam application system 1 for applying steam to a paper, board, or fibrous web 2. The steam application system 1 comprises a steam blow box 3, a control system 6, a measuring system 5, as well as the lines for transporting steam, compressed air, and / or signals. The steam blow box 3 is designed to apply steam in varying quantities to the paper, board, or fibrous web 2 by means of a plurality of application zones 4. The application zones are advantageously distributed in the cross-machine direction CD across the paper, board, or fibrous web 2. The application zones 4 are advantageously between 5 and 50 cm wide (in CD). For a typical web width of 3 to 13 m, a steam blow box 3 advantageously comprises between 10 and 300 application zones 4.A zone width in CD of 4 - 40 cm and a number of 25 - 250 application zones are particularly advantageous, as this allows particularly precise control of the steam application quantity in CD. Each application zone 4 has a distribution chamber, with and advantageously via steam outlet openings or steam application nozzles. The distribution chamber of each application zone is connected to an application valve 8 and is supplied with steam from a common steam line 9. The steam line 9 is advantageously designed with a sufficiently large volume to provide the same pressure at all application zones. A steam line 9 which has a cross-sectional area downstream of a steam flow valve 10 of 100 cm 2 to 1000 cm 2 is particularly advantageous. The steam blow box comprises the application zones 4, the application valves 8, the steam line 9, a steam flow valve 10 and a pressure measurement device 7 which records the pressure in the steam line 9 downstream of the steam flow valve 10.The steam line 9 advantageously further comprises (not shown) additional valves for draining condensate and / or heated chambers for reducing condensation in the steam blow box. The application valves 8 advantageously have a position detection system for the valve position, whereby the steam throughput can be represented via a characteristic curve as a function of the valve position and the pressure difference upstream and downstream of the application valve 8. These characteristic curves are advantageously stored as data in the control device 6 for each application zone. The control device 6 advantageously comprises a computer system, the technical devices for signal processing (IO interfaces, DA / AD converters), and corresponding converters for transmitting control signals to the application valves and achieving a corresponding adjustment there.The application valves 8 transmit the current valve position as input variables for the control device 6, and the data of a measuring system 5 is also transmitted to the control device 6. The control system is also connected to the pressure measurement 7 from the steam supply, wherein the pressure measurement 7 is usually designed for a steam pressure in the range 0 - 8 bar overpressure, and in particular for a range of 0 - 2 bar overpressure. The measuring system 5 is designed to record quality values ​​16 of the paper, board or fibrous web 2 and is arranged downstream of the steam blow box in the production process. The measuring system 5 is designed to carry out a plurality of measurements of the quality values ​​16 across the web width in the cross-machine direction CD, such that a profile value 14 can be determined.The measuring system 5 is advantageously designed to determine quality values ​​16 for the moisture, the temperature and / or the basis weight of the paper, board or fibrous web 2. Typically, further production sections are arranged between the steam blower box 3 and the measuring system, such as (not shown) a press section, a dryer section and / or a size press. The control device 6 is designed to process the transmitted profile values ​​14 and output control signals to the application valves 8. Advantageously and optionally, further signals from the production process and / or the environment of the machine for producing the paper, board or fibrous web 2 are processed in the control system. The speed value 12 is particularly advantageously used in the control device 6 to adjust the application quantity of steam.The speed value correlates linearly with the amount of steam applied that can be condensed on the paper, board, or fiber web 2. In a similar way, a temperature value determined by means of a temperature sensor 15 can also influence the condensation and be used accordingly in the control device 6. Particularly advantageously and optionally, the temperature of the paper, board, or fiber web and / or an ambient temperature and / or a process temperature can be measured. The condensation rate on the paper, board, or fiber web 2 is lower the higher the temperature of the paper, board, or fiber web 2 is. The control device 6 can also take differences in the paper, board, or fiber web 2 into account in the control; in particular, information such as the grade value 13, which is an aggregate value of several quality values ​​16, can advantageously and optionally be used in the control. List of reference symbols

[0030] 1Steam application system 2Paper, board or fiber web 3Steam blow box 4Application zones 5Measuring system 6Control device 7Pressure measurement 8Application valve 9Steam line 10Steam flow valve 11Steam supply 12Speed ​​value 13Grade value 14Profile value 15Temperature sensor 16Quality value CDCross Direction MDMachine Direction

Claims

1. Steam application system (1) for the efficient heating of a paper, cardboard or fibrous web (2) by means of condensation of steam, comprising a steam blow box (3) which comprises a plurality of application zones (4) which are connected to a steam line (9) by means of application valves (8), characterized in that the steam application system (1) comprises a control device (6) which is designed to control the application quantity of steam for each application zone (4), wherein the application valves (8) comprise a device for detecting the valve position, and the steam line (9) comprises a pressure measurement (7), and wherein the control device (6) is designed to calculate the application quantity from the valve position and the measured value of the pressure measurement (7).

2. Steam application system (1) according to claim 1, characterized in thatthe control device (6) comprises a speed value (12) of the paper, cardboard or fiber web (2) and controls the application quantity of steam in correlation with the speed value (12).

3. Steam application system (1) according to claim 1 or 2, characterized in that the control device (6) comprises a grade value (13) of the paper, cardboard or fibrous web (2) and controls the application quantity of steam in correlation with the grade value (13).

4. Steam application system (1) according to one of the preceding claims, characterized in that the steam application system (1) comprises a measuring system (5), wherein the measuring system (5) determines quality values ​​of the paper, cardboard or fibrous web (2) as profile values ​​(14) over the cross-machine direction (CD) and transmits them to the control device (6), wherein the control device (6) controls the application quantity in correlation with the profile values ​​(14) for each application zone (4).

5. Steam application system (1) according to one of the preceding claims, characterized in that the steam application system (1) comprises a measuring system (5), wherein the measuring system (5) determines a moisture value and / or basis weight value of the paper, cardboard or fibrous web (2) as profile values ​​(14) over the cross-machine direction (CD) and transmits them to the control device (6), wherein the control device (6) controls the application quantity in correlation with the profile values ​​(14) for each application zone (4).

6. Steam application system (1) according to one of the preceding claims, characterized in that the steam application system (1) comprises a temperature sensor (15), wherein the control device (6) is designed to control the application quantity in correlation with the measured value of the temperature sensor (15).

7. Steam application system (1) according to one of the preceding claims, characterized in that the steam pipe (9) has a cross-sectional area of ​​100 - 3000 cm over its length in the cross-machine direction (CD) 2 in particular a cross-sectional area of ​​100 - 1000 cm 2 .

8. A method for applying steam to a paper, cardboard or fibrous web (2) by means of a steam application system (1) according to one of the preceding claims, wherein the steam application system (1) comprises 10 - 250 application zones, and wherein each application zone (4) is connected to an application valve (8), characterized in that the following process steps are carried out: • Measuring the valve position for each application valve (8) and transmitting the measured values ​​to a control device (6) • Pressure measurement (7) of the steam pressure in the steam line (9) and transmitting the measured values ​​to a control device (6) • Calculating the application quantity for each application zone (4) in the control device (6) using the measured values ​​mentioned above • Controlling the application quantity for each application zone (4) by adjusting the application valves (8).

9. Method according to claim 8, characterized in thatIn a further process step, temperature values, type values ​​and / or speed values ​​are transmitted to the control device (6) and are taken into account for the control of the application quantity.

10. Method according to claim 8 or 9, characterized in that the steam application system (1) comprises a measuring system (5), wherein the measuring system (5) transmits a profile value (14) of a quality value of the paper, cardboard or fiber web to the control device, wherein the target value for the control of the application quantity for each application zone (4) is carried out taking into account the profile value (14).

11. Method according to claim 10, characterized in that the quality values ​​include the moisture and / or the basis weight of the paper, board or fibrous web (2).

12. Method according to one of claims 8 to 11, characterized in thatin the control device (6) a condensation potential of the paper, cardboard or fiber web (2) is calculated, wherein the condensation potential is taken into account in the control device (6) for the control of the application quantity of steam.

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