| Method for producing a fibrous material web and monitoring system -> Monitor Keywords |
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Method for producing a fibrous material web and monitoring systemRelated Patent Categories: Paper Making And Fiber Liberation, Processes And Products, With Measuring, Inspecting And/or TestingMethod for producing a fibrous material web and monitoring system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060027350, Method for producing a fibrous material web and monitoring system. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application is a U.S. National Stage of International Patent Application No. PCT/EP2003/050706 filed Oct. 9, 2003, and claims priority of German Patent Application No. 102 47 555.5 filed Oct. 11, 2002. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The invention relates to a method for producing a fibrous web, in particular a paper or board web, from at least one fibrous suspension having a fibrous suspension density, having at least one circulating wire to which, by means of at least one headbox, the fibrous suspension is applied with a fibrous suspension height and which is led over a series of dewatering elements. [0004] The invention also relates to a monitoring system for at least one fibrous suspension used during the production of a fibrous web, in particular a paper or board web, and having both a fibrous suspension density (FSD) and a fibrous suspension height (FSH), which is brought by at least one headbox to at least one circulating wire, which is led over a series of dewatering elements. [0005] 2. Discussion of Background Information [0006] The aforementioned properties of the fibrous suspension, in particular the fibrous suspension density and the fibrous suspension height, are currently determined with the aid of transportable measuring instruments, such as the Gamma Gage and the Ultra Sonus, at an extremely wide range of points in a paper or board machine. This extremely wide range of points is in this case preferably located at the wet end of a paper or board machine, this wet end generally comprising the stock approach, the headbox and the wire section, for example in the form of a gap or hybrid former. [0007] At measuring points of interest which cannot be reached via transportable measuring instruments of this type, the theoretical fibrous suspension height is calculated, provided the throughput quantities can be determined. The same procedure is normally used when determining the theoretical fibrous suspension density. Measuring points of this type which are of interest are, for example, the forming units of gap or hybrid formers, accurate measurements in these regions being difficult because of their inaccessibility or possible only with considerable effort. SUMMARY OF THE INVENTION [0008] Therefore, the instant invention provides an improved method and an improved monitoring system of the type mentioned at the beginning with which economic and reliable determination and monitoring both of the fibrous suspension height and of the fibrous suspension density are ensured at all measuring points of interest, which may also be complicated or difficult to access. [0009] In a method of the type mentioned at the beginning, according to the invention the fibrous suspension height and/or the fibrous suspension density is measured by means of at least one measuring cell which is fitted in a stationary manner and is not in direct contact with the fibrous suspension, in that the measured value obtained is evaluated in an associated process control system of the appropriate paper or board machine and is preferably compared with two predefinable limiting values (upper limiting value, lower limiting value), and in that, depending on the result of the evaluation or if at least one of the predefinable limiting values is violated, at least one actuating element is appropriately automatically activated or influenced via the process control system, in order to signal the violation of the limiting value and/or to initiate at least one appropriate countermeasure, with which a further increase or reduction in the fibrous suspension height and/or the fibrous suspension density of the region monitored is counteracted. [0010] On the basis of this configuration, not only is the determination both of the fibrous suspension height and of the fibrous suspension density ensured at all measuring points of interest, which may possibly also be complicated or difficult to access, it is also ensured that, for example in the case in which a critical value is reached, countermeasures are initiated automatically by means of the process control system in order to prevent further developments and therefore possible production disadvantages. [0011] Furthermore, in further refinement, the measured value determined can also be used as a controlled variable for the already known control of the predewatering section by means of the measured throughput quantities in the hybrid part (previous controlled variable) by means of the fibrous suspension height determined and/or fibrous suspension density determined, as a new controlled variable. [0012] Furthermore, the invention provides for the fibrous suspension height and/or the fibrous suspension density to be measured by at least one measuring cell fitted in a stationary manner close to the surface in the headbox and/or in the dewatering element and/or in the framing of the paper or board machine. By means of this stationary fitting of the measuring cell, continuous and reliable process measurement with constant measuring conditions and high runnability is ensured. [0013] It is also advantageous if the fibrous suspension height and/or the fibrous suspension density--viewed at right angles to the machine running direction--is measured at a plurality of points at a respective distance from one another by means of a plurality of measuring cells fitted in a stationary manner. In this case, the distance between the measuring points can assume a value in the range from 50 mm to 1000 mm, preferably from 100 mm to 500 mm. By means of this kind of fitting, in addition to a longitudinal direction profile in the machine running direction, a tranverse profile at right angles to the machine running direction can be set up in a particular way with substantially higher meaningfulness. [0014] According to a preferred refinement of the method according to the invention, the measurement is part of a control system which, moreover, comprises signal conversion following the measurement and data processing to be carried out by means of the process control system. By means of the measurement, for example, the structure of the fibrous web to be formed can be determined in the z direction and, if appropriate, can be regulated or controlled by means of adapting the dewatering performance (vacuum, foil angle and the like) in the machine direction upstream of the measuring point. [0015] If a relevant limiting value is violated, at least one of the following countermeasures is advantageously initiated: [0016] a) a reduction or increase in the wire speed of the paper or board machine; [0017] b) a reduction or increase in the dewatering performance in the machine running direction upstream of the measuring cell; [0018] c) a reduction or increase in the fibrous suspension density of the fibrous suspension supplied; by means of [0019] d) a reduction or increase in the quantity of fibrous suspension applied to the circulating wire. [0020] In this case, at least one of the following steps can be initiated: [0021] In order to change the wire speed, for example, at least one drive of the paper or board machine can be influenced appropriately; in order to change the dewatering performance, for example, the suction performance of an upstream dewatering element can be influenced appropriately; in order to change the fibrous suspension density, at least the quantity of dilution water supplied to the fibrous suspension, the levels of vacuum on individual or a plurality of dewatering elements and/or forming roll vacuum, the metering of chemicals, such as retention aid and the like, and/or the wire tension on the former, for example on the gap former, can be influenced appropriately and, in order to change the quantity of fibrous suspension applied to the circulating wire, at least one headbox pump of the headbox can be influenced appropriately. The actuating elements mentioned previously can therefore be, for example, drives of the paper or board machine, valves, pumps, signal generators and/or the like. [0022] If a relevant limiting value is violated, for example an alarm signal can be generated. [0023] According to an expedient refinement of the method according to the invention, if a first limiting value is violated, first of all a warning signal is generated and, if a further limiting value is violated, at least an appropriate countermeasure is initiated. [0024] In preferred embodiments, the headbox comprises at least one headbox slice, a dividing element, a slat and/or the like, and the dewatering element comprises at least one forming roll, a forming foil, a skimmer strip, a supporting strip, a sealing strip, a dewatering box, a foil box and/or the like. [0025] The monitoring system according to the invention accordingly comprises at least one measuring cell which is fitted in a stationary manner and is not in direct contact with the fibrous suspension for measuring the fibrous suspension height and/or the fibrous suspension density, which is connected to a process control system associated with the paper or board machine, the measured value determined by the measuring cell being evaluated in the process control system and preferably compared with the at least two predefinable limiting values (upper limiting value, lower limiting value) and, depending on the result of the evaluation or if at least one of the predefinable limiting values is violated, it being possible for at least one actuating element to be automatically activated or influenced appropriately, in order to signal the violation of the limiting value and/or to initiate at least one appropriate countermeasure, with which a further increase or reduction in the fibrous suspension height and/or the fibrous suspension density of the region monitored is counteracted. 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