WO2004033998A1

WO2004033998A1 - Method for monitoring a paper grade shift in a paper or board machine and monitoring panel for the same

Info

Publication number: WO2004033998A1
Application number: PCT/FI2003/000742
Authority: WO
Inventors: Antero Lattu; Matti Rantanen
Original assignee: Stora Enso Oyj
Priority date: 2002-10-09
Filing date: 2003-10-08
Publication date: 2004-04-22
Also published as: FI20021800A0; FI20021800A; FI115669B; AU2003268977A1

Abstract

The invention relates to a method and a display system for monitoring a grade shift in a paper or board machine. The monitoring is based on process parameters measured by sensors (9) in the process, the parameters being monitored centrally on a common display (12). In accordance with the invention, the display (12) comprises adjacent meters (13) equipped with rotating indicators (14), the indicators having a common base direction, such as, for instance, pointing straight upward, corresponding to a situational set value specified for each parameter. During the grade shift, the set values are gradually changed in accordance with the new paper or board grade. Consequently, any malfunctions or deviations from the expected shift process appear as a deviation of the indicator from the common base direction. By the same principle, the display can be used for monitoring a normal process state between grade shifts.

Description

Method for monitoring a paper grade shift in a paper or board machine and monitoring panel for the same

The invention relates to a method and to a display system for monitoring a shift of paper grade in a paper or board machine.

A shift of paper grade means that the thickness or grammage of the paper or board to be produced is changed in the course of the machine run without interrupting the process. In a typical situation, there is a shift from a thinner or lighter paper or board grade to a thicker or heavier grade by decelerating the web speed. However, a change of grade may also involve a change of some other product parameter of paper or board.

The monitoring of a paper or board manufacturing process may be performed on special monitoring panels in the monitoring room of a paper mill, or on a computer display only simulating such a panel. Monitoring is based on selected process parameters revealing the current process state, which are continuously measured and monitored on a monitor or any similar indicating means in the monitoring room. A display in the monitoring room comprises typically the process chart of the paper or board machine, in which signals of different colours indicate the respective process state. These signals allow the monitoring person to readily conclude whether the monitored parameter is in the "green" region implying the normal process state, in the "yellow" area indicating a slight deviation, or in the "red" region indicating process failure. Besides these light signals, the display may also provide numerical indications of the respective values of parameters to be monitored.

The display of monitored parameters as defined above has the drawback that rapid and accurate perception of the overall process situation is difficult. This is especially true for changes within the green and yellow regions mentioned above. Minor changes that might grow gradually within the green region may already be a sign of process failure in progress, which it would be vital to detect while it is still in progress in order to start remedies as soon as possible. With current monitoring displays, such changes in their initial state risk being ignored, since it is arduous to immediately perceive parameters and parameter changes that are presented numerically, and the display does not give a well noticeable alarm until the parameter value has already reached the yellow region.

The problems in process monitoring mentioned above become especially tangible in conjunction with a grade shift in the machine, the change entraining a shift of many process-monitoring parameters. Also, during the shift, the process is more susceptible to various malfunctions and deviations from the expected ideal shifting process.

The purpose of this invention is to improve the monitoring of a paper or board manufacturing process, especially in connection with grade shifts, by measuring process parameters in the machine and subsequently indicating these parameters so as to immediately show the current process state and any deviations from predetermined expected values. The method of the invention is characterised in measuring the process parameters of the machine, which are monitored with meters centrally provided on a common display, the meters having rotating indicators with a common base direction, which corresponds to a situational set value determined for each parameter, each deviation from the set value appearing as a rotation of the indicator departing from the common base direction, and in that the set values at which the indicators point in the base direction are stepwise changed as the grade shifts proceeds.

The inventive idea involves basing the monitoring on indicators of adjacent meters within the view of the monitoring person, the indicators pointing principally in one single direction, so that any deviation from the normal state complying with the current set values of the process at each moment is immediately perceived, as an indicator deviates from the direction of the other indicators. In an ideal grade shift, all the monitored parameters maintain their constant or variable set values, and all the indicators point in the same and one base direction, such as straight upwards, for instance. Any deviation from the set values of the ideal situation will thus be perceived as inclination ofthe indicator into an oblique position.

The indicator rotation departing from the base direction may be proportional to the deviation of the monitored parameter from its set value, and then the indicator position and the movement it might make would immediately show the degree of the malfunction in progress and its current state. The indicator may be disposed to rotate steplessly to both sides of the base direction relating to the set value, and the display scale may be given a linear or logarithmic or any other similar form in accordance with the requirement in each case. Instead of one single exact set value, the parameter may have a relatively narrow variation range including the set value, which corresponds to the state expected for the process at each moment, the indicator pointing to the base direction in this range and starting to deviate from the base direction only when the limit of this range is exceeded. Such control eliminates any minor parameter deviations from the display that have no impact on the course of the process and the process control. This yields the advantage of retaining the indicators principally in the base direction, so that parameter deviations from the ideal situation that are significant and may require actions are particularly easy to detect. Adequate fine-tuning of an indicator having non-linear rotation may achieve substantially similar results.

A shift of set values may occur in small successive steps in a grade shift, and then the indicator oscillates on the display in analogy with each shift, or the set value shift may be performed as a gliding shift more or less adapted to changes in the process conditions, so that, in the ideal shift, the indicator does not oscillate at all from the base direction during a grade shift.

In accordance with the invention, the meters included in the display can be advantageously disposed next to each other in horizontal alignment, for instance, indicating the monitored parameters in the same order as the process ofthe paper or board machine proceeds. Consequently, the location of any deviations or malfunctions in the process state can be immediately located, and the progress of any process failure can be observed on the display.

The measurement of process parameters required in the invention can be performed by sensors, which are located in different parts of the paper machine for measuring parameters in the machine proper, in the stock, in the moving web or in the liquid and vapour phases of the process, such as temperatures, vapour pressure, the pH value of the liquor, various chemical concentrations in the liquid phase, pulp consistency, web thickness, web speeds and/or rotational speeds of the machine rolls.

The display system ofthe invention for monitoring a grade shift in a paper or board machine is characterised in the system comprising sensors mounted in the machine for measuring various process parameters and also a centrally disposed display for monitoring the parameters with adjacent meters on the display, whose rotating indicators have a common base direction corresponding to a situational set value determined for each parameter to be monitored, the meters being adjustable so as to allow adaptation ofthe set values to the grade shift in progress.

Besides monitoring of grade shifts, the display system described above naturally allows also monitoring of the paper or board production process between grade shifts, i.e. conventional process monitoring during the production of one and the same paper or board grade. This yields the advantage of the meters, which in the normal process condition point to the common base direction, giving efficient alarm of any malfunction or deviation from the ordinary process course.

The invention is explained in greater detail below by means of examples and with reference to the accompanying drawings, in which

Figure 1 shows a paper production process in a paper machine and a display system of the invention connected to the process for monitoring the process and its grade shifts,

Figure 2 shows a monitoring system of the invention, which monitors steam drying ofthe web in the drying section of a paper machine, and

Figure 3 is a general view of the monitoring display of the wet end of a paper machine as defined in the invention.

Figure 1 shows the paper production process in a paper machine monitored in accordance with the invention. High-consistency pulp having a consistency of approx. 3% is mixed in a tank 1 with short circulation stock having a consistency of approx. 0.2% and is pumped with an approx. 0.5% consistency by means of pump 2 to the machine head box 3, from where the stock is fed through the slice 4 onto an endless wire 5 with a view to forming a pulp path. The formed web 6 is detached from the wire 5 at the roll 7 and continues to the press rolls of the press section 8 and from there to the drying section, which comprises three successive drying units 10a- 10c. In the drying section, the web 6 is dried with pressurised hot drying steam. After the drying section, the web continues to the coating unit (not shown), is calendered and is eventually wound as finished paper on a roll. In accordance with the invention, the monitoring of the process and its grade shifts is based on process parameters measured by sensors 9 placed at suitable locations and on continuous monitoring of the parameters. The sensors 9 are connected by conductors 11 to a common centralised display 12, which may be a display panel located in the monitoring room of a paper mill or the screen of a computer. The display 12 consists of adjacent disc meters 13 a- 131, which are physical or have been generated electronically with display techniques, and are equipped with indicators 14. The meters 12 monitor process parameters continually measured by the sensors 9 in the process, each of the meter having been assigned a standard set value or a set value that changes in analogy with the controlled grade shift in the machine. In accordance with the invention, the display 12 has the following principle: at set values applied each moment of the process, the indicators 14 of the meters 13 point to a common base direction as in the figure, which is straight upwards. This situation, in which all the indicators 14 point to the base direction, is the normal process state, the maintaining of which the process supervisor is practically monitoring. Any deviation from this normal state appears as an easily detected deviation of one or more indicators from the common base direction, i.e. as rotation into an oblique direction either to the right or to the left from the vertical direction.

In the schematic exemplified case of figure 1, the meters 13a- 131 included in the display 12 follow the process parameters, which typically change in conjunction with a grade shift in the machine. During the grade shift, the machine proceeds to producing a new paper grade different from the preceding one without interruption of the process, in other words, the shift is brought about by a controlled change of the process parameters over a specific relatively short period. In the same conjunction, the set values ofthe meters 13 are gradually changed by simulating the changes of the process parameters in an optimal grade shift. The changes of the set values can be performed either stepwise or slidingly, which is preferred. With ideally performed grade shift, the meter indicators 14 will remain in their vertical direction during the entire shift.

In figure 1, the meter 13a of the display 12 indicates the flow rate of high- consistency pulp. Any changes in the flow rate have a bearing on the dry weight of the paper obtained as an end product. The meter 13b monitors the ratio jet/wire (ratio of stock sprayed onto the wire to wire speeds) on the basis of the head box pressure, the slice and the wire speed, the ratio influencing the flow pressure in the slice and the formation on the wire 5. The vertical adjustment of the slice 4 is monitored by the meter 13c. The meter 13d monitors the speed of the wire 5 measured on the roll 7, and the meter 13e monitors the rotational speed of the roll and consequently the speed ofthe web 6 in the press section 8. In the drying section 10a, the web speeds ofthe drying units 10a- 10c are monitored with meters 13g, 13i and 13k, the difference between the web speeds of the press section 8 and the first drying section with the meter 13f and the differences between the web speeds ofthe diying sections 10a- 10c with meters 13h and 13j. Finally the meters 131 serve for monitoring the web moisture measured after the last drying section 10c.

If, for instance, a grade shift from a lighter paper grade to a heavier one is performed without altering the machine speed and the web formation, the adjustment of the dry weight of the web will require an increase in the amount of stock feed to the wire 5. To this end, the input of high consistency pulp to the tank 1 and the number of rotations of the pump 2 are increased so as to maintain the consistency of the stock supplied to the head box 3 constant. In analogy with the change, the set values of the parameters monitored by the meters 13a and 13b increase gradually and the meters are adjusted in accordance with the invention, so that the indicators point in the vertical direction at each set value. For the pressure of the head box 3 not to exceed the target due to the increased supply, the slice 4 is opened, which implies an increase of the set value of the meter 13c and adjustment of the meter in accordance with the invention, in order to maintain the indicator in the vertical direction at each set value. As the slice 4 increases, the amount of stock feed to the web increases, and with constant speed of the wire 5, paper with higher grammage will be produced. In other words, the set value of the meter 13d monitoring the wire speed is kept constant in this exemplified case.

Figure 2 shows a monitoring system of the drying section of a paper machine, the system being based on measurement of the steam pressure. The paper web 6 moving in the process is dried in three successive drying units 16a to 16c, through which hot pressurised drying steam is conducted counter-current to the path. The steam flows in a piping 17a to 17d passing through the drying units 16a to 16c, thus passing through the drying cylinders 18a to 18c guiding the web 6 to be dried, there being three drying cylinders connected in parallel in each drying unit. Before 17a the drying units in the ducts, between 17b, 17c the successive drying units and after 17d the drying units, sensors 9a to 9d have been mounted for measuring the steam pressure, the sensors being connected with conductors 11 to adjacent pressure indicators 13a to 13d on the display screen 12. In the exemplified case, the set values of the successive meters 13a to 13d are 150, 120, 90 and 60 kPa, respectively, in other words, the steam pressure drops in the direction of movement of the steam, in a counter-direction to the web 6 to be dried. The reading of the last meter 13d in the direction of motion of the web in the figure has dropped from the set value, implying increased heat transfer in the last drying unit 10c, which initially encounters the web 6 arriving with a view to drying, the heat transfer being possibly due to increased web moisture.

A grade shift in a paper machine requires a change of the set values of the steam pressures. One way of proceeding is increasing the pressure of the steam supplied to the drying process, and in that case the set values of all of the pressure indicators 13a to 13d in figure 2 will change. Such display adjustment is carried out electronically on the display screen, while maintaining the basic monitoring principle, i.e. the common straight upward direction of all the indicators 14a to 14d when the process is under control. New set values can be adjusted for the meters, either by changing them all at once, or slidingly, in consistency with the gradual change of the process. In the ideal case, the meter indicator may remain in its vertical basic position over the entire duration ofthe change.

During monitoring of the drying section of a paper machine, other process parameters can be simultaneously monitored, such as e.g. web moisture before and after drying, and possibly also between the drying units. The monitoring of other parameters can be arranged in accordance with the invention, and the meters can be located next to the pressure indicators 13a to 13d on the monitor, as shown in figure 2. In this manner, all the parameters to be monitored can be assembled on a common display, where the entire process state can be monitored following the principle ofthe invention.

Figure 3 shows the monitoring display 2 of the wet end of a paper machine, where several measurements of various process parameters are centrally monitored, the figure showing central monitoring of measurements of fibre stock consistencies at different monitoring locations by meters 13, of flow speeds or flow rates by meters 13', of chemical concentrations in the aqueous phase by meters 13", and of the pH of the aqueous phase at different monitoring locations by meters 13'". In accordance with the invention, the meter indicators are principally at set values during normal runs and grade shifts, the indicator pointing straight upwards, with deviations appearing as indicators inclined from the vertical base direction.

It is obvious to those skilled in the art that the applications of the invention are not confined to the exemplified cases above, but may vary within the scope of the accompanying claims. Thus, for instance, the indicators do not necessarily point upward in their base direction, but instead, the common base direction may also point downward, laterally to the right or to the left, or obliquely upward or downward.

Claims

1. A method for monitoring a grade shift in a paper or board machine, characterised in that process parameters of the machine are measured, the parameters being monitored by means of meters (13) centrally provided on a common display (12), the meters having rotating indicators (14) with a common base direction, which corresponds to the situational set value specified for each parameter, so that any deviation from the set values appears as a deviation of the indicator from the common base direction, and that the set values at which the indicators point to the base direction are gradually changed as the grade shift proceeds.

2. A method as defined in claim 1, characterised in that the changes of the set values ofthe meters (13) are performed stepwise.

3. A method as defined in claim 1, characterised in that the changes of the set values ofthe meters (13) are performed slidingly.

4. A method as defined in any ofthe preceding claims, characterised in monitoring process parameters that have been measured on the moving machine parts, the stock, the moving web and/or in the aqueous or vapour phase.

5. A method as defined in claim 4, characterised in that the web speeds are monitored in the press section or the drying section ofthe machine.

6. A method as defined in claim 4 or 5, characterised in monitoring the speeds of rotation ofthe rolls guiding the path.

7. A method as defined in claim 4 to 6, characterised in monitoring moisture values of the paper or board web that have been measured in the machine.

8. A method as defined in claim 4 to 7, characterised in monitoring the drying steam pressure in the drying section ofthe machine.

9. A method as defined in any of claims 4 to 8, characterised in monitoring the stock consistency and flow and also the ratio jet/wire during stock feed from the machine head box onto the wire.

10. A display system for monitoring a grade shift in a paper or board machine, characterised in that the system comprises sensors (9) mounted in the machine for measuring various process parameters, and a centrally disposed display (12) for monitoring the parameters by means of meters (13) located adjacent each other on the display, the rotating indicators (14) of the meters having a common base direction, which corresponds to a situational set value specified for each parameter to be monitored, the meters being adjustable so as to allow the set values to be adapted to the grade shift in progress.

11. A display system as defined in claim 10, characterised in that the common base direction of the indicators (14) is straight upward.

12. A display system as defined in claim 10 or 11, characterised in that a deviation of an indicator (14) from the base direction is proportional to a deviation of the monitored parameter from its set value.

13. A display system as defined in any of claims 10 to 12, characterised in that the meters (13) are disposed adjacent each other so as to indicate the monitored parameters in the same order as the process proceeds.