Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
1998-11-17
2001-12-11
Fortuna, Jose (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162S190000, C162S258000, C162S259000, C162S263000, C162SDIG006, C162SDIG004, C700S128000
Reexamination Certificate
active
06328851
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for controlling properties of paper, in which method the basis weight of the paper is measured and the basis weight is adjusted by controlling the stock flow on the basis of the measurement result of the paper basis weight.
The invention also relates to equipment for controlling properties of paper, comprising means for measuring the basis weight of the paper and control means for controlling the stock flow in order to adjust the basis weight based on the measurement result.
BACKGROUND
As regards controls in so-called short circulation of a paper machine, paper properties are controlled at present for example by adjusting the white water total consistency through adjustment of the flow rate of the retention agent. In such a case, the result of the measurement of the white water consistency forms the basis for controlling a retention agent pump or valve in order to adjust the flow rate of the retention agent to be supplied. Further, in the prior art the ash content of paper is controlled by measuring the ash content for example from the finished paper with a measuring beam and/or by measuring the ash content in the headbox and/or the ash content of the stock and by controlling the flow rate of the filler to be added to the stock. The basis weight of the paper is controlled by means of stock flow control, which also takes into account changes in the stock consistency on the basis of total headbox consistency and/or a measurement result obtained from the measuring beam on the basis weight of the paper. Each control operates independently regardless of the other controls. Such an arrangement is disclosed for example in the reference “Lyhyen kierron sakeuss{umlaut over (aa)}döt, AEL/INSKO P906202/96 V, Nokelainen J., 1996” (consistency controls in the short circulation). Controlling one property also affects other properties; for example variation in the amount of retention agent and/or filler affects the basis weight, and therefore one or more controls are adjusted to operate so slowly that they do not interfere with the faster controls. Such a slow control cannot naturally compensate for rapid changes occurring in the property it controls. On the other hand, for example during grade changes the controls are carried out at consecutive stages and therefore the total time required for the changes is rather long. The situation is especially difficult with paper grades having a considerable ash content or with paper grades utilizing coated broke, which means that the papermaking process will be subjected to problems with the ash due to variation in the amount of broke or in the ash content of the broke, since in such a case changes in the amount of retention agent strongly affect the paper ash content and, correspondingly, changes in the amount of filler strongly affect the white water consistency.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide a method and equipment for rapid and effective control of paper properties.
The method according to the invention is characterized by modelling the effect of the flow of retention agent and the stock flow on the basis weight of the paper and adjusting, on the basis of said modelling, the basis weight by simultaneously controlling the flow of retention agent and the stock flow.
Further, the equipment according to the invention is characterized in that the equipment comprises a model of the effect of the flow of retention agent and the stock flow on the basis weight of the paper, and that the control means comprise means for controlling simultaneously the flow of retention agent and the stock flow in order to adjust the basis weight of the paper based on said model.
The invention is based on the idea of modelling the effect of the amount of retention agent on the basis weight of the paper and similarly the effect of the stock flow on the basis weight of the paper, and the executed modelling is used to adjust the basis weight of the paper by controlling simultaneously the flow of retention agent and the stock flow. The idea of a preferred embodiment is to model the effect of the flows of retention agent and filler both on the amount of filler in the white water and on the paper ash content and to adjust the latter two by controlling simultaneously the flow of retention agent and the flow of filler on the basis of the modelling.
In connection with the present application, the term “paper” also refers to board in addition to paper.
The invention has the advantage that it provides faster and more effective control of paper properties in paper machine short circulation than the previous methods.
REFERENCES:
patent: 495400 (1975-12-01), None
Camacho, E.F., et al., Model Predictive Control in The Process Industry (1995, Springer Verlag London Limited.
David Clarke, “Advances in Model-Based Predictive Control” Oxford University Press 1994.
I.C. Roberts, “Paper Chemistry” Blackie Academic and Professional 1996.
Haggman, Borje “Matematiska modeller for pappersmaskiner.” Svensk Papperstidning, vol. 79 (1976) pp 44-49.
Dorozhinskii, Y. B., “Method of Automatically Controlling Stock Flow to the Paper Machine Wire.” Otkryt. Izobret, 52 No. 46: 74 (1975) RU-C-495400.
Nokelainen, Jukka “Lyhyen Kierron Sakeussaadot.” AEL/INSKO P906202/96 V (1996).
Huhtelin Taisto
Kuusisto Risto
Nokelainen Jukka
Rantala Timo
Tian Lin
Fortuna Jose
Ladas & Parry
Metso Paper Automation Oy
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