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  • 1.
    Dahlquist, Erik
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Tomas-Aparicio, Elena
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Jansson, Johan
    SAPPI South Africa.
    On-line simulations for diagnostics and control2010In: International Control Systems 2010 Proceedings / [ed] Alf Isaksson, Stockholm: SPCI , 2010Conference paper (Refereed)
    Abstract [en]

    The main objective of this project is to develop an application where physical models of fibre lines are run in parallel to the real processes. This application can be useful as a diagnostic tool to detect faults and improve process operations. By running the simulation models continuously, feeding input data from the process data base at a pre-determined time interval, the simulation will show results from the “normal operations”. These simulation results are compared to the measured data and hence faults can be detected e.g. hang-ups in the digester and channelling. NIR-spectra lab measurements of the wood chips fed into the digester can as well be considered. This feature give us the possibility of correlating the quality of the obtained pulp to the raw material used, which can be of help when tuning the process parameters.

    In this paper results from the use of the application described above in several mills in South Africa and results from some preliminary tests in a mill in Sweden are presented. Moreover, the system structure for the interaction between the physical models designed in Modellica language and the real process data is described.

  • 2.
    Jansson, Johan
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Digester modelling for diagnostics and control2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis will show the possibility for the development and use of an on-line model for application to continuous digesters for pulp production. The model is developed by using a program called Dymola (Dynamic Modeling Laboratory). What makes the Dymola software so well suited is that the program solves equations simultaneously. The model is a further development from the Purdue model [Bhartiya et al, 2003]. The main difference between this model and the Purdue model however, is the dynamics in the model. The dynamics are very important when you use the model for control purposes because the cooking process has long dead and retention times. The main purpose of this model is to use it for the advanced control of continuous digesters as well as giving the operators a better understanding of what happens in the cooking process when changes are made. The model will also be used for diagnostic purposes. Advanced control in this case is Model Predicted Control (MPC). The MPC will control the quality of the pulp “kappa” number and the chemical consumption during digestion. This thesis describes the model and results are shown for applications of on-line diagnosis in three pulp mills in South Africa. Real time process data from the pulp mills is fed into the model and a simulation is performed. Thereafter, the results from the simulation are compared to the actual measured data for a number of key variables. By comparing the simulation results to the real process data and following the trends of the deviations between the two, different types of faults and upsets can be detected in both the process and sensors.

  • 3.
    Jansson, Johan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Model based control and optimization in pulpindustry2004In: SIMS, Copenhagen, September 2004, 2004Conference paper (Refereed)
  • 4.
    Jansson, Johan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Dalhquist, Erika
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Lindberg, T
    Subramani, S
    Applications ofphysical models for optimization and control in pulp and paper industryIn: TAPPSA,Durban , October 2002Conference paper (Other academic)
  • 5.
    Jansson, Johan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Groble, Fran
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Avelin, Anders
    Mälardalen University, School of Business, Society and Engineering.
    On-line simulation of continuous pulp digester2009In: TAPPSA JournalArticle in journal (Refereed)
    Abstract [en]

    Continuous cooking is the dominant process in the kraft pulping industry.  Our general knowledge and understanding of process conditions inside the digester is limited. Process control systems comprise of groups of measurements, which give information about conditions at the outer shell of the digester.  These measurements mostly tell about cooking liquor inflows and outflows, temperature and it is also possible to measure pressure or pressure difference at the screen section of the digester shell.  But ultimately process conditions inside the digester are based on measurements at the shell and intelligent approximations.

     

    The aim of this paper is to describe more accurately the cooking conditions and phenomena inside the digester.  A model of a continuous digester was developed as an extension of the well known Purdue model [Bhartiya, 2003].  The model was adapted to simulate an industrial Lo-Solids pulp digester as well as an ITC digester.  The models were then used to do online predictions and these predictions were compared with the actual plant performance.

  • 6.
    Jansson, Johan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Grobler, Fank
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Model based control and optimization of  continuous digester2008In: TAPPSA JournalArticle in journal (Refereed)
    Abstract [en]

    Continuous pulp digesters are large reactors with significant residence time. They play a critical role in shaping the pulp qualities achieved at the product-end.  For this reason, there is a big drive towards developing fundamental dynamic models to be used for better process understanding and control (especially in the development of model based controllers).

    In this paper we discuss the use of physical models for diagnostics and process optimization of a continuous digester.  

     

    Accurate diagnostics are not possible without the use of a pressure-flow net. The pressure-flow net also makes it possible to validate pressure and flow sensors in the circulation around the digester.  For control purposes however, the pressure-flow net is not so important.

     

    Two dynamic physical models were built for a continuous digester, one with a pressure-flow net and one without.  The model without the pressure-flow net has been tuned and tested with good results at Ngodwana mill.  It was not possible to get the model which included  the pressure-flow net running with as many digester section blocks as we wanted due to the he system becoming stiff. However, for a lower number of sections results were obtained. With an adjustment of the boundary conditions, higher number of sections should be possible to test as well.

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