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  • 1.
    Dahlquist, Erik
    et al.
    Mälardalen University, Department of Public Technology. IST.
    Jones, Andrew
    International Paper, USA.
    Presentation of a dry black liquor gasification process with direct causticization2005In: TAPPI Journal, Vol. 4, no 6, p. 15-19Article in journal (Refereed)
    Abstract [en]

    In a new black liquor gasification process, black liquor is injected into a circulating fluidized bed, with sodium titanate (Na 2O· (TiO 23) as the fluidizing medium.The organics are gasified mainly by steam reforming because the temperature is relatively low (below 870°C) and the water content of the black liquor is relatively high (>20% water).The black liquor inorganics consist mainly of sodium carbonate and sodium sulfate. In the reactor, sodium carbonate is converted into Na 2O·TiO 2, which is removed from the bed and dissolved in water to give 4 NaOH + Na 2O·(TiO 2)3. After dewatering, this material is reinjected into the fluidized bed.The sulfate is reduced to Na 2S, and most of the sulfur is evaporated as H 2S after Na 2S reacts with CO 2 + H 2O. In a scrubber, the H 2S is selectively absorbed without CO 2. The direct causticization makes the lime kiln unnecessary. The gas is reheated after dust is removed and then combusted in a gas turbine/steam turbine cycle, to produce 2-3 times more electricity than produced in steam cycles with conventional recovery boilers.

  • 2.
    Dhak, Janice
    et al.
    Mälardalen University, Department of Mathematics and Physics.
    Dahlquist, Erik
    Mälardalen University, Department of Mathematics and Physics.
    Holmström, Kenneth
    Mälardalen University, Department of Mathematics and Physics.
    Ruiz, Jean
    Centre Technique du Papier, Domaine Universitaire, France.
    Belle, Jurgen
    Papiertechnische Stiftung, Germany.
    Goedsch, Frank
    Papiertechnische Stiftung, Germany.
    Developing a generic method for paper mill optimization2004In: Proceedings of the PAPTAC Control Systems 2004 Conference, (Quebec City, Canada, June 14-18), 2004, p. 207-214Conference paper (Refereed)
    Abstract [en]

    A generic method for formulating pulp and paper optimization problems is presented. Two ongoing projects in the framework of the DOTS project illustrate the method: optimization of sizing quality at a specialty paper mill, and optimization of the water and broke systems at a coated paper mill. Explicit and implicit formulations are compared, and different usages of external simulators in conjunction with optimization are discussed. The problems are solved using MATLAB/TOMLAB. Some results from different optimization algorithms are also presented.

  • 3.
    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.

  • 4.
    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.

  • 5.
    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.

  • 6.
    Nylander, Michelle
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Aparicio Tomas, Elena
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    ANALYSIS AND OPTIMIZATION OF ENERGY FLOWS IN A PULP MILL2008In: Proceedings of Control Systems,  2008 / [ed] Andrea Borrelli, Vancouver: TAPPI Press , 2008Conference paper (Refereed)
    Abstract [en]

    In this paper the digester house process variables

    are first studied to identify the process variations in

    different time perspectives. The focus is on the

    perspective of controlling the process on-line for

    the next 24 hours. With a mathematical model first

    the cook and the flows associated with the digester

    house are modelled. From this different scenarios

    with different “faults” are implemented in the

    model and compared to the process data. From this

    the performance can be predicted for different

    conditions. Key numbers are determined from this

    and these are used together with suitable objective

    functions to make optimal production planning for

    model based control. The set points are sent to the

    control system. By determining the reactivity of

    different qualities of wood chips by measuring NIR

    and measuring final kappa, a tool for feed forward

    control is developed.

  • 7.
    Porian, Bijan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Modelling of the Chemical Reactions in a Continuous Pulping Digester in the Presence of the Channelling Phenomenon2009In: International Review of Chemical Engineering Rapid Communications, ISSN 2035-1755, Vol. 1, no 5, p. 419-427Article in journal (Refereed)
    Abstract [en]

    Pulping digester including the channelling phenomenon and chemical reactions in the channel is modelled using the CFD, finite volume method, FLUENT. The objective of this paper is to predict the chemical and hydraulic behaviour of the digester under the hazardous situations.

    A 2D geometry of the digester is built and symmetric planes are defined in the Gambit. The mesh is then exported to the FLUENT and then the created half geometry was treated by axisymmetric function to establish a complete model of the digester. The Eulerian scheme is applied which    represent the multiphase flows in the digester. A heterogeneous porous media is defined for the compressible bed. Species transport is applied to define a mixture template of the wood chips components. The kappa number is predicted in the channel and around it to characterize the cooking development under hazardous conditions.               

  • 8.
    Pourian, Bijan
    Mälardalen University, School of Sustainable Development of Society and Technology.
    ANALYZING THE HYDRO DYNAMICS AND THE CHEMICAL REACTIONS IN PULP DIGESTER SYSTEMS USING CFD MODELLING2011Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The aim of this thesis is to use differential analysis and finite volume method (FVM) to model and analyze a continuous pulp digester in order to create a detailed picture of the flow behaviour and chemical reactions in the digester. This information will be used to optimize wood chip flow and reactions and to diagnose and avoid faults such as hang-ups and channelling.

    As digesters increase in size, the importance of control of the liquor flow in the wood chip bed also increases. Pulping reactors are often faced with production disturbances that cause reduced fibre quality, non-uniform chemical reactions and damaging channelling phenomena.

    The models that are proposed in this thesis aim to consider the fluid dynamics, thermodynamics and chemical reactions together in order to create a model with more detail than has been previously reported.

    The digester is of the continuous type and has a circular cross-section, with a height of 60 m and a diameter that increases stepwise from 6 m at the top to 7 m at the bottom. The geometry of the digester, including an internal pipe with three different diameters, three inlet flows at three levels of the digester, inlets and outlets at the top and bottom, and a number of peripheral circulation pipes connected to the screens at three levels, is represented in simulations by a 2D axisymmetric model constructed in Gambit.

    The interactions between the two phases - the wood chips and the alkaline liquor - are studied using the finite volume method (FVM). Eulerian and Mixture numerical methods are evaluated for solving a mass transfer multiphase model with a porous matrix, species transport and reaction system in FLUENT. Variable porosity is used to model channelling in the digester.

    Comparisons of the results of simulations with real digester data indicate that the multiphase model, with the species transport and mass transfer modules accurately predict the pulping chemical reactions inside the digester and are able to evaluate pulp quality.

    The species transport model with reaction scheme is able to predict the mass balance equation and stoichiometry of the pulping reaction. The porous media scheme complements this approach to give a more complete view of pulp production, including the effect of faults in the process.

    The approaches to the FVM described in this thesis enable an accurate view of the pulping process which can contribute to improved control and optimization of the process.

  • 9.
    Pourian, Bijan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    CFD modelling of solid-liquid multiphase and mathematical separation of the phases in a continuous pulp digester2010In: International Journal of Modelling and Simulation, ISSN 0228-6203, Vol. 30, no 3, p. 384-395Article in journal (Refereed)
    Abstract [en]

    This paper describes the use of a CFD multiphase model using commercial FLUENT software to aid understanding of the physical behavior of solid and liquid flows in the digester of the pulping process. We take into consideration the mass balance of the multi-inlets, outlets and circulation flows in the digester. We also look at the application of a Porous media model to describe the dynamic behavior of the liquor flow through a bed of solid particles.

    The cylindrical Korsnas/vallvik pulping digester in Sweden is represented in the models as an axisymmetric two-dimensional model, which includes multiple feeds, outlets, pressure adjustment valves and circulation pipes.

    Separation of the phases is an important part of the pulping process. A number of multiphase models are evaluated for their potential use in phase separation.

    For this evaluation we constructed the two-dimensional digester model in the Gambit software package, a pre- processor tool for FLUENT 

    Physical strainers at the entrances of outlet pipes were designed in Gambit, in order to investigate the possibility of physically separating large solid particles from the liquid flow where both phases are subject to suction into the circulation pipes.

    The compaction of the wood chips is also considered in the modeling. In the Porous model, the digester is divided into sections of different porosity, and the behavior of individual suspension particles  is not considered. The bulk of this paper concerns modeling mass balances and phases of the mixture in the digester using Eulerian and Mixture strategies.

  • 10.
    Pourian, Jan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Modelling of the channelling phenomenon of the pulping digester using porous Media2009In: SIMS, Scandinavian Modelling and Simulation  Society 50, conference in Fredrice, Denmark, October 7-8 (2009) / [ed] Brian Elmegard, Fredrice: SIMS electronic , 2009Conference paper (Refereed)
    Abstract [en]

    A dynamic model is developed for a continuous pulping digester to characterize the channeling phenomenon. The commercial CFD codes, FLUENT, are used to compute the hydraulic behavior of the digester under the normal and particular operational conditions. All the circulation flows, extractions, multiple inlets and outlets are included in this model. The digester is designed in the Gambit and an axisymmetric 2d model is applied. A porous scheme is implemented in the model in order to design the fluid flow and channelling phenomenon inside the digester. A heterogeneous porous media is specified in order to take the compression of the pulp into account. The simulation can serves as a prognosis model to predict the risk situations and probably to hinder high economical damage. The k- model contributes to compute the flow “regimes” or eventual eddies in some turbulent zones of the digester.

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