Paper Machine Headbox Research Articles

311 抄紙機ヘッドボックスにおける分散部の流動特性(流体工学II)

311 抄紙機ヘッドボックスにおける分散部の流動特性(流体工学II)

Model-based direct search optimization of the broke recirculation system in a newsprint mill

This work is concerned with the dynamic modelling of the papermaking section of an integrated newsprint mill, and the subsequent application of two direct search methods in a proof-of-concept optimization study of broke recirculation strategies. The effect of the current broke recirculation policy on the mixed pulp properties at the paper machine headboxes was quantified using a dynamic simulation generating data for an objective function which reflected the rate of change in measurable (flow, consistency and temperature) and immeasurable (total dissolved solids and fibre length distribution) parameters. Genetic Algorithm and the Nelder–Mead simplex methods were then linked dynamically to the simulation and used to find improved ways of recirculating broke pulp. Specifically, the profile of the changes to the broke ratio was modelled using a quadratic function and a second-order transfer function, and the coefficients of these functions were optimized. The optimized broke recirculation resulted in a significant reduction in the value of the objective function, thus, suggesting that the fluctuations in the properties of the mixed pulp stream could be dampened and paper machine headbox stability improved. It is expected that this process enhancement strategy would contribute to an increase in production yield (via a reduction in the occurrence of paper machine breaks), and thus an overall reduction in the waste of materials and energy.

Modeling a turbulent fibre suspension flowing in a planar contraction: The one-dimensional headbox

An Eulerian model of a turbulent fibre suspension flowing through a planar contraction is proposed to predict the fibre orientation distribution. The model specifically applies to the flow of pulp suspensions through a papermachine headbox. The model accounts for the convection of orientation distribution of the mean fluid velocity and the dispersion caused by the turbulent velocity fluctuations and describes each by a dimensionless dispersion coefficient and a dimensionless velocity gradient characterized by the contraction ratio (ratio of duct inlet height to outlet height) of the duct. A numerical solution of the model equations was shown to compare well to two different experimental studies available in the literature. From comparison with experiment the rotational dispersion coefficient was estimated to be 2 s −1 for both studies. Using the experimental value of the rotational dispersion coefficient and assuming it remains constant, the fibre orientation distributions was calculated for a range of dimensionless dispersion coefficients and contraction ratios. It was demonstrated that increasing the contraction ratio, over the industrial range of 5–50, significantly increases the alignment of fibres exiting the headbox. It was also shown that varying the inlet fluid velocity, over a practical range, provides only small changes in the fibre orientation distribution. Both predicted effects agree with experimental observation. Furthermore, this study suggests that fibre orientation is approximately dependent on a single dimensionless Peclet number that is a function of the fluid contraction ratio, inlet velocity, contraction length and rotational dispersion coefficient and that this parameter can be used to guide the design and operation of commercial headboxes.

Interactive Solution Approach to a Multiobjective Optimization Problem in a Paper Machine Headbox Design

A successful application of the interactive multiobjective optimization method NIMBUS to a design problem in papermaking technology is described. Namely, an optimal shape design problem related to the paper machine headbox is studied. First, the NIMBUS method, the numerical headbox model, and the associated multiobjective optimization problem are described. Then, the results of numerical experiments are presented.

New Approach on the Automatic Tuning of Multivariable PI Controllers Using Relay Feedback

A new algorithm for automatic tuning of multivariable PI controllers for multi-input multi-output processes is presented. The tuning procedure consists of four stages. In the first, the critical point of each possible loop is identified using the conventional relay feedback test. In this phase, a set of critical frequencies is formed. In the second stage, among the process critical frequency set, a design frequency is chosen. The choice of this design frequency is done with respect to the interaction problem in the multivariable system. In the third stage, the process steady state and frequency response matrices at the design frequency are estimated with good accuracy. In the fourth stage, the information about the process is used to tune the multivariable PI controller. For the multivariable PI controller, a new design technique is derived taking into account the decoupling condition at the low- and high-frequency range of the process. The proposed method is applied to various typical processes and experimented on using a laboratory-scaled model of a paper machine head-box. The experimental test has shown good results where significant performance improvement over the existing tuning methods is demonstrated.

Designing Paper Machine Headbox Using GA

A non-smooth biobjective optimization problem for designing the shape of a slice channel in a paper machine headbox is described. The conflicting goals defining the optimization problem are the ones determining important quality properties of produced paper: 1) basis weight should be even and 2) the wood fibers of paper should mainly be oriented to the machine direction across the width of the whole paper machine. The novelty of the considered approach is that maximum deviations are used instead of least squares when objective functions are formed. For the solution of this problem, a multiobjective genetic algorithm based on nondominated sorting is considered. The numerical results demonstrate the ability to obtain a large set of nondominated designs.

Tuning of PI controllers with one-way decoupling in 2×2 MIMO systems based on finite frequency response data

Abstract A method of tuning for PI controllers with one-way lead/lag decoupling tuning is demonstrated for 2×2 input-output systems, based on finite frequency response data. The frequency response estimates are obtained from closed loop tests using an identification technique based on bandpass filters. The open-loop frequency response is calculated and used to tune PI controllers and to fit lead-lag compensators for decoupling by weighted least-squares. Separate optimization of the PI controllers and the lead-lag compensator is preferred. The tuning takes into account violations of desired multivariable robustness criteria. The method is illustrated by application to a paper machine headbox simulation and by experiments in distillation column temperature control.

Robustness of discrete-time state feedback control systems

Abstract This paper presents stability robustness results for linear multivariable discrete-time systems with uncertainties. Robust stability of the full-state feedback linear quadratic regulator in the presence of perturbations of the system parameters is investigated. These results are based on recently developed bounds on structured perturbations of a stable linear discrete-time system. The paper applies these results to a paper-machine head box system example.

Instability analysis of some fluid–structure interaction problems

In this paper, we present instability analysis of two fluid–structure interaction (FSI) problems in the papermaking process. The first mathematical model is related to a pipe mixing unit which involves the submerged and inclined concentric pipes with different lengths. In the case of steady flow, both buckling and flutter instabilities are investigated. In the case of pulsatile flow, we use the numerical Floquet method to compute the eigenvalues of the monodromy matrix derived from the discretized linear system with periodic coefficients. In addition, for a special case, in which the concentric pipes have the same length, we also introduce a traditional Bolotin approach for comparison. The second mathematical model is derived from a vane/fluid interaction system within the papermachine headbox in which high-speed flows are separated by long flexible vanes. It is shown that for both laminar and turbulent flow conditions, the steady results derived from such analytical approaches match the corresponding computational solutions obtained using a general-purpose FSI computational package. Although, for certain cases, when geometries of fluid or solid domains are complex, it is very advantageous to use such a general-purpose program, we also point out, through the discussion of the selection of the critical time step in the numerical Floquet analysis and the dynamic stability analysis involving pulsatile flows, that there is still a need for analytical approaches as discussed in this paper.

Identification of Bilinear Models for Chemical Processes Using Canonical Variate Analysis

The identification of nonlinear models for chemical processes solely from experimental data is described in this paper. The canonical variate analysis (CVA) technique that has served well in the identification of empirical linear process models is extended to construct data-based bilinear models in an iterative fashion. Numerous examples involving engineering systems are included to illustrate the practicality of the suggested approach for bilinear model identification. Finally, the use of the identified nonlinear models for control is demonstrated using the example of a simulated paper machine headbox system.

An Anti-Windup Decoupling Nonlinear Control for a Paper Machine Headbox

Abstract Since most of the chemical processes are represented typically by nonlinear models, the use of nonlinear geometric control in chemical processes is straightforward. This paper presents a decoupling application in a paper machine headbox. The nonlinear geometric control is implemented with blocks for reference trajectory, tracking error, integrators of error feedback and with an anti-windup scheme. The results show a clear implementation scheme and good dynamical responses.

Fragility and robustness: a case study on paper machine headbox control

We discuss the fragility of controllers against small inaccuracies of controller parameters. A useful way to gain insight into controller fragility is to consider the fragility of poles and zeros. Certain controller design methods and controller parametrizations are especially vulnerable to fragility problems. It is hoped that the controversy and debate around the claimed fragility of designs obtained by modern robust and optimal control theories calls attention to the relevance of the work on fixed wordlength effects in controller implementation. A case study on a paper machine headbox control problem is included to illustrate that if a good robust control design method is used, together with a reasonable controller realization (parametrization), it should be possible to combat controller fragility in a fairly satisfactory, although indirect, manner. However, it would certainly be interesting to study whether controller fragility could be directly addressed within some generalized robust control design theory.

Optimal design of paper machine headboxes

A shape optimization problem for incompressible flows within a stabilized finite element framework is studied. The goal is to develop and test numerical realizations of optimal shape design problems that could be applied to non-trivial industrial problems. The resulting algorithm is applied to the optimization of the geometry of a tapered header in a paper machine headbox. Copyright © 2000 John Wiley & Sons, Ltd.

Optimization of Neural Network Topologies using Genetic Algorithm

ABSTRACTNeural networks (NN) are widely applied in modeling. The modeling process in which neural networks are applied involves the same problems as identification in general. In addition, the parameterization selected for the NN model is a key issue i.e., what number of hidden nodes is appropriate and what is their connectivity.This paper describes an evolutionary method for selecting the topology of a feedforward neural network by means of a genetic algorithm. The approach is a hybrid method utilizing a genetic algorithm for structure selection and a second-order training algorithm for parameter estimation. The method is tested with two modeling problems, one a well-known benchmark of an infra-red laser and the other modeling of a laboratory-sized pilot process imitating a paper machine head box.

Optimal digital control of a laboratory-scale paper machine headbox

This paper describes the design of a multi-input multi-output (MIMO) digital-linear-quadratic-regulator (DLQR) control system for the headbox of a paper machine. The complete design procedure is described from development of a mathematical model of the nonlinear headbox system, through experimental identification of linear model, to demonstration of closed-loop system performance on a laboratory-scale mock-up of an actual headbox. The important role of computer-aided-design tools is illustrated using Matlab and associated toolboxes. The control algorithm is implemented on a personal computer running the Labtech Notebook control program. The controlled system satisfactorily controls set point changes in total pressure and water level, and rejects disturbances in feedwater pressure. The material presented in the paper is used in a senior level course in digital process control at the University of Idaho. The course is jointly offered by the chemical and electrical engineering departments.

デュアルシステムによるコート原紙の操業性改善

With the purpose to improve main paper properties, the head-box of papermachine No 2 in the Iwanuma mill was reconstructed and the wire-part was remodeled to an on-top type in October 1996. Base paper for coating is produced on this machine and after the reconstruction paper properties such as two-sidedness, formation and ash profile were improved. However, at the same time one-pass retention (OPR) dropped resulting in some other quality and operational problems. After consideration it was judged that a dual retention aid system may be the most suitable way to over-come these problems to a reasonable chemical cost.In January 1997 machine trials started with this dual retention aid system and in October the same year the machine went into comercial operation with this system. Sometimes paper formation is harmed by too high OPR. Therefore high OPR and good formation at the same time became an important issue. When the dual system was selected it was under the condition that formation would not be harmed and it was found that a microparticle system fulfilled this requirement.After the introduction of the dual system remarkable improvements in operation and paper quality have been recognized. The chemical costs are also low and therefore we can conclude that all our targets have been realized. However some new issues have come up and we are now working to understand and solve these issues in order to further improve our situation.

Multivariable PI Control of Industrial Paper Machine Headboxes

Production rates in modern paper machines are increasing all the time. This poses challenging requirements for control of different subprocesses in the paper machine, e.g. for the headbox. Currently, scalar controllers are used for headbox control in industrial practice almost everywhere. Headbox control has been a favorite example of multivariable control in many simulation and laboratory studies but not in industry. This paper presents an application of multivariable PI controller to the paper machine headbox. The procedure takes into account the limited tests that can be performed in practice, simplicity in structure and tuning, and realization using modern distributed automation systems.

Impinging jet studies of the kinetics of deposition and dissolution of calcium carbonate particles

The deposition onto and detachment of calcium carbonate particles from cellophane and glass with and without retention aids, polyethylenimine and polyacrylamide, were studied under well-defined hydrodynamic conditions in a stagnation point flow field created in an impinging jet apparatus. With one exception, all deposition efficiencies were found to be in agreement with expectations based on electrostatic attractive or repulsive forces. The efficiency of deposition onto polyacrylamide-treated cellophane was found, however, not to be reduced by electrostatic repulsion, implying that polyacrylamide functions as a bridging agent. The bond strength between polyethylenimine and cellophane is shown to be much higher than the bond strength between polyethylenimine and pulp fibers. The calcium carbonate particles deposited onto cellophane using either of the retention aids were able to withstand shear rates of the order of 8000 s −1. These shear rates are comparable to the shear rates prevailing in a paper machine headbox. The lack of time for the establishment of an equilibrium ion concentration close to the surface of a dissolving calcium carbonate particle is shown to be responsible for the two to three orders of magnitude difference between experimentally observed dissolution rates and the much higher rates calculated for diffusion-controlled dissolution.

Sensor Fault Detection and Diagnostics of Nonlinear Systems with Application to Paper Machines

This paper presents an efficient real-time method of sensor fault detection, isolation and estimation for a class of MIMO nonlinear time-varying stochastic systems. The sensor faults may be a jump or slow drift type. The presented approach is based on the combination of the separate-bias estimation algorithm to randomly time-varying bias of nonlinear systems proposed by the authors and the modified Bayes' decision algorithm. The proposed technique is used to design a sensor fault diagnostics system for the headbox of an actual paper machine. Actual headbox data have demonstrated the effectiveness of the proposed method

University and Industry Joint Project for Control Education

Effort has been made in integrating industrial applications with engineering education in the Department of Chemical Engineering, University of Alberta. lbey invited industrial people or other persons who have industrial experience to give seminars of lectures in the university, organize the students to visit industry and industrial research center, give the chance to the students to attend industrial conference, defining graduate student thesis projects from industry and establish joint research projects, and so on. With the financial and technique support from the industry, they successfully integrated industrial application cases into education software PCET (Process Control Engineering Teachware). The industrial application cases in PCET are represented in this paper. As an example, a paper machine headbox control system with a cascade configuration is mentioned in detail in the paper.