Paper Machine Headbox Research Articles

A new drying approach deploying solid-solid phase change material: A numerical study

Recently, phase change materials are emerging in thermal drying technology. This study offers a new approach in thermal drying of a moist paper sheet deploying solid-solid phase change material, tentatively as an alternative to solid-liquid micro-encapsulated PCMs uniformly dispersed inside the void part of porous sheet. In contrast to SL-MEPCM scenario, SS-PCM is fabricated in solid matrix of porous medium, remaining the sheet porosity intact. Additionally, comparing to its SL-MEPCM counterpart, any costly PCM encapsulation process or change in the design of headbox of commercial paper machine is avoided. As well, volume change during phase transition is negligible. This configuration is particularly ideal for drying applications where a low porosity, initially highly moist sheet is to be dried. A numerical experiment is carried out to investigate the dewatering behavior of SS-PCM fabricated paper in a drying process. A real shape-stabilized polymeric SS-PCM is used in this study. A pattern search optimization technique is employed to minimize the target moisture content. This study shows SS-PCM primarily becomes effective in last stage of drying where it internally releases the heat gained in previous stages. The numerical results indicate the moisture removal is enhanced by approximately 29% utilizing SS-PCM. The effect of SS-PCM volume percentage and particularly infrared emitters are studied, as well. It is observed that SS-PCM equipped paper does not perform effectively in drying sectors where IR emitters are retrofitted. Eventually, a comparative study is performed to fairly compare the thermal performance of SL-MEPCM and SS-PCM in paper drying.

Design and Simulation of PID Controller based Pressurized Head Box in Paper Machine

The head box in a paper machine is a critical component. Head box control is required for quality paper formation. Stock level and Total pressure in the paper machine head box determines the quality of the paper. This paper determines the design of PID controller for the pressure type head box. The stock level and pressure are the parameters taken into consideration.

Brief Review and Mathematical Modelling of Air Cushioned Pressurized Paper Machine Headbox

Today, the requirement of high grade papers is increasing day by day. To cater the need of high quality papers, new high-speed paper machines are being developed constantly. The whole economy of a pulp and paper industry depends on the quality of paper produced, quality of paper depends on the efficient operation of the major part of paper industry – paper machine. Paper machine is the heart of paper industry and has many subsystems. One of the important subsystem of paper machine is Headbox. To have the desired quality papers, efficient working of headbox is highly required. To have desired operation from headbox, its precise control is necessary. The precise modelling of headbox, leads to design of efficient controllers for its proper control to get the desired response. This paper presents the mathematical modelling of headbox along with a brief review of various research performed on headbox.

Stability analysis of paper machine headbox using a new PI(D) tuning technique

Paper, today, has made an important place in human’s life. Being an important commodity, paper has different qualities throughout the globe. As the technology is advancing, paper is being used for numerous applications and need of good quality paper is increasing daily. To have papers of desirable quality, paper machines with latest technology are developed. However, the quality of paper principally depends on the prime element of paper machine i.e. Headbox. Headbox is a highly non-linear Multi-input Multi-output (MIMO) component of paper machine and requires a precise control of its major parameters to get good quality papers which eventually responsible for sustained economy of pulp and paper industry. In past few decades, headbox has been a key element for research. Researchers have developed different control algorithms for headbox. This paper presents stability analysis of paper machine headbox using a new technique of Proportional – Integral – Derivative (PID) controller design namely Extended Forced Oscillation method (EFO). Also, the paper presents a comparative analysis of EFO method of PID tuning with the conventional Ziegler - Nichols(ZN) tuning technique based on transient characteristics and performance indices of headbox.

Modelling the Dynamics of Flexible and Rigid Fibres

Abstract A particle-level simulation technique has been developed for modelling fibre suspension flow in a converging channel of a papermachine headbox. The fibre model is represented by a chain of elements connected together. The model was verified by the simulation of rigid fibre dynamics in a simple shear flow. The period of rotation was found to be in a very good agreement with theory and reference data. The model was then employed to simulate fibre motion in a converging channel of a papermachine headbox. Fibre suspension motion was resolved using two-step procedure. Velocity field was calculated by means of a commercial CFD code ANSYS Fluent with RSM turbulence model applied and used as an input to the in-house code allowing to simulate fibre dynamics. Results of the calculations were used to construct the fibre orientation probability distribution (FOPD) which was found to be consistent with available experimental data.

Planar contraction design with specified fibre orientation distribution at the outlet

In the present study, an optimal shape design problem of a papermachine headbox is considered to control the fibre orientation distribution at the outlet of contraction. First, by the aid of a bijective transformation, we transform the optimization problem governed by weak formulation on a fixed domain. Then, by means of a process of embedding, the class of admissible shapes is replaced by a class of non-negative Radon measures. The modified problem consists of the minimization of a linear functional over a set of pairs of positive Radon measures satisfying linear constraints. Each measure of optimal pair is approximated by a finite combination of unitary atomic measures and furthermore the approximate solution of the first problem is found by the optimal solution of a finite-dimensional linear programming problem. The solution of this problem is used to construct an optimal piecewise constant control. Finally, using the approximate control signals, we obtain the approximate optimal shapes.

The Design of Decoupling Control System for Air-Cushioned Head Box of Paper Machine Based on Siemens S7-PLC300

Small motions will result in heavy influence to the production in high-speed paper machine, therefore, decoupling control is necessary. This passage Puts forward the opposite angles strategies to solve the function of decoupling aiming at solving the difficulty that occurs in practice, like the characteristic of hard-coupling and non-linear. According to the mathematics model of the flow box, decoupling the quantity of the two couplings in the processes. Meanwhile, Introduces the SIEMENS S7-300 PLC and the DCS system that is realized by the it.

The Design of Decoupling Control System for Air-Cushioned Head Box of Paper Machine Based on Siemens S7-PLC300

Small motions will result in heavy influence to the production in high-speed paper machine, therefore, decoupling control is necessary. This passage Puts forward the opposite angles strategies to solve the function of decoupling aiming at solving the difficulty that occurs in practice, like the characteristic of hard-coupling and non-linear. According to the mathematics model of the flow box, decoupling the quantity of the two couplings in the processes. Meanwhile, Introduces the SIEMENS S7-300 PLC and the DCS system that is realized by the it.

Model Predictive Control of Important Parameters in a Paper Machine Headbox

The modern headbox has many attributes that are highly significant for all paper-makers. Uniformity of flow, absence of streaks and large eddies, headbox stability and ease of operation are required features for all paper grades. Consistency in a headbox is a very important parameter in paper mills in their various stages of operations. Without the knowledge of consistency, it is not possible to optimize productivity with optimal quality. In the present study, a multivariable, linearized, state space model of a paper machine headbox was selected for control of consistency and liquid level in the headbox of a paper machine using the advanced control strategy Model Predictive Control (MPC). MPC uses a model to predict the process output along a future time horizon. It performs the calculation of a control sequence to optimize a performance index. It is based on receding horizon strategy so that at each instant the horizon is moved towards the future, involving the application of the first control signal of the sequence, calculated at each step.

Numerical Simulation of Inner Flow Yield of Turbulence Generator of Papermachine Headbox and Structure Optimal Design

Turbulence generator is a key part of head box of middle or high speed papermachine. It is used to make the fiber flow smooth and steady. This paper gives simulation researches of the flow status on one turbulent tube of combined-turbulence generator, result shows that there is an optimal rate between the square tube and its equivalent diameter for Round-Square turbulence generator, and the equivalent diameter is 6.5. This guides the design of turbulence generator significantly.

Shape Optimization for Navier–Stokes Equations with Algebraic Turbulence Model: Numerical Analysis and Computation

We study the shape optimization problem for the paper machine headbox which distributes a mixture of water and wood fibers in the paper making process. The aim is to find a shape which a priori ensures the given velocity profile on the outlet part. The mathematical formulation leads to the optimal control problem in which the control variable is the shape of the domain representing the header, the state problem is represented by the generalized Navier-Stokes system with nontrivial boundary conditions. This paper deals with numerical aspects of the problem.

Shape Optimization for Navier–Stokes Equations with Algebraic Turbulence Model: Existence Analysis

We study a shape optimization problem for the paper machine headbox which distributes a mixture of water and wood fibers in the paper making process. The aim is to find a shape which a priori ensures the given velocity profile on the outlet part. The mathematical formulation leads to an optimal control problem in which the control variable is the shape of the domain representing the header, the state problem is represented by a generalized stationary Navier–Stokes system with nontrivial mixed boundary conditions. In this paper we prove the existence of solutions both to the generalized Navier–Stokes system and to the shape optimization problem.

Control the Fibre Orientation Distribution at the Outlet of Contraction

A two dimensional model of the orientation distribution of fibres in a paper machine headbox is studied. The goal is to control the fibre orientation distribution at the outlet of contraction by changing its shape. The mathematical formulation leads to an optimization problem with control in coefficients of a linear convection-diffusion equation as the state problem. Then, the problem is expressed as an optimal control problem governed by variational forms. By using an embedding method, the class of admissible shapes is replaced by a class of positive Radon measures. The optimization problem in measure space is then approximated by a linear programming problem. The optimal measure representing optimal shape is approximated by the solution of this linear programming problem. In this paper, we have shown that the embedding method (embedding the admissible set into a subset of measures), successfully can be applied to shape variation design to a one dimensional headbox. The usefulness of this idea is that the method is not iterative and it does not need any initial guess of the solution.

Turbulent flow through a rectangular duct with a partially blocked exit

This paper contains data on and insights into the origins of turbulence associated with a partial blockage at the exit of a two-dimensional, laminar, horizontal duct flow. In essence, this is the upstream approach region of the forward-facing step problem. This work was motivated by the need to identify and control unsteady streamwise vortices generated in the headbox (i.e. contraction section) of an industrial paper machine. The duct was 57.2 cm wide × 10.16 cm high, with up to a 50 % blockage. Experiments were scaled to match Reynolds numbers found in paper machines; exit velocities were as large as 200 cm s−1. The goal of the research was to map the flow at the exit and to examine the response of the flat-plate turbulent boundary layer on the opposing wall under the partial blockage. Laser-induced fluorescence (LIF) and digital particle image velocimetry (DPIV) were used to examine flow in three orthogonal planes at various stations upstream of the duct exit. Mean and instantaneous DPIV vector fields clearly show that an unsteady spanwise vortex forms in the corner formed by the top nozzle wall and partial blockage which, in turn, gives rise to turbulent streamwise vortices.A turbulent boundary layer was initiated on the duct wall opposite the blockage, upstream of a two-dimensional contraction. Results show that even though the acceleration parameter, K, exceeded the nominal critical level of 3.0 × 10−6 for relaminarization beneath the blockage, the flow did not reach a quasi-laminar state. In addition, there did not appear to be direct interaction between unsteady vortex formation at the partial blockage on the upper wall and bottom-wall turbulent boundary layer structures.

Optimal shape design in a fibre orientation model

We study a 2D model of the orientation distribution of fibres in a paper machine headbox. The goal is to control the orientation of fibres at the outlet by shape variations. The mathematical formulation leads to an optimization problem with control in coefficients of a linear convection-diffusion equation as the state problem. Existence of solutions both to the state and the optimization problem is analyzed and sensitivity analysis is performed. Further, discretization is done and a numerical example is shown.

Control of tacky deposits on paper machines – A review

SUMMARY: Wood-derived pitch and tacky materials of synthetic origin in recovered fiber streams often cause serious deposit problems on papermaking equipment. Ideally such materials would be completely removed in processes such as screening, cleaning, washing, or flotation de-inking. In practice, tacky materials that remain in the fiber furnish can build up within paper machine headboxes, forming fabrics, press sections, and dryer sections, reducing production efficiency. Product quality is likely to suffer, especially if deposited material ends up in the sheet. This review considers a variety of chemical additives that papermakers have used to combat deposit problems. The premise of this article is that knowledge of the chemistry and colloidal behavior of existing deposit-control agents can guide us in the selection, usage practices, and further development of strategies for the control of tacky deposits, especially in the case of pitch, adhesive-based stickies, and wax-like deposits.

OPPORTUNITY FOR REAL-TIME OPTIMIZATION IN A NEWSPRINT MILL: A SIMULATION CASE STUDY

Real-time optimization (RTO) is applied for the broke recirculation in the stock approach system of an integrated newsprint mill simulation. New optimal broke ratio profiles are set for the paper machine recipes each time the process is confronted with an important disturbance. The variability in the four paper machine headboxes is minimized while the inventory management is handled. The proposed approach is compared to the actual mill operation, making use of a detailed plant simulation. While maintaining broke tank level within an acceptable range, RTO brings the pulp variability down about an order of magnitude. It is expected that it could significantly reduce the sheet break occurrence in a real plant and therefore enhance its economical efficiency.

A flow loop system for study of fibre suspension flocculation

A flow loop system for study of fibre flocculation in Suspensions has been developed. The system is designed to simulate the flow conditions in a paper machine headbox. It is equipped with a radial distributor feeding a step diffuser pipe package, after which the flow is contracted in a 2-D nozzle. The flow system is also equipped with a secondary flow contraction, which is aimed for studies of fibre floc rheology. The conditions of the secondary contraction can be changed in order to generate different acceleration rates. The flow system is also equipped for dosage of retention/formation aids to Study the chemical effects oil fibre flocculation. The maximum flow velocity in the system is 16 m/s. Fibre Suspension flows were Studied using a high speed video camera and transmitted infra-red laser light pulse illumination. Images were taken either separately before and after or along the secondary contraction. Images of-fibre flocculation were evaluated by using power spectrum and wavelet transform analysis. By comparing the fibre flocculation before and after the secondary contraction, or by following the fibre floes during the secondary contraction, rheology information oil the fibre flocs call be obtained. By comparing the fibre flocculation information with and Without chemical additions, the effects of chemicals on fibre flocculation can also be studied.

Fibre length effect on fibre suspension flocculation and sheet formation

Fibre suspension flocculation was studied in a flow loop system, simulating the flow conditions in a modern paper machine headbox. The fibre suspensions after the headbox were accelerated by a secondary contraction, mimicking flow accelerations that may take place during forming. Fibre suspensions were studied using an optical detection method. Images were taken by a high speed video camera with transmitted infrared laser light pulse illumination separately before and after the secondary contraction. The mean fibre floc size was evaluated by power spectrum analysis in MID and CID respectively. A series of twelve pulp samples, four different commercial bleached softwood kraft pulps refined to three different levels, were used in the experiments. The fibre physical properties and formation number for paper sheets produced on a pilot paper machine with these pulp samples were characterised. Refining shortened the fibre length, thus decreased the fibre floc size in flowing suspensions and improved the formation in paper sheets. A series of mixtures at different ratios of bleached softwood and hardwood kraft pulps were also used in the experiments. The fibre physical properties of the mixtures were also characterised. The fibre length increases when increasing the ratio of softwood pulp in the mixture, thus fibre floc size in the suspension increases.

Some ways to decrease fibre suspension flocculation and improve sheet formation

Fibre suspension flocculation was studied in a flow loop system, simulating the flow conditions in a modern paper machine headbox. Fibre suspensions were studied using an optical detection method. ...