QualTech AB

Tyringe, Sweden

QualTech AB

Tyringe, Sweden
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Hill J.,QualTech AB | Johansson L.,Paper And Fibre Research Institute | Morseburg K.,Paper And Fibre Research Institute
Nordic Pulp and Paper Research Journal | Year: 2017

ATMP pilot refining trials on Norway spruce were conducted. The ATMP configuration consists of selective wood disintegration and targeted application of chemicals when defibration already is initiated in order to achieve energy-efficient final fibre separation and development. ATMP was compared to TMP and RTS. The TMP like character was maintained despite of differences in pre-treatment, chemicals and primary stage refining energies. The fractional composition of the pulps was, however, altered. Bauer McNett R14 fraction exhibited the largest differences followed by P200 fraction. Thus different process alternatives produced pulps with different fingerprints. The amount of the R14 fibres is important as these tend to cause surface roughness impairing printability. Regardless of strategy, the ATMP pulp properties at equal tensile index (44 Nm/g) were equal or superior to those achieved by TMP or RTS refining. The main difference was the required specific energy input, ranging from 1.71 (TMP) to 1.05 MWh/BDT (ATMP with bisulphite addition). Primary stage refining was explored from multiple trials with the same process configuration and chemistry. The higher the specific energy applied the better is the energy efficiency. Furthermore established refining theories appear inadequate in describing the differences between process alternatives with respect to energy efficiency and pulp property development.


Karlstrom A.,Chalmers University of Technology | Hill J.,QualTech AB
Nordic Pulp and Paper Research Journal | Year: 2017

In this paper, internal variables (e.g. temperature, consistency and fiber residence time) are introduced and defined as physical states obtained in different parts of the refining zones. In short, they differ from the traditional external variables (e.g. dilution water feed rate and specific energy), which are not available as distributed variables from refining zone measurements. The internal variables can be seen as the backbone of physical models and we illustrate that based on a model for a CD-82 refiner in a CTMP production line. Such a model can be used for on-line implementation of soft sensors for advanced process control and it is shown that the refining segment pattern affects the temperature profile. It is particularly interesting to study how the segment parameters in terms of the distributed width of the bars and grooves together with the segment taper affect the back-flowing steam, the cross-sectional area and thereby the fiber residence time. To illustrate the capability to use a modeling strategy it is shown how to reach a 40% reduction in specific energy without violating the required pulp properties.


Karlstrom A.,Chalmers University of Technology | Eriksson K.,CIT Industriell Energi AB | Hill J.,QualTech AB
Nordic Pulp and Paper Research Journal | Year: 2015

This paper focuses on three important issues; Process understanding in relation to control of nonlinear processes; Natural decoupling by using internal state measurement devices; Long term follow up procedures of process control investments. As an example, a new control system for Thermo Mechanical Pulp (TMP) refiners is used, based on a cascaded control structure. The internal states, in this case the refining zone temperature profiles, are controlled in the inner loop whereas the outer loop handles pulp properties. The characteristics of the temperature profile dynamics makes it possible to introduce a decoupling scheme where the anti-diagonal elements in the transfer function matrix describing the process, can be eliminated naturally. The system can handle several pulp propertied simultaneously but in this study mean fiber length (MFL) is the target variable. The process is followed about 200 days in manual mode control and 200 days in automatic mode. It is shown that the standard deviations in the pulp property variables freeness (CSF) and MFL were decreased about 40 and 60%, respectively. Significant reductions in variability of shives and a motor load standard deviations was achieved. On top of this, an increased production was obtained and the control system runnability was raised from 50% to 98%, levels that are far from commercial MPC-control concepts in TMP refining control.


Morseburg K.,Institute PFI | Hill J.,QualTech AB | Johansson L.,Institute PFI
Nordic Pulp and Paper Research Journal | Year: 2016

Defibration and fibre development patterns were investigated for the novel ATMP refining process, based on pilot scale trials with Norway spruce chips. ATMP refining with different chemical agents was compared to RTS refining with and without Impressa-finer (RT) and Fiberizer (F) pre-treatment. RT-F pre-treatment significantly improved both initial defibration, axial fibre splitting and fibre flexibility, compared to RTS primary stage refining without pre-treatment. Both types of investigated ATMP process chemistry - hydrogen peroxide combined with magnesium hydroxide under alkaline conditions (P) or acid sodium bisulphite (S) added to the primary refiner dilution water - further improved the fibre separation of RT-F pre-treated wood during primary stage RTS refining. This is largely attributed to enhanced fibre swelling. S-treatment facilitated frequent fibre separation within or close to the S2 wall layer, yielding extremely low shive levels and well-fibrillated, thin-walled fibres early in the process. S-treatment also rendered stiffer fibres, which made them susceptible to breakage, axial splitting and internal delamination. P-application is proposed to affect primarily the interior layers of the fibre walls, facilitating rapid fibre wall swelling towards the lumen, fibre softening and flexibilization.


Karlstrom A.,Chalmers University of Technology | Hill J.,QualTech AB
Nordic Pulp and Paper Research Journal | Year: 2015

In TMP-refining processes, the stabilization of the fiber pad inside the refining zone requires a new control approach. Specific energy control tends to be complex and most often affected by a number of disturbances not so well specified in traditional MPCconcepts. To describe the dynamics in such nonlinear processes is difficult, tedious and requires significant maintenance support. This paper focuses on two important issues related to modeling in mechanical pulping processes: measurements of internal states inside the refining zone and in particular natural decoupling to find a model suitable for future process optimization and improved control concepts of complete refiner lines. The idea is to show how this complex process, with serially linked refiners or refining zones, can be modeled and controlled using a simplified process description. In this series of papers, data from a commercial Twin-refiner and a CD-refiner are available as inputs. As an example of internal state measurements, refining zone temperature profiles and estimated distributed consistency in the refining zone are used. We show that the characteristics of the temperature profile dynamics makes it possible to introduce a decoupling scheme where the antidiagonal elements in the transfer function matrix describing the process can be eliminated naturally, independent of which refiner is to be controlled.


Karlstrom A.,Chalmers University of Technology | Hill J.,QualTech AB
Nordic Pulp and Paper Research Journal | Year: 2014

The study focuses on dynamic considerations in a mill-wide perspective showing that mill economy is closely linked to optimization of TMP and power plant. Special attention is given to stability issues in the refining processes. Describing the dynamics in such nonlinear processes is difficult and tedious and requires significant knowledge about where in the operating window to run the refiners. Results show the dynamics in the internal states, temperature profiles and the plate gap sensors responses and how they correspond to the refiner motor load. Disturbances in production affect the plate gap sensors and the temperature profiles in the same direction, while deliberate changes in the plate gap result in a dynamic situation where the motor load and temperature profile change in opposite directions. It is shown that the total residence time and the ratio between the residence time before and after the maximum temperature will be important when formulating specifications for energy efficient refining. As an example of how the refining process affects the mill economy, the start-up procedures for two different types of refiners will be penetrated. It is shown that the start-ups are most often associated with an over shoot in the motor load, which is easy to overcome. © 2014, SPCI. All rights reserved.


Karlstrom A.,Chalmers University of Technology | Hill J.,QualTech AB
Nordic Pulp and Paper Research Journal | Year: 2014

The present study used a system identification ARMAX modeling approach to analyze how the pulp properties can be predicted from the traditional input variables such as hydraulic pressures and dilution water feed rates at stable production. As a complement internal states from the refining zones are used as inputs in a commercial production line comprising two serially linked Twin refiners. It is shown that neither the hydraulic pressures and dilution water feed rates nor the motor loads from primary and secondary refiners are sufficient as inputs to the ARMAX model to describe the dynamics in the pulp properties. Instead, the temperature profile measurements from the refining zones outperform these traditional inputs and capture the major dynamics in the pulp property studied. It is also shown that the process should be controlled in a way that reduces as much variations inside the refining zones as possible. It is not only necessary to include the maximum temperatures in the refining zones as internal states when estimating pulp properties but also the periphery temperature since temperature profiles are affected differently depending on whether the changes are made in the hydraulic pressure, production or the dilution water feed rates. From a control perspective, refining zone temperature control is preferable to any concepts based on specific energy for minimization of pulp quality variations. © 2014, SPCI. All rights reserved.


Karlstrom A.,Chalmers University of Technology | Hill J.,QualTech AB | Ferritsius O.,Mid Sweden University | Ferritsius R.,Mid Sweden University
Nordic Pulp and Paper Research Journal | Year: 2016

This paper focuses on the pulp properties obtained from ThermoMechanical Pulp (TMP) CD refiners. Undersampled pulp variables are expanded into an oversampled set of process data, which makes it possible to analyze pulp properties in a dynamic time frame. It is shown that, in order to gain deeper insight into the defibration/fibrillation at a specific energy input, one needs to know the fiber residence time and the consistency profile. Moreover, the fiber residence time in the flat zone (FZ) and conical zone (CD) are intertwined with the consistency out from FZ and CD. Together with an external variable (production), these internal variables are essential for predicting the pulp properties. It is also shown that internal process conditions from different test series can be manipulated in the operating window using a low-frequency gain description obtained from an ARX model. The same mapping procedure can be applied to pulp and handsheet properties (in this paper represented by the tensile index), and this opens for implementation of new optimization routines to find more energy efficient operating points while maintaining prespecified pulp quality.


Karlstrom A.,Chalmers University of Technology | Hill J.,QualTech AB | Ferritsius R.,Mid Sweden University | Ferritsius O.,Mid Sweden University
Nordic Pulp and Paper Research Journal | Year: 2016

It is shown in this paper that knowledge of the spatially measured temperatures inside the refining zone in TMP refiners is essential in describing non-linear dynamics of high consistency refining. By expanding the pulp and handsheet properties using piece-wise linear functions into the time domain, an auto-regressive model can be applied to verify that the tempera-ture and the consistency profiles, in combination with the motor load and production rate, are key input candidates when modeling changes in different pulp properties. The model accuracy is analyzed using process information captured at different time and operating conditions. It is also shown that it is more complex to estimate and validate the tensile index than the mean fiber length and Somerville shives content, especially close to refiner operating limits where a shift in the process gain may occur. This type of switched dynamics in tensile index estimation at a specific consistency is related to non-linear behaviors where the fiber pad distribution most likely undergoes a local collapse.


Karlstrom A.,Chalmers University of Technology | Hill J.,QualTech AB | Ferritsius R.,Mid Sweden University | Ferritsius O.,Mid Sweden University
Nordic Pulp and Paper Research Journal | Year: 2015

Thermo-Mechanical Pulp (TMP) refiners served in this work as an example of how to combine oversampled and undersampled variables on a common timeframe for further analysis. To get more information from the refining process, temperature measurement arrays in the refining zones were studied alongside process measurements such as motor load, production rates, plate gaps, dilution waters, pulp properties and manually measured blow-line consistency. The undersampled data set consisted of 63 laboratory samples obtained at a Swedish TMP mill, which were tested for tensile index, mean fiber length and Somerville shives content. The pulp samples were obtained at five different periods during three months to cover a large dynamic operating window. The data set was expanded using a piece-wise linear approach. The measurements inside the refining zone were shown to be important variables when interlacing the undersampled pulp properties with the oversampled process data set, consisting of 350 000 samples. Use of an extended entropy model provided a palette of information about the process conditions inside the refining zone. Particularly, the residence time and the consistency in the refining zones were essential for the pulp property development, as a link between the refining segment pattern used and the current state of refiner operation.

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