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Ferritsius R.,Mid Sweden University | Ferritsius R.,Stora Enso | Hill J.,QualTech AB | Ferritsius O.,Mid Sweden University | Karlstrom A.,Chalmers University of Technology
International Mechanical Pulping Conference, IMPC 2014, part of PulPaper 2014 Conference | Year: 2014

The quality of TMP has been investigated for a CD82 chip refiner both with respect to normal variations and as a result of step changes of production rate, dilution water feed rates and plate gaps. A given level of tensile index was reached over a wide range in specific energy input. The energy efficiency with respect to tensile index decreased if the pulp consistency in the blow line exceeded 55 %. The extended entropy model applied on the refiner showed that the calculated pulp consistency after the flat zone could be extremely high, leading to lower energy efficiency. This was not possible to detect by the measured values for the pulp consistency in the blow line. The short time variations in tensile index correlated more strongly with the model based total residence time in the two refining zones than with the motor load.


Karlstrom A.,Chalmers University of Technology | Hill J.,QualTech AB | Ferritsius O.,Mid Sweden University | Ferritsius R.,Mid Sweden University | And 2 more authors.
International Mechanical Pulping Conference, IMPC 2014, part of PulPaper 2014 Conference | Year: 2014

Currently some 5 % of the electrical energy input in high consistency refining can be attributed to fibre development work. The rest is related to thermo- dynatnical steam generation. Can this unfavourable relation between fibre development and heat generation eventually be improved? A pre-requisite to consistent improvement is a stable process, controlled to targets deduced from profound process evaluations. This statement is elaborated based on two case studies and extensive refiner modelling. It is indicated that a well designed process including its basic process control can with proper refiner control reach energy reductions in excess of 20 %. Proper selections of process targets aligned with choice of segments can further increase the energy reduction in existing lines. These drastic energy reductions will demand concurrent observations and process modelling based on spatial measurements in the refining zone rather than slow, inadequate feedback control from pulp property measurements downstream. This will furthermore stress the need for more advanced control schemes if the full potential is to be captured. Additionally this approach will be a key element in the development of novel process approaches with even larger potential of energy reduction.


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
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: 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.

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