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You can download more information about the control concept LESS – Low Energy Strategic Systems here. The idea is to provide you with the latest results concerning Temperature control (TCtrl), Consistency control (CCtrl), Quality control (QCtrl) and Energy optimization (ECtrl). Simply browse the short summaries to find requested article on pdf-format.
Intensified Refining and Optimal Control in Chip Refiners
This overview comprises a short summary of the major findings when optimizing refining systems and three different intertwined research areas are analysed:
- "Physical Modeling"
- "Process Optimization and Control"
- "Pulp and Handsheet Property Estimation"
The primary goal of project has been to show how the refining energy can be reduced by 15 % through better control of the fiber flow in the refining zone. A second goal has been to supply the industry with modeling tools to improve the refining technology, and thus improve the the energy efficiency even further.
Refiner Optimization and Control Part III: Natural
decoupling in TMP refining processes
In this paper we will focus on two important issues related to modeling in mechanical pulping processes; measurements of internal states inside the refining zone and particularly natural decoupling to find a model suitable for future process optimization and improved control concepts of complete refiner lines.
It is shown that 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 independent on which refiner to be controlled.
Refining Efficiency for Future CTMP and TMP systems
The internal variables are the backbone of physical models and such models can be used for on-line implementation of soft sensors and advanced process control. Of special interest are the temperature and consistency profiles together with fiber residence time, which are the internal variables in focus of (in) this study. Moreover, they are directly linked to pulp and handsheet property development.
To illustrate the capability to use a modeling strategy, two examples are given; one where it is shown how to reach a 40% reduction in specific energy in a CD82-refiner using a new control strategy without violating the pulp properties studied and one example where the consistency can be controlled individually in two parallel Twin refining zones. Hence, the article comprises both temperature and consistency control to reach optimal process conditions.
CTMP Process Optimization Part I: Internal and External Variables Impact on Refiner Conditions
Internal variables (e.g. temperature, consistency, fiber residence time, backward flowing steam and forces acting upon the chips and pulp) 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, specific energy and plate clearance) 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. It is shown that such a model can be used for on-line implementation of soft sensors for advanced process control. Of special interest are the fiber residence time and consistency profiles in the flat and conical zones, which are the internal variables in focus in this study as they are directly linked to pulp and handsheet property development.
It is also shown that the refining segment pattern affects the temperature profile, which must be considered vital in the modeling efforts. 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.
Refiner Optimization and Control Part IV: Long term
follow up of control performance in TMP processes
In this paper we will focus on 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 we will use a new control system for Thermo Mechanical Pulp (TMP) refiners. It is based on a cascaded control structure where the internal states, in this case the refining zone temperature profiles, are controlled in the inner loop whereas the outer loop handles pulp properties. It is shown that the standard deviations in the pulp property variables freeness (CSF) and MFL were decreased about 40 and 60%, respectively. The reduction in variability of shives was approximately 25% when running the process control system and a significant reduction in the motor load standard deviations was also achieved. On top of this process stabilization, an increased production was obtained at the same time as the control system runnability was raised from 50 % to 98 %, levels that are far from commercial MPC-control concepts in TMP refining control.
Fiber energy efficiency Part II Forces acting on the
refiner bars
In this paper it is shown that the defibration and fibrillation work in thermo mechanical pulp refiners can differ significantly dependent on the process conditions. This has a direct impact on the distributed force in the refining zones obtained when the bars hit the fibers or fiber bundles. The distributed force, which is defined as a vector along the surface of the refining segments, is estimated using a model where the total work can be split into reversible and irreversible work. Besides traditional refiner variables such as motor load, dilution water added and inlet- and casing pressures, measurements of temperature profiles in the refining zone and plate gaps from a full-scale CD-refiner are available as inputs.
Three data sets are analyzed and it is shown that the shape of the temperature profile and the force distribution vary significantly. This means that the fiber distribution in the refining zone varies as well which affect the final development of the pulp properties. The refining segment pattern and taper play an important role when estimating the force distribution and it is stated that the force distribution close to the contraction part of the flat zone as well as the outer part of the conical section are larger than in other positions. Therefore, specific energy which can be seen as the integral of the total energy distribution along the refining segments cannot be used when describing the variations in the distributed forces.
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