To estimate the consistency profile inside the refining zone, we need a physical model which uses the temperature profile together with traditional measured variables (like motor load, dilution water feed rate, hydraulic pressure or plate gap, casing pressure, the estimated production etc.) as inputs. The model is rather complex and therefore not described in details in this overview. However, it is important to understand that it comprises several interacting blocks needed to describe the complete refiner, see Figure 1 which describes the blocks for a CD-refiner. A similar concept can be used for all other types of refiners as well.

When using the model, it is possible to derive a number of important variables impossible to measure in the daily work. As an example, it is possible to estimate fiber residence time, forces related to fiber-to-bar interaction, the velocities of the tree phases, defibration work, thermodynamical work and thereby the backward and forward flowing steam. All these variables are important when estimating the consistency profile.

The consistency profile can be stabilized if the outlet consistency in the refining zone is controlled. In a CD refiner, the consistency cannot be measured in the flat zone. This means that the estimated consistency profile become essential when introducing more advanced control concepts, like CCtrl. Similar motivation is valid also for a Twin refiner where the consistencies in the parallel refining zones are unknown.

Lately, the estimated consistency out from a CD refiner have been validated using manual consistency measurements from pulp taken in the blow-line, see Figure 2. As the consistency out from the flat zone is impossible to measure it can be validated indirectly by performing step changes in dilution water to the flat zone at the same time as the response in the blow-line consistency is measured manually.

In Twin refiners the estimated blow-line consistency has been validate using an on-line device for consistency measurements, see Figure 3. The consistency profile control is now installed as an on-line “soft sensor” with good results. The consistency response in each refining zone follow the dilution water changes, see Figure 4. Thus, to stabilize the consistency profile in each refining zone will open for an increased production and improved pulp quality.

As described above, CD refiners and Twin refiners get a clear attention and it is of course possible to implement the consistency profile control concept also for other SD refiners as well.

For further reading, please download "Refining Efficiency for Future CTMP and TMP systems".