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InlIne meaSurement world pulppaper36 accurately measuring the consistency at each stage is extremely important since the right consistency entering a stage will determine its fibre fractionation effectiveness PulPer total conSIStencY StaBIlISeS ProceSS Being able to accurately and repeatedly measure consistency after a pulper in a recycled fibre process is very challenging. Firstly trash and fibre clumps from the pulper are major problems for blade-type shear force transmitters. Secondly mixed waste paper is comprised of many different fibres and contains fine materials and fillers that are not measured by shear force. An absolute inline total consistency transmitter is needed after the pulper that is the basis for total mass flow at the beginning of the process and the accurate calculation of overall process yield in the mill. This need can be filled by a TCR-2501 total consistency transmitter that uses an optical signal peak detection method. The transmitter measures the total mass of fibres of all types small fine particles and ash. A recycled fibre linerboard mill using this transmitter confirmed that the pulper exit consistency measured by the new transmitter is more varied than that indicated by the previous consistency transmitter. Having this knowledge the mill implemented a consistency control loop using the conveyor speed and dilution water in order to control the consistency at this point. This had the additional benefit of stabilising the entire downstream process. Yield calculations became accurate and further improvement steps could be taken at the right point in the process. As the consistency in the pulper is stable at 5 enough pulp is available to run the paper machine at full speed. The pulper sets the initial consistency level. From here on the consistency is reduced in all chests that are between the pulper and the linerboard machine. Furthermore low consistency pulp that comes from a side stream does not disturb the process. At another testliner mill a TCR transmitter was installed after the RCF pulper pictured in figure 4 above and before high consistency cleaners operating at 3. Before the control loop implemented with the new transmitter the consistency varied between 2 and 4. When the consistency was too high the cleaners plugged. Also at very high consistency the pulper motor load was high and some pulp did not pass through the screen plate. When the consistency figure 4. TCR-2501 total consistency transmitter installed after a pulper was too low the efficiency of the cleaners was poor. These problems have been solved now that the consistency is maintained at 3 to 3.5. Managing to avoid the cleaners plugging once and thus risking a shutdown of the machine paid off immediately for the TCR measurement. oPtImum fIBre fractIonatIon The fibre fractionation processes required for a multi-ply forming process requires precise separation of long and short fibres so the right level of refining is applied. The sheet plies are then formed to give the optimum drainage on the formers and to ensure the required fibre-to-fibre bonding and sheet strength properties can be achieved. Accurately measuring the consistency at each stage is extremely important since the right consistency entering a stage will determine its fibre fractionation effectiveness and avoid plugging if the consistency is too high. ACT-2500 transmitters measure the amplitude of oscillation of a specially designed active blade oscillating at its resonant frequency. The measurement is sensitive to both the shear forces and the viscoelastic properties of the fibre matrix in the pulp slurry. Its measurement range is extended down to 1.0. The transmitter has a higher accuracy than a standard blade transmitter with a price point below an optical measurement. A typical fibre fractionation instrument layout is shown in figure 5.