STEPS TO BETTER PULP STOCK CONSISTENCY CONTROL

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. . STEPS TO BETTER PULP STOCK CONSISTENCY CONTROL.

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. . Proper installation and calibration QThe consistency transmitter and valve must be properly installed QThis includes the right location and orientation Qlt is best to install the consistency meter far enough downstream to allow adequate mixing QThe best location would be after a significant mixing event, such as after a pump. QTransmitter manufacturer's recommendations should be followed like distances, velocities, pipe angles QAIso, since most consistency transmitters are sensitive to air, they should be located on the side of horizontal pipes, rather than the top.

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. . The ri#llt valve *Consistency is controlled by manipulating a flow of dilution fluid into the thicker stock + The valve must be properly sized to handle the full range of operation under both normal and abnormal situations *The time required for the dilution to reach the pump should be short + The dilution water flow must not interfere with the free flow of stock to the pump. *Dilution header pressure must be constant the dilution control valve with a high resolution and suitable range.

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. . The rl#llt measurenyent >One of the most common consistency measurement devices is the blade type, or shear force sensor > The blade is inserted in the pipe, parallel to the fluid flow > The shear force of fibers flowing over the blade is measured to estimate the consistency Figaro 1. Blade type shear force consistency transrnitter..

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. . controller tuning QThe process dynamics of in-line consistency control are straightforward. Qlt is important to understand if different production rates or product grades will result in different pulp flow rates a Tuning should be selected to ensure stable operation across the full range of deadtimes and process responses. OCycles in consistency can be seen as cycles in basis weight of the finished product. 4. tuning list Of bLnnp tests.

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. . Filtering QTurbulent flows, inconsistent mixing, and pulp clumping can all create measurement noise QEnsure good mixing, correct mixing of the suspended solids and water is essential QA small filter can be applied to the signal, which will dramatically reduce the high-frequency noise, while still passing the important process dynamics QAdding a filter does more than just give a clear picture of the consistency but the valve movement has also dramatically decreased QReducing valve travel in this way helps to stabilize the process and extend valve life..