Near Infrared Optical Sensing Protocols for Wet End Pulp Slurry Verification
Inline NIR transflectance sensors stabilize wet end pulp slurry consistency within +/- 0.3 percent, cutting fiber giveaway and dryer steam consumption.
Pulp Consistency
Fibre Concentration
Weight percentage of oven-dry wood fibres in a liquid pulp slurry represents the fundamental variable that dictates the behavior of stock during transport, refining, and forming. Adjusting the pulp consistency allows paper mills to control the viscosity and flow characteristics of the material before it reaches the headbox. Higher values of this property reduce pumping costs but increase the risk of fibre clumping, which ruins the sheet formation.
Precise control is necessary to maintain a uniform paper web.
Drainage Control
Low concentrations of fibres in the headbox slurry improve the sheet formation by allowing the fibres to move freely during drainage. Maintaining the correct pulp consistency at the wet end prevents weight variations in both the machine direction and cross direction. If the concentration deviates from the target, the paper sheet will exhibit uneven density, which causes problems during printing and converting.
Measurement Protocol
Automated transmitter probes mounted in the stock pipelines measure the shear force or optical properties of the moving slurry. These transmitters provide real-time data to control valves that add dilution water to maintain the pulp consistency within narrow tolerances. In the refining stage, consistency must be kept stable to ensure uniform mechanical treatment of the fibres.
When the concentration is too low, the refining plates can make direct metal-to-metal contact, which damages the plates and chops the fibres rather than brushing them. Regular calibration of these sensors ensures that the mill operates at maximum efficiency and produces paper with consistent strength.