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Pulp Mills optimize brown stock washing efficiency and cut defoamer chemical consumption based on real time measurement of the amount of entrained air in the pulp.
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Benefits
- Enables closed loop entrained air content control
- Enables optimum vat rotational speed and control to optimize washing performance
- Accurate dosing of chemicals leads to substantial savings opportunity
- Improved washing efficiency creates savings through improved chemical recovery, savings of chemicals in bleaching, lowered waste water treatment costs, reduced fiber losses and improved pulp quality
- Clamp-on measurement installed without process downtime
Process:
The key targets of brown stock washing are:
- Remove residual liquor that would contaminate the pulp during subsequent processing steps.
- Recover the maximum amount of spent chemicals with minimum dilution.
- Minimize chemical remains in water treatments.
Entrained air in pulp hampers pulp filtration in washers causing lowered washing efficiency. Substantial amounts of defoamer chemical are added prior to each washing stage or prior to the screening stages to minimize the air content.
Customer Case:
The SONARtrac Gas Volume Fraction (GVF) meter was installed on a 24" line from the screens to the decker. The unit was measuring +/-15% air. A cup of defoamer was injected into the second stage repulper and within 60 seconds the air dropped to 4%. This test was done multiple times with very repeatable results.
Application Solution
With the SONARtrac GVF meter it is possible to make a real time entrained air measurement in a specific process location.
The SONARtrac GVF meter utilizes an array of sensors that are clamped to the pipe. The amount of entrained air is determined using CiDRA's array processing techniques to measure the speed of sound, or speed at which sound propagates through the pulp in the pipe. The entrained air percentage is then calculated directly from the measured sound speed.
SONARtrac Value Proposition
The SONARtrac GVF meter is well suited for brown stock washing applications. This passive sonar listening approach provides an in-situ real time measurement of the entrained air present in the process fluid with a high degree of accuracy and repeatability. The accurate, continuous, real-time measurement enables automated brown stock air content control that can significantly cut down the consumption of defoamer chemicals and simultaneously improve pulp washing efficiency, pulp quality and process efficiency in the bleaching stages.
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