Title:
The Effects of Retention Aid Dosage and Mechanical Energy Dissipation on Fiber Flocculation in a Flow Channel
The Effects of Retention Aid Dosage and Mechanical Energy Dissipation on Fiber Flocculation in a Flow Channel
Author(s)
Weseman, Brian D.
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Abstract
Formation plays an important role in the end-use properties of paper products,
but before formation can be optimized to achieve superior properties, an understanding
about the causes of formation must be developed. Formation is caused by variations in
the basis weight of paper that are results of fiber floc formation before and during the
forming of the sheet. This project is a first step in a larger research program aimed at
studying formation. By observing the effects that mechanical energy dissipation (in the
form of turbulence) and retention chemical dosage have on floc formation, we may
develop a better understanding of how to control formation.
In this study, a rectangular cross-section flow channel was constructed to aid in
the acquisition of digital images of a flowing fiber suspension. The furnish consisted of a
55:45 spruce:pine bleached market pulp mix from a Western Canadian mill. Turbulence
was varied by changing the flow rate; Reynolds numbers achieved range from 20,000 to
40,000. The retention aid used was a cationic polyacrylamide with a medium charge
density. Dosage of the retention aid was varied from 0 to 2 pounds per ton OD fiber.
Digital images of the flowing fiber suspension were acquired with a professional digital
SLR camera with a forensics-quality lens. Three separate image analysis techniques were
used to measure the flocculation state of the fiber suspension: morphological image
operations, formation number analysis, and fast Fourier transform analysis.
Morphological image analysis was capable of measuring floc size increases seen in
the acquired floc images. It was shown how floc diameter could increase simultaneously
with decreasing total floc area and total floc number. A regression model relating
retention aid dosage and energy dissipation was constructed in an effort to predict
flocculation. The regression model was used to predict F2 (formation number squared)
results from the study. The interaction effect RE was shown to have a differing effect across the retention aid dosage levels. As a result, this model and technique may prove to
be a beneficial tool in optimizing retention aid applications.
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Date Issued
2004-12-23
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24575553 bytes
Resource Type
Text
Resource Subtype
Dissertation