Predicting Drainage Retention and Formation Development on High Ash Alkaline Paper Machines, 1992 Papermakers Conference Proceedings

High ash alkaline furnish (with ash contents > 15%) may be the future for manufacturing fine white papers because of the low cost, high brightness fillers available.

A new drainage tester (BPDD) is used to explore the drainage, retention, and formation (DRF) characteristics of high-ash pulp slurries on paper machines. The BPDD uses a rotary hydrofoil to generate pulsation forces. It assesses the pulsation/gravity and the vacuum drainage rates sequentially. It also measures the wet pad air-flow resistance as an indication of formation. “Equilibrium Drainage Analysis” predicts the final DRF after the white water system reaches equilibrium. As such, new drainage mechanisms were identified.

Various flocculation mechanisms were also identified. Alum promotes homo-flocculation of fillers. Starch fosters fiber-fiber flocculation. A combination of alum, starch, and anionic polymers show flexibility in promoting the drainage and retention performances of the high-ash systems. The degree of fibrillation of furnishes effects specific filler fiber interactions. All results suggest that the DRF behaviors of the alkaline fine furnish can be explained (or predicted) from their flocculation mechanisms and machine dynamics.

The BPDD will be described with remarks on how it simulates a paper machine. New methods and terminology will be identified. Experimental set-up and design will be presented. Testing results will be displayed and conclusions made. Equilibrium Drainage Analysis (EDA) will be used to prove that fiber fines impede drainage. However, an effective retention program drains faster than poor retention programs. EDA allows one to choose an effective drainage/retention program with minimal detrimental effect on formation.