Filtration Resistance Determination of Fibrous Suspension Utilizing a Rapid Drainage Tester, 1998 Engineering Conference Proceedings

The drainage rate during sheet forming is a critical issue in the operation and design of the wet-end of a paper-machine. Previous attempts to correlate laboratory pulp drainage tests with pulp drainage on a papermachine have had limited success. Laboratory pulp drainage usually involved thick stock suspensions drained to form a high basis weight mat. In this study, a laboratory drainage tester has been developed to characterize the drainage of pulp slurries under industrial process conditions. Typical ranges for operating parameters such as headbox consistency, basis weight, and average drainage velocity, were incorporated into the device design. Average drainage velocities were measured for several grades and former arrangements during pilot papermachine trials. Evaluation of these three parameters indicates the drainage process can occur quickly, usually in under a second, and data collection must occur instantaneously and at a high frequency.

Drainage rate is continuously monitored by measuring the height change of the free surface of a suspension with a high speed triangulation sensor. Instantaneous drainage velocity is determined and applied to Darcy’s Law to determine the magnitude of viscous resistance. The viscous resistance was determined for several headbox suspensions as a function of basis weight for drainage velocities similar to those in a papermachine forming section. The results indicate that viscous resistance is not constant, but increases as drainage occurs.