Sampling of Pulp Slurry, 1999 Pulping Conference Proceedings

Ari Ämmälä, Tero Hietanen, Jouko Niinimäki, Raimo Ylinen

Sampling of pulp slurry is a common operation in any pulp or paper mill. In general sampling causes most uncertainty in the analyses of samples, while laboratory analyses are relatively more accurate thanks to the standardized analysis methods. Depending on the process conditions, erroneous sampling may be caused by a dilution effect due to the flow geometry of the sampling device, anisotropy of the fiber suspension or local changes in consistency.

Two sampling methods are compared in this study: sampling with manual ball valves and sampling with semi-automatic pneumatic piston valves. The data were collected from mill screening experiments made with TMP. Samples were taken from the feed, accept and reject pipes during steady-state screening. The consistency of samples was analyzed and the accuracy of the sampling methods was evaluated as the standard deviation and the mean of the calculated mass balance error over the screen.

There is an obvious difference between the tested sampling methods. The average of mass balance errors is practically zero in the case of semi-automatic sampling, but clearly different from zero in the case of manual sampling, indicating a systematic dilution effect. The smaller standard deviation of errors with the semi-automatic sampling method suggests more stable flow conditions in the sampling valve than in the case of manual sampling. As a conclusion, an obviously better reliability of the sampling of pulp slurry was achieved with the semi-automatic sampling method than with the manual one.