Viscoelastic Characterization of Medium Consistency Pulp Suspensions, 1991 Forest Products Symposium Proceedings

Over the last decade there has been considerable interest in the processing of pulp fiber suspensions at concentrations much higher than those used previously. A variety of economic factors as well as environmental concerns favor the redesign of unit operations to function at higher consistencies. Pumping was one of the first unit operations to receive widespread attention for medium to high consistency operation (Gullichsen and Harkonen, 1981; Bennington, Grace and Kerekes, 1990). New screening (Wahren, 1980) and forming (Norman, 1990; Normura, Wada and Shimizu 1989) (among others) processes have also been explored for use at higher consistencies than previously.

The present work is motivated by this current commercial interest. Nearly all earlier studies of the viscoelasticity of pulp suspensions (e.g., see reviews of Norman, 1990; Wahren, 1980; Kerekes, Soszynski and Tam Doo, 1986)

used pulp suspensions that were characteristic of an earlier generation of unit operations that functioned at low consistencies. Here we study suspensions that fall in the range from what Kerekes and his coworkers (1986) define as low (0 to 8%) and medium (820%) consistencies. We also note that such definitions of ‘low” and “medium” may be readily applied to unit operations such as pumping and screening, high consistency forming usually deals with

consistencies of 3%. Our work spans the range of consistencies from 2% to 13%.