Pilot-Scale Examination of Mixing Liquid into Pulp Fiber Suspensions in the Presence of an In-Line Mechanical Mixer

The quality of liquid mixing into the main stream for an in-line mechanical mixer was investigated for water and pulp suspensions over a range of mass concentrations (0–3.0%), main-stream velocities (0.5–3.0 m/s), jet velocities (3.8–12.6 m/s), and rotational speeds (0–800 rpm) based on electrical resistance tomography and a modified mixing index, derived from the coefficient of variation of conductivity values. The mixing quality was worse when the jet penetrated to the far wall of the pipe for all fiber mass concentrations investigated, whereas this only applied at higher mass concentrations without the impeller. For water flow, the residence time had a significant effect on mixing at higher impeller speeds. With the impeller present, the mixing quality in pulp suspensions improved substantially and was similar to that for water when the flow approached the turbulent regime, with a considerably lower main-stream velocity required for mixing compared to a tee mixer alone. At higher mass concentrations, t...