Macroscale mixing and dynamic behavior of agitated pulp stock chests

Agitated pulp chests provide attenuation of high-frequency disturbances in fibre mass concentration, freeness and other quality factors. Dynamic tests made on industrial stock chests show the existence of non-ideal flows such as channeling, recirculation and dead zones. A new identification method was developed for estimation of dynamic model parameters.; A scale-model stock chest was designed and built to study macroscale mixing and disturbance attenuation in a laboratory setting. First preliminary batch studies were made on the scale model chest to characterize its behavior and to develop test protocols for use in dynamic tests. Dynamic response of liquid and solid phase tracers showed that a liquid phase tracer (saline solution) can be used to trace the fibre phase provided the fibre mass concentration is ≥2%. It was found that mixing-time for the laboratory chest is both a function of impeller momentum flux and fibre mass concentration.; The extent of non-ideal flow in the scale-model chest was evaluated by exciting the system.; Dynamic test results showed that the extent of non-ideal flow and the degree of disturbance attenuation are significantly affected by the location of the input and output in the chest, the fibre mass concentration, the impeller speed and diameter, and the pulp flow rate through the chest.; It was found that the degree of upset attenuation is a function of the impeller momentum flux, rather than the power input. Dynamic tests made on scale-model and industrial chests showed that the power calculated based on smooth surface motion and even the onset of complete motion inside the chest does not completely eliminate dead volume and channeling. Additional power is required to have a desired dynamic response from the chest.