(8f) The Effect of Impeller off-Wall Clearance On the Performance of Pulp Suspension Mixing in a Side-Entering Cylindrical Stock Chest
AIChE Spring Meeting and Global Congress on Process Safety
2010
2010 Spring Meeting & 6th Global Congress on Process Safety
North American Mixing Forum
Advances in Industrial Mixing Applications
Monday, March 22, 2010 - 10:05am to 10:30am
Impeller clearance from the vessel wall, characterized by E/D, affects the mixing quality attained in a side-entering stock chest. In the agitation of pulp suspensions, the mixing can be characterized by the size of cavern produced by the impeller. In this work, we have investigated cavern size as a function of the impeller off-wall clearance in a laboratory-scale cylindrical stock chest. Hardwood pulp suspensions of Cm = 2, 3 and 4% (fibre mass concentration) were agitated using an axial flow impeller with E/D varied from 0.14 to 0.68. Cavern size was measured using electrical resistance tomography (ERT) in batch operation and by dynamic mixing tests in continuous operation, with cavern size increasing with increasing E/D. At E/D = 0.14, throttling of the impeller suction occurs which reduced cavern size. CFD simulations for steady state operation under-predicted the cavern size, but correctly captured the trend in size variation with E/D. The measured cavern volumes compared well with predictions of an axial force model that accounted for interaction between the cavern and the vessel.