Successful Agitator Operation in Blow Tanks and High Density Towers

Authors:

Thomas C. DeVries, Manager, Market Development

Michael D. Doyle, P.E., Senior Application Engineer 

Presented at the 94th AICHE National Conference, Atlanta, GA 

This paper outlines the principles for successful operation of blow tanks and high-density towers, emphasizing the critical role of controlled dilution water addition and proper agitator design. Key factors include maintaining appropriate stock consistency, residence time, and agitated zone volume to ensure smooth plug flow and prevent mechanical issues. The study highlights that careful mechanical design, correct agitator sizing, and proper start-up procedures are essential for reliable, efficient mill operations.

Key Learnings

• Proper control of dilution water through feedback consistency is critical for maintaining desired stock consistency in blow tanks and high-density towers.
• Agitated zone volume, residence time, and correct agitator sizing directly impact performance and consistency control.
• Mechanical design must account for high-amplitude fluctuations, intermittent shock loads, and potential plug flipovers to prevent agitator failure.
• Start-up procedures should include gradual transitions and proper stock spreading to avoid upsets and ensure smooth operation.
• Operating multiple agitators in low-consistency stock can cause interference and mechanical damage; one properly sized agitator is often sufficient.
• Regular monitoring and adherence to recommended main/trim dilution water ratios help prevent poor consistency control and system upsets.
• Conservative selection of agitator horsepower and robust mechanical fastening methods increase reliability and longevity of equipment.