Challenges in tracing material flow passing a loss-in-weight feeder in continuous manufacturing processes

Area of Science:

• Chemical Engineering
• Process Control
• Manufacturing Systems

Background:

• Loss-in-weight feeders are critical for continuous manufacturing, maintaining constant mass flow.
• These feeders introduce significant back-mixing, complicating disturbance management.
• Semi-continuous refilling contradicts steady-state assumptions in feeder modeling.

Purpose of the Study:

• To investigate dynamic back-mixing in loss-in-weight feeders.
• To understand the impact of low filling levels and material addition on feeder behavior.
• To develop an extended model accounting for varying fill levels and dead zones.

Main Methods:

• Experimental investigation using a fluorescent tracer at low feeder filling levels.
• Analysis of material draw-in and dead material in the hopper.
• Extension of steady-state models to incorporate dynamic back-mixing and dead zones.

Main Results:

• Material addition significantly impacts feeder dynamics, likely due to non-uniform screw draw-in and dead material.
• Dead material can constitute up to 50% of the hopper's content.
• The extended model reduced root-mean-squared deviation by 41% compared to existing models.
• Model predicts state-dependent responses to disturbances based on feeder fill level.

Conclusions:

• Dynamic back-mixing and dead zones in loss-in-weight feeders are significant, especially at lower fill levels.
• These phenomena challenge material diversion and traceability in continuous processes.
• Feeder selection and operation must account for state-dependent back-mixing and dead zones.