Modeling of Sludge Behavior in a Steam Dryer

Abstract

Steam dryers are in widespread use for sewage sludge treatment. The effectiveness of the steam dryer could be improved by increasing the drying rate, which is influenced by the movement of the sludge in the dryer. Therefore, it is necessary to understand the movement of sludge and water evaporation in the dryer. In this study, tracers were used to elucidate the behavior of sludge in the dryer. The experiment confirmed that sludge did not simply flow in one direction; instead, part of the sludge flowed in the reverse direction (back-mixing). A tanks-in-series model analysis was performed to analyze the back-mixing phenomenon. This analysis provided insight into the behavior of sludge in the dryer, and the drying rate of each segment was determined.

Keywords:

• Back-mixing
• Movement of sludge
• Residence time in dryer
• Sewage sludge dryer
• Tanks-in-series model

ACKNOWLEDGMENTS

We appreciate the valuable advice of Mr. Kurihara, President of Senshu Koki Co., Ltd. I thank my former colleagues at Kubota Corp. for sharing so much in this experiment.

Notes

DS: Dried Solid, WB: Wet Base.

The tracer materials were crushed, dissolved in water, and mixed with dried sludge.

DB: Dry Base, WB: Wet Base.

Treated sludge solid weight = 3000 × (1–0.811) = 567 kgDS/h.