Experiment study on particle pulverization-assisted convective air drying of sewage sludge

Abstract

Sewage sludge drying is a pivotal step in sludge reduction, harmlessness, and resource utilization. Pulverizing sewage sludge can significantly increase the surface area of sludge particles available for contact with the air medium, consequently strengthening the convective drying process of the sludge. In this paper, the adopted deep drying system mainly combined sewage sludge pulverization and sewage sludge drying functions. Parametric studies were carried out to investigate the effects on the drying process. The moisture content of the sewage sludge decreased from 50.3% to 26.8% when the linear speed of the rotating blade tip of the pulverizing dryer and induced draft fan reached 28.3 m·s−1, 62.8 m−1, and air velocity reached 9.5 m·s−1, respectively. Furthermore, this work also preliminarily reveals the mechanism of the pulverizing dryer. The pores on the sludge particle surfaces are destroyed during the drying process. As the linear speed of the rotating blade tip in the pulverizing dryer increased, the hydrophilicity and the average particle size of the sewage sludge particles decreased, with the particle size representing the highest volume fraction being reduced by 62% in the particle size distribution. The pulverizing dryer not only breaks up the sludge to increase the surface area of the sludge in contact with the air but may also have a centrifugal effect. As the intensity of the pulverizing dryer increases, Nuclear Magnetic Resonance (NMR) measurements show a leftward shift in the peak of the weakly bound water in the sludge and a noticeable shortening of the transverse relaxation time. Overall, the results suggested that pulverizing is a suitable assistive method to improve the drying effect of the sewage sludge.