Volume 23
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Donatelli, A., Garzone, P., & Iovane, P. (2015). Discharging granular material from a rotary kiln in a slumping regime: Theoretical and experimental studies. Particuology, 23, 56-61. https://doi.org/10.1016/j.partic.2015.02.003
Discharging granular material from a rotary kiln in a slumping regime: Theoretical and experimental studies
A. Donatelli a *, P. Garzone b, P. Iovane b
a ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, SS 7 Appia km 706.00, 72100 Brindisi, Italy
b ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, SS 106 Jonica km 419.500, 75026 Rotondella (MT), Italy
10.1016/j.partic.2015.02.003
Volume 23, December 2015, Pages 56-61
Received 23 October 2014, Revised 7 January 2015, Accepted 2 February 2015, Available online 21 May 2015, Version of Record 2 December 2015.
E-mail: antonio.donatelli@enea.it

Highlights

• Theoretical model for studying granule discharge from rotary kiln in slumping mode was developed.

• Theoretical data showed good agreement with experimental results of mean residence time.

• Axial segregation of particles indicated a dependence of residence time on particle diameters.


Abstract

This study developed a theoretical approach to understanding how a set amount of a granular bed is discharged from a tilted rotary kiln (an empty cylinder) once its particle size distribution (PSD) is known and slumping motion occurs. The basis of the study is that the preparation of material for thermal treatment inside a rotary kiln (pyrolysis, gasification, and/or combustion) involves shredding to a desired particle size. Further mechanical stress results from the feeder screws moving material from storage toward the reactor. The most common PSDs found in uniform size reduction processes and mechanical stresses are Gaussian, log-normal, and Rosin–Rammler, of which the latter best fits the PSD in our study. Different particle diameters in the distribution result in an axial segregation when a slumping motion occurs, resulting in particles of different diameters leaving the kiln at different instants. After developing the model, the theoretical data showed good agreement when compared with experimental results obtained from downloading previously shredded carbonaceous material from a rotary kiln at 2 and 4 rpm rotational speeds. The mean residence times at steady state were determined for both rotational speeds and showed good agreement with data provided in the literature.

Graphical abstract
Keywords
Rotary kiln; Slumping motion; Axial segregation; PSD; Mean residence time