[en] X-ray microtomography is proposed as a new tool to investigate the evolution of size, shape and texture of soft materials during a drying operation. This study is focused on the drying of mechanically dewatered sludges from a secondary wastewater treatment. The shrinkage phenomenon is shown to play a crucial role in the control of the drying process. The shrinkage curves are determined by analysing the shape and size of cross sectional microtomographic images of sludge extrudates at different levels of drying. The observation of drying and shrinkage curves allows us to determine 3 critical water content values, which define different drying zones where extragranular, intragranular or mixed limitations prevail. When drying is externally controlled. the decrease of the drying rate observed during experiments can be related to the reduction of the external area of the sample, i.e., to shrinkage. When drying is internally controlled, resistances inside the solid govern the process. Between these two extreme situations, the drying rate reduction is the result of both the external area decrease and the development of internal resistances limiting drying. A multizone model is proposed to describe quantitatively these observations. The analysis of the internal texture of the Sludge extrudates reveal, crack formation at the end of the drying process. The onset of crack formation is clearly related to the appearance of internal transfer limitations. i.e., humidity and temperature gradients inside the material.
Disciplines :
Chemical engineering Mechanical engineering
Author, co-author :
Léonard, Angélique ; Université de Liège - ULiège > Département de chimie appliquée > Génie chimique - Opérations physiques unitaires - Département de chimie appliquée
Blacher, Silvia ; Université de Liège - ULiège > Département de chimie appliquée > Labo de génie chimique
Marchot, Pierre ; Université de Liège - ULiège > Département de chimie appliquée > Génie chimique - Systèmes polyphasiques
Crine, Michel ; Université de Liège - ULiège > Département de chimie appliquée > Génie chimique - Opérations physiques unitaires
Language :
English
Title :
Use of X-ray microtomography to follow the convective heat drying of wastewater sludges
Alternative titles :
[fr] Utilisation de la microtomographie à rayons X pour suivre le séchage convectif de boues d'épuration
Publication date :
2002
Journal title :
Drying Technology
ISSN :
0737-3937
eISSN :
1532-2300
Publisher :
Marcel Dekker Inc, New York, United States - New York
Volume :
20
Issue :
4-5
Pages :
1053-1069
Peer reviewed :
Peer Reviewed verified by ORBi
Funders :
F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE]
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