Transverse motion of cohesive powders in flighted rotary kilns: experimental study of unloading at ambient and high temperatures

doi:10.1016/j.powtec.2013.04.007

Powder Technology

Volume 245, September 2013, Pages 56-63

https://doi.org/10.1016/j.powtec.2013.04.007 Get rights and content

Highlights

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Transverse flow of cohesive powder in flighted rotary kiln is experimentally studied.
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Cohesive powders (uranyl difluoride and uranium oxides) are employed.
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Measurements are interpreted using partly manual image analysis techniques.
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The effect of kiln hold up, rotational speed and temperature are presented.
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A geometrically calculated flight unloading law is compared with experimental results.

Abstract

The transverse flow of cohesive powders in rotary kilns equipped with lifters was studied experimentally and theoretically. A laboratory device was built up in which the flow of uranyl difluoride (UO₂F₂), uranium sesquioxide (U₃O₈) and uranium dioxide (UO₂) powders was filmed, recorded and analyzed using partly manual image analysis techniques. Experiments were performed both at room temperature and at high temperature. A constitutive law describing the powder discharge was derived, involving a relationship between the volume fraction of powder contained in a lifter and the angular position of this lifter. This law based on geometrical calculations is successfully compared with the experimental results of unloading.

Graphical abstract

Section snippets

Introduction and Background to the Problem

For over a century [1], rotary kilns have been widely used in the inorganic chemistry industry. They are a key element in the production processes of cement, lime and pigments (titanium dioxide calcination) and in extractive metallurgy for the reduction of ore [2]. Rotary kilns are well suited for drying [3], [4], for the pyrolysis of solid waste [5], and are also used to convert uranium fluoride into uranium dioxide for the manufacture of nuclear fuel [6], [7], [8].

Natural uranium cannot be

Flow at Ambient Temperature

The transverse flow of various powders (UO₂F₂, U₃O₈ type 1 and type 2 and UO₂) was studied at ambient temperature using two experimental devices. The first one, denoted drum 1, represents a slice of kiln 1. The second, denoted drum 2, represents a slice of kiln 2. For both drums, the diameter and the internal equipment are the same as in the corresponding industrial kiln; the length is 0.3 m. The dimensions of kilns and lifters are given in Table 1. Each has a glass front to enable visual

Results and Discussion

The lifters transport large quantities of powder and discharge very gradually, inducing highly efficient contact between the powder and the gas phase. Typical images are shown in Fig. 5.

Conclusions and Perspectives

A law describing the discharge of lifting devices used in industrial rotary kilns for defluorinating and reducing uranyl difluoride has been established both theoretically and experimentally. For the types of powders studied (UO₂F₂, U₃O₈ type 1 and type 2 and UO₂) and in the range of variation considered, no significant influence of the rotational speed, the kiln hold up (on condition that it is neither too high nor too low), the nature of the powder or the kiln dimensions is observed. The

Symbols Used

β [°]

angle characterizing the contact between the powder and the kiln wall

δ [°]

avalanche angle (instantaneous angle of repose made by particles in a flight with respect to horizontal)

γ [°]

angular position of the lifter (with respect to the horizontal)

γ_A [°]

first limiting angular position

γ_B [°]

second limiting angular position

γ_D [°]

detachment angle

γ_F [°]

angle at the end of discharge

γ_I [°]

angle at the start of effective discharge (at room temperature)

γ_I′ [°]

angle at the start of effective

Acknowledgements

This work was supported by a grant from FBFC² Romans (France) and Cogema³ Pierrelatte (France). We gratefully acknowledge André Feugier and Didier Hartmann for their kind help in this work and Alain HAZOTTE for his assistance in developing the image analysis program.

Marie Debacq is an associate professor in chemical engineering at Conservatoire National des Arts et Métiers (France) since 2002. She received her PhD in chemical engineering in 2001 from Institut National Polytechnique de Lorraine (France). Her research works concern modelling, hydrodynamics and heat transfer in heterogeneous reactors such as rotary kilns.

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Citation Excerpt :
Several authors have focused on the granular motion occurring inside the rotary kiln. Debacq et al. [6] carried out a theoretical and experimental study of the transverse flow of cohesive powders in rotary kilns equipped with lifters. The constitutive law governing the powder discharge, which involves a relationship between the volume fraction of powder contained in a lifter and the angular position of this lifter, was derived and compared with experimental results.
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Stéphane Vitu is an associate professor at Conservatoire National des Arts et Métiers (France), in the chemical engineering team since 2008. He received his PhD in chemical engineering in 2007 from Institut National Polytechnique de Lorraine (France). The subject was the development of a group contribution method to calculate the binary interaction parameter of the Peng–Robinson equation of state. Now, he studies heat exchange phenomena and transverse motion of granular materials in rotary kilns equipped with lifters.

Denis Ablitzer is an emeritus professor at Université de Lorraine, France. From 1980 to 2009, he taught as a professor at Ecole des Mines de Nancy and in 2008 became head of the “Materials Processing” research group, which is now a part of Institut Jean Lamour. His fields of activity cover gas–solid reaction, liquid metal treatment, remelting processes and clean processes. He is the author of more than 370 journal publications and communications. In 2003, he was awarded the Champion H. Mathewson Award from TMS, in 2005 an International Career Award from ASM and in 2007 the Chaudron Award from SF2M.

Jean-Léon Houzelot was a professor at École Nationale Supérieure des Industries Chimiques Nancy, a branch of Institut National Polytechnique de Lorraine, France. From 2002 to 2011, he was adviser to the French Research Ministry. He received his PhD in chemical engineering in 1974, and he made his research activities in the Laboratory of the Sciences of the Chemical Engineering (CNRS Nancy). In 2003, he was awarded the Champion H. Mathewson Award, from TMS (The Minerals, Metals & Materials Society), USA.

Fabrice Patisson is a professor at École des Mines de Nancy, a branch of Université de Lorraine, France. From 1988 to 2009, he has been a research scientist with CNRS, the French national center for scientific research. He received his PhD in materials engineering in 1987 from Institut National Polytechnique de Lorraine, France. He has been responsible for various collaborative research programs, including chairman of the hydrogen subproject in the European ULCOS (Ultra-low CO2 steelmaking) project. In 2003, he was awarded the Champion H. Mathewson Award, from TMS (The Minerals, Metals & Materials Society), USA.

^☆: Note: The results and calculations presented here were obtained in 1998 during a confidential study.

¹: Present address: Laboratoire de Génie des Procédés pour l'Environnement, l'Énergie et la Santé (LGP2ES-EA 21), Conservatoire National des Arts et Métiers (Cnam), case 2D1P20, 292 rue Saint-Martin, 75141 Paris cedex 03, France.

View full text

Transverse motion of cohesive powders in flighted rotary kilns: experimental study of unloading at ambient and high temperatures☆

Highlights

Abstract

Graphical abstract

Section snippets

Introduction and Background to the Problem

Flow at Ambient Temperature

Results and Discussion

Conclusions and Perspectives

Symbols Used

Acknowledgements

Chemical Engineering and Processing

Powder Technology

Chemical Engineering and Processing

Chemical Engineering Science

Powder Technology

Powder Technology

Powder Technology

Chemical Engineering Research and Design

Powder Technology

Powder Technology

Chemical Engineering Science

Powder Technology

The development of the rotary kiln and its application to various chemical and metallurgical processes

Industrial and Engineering Chemistry

Rotary Kilns