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Technical Briefs

Simulation and Optimization of Drying of Wood Chips With Superheated Steam in a Rotary Kiln

[+] Author and Article Information
P. S. Ghoshdastidar1

Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur UP 208016, Indiapsg@iitk.ac.in

Ankit Agarwal

Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur UP 208016, India

1

Corresponding author.

J. Thermal Sci. Eng. Appl 1(2), 024501 (Sep 30, 2009) (8 pages) doi:10.1115/1.3224964 History: Received October 24, 2008; Revised August 14, 2009; Published September 30, 2009

The present work reports a computer simulation and optimization study of heat transfer in a rotary kiln used for drying and preheating wood chips with superheated steam at 1 bar. A rotary kiln employed for drying and preheating wet solids consists of a refractory lined cylindrical shell mounted at a slight incline from the horizontal plane. The kiln is slowly rotated about its longitudinal axis. Wet solids are fed into the upper end of the cylinder, and during the process, they are dried and heated by the counter-current flow of the hot gas. Finally, it is transferred to the lower end, where it reaches the desired temperature and is discharged. The heat transfer model includes radiation exchange among hot gas, refractory wall and the solid surface, transient conduction in the refractory wall, and mass and energy balances of the hot gas and solids. A finite-difference based computational heat transfer approach is used. A univariate search method has been used to obtain the minimum kiln length with respect to various kiln operating parameters subject to a constraint on the inlet gas temperature. The parametric study lent a good insight into the physics of the drying process in a rotary kiln. The optimization study reveals that for the same predicted kiln length, lower inlet steam temperature can be used, which will result in saving of energy cost.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of a rotary kiln

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Figure 2

Schematic cross section of a rotary kiln

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Figure 3

Schematic diagram showing heat transfer processes in rotary kiln

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Figure 4

Section of the kiln showing wall and solid surface elements

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Figure 5

Section of the kiln showing the coordinate system

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Figure 6

Axial gas and solid temperature distributions

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Figure 7

Axial gas and solid temperature distributions for various proportions of water in solid feed

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Figure 8

Axial gas and solid temperature distributions for different mass flow rates of the (dry) solid

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Figure 9

Axial gas and solid temperature distributions for different mass flow rates of the gas

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Figure 10

Velocity vector diagram for a solid particle in the kiln

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