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Research Papers

Investigation of Potential Benefits of Using Bricks of High Thermal Capacity and Conductivity in a Rotating Calcining Kiln

[+] Author and Article Information
Lei Zhao

Energy Conversion and Conservation Center, University of New Orleans, New Orleans, LA 70148

Ting Wang1

Energy Conversion and Conservation Center, University of New Orleans, New Orleans, LA 70148twang@uno.edu

1

Corresponding author.

J. Thermal Sci. Eng. Appl 1(1), 011009 (Aug 10, 2009) (12 pages) doi:10.1115/1.3192772 History: Received December 06, 2008; Revised June 24, 2009; Published August 10, 2009

Petroleum coke is processed into calcined coke in a rotary kiln, where the temperature profiles of flue gas and coke bed are highly nonuniform due to different flow and combustion mechanisms. Motivated by saving energy costs, the effect of refractory brick’s thermal properties on potential energy savings is investigated. This study focuses on investigating potential energy savings by replacing inner one-third of existing bricks with higher thermal capacity (Cp) and/or higher thermal-conductivity (k) bricks. This paper investigates the postulation: the bricks with higher thermal capacity could store more thermal energy during the period in contact with the hot gas and would release more heat to the cock bed when the bricks rotate to the position in contact with the coke bed. A rotational transient marching conduction numerical simulation is conducted using the commercial software FLUENT . The impact of brick heat capacity and thermal conductivity on transporting thermal energy to the coke bed is analyzed. The results show the following: (a) Increasing the heat capacity of brick layer reduces brick temperature, which helps increase the heat transfer between the hot gas and brick. In other words, it does help brick to store more heat from the hot gas, but heat transfer between brick and coke is reduced, which is opposite to the original postulation. (b) Higher brick thermal conductivity decreases brick temperature, thus increases heat transfer between hot gas and the brick layer. The heat transfer from brick to coke bed is also increased but not significantly. (c) Since usually a brick with a higher Cp value also has a higher k-value, simulation of a brick layer with both four times higher Cp and k-values actually shows a reduction in the brick temperature, and hence a degradation of the heat transfer between the brick and coke bed. Therefore, replacing the existing brick layer with a high Cp- and/or high k-value brick is not recommended.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Modes of heat transfer in a rotary kiln (2)

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Figure 2

Physical configuration of the kiln. The inner one-third layer is furbished with high heat capacity and/or high-thermal-conductivity bricks.

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Figure 3

Rotational coordinate for the governing equations (10)

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Figure 4

The 2D cross section geometry and computational interfaces

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Figure 6

Mass weighted average gas temperature distributions in the kiln from the 3D CFD results from Zhang and Wang (11) and the centerline temperature distribution from 1D calculation results from the report in Ref. 14. With the matching scheme, the spatial coordinate (distance from the kiln feed end) is transformed to the temporal coordinate (time after petcoke is fed in the kiln) for 3 rpm.

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Figure 7

Temperature and heat flux distributions of Case 2C, starting cold

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Figure 8

Integral of heat flux over various interfaces of Case 2C, starting cold

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Figure 9

Temperatures and heat flux distributions of Case 4C, starting cold

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Figure 10

Integrate heat flux over various interfaces of Case 4C, starting cold

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Figure 11

Temperatures and heat flux distribution of Case 2H, starting hot

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Figure 12

Temperatures and heat flux distribution of Case 4H, starting hot

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Figure 13

Integral heat flux over various interfaces of Case 2H, starting hot

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Figure 14

Integral heat flux over various interfaces of Case 4H, starting hot

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Figure 15

Temperatures and heat flux distribution of Case 2, 1200 K start

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Figure 16

Temperatures and heat flux distribution of Case 4, 1200 K start

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Figure 17

Integral heat flux over various interfaces of Case 2, 1200 K start

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Figure 18

Integral heat flux over various interfaces of Case 4, 1200 K start

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