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Research Papers

Investigation of Combustion and Thermal-Flow Inside a Petroleum Coke Rotary Calcining Kiln With Potential Energy Saving Considerations

[+] Author and Article Information
Zexuan Zhang

Research Assistant
e-mail: Seanzhang98@gmail.com

Ting Wang

Professor
e-mail: Twang@uno.edu
Energy Conversion and Conservation Center,
University of New Orleans,
New Orleans, LA 70148

Manuscript received March 25, 2012; final manuscript received October 1, 2012; published online March 18, 2013. Assoc. Editor: S. A. Sherif.

J. Thermal Sci. Eng. Appl 5(1), 011008 (Mar 18, 2013) (10 pages) Paper No: TSEA-12-1042; doi: 10.1115/1.4007914 History: Received March 25, 2012; Revised October 01, 2012

Calcined coke is a competitive material for making carbon anodes for smelting of alumina to aluminum. Calcining is an energy intensive industry and a significant amount of heat is exhausted in the calcining process. Efficiently managing this energy resource is tied to the profit margin and survivability of a calcining plant. To help improve the energy efficiency and reduce natural gas consumption of the calcining process, a 3D computational model is developed to gain insight of the thermal-flow and combustion behavior in the calciner. Comprehensive models are employed to simulate the moving petcoke bed with a uniform distribution of moisture evaporation, devolatilization, and coke fines entrainment rate with a conjugate radiation-convection-conduction calculation. The following parametric studies are conducted: rotation angles, tertiary air injection angles, devolatilization zone length, discharge end gas extractions without injecting natural gas, variations of coke bed properties (thermal conductivity and heat capacity), and coke bed sliding speed. A total of 19 cases have been simulated. The results of studying the effect of tertiary air injection angles show that employing 15 deg tertiary air injection angle provides the best calcining condition than using 30 deg and 45 deg injection angles by achieving a higher coke bed temperature and less coke fines entrainment and attrition rate. In an attempt to reduce natural gas consumption, employing gas extraction at the discharge end successfully draws the hot combustion gas from the tertiary air zone towards the discharge end without burning natural gas. The coke bed temperature between 6 and 21 m from the discharge end is successfully raised 10–100 K higher, but discharge end temperature is reduced 150 K without burning natural gas. The extracted gas at 1000 K is too low to be returned to the kiln, but it could be used to preheat the tertiary air.

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References

Ellis, P. J., and Paul, C. A., 2000, “Tutorial: Petroleum Coke Calcining and Uses of Calcined Petroleum Coke,” AIChE 2000 Spring National Meeting, 3rd International Conference on Refining Processes, Session No. T9005.
Bagdoyan, E. A., and Gootzait, E., 1985, “Refiners Calcine Coke,” Hydrocarbon Process., 64(9), pp. 85–90.
Li, X., Wang, T., Tonti, R., and Edwards, L., 2007, “Analysis of Energy Savings by Painting a Rotary Kiln Surface,” Proceedings of 29th Industrial Energy Technology Conference, New Orleans, LA, Paper No. 9–5.
Zhao, L., and Wang, T., 2009, “Investigation of Potential Benefits of Using Bricks of High Thermal Capacity and Conductivity in a Rotating Calcining Kiln,” ASME J. Thermal Sci. Eng. Appl., 1(1), p. 011009. [CrossRef]
Zhang, Z., and Wang, T., 2010, “Simulation of Combustion and Thermal-Flow Inside a Petroleum Coke Rotary Calcining Kiln—Part I: Process Review and Modeling,” ASME J. Thermal Sci. Eng. Appl., 2(2), p. 021006. [CrossRef]
Zhang, Z., and Wang, T., 2010, “Simulation of Combustion and Thermal-Flow Inside a Petroleum Coke Rotary Calcining Kiln—Part II: Analysis of Effects of Tertiary Airflow and Rotation,” ASME J. Thermal Sci. Eng. Appl., 2(2), p. 021007. [CrossRef]
Mason, H. B., and Spalding, D. B., 1973, “Prediction of Reaction Rates in Turbulent Premixed Boundary-Layer Flows,” Combustion Institute European Symposium, F. J.Weinberg, ed., Academic, New York, pp. 601–606,
Patankar, S. V., 1980, Numerical Heat Transfer and Fluid Flow, Hemisphere, New York.
Kunii, D., and Levenspiel, O., 1991, Fluidization Engineering, 2nd ed., Butterworth-Heinemann, Newton, MA.

Figures

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Fig. 1

Petcoke calcination with tertiary air

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Fig. 2

A 3D view of the simulated calcining rotary kiln

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Fig. 3

(a) Relative coke bed and tertiary air inlet position (rotational angles) and (b) three different tertiary air injection angles

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Fig. 4

Tertiary air injector locations and labeling

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Fig. 5

Meshed geometry for the rotary calcining kiln

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Fig. 6

Temperature contours on the vertical midplane X = 0 for various tertiary air injection angles

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Fig. 7

Temperature contours on the horizontal midplane Y = 0 for various tertiary air injection angles

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Fig. 8

Temperature contours on the coke bed surface plane Y = −0.9144 for various tertiary air injection angles

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Fig. 9

Temperature contours at each tertiary air injection location for various tertiary air injection angles

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Fig. 10

Mass flow weighted gas static temperature for various tertiary air injection angles

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Fig. 11

Coke bed surface centerline static temperature for various tertiary air injection angles

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Fig. 12

Streamwise velocity profiles on the vertical midplane X = 0 for various tertiary air injection angles

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Fig. 13

Streamwise velocity profiles of the horizontal mid-plane Y = 0 for various tertiary air injection angles

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Fig. 14

Velocity profiles at each tertiary air injection location for various tertiary air injection angles

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Fig. 15

Temperature contours on the vertical midplane X = 0 for various discharge end flow control cases

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Fig. 16

Temperature contours on the horizontal midplane Y = 0 for various discharge end flow control cases

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Fig. 17

Temperature contours of the coke bed surface on the horizontal plane at Y = −0.9144 for various discharge end flow control cases

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Fig. 18

Cross-sectional temperature contours at each tertiary air injection location for various discharge end flow control cases

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Fig. 19

Mass flow weighted gas static temperature for various discharge end flow control cases

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Fig. 20

Coke bed surface centerline static temperature for various discharge end flow control cases

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Fig. 21

Centerline static temperature ½ coke bed depth for various discharge end flow control cases

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Fig. 22

Static temperature for the effect of suction with refeed

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Fig. 23

Streamwise velocity profiles of vertical midplane at X = 0 for various discharge end flow control cases

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Fig. 24

Streamwise velocity profiles of horizontal midplane at Y = 0 for various discharge end flow control cases

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Fig. 25

Cross-sectional velocity profiles at each tertiary air injection location for various discharge end flow control cases

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Fig. 26

Mass flow weighted gas static temperature for conditions with coke fine burning, without coke fine burning and with a shortened devolatilization zone

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Fig. 27

Schematic of 2D simulation domain

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Fig. 28

2D coke bed temperature distributions for various bed properties (thermal conductivity/specific heat/bed moving velocity)

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