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Research Papers

Evaluation of Applying Low Calorific Fuel as Reburn Fuel in an Opposed Wall Fired Boiler

[+] Author and Article Information
Guang Xu, Wei Zhou, Larry W. Swanson, David K. Moyeda, Quang Nguyen

 GE Environmental Services, 1831 E. Carnegie Avenue, Santa Ana, CA 92705

J. Thermal Sci. Eng. Appl 1(3), 031007 (Apr 06, 2010) (6 pages) doi:10.1115/1.4000985 History: Received January 06, 2009; Revised December 01, 2009; Published April 06, 2010; Online April 06, 2010

The alternative fuels, such as biomass, municipal wastes, and underground coal gasification gas, become attractive to the power plants as renewable energy sources or economical fuels. However, the alternative fuels usually have much lower heating value and different chemical compositions from those of coal and natural gas. Firing these alternative fuels in the boilers that are originally designed for coal firing or natural gas firing may cause unexpected boiler operating issues and/or thermal performance degradation. A careful evaluation study is often required prior to implementation. This paper presents the results of a study that evaluated the feasibility of using an underground coal gasification gas as a reburn fuel. The evaluation was done on Eskom’s Majuba Unit 5, a 710 MWe opposed wall-fired boiler, located in South Africa. The study utilized heat transfer analysis and computational fluid dynamics models to (1) evaluate the impacts of firing low calorific fuel on boiler efficiency and the boiler auxiliary system performance, (2) develop a conceptual gas reburn injection system, and (3) evaluate the impacts of gas reburn on the boiler thermal performance and boiler NOx emissions. The results indicate that the underground coal gasification gas can be an effective reburn fuel for the Majuba boiler with upgrades on the auxiliary systems.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 2

Application of reburn process to a utility boiler

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Figure 3

Small-scale reburn results of gasified biomass products

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Figure 4

Impacts of reburn stoichiometric ratio on reburn performance

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Figure 5

Majuba boiler model

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Figure 6

Majuba burner model

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Figure 7

Comparison of temperature profiles between baseline and reburn operations

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Figure 8

Comparison of CO profiles for different wall injection options

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Figure 9

Schematic of Majuba Unit 5 thermal model

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Figure 10

Predicted bulk furnace gas temperatures

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Figure 11

Comparisons of attemperation rates

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Figure 12

Flue gas flow rate increases with UCG heat input at Majuba plant

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Figure 13

Boiler efficiency decreases with UCG heat input increase at Majuba plant

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Figure 14

Projected NOx reduction

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