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Research Papers: Fuel Combustion

Reduction of Sulfur Dioxide Emissions by Burning Coal Blends

[+] Author and Article Information
Emad Rokni

Department of Mechanical
and Industrial Engineering,
334 SN, Northeastern University,
360 Huntington Avenue,
Boston, MA 02116
e-mail: rokni.e@husky.neu.edu

Aidin Panahi

Department of Mechanical
and Industrial Engineering,
334 SN, Northeastern University,
360 Huntington Avenue,
Boston, MA 02116
e-mail: panahi.a@husky.neu.edu

Xiaohan Ren

Department of Mechanical
and Industrial Engineering,
334 SN, Northeastern University,
360 Huntington Avenue,
Boston, MA 02116;
School of Energy Science and Engineering,
Harbin Institute of Technology,
531 Dongli Building,
92 West Dazhi Street,
Harbin 150001, China
e-mail: xiaohan09126@gmail.com

Yiannis A. Levendis

College of Engineering Distinguished Professor
Fellow ASME and SAE
Department of Mechanical
and Industrial Engineering,
334 SN, Northeastern University,
360 Huntington Avenue,
Boston, MA 02116
e-mail: y.levendis@neu.edu

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received September 24, 2015; final manuscript received November 20, 2015; published online January 11, 2016. Editor: Hameed Metghalchi.

J. Energy Resour. Technol 138(3), 032204 (Jan 11, 2016) (8 pages) Paper No: JERT-15-1362; doi: 10.1115/1.4032239 History: Received September 24, 2015; Revised November 20, 2015

Given that sulfur contents of coals vary widely, this work investigated whether cofiring of high-sulfur coals with low-sulfur coals of different ranks has any distinct advantages on lowering the sulfur dioxide emissions of the former coals, beyond those predicted based on their blending proportions. Such cofiring intends to take advantage of documented evidence in previous investigations at the author's laboratory, which demonstrated that lignite coals of low-sulfur, high-calcium, and high-sodium content undergo massive bulk fragmentation during their devolatilization. This particular behavior generates a large number of small-sized char particles which, upon effective dispersion in the gas, can heterogeneously absorb the emitted sulfur dioxide gases, i.e., act as defacto sorbents, and then retain them in the ash. This study included two high- and medium-sulfur bituminous coals, two low-sulfur lignite coals, and a sub-bituminous coal. Results showed that bituminous coals burning under substoichiometric (fuel-lean) conditions release most of their sulfur content in the form of SO2 gases, whereas low-ranked coals only partly release their sulfur as SO2. Furthermore, the SO2 emission from coal blends is nonlinear with blend proportions, hence, beneficial synergisms that result in substantial overall reductions of SO2 can be attained. Finally, NOx emissions from coal blends did not show consistent beneficial synergisms under the implemented fuel-lean combustion conditions.

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Figures

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Fig. 4

Mole fractions of carbon dioxide (%) with corresponding emission factors (kg/GJ), and mole fractions of oxygen in the combustion effluents (%)

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Fig. 3

Bulk (global) combustion equivalence ratios, φ, and combustion efficiencies of five neat coals as well as of 50–50 wt. % blends thereof

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Fig. 2

High-speed, high-magnification cinematography of typical combustion events of group particles for the two of the fuels of this study and their blend burning in air under active furnace gas flow condition (1 lpm in furnace).The displayed numbers in each frame denote milliseconds, where zero does not mark the beginning of combustion, it merely represents the beginning of each depicted sequence. The diameter of the wire shown at the bottom of each photograph is 240 μm (a) bituminous coal (Illinois #6 Macoupin), (b) lignite coal (Beulah, ND), and (c) 50–50 wt. % blends of Illinois bituminous and Beulah lignite.

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Fig. 1

Schematic of the electrically heated, laminar-flow DTF used in this work

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Fig. 5

Mole fractions of sulfur dioxide in the combustion effluents (ppm), corresponding emission factors (kg/GJ) and conversion amounts of the fuel sulfur to SO2

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Fig. 6

Coal sulfur emitted as sulfur dioxide versus Ca/S ratio or Total Alkalis/S ratios

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Fig. 7

Mole fractions of nitrogen oxide (NOx = NO + NO2) in the combustion effluents (ppm), corresponding emission factors (kg/GJ) and conversion amounts of the fuel sulfur to NOx

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