Influence of carbon structure and mineral association of coals on their combustion characteristics for pulverized coal i
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to characterize the heterogeneous nature of minerals of discrete coal particles. The TGA char reactivity was related to the proportion of coal particles displaying strong association of calcium/sulfur phases with carbon matrix to highlight the catalytic influence of minerals on char reactivity at low temperatures. The study suggested that during DTF combustion tests at 1200 °C, char reaction rates might have been catalyzed by coal minerals, particularly due to illite and its association with carbon. Under the same combustion conditions, most of the coal minerals did not transform significantly to slag phases. Coal burnout was found to improve significantly in a combustion temperature range of 1200 °C to 1500 °C. The improvement of coal burnout with temperature appeared to be influenced by coal properties, particularly as a function of the chemical nature of minerals, as well as the degree of associations with other minerals. The study implies that coals with similar mineral compositions might not necessarily reflect similar combustion behavior due to the differences in their associations with other phases. The study highlighted the significance of the characterization of the heterogeneity of coal particles including mineral associations for a comprehensive and reliable assessment of the combustion performance of PCI in an operating blast furnace.
I. INTRODUCTION
PULVERIZED coal injection (PCI) has become a standard technology to improve blast furnace (BF) operation and environmental efficiency by minimizing coke consumption, and efforts are being made to increase coal injection rates up to 250 kg/THM in the future. Despite the obvious economic and environmental advantages of PCI technology, some coalrelated technical difficulties arise, such as insufficient coal combustion due to the extremely short residence time ("20 ms) in the raceway.[1] At high injection rates ("200 kg/THM), approximately 50 pct of the injected coal is believed to burn in front of tuyeres.[2] Consequently, significant amounts of unburnt char are carried from the raceway, which could accumulate in different regions of a blast furnace, leading to many operational problems (e.g., reduced bed permeability, undesirable gas and temperature distributions). Therefore, keeping the extent of unburnt char under a reasonable limit in a blast SUSHIL GUPTA, Research Associate, and VEENA SAHAJWALLA, Professor, are with the School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. Contact e-mail: [email protected] YASER AL-OMARI, formerly a Research Student with the School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW, Australia, is now with TAFE International WA, Perth, Australia. DAVID FRENCH, Mineralogist, is with CSIRO Energy Technology, Lucas Heights Science and Technology Centre, Private Mail Bag 7, Bangor, NSW 2234, Australia. Manuscript submitted February 15, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS B
furnace is one of the key requirements for
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