Structure and Reactivity of Low-Rank Coal Chars Prepared from Fluidized Bed and Moving Bed Pyrolyzers and the Potential
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PULVERIZED coal injection (PCI) technology enables cheaper pulverized coal to be partially used as substitutes for the increasingly expensive metallurgical coke in a blast furnace. Therefore, this approach can reduce the coke ratio and pig iron cost, while simultaneously optimizing the fuel structure for ironmaking. Besides, as high-quality ‘PCI coal’ resources start diminishing over time, it becomes imperative to seek a high-quality alternative fuel for partly replacing PCI coal. In recent years, novel injection fuels such as biomass charcoal, waste plastics, and waste tires have been widely explored by different studies.[1–5] While these fuels are either renewable themselves or can enable the reutilization of waste resources, their large-scale application is still hindered by several issues, including the large variations
CHONG ZOU, JIANGYONG HE, JUNXUE ZHAO, XIAOMING LI, RUIMENG SHI, CHENG MA, YI KANG, and XIAORUI ZHANG are with the School of Metallurgical Engineering, Xi’an University of Architecture and Technology, Xi’an 710311, P.R. China. Contact e-mails: [email protected], [email protected] Manuscript submitted December 6, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
in their compositions, accumulation of hazardous elements in the blast furnace, and the difficulties faced in collecting and processing the raw material. There is a huge amount of low-rank coal resource available worldwide. More than 50 pct of the world’s total coal reserves consist of lignite and sub-bituminous coal.[6] Compared with high-rank coal, the low-rank coal has a higher content of volatile matter and moisture, a lower content of fixed carbon, and a lower calorific value. These features result in low thermal efficiency when using the coal directly as boiler fuel for power generation. The pyrolysis of these low-rank coals to 550 C to 700 C can remove the moisture content and partially the volatile matter from the raw coal and, further, obtain certain amounts of tar and gas with high added values. Therefore, this method is a promising approach to realize the graded cascade utilization of low-rank coal. A variety of pyrolysis technologies have been developed using moving bed and fluidized bed pyrolysis as the core pyrolysis methods.[7,8] Owing to the advantages such as high production efficiency, high availability of powdery coal, and high coal tar yield, the fluidized bed pyrolysis technology is developing rapidly in industry. However, the powdered char produced by fluidized bed pyrolysis has not yet found high-value utilization.
Recently, some studies have reported the use of chars prepared by moving bed pyrolysis of low-rank coal as the PCI fuel in a blast furnace. Anthony et al. studied l[9,10] the structure and combustion performance of chars prepared from the pyrolysis of Yallourn brown coal. The results from their study showed that Yallourn chars satisfy the injection fuel requirement in a blast furnace even though their ignition temperature is slightly higher than that of PCI coal. A better injection fuel can be obtained by mi
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