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Ignitability and combustibility of Yallourn pyrolysis char blended with PCI coal under simulated blast furnace conditions Anthony De Girolamo, Alex Grufas, Ilia Lyamin, Iori Nishio, Yoshihiko Ninomiya, and Lian Zhang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02425 • Publication Date (Web): 27 Dec 2015 Downloaded from http://pubs.acs.org on January 2, 2016
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Ignitability and combustibility of Yallourn pyrolysis char blended with PCI coal under simulated blast furnace conditions
Anthony De Girolamo1, Alex Grufas1, Ilia Lyamin1, Iori Nishio2, Yoshihiko Ninomiya2 and Lian Zhang1, *
1
Department of Chemical Engineering, Monash University, Clayton, Victoria 3800, Australia 2
Department of Applied Chemistry, Chubu University, Kasugai, Aichi 387-8501, Japan
*: Corresponding author, Tel: +61 3-9905 2592, Email:
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Abstract Pulverized coal injection (PCI) is a widely used blast furnace technology aimed at reducing costs and increasing productivity. The prospect of blending PCI coal with a lower cost char, derived from Yallourn brown coal, is evaluated in this study by means of thermogravimetric analysis (TGA), flat flame burner reactor and drop tube furnace experiments at four different blending ratios as well as CFD modelling. Yallourn char has desirable properties compared to PCI coal including a lower ash content and a higher heating value, although the reactivity is lower and ignition temperature is higher. Since the combustion behaviour of a blend is not always easily predicable based on the performance of the individual parent fuels, two Yallourn char samples (YC-1 and YC-2) are analysed after blending with PCI coal at four ratios. According to particle ignition time, a maximum 40 wt% is allowable for YC-1 char which is comparably reactive with the commercial PCI coal. However, a maximum 20 wt% is only allowed for YC-2 which is less reactive. The negative heat sink effect of YC-2 char is influential, whereas the heterogeneous ignition of YC -1 overlapped considerably with the ignition of PCI coal which is mainly in the homogeneous gas phase. In addition, it was found that the later char oxidation rate was accelerated greatly for the PCI coal blended with YC-1, irrespective of its blending ratio. In contrast, the heat sink effect is further obvious for the YC-2, the increase on the blending ratio of which greatly decreased the overall burnout rate, especially at low furnace temperatures (800°C and 900°C) and a shorter residence time such as 0.8 s. For YC-1 char, its blending ratio is insignificant in the overall burnout. Increasing the furnace temperature to 1000°C and the O2/C ratio of 1.2 can assist in achieving a nearly complete burnout for all of its blends, even at a short residence time of 0.8 s. In contrast, for YC-2 char, a furnace temperature of 1200°C and O2/C ratio of 1.2 are essential to complete the burnout of all its blends. The Yallourn pyrolysis conditions for the preparation of its char is critical. A good synergistic interaction between Yallourn char and commercial PCI in terms of reactivity is also essential for a broad blending ratio to be used in the blast furnace.
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Keywords: Pulverised coal injection, blending, Yallourn pyrolysis char, blast furnace
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1. Introduction Currently, 70% of iron production for steelmaking is attained through smelting iron ore by reduction with a carbon source (coke/coal) in a blast furnace 1. To reduce the consumption of expensive coke and increase productivity, the pulverised coal injection (PCI) method is used to replace a portion of the coke used in the blast furnace 2. This has been implemented in nearly all blast furnaces in China, Japan, Korea and Taiwan and over half of those in North America, South America and Europe3. As a result of this, the demand for coal suitable for PCI has been increasing steadily 4.
Victorian brown coal (VBC) contains a relatively high amount of moisture and has a low ash yield. It is predominantly used for electricity generation at local power plants where it is inefficient and very carbon intensive 5. One of the promising applications for VBC is as a substitute for bituminous coals used in PCI in a blast furnace. Unprocessed Brown coal is not suitable for blast furnace applications due to its high moisture content and low calorific value. Through a mild pyrolysis process, VBC could be upgraded to a higher value char which is produced alongside other derivatives, coal gas and coal tar 6. The VBC char could then be injected via the PCI method as a complete replacement for the commercial PCI coal or as a blend.
A previous study has confirmed the viability of a complete replacement of commercial PCI coal with two chars derived from Yallourn brown coal 7, 8. The char replacement has both advantages
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and disadvantages compared to the PCI coal. Yallourn char has a lower cost than the PCI coal and contains a higher calorific value, meaning it can replace a greater portion of coke. It also has lower ash (
