Ignitability and Combustibility of Yallourn Pyrolysis Char Blended with Pulverized Coal Injection Coal under Simulated Blast Furnace Conditions

摘要

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 computational fluid dynamics (CFD) modeling. 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 the ignition temperature is higher. Because the combustion behavior 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 analyzed after blending with PCI coal at four ratios. According to the particle ignition time, a maximum of 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 more obvious for the YC2, the increase on the blending ratio of which greatly decreased the overall burnout rate, especially at low furnace temperatures (800 and 900 degrees 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 02/C ratio to 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 2/C ratio of 1.2 are essential to complete the burnout of all of its blends. The Yallourn pyrolysis conditions for the preparation of its char are 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.