Particle size-dependent properties of a char produced using a moving-bed pyrolyzer for fueling pulverized coal injection and sintering operations

Abstract

Pyrolytic chars are a potential high-quality fuel for use in iron ore sintering and pulverized coal injection (PCI) operations of blast furnace. In this study, industrial char produced from a moving-bed pyrolyzer was screened into four particle size ranges and compared with coke used in an industrial sintering process and a PCI coal used in an industrial blast furnace, and their basic compositions, micropore structures, functional group distributions, carbonaceous structures, reactivities, and gas release behaviors during combustion were analyzed. Furthermore, the mechanism underlying the particle size-dependent properties of the char was analyzed by comparing it with a char prepared under laboratory-simulation conditions. Results demonstrate that char particles larger and smaller than 3 mm (the turning point) have different structures and properties. More specifically, particles larger than 3 mm have stable properties, better developed pore structures, carbonaceous structures that are more ordered, superior reactivities, and lower releases of SO2 and NOx. Therefore, they represent a desirable option for use in fueling sintering and PCI operations. Char particles smaller than 3 mm were further investigated by screening them into particle size ranges, and results showed that they had significantly varied compositions and structures, which further confirmed their unsuitability for use in the two operations. Finally, the particle-size-dependent properties of the char can be explained by the differing residence times, the radial variations in pyrolysis degrees, and the mechanical (or thermal) stresses experienced by the different raw coal particles within the pyrolyzer.