Particle characteristics of anthracite powder preheated quickly in circulating fluidized bed

Experimental studies were carried out on a bench-scale rig of pulverized anthracite combustion preheated by circulating fluidized bed (CFB). The preheated anthracites were sampled at the outlet of CFB and the effect of preheating temperature on particle characteristics was investigated. The particle size distribution of preheated anthracite powder was tested by a Malvern Mastersizer 2000 laser analyzer. The specific surface area, pore volume and pore diameter were analyzed by nitrogen absorption method. Scanning electron microscope (SEM) was used for a better observation on particle surface. It is found that when the preheat temperature is 900°C, the 50% cut size (d₅₀) of the anthracite before and after being preheated decrease from 82 μm to 23 μm. For the preheated fuel, the pores in micro-size with the diameter smaller than 2 nm and meso-size with the diameter ranging from 2 nm to 10 nm are major contributors for the overall specific surface area and pore volume. Furthermore, variations of specific surface area and pore volume versus preheating temperature can be divided into two regions: below 900°C and above 900°C. In the first region, the specific surface area and pore volume increase as the preheating temperature increases, while in the second region they decrease with the increase in the preheating temperature. Based on the SEM analysis, after being preheated, a lot of cracks and pores appear on the particle surface, and the pore structure is well developed.