Surface Morphology and Porosity Evolution of CWS Spheres from a Bench-Scale Fluidized Bed

Fluidization suspension combustion technology is an effective method to utilize coal water slurry (CWS) as fuel in industrial boilers. The evolution of surface morphology and pore structure of CWS spheres under fluidization suspension combustion is studied. A bench-scale fluidized bed was used for combustion of CWS spheres with a bed temperature of 850 degrees C, fluidization number of 4, and bed height of 90 him. After 15, 30, and 45 s of combustion, the samples were removed from the bed for scanning electron microscope (SEM) and N-2 adsorption tests. The combustion mechanism of CWS spheres in the fluidization-suspension combustion state is discussed. The results show that after 15 s, the CWS spheres burst due to volatile release, and some particles fragmented to produce a large number of pores. Thus, the specific surface area and volume of pores increased rapidly. After 30 s, combustion occurred mainly at the exterior surface of CWS spheres and appeared as layer by layer inward combustion. This was confirmed by the fact that the specific surface area and volume did not change. After 45 s, as combustion proceeded, the flame front entered the interior surface through pores, and burnt the interior framework to make the pores collapse. Thus, the specific surface area and volume of pores decreased rapidly. In the whole combustion process, the fractal dimension first increased and then decreased, which demonstrates that the pore structure had experienced a process that went from complicated to simple.