Fly ashes from the Lansing and Ottumwa power plants in Iowa were agglomerated by means of a continuous pan agglomerator, a continuous auger and a batch turbine agglomerator. In order to compare agglomeration mechanisms the following parameters were determined: (a) particle size distributions of the untreated fly ashes; (b) particle size distributions of the agglomerated fly ashes; (c) pore size distribution of agglomerates; (d) crystalline hydration products by X-ray diffraction; and (e) morphological characterization by scanning electron microscopy.
In the batch system coalescence mechanisms were favoured. The agglomerates were fairly irregular in shape and had a rough surface texture. As residence time in the system increased breakage of agglomerates occurred, reducing the average agglomerate size. In the continuous systems layering of the fine feed particles onto established agglomerates was the predominant growth mechanism. The agglomerates were smooth and spherical. The layer structure was observed by scanning electron microscopy. Agglomerates of widely varying size, strength, and pore matrix can be produced in both systems. It is envisaged that while agglomerates could be produced with characteristics essential for their proposed end use by either method, continuous pan agglomeration would be the most versatile system to utilize.