Investigations on the Composition of Individual Fly Ash and CFB-Ash Particles
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INVESTIGATIONS ON THE COMPOSITION OF INDIVIDUAL FLY ASH AND CFB-ASH PARTICLES I. ODLER and K.-H. ZYSK Technical University Clausthal, Institute of Nonmetallic Minerals, Zehntnerstrale 2A, D-3392 Clausthal-Zellerfeld, Federal Republic of Germany Received October27, 1988; refereed
ABSTRACT The individual particle compositions of three circulating fluidized bed combustion (CFB) ashes and one Type C fly ash were studied to determine differences in composition existing between the individual particles within a single ash. The methods used for the investigation included optical microscopy, XRD and XRF analysis. It was found that all the ashes studied consisted of several types of particles that differed in morphology, color and composition. INTRODUCTION It is known that the composition of individual particles in industrial ashes may vary from particle to particle [1,2]. Thus, the actual composition of such particles may differ from that found in a bulk ash sample. The aim of the present work was to study quantitatively the variations in the composition of the individual particles within a single ash. The work was done on one Type C fly ash and three ashes produced in circulating fluidized bed combustion units (CFB-ashes). These ashes were selected as they contained both a large proportion of crystalline phases and a substantial fraction of larger particles, making them better suited for investigation. EXPERIMENTAL
METHODS AND RESULTS Materials The CFB ashes (i.e. samples 1, 2 and 3) are identical to those of similar sample notations described in our, previous papers [3]. Sample 4 was a high lime fly ash which was not among the samples studied in the past. The present studies were performed on particles in the size range 500700 gtm which were separated by sieving. This size range of particles was selected as representing the smallest that could be studied by X-ray diffraction. Optical Microscopy Optical microscopy revealed the presence of variable color and morphology in the particles. The nature of the fraction as well as the average weight of the particles constituting each fraction are listed in Tables I-IV. It appeared that besides variations in coloration, the fractions differed also in particle morphology. In most instances, the particles appeared to be aggregates of crystalline phases. Some fractions, however, consisted of glassy particles or particles of residual coal. Spherical particles were not found in these samples. X-Ray Diffraction The following approach was employed to determine the phase composition of individual particles. The particle to be studied was first ground in a small agate mortar; the ground material was then transferred to a sample holder which consisted of a thin plate cut out of a silicon monocrystal. Using this approach, amounts of material down to -0.1 mg could be analyzed.
Mat. Res. Soc. Symp. Proc. Vol. 136. C1989 Materials Research Society
132
Table I Mineralogical Composition
Sample 1'
-
Fraction
White
Pink
Light Brown
Brown
Dark Brown
Grey
Black
Avg. wt. (mg)
0.33
0
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