Ash and slag characterization

Conference · Wed May 01 04:00:00 EDT 1985

OSTI ID:5637591

Schobert, H H

In the past year, the key accomplishments of this project have been progress toward elucidating the mechanism of formation of melilites during ashing and development of studies of coal ash slag surface tension. Melilites are a family of aluminosilicate minerals of which gehlenite, Ca/sub 2/Al/sub 2/SiO/sub 7/, is a typical member. The importance of melilites is that they seem to be ubiquitous in high-temperature processing of low-rank coals, having been identified in gasification slags, ash deposits on boiler tubes, and ash agglomerates in fluid bed combustion. Our current hypothesis of the mechanism of melilite formation is that the near-simultaneity of two events is crucial. First, thermal cleavage of the carboxylic acid groups in the coal structure frees the alkali or alkaline earth cations which had been associated with these groups. Second, in approximately the same temperature range (and thus at about the same time during ashing) the clay minerals begin to undergo a structural rearrangement caused by thermal expansion and dehydration. Hence sodium or calcium cations become available for reaction just when the clay lattices are opening up and are susceptible to substitution. The cations are able to penetrate the clay lattice, forming substituted structures typical of relatively low-melting aluminosilicates. It is tempting to speculate that sodium and calcium should behave very much alike, since the oxides of both elements are strong bases and the cations have virtually identical radii. However, sodium acetate reacts with kaolinite for form nepheline, NaAlSiO/sub 4/, whereas calcium acetate reacts to form gehlenite. Nepheline and gehlenite have different structures and different melting behaviors.

• Research Organization: North Dakota Univ., Grand Forks (USA). Energy Research Center
• DOE Contract Number: FC21-83FE60181
• OSTI ID: 5637591
• Report Number(s): DOE/FE/60181-149; CONF-850625-1; ON: DE85012822
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010600* -- Coal
Lignite
& Peat-- Properties & Composition
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
ASHES
BROWN COAL
CARBONACEOUS MATERIALS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
CLAYS
COAL
COHERENT SCATTERING
DECOMPOSITION
DIFFRACTION
DRY ASHING
ENERGY SOURCES
FOSSIL FUELS
FUELS
LIGNITE
MATERIALS
MEASURING INSTRUMENTS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PYROLYSIS
RESIDUES
SCATTERING
SILICATES
SILICON COMPOUNDS
SLAGS
SUBBITUMINOUS COAL
SURFACE PROPERTIES
SURFACE TENSION
TEMPERATURE EFFECTS
THERMOCHEMICAL PROCESSES
VISCOSIMETERS
VISCOSITY
X-RAY DIFFRACTION