Exposure of tubular ceramic heat exchanger materials to refractory coal ash from coal-oil-mixture combustion

Technical Report · Sat Sep 01 04:00:00 EDT 1984

OSTI ID:6458348

Ferber, M K; Tennery, V J; Willmering, J F

Tubes of six structural ceramic materials were exposed to hot combustion gases from a coal-oil-mixture fuel. The coal ash had an extremely low base-to-acid ratio (<0.10) and an ash fusion temperature of at least 1400/sup 0/C. Although a nonsticking refractory ash was expected, severe fouling was encountered throughout the exposure. This experiment (designated Ceramic Recuperator Analysis Facility Test 4) operated 460 h, including 234 h at the maximum temperature of 1300/sup 0/C. In addition, several extreme temperature cycles were experienced because of combustion instability, which was apparently related to coal ash fouling. The ceramics examined included a high-purity alumina, an Si/sub 3/N/sub 4/-bonded SiC, a dense single-phase SiC, and three types of siliconized SiC. All tubes except the Si/sub 3/N/sub 4/-bonded SiC and Al/sub 2/O/sub 3/ survived without failure. Insufficient thermal shock resistance was apparently responsible for the severe cracking in these two materials. As-received and exposed materials and solidified coal slag were analyzed. In general, reactions between the coal slag and ceramic tubes were limited. We found no aggravated corrosion like that observed previously with a basic coal slag. This lack of reactivity was probably due to the highly refractory (viscous) nature of the slag. Mullite was the typical phase observed in the oxide slag matrix glass found on the tubes after the exposure. Other minor crystalline phases were present, in some cases. Several important properties, including room-temperature helium permeability and room-temperature C-ring fracture strength, were measured for both as-received and exposed specimens. No major changes in permeability were found. This was also true of the C-ring-strength for all materials examined except the Si/sub 3/N/sub 4/-bonded SiC. The strength of this material increased slightly in response to a flaw healing process facilitated by the coal slag.

• Research Organization: Oak Ridge National Lab., TN (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6458348
• Report Number(s): ORNL/TM-9052; ON: DE84017290
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360205* -- Ceramics
Cermets
&amp; Refractories-- Corrosion &amp; Erosion
42 ENGINEERING
421000 -- Engineering-- Combustion Systems
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ASHES
CARBIDES
CARBON COMPOUNDS
CARBONACEOUS MATERIALS
CHALCOGENIDES
COAL
COMBUSTION PRODUCTS
COMPATIBILITY
DISPERSIONS
ENERGY SOURCES
FOSSIL FUELS
FRACTURE PROPERTIES
FUEL OILS
FUEL SLURRIES
FUELS
HEAT EXCHANGERS
LIQUID FUELS
MATERIALS
MATERIALS TESTING
MECHANICAL PROPERTIES
MIXTURES
OILS
ORGANIC COMPOUNDS
OTHER ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PERMEABILITY
PETROLEUM PRODUCTS
RESIDUES
SILICON CARBIDES
SILICON COMPOUNDS
SLURRIES
SUSPENSIONS
TESTING
VERY HIGH TEMPERATURE