Exposure of tubular ceramic heat exchanger materials to refractory coal ash from coal-oil-mixture combustion
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
- Resource Relation:
- Other Information: Portions are illegible in microfiche products. Original copy available until stock is exhausted
- Country of Publication:
- United States
- Language:
- English
Similar Records
Behavior of tubular ceramic heat exchanger materials in acidic coal ash from coal-oil-mixture combustion
Evaluation of tubular ceramic heat exchanger materials in acidic coal ash from coal-oil-mixture combustion. [Sialon; alumina; CVD, sintered, and siliconized SiC]
Related Subjects
42 ENGINEERING
ALUMINIUM OXIDES
COMPATIBILITY
HEAT EXCHANGERS
MATERIALS TESTING
SILICON CARBIDES
ASHES
COAL
COMBUSTION PRODUCTS
FRACTURE PROPERTIES
FUEL OILS
FUEL SLURRIES
PERMEABILITY
VERY HIGH TEMPERATURE
ALUMINIUM COMPOUNDS
CARBIDES
CARBON COMPOUNDS
CARBONACEOUS MATERIALS
CHALCOGENIDES
DISPERSIONS
ENERGY SOURCES
FOSSIL FUELS
FUELS
LIQUID FUELS
MATERIALS
MECHANICAL PROPERTIES
MIXTURES
OILS
ORGANIC COMPOUNDS
OTHER ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PETROLEUM PRODUCTS
RESIDUES
SILICON COMPOUNDS
SLURRIES
SUSPENSIONS
TESTING
360205* - Ceramics
Cermets
& Refractories- Corrosion & Erosion
421000 - Engineering- Combustion Systems