Ash fouling and erosion of silicon-based ceramic expanders in coal-fired power plants

Technical Report · Thu Jan 26 04:00:00 EST 1978

OSTI ID:5190796

Taylor, R W; Shell, T E

Lysholm-type helical-screw engines (expanders) are proposed as a means of generating electrical power from coal-fired power plants (topping cycle). Ash erosion and deposition (fouling) of silicon-based ceramic materials exposed to coal ash at topping-cycle temperatures (approximately 1270 K) was studied at the Lawrence Livermore Laboratory to select suitable expander materials. Silicon carbide (SiC) or silicon nitride (Si/sub 3/N/sub 4/) blocks exposed to an ash-injected flame at 1270/sup 0/K fouled; however, fouling was prevented when blocks or wheels of the material were rubbed or spun against each other, simulating expander rotors. The sliding friction coefficient between contacting SiC or Si/sub 3/N/sub 4/ surfaces was 0.5 at room temperature, increased to 0.9 at 1270/sup 0/K, but returned to approximately 0.5 when hot, soft ash was injected between the surfaces. When rubbed together, blocks of SiC wore 9.5 mg/h at topping temperatures, 25 times greater than at room temperature. Increase in wear with temperature likely occurs because the SiC surface oxidizes to soft and easily worn silicon oxide. The cooler, harder ash downstream of the expander outlet could erode plant boiler parts. In our tests, high-speed, hard fly ash particles eroded Si/sub 3/N/sub 4/ blocks at 0.2 to 1 mg per g ash at room temperature. This erosion rate is expected to decrease significantly with increasing temperature, particularly above the ash-softening temperature, 870/sup 0/K. Relative to other ceramics and metals, SiC and Si/sub 3/N/sub 4/ are resistant to high temperatures, ash erosion, and fouling under simulated expander conditions and would be equally suitable materials for a topping-cycle Lysholm-type engine.

• Research Organization: California Univ., Livermore (USA). Lawrence Livermore Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5190796
• Report Number(s): UCRL-52390
• Country of Publication: United States
• Language: English

Related Subjects

20 FOSSIL-FUELED POWER PLANTS
200104* -- Fossil-Fueled Power Plants-- Components
36 MATERIALS SCIENCE
360205 -- Ceramics
Cermets
& Refractories-- Corrosion & Erosion
ABRASION
AEROSOL WASTES
CARBIDES
CARBON COMPOUNDS
CARBONACEOUS MATERIALS
CERAMICS
CHEMICAL REACTIONS
COAL
COMBUSTION PRODUCTS
ENERGY SOURCES
EROSION
FLY ASH
FOSSIL FUELS
FOSSIL-FUEL POWER PLANTS
FUELS
GAS TURBINES
NITRIDES
NITROGEN COMPOUNDS
OXIDATION
PNICTIDES
POWER PLANTS
SILICON CARBIDES
SILICON COMPOUNDS
SILICON NITRIDES
TEMPERATURE DEPENDENCE
THERMAL POWER PLANTS
TOPPING CYCLES
TURBINES
TURBOMACHINERY
VERY HIGH TEMPERATURE
WASTES
WEAR