Mechanisms of coal-water mixture combustion in fluidized beds
The goal of this research program was to ascertain the fundamental mechanisms of coal combustion and limestone utilization when firing coal water-limestone mixtures (CWLM) in fluidized beds. Experiments were performed in an 8-inch diameter bubbling fluidized bed combustor. The combustor was equipped for firing wither CWM or dry coal. Experiments were designed to answer questions about combustion efficiency and limestone utilization for CWM compared to dry coal. We observed that coal-water-mixtures generally burn with higher combustion efficiency than crushed coal. Although water vapor released from CWM can react directly with char, this reaction is negligibly slow at FBC temperatures compared to the char-oxygen reaction. A physical, rather than chemical, mechanism appears to active. Our experiments demonstrated that differences in combustion efficiency cannot be attributed to fundamentally different carbon elutriation mechanisms. The fact that CWM burns with higher combustion efficiency than dry coal simply reflects the fact that char-sand agglomerates formed from CWM injected into a fluidized bed are generally larger than dry coal particles fed into a bed. Calcination and sulfation tests showed that CWLM and dry coal have optimum bed temperature for sorbent utilization when burning CWLM is lower than for dry sorbent. Furthermore, the optimal sorbent utilization is higher for CWLM compared to dry sorbent. We excluded the possibility that local reducing or gasification conditions are responsible for higher sulfur retention obtained with CWLM. We conclude that intimate contact of coal and limestone in agglomerates is the primary reason for improved sorbent utilization. 42 refs., 24 figs., 9 tabs.
- Research Organization:
- Iowa State Univ. of Science and Technology, Ames, IA (USA)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (USA)
- DOE Contract Number:
- FG22-87PC79915
- OSTI ID:
- 6247976
- Report Number(s):
- DOE/PC/79915-T12; ON: DE91008417
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COAL
FLUIDIZED-BED COMBUSTION
FUEL SLURRIES
SULFUR DIOXIDE
SORPTION
AIR POLLUTION CONTROL
CALCINATION
COMPARATIVE EVALUATIONS
EFFICIENCY
FRAGMENTATION
LIMESTONE
PARTICLE SIZE
PROGRESS REPORT
SULFATES
WATER
WATER VAPOR
CARBONACEOUS MATERIALS
CARBONATE ROCKS
CHALCOGENIDES
CHEMICAL REACTIONS
COMBUSTION
CONTROL
DECOMPOSITION
DISPERSIONS
DOCUMENT TYPES
ENERGY SOURCES
FLUIDS
FOSSIL FUELS
FUELS
GASES
HYDROGEN COMPOUNDS
MATERIALS
MIXTURES
OXIDATION
OXIDES
OXYGEN COMPOUNDS
POLLUTION CONTROL
PYROLYSIS
ROCKS
SEDIMENTARY ROCKS
SIZE
SLURRIES
SULFUR COMPOUNDS
SULFUR OXIDES
SUSPENSIONS
THERMOCHEMICAL PROCESSES
VAPORS
014000* - Coal
Lignite
& Peat- Combustion