Alkali-induced agglomeration of aluminosilicate particles during coal combustion and gasification
This study focuses on the effect of alkali adsorption on the agglomeration of particles of bauxite, kaolinite, emathlite, lime, and two types of coal ash. An agglomeration (adhesion) temperature is defined which characterizes the adhesion propensity of particles. Using a small fluidized bed, a unique experimental technique is developed to measure this agglomeration point in-situ. The effects of alkali adsorption on the agglomeration characteristics of the substrates are determined. The agglomeration temperature of all substrates decreases as the alkali content increases. At low alkali loadings, alkali adsorption enhances particle agglomeration by forming new compounds of lower melting points. At high alkali concentrations, adhesion and agglomeration are caused by a layer of molten alkali which covers the exterior of the particles. Alkali surface composition of particles is studied using a Scanning Auger Microprobe (SAM). Results indicate that the alkali surface concentration decreases as agglomeration temperature increases. The use of additives to scavenge alkali vapors is further studied in a pilot scale downflow combustor under more typical combustion conditions. SAM surface analyses of additive particles indicate three mechanisms of alkali capture: alkali adsorption by reaction, alkali surface condensation, and alkali nucleation and coagulation with additive particles. Modeling results indicate that the absorption-reaction process is influenced by diffusion of alkali through the surface product layer. The model predictions of the alkali absorbed as a function of minimum agglomeration temperature agree very well with the experimental results. Alkali-additive interactions in a downflow combustor are also modeled to predict the mechanism of alkali capture and the overall alkali removal efficiency. Model predictions of the alkali capture agree well with the experimental results.
- Research Organization:
- Arizona Univ., Tucson, AZ (United States)
- OSTI ID:
- 6096332
- Resource Relation:
- Other Information: Thesis (Ph.D)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM OXIDES
AGGLOMERATION
SORPTIVE PROPERTIES
ASHES
BAUXITE
CALCIUM OXIDES
COAL
COMBUSTION KINETICS
COAL GASIFICATION
CHEMICAL REACTION KINETICS
KAOLINITE
SILICON OXIDES
ADDITIVES
ADHESION
ADSORPTION
ALKALI METALS
AUGER ELECTRON SPECTROSCOPY
COMBUSTORS
DESIGN
DIFFUSION
ELECTRON MICROPROBE ANALYSIS
FLUIDIZED BEDS
MATHEMATICAL MODELS
MELTING POINTS
NUCLEATION
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
VAPOR CONDENSATION
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM ORES
ALUMINIUM SILICATES
CALCIUM COMPOUNDS
CARBONACEOUS MATERIALS
CHALCOGENIDES
CHEMICAL ANALYSIS
COMBUSTION PRODUCTS
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY SOURCES
FOSSIL FUELS
FUELS
GASIFICATION
KINETICS
MATERIALS
METALS
MICROANALYSIS
MINERALS
NONDESTRUCTIVE ANALYSIS
ORES
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
REACTION KINETICS
RESIDUES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SORPTION
SPECTROSCOPY
THERMOCHEMICAL PROCESSES
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
010800* - Coal
Lignite
& Peat- Waste Management
014000 - Coal
Lignite
& Peat- Combustion
010404 - Coal
Lignite
& Peat- Gasification