Mechanism of surface enrichment and adhesion of coal combustion particulates
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. SAM surface analyses of additive particles indicate three mechanisms of alkali capture. Adsorption by reaction, surface condensation, and nucleation and coagulation with additive particles. These mechanisms may occur independently or simultaneously depending primarily on the alkali vapor concentration and the temperature profile along the combustion furnace. A mathematical model is developed to represent the kinetics and mechanisms of the alkali adsorption and agglomeration process. Modeling results indicate that the adsorption-reaction process is influenced by diffusion of alkali through the surface product layer. The model predictions of the alkali adsorbed as a function of minimum agglomeration temperature agree very well with the experimental results.
- Research Organization:
- Arizona Univ., Tucson, AZ (United States). Dept. of Chemical Engineering
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG22-86PC90505
- OSTI ID:
- 7104653
- Report Number(s):
- DOE/PC/90505-T9; ON: DE92040421
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALKALI METAL COMPOUNDS
ADSORPTION
PARTICULATES
AGGLOMERATION
ADHESION
ASHES
BAUXITE
COAL
COMBUSTION
FLOCCULATION
FLUIDIZED BEDS
FLY ASH
KAOLINITE
MATHEMATICAL MODELS
MELTING POINTS
NUMERICAL DATA
PROGRESS REPORT
TEMPERATURE DEPENDENCE
AEROSOL WASTES
ALUMINIUM COMPOUNDS
ALUMINIUM ORES
ALUMINIUM SILICATES
CARBONACEOUS MATERIALS
CHEMICAL REACTIONS
COMBUSTION PRODUCTS
DATA
DOCUMENT TYPES
ENERGY SOURCES
FOSSIL FUELS
FUELS
INFORMATION
MATERIALS
MINERALS
ORES
OXIDATION
OXYGEN COMPOUNDS
PARTICLES
PHYSICAL PROPERTIES
PRECIPITATION
RESIDUES
SEPARATION PROCESSES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SORPTION
THERMOCHEMICAL PROCESSES
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
WASTES
200202* - Fossil-Fueled Power Plants- Waste Management- Noxious Gas & Particulate Emissions