Pilot Demonstration of Technology for the Production of High Value Materials from the Ultra-Fine (PM2.5) Fraction of Coal Combustion Ash
The overall objective of this research was to determine the feasibility of recovering a very fine fraction of fly ash, that is 5 microns in diameter or less and examining the characteristics of these materials in new or at least less traditional applications. These applications included as a polymer filler or as a 'super' pozzolanic concrete additive. As part of the effort the ash from 6 power plants was investigated and characterized. This work included collection from ESP Hoppers and ponds. The ash was thoroughly characterized chemically and physically. Froth flotation was used to reduce the carbon and testing showed that flotation could effectively reduce carbon to acceptable levels (i.e. 0.5% LOI) for most of the substrates tested. in order to enable eventual use as fillers. Hydraulic classification was used in the separation of the fine ash from the coarse ash. Hydraulic classification requires the ash to be dispersed to be effective and a range of dispersants were tested for adsorption as well as sedimentation rate. A wide range of dosages were required (0.3 to 10 g/kg). In general the ponded ash required less dispersant. A model was developed for hydraulic classification. A pilot-scale hydraulic classifier was also designed and operated for the project. Product yields of up to 21% of feed solids were achieved with recoveries of <5 {micro}m particles as high as 64%. Mean particle sizes (D{sub 50}) of the ultra fine ash (UFA) products varied from 3.7 to 10 {micro}m. A patent was filed on the classifier design. A conceptual design of a Process Demonstration Unit (PDU) with a feed rate of 2 tons of raw ash feed per hour was also completed. Pozzolanic activity was determined for the UFA ashes in mortars. In general the overall strength index was excellent with values of 90% achieved in 3 days and {approx}100% in 7 days. Three types of thermoplastic polymers were evaluated with the UFA as a filler: high density polyethylene, thermoplastic elastomer and polyethylene terphthalate filled polymers were prepared and subjected to SEM analysis to verify that the UFA was well dispersed. The addition of fillers increased the modulus of the HDPE composite, but decreased both the offset yield stress and offset yield strain, showing that the fillers essentially made the composite stiffer but the transition to plastic deformation occurred earlier in filled HDPE as stress was applied. Similar results were obtained with TPE, however, the decrease in either stress or strain at offset yield were not as significant. Dynamic mechanical analyses (DMA) were also completed and showed that although there were some alterations in the properties of the HDPE and TPE, the alterations are small, and more importantly, transition temperatures are not altered. The UFA materials were also tested in expanded urethanes, were improvements were made in the composites strength and stiffness, particularly for lighter weight materials. The results of limited flammability and fire safety testing were encouraging. A flowsheet was developed to produce an Ultra-Fine Ash (UFA) product from reclaimed coal-fired utility pond ash. The flowsheet is for an entry level product development scenario and additional production can be accommodated by increasing operating hours and/or installing replicate circuits. Unit process design was based on experimental results obtained throughout the project and cost estimates were derived from single vendor quotes. The installation cost of this plant is estimated to be $2.1M.
- Research Organization:
- Univ. of Kentucky, Lexington, KY (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-03NT41726
- OSTI ID:
- 949201
- Country of Publication:
- United States
- Language:
- English
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