Grantee Research Project Results
1997 Progress Report: Optimization of In-Situ Capture by Sorbents of Toxic Metals in Combustion Processes
EPA Grant Number: R825389Title: Optimization of In-Situ Capture by Sorbents of Toxic Metals in Combustion Processes
Investigators: Wendt, Jost O.L.
Institution: University of Arizona
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 1999
Project Period Covered by this Report: October 1, 1996 through September 30, 1997
Project Amount: $293,068
RFA: Exploratory Research - Air Engineering (1996) RFA Text | Recipients Lists
Research Category: Land and Waste Management , Air , Safer Chemicals
Objective:
The overall objective of this research is to develop quantitative models able to predict how sorbents and toxic metals interact at high combustion temperatures and to determine optimum sorbent composition for the most effective and efficient removal of multiple toxic metals (multimetals) with and without the presence of chlorine and sulfur.Progress Summary:
Progress this past year included designing and constructing a new baghouse, upgrading the sorbent particle feed system, incorporating data acquisition and control systems to increase system integration of all apparatus involved in furnace operations, control, and sample collection, and purchasing a graphite furnace AA, which will greatly enhance the resolution on our sample analysis.
Initial multi-metal tests were also carried out this year. Sorbent was not injected in these experiments. The purpose of these experiments was to gain insight into the competition between metal condensation and aerosol coagulation processes that affect the partitioning of toxic heavy metals during combustion. Experiments were conducted on a 12-16 kW downflow furnace, which supported a natural gas flame through which sprays of aqueous solutions of metal salts were injected. The behavior of both single metals and binary mixtures of lead and cadmium (both semi-volatile) and of cadmium and nickel (the latter of which is refractory) was investigated. Particulate samples were withdrawn isokinetically through a rapid-dilution sampling probe from which they were quickly size segregated in a Berner low pressure impactor, allowing physical and chemical resolution in the submicron particle size range.
Experimental data agreed with theoretical predictions using an existing literature model. This model solved the General Dynamic Equation numerically, but was modified here to include the effects of film condensation in a simple manner. For samples withdrawn above the semi-volatile metal dew points, theory showed that nucleation of the semi-volatile metals in the probe, followed by coagulation, could explain completely, the measured size segregated composition. With similar dew points and number concentrations, cadmium and lead particles interacted primarily through coagulation. However, cadmium and nickel partilces did not interact by coagulation in the probe because of disparities in particle size and number concentrations. Both model and data showed that the composition of particles from the Ni/Cd system was the result of condensation of cadmium on existing nickel particles, rather than by nucleation of the semi-volatile component (cadmium), followed by coagulation
Accomplishments And Research Results
Facility Upgrade
Sorbent Feeder: FeederA K-TRON screw feeder was purchased, which will allow kaolinite or similar sorbent material (powders with density in the range of 30-45 lb/ft3) to be fed anywhere from 0.5 to 5.0 g/min accurately and steadily without constant supervision. In addition, a new pneumatic transport system was designed and built to work with this feeder to provide the best possible feed stability. This new feeder increases our confidence in the measurable feedrate of clay sorbents by several orders of magnitude.
Graphite Furnace AA: A Perkin-Elmer graphite furnace atomic absorption (AA) spectrometer has been purchased, which has an order of magnitude greater resolution than the flame ionization AA. Increased resolution from atomic absorption analysis will translate into more accurate mass balance and kinetic information. In addition, it will allow lower concentrations of metals in the furnace to be sampled and analyzed, which are more indicative of conditions in some combustion environments.
New Baghouse: Due to deficiencies in our previous baghouse, a new baghouse was designed and constructed. The new design features a much improved pulse system design for bag cleaning and bags that are hung vertically, instead of supported horizontally.
Automation: Integration of instruments and controls via data acquisition has made a vast imporvement in the operation of the downflow furnace and associated systems.
Research Results
Elucidation of the partitioning of multiple semi-volatile metals in a downflow combustor was accomplished. In addition, multi-component coagulation and condensation of toxic metals in combustors was investigated. As a result, the competition between metal condensation and aerosol coagulation processes that affect the partitioning of toxic heavy metals during combustion are better understood.
Confirmation was obtained of both experimental observations (Scotto, M., Bassham, E.A., Wendt J.O.L., and Peterson, T.W., Twenty-second Symposium (Intern.) on Combustion, The Combustion Institute, Pittsburgh, Pa. 1988, 239-247.) on the effect of combustor cooling on the particle size distribution (PSD) of sodium from pulverized coal combustion and the theoretical prediction (McNallan, M.J., Yurek, G.J., and Elliott, J.F., Combust. Flame, 42, 1981, 45-60.) that at temperature quench rates less than 600 K/s, film condensation dominates.
Future Activities:
1. Single metal/sorbent experiments will be performed to determine the capture potential of individual metals by various sorbents.
2. Multi-metal/sorbent experiments will also be performed to investigate the interactions (competition/inhibition) between metals in sorbent capture.
3. Multi-metal experiments with various sorbent mixtures will also be performed.
4. Screening and parametric tests will be performed to determine the affinity of metals for capture by sorbents and the effect of temperature, residence time, sorbent compositiion, sorbent particle size, and metal concentration in the furnace on metal capture.
5. In-depth particle analysis will take place this year to determine the structure, compositon, and morphology of sorbent/metal product particles collected from the furnace. Ultimately, the mechanisms of capture will be determined.
6. A procedure for running experiments in the furnace at low metal concentrations will be developed.
Journal Articles:
No journal articles submitted with this report: View all 10 publications for this projectSupplemental Keywords:
RFA, Scientific Discipline, Air, Waste, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Ecology, Mathematics, Environmental Chemistry, Fate & Transport, Incineration/Combustion, Engineering, Engineering, Chemistry, & Physics, fate and transport, fate, particulates, quantitative models, atmospheric particles, Chlorine, toxic metals, sulfur, combustion process, chemical kinetics, kinetic models, sorbents, combustionProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.