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Final 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: Shapiro, Paul
Project Period: October 1, 1996 through September 30, 1999
Project Amount: $293,068
RFA: Exploratory Research - Air Engineering (1996)
Research Category: Engineering and Environmental Chemistry
Description:
Objective:The overall objective of this research was to predict, fundamentally, how sorbents and toxic metals interact at high combustion temperatures, and to determine optimum sorbent compositions for the most effective and efficient removal of multiple toxic metals (multi-metals) from high temperature combustion environments.
Summary/Accomplishments (Outputs/Outcomes):A 16 to 18 kW, cylindrical (inside diameter = 15 cm), 6 m high, natural gas-fired laminar, downflow reactor was used to conduct experiments where aqueous metal solutions were injected through the center of a natural gas flame at temperatures well above the metal dew points. Sorbent powders were injected below the flame along the furnace centerline. Metal, sorbent, and metal/sorbent product particles were isokinetically sampled from the exhaust and size segregated using a Berner low pressure impactor. Analysis of these samples included graphite-furnace and flame-ionization atomic absorption, and Field Emission Scanning Electron Microscopy (FE SEM) and Energy-Dispersive Spectroscopy (EDS).
Multi-metal interactions were successfully investigated with a constant temperature/time profile for simplified run sets, using average global reaction rate constants, while FE SEM and EDS were used to study sorbent particle morphological changes due to metal/sorbent interactions. It was found that lead reacts much faster with kaolinite than with hydrated lime, while cadmium reacts much faster with hydrated lime than with kaolinite, and sodium reacts fast with either hydrated lime or kaolinite. In agreement with low temperature bench-top studies, it was found that lead reacts primarily with kaolinite particles containing similar amounts of alumina and silica, cadmium reacts predominantly with particles containing a high concentration of alumina (with or without silica), and sodium reacts equally well with both alumina and silica dominant particles.
It also was found that lead reacts with kaolinite to cause a melt-like restructuring (see Figure 1), which aids lead in the reaction process, and possibly enhances the reaction of kaolinite with metals like cadmium, by renewing kaolinite particle surface active sites. However, sodium and cadmium cause less melt-like restructuring of kaolinite particles than lead (see Figures 2 through 4), which may be a reason why they tend to inhibit lead capture on kaolinite. As shown in Figure 5, cadmium actually inhibits the melt-like restructuring of kaolinite by lead and sodium. However, at high concentrations of lead and sodium, the inhibition of melting by cadmium is completely overcome.
It also was concluded that sorbent mixtures, such as hydrated lime mixed with kaolinite, may be used successfully to optimize the removal of multiple toxic metals from combustion environments. In addition, it was shown that industrial waste products (i.e., CDEM, a product derived from pulp and papermill waste) can be used successfully to remove multiple toxic metals from combustion environments. Municipal, medical, and industrial waste incineration operations may benefit from this technology, as well as other industrial or power generating process plants. Work in these areas continues at the University of Arizona.
Figure 1. An example of lead/kaolinite particles collected on plate 8 of the BLPI (a 50% cut-off diameter of 1.98 mm) after high temperature (~1150oC) reaction in a downflow combustor for a residence time of 0.83 seconds.
No journal articles submitted with this report: View all 12 publications for this project
Supplemental Keywords:air, atmosphere, health effects, toxics, heavy metals, particulates, pollution prevention, chemical engineering, kinetics modeling, atomic absorption, scanning electron microscopy, incineration, power generation. , Ecosystem Protection/Environmental Exposure & Risk, Air, Scientific Discipline, Waste, RFA, Engineering, Chemistry, & Physics, Mathematics, Ecology, Incineration/Combustion, Fate & Transport, particulate matter, Environmental Chemistry, fate, fate and transport, sulfur, quantitative models, combustion, chemical kinetics, particulates, atmospheric particles, combustion process, sorbents, Chlorine, mathematical formulations, kinetic models
Progress and Final Reports:
1997 Progress Report
1998 Progress Report
Original Abstract