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PARTITIONING OF THE REFRACTORY METALS, NICKEL AND CHROMIUM, IN COMBUSTION SYSTEMS
Citation:
Linak*, W P. AND J. Wendt. PARTITIONING OF THE REFRACTORY METALS, NICKEL AND CHROMIUM, IN COMBUSTION SYSTEMS. COMBUSTION SCIENCE AND TECHNOLOGY 134(1-6):291-314, (1998).
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The partitioning of nickel (Ni) and Chromium (Cr) in combustion systems was investigated theoretically and experimentally. In comparison to other volatile and semi-volatile metals, both Ni and Cr are usually considered to be refractory (non-volatile). Theoretical predictions based on chemical equilibrium confirmed that Ni and Cr (trivalent and hexavalent) remained non-volatile under baseline combustion conditions. Chlorine, however, was predicted to notably increase the volatility of Ni at high temperatures due to formation of volatile Ni-chloride compounds. Chlorine's predicted effect on Cr volatility at high temperatures was minimal, although some volatile Cr-chloride compounds were predicted at low temperatures.
Experimental studies employed a 59 kW laboratory scale combustor with a swirling natural gas diffusion flame through which aqueous Ni and Cr solutions were sprayed. Particle size distributions (PSDs) were measured by three different techniques: electrical mobility and inertial impaction for sampled aerosols and light scattering for in-situ in-stack analysis. All three methods produced consistent PSDs. Experimental data for Ni were also consistent with the theoretical predictions and confirmed the large increase in Ni volatility due to chlorine. Also consistent with equilibria, data for Cr (trivalent and hexavalent) did not indicate notable increases in volatility due to chlorine addition. However, introducing hexavalent Cr [Cr(VI)] in the feed produced smaller Cr particles in the exhaust than did trivalent Cr [Cr(III)]. Experimental evidence suggests that, contrary to equilibrium predictions, Cr(VI) vaporized in the flame while Cr(III) did not. This result, however, may not be related to the initial Cr valency but, rather, due to the particular choice of Cr(III) [Cr(NO3)3(III)] and Cr(VI) [CrO3(VI)] species examined. Speciation of Cr in the exhaust, however, was independent of the initial Cr valency, with exhaust values of Cr(VI) typicall
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