The impact of chlorine on chromium speciation in a laminar diffusion flame

Guo, Bing; Kennedy, Ian M.

doi:10.1016/s0010-2180(01)00270-x

Cited by 8 publications

(5 citation statements)

References 14 publications

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“…In contrast, the reduction on the retention of Cr with HCl addition to flue gas indicates the promoting effect of HCl on the vaporization of Cr via chlorination. The resulting Cr vapor can be Cr(VI) with a formula of CrO 2 Cl 2 , as has been confirmed by thermodynamic equilibrium modeling 19,20 or Cr(III) chloride in a form of CrCl 3 , which has a lower boiling point than the corresponding oxides. For both gas species, they mostly escaped the collection system as fugitive species rather than condensing into solid ash particles.…”

Section: Environmental Science and Technologymentioning

confidence: 57%

“…Two impurity gases including HCl of 250 ppmV and SO 2 of 1000 ppmV were also dosed individually into the O 2 /CO 2 mixture. The brown coal tested here is not chlorine-free, containing water-soluble NaCl in its bed moisture , The accumulation of HCl with flue gas recirculation is thus expected to promote the vaporization of Cr as a Cr(VI)-bearing gaseous species such as CrO 2 Cl 2 . , Besides that, two solid additives at a mass percentage of 0.2 wt %, including Na 2 SO 4 and CaO were physically added to the Cr-doped coal to examine their potential on scavenging Cr vapors. The exit O 2 content remains approximately 10% to ensure a completion burnout of coal in DTF.…”

Section: Methodsmentioning

confidence: 99%

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Use of Synchrotron XANES and Cr-Doped Coal to Further Confirm the Vaporization of Organically Bound Cr and the Formation of Chromium(VI) During Coal Oxy-Fuel Combustion

Chen

Jiao

Zhang

et al. 2012

Environ. Sci. Technol.

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Through the use of synchrotron XANES and Cr-doped brown coal, extensive efforts have been made to clarify the volatility of organically bound Cr during oxy-fuel combustion and the mode of occurrence and leachability of Cr in resulting fly ashes. As the continuation of our previous study using raw coal, the Cr-doped coal has been tested in this study to improve the signal-to-noise ratio for Cr K-edge XANES spectra, and hence the accuracy for Cr(VI) quantification. As has been confirmed, the abundant CO(2) as a balance gas for oxy-firing has the potential to inhibit the decomposition of organically bound Cr, thereby favoring its retention in solid ash. It also has the potential to promote the oxidation of Cr(III) to Cr(VI) to a minor extent. Increasing the oxygen partial pressure, particularly in the coexistence of HCl in flue gas, favored the oxidation of Cr(III) into gaseous Cr(VI)-bearing species such as CrO(2)Cl(2). Regarding the solid impurities including Na(2)SO(4) and CaO, Na(2)SO(4) has proven to preferentially capture the Cr(III)-bearing species at a low furnace temperature such as 600 °C. Its promoting effect on the oxidation of Cr(III) to Cr(VI), although thermodynamically available at the temperatures examined here, is negligible in a lab-scale drop tube furnace (DTF), where the particle residence time is extremely short. In contrast, CaO has proven facilitating the capture of Cr(VI)-bearing species particularly oxychloride vapors at 1000 °C, forming Ca chromate with the formulas of CaCrO(4) and Ca(3)(CrO(4))(2) via a direction stabilization of Cr(VI) oxychloride vapor by CaO particle or an indirect oxidation of Cr(III) via the initial formation of Ca chromite. The fly ash collected from the combustion of Cr-doped coal alone has a lower water solubility (i.e., 58.7%) for its Cr(VI) species, due to the formation of Ba/Pb chromate and/or the incorporation of Cr(VI) vapor into a slagging phase which is water-insoluble. Adding CaO to coal increased the water-solubility of both Cr(VI) and Cr(III) by forming Ca chromite and chromate, respectively.

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Section: Environmental Science and Technologymentioning

confidence: 57%

Section: Methodsmentioning

confidence: 99%

Use of Synchrotron XANES and Cr-Doped Coal to Further Confirm the Vaporization of Organically Bound Cr and the Formation of Chromium(VI) During Coal Oxy-Fuel Combustion

Chen

Jiao

Zhang

et al. 2012

Environ. Sci. Technol.

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“…As shown in Figure , different with the increase of Cr retention by H 2 O, doping HCl to flue gas significantly reduced Cr retention from 31% for the oxy-8%H 2 O case to 17.5% for oxy-8%H 2 O-500ppmHCl in coarse ash. The presence of HCl in flue gas favored the formation of gaseous Cr species consisting primarily of CrO x Cl y such as CrO 2 Cl 2 , and some CrCl 3 , which have a lower boiling point and a lower reaction rate with minerals than the corresponding oxide/hydroxide. These Cr gaseous species mostly escaped the collection system as fugitive species rather than condensing into solid ash particles.…”

Section: Results and Discussionmentioning

confidence: 99%

Transformation of Organically Bound Chromium during Oxy-coal Combustion: The Influence of Steam and Mineral

Dong

Chen

et al. 2018

Energy Fuels

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The influence of steam and minerals on Cr transformation during oxy-coal combustion has been examined in a drop tube furnace at 1273 K. An extra 500 ppmv HCl and 1000 ppmv SO2 were also added to flue gas to examine the competition of H2O, HCl, and SO2 on Cr behaviors during oxy-coal combustion upon the recirculation of impurities in flue gas. It was found that CaO and Fe2O3 exhibited high capability on capturing Cr-bearing vapors during combustion compared to limestone and kaolin. Changing air to oxy-coal combustion obviously weakened the role of CaO, whereas it promoted reaction between Fe2O3 and Cr vapors. The existence of H2O in flue gas facilitated the oxidation of trivalent Cr(III) to high valence Cr vapors in a short second time scale. CaO, particularly in the coexistence of H2O during coal combustion, remarkably enhanced the toxic Cr(VI) fraction in solid ash. H2O affected the behavior of minerals reacted with Cr. CaO was inhibited and Fe2O3 was enhanced by steam to react with Cr during oxy-coal combustion. The retention of Cr in ash reduced with a H2O increase from 5% to 20% during oxy-coal combustion. HCl significantly promoted the release of Cr through chlorination reaction. The presence of H2O offset the negative effect of HCl on Cr recovery when H2O was coexistent with HCl in flue gas. SO2 favored the retention of Cr via sulfation reaction to form Cr2(SO4)3 condensed into solid ash. Moreover, it was found that Cr vapors preferred to react with HCl than SO2 during combustion.

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“…17 Nevertheless, the possible presence or lack thereof of vapor-phase Cr(VI) was resolved by sampling using a modified California U.S. Environmental Protection Agency (CalEPA) method 425 impinger train. 18 Vapors were drawn through the impinger train after the airstream was passed through the high-efficiency glass fibers on the enclosure exhaust and through another glass fiber filter holder immediately ahead of the impingers.…”

Section: Resultsmentioning

confidence: 99%