https://ogma.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:18766 Wed 11 Apr 2018 13:45:38 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:19400 tot), elemental (Hg⁰) and oxidized (Hg) mercury as well as SO₃ concentrations was obtained before and after the combustion rig's baghouse filter for in total 14 air and oxy-fuel experiments with 3 Australian coals. Based on this data, an assessment in respect to Hg oxidation, SO₂/SO₃ conversion and Hg and SO₃ capture on the test rig's filter was performed. The air and the oxy-fuel experiments with different extents of recycle gas cleaning, revealed differences in the Hg and SO₃ formation and capture behavior: the Hg/Hg^tot ratios in the flue gas are higher during oxy-fuel combustion compared to air-firing. This effect is even more pronounced at the filter outlet, after flue gas has passed through the filter ash. In some experiments, even a net oxidation of Hg⁰ entering the filter to Hg was observed. The Hg capture by ash in the baghouse filter has been found to reduce the Hg emissions considerably. However, the Hg capture was altered by the different oxy-fuel recycle configurations, leading to decreased Hg capture efficiencies on the filter for one of the coals. A coal-specific trend of increased SO₂/SO₃ conversion ratios with increased flue gas SO₂ levels was observed that could be related to the ash composition of the three different coals. This and the higher SO₂ concentrations in the flue gas lead to considerably higher SO₃ levels in oxy-fuel combustion with SO₂ recycling. During the experiments, also a considerable capture of SO₃ in the baghouse filter was observed (up to 80% under air- and up to 66% under oxy-fired conditions). A reduction of the SO₃ capture on the filter under oxy-fuel conditions may be related to the higher SO₃ levels in this process.]]> Wed 11 Apr 2018 13:19:47 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:12876 Tue 11 Dec 2018 15:24:20 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:651 5 M), where alpha-MnO2 is formed, and high temperatures (>80degreesC) where beta-MnO2 is formed. The structural variety of gamma-MnO2 in this domain of stability is interpreted in terms of: (i) the fraction of De Wolff defects (P,), which is found to increase as the H2SO4 concentration is decreased and the temperature is increased; (ii) microtwinning (T-w), which despite being less statistically significant, is found to follow a similar trend; (iii) the cation vacancy fraction; (iv) the Mn(III) fraction. Both the latter structural properties decrease as the temperature is increased; but decreasing the H2SO4 concentration leads to a decrease in cation vacancy fraction and an increase in Mn(III) fraction. These structural characteristics, in particular the De Wolff defects, are interpreted on a molecular level in terms of soluble Mn(III) intermediate condensation, in which the electrolyte conditions determine the relative proportions of equatorial-axial edge sharing (ramsdellite domains only), and equatorial-axial corner sharing (both ramsdellite and pyrolusite domains) that occurs. Morphological differentiation is easily established due to the different characteristics of each phase. gamma-MnO2 exists as fine needles (250 nm x 50 nm), beta-MnO2 is formed as much larger columns (1 mum x 100 nm), while alpha-MnO2 is present as small spheres of up to 400 nm in diameter. Electrochemical characterization by voltammetry in an aqueous 9 M KOH electrolyte demonstrates that the performance of gamma-MnO2 Samples is comparable with that of commercial EMD, whereas alpha- and beta-MnO2 suffer from diffusional limitations which lower their operating voltage. For gamma-MnO2, superior performance results when lower temperatures and H2SO4 concentrations are used. This corresponds to intermediate levels of De Wolff defects and microtwinning, and to a cation vacancy fraction minimum.]]> Thu 25 Jul 2013 09:10:27 AEST ]]>