Oxygen-deficient conditions

Reburning is a process involving staged addition of fuel into two combustion zones. Coal is fired under normal conditions in the primary combustion zone and additional fuel, often gas, is added in a reburn zone, resulting in a fuel rich, oxygen deficient condition that converts the NO, produced in the primai y combustion zone to molecular nitrogen and water. In a burnout zone above the reburn zone, OFA is added to complete combustion. 

The exact synthetic chemistry which produces PAH in a fuel-rich flame is not well known, even today. It is clear, however, that PAH can be produced from almost any fuel burned under oxygen deficient conditions. Since soot is also formed under these conditions, PAH are almost always found associated with soot. As an example of the PAH assemblage produced by combustion systems. Figure 1 shows gas chromatographic mass spectrometry (GCMS) data for PAH produced by the combustion of kerosene ( ). The structures of the major compounds are also given in Figure 1. We draw the reader s attention to a number of features of this PAH mix-... 

Thermodynamically, the oxidation of hydrocarbons to carbon dioxide and water is preferred to any partial oxidation reaction. The possibility of forming partial oxidation products is thus entirely dependent on the kinetics of the oxidation process. The oxidation of hydrocarbons, is in general, a stepwise process. One way to confine the depth of oxidation, therefore, is to apply a low oxygen to hydrocarbon ratio and a short reaction time. However, to avoid a multitude of products with different oxidation depths, the use of a catalyst is obviously required. In that case, the above two factors (oxygen deficient conditions and short reaction time) may loose their importance. 

Under Oxygen deficient conditions, the formation of detonation product gases from TATB are as follows ... 

The purpose of this study was to clarify the change of density with species, heating rate, and temperature under oxygen-deficient conditions. The major constraint was an arbitrary specimen size (10-mm cube), based on the observation that thicknesses equal to or greater than about 6 mm (approximately the half-thickness of the cubes) produce consistent charring rates (5). The effect of thickness on density changes is currently being studied. 

It is interesting to note that reduced heteropoly compounds show higher selectivity towards methacrylic acid than the non-reduced ones in the oxidation of isobutane. Mizuno and coworkers have also reported the oxidation of isobutane under oxygen-deficient conditions [67]. Ueda and coworkers have studied reduced 12-molybdophosphoric acid for the oxidation of propane [79]. This highly reduced... 

Cline, J. D., and Richards, F. A. (1972). Oxygen deficient conditions and nitrate reduction in the eastern tropical North Pacific Ocean. Limnol. Oceanogr. 17, 885—900. 

While these expressions reproduce the main features of the experimental results well, Pignet and Schmidt suggest that they fail to represent adequately changes in surface chemistry. There was, for example, a lack of reproducibility between 200 and 400 °C in oxygen-deficient conditions. They therefore do not claim any basic significance for the values of the parameters fitted to their Langmuir-Hinshelwood expressions, e.g. the adsorption constants Ko and Ko had different values as did A nh, and A nh3 -... 

NOH is changed to nitrous oxide under oxygen-deficient conditions (Hooper and Terry, 1979), though the reduction of nitrite (or nitrous acid) once fronted to the gas may also occur (Poth and Focht, 1985 Yoshida, 1988). Indeed, the bacterium has a copper protein-type nitrite reductase which catalyzes the reduction of nitrite to nitric oxide and/or nitrous oxide (Hooper, 1968 Ritchie and Nicholas, 1972, 1974 Miller and Wood, 1983 DiSpirito et al., 1985). However, as Beaumont et al. (2002) have recently found that nitrous oxide is produced even by N. europaea in which the DNA encoding nitrite reductase has been destroyed, the formation of nitrous oxide by the bacterium seems attributable to the decomposition of NOH. Camera and Stein (2007) have recently reported similar results about the formation of nitrous oxide by the nitrite reductase-deficient mutant of the bacterium. 

Complete oxidation of methane to carbon dioxide and water occurs when it is burned in air and controlled combustion is an extremely important source of thermal energy. Methane and O2 also form extremely dangerous mixtures in the gas phase and explosions are easily detonated. Explosions occur under oxygen-deficient conditions and CO is an important and toxic product. 

Naqvi, S.W.A. (1987) Some aspects of the oxygen-deficient conditions and denitrification in the Arabian Sea. Journal of Marine Research, 49, 1049-1072. 

PAHs may be synthesized from saturated hydrocarbons under oxygen-deficient conditions. Hydrocarbons with very low molecular masses, including even methane, may act as precursors for the polycyclic aromatic compounds. The process of PAH formation from low molar mass HCs is called pyrosynthesis. This happens at temperatures exceeding 500 C at which C - H and C - C bonds are broken to form free... 

Of the different catalytic coatings tested sample No. 3 did not show any evidence of soot oxidation. Incipient soot oxidation was evident on samples No. 4, 5 (a less steep pressure drop trace increase than sample No. 3). Samples No. 6, 7 (foam) exhibited clearly soot oxidation as their pressure drop trace was decreasing with temperature. All pressure drop decreases with the catalytic filters have been observed above 650°C under oxygen deficient conditions and therefore it can be stated that the soot is oxidized catalytically by other species than oxygen in these experiments. The best catalyst formulation appears to be the combination of reducible oxide/alkali metal and precious metal. 

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