High temperature combustion

Alundum is used for highly refractory bricks (m.p. 2000-2100 C), crucibles, ref ractory cement and muffles also for small laboratory apparatus used at high temperatures (combustion tubes, pyrometer tubes, etc.). 

Following the movement of airborne pollutants requires a natural or artificial tracer (a species specific to the source of the airborne pollutants) that can be experimentally measured at sites distant from the source. Limitations placed on the tracer, therefore, governed the design of the experimental procedure. These limitations included cost, the need to detect small quantities of the tracer, and the absence of the tracer from other natural sources. In addition, aerosols are emitted from high-temperature combustion sources that produce an abundance of very reactive species. The tracer, therefore, had to be both thermally and chemically stable. On the basis of these criteria, rare earth isotopes, such as those of Nd, were selected as tracers. The choice of tracer, in turn, dictated the analytical method (thermal ionization mass spectrometry, or TIMS) for measuring the isotopic abundances of... 

The gas turbine in the simple cycle mode consists of a compressor (axial or centrifugal) that compresses the air, a combustor that heats the air at constant pressure and a turbine that expands the high pressure and high temperature combustion gases and produces power to run the compressor and through a mechanical coupling to the driven equipment. The power required to compress the gases varies from about 40-60 percent of the total power produced by the turbine. 

Nitric oxide, NO, results from high-temperature combustion, both in stationary sources such as power plants or industrial plants in the production of process heat and in internal combustion engines in vehicles. The NO is oxidized in the atmosphere, usually rather slowly, or more rapidly if there is ozone present, to nitrogen dioxide, NO2. NO2 also reacts further with other constituents, forming nitrates, which is also in fine parhculate form. 

There are well over 100 gaseous and aqueous phase reactions that can lead to acid formation and more than fifty oxidizing agents and catalysts may be involved. However, in the simplest terms sulfur in fuels is oxidized to SO2, and SO2 in the atmosphere is further oxidized and hydrolyzed to sulfuric acid. Most nitric acid is formed by the fixation of atmospheric nitrogen gas (N2) to NO. (NO and NO2) during high temperature combustion, followed by further oxidation and hydrolysis that produces nitric acid in the atmosphere. These materials can be dry-... 

Nitrogen oxides are generated by both human and nonhuman action, but the major sources of NO, are high-temperature combustion processes such as those occurring in power plants and automobile engines. Natural sources of NO., include lightning, chemical processes that occur in soil, and the metabolic activities of plants. 

Fine Aitken nuclei, transient lifetime High temperature combustion processes, condensation from the vapour... 

Nitrogen Dioxide (NO2) Is a major pollutant originating from natural and man-made sources. It has been estimated that a total of about 150 million tons of NOx are emitted to the atmosphere each year, of which about 50% results from man-made sources (21). In urban areas, man-made emissions dominate, producing elevated ambient levels. Worldwide, fossil-fuel combustion accounts for about 75% of man-made NOx emissions, which Is divided equally between stationary sources, such as power plants, and mobile sources. These high temperature combustion processes emit the primary pollutant nitric oxide (NO), which Is subsequently transformed to the secondary pollutant NO2 through photochemical oxidation. 

This demonstrates how the oxygen is depleted resulting, as summarized in Chapter 6, in an irrespirable atmosphere rich in nitrogen. High temperature combustion may also result in the generation of oxides of nitrogen, NO, which are respiratory irritants. 

Role of A- and B-Cations in Catal3d ic Property of Substituted Hexaaluminate (ABAlnOig-a) for High Temperature Combustion... 

The merits and limitations of wet chemical oxidation, high-temperature combustion, and photo-oxidation methods for seawater analysis were summarised by Gershey et al. [58]. 

The dry combustion-direct injection technique provides many advantages over other methods, such as quick response and complete oxidation for determining the carbon content of water. Its primary shortcoming is the need for rapid discrete sample injection into a high-temperature combustion tube. When an aqueous sample is injected into the furnace, it is instantaneously vapourised at 900 °C and a 5000-fold volume increase can be expected. Such a sudden change in volume causes so-called system blank and limits the maximum volume of injectable water sample, which in turn limits the sensitivity [106,107]. 

An alternative method for the determination of particulate organic carbon in marine sediments is based on oxidation with potassium persulfate followed by measurement of carbon dioxide by a Carlo Erba non-dispersive infrared analyser [152,153]. This procedure has been applied to estuarine and high-carbonate oceanic sediments, and results compared with those obtained by a high-temperature combustion method. 

We shall retain this assumption even for the high-temperature combustion case, realizing that it is quite severe. However, its neglect will undoubtedly be compensated through ultimate experimental correlations. With assumption 7 we approximate... 

At high pressures the presence of the H02 radical also contributes via HCO + H02 — H202 + CO, but H02 is the least effective of OH, O, and H, as the rate constants in Appendix C will confirm. The formyl radical reacts very rapidly with the OH, O, and H radicals. However, radical concentrations are much lower than those of stable reactants and intermediates, and thus formyl reactions with these radicals are considered insignificant relative to the other formyl reactions. As will be seen when the oxidation of large hydrocarbon molecules is discussed (Section H), R is most likely a methyl radical, and the highest-order aldehydes to arise in high-temperature combustion are acetaldehyde and propionaldehyde. The acetaldehyde is the dominant form. Essentially, then, the sequence above was developed with the consideration that R was a methyl group. 

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