Fuel-bound nitrogen reaction

At the high temperatures found in MHD combustors, nitrogen oxides, NO, are formed primarily by gas-phase reactions, rather than from fuel-bound nitrogen. The principal constituent is nitric oxide [10102-43-9] NO, and the amount formed is generally limited by kinetics. Equilibrium values are reached only at very high temperatures. NO decomposes as the gas cools, at a rate which decreases with temperature. If the combustion gas cools too rapidly after the MHD channel the NO has insufficient time to decompose and excessive amounts can be released to the atmosphere. Below about 1800 K there is essentially no thermal decomposition of NO. 

Thus, the reaction system cannot be quenched to prevent NO formation from fuel-bound nitrogen, as is the case with atmospheric nitrogen. In fact, in the... 

Despite the authors assertion that alkylated heteroaromatic compounds provide a better model for fuel-bound nitrogen than do the unsubstituted heterocycles, their pyrolytic study remains the most comprehensive look at substituted heteroaromatic chemistry, even several years later/ Kinetic studies are more common in the literature Frerichs et al. examined the reaction of the picolines with oxygen atom, while Yeung and Elrod studied reactions of HO with pyridine and its methyl- and ethyl-substituted derivatives.Both groups noted that the presence of nitrogen did not demonstrably affect the species chemistry generally, reactivity is comparable to toluene. 

An LHV gas may contain up to a few thousand ppm of ammonia, produced from fuel-bound nitrogen during the gasification of a solid fuel. One of the major challenges in the catalytic combustion of LHV gases is to circumvent the formation of NO from this ammonia. The selectivity for this reaction is strongly dependent on the air-fuel ratio in the catalytic combustor and on the catalyst type [102,105], Clark et al. [102] and Tucci... 

When waste materials contain nitrogen bound in organic molecules, they can contribute to the formation of nitrogen oxides. The primary mechanism of NO t formation in this case is the conversion of fuel-bound nitrogen to HCN and HNCO, followed by the conversion of these species into NH and then to NO, as described above. NO2 and N2O can also form in combustion processes through reactions such as ... 

The reactions of NH2 and NH with O2 and 0 play important roles in the oxidation of ammonia and fuel bound nitrogens as well as in the reduction of NOy (1-12). However, the rate constants for these reactions differ drastically in the various chemical reaction models which have been developed (1-6). Even the experimentally measured rate constants show a wide variation and differ significantly from the corresponding isoelectronic counter-... 

Most models assume that the fuel-bound nitrogen that is released by the devolatilization of coal is in the form of HCN, or some instantaneous transforms of HCN, which in turn form the base species of NO formation. It is believed that the HCN not only contributes to fuel NOx formation but also to some destruction of NOx and that the net formation might depend on the chemical as well as the thermal state of the mixture. The global chemical reactions involved for coal flames might therefore be expressed as... 

Table 6.18.1 shows a typical composition of an untreated exhaust gas of a gasoline powered engine. CO2 and H2O are the main products resulting from complete combustion. CO is formed by incomplete combustion, and hydrocarbons (HCs) mainly originate from r ons in the combustion chamber that are not reached by the flame, for example, near the chamber waD. Nitrc en oxides (NO, NO2, N2O) are formed by reaction of N2 and O2, if the temperature is high (>1400 C). They are denoted as NO and consist mainly of NO. The NO, is not only formed from atmospheric N2 but also from fuel-bound nitrogen (Section 6.18.2.2), but this is more relevant for coal or... 

NO and NO2 are undesirable by-products of the combustion of coal, natural gas, or fuel oil in boilers of power plants. Nitrogen oxides are formed during combustion by the reaction of atmospheric N2 and O2 at temperatures > 1200 °C (thermal NO ). If nitrogen-containing fuels such as coal and heavy oils are burned, fuel NO, is produced by the combustion of the fuel-bound nitrogen. The third, usually small, source is prompt NO which is attributed to the reaction of N2 with radicals derived from the fuel. 

Fuel-bound NO. is formed at low as well as high temperatures. However, part of the fuel nitrogen is directly reacted to N2. Moreover, N2O and N2O4 are also formed in various reactions and add to the complexity of the formation. It is virtually impossible to calculate a precise value for the NO, emitted by a real combustion device. NO, emissions depend not only on the type of combustion technology but also on its size and the type of fuel used. 

The high yields on the lean side of stoichiometric pose a dilemma. It is desirable to operate lean to reduce hydrocarbon and carbon monoxide emissions but with fuel containing bound nitrogen, high NO yields would be obtained. The reason for the superequilibrium yields is that the reactions leading to the reduction of NO to its equilibrium concentration, namely,... 

Emissions of nitrogen oxides and sulfur oxides from combustion systems constitute important environmental concerns. Sulfur oxides (SO ), formed from fuel-bound sulfur during oxidation, are largely unaffected by combustion reaction conditions, and need to be controlled by secondary measures. In contrast, nitrogen oxides (NO ) may be controlled by modification of the combustion process, and this fact has been an important incentive to study nitrogen chemistry. Below we briefly discuss the important mechanisms for NO formation and destruction. A more thorough treatment of nitrogen chemistry can be found in the literature (e.g., Refs. [39,138,149,274]). 

Although the prediction of N0X emissions under lean and stoichiometric combustion with the extended Zeldovich mechanism is adequate for certain applications, predictive methods for fuels containing bound nitrogen and for rich combustion conditions require substantial improvement. However, the early studies of Fenimore (13, 14) demonstrated the potential importance of HCN and NH type species in fuel-nitrogen interactions. To illustrate the critical importance of the coupling of nitrogenous species reactions in rich combustion, predictions of NO emissions from rich iso-octane combustion in a jet-stirred combustor are shown in Table III. C2 hydrocarbon fragmentation and oxidation creates... 

During combustion, N0X is formed either by the reaction of oxygen and atmospheric nitrogen (thermal N0X) or the oxidation of chemically bound nitrogen in the fuel (fuel N0X). The production of thermal N0X can be minimized by various techniques which lower the flame temperature. The reduction of thermal N0X alone may not lower N0X emissions to within acceptable regulatory limits. Thus, it will be necessary to limit fuel N0X emissions. 

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