Fuel nitrogen, conversion

J.E. Fuel nitrogen conversion in solid fuel fired systems, Prog. Energy Combust. Sci., 29, 89-113, (2003). 

The formation of prompt NO increases the complexity of the nitrogen chemistry in gas flames considerably. This is illustrated in Fig. 14.9, which shows the most important reaction paths in prompt NO formation, as well as fuel nitrogen conversion—two mechanisms that share some common features. Prompt NO is, as the name indicates, a very rapid mechanism. The initiating step (R117) takes place in the flame zone, where methylidyne radicals (CH) may be formed in significant quantities. 

Beer, J. M., Jacques, M. T., Farmayan, W., and Taylor, B. R., "Fuel-Nitrogen Conversion on Staged Combustion of a High Nitrogen Petroleum Fuel", pp 101-10, Eighteenth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, 1981. 

A Study ot Fuel Nitrogen Conversion in Jet-Stirred Combustors... 

Table I. Results from fuel nitrogen conversion experiments - isooctane fuel.

Table II. Combustor < > Results from fuel nitrogen conversion experiments - toluene fuel. t TFN NO hc soar (ms) / % of v, % ofv, vol. %v, % of v fuel N TFN" las CH fuel C ...

Data from the present set of experiments suggest that the conversion of fuel nitrogen to TFN in jet-stirred combustors depends upon the equivalence ratio and average residence time of gases within the combustor, the fuel type and certain physical characteristics of the combustors. However, the effects of these primary variables on fuel nitrogen conversion appear to be related to their effects on the concentrations of unburned hydrocarbons and soot in the exhaust gases. These effects and their relationships to unburned hydrocarbon and soot concentrations are discussed below. 

The pattern of increasing conversion for equivalence ratios richer than the hydrocarbon breakthrough equivalence ratio appeared to depend on the fuel, however. Figure 3 provides a comparison of fuel nitrogen conversion from isooctane and toluene at the richest equivalence ratios tested in the JSC. For both fuels, HC s increased as the equivalence ratio was increased from 1.6 to 1.8. Corresponding increases in fuel nitrogen conversion were found for isooctane mixtures at 3, 6 and 10 ms residence times, but toluene mixtures at these conditions produced either smaller increases or decreases in conversion with increasing... 

Any interaction between fuel nitrogen conversion and soot concentrations, however, may be peculiar to the mixture equivalence ratios. Data from the limited LFJSC experiments, which were obtained at relatively leaner equivalence ratios (< >=1.2,... 

JSC cases, an interaction between HCN and soot appears to be a possible explanation of the observed fuel-type effects on fuel nitrogen conversion in the JSC. 

The effects of residence time on fuel nitrogen conversion may... 

Comparisons of the results from the two different diameter JSC s at a residence time of 8 ms suggested that fuel nitrogen conversion was similar at the leaner equivalence ratios (<(>=1.2, 1.4), but at richer equivalence ratios fuel nitrogen conversion and HC concentrations were larger in the larger J SC (Figure 7). 

The observed differences among the data obtained at similar JSC and LFJSC operating conditions suggest that comparisons of data from the various combustors must allow for possible effects of combustor type in the results. Extensions of the results to larger, commercial size gas turbine combustors or to similar laboratory combustors should also be made with extreme caution. Qualitative trends such as the dependence of fuel nitrogen conversion on HC concentrations should be valid within a given combustor however, quantitative numerical results may depend strongly on specific combustor characteristics. For example,... 

This research was conducted for the U. S. Department of Energy as part of Contract No. DE-AC22-77ET11313. Funding for the fuel nitrogen conversion experiments was provided by Exxon Research and Engineering Company. 

During the evaluation of the influence of the air to fuel ratio on the fuel nitrogen conversion, the total volume flow have been kept constant by replacing some of the primary air with nitrogen, thereby maintaining the linear velocity through the fluidised bed. 

The fuel nitrogen to NH3 conversion values are comparable to and in-line with values reported by VTT, where a slightly smaller scale pressurised fluidised bed is operated (ca. 500 kWth), for experiments with straw, a fuel quite comparable to Miscanthus, see e.g. Kurkela et al. [13]. Using straw with dolomite as additive they found values in the range of 60-71% fuel nitrogen conversion to NH3, at air stoichiometry values between 0.28 and 0.31. 

LOffler, G. (2000) A Modeling Stuefy on Fuel-nitrogen Conversion to NO and AjO related to Fluidized Bed Combustion. Ph.D. diesis, Vienna University of Technology, Vienna, Austria. 

Chemistry of NOx Formation from Fuel Nitrogen Conversion... 

Second, there is considerable experimental evidence that increased oxygen availability results in increased fuel nitrogen conversion and higher NO emissions. The data of Martin and Berkau (29) (Figure 8) indicate that NO is proportional to Po2 for the system studied Turner et al, 34) found similar results. Further, both investigators found little eflFect of bulk temperature on the formation of fuel NOa-. 

Figure 8. Background and fuel nitrogen conversion NO as a function of stoichiometric ratio in an experimental furriace...

---