Char nitrogen

The oxidation of chars prepared from nitrogen-containing precursors has been investigated. Chars produced from the nitrogen-containing compounds acridine and phenanthridine were oxidized at atmospheric pressure at temperatures of 773-873 K. The relative rates of nitrogen and carbon release and the formation of NO have been determined in relation to char nitrogen content and precursor type. 

There have been a limited number of studies which indicate that the conversion of char nitrogen to N0X can make a significant contribution to the total N0X emissions. The oxidation of char nitrogen... 

In the present work the oxidation of nitrogen-containing chars prepared from model compound precursors was studied. The relative rates of nitrogen and carbon depletion and the mode of nitrogen release were investigated. The influence of the char nitrogen content, the precursor composition, and the oxidation temperature on N0X production were studied. 

Figure 1. Retention of Acridine Char Nitrogen as a Function of Burnoff in Air at 773 K...

Char nitrogen enrichment which occurs at low burnoff at 773 K, has been observed during the partial combustion of shale particles (4). The results at 798 and 823 K are in agreement with the results of Song 05) for the oxidation of a 1750 K lignite char at 1250 K. It appears that the rates of oxidation of char carbon and nitrogen are equal at the temperatures of interest in practical combustors. 

Effect of Temperature on Conversion of Char Nitrogen to N0X. The ef-fect of oxidation temperature upon the proportional release of N0X is tabulated in Table II for pure acridine and phenanthridine chars at... 

Table II. Effect of Temperature on Conversion of Char Nitrogen to N0X...

The dramatic decrease in char nitrogen to N0X conversion for the acridine char cannot be attributed only to a 50 K increase in temperature. The char ignited at 873 K but not at 823 K. The bed temperature during oxidation at 873 K was probably considerably higher than 873 K. The bed temperature during oxidation of the phenanthridine char at the furnace temperature of 873 K is shown in Figure 9. A maximum temperature of 1006 K was reached within 3 minutes and the bed temperature remained 50 K higher than the furnace temperature even after 30 minutes. 

It was also found that the conversion of released nitrogen to N0X decreased with increasing reaction temperature, increasing char nitrogen content (for both acridine and phenanthridine-based chars) and with increasing sample weight (bed height). 

Acridine char nitrogen, retention as function of burnoff, 307/, 308/ Advection fluxes, calculation, 41-43 Aerosol particle size distribution, molecular clusters, 317 Aerosol scavenging pathway, acetic and formic acid formation, 223 Aerosol species, transformation over the western Atlantic, 52 Aerosol sulfate airborne determination, 298 See also Sulfate... 

Increases in fly ash recirculation means that more char is available for reducing NO,. The increases in N2O emissions can be attributed to the increased availability of char for reaction, de Soete (1990) found that during char burning a small amount of the char-small amount of the char-nitrogen is oxidized to N2O. The rate of N2O formation is... 

Molina, A., E.G. Eddings, D.W. Pershing, and A.F. Sarofim. 2000. Char nitrogen conversion implications to emissions fix>m coal-fired utility boilers. Progress in Energy and Combustion Science. 26 507-531. 

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