The Fate of Ammonia and Hydrogen Cyanide during Flameless Combustion of Low Calorific Value Gases

Abstract

In this paper, a review of the experimental investigations on the fuel-NOx formation during flameless combustion is presented. The first series of experiments described in the paper were conducted using ammonia doped synthetic gases with different compositions. During these experiments, the influence of gas composition on the conversion of ammonia (NH3) to NOx is investigated. The second series of experiments were conducted using product gas generated in a fluidized bed gasifier. These results show the dependencies between the gasifier operating parameters, product gas composition and final NOx emissions. Moreover, the concentrations of the ammonia and hydrogen cyanide (HCN) in the product gas were measured in order to calculate the conversion ratios of these compounds to NOx. The results show the significant influence of the gas composition and the gasifier process parameters on the final NOx emissions. In particular, the hydrocarbon content influences the ammonia to NOx conversion. The lowest NOx emissions and therefore the lowest conversion ratios were measured while burning gases with a low hydrocarbon content. An increase of the hydrocarbon concentration in the gas corresponded to a rapid increase in the conversion ratios.

Keywords

• Fuel-NOx, Flameless Combustion, FLOX, nitrogen chemistry

References

1. Wünning J.A. and Wünning J.G., 1997, Flameless oxidation to reduce thermal-NO formation, Prog. Energy Combust. Sci. 23, pp.81–94.
2. Becidan M., Skreiberg Ø., Hustad J.E., 2007, NOx and N2O Precursors (NH3 and HCN) in Pyrolysis of Biomass Residues, Energy Fuels 21, p. 1173-1180, (2007).
3. Cavaliere A., De Joannon M., 2004, Mild Combustion, Prog. Energy Combust. Sci. 30, pp. 329-366.
4. Choudhuri A.R., Gollahalli S.R., 2003, Characteristics of hydrogen-hydrocarbon composite fuel turbulent jet flames, Int. J. Hydrogen Energy 28, pp 445 – 454.
5. Galletti C., Parente A., Tognotti L., 2007, Numerical and experimental investigation of a mild combustion burner, Combust. Flame 151, pp. 649-664.
6. German Standard DIN 38406-E5, 1983, Methods for the examination of water, waste water and sludge; determination of ammonia-nitrogen (E5).
7. German Standard DIN 38405-D13, 1981, Methods for the examination of water, waste water and sludge; determination of cyanides (D13).
8. Leppälahti J., Koljonen T., 1995, Nitrogen evolution from coal, peat and wood during gasification: Literature review, Fuel Proc. Tech. 43, pp. 1-45.

9. Schuster A., Zieba M., Wünning J.G., Scheffknecht G., of combustion system by applying flameless oxidation”, Proceedings of 15th IFRF Members’ Conference, Pisa.
10. Schuster A., Zieba M., Scheffknecht G., Wünning J.G., 2007, “Application of FLOX® Technology for the utilisation of low-grade biofuels”, Proceedings of 15th European Biomass Conference, Berlin, Germany, pp. 1703-1706.
11. Skreiberg Ø., Kilpinen P., Glarborg P., 2004, Ammonia chemistry below 1400 K, Combust. Flame 136, pp. 501- 518.
12. Zieba. M, Schuster A., Scheffknecht G., 2009a, Influence of gas composition on ammonia to NOx conversion during flameless combustion of low calorific value gases, Proceedings of 16th IFRF Members’ Conference, Boston.
13. Zieba. M. Brink. A., Schuster A., Hupa M., Scheffknecht G., 2009b, Ammonia chemistry in a flameless jet, Combust. Flame 156, pp. 1950-1956.