• Gas-Phase Conversion of NH3 to N2 in Gasification – Part II: Testing the Kinetic Model

  • Publication date:

    March 2001


Gasification of solid fuels such as coal, biomass and peat results in a fuel gas containing high concentrations of ammonia (NH3). This ammonia may give rise to high NOx emissions when the fuel gas is burned. In Part I of this paper, Kilpinen et al. (1999) examined a promising possibility to convert the NH3 to molecular nitrogen (N2). The ammonia conversion was predicted upon the addition of suitable oxidizers such as O2 and NO.

The optimum conditions for this technology were estimated by homogeneous, detailed gas phase kinetic modeling. A chemical explanation of the related phenomena was also given. However, at the time of writing Part I, no experimental data were available to validate the modeling. In Part II, the predictive ability of four comprehensive mechanisms, including the one proposed for kinetic modeling in Part I, is tested against recent experimental data.

The investigation is limited to atmospheric, premixed, one-dimensional, plug flow conditions. As part of the investigation, the optimum conditions for ammonia conversion into gasification products are rechecked, and a chemical interpretation is proposed. Both Kilpinen mechanisms, especially version 97, are useful tools for investigating ammonia oxidation technology. Dagaut 00 mechanism has major limitations, and GRI-Mech 3.0 is not appropriate for the conditions studied.

The thermal history of the reactive gas mixture is a crucial parameter to take into account. The optimum conditions for NH3 conversion extrapolated in Part I, are updated here. Both O2 and NO are suitable oxidizers for ammonia, the first causing faster reactions. Hydrocarbons and H2 are other important compounds affecting the NH3 oxidation chemistry.

Both Kilpinen mechanisms predict the reduction of ammonia via amino species; nevertheless the reactions leading to N2 and NO differ substantially. Detailed kinetic simulation is clearly an attractive tool to investigate gasification, but more experimental data is needed to validate and improve the models.