Gasification of solid fuels like coal, biomass or peat results in a fuel gas containing high concentrations of ammonia. This ammonia may give rise to high NOx emissions when the fuel gas is burned. The paper examines a promising possibility to convert this ammonia to molecular nitrogen by homogeneous gas phase reactions. The paper shows that additions of small amounts of nitric oxide and/or oxygen in the fuel gas before the combustion stage may convert parts of the ammonia to molecular nitrogen at temperatures 800-1000 °C.
A reaction scheme consisting of about 250 elementary reactions between 49 species was applied to study the influence of various factors, such as temperature, reaction time, initial gas composition, etc. on the ammonia conversion. The modeling was based on isothermal premixed plug flow conditions under atmospheric pressure.
With O2 the conversion of the ammonia was very rapid typically occurring in less than 10 ms. With NO the reaction was slower and the conversion required one or several seconds. Simultaneous addition of both gases did not generally improve the conversion. The N2 yield increased with increasing temperature and reached 90% at temperatures above around 1000C. In the presence of hydrocarbons, modeled as methane, the ammonia conversion was significantly inhibited.
The paper gives a detailed discussion on the reaction paths in the different conditions.
The paper will be followed by a second, complementary part where the model calculations are compared with available experimental data from laboratory reactors.