2019 Volume 61 Issue 198 Pages 299-303
Ammonia is expected as a potential fuel to substitute fossil fuels, because it does not discharge carbon dioxide and is easily handled by liquefaction. One of the possible applications for the direct use of ammonia as a fuel is the combustion use in thermal power plants. In particular, co-firing of ammonia in coal-fired power plants seems to have a relatively great advantage on the suppression of greenhouse gases, because coal is one of the main emission source of carbon dioxide. On the other hand, it is concerned that concentration of nitrogen oxides (NOx), which is one of the typical atmospheric pollutant, in the flue gas would considerably increase due to the oxidation of ammonia. In this study, we examined the influence of ammonia co-firing with coal on NOx emissions and investigated the methods to reduce NOx emissions using two coal combustion test furnaces, a single-burner test furnace and a multi-burner test furnace. When the ammonia co-firing rate was increased up to 20% of the low heat value (LHV), there was no significant increase in NOx concentration at the furnace exit. In the case of injecting ammonia into the pulverized coal combustion flame through the side port of the furnace wall using a single-burner test furnace, NOx concentration could be reduced at the appropriate location of ammonia injection. As a result of examining the effect of changing the burner stage for injecting ammonia using a multi-burner test furnace, it became clear that NOx concentration could be reduced by injecting ammonia concentrated in the lower burner rather than injecting ammonia evenly throughout all of burners.