Applicability of Ammonia Co-firing Technology in Pulverized Coal-Fired Boilers

Ammonia is a potential substitute for 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 combustion in thermal power plants. In particular, the co-firing of ammonia in coal-fired power plants seems to have a relatively great advantage in the suppression of greenhouse gases because coal is one of the main emission sources of carbon dioxide. However, the concentration of nitrogen oxides (NOx), which are typical atmospheric pollutants, in the flue gas would considerably increase owing to the oxidation of ammonia. In this study, we examined the influence of ammonia co-firing with coal on NOx emissions and investigated 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. When ammonia is injected into the pulverized coal combustion flame through the side ports of the furnace wall using a single-burner test furnace, the 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 the NOx concentration could be reduced by injecting ammonia concentrated in the lower burner rather than injecting ammonia evenly throughout all the burners.