Effect of Low-NO_<i>x</i> Combustion on PM₁₀ Emissions from Pulverized-Coal-Fired Boilers

The effect of low-NOx combustion technologies on particulate emissions from coal-fired boilers is much less known. It is investigated in this work by experiments on two 200 MW coal-fired boilers, one with low-NOx combustion and the other with conventional combustion. Collection of particulate matter with an aerodynamic diameter of up to 10 μm (PM10) was carried out at the inlet of the electrostatic precipitators of both boilers. The particulates were classified into 13 size fractions by a low-pressure impactor. Their emissions and size distributions were obtained. Particle chemical composition was characterized by an X-ray fluorescence analyzer. The data show that low-NOx combustion results in higher concentrations of total suspended particulate (TSP) and PM10 but lower concentrations of PM2.5 and PM1. The size distribution of PM10 from both boilers shows a trimodal feature that is not significantly affected by low-NOx combustion. However, it is found for the first time that the size distribution of PM10 from low-NOx combustion shifts to a larger size compared to that from conventional combustion. The size distributions of Al, Si, S, and Ca in the <10 μm size range suggest three particle modes that are formed by different mechanisms. The inconsistency in the literature as to whether there is a relationship between PM1 and NOx is thought to be due to the fact that PM1 is not totally formed by the vaporization and condensation mechanism. The preliminary data presented in this work suggest that, for the test cases, there seems to be a positive correlation between NOx and PM0.1 that is formed by solid–vapor–particle processes.