Effect of Low-NO_x Combustion on PM_(10) Emissions from Pulverized-Coal-Fired Boilers

摘要

The effect of low-NO_x 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-NO_x combustion and the other with conventional combustion. Collection of particulate matter with an aerodynamic diameter of up to 10 μm (PM_(10)) 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-NO_x combustion results in higher concentrations of total suspended particulate (TSP) and PM_(10) but lower concentrations of PM_(2.5) and PM_1. The size distribution of PM_(10) from both boilers shows a trimodal feature that is not significantly affected by low-NO_x combustion. However, it is found for the first time that the size distribution of PM_(10) from low-NO_x 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 PM_1 and NO_x is thought to be due to the fact that PM_1 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 NO_x and PM_(0.1) that is formed by solid-vapor-particle processes.