Characteristics of fine particle formation during combustion of high-alkali coal in a new full-scale circulating fluidized bed boiler

Abstract

High-alkali coal generated an increased number of fine particles during the combustion process. Understanding the transformative characteristics of particulate matter (PM) in a full-scale boiler that burns 100 % Zhundong (ZD) coal is key for controlling pollutant emissions. This paper investigated PM formation in a novel full-scale Circulating Fluidized Bed (CFB) boiler. PM samples were collected from various points along the steam-cooled flue at 50 %, 67 %, and 100 % boiler load. Utilizing Low-pressure impactors and scanning electron microscopy coupled with energy disperse spectroscopy (SEM-EDS) were applied to analyze the mass-based particle size distribution(MPSD), elemental compositions, and morphology of PM. The results show that sub-micron particles produced under low boiler load consist primarily of AAEMs sulfates, whereas under high load, they consist primarily of alkali metal chlorides. Super-micron particles are predominantly sulfates and silicates. The concentrations of Na, K, and Cl in PM0.4 decreased as the flue gas cooled down in the steam-flue of the CFB. At 100 % boiler load, Na, K, Cl and S account for more than 90 % of the total elements in the sub-micron particles. However, these four elements demonstrated a 25 % decrease at a boiler load of 67 % compared to 100 % load. Interestingly, the compositions of super-micron particles seemed to be minimally affected by the boiler load.