Study on the formation of ultrafine particulate matter (PM) during char combustion in a wet oxy-combustion atmosphere

Abstract

In this study, the effect of H2O on the formation of ultrafine particulate matter (PM) in an oxy-combustion atmosphere with various O2 contents of 21%, 27%, and 33% was investigated in a high-temperature drop tube furnace at 1800 K. The combustion-generated ultrafine PM was collected by a 14-stage electrical low-pressure impactor for analyzing the mass- and number-based particle size distribution (PSD). The element composition of ultrafine PM was identified using inductively coupled plasma mass spectrometry. The results indicated that all the primary peaks of the mass- and number-based PSD of ultrafine PM were located nearby 0.2 μm under various O2/CO2/H2O atmospheres. As H2O content increased, both the mass and the number yield of ultrafine PM decreased initially and then increased, with an inflection point at 5% H2O content. The inhibitory effects of 5% H2O content on the formation of ultrafine PM at 21%, 27% and 33% O2 contents were −12.3%, −28.5%, and −33.5%, respectively, while the promoting effects of 30% H2O content were 105.4%, 54.0%, and 7.0%, respectively. Thus, the yield of ultrafine PM in the oxy-combustion atmosphere with low O2 content fluctuates more with the increase of H2O, and was more sensitive to H2O. Moreover, with the increase of H2O and O2 content, the average mass of ultrafine PM exhibited an enlarged tendency. And high H2O content (30%) evidently favored the enrichment of alkali and alkaline earth metals (e.g. Na, K, Ca and Mg), as well as Fe in PM0.1, whereas the volatilization of Si and Al was suppressed.