Formation factors and emission characteristics of ultrafine particulate matters during Na-rich char gasification

Abstract

In this study, the release and formation characteristics of ultrafine particle matters (PM) during the gasification of Na-rich char are investigated. Two different pre-treatment methods, i.e., water washing and mineral loading, were employed to figure out the effects of various minerals on the deconvolution behaviors of PM, enabling the development of countermeasures. Furthermore, the mineralogical characteristics of the ash resulting from the mineral loading were also discussed. Results showed that a large amount of fine NaCl particles was generated during Na-rich char gasification. Gasification temperature and pressure essentially govern the concentration of Na and Cl species in the gas phase, which determines the quantity and morphology of PM. Specifically, the particle size of PM obtained at 1000 and 1050 °C is mainly distributed in the range of 0.2–0.4 μm. For the W-char gasified at 1100 and 1150 °C, the PM with the size between 0.6 and 1.2 μm is predominant. On the other hand, the particle size of PM decreased remarkably as the gasification pressure increased from 0.1 to 3 MPa. Additionally, due to the low carbon conversion rate of W-char during the CO2 gasification at 1100 °C, over 75% of the total PM were in the size range of 0.2–0.6 μm. The gasification of kaolin loaded W-char generated abundant spherical particles mainly present as alkali and alkaline earth metal aluminosilicates rather than NaCl particles. When it comes to adding diatomite into char, only a few spherical particles, mainly present as aluminosilicates, were detected, indicating the superior performance of diatomite on restraining PM release. The addition of diatomite into W-char could reduce ash fusion temperature, and the agglomerated coarse particles in bottom ash could capture the PM, which inhibited the release of PM to some extent. In contrast, the CaO added in char reacted with the clay and quartz that would otherwise immobilize Na, leading to the more intense release of Na- and Ca-bearing PM.