Ash Deposition and Slagging Behavior of Xinjiang High-Alkali Coal in a 20MW_th Cyclone Combustion Test Facility

Abstract

The high content of AAEMs (alkali and alkaline earth metals) in ash as well as its relating serious ash fouling slagging problems are the main reason for the unit boiler, which cannot absolutely fully use high-alkali coal at full generating capacity. In order to fully use those kinds of coal, the cyclone-fired boiler with slagging tap is induced in this paper. The ash melting behavior as well as the migration and transformation characteristics of AAEMs during cyclone-fired process were performed in a 20MWth cyclone combustion test facility. A number of slagging and deposit samples at different locations of boiler were selected and analyzed by using XRF, XRD and SEM–EDX analysis. The experimental results showed that the slag in cyclone burner contains higher content of Fe₂O₃, around 37.5–52.6 wt%, which is about 2.4 and 3.5 times than that of their parent coal ash. The content of Na₂O in slag is around 2.3–8.6 wt%, especially for the slag at location C, D and E, where can provide sufficient reaction time and contact area between flue gas and slag. The main existence form of sodium is Na–Al–Si eutectic compounds and being completely melted in cyclone with smooth surface. For the deposit ash on convective tubes, some Na–Al–Si and Ca–Mg–Si low melting eutectic compounds have a rounded boundary in the main particles due to the low melting temperature and low viscosity, which can adhere to the surface of other ash particles to agglomerate each other.