Experimental Investigation into Ash Deposition and Na Migration Characteristics during Combustion of High Sodium Zhundong Lignite in a Circulating Fluidized Bed Operating at Low Temperatures

摘要

The mineralogical, morphological, and chemical characteristics of ash deposits during combustion of Zhundong lignite (<3 mm) in a 0.2 t d(-1) circulating fluidized bed (CFB) operating at relatively low temperatures, that is, 800-760 and 750-680 degrees C, were investigated. Two air-cooled probes were installed in the furnace dilute phase (P-1) and the cyclone outlet (P-2) to simulate ash deposition. The deposits along with the bottom ash and fly ash were collected and analyzed by using scanning electron microscopy energy-dispersive X-ray spectroscopy, X-ray diffraction, and inductively coupled plasma optical emission spectroscopy. Results showed that the P-1 deposit composed of melted Ca/Na sulfate particles at 800 degrees C but became granular Na/Ca/Mg aluminosilicate particles at 750 degrees C. Likewise, the P2 deposit comprised agglomerated particles rich in Na2SO4 and CaSO4 at 800 degrees C but became discrete Na2SO4 and NaCl particles at 750 degrees C. The bottom ash was enriched with (Ca,Na)(Si,Al)(4)O-8 and Na2SO4 at 800 degrees C but turned into Na2SO4, (Na,K)(Si3Al)O-8 at 750 degrees C. The Na content in the bottom ash correspondingly increased from 31.3 to 36.S mg g(-1), retaining more Na in the bottom ash at 750 degrees C. The fly ash also became discrete particles enriched in Na2SO4 and NaCl. The CFB combustion at 750-680 degrees C thus decreased the release of Na and the sintering propensity of ash particles and consequently lessened their deposition propensity.