COMPARATIVE ANALYSIS OF LIGNITE AND BITUMINOUS COAL PARTICLES BURNING IN O{sub}2-N{sub}2 O{sub}2-CO{sub}2 ENVIRONMENTS

摘要

In this paper the combustion characteristics of pulverized coal, both a bituminous and a lignite type, were investigated. Experimental work was carried out in a drop-tube furnace in two different gaseous environments: O{sub}2-N{sub}2 and O{sub}2-CO{sub}2, at a furnace wall temperature of 1400K. The coal particles were burned in oxygen partial pressure intervals that increased every 0.2atm, starting from air-like environments up to pure-oxygen environments. Entire luminous combustion histories of single particles were monitored with optical pyrometry. Observed temperatures and burnout times of bituminous and lignite particles, in the size cut of 75-90μm, were evaluated during both their volatile- and char-combustion phases. For every experimental condition at least 20 samples (burning particle histories) were collected and burnout-times are presented together with deduced temperatures. Increasing the oxygen mole fraction enhanced the temperature of both volatiles and chars, while it reduced their combustion durations. Volatile and char combustion temperatures were higher in N{sub}2 than in CO{sub}2 at the same O{sub}2 mole fraction, whereas corresponding combustion burnout times were shorter. Furthermore, the two coals exhibited dissimilar combustion behaviors. The bituminous coal burned with distinct volatile and char combustion stages, whereas the lignite coal burned with seemingly overlapping stages. The bituminous combustion burnout times were much more affected by the substitution of N{sub}2 with CO{sub}2 than the lignite burnout times. To the contrary, the temperatures of the two coals were affected in the same manner.