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• The mono-combustion of coal slime was achieved on a 75 t/h CFB boiler. • Temperatures in middle of the furnace were the lowest in this coal slime CFB boiler. • Post-combustion air was an effective means to adjust the main steam parameters. • NO x emissions were decreased below 50 mg/m3 by post-combustion technology. Coal slime was a kind of industrial solid waste and it was hard to utilize. To realize the resource utilization of coal slime, a 75 t/h circulating fluidized bed (CFB) boiler with post-combustion technology was built. The operating and emission characteristics during mono-combustion of coal slime were investigated in detail. The fuel characteristics of coal slime and feeding from the top of the furnace resulted in the temperatures at the top and the bottom were higher than the middle of the furnace. When the furnace differential pressure increased, the furnace temperature and the main steam temperature both decreased, but the main steam flow increased. The main steam temperature could significantly increase after the soot blowing. The post-combustion air (PCA) was an effective means to adjust the main steam parameters. The main steam temperature increased as PCA increasing. The average SO 2 emissions were only 8.4 mg·m−3 benefited from the excellent desulfurization effect of the combination of dry and semi-dry desulfurization. Nevertheless, due to the fluctuations of coal slime characteristics, the standard deviation of SO 2 emission reached 8.6 mg·m−3. Under the conditions without desulphurization and SNCR, the NO x emissions of coal slime could be decreased to 38 mg·m−3 and reach the ultra-low NO x emission when post-combustion technology was used. [ABSTRACT FROM AUTHOR]

Zhundong (ZD) coal gasification/combustion fly ash is a high Na content residual product and contains a large quantity of harmful elements, including as Cl, S, and Na that must be removed and recovered. Water-soluble Na is the predominant Na form in ZD coal fly ash, accounting for 34.7–92.8% of the total Na. The main minerals of Na identified were NaCl and Na 2 SO 4 . Most of the water-soluble Na in the ZD coal fly ash can be effectively removed by water washing, the removal yields have been found to be 31–93%. Increasing the washing time, water temperature, liquid–solid ratio and acid concentration can increase the Na removal yield. For the ZD coal combustion fly ash (SEHcf) and gasification fly ash (SEHf), NaCl particles are present on the fly ash surface, most water-soluble Na was washed by water in 5 min at 30 °C. However, the removal of Na by water washing was inhibited by the water insoluble calcium oxides and sulfides that covered the surface of the ZD coal gasification fly ashes (TCf and SHf), Na removal required higher wash water temperatures and longer washing times. It is feasible to recover Na from ZD coal fly ash by water washing, and the recovered Na products are primarily NaCl and Na 2 SO 4 . The recovery yields of Na in the SEHcf, SEHf and TCf were 49.4%, 81.2%, and 65.4%. But the recovery yield of Na in SHf was 16.6%. SEHcf, SEHf and TCf were more suitable for recovering Na. the recovery of Na from ZD coal fly ash is economically feasible. [ABSTRACT FROM AUTHOR]

The surface properties of coal play a crucial role in its flotation, therefore it is of great significance to investigate the changes in both chemical structure and surface morphology in oxidation process of low rank coal. In this paper, the mechanism of difficult floatation of oxidized coal was highlighted. The surface hydrophobicity and floatability of Meizhiyou long-flame coal before and after oxidation processing with H 2 O 2 solution at different concentration were evaluated by induction time and contact angle analyses as well as flotation tests, while the changes in its surface properties in the oxidation process were analyzed by XPS, FTIR, BET and SEM measurements. The maximum increase extent of induction time between bubbles and oxidized coal particles reached to 13217% while the maximum reduction extent of combustible matter recovery reached to 95.28%, which indicated the floatability of oxidized coal particles almost decreased exponentially along with the increase of concentration of H 2 O 2 solution. Additionally, the results suggested the active chemical functional groups of >CH 2 peak at 1437 cm −1 , CH 3 peak at 1373 cm −1 and C O C peak at 1215 cm −1 were susceptible to oxidation. After oxidation processing, on the one hand, the content of hydrophobic groups on coal surface showed an obvious decrease while that of hydrophilic groups showed a significant increase. What’s more, the content of carbonyl group had a close correlation with the extent of oxidation of the coal sample. On the other hand, it was found that the surface morphology of coals was significantly changed after oxidation process, and there were more pores and cracks on the coal surface. As a result, the contact angle of coals showed a significant decline after oxidation processing and it declined more quickly with the increase of contact time. Consequently, the poor flotation performance of oxidized coals may be attributed to the dramatic changes in both surface chemical structure and surface morphology in oxidation process. [ABSTRACT FROM AUTHOR]