Absorption of SO2 by Fly Ash/Ca(OH)2 sorbents at High Temperature
Date Issued
2006
Date
2006
Author(s)
Chang, Chih-Wei
DOI
zh-TW
Abstract
A differential fixed-bed reactor was employed to simulate the furnace dry injection process in order to study the reaction between
sorbents and SO2. The effects of fly ash/Ca(OH)2 weight ratio, the type of fly ash, the process of calcination, the process of slurrying ,and reaction time on sorbent reactivity were studied.
The fly ash/Ca(OH)2 mixture was slurried at a liquid/solid ration of 10/1 and 65℃,for 16h, and then dried for 6h. The sorbent was calcined at 950℃ for 20 min. The sulfation of sorbent was carried out at an air flow rate of 4L/min, 3000 ppm SO2, and 950℃.
Foil-like calcium silicate hydrates, which were formed by the reaction between Ca(OH)2 and SiO2 in the slurry, were found in the fly ash/Ca(OH)2 sorbents. The fly ash/Ca(OH)2 sorbents have greater surface areas than Ca(OH)2 or fly ash. But these sorbents tended to inter at high temperatures when the flyash content was high, and their reactivities were thus reduced. The on hour Ca utilization for a fly ash/Ca(OH)2 sorbent was higher than that of Ca(OH)2 alone when the weigh ratio was less than about 4/6; but the on hour SO2 capture decreased as the fly ash content increased. Fly ash itself was unreactive.
The type of fly ash affected only the initial reaction rate of a fly ash/Ca(OH)2sorbent;the one with lower Ca/Si ratio gave a higher initial rate. The uncalcined sorbents were more reactive than the calcined ones in the initial period of reaction, but they did not differ much at long reaction time. Whether the sorbent was slurried or not had freat effect on the sorbent reactivity. The unslurried sorbents were much more reative than the slurried ones when the fly ash/Ca(OH)2 ratio was higher than 3/7.
In high-temperature desulfurization, adding proper amount of fly ash to Ca(OH)2 sorbent could raise the utilization of Ca(OH)2, but would reduce the amount of SO2 captured per unit weight of the sorbent mixture.
Subjects
飛灰
氫氧化鈣
硫酸化
二氧化硫
fly ash
Ca(OH)2
sulfation
high temperature
SO2
Type
thesis
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