飛灰/氫氧化鈣吸收劑高溫吸收二氧化硫之研究

Abstract

本研究以微分反應器模擬火爐乾吸收劑注入法，針對飛灰/氫氧化鈣吸收劑的飛灰/氫氧化鈣組成、不同種類之飛灰、硫酸化反應前的煅燒處理及吸收劑前處理的漿化處理等四種可能影響反應性之變因作一探討，並分別探討各情況在短時間及長時間（1小時）之結果。 吸收劑的漿化處理是將飛灰/氫氧化鈣混合物於水固比10/1、溫度65℃下漿化16小時後予以乾燥6小時；煅燒處理是將吸收劑，於950℃下煅燒20分鐘；硫酸化反應是在空氣流速4 L/min、二氧化硫濃度3000 ppm、反應溫度950℃下進行反應。 飛灰/氫氧化鈣吸收劑經漿化處理後生成箔片狀矽酸鈣水合物，其比表面積較氫氧化鈣及飛灰大，但高溫下吸收劑會因燒結而降低反應性，飛灰含量越高，燒結越嚴重。吸收劑一小時的鈣利用率在飛灰/氫氧化鈣配比小於約4/6時高於Ca(OH)2本身，但二氧化硫捕捉率則隨飛灰含量增加而下降，飛灰本身無反應性。 所用的兩種飛灰其鈣/矽比較小者所製備的吸收劑之初始反應速率較快，但長時間的結果則受飛灰影響不大。吸收劑未經煅燒時初使反應性較經煅燒者佳，但長時間下二者差異不大。漿化處理與否對於一小時鈣利用率及二氧化硫捕捉率皆有明顯的影響，在飛灰/氫氧化鈣比配比高於3/7以上時，未經漿化處理之吸收劑則以之反應性明顯高於經漿化者。 在高溫下除硫，於Ca(OH)2中添加適量的飛灰可以提升其鈣利用率，但會抑制整體吸收劑的二氧化硫捕捉率。

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.