【作者】 张鹏宇；

【导师】 曾汉才；

【作者基本信息】 华中科技大学 ， 热能工程， 2004， 硕士

【摘要】 燃煤电站产生大量的污染物如SO2、NOx、Hg、Pb等。其中,SO2和NOx在太阳的紫外线照射以及某些粉尘颗粒的催化作用下,经过一系列的光化学反应,他们和空气中的水蒸气相遇,形成酸雨。酸雨会造成森林、水生物生态平衡破坏,影响人体健康。而Hg、Pb等痕量元素在温度较低的尾部烟道会发生一系列物理、化学反应,形成电除尘器难以捕获的细微粒子并排入大气,造成大气的重金属污染。因此,对燃煤电站污染物排放进行控制,尤其是SO2和NOx已经刻不容缓。本文采用活性炭,并且采用一定的方法进行活化处理,进行脱硫脱硝除汞的试验研究。分析比较各种处理方法的优劣、讨论其可能的机理以及各种因素对活性炭质材料脱硫脱硝除汞性能的影响。活性炭一般包括活性炭颗粒和活性炭纤维。本文采用了粘胶基活性炭纤维进行试验,用两种方法进行活化处理。方法一:先硫酸后氨水浸泡;方法二:先氨水后硫酸浸泡。样品的分析测试、XPS研究以及试验表明:方法一是可行的,能有效的引入含氧官能团、含氮官能团,并且它的比表面积、孔容表小,平均孔径变大。方法二不可取,它严重改变了活性炭纤维的孔隙结构,不能有效的引入含氧官能团、含氮官能团,降低活性炭纤维的脱硫性能。活性炭纤维脱硫就是把SO2吸附于活性位上,并把其氧化成SO3,有水的情况下转化成H2SO4,因此,温度、W/Q(W为活性炭纤维的质量、Q为气体流量)等影响吸附的因素以及氧含量、水的体积分数等势必影响活性炭纤维脱硫性能。试验表明:水是活性炭纤维脱硫中的关键步骤,控制整个反应的速率,随着水分的体积分数的增加脱硫效率增加,当水分达到8%后,增加的趋势不是很明显。氧在活性炭纤维脱硫中是必不可少的,它吸附于活性炭纤维的表面形成C-O,当氧含量增加时,脱硫效率提高,当氧含量增加到5%后,增加的趋势不是很明显。活性炭纤维是一种低温吸附剂,随着温度的升高,水蒸汽不能有效的凝结,脱硫效率降低。W/Q增加,活性炭纤维能提供的活性位增加,提高脱硫效率,考虑到经济性,推荐值W/Q为2.5×10-3～3×10-3Kg*min/L,此时脱硫效率平均为85%。在没有NH3的条件下,活性炭纤维把NO吸附转化成NO2,有水的情况下转变成<WP=4>HNO3。其中氧含量、水的体积分数、NO的起始浓度、温度等因素影响转化效率。试验结果表明:随着氧浓度的增加,转化提高,当氧浓度增加到5%后,增加的趋势不是很明显。在水分≦8%,水分对于NO转变成NO2是不利的。温度对NO的转化也是不利,随着温度的升高,转化率降低。当SO2、NO同时存在时,SO2和NO相互竞争吸附位,根据吸附理论,SO2的分子直径、沸点、偶极矩等都大于NO的,SO2要优先吸附,影响了NO向NO2的转变,并且,在吸附的SO2和形成的NO2之间存在一种相互作用,形成吸附态中间产物[(NO2)(SO3)],在水的作用下,形成H2SO4和HNO3,并释放出NO,对活性炭纤维脱硫有好处。对于除汞而言,本文采用活性炭颗粒以及活性炭纤维。活性炭表面的羰基、内脂基是Hg0氧化的活性中心,发生了电子转移,把Hg0氧化成Hg2+。用硫化钠预先对活性炭进行活化处理,可以有效提高汞的吸附量,并且与氯化锌浸泡的进行了比较,结果表明:氯化锌浸泡的汞吸附量大于硫化钠浸泡的。对于活性炭纤维,按照方法一进行活化后用来吸附汞,求出其吸附效率。同时,也进行了铅的吸附。更多还原

【Abstract】 Much contamination such as SO2,NOx,Hg and Pb comes from the coal-fired plants. After a series reaction by ultraviolet radiation and dust, SO2 and NOx are combined with H2O,at last form acid rain. Acid rain will do harm to environment and mankind health. The trace element such as Hg and Pb will have a series physics and chemic reaction in the low temperature flue gas. At last they escape from ESP, and at last emit to the air. Therefore it is very urgent to control the contamination, especially SO2 and NOx. In order to desulfurization 、denitrification 、adsorption of mercury, the paper uses activated carbon, adopt some method to catalyse it ,compares some method, discusses the mechanics and factor of desulfurization 、denitrification mercury adsorption by activated carbon.Activated carbon includes activated carbon fibers (ACF)and granular activated carbon(GAC), but the paper uses ACF, and adopts two manners to catalyse it. One is immersion in sulfuric acid before impregnated with ammonia, the other is immersion in ammonia before impregnated with sulfuric acid. The result shows that the first way is feasible, and can efficiently increase the oxygen functional group 、the nitrogen functional group. Furthermore after catalysis, the BET surface area and the capacity of pores become smaller, the average width of pores becomes bigger. The second way reduces the performance of activated carbon fibers.ACF adsorbs SO2 at active sites, then SO2 is converted to SO3, if there is water , sulfuric acid is formed. SO the performance of ACF is influenced by temperature、oxygen、moisture and so on. The results show that moisture is vital, controls the velocity of desulfurization. With the moisture increasing , the efficiency of desulfurization also improves, but when the moisture increases to 8%, the trend of augment is not visible . Oxygen is very important, and is adsorbed at the surface of ACF ,then C-O is formed. When the oxygen increases, the efficiency raises too, but after the oxygen increases to 5%, the trend is not obvious. We know that the ACF is a kind of low temperature adsorbent, so with temperature increasing, the vapor is not efficiently dewed and the efficiency of desulfurization decreases. With W/Q increasing, the activated sites that ACF supplies add , which can improve the efficiency. But we take into account the economics , we recommend that W/Q is 2.5×10-3～3×10-3Kg*min/L. <WP=6>Without ammonia, ACF converts NO into NO2. If there is water, NO2 goes on converting HNO3. There are many factors that influence the efficiency of conversion such as oxygen、temperature、water et al. The results show that the conversion increases with the oxygen, and the water is bad for conversion. Furthermore the temperature is also bad for conversion.If there is SO2 and NO, SO2 competes active sites with NO. According to the adsorption theory, the molecule diameter 、boiling point、dipole of SO2 are bigger than that of NO, so SO2 is adsorbed before NO, and influences the conversion of NO. Furthermore there is interaction between adsorbed SO2 and formed NO2, then intermediate product is formed. At last, H2SO4 and HNO3 are formed by water ,NO gives off. It is good for desulfurization by ACF.As is concerned for adsorption of mercury, the paper uses GAC and ACF. There are carbonyl group and lactone that are the active site for Hg0 capture. It involves an electron transfer process during Hg0 adsorption. Activated carbon is catalyzed by Na2S, which can enhance the adsorption of mercury. The result is compared with that of impregnated by ZnCl2. The paper concludes that activated carbon impregnated by ZnCl2 is better than by Na2S. ACF catalyzed by the first way also adsorb Hg and Pb.更多还原