n(Na^＋)/n(Cl^-)对烟气脱氯及脱硫废水零排放的影响

Effect of n(Na^+)/n(Cl^-) on Semi-dry Dechlorination in Coal-fired Flue Gas to Realize Zero Emission of FGD Waste Water

半干法脱氯是通过碱基物质将燃煤烟气中的大部分HCl固定到飞灰中,同时将大幅度减少的脱硫(flue gas desulfurization,FGD)废水作为碱基溶剂回喷烟道,从而可实现脱硫废水零排放.通过搭建实验台对碱基物质与烟气中HCl和SO_2的反应效率随n(Na^+)/n(Cl^-)的变化进行了实验研究.结果表明:碱基物质与HCl的反应效率与n(Na^+)/n(Cl^-)呈正相关,且随n(Na^+)/n(Cl^-)的增大,其增长趋势逐渐变缓,在n(Na^+)/n(Cl^-)为4.8时,反应效率已经达到70%以上.针对一台660 MW燃煤机组进行计算,采用半干法烟气脱氯后,脱硫废水量显著下降,由8.01m^3/h降为2.31m^3/h;利用脱硫废水作为碱基溶剂回喷空气预热器后烟道,烟气温降较小,仅为2.49℃.半干法脱氯系统简单,运行成本较低,不会对粉煤灰的综合利用造成显著的不利影响.

Semi-dry dechlorination technology is put forward to attach most chlorine in coal-fired flue gas to fly ash by spraying in alkaline solution to realize the zero emission of desulfurization waste water. Simultaneously, drastically reduced FGD （flue gas desulfurization） waste water was used as the solvent of alkali, which could help to realize the target of zero emission of desulfurization waste water. Effects of n（Na^＋）/n（Cl^- ） on reaction efficiencies of base material with HCl^- and SO2 were analyzed. It shows that the reaction efficiency of HCl^- is positively correlated with n（Na^＋）/n（Cl^- ）. As n（Na^＋ ）/n（Cl-） continues increasing, there is a slower growth of HCl^- reaction efficiency. When n（Na^＋ ）/n（Cl^- ） is 4.8, reaction efficiency of HCl^- increases beyond 70%. For a 660 MW unit, after semi-dry dechlorination, the amount of FGD waste water decreases significantly from 8.01 m^3/h to 2.31 m^3/h, and the decrease of flue gas temperature is only 2.49 ℃ when waste water is sprayed back as the solvent of alkali. The system of semi-dry dechlorination is simple and the cost is relatively low. There is no significantly negative effect on the comprehensive utilization of fly ash after semi-dry dechlorination. KEYWORDS coal-fired flue gas, hydrogen chloride, semi-dry dechlorination, FGD waste water, zero emission, n（Na^＋）/n（Cl- ）