尿素对减少铁矿烧结过程二恶英排放的作用机理

Reaction Mechanism of Emission Reduction of Dioxin by Addition of Urea in Iron Ore Sintering Process

研究了添加尿素抑制剂对钢铁厂烧结烟气二恶英减排的影响,结果表明,加入0.05%,0.1%,0.5%(ω)尿素,二恶英的毒性当量排放浓度分别为0.287,0.258,0.217ng-TEQ/m3,比未加尿素的排放浓度0.777ng-TEQ/m3大幅度减少.综合考虑二恶英的减排效果和是否产生二次污染,0.05%为尿素减排二恶英的适宜配比.烧结过程中尿素抑制二恶英形成的作用主要体现在低温合成反应,既通过与Cu2+反应形成稳定的氮化物,削弱Cu2+的催化活性,又通过与HCl反应,减少了形成二恶英的氯源.高温气相合成反应中,尿素并没有明显的抑制作用,反而因产生的HCl可能导致低温反应合成二恶英浓度增加.

The emission reduction experiments of dioxin of exhaust gas from iron ore sintering with addition of urea as inhibitor were carried out,the results show that when adding 0.05%,0.1% and 0.5%（ω） urea,the emission concentrations of dioxin are 0.287,0.258 and 0.217 ng-TEQ/m3,the dioxin emissions rate are remarkably decreased compared with 0.777 ng-TEQ/m3 without urea.Comprehensively considering the effects of dioxin emission reduction and whether the secondary pollution would occur,addition of 0.05% urea is relatively the most appropriate.The function of inhibiting the formation of dioxin by urea mainly depends on the low-temperature synthesis reactions,stable nitride forms through the reaction of ammonia and Cu2＋,reducing the catalytic activity of Cu2＋,and through the reaction of ammonia and HCl,reducing the chlorine source of dioxin formation.For the high temperature gas synthesis reaction,urea has no obvious inhibition effect,in contrast,the HCl formed in the high-temperature reaction may lead to the increase of dioxin concentration from the low-temperature synthesis reactions.