飞灰酸碱性对二噁英从头合成的影响

Effects of acidity and alkaline of fly ash on de novo synthesis of dioxins

飞灰表面的酸碱性对二噁英的从头合成反应影响较大,不仅能够改变二噁英的生成量,而且对二噁英同分异构体的分布也存在一定的影响。本文通过在实验室可控条件下添加不同比例的Ca(H2PO4)2和CaO酸碱性物质,改变模拟飞灰表面的pH,研究不同酸碱性对二噁英从头合成反应的影响。研究表明,添加5%(质量)的Ca(H2PO4)2时,飞灰表面的pH由原始的5.5下降至4.3,二噁英总量增加,而毒性当量基本不变;添加20%(质量)的Ca(H2PO4)2时,pH降低到3.6,生成的二噁英总量和毒性当量均下降;而添加0.4%(质量)、5%(质量)和20%(质量)的CaO调节pH至9.8、12.4和12.6时,二噁英总量及毒性当量均有减少。因此,飞灰表面碱性环境较酸性环境对二噁英从头合成反应的抑制效果好。此外,本文还研究实际焚烧炉飞灰中二噁英总量与碱酸比的相关性,结果表明流化床飞灰中二噁英总量与碱酸比的相关系数高达0.95,而炉排炉飞灰中两者之间不存在相关性。

The acidity and alkaline of fly ash could significantly affect the de novo synthesis of dioxins. It could not only influence the total concentration of dioxins, but also the distribution of congeners. In this study, different amounts of Ca（H2PO4）2 and CaO were added to control the pH values of model fly ashes. Experiments were conducted to study the effects of acidity and alkaline of fly ash on de novo synthesis of dioxins. The results suggested that the amount of dioxins increased and the I-TEQ values didn＇t change when pH values decreased from 5.5 to 4.3 with an addition of 5%（mass） Ca（H2PO4）2. When pH value decreased to 3.6 with an addition of 20%（mass） Ca（H2PO4）2, the total concentration of dioxins and I-TEQ value went down. While with additions of 0.4%（mass）, 5%（mass） and 20%（mass） CaO, the pH values increased to 9.8, 12.4 and 12.6 and the total concentration of dioxins went down as well as the I-TEQ values. Therefore, the alkaline environment of fly ash could be better to suppress the formation of dioxins than the acidic environment. Meanwhile, the correlations between the total concentrations of dioxins in fly ash and base/acid ratios were studied. The results revealed that the correlation value for fly ashes produced from fluidized bed was 0.95, however, there is no relationship for fly ashes which were collected from grate furnace.