Abstract: The objective of this article is to study the inhibition characteristics of SO₂ on de novo formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) at various temperatures and to explore its inhibition mechanism by simulation of reaction process utilizing HSC Chemistry 6.1 software. Model fly ash and flue gas (10%O₂/5%H₂O/85%N₂) were used as materials of the de novo formation of PCDD/Fs in a temperature range of 200-400℃. SO₂ of concentration 200 mg·m^-3 was added as inhibitor in inhibiting experiments. The suppression rate and homologue distribution of PCDD/Fs were analyzed to find SO₂ inhibiting characteristics. The results showed that the control ability of SO₂ was obvious and became stronger along with increase of temperature. Both total suppression rates and toxic equivalent concentration of PCDD/Fs increased with temperature, at 200℃ both below 20%, at 300℃ 75.6% and 77.3%, and at 400℃ up to 89.2% and 80.5% respectively. SO₂ caused a lower-chlorinated distribution of PCDD/Fs, especially for PCDDs. At higher temperature, SO₂ restrained chiefly PCDFs while at lower temperature PCDDs was mainly inhibited. Besides, SO₂ showed selective inhibition for dioxin isomer. At 300℃ de-chlorination of high-chlorinated PCDFs, like HpCDF and OCDF, made 2,3,7,8-TCDF increase. Based on the computation for Gibbs free energy of pivotal reactions and their equilibrium composition, SO₂ preferentially reacted with CuCl₂, and CuSO₄ formed had no catalytic activity. Then, reaction of SO₂ with Cl₂ made decrease of chlorine source. So, formation of PCDD/Fs was brought down. The results of reaction simulation could not only verify and replenished the sulfur inhibition mechanism existed but also could be an effective and creative method for exploring inhibition mechanism of different kinds of inhibitors like nitrogen-compounds. This could help develop high-effective inhibitors and apply in municipal solid waste incinerator practically.

Key words: sulfur dioxide, PCDD/Fs, chemical reaction, inhibition mechanism, simulation, phase equilibrium, Gibbs free energy

摘要： 实验研究了不同温度下SO₂对二 英（PCDD/Fs）从头合成的抑制特点，运用HSC Chemistry 6.1软件对主要无机化学反应过程进行模拟，探究了SO₂的抑制机理。结果表明，SO₂对PCDD/Fs总浓度和I-TEQ浓度的抑制效果随温度的升高而增强。PCDD/Fs总浓度和I-TEQ浓度抑制率从200℃不足20%分别提高到300℃时的75.6%和77.3%及400℃时的89.2%和80.5%；SO₂的添加促进了PCDD/Fs尤其是PCDDs同系物分布的低氯代化。在从头合成的高温段和低温段，SO₂分别侧重抑制PCDFs和PCDDs。相平衡计算和Gibbs自由能计算表明，SO₂优先与催化剂CuCl₂反应生成无催化活性的CuSO₄，其次与氯源Cl₂反应，最终实现PCDD/Fs的生成抑制。模拟结果对现有硫基抑制机理进行了验证和补充，对高效、廉价抑制剂的开发及工程使用具有重要意义。

关键词: SO₂, 二英, 化学反应, 抑制机理, 模拟, 相平衡, Gibbs自由能