ZERO FORMATION OF DIOXINS AND SUPPRESSION OF DE NOVE SYNTHESIS

通过燃烧实验和热力学评价的基础研究，阐明了二恶英/呋喃（Dioxins/furans，简称Dioxins）主要在燃烧气体中残留的飞碳（C^*）物质表面的边界层，即CO/CO_2比值较高的非均质位置生成。因此，可以认为二恶英几乎不会通过蝇C^* 物质的分解或消失以及蝇C^* 物质的脱氯而形成。本文研究了用CaO对飞灰C^* 物质脱氯，以及用高能量密度的电磁波对燃烧气体进行辐照，使飞灰C^* 物质周围高CO/CO_2比的边界层弥散，能否实现二恶英的零生成。其中二恶英的浓度为85 ng-TEQ/m^3（标准温度）。辐照条件为：功率1.8kW，频率915 MHz，辐照时间6s，温度423 K。电磁波辐照后二恶英浓度降至2.4 ng-TEQ/m3（s. t. p.），分解率在97%左右。据认为，大量二恶英是通过在二恶英形成的飞C^* 物质周围的边界层的扩散以及飞C^* 物质随加热而分解或燃烧而分解的。在高温区设置CaO屑床层，二恶英的分解率从1 ng-TEQ/m^3（s. t. p.）至0.007 ng-TEQ/m^3（s.t.p.）因为在苍蝇C* 物质中和周围的氯被脱氯成化学稳定的CaCl 2。高温区脱氯对二恶英的零生成非常有效。

From our fundamental studies on combustion experiments and thermodynamic evaluations, it is clarified that dioxins/furans (Dioxins) are mainly formed at the thermodynamically heterogeneous site with high CO/CO_2 ratio, which is the boundary layer on the surface of the fly carbonaceous (C^*) matters remaining in combustion gas. Therefore, it is considered that Dioxins are hardly formed by the decomposition or the disappearance of the fly C^* matters and by the dechlorination from the fly C^* matters. The present study has investigated whether zero formation of Dioxins was achieved or not by the dechlorination from the fly C^* matters with CaO, and by the dispersion of the boundary layer with high CO/CO_2 ratio around the fly C^* matters through an irradiation of electromagnetic wave with high energy density to combustion gas.Electromagnetic wave was irradiated to an exhaust gas of PVC combustion, in which Dioxins concentration was 85 ng-TEQ/m^3 (s.t.p.). The irradiation conditions were the power of 1.8 kW, the frequency of 915 MHz, the irradiation time of 6 s, and the temperature of 423 K. Dioxins concentration after the irradiation of electromagnetic wave decreased to be 2.4 ng-TEQ/m3 (s.t.p.), the decomposition rate of about 97 %. It is regarded that a lot of Dioxins is decomposed by the dispersion of the boundary layer around the fly C^* matters, where Dioxins are formed, and by the decomposition or the burning out of the fly C^* matters with heating up. Decomposition rate of Dioxins are expected to improve more at higher temperature zone.By setting CaO chips bed in the high temperature zone, Dioxins extremely decreased from 1 ng-TEQ/m^3 (s.t.p.) to 0.007 ng-TEQ/m^3 (s.t.p.) because chlorine in and around the fly C* matters was dechlorinated to thermodynamically stable CaCl2. The dechlorination at the high temperature zone is very effective for zero formation of Dioxins.