Patent ID: 6383362
Filing Date: 2002-05-07
Classification: A62D,C02F

Abstract:
A process for eliminating dioxins, which are generated from a refuse incinerator and have a structure such that two unit substances having a benzene nucleus are bound together via one or two oxygen atoms and at least one chlorine atom is bound to at least one benzene nucleus, from a mixed gas composed of smoke and ash carrying dioxins adhering thereto, which process comprises the steps of:passing the above mixed gas through a particulate matter separator and thus passing the mixed gas through a water curtain to thereby cause the dioxin-entraining ash to be taken up in water and discharging only harmless smoke thus separated alone into the atmosphere, separating the resulting mixture of water and dioxin-carrying ash into dioxin-carrying ash and water in a separator, washing the dioxin-carrying ash separated in the above manner with washing water to thereby elute the oleaginous dioxins entrained by the ash to give an emulsion-like oil-water mixture, and separating the resulting mixture, by means of a separator, into ash, which is now dioxin-free, and the emulsion-like oil-water mixture in which dioxins are dissolved, washing the dioxin-free ash first with acidified water, then with alkaline washing water and further with neutral water, to give moist ash and aqueous washings and recovering the ash, combining the water separated from the above-mentioned dioxin-carrying ash, the dioxin-containing emulsion-like oil-water mixture and the above washings and admixing the whole mixture with a pH adjusting solution, to give a liquid mixture, electrolyzing the liquid mixture in a primary electrolyzer equipped with an anode and a cathode to thereby decompose dioxin components into unit benzene nucleus substances and substitute a hydrogen atom(s) for the chlorine atom(s) on the unit benzene nucleus substances, to give a harmless aromatic oil fraction and gaseous chlorine in the upper layer of the electrolyzer, and separating and recovering the aromatic oil fraction and gaseous chlorine, respectively, transferring the dilute liquid mixture remaining after recovery of the aromatic oil fraction and gaseous chlorine and now mainly consisting of water to a secondary electrolyzer equipped with a metal anode and a metal cathode and electrolyzing the mixture therein to generate hydrogen at the cathode as a result of electrolysis of water and a metal hydroxide at the anode, thus decomposing the remaining trace amounts of dioxin components into unit benzene nucleus substances and substituting a hydrogen atom(s) for the chlorine atom(s) on the unit benzene nucleus substances, to give a harmless aromatic oil fraction and a trace amount of gaseous chlorine in the upper layer, and separating and recovering the harmless liquid aromatic oil fraction, allowing the above metal hydroxide to take up those substances that are contained in the dilute liquid mixture as well as the above-mentioned trace amount of gaseous chlorine and thus precipitate in the bottom layer, recovering this precipitate and discharging or draining the middle layer electrolysis liquid.