Experimental Study On The Effect Of Pyrite On The Formation Of Dioxins And The Emission Of Dioxins In Medical Waste Incineration

Incineration treatment is currently becoming one of the main disposal technologies for municipal solid waste(MSW) and medical waste(MW) in China, however dioxin as highly toxic substances which are mainly generated from the process of waste incineration can be emitted to the environment by means of flue gas and fly ash. It will be a huge threaten to the environment and human health. The aim of this article is to find one suitable way to inhibit the formation of dioxin during the process of waste incineration. A series of fundamental studies involving of control technology for dioxin were conducted by means of experimental and large-scale waste incineration device. The main contents of the dissertation are formed as follows.1) Experimental study on the mechanism of pyrite oxidation was conducted. It was found that pyrite can be directly oxidized into sulfur dioxide and ferric oxide in the air atmosphere above 500℃. The oxidation of pyrite follows the unreacted core model.2) The effect of pyrite on the formation of dioxin was studied in tubular furnace. It was found that when pyrite added at low S/Cl molar ratio, it didn't inhibit the formation of dioxin but also promote it. While at high S/Cl molar ratio, the addition of pyrite could effectively inhibit the formation of dioxin. The higher S/Cl ratio leads to the higher efficiency of inhibition. Reduction efficiency of total and I-TEQ concentration for PCDD/Fs were respectively obtained to 98.9% and 98.3%, when S/Cl molar ratio was 1.95. The congener distribution and [PCDD]/[PCDF] ratios varied with the different S/Cl ratio, which means different inhibition mechanisms occurred. It can be proposed that sulfur plays a major role when ratio of S/Cl belows 1.5. While ferric oxide plays a major role when ratio of S/Cl equals 1.95. The inhibition of PCDD/Fs formation by pyrite can be attributed to sulfur dioxide and ferric oxide.3) The formation and emission of dioxins in new waste incineration device Rotary Kiln-Fluidized Bed at different rotary speed was conducted. It was observed that the emission of dioxins increases with the increased rotary speed and the higher rotary speed leads a higher emission of dioxins. Total and I-TEQ concentration for PCDD/Fs were respectively obtained to 41.05ng/g fly ash and 7.58 ng I-TEQ/g fly ash., when rotary speed equals 0.82 r/min. Compared to the fly ash sample, the formation of dioxin on slag is much less. Since real-time measurement of PCDD/Fs in a full-scale waste incinerator is impossible, the correlation of PCDD/Fs with emission levels of other more easily measured pollutants could be a tool in predicting the PCDD/Fs formation levels. It can also give some suggestions to keep the operation at a state condition to reduce the formation of dioxins. It was found that the emission of dioxin decreased at higher concentration of NOx and H₂O in the flue gas. At the same time, the formation of dioxin increased with higher concentration of O₂.