Experimental Study On The Inhibition Of PCDD/Fs Formation By Phosphorus-based Inhibitors

Aiming at the problems of insufficient understanding of the inhibition mechanism of dioxin inhibitors in the waste incineration process and the insignificant suppressing effects of engineering applications,a new type of low-cost and efficient phosphorus-based inhibitor was developed.Through literature research and analysis,this paper sorted out phosphorus-based inhibitors,and the inhibition mechanism and engineering application experiments of phosphorus-based compounds represented by ammonium dihydrogen phosphate and potassium dihydrogen phosphate were carried out,and obtained valuable conclusions.The conclusions mainly include the following:（1）In this paper,we studied the inhibitory effects of two phosphorus-based inhibitors,ammonium dihydrogen phosphate and potassium dihydrogen phosphate and thiourea on the de novo synthesis of dioxin.Both 8%thiourea and 8%ammonium dihydrogen phosphate showed significant inhibitory effects on de novo synthesis of 17toxic dioxins from fly ash The inhibitory effects on the concentration of dioxin formation is 97.2%and 98.2%,respectively,and the inhibitory effect on the toxic equivalent is as high as 96.4%and 96.7%,respectively.Using XPS and XRD to explore the effect of inhibitors on the morphological characteristics change of carbon,chlorine and catalytic metals in fly ash.The chemical thermodynamic calculation software HSC Chemistry 6.0 was used to simulate the equilibrium concentration and substance conversion of key factors such as catalyst and chlorine in the process of de novo synthesis and the inhibition of dioxins at different temperature in the low temperature section,in order to explore inhibition mechanism.The results showed that the phosphorus in the phosphorus-based inhibitor can react with copper chloride to form Cu₂P₂O₇,which reduced the catalytic activity.At the same time,the sulfur in thiourea can also react with copper chloride the generate Cu S/Cu₂S,which deactivated the catalyst and inhibited the formation of dioxin.In addition,the nitrogen in thiourea and ammonium dihydrogen phosphate would form ammonia,which would react with Cl₂to form HCl with weak chlorination ability,weakening the carbon chlorination reaction and inhibiting the formation of dioxin or its precursors.（2）In this paper,calcium oxide,urea and sodium bicarbonate are selected,and these three alkaline materials are respectively coupled with ammonium dihydrogen phosphate and potassium dihydrogen phosphate to explore the effect of phosphorus-based coupling base blockers on the de novo synthesis of dioxins from fly ash.At the same time,TG-FTIR was used to analyze the weight loss of the fly ash added with inhibitors during the continuous heating process and to detect their decomposition products,further analyzing the inhibitory mechanisms of the phosphorus-based inhibitors couple with alkaline materials.The results showed that after the addition of 4%potassium dihydrogen phosphate coupled with 4%calcium oxide,urea and sodium bicarbonate,the ability of inhibiting dioxins formation was significantly imporved.Coupled with calcium oxide,the inhibition efficiency increased from-699.7%to 84.98%.Coupled with urea,the inhibition efficiency increased to-152.1%,and coupled with sodium bicarbonate,the inhibition efficiency increased to 59.75%.And coupled with three alkaline materials could all significantly reduce the degree of chlorination of dioxins.After the addition of 4%ammonium dihydrogen phosphate coupled with 4%calcium oxide,urea,and sodium bicarbonate,the inhibition efficiency is slightly lower than that of pure ammonium dihydrogen phosphate.Compared with addition of ammonium dihydrogen phosphate,the inhibition efficiency of 2,3,7,8-substituted dioxins was slightly reduced to 97.15%,the inhibition efficiency was reduced to 84.68%after coupling with urea,and the inhibition efficiency after coupling with sodium bicarbonate is reduced to 82.41%.The thermogravimetric-Fourier transform infrared results showed that the modle fly ash added with ammonium dihydrogen phosphate,ammonium dihydrogen phosphate coupled with calcium oxide and thiourea had a higher equilibrium weight than pure modle fly ash after continuous thermal decomposition,indicating that inhibitors could react with the components in the fly ash to produce stable and difficult to decompose substances,which increased the balance weight.Infrared spectroscopy detected the absorption peaks of SO₂ and NH₃.Therefore,thiourea and ammonium dihydrogen phosphate may decompose SO₂ and NH₃ to inhibit the synthesis of dioxins.（2）In this paper,we analyzed the dioxins in the fly ashes of three typical domestic waste incinerators using phosphorus-based inhibitors,and we analyzed the effect of inhibitors on dioxin concentration and distribution in the fly ash,and economic analysis of inhibitors has been done.The results showed that after adding various inhibitors,there are differences in the inhibition effects.In the incinerator A,the inhibition efficiency of the inhibitor on the2,3,7,8-PCDD and PCDF were 76.34%and 76.25%,respectively.In the incinerator B,the inhibition efficiency of the inhibitor on the 2,3,7,8-PCDD and PCDF were 67.85%and 49.52%,respectively.In the incinerator C,the inhibition efficiency of the inhibitor on the 2,3,7,8-PCDD and PCDF were 19.16%and 30.58%,respectively.The use of ammonium dihydrogen phosphate and alkaline materials can reduce the operating cost of the inhibitors and also ensure a better dioxin suppression effect.The above results provide important reference for the industrial application of phosphorus-based inhibitors.