Mechanism Of Inhibiting The Formation Of PCDD/Fs By Adding Urea In Iron Ore Sintering Process

Iron ore sintering process is an important sector for iron and steel industry as well as major pollution emission source of SO₂,NOx and PCDD/Fs.Since flue gas owns the following characteristics,including large amount,remarkable flow fluctuations and lower pollutant concentration,PCDD/Fs emission of sintering process has not been properly controlled.The majority of reduction technology are belong to end treatment,which are characterized by giant investment cost and easily causing secondary pollution.It is critical and urgent to develop an innovative on-line PCDD/Fs reduction method with higher efficiency and lower cost.The raw material of sintering machine was used in this research.The effects of adding methods on suppression efficiency and the differences of PCDD/Fs homologue suppression efficiency are systematically studied.The chemical mechanism of urea as an inhibitor to suppress PCDD/Fs formation in sintering process is revealed.The differences of PCDD/Fs homologue suppression after adding urea are analyzed,and as a result,the acting mechanism is investigated.With adding 0.02%,0.035%,0.05%urea solid particles to sintering mixture,the emission concentration of PCDD/Fs are decreased from 0.5 to 0.20,0.12,0.20ng-TEQ/m³,respectively.The results show that the urea has significant inhibition to PCDD/Fs formation.The function of inhibiting the formation of PCDD/Fs by urea mainly because the urea weaken or eliminate activity of the catalyst,while the urea is adsorbed on the active site catalytic surface.On the other hand,while the ammonia,generated by urea,suppresses Deacon reaction,the ammonia radicals can react with the carbon atoms at the edge sites by replacing the functional groups.Compared with adding urea solution and adding urea particles into 100 mm height from grate,the urea particles mixed with sintering mixture is the best way to inhibit PCDD/Fs formation.With adding urea,the emission concentration of high-chlorinated PCDD/Fs decrease sharply,while the low-chlorinated PCDD/Fs has an increase.This suggests that the urea addition led to a remarkable decrease in high-chlorinated PCDD/Fs,and suppression effect is strengthened with the increase of chlorination coefficient.On the contrast,the urea can promote the formation of TeCDF and TeCDD.The emission concentration and percentage content of low-chlorinated appear to increase remarkably,which is attribute to the urea greatly promoting the dechlorination reaction.