Model predictions of PCDD and PCDF emissions on the iron ore sintering process based on alternative gaseous fuels

Abstract

The technology of fuel gas utilization on the iron ore sintering process has been proposed as an alternative for reducing the environmental load and improvements on the sinter quality have been obtained with additional decrease on the return of fines (<5mm). This paper deals with the numerical simulation of this innovative technology in order to evaluate the emissions of poly chlorinated di-benzene dioxin (PCDD) and Poly Chlorinated di-benzene furan (PCDF). The methodology is to partially replace solid fuel (coke breeze) by steelworks gaseous fuels; coke oven gas (COG), blast furnace gas (BFG) and mixture of these gases. A multiphase mathematical model based on transport equations of momentum, energy and chemical species coupled with chemical reaction rates and phase transformations is proposed to analyze the inner process parameters and the rates of PCDD and PCDF formations. A base case representing the actual industrial operation was used to validate the model and afterwards used as reference to predict four cases of fuel gas utilization: (a) 10% of the wind boxes inflow from N01 to N12 wind boxes with COG, (b) same condition with BFG, (c) same condition with 50% COG and 50% BFG and (d) mixture of 25% COG and 75% BFG. The model predictions indicated that for all cases, except only BFG, the sintering zone is enlarged and the solid fuel consumption is decreased. In order to maximize the steelworks gas utilization it is recommended the use of mixture of COG and BFG with optimum inner temperature distribution. It was found out that for all cases of gas utilization the PCDD and PCDF emissions could be decreased due to enlargement of the high temperature zone on the sintering bed and hence increasing the residence time of the reacting gas within the high temperature zone.