Selective non-catalytic reduction of nitrogen oxides in the production of iron ore pellets

Abstract

Purpose. Using mathematical modeling, to assess the feasibility of introducing a Selective Non-Catalytic Reduction (SNCR) system as a measure to reduce nitrogen oxide emissions from the production of iron ore pellets. To determine the peculiarities of using ammonia solution and urea solution as reagents for the SNCR process, the influence of the injection of these reagents on the temperature regime during iron pellet production, as well as assess the expected efficiency of the SNCR method for purification of exhaust gases from nitrogen oxides. Methodology. The research results have been obtained using CFD-modeling in the ANSYS Fluent software package. To model this process, a computational domain is constructed, which corresponds in size to the preheating zone (PRE zone) of the actual iron pellet production plant. Two series of calculations are performed for this domain: the first, without adding a reagent, and the second, with a urea solution as a reagent for the SNCR system. Findings. For the first series of calculations, the temperature field and the pressure field in the computational domain is obtained. Experimental research makes it possible to assert that the physical conditions of the mathematical model are close to those at a real plant for the production of pellets. In the second series of calculations, the temperature field in the computational domain is obtained and the influence of the reagent injection of the SNCR system is determined, namely, the temperature decrease in the PRE zone of the pellet production plant by 1025 . The expected efficiency of reduction of nitrogen oxides using a 50% urea solution is about 60%. Originality. It has been revealed that the process of urea solution evaporation is intense, which accelerates the beginning of urea decomposition and, accordingly, the reduction reaction of nitrogen oxides. The temperature drop in the zone of moisture evaporation does not exceed 1025 C. The reagent injection (50% urea solution) with a consumption of 219 kg/h does not significantly affect the temperature regime in the PRE zone. Modeling the chemical reactions of the SNCR process with the injection of 50% urea solution droplets through lances into the PRE zone chamber indicates a 60% reduction in nitrogen oxide emissions. Practical value. The introduction of the SNCR system at pellet production plant can reduce nitrogen oxide emissions, which will have a positive impact on the environmental situation in metallurgical regions.