CFD-modelling of the SNCR process in iron ore grate-kiln plants

Abstract: LKAB (Luossavaara-Kiirunavaara AB) is an international company that produces iron ore products for the steel industry; their main product is iron ore pellets. The aim with this research project is to numerically investigate if it is possible to use selective non-catalytic reduction (SNCR) technologies in grate-kiln pelletizing plants for NOx reduction. The technique had, to the best knowledge of the author, never been used in this context before despite that it is commonly used in cement and waste incineration plants. The investigation is done in several stages: 1) Reveal if the technique is possible to use with the two most commonly reagents ammonia and urea. 2) Derive a chemistry model for cyanuric acid so that this reagent also can be scrutinized. 3) Compare the reagents urea and cyanuric acid in the grate-kiln pelletizing process. A CFD model of parts of the real grate was created and numerical simulations with the commercial code ANSYS CFX was carried out solving the flow field. A model for spray injection into the grate was then included in the model enabling a study of the overall mixing between the injected reagent droplets and the NOx polluted air. It is shown that the SNCR technique with ammonia does not work in the grate-kiln process. Urea on the other hand can be used under some conditions and also cyanuric acid. The results lay grounds for a continued development of the proposed chemistry model.