CFD modelling of the flow through a grate-kiln

Abstract: LKAB is an international high-tech minerals group, one of the world's
leading producers of upgraded iron ore products for the steel industry and a
growing supplier of industrial minerals products to other sectors. Over the
last years, the swedish industry has been facing increasing governmental
pressure to control and reduce pollutant emissions, one of which is nitrogen
oxides NOx. The pelletizing process requires high excess air levels and high
temperatures, which promotes the production of NOx. Consequently, LKAB is
running several research projects with the objective to reduce NOx emissions
from the company's pellet production plants, including both primary and
secondary measures.

This work is part of an investigation whether Selective Non-Catalytic
Reduction (SNCR) is suitable for reducing NOx emissions in LKAB's grate-kiln
iron ore pelletizing plant SK. The motivation of this specific research is
to develop a CFD model that enhances the understanding of the aerodynamics
and mixing of species inside the rotary kiln. At first, a parametric study
of the pure airflow through the kiln is carried out and under certain
conditions, a transient behaviour similar to that of vortex shedding is
observed, with a strong dependence on momentum flux ratio between the
secondary air jets. Further, the development of a preliminary coal
combustion model is set out, which is in need of continued work in order to
produce reliable predictions of various parameters relevant to the SNCR
process. However, the effect of the combustion on the flow field is limited,
indicating that the pure airflow model can be used to broadly investigate
the influence of the secondary air flow.