Dispersing of a highly laden particle jet in a lab-scale pulverized coal injection (PCI) experiment
Sprache des Titels:
Proceedings of 4th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking
In many blast furnace based steel plants pulverised coal is used to reduce the amount of coke necessary in iron making. Beside a proper preparation of the pulverised coal a good design of the injection system is crucial for high PCI rates and an effective conversion in the raceway. To get to a better understanding of the injection process a lab-scale experiment under cold conditions was designed to investigate fluid flow and particle dispersion directly downstream the injection lance. In parallel the experimental setup is also simulated with CFD in order to compare the results and to validate the numerical particle models.
In the pneumatic test facility ceramic powder is injected by a lance into a main gas flow. While the main gas velocity can be adjusted from 0..40m/s the mass flow ratio between the powder and the gas in the injection lance which is controlled by the pressure in the powder storage hopper can reach values up to 100. The material density was chosen to match the particle relaxation time best to coal as this is the most important factor in guaranteeing similar dispersion behaviour. The particle distribution behind the lance is investigated by use of a high-speed camera.
In a second investigation effort the same flow situation is pictured by numerical simulations. Thereby, a hybrid Eulerian-Lagrangian particle model is applied. While the bulk particle flow inside the jet is modelled by a kinetic theory based Eulerian particle model further physical effects like particle rotation and poly-dispersity are introduced by additional Lagrangian tracer particles. Classical Reynolds averaged turbulence model fail in predicting the unsteady dispersion behaviour while the results of scale resolving models agree with the experiments. Since the detailed particle dispersion behaviour determines the transport controlled reaction rate the use of large eddy turbulence modelling seems to be mandatory.