Three dimensional DEM-CFD simulation of an intermittent operating parallel flow regenerative lime shaft kiln
A parallel flow regenerative kiln (PFR-kiln) consists of two vertical shafts and a connecting crossover channel. The two shafts periodically switch their function at regular intervals of about 12 min. While one shaft calcines the product in parallel flow with gas temperatures above 900 °C, the other preheats the stones in counter flow.
The transient processes occurring in an industrial scale PFR-kiln are described with a DEM-CFD approach. DEM describes the moving and reacting limestone bed in the kiln and is coupled with a 3D CFD simulation describing the interstitial gas phase. The kiln height is 18 m. The limestone bed is polydisperse with particle diameters between 5 and 9 cm. The heat needed for the endothermic calcination reaction is provided by methane combustion. The methane is supplied through multiple vertical burner lances.
The video visualizes the simulation results in the plane of symmetry after a quasi-steady state is reached. On the left side the particle surface temperature of the solid limestone phase (DEM side) is plotted. On the right side the gas phase temperature (CFD side) is shown. Each shaft cycles through the burning and regenerative mode at intervals of about 12 minutes (one cycle). Thus, both shafts spend the same amount of time in each operation mode. Due to this unsteady cycling process the combustion air in the burning shaft is preheated by the limestone, whereas the limestone was heated up in the regenerative shaft the cycle before. The video shows the kiln behavior for eight cycles. After each cycle the two shafts switch their function.
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