Conference article

In the current work, computational particle and fluid dynamics (CPFD) simulations are used to study an electrically heated bubbling fluidized bed (BFB) used as a calciner in a cement manufacturing process, applying a binary-particle fluidization system. Owing to the fine particle size (0.2 – 180 µm) of the limestone used as a raw meal in the cement kiln process, a conventional bubbling fluidized bed may be difficult to apply due to particle cohesion causing poor fluidizability of the particles smaller than 30 µm. In the current study, to enhance the fluidization of the raw meal particles, they are mixed with coarse (550 – 800 µm), inert particles. The aggregation and clustering of the fine particles will decrease due to collisions with inert coarse particles, and hence a more homogeneous distribution of raw meal particles may be achieved. The inert particles will also provide a thermal energy reservoir through their heat capacity and thereby contribute to a very stable bed temperature, which is advantageous in the control of the process. After the raw meal particles have been calcined, they have to be separated from the coarse, inert particles. This can be done by increasing the velocity of the CO2 used for fluidization to a value sufficiently high to entrain the raw meal particles, but still sufficiently low that the coarse, inert particles are not entrained. The commercial CPFD software Barracuda was used for simulations to investigate suitable operational conditions at 1173 K, such as the particle size distribution of the inert particles and the fluidization gas velocity. The impact of gas velocity variation on the fluidization of the particle mixture was studied, and an appropriate range of velocities for the calcination and entrainment modes could be determined. The simulations revealed that mixing raw meal particles with inert coarse particles can enhance the flowability in the FB reactor indicating that it is possible to apply the concept in a full-scale calcination process.

electrification, fluidized bed, calciner, CPFD, Barracuda, limestone