Insights in distributed secondary gas injection in a bubbling fluidized bed via discrete particle simulations

Experiments have shown that distributed secondary gas injection via a fractal injector in fluidized beds can significantly reduce the bubble size, and may also decrease the bubble fraction. In order to gain insight into the distribution of the gas between the phases and the mechanisms behind these effects simulations of small bubbling fluidized beds with one or two secondary gas injection points were carried out using a discrete particle model. Although the systems are very small, so that wall effects cannot be excluded, the model predicts that the bubble size and bubble fraction both decrease with secondary gas injection, while the gas flow through the dense phase increases. The secondary gas tends to stay in the dense phase, which limits the amount of gas available to form bubbles and is the main contributor to the decrease in the bubble size and fraction. The gas–solid contact improves as a result.

Graphical AbstractDiscrete particle simulations of a fluidized bed with secondary gas injection were performed to determine the mechanisms behind the reductions in bubble size and bubble fraction seen in experiments. The results indicate that the secondary gas stays in the dense phase, limiting the amount of gas available for bubbles and reducing the bubble fraction, which improves the gas­solid contact.Figure optionsDownload as PowerPoint slide