The vertical velocity improvement can be observed more clearly with an iso-view of just the vertical velocities over a fixed amount.  For example, the following two CFD animation sketches show the locations within the furnace where the velocities are greater than or equal to 8-meters/second.

FG Flow > 8 m/s – Conventional System:

FG Flow > 8 m/s – “Stacked-Air” System:

These two iso-views show that the vertical velocities are much slower in the stacked air system versus a conventional air system. All areas within the brown color have vertical velocities 8 m/sec or greater. Clearly, the stacked air system is able to reduce the upward velocities throughout the furnace, and this has a major impact on the physical carry over of material.