The following animations from CFD modeling show the flue gas patterns on a boiler with a conventional air system (left side) versus that same boiler modified to a “stacked-air” system. This clearly shows the improved vertical turbulence.

Conventional System:

“Stacked-Air” System:

As shown in both air systems, the combustion air system initiates the mixing inside the furnace. Where air is introduced, mixing energy is created, but quickly dissipates. The stacked air system provides more turbulence than the conventional systems over the furnace height. Another advantage that is easily recognized is that the full furnace volume is better utilized with the stacked air system. The CFD Model animations also show that the temperature around the char bed is much hotter, but the flue gas temperature at the bull nose is lower with the stacked air system.

Physical sampling of carry over at the bull nose level indicated that the material carry over substantially reduced by more than 70 percent for the same boiler loading. This is due to:

• Better material burnout
• Hotter/more stable char bed, which allows more tertiary airflow percentages and improved liquor spray/temperature adjustments
• Full furnace utilization, which results in slower vertical velocities