Foster Wheeler developed and installed the first boundary air systems in the 1960's as a solution to manage slagging due to the low ash fusion temperatures found in eastern bituminous coals. The role of the boundary air system has since expanded as a result of its ability to reduce lower furnace wastage caused by reducing atmospheres.

Foster Wheeler continues to be an advocate for the benefits of boundary air systems and remains a leader in their design. A significant number of past retrofits and new Foster Wheeler boilers are currently operating successfully with boundary air systems.

Each system consists of lower furnace air ports normally located between the lower outer burners and adjacent waterwalls, see sketch in Figure. The jets from the ports inject air into the region between the side waterwalls and the outer burner columns. This effectively increases the local excess oxygen level along the waterwalls preventing the formation of gas constituents such as hydrogen sulfide and carbon monoxide, which can cause waterwall corrosion. Generally only a small quantity, approximately 4% to 8%, of the total combustion air is required for the boundary air system.