Instead of creating a new belt duct for the secondary level, a new primary “open windbox” wall duct replaces the existing primary windboxes. Each wall then has a single contiguous windbox that is fed from the same existing belt duct, but through a single, new feeder duct, which contains the Flowmatictm system and bridges the gap between the primary belt duct and the new contiguous primary windbox. Primary airflow and pressure are measured to each wall independently.

With these known parameters, imbalances to different areas of the boiler can be corrected to avoid bed disturbances. This allows the pressure in the existing primary belt duct to be operated at a pressure level that adequately supplies the secondary air port requirements, and the Flowmatic™ system will drop the pressure to the primary level to the correct pressure required at that level. The system resistance at the port can be controlled by adjusting the new port dampers to get “balanced” airflow among the walls. Conversely, if the primary windboxes are not replaced, a Flowmatic™ can be installed at each secondary windbox/nozzle to measure the secondary airflow.