STEAG SCR-Tech, Inc.

Overfire Air Systems

Overfire Air (OFA) works by diverting a portion of the total combustion air away from the primary combustion zone. Overfire air lowers the air-to-fuel ratio at the burners, lowering the oxygen in the primary flame zone, which reduces NOx conversion of fuel-nitrogen in volatiles and reduces thermal NOx formed in the primary flame zone.

STEAG SCR-Tech has conceived, designed and installed overfire air systems of various types. Overfire air systems range in complexity of design, cost of installation and effectiveness of NOx reduction. We use CFD modeling (see section under Combustion Optimization) to design overfire air flow, duct size, nozzle size, flow orientation and various other system designs, as well as predict eventual performance.

A simple but cost-effective overfire air design STEAG SCR-Tech has implemented involves direct flow of air from the windbox to the main furnace above the burner zone. This is accomplished by removal of refractory webbing between waterwall tubes between furnace and windbox. While overfire airflow control with such a design is limited, the resulting combustion staging reduces NOx.

Another simple and effective overfire overfire air system STEAG SCR-Tech has tested and implemented applies to wall fired boilers with multiple burner elevations. By removing the uppermost burners from service (stopping coal flow while allowing combustion air flow) staged combustion can be created. STEAG SCR-Tech has employed this technique in combination with split flame burners to achieve significant NOx reductions (over 40% below baseline levels for a 200 MW wall fired unit).

STEAG SCR-Tech’s engineering and design team can build overfire air systems for your boiler

For existing OFA installations, STEAG SCR-Tech optimizes and tunes your equipment using CFD modeling, maximizing NOx removal



Roger Glickert
Business Manager
(412) 429-3576

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