NOx Control for Stoker Boilers

Overfire Air Systems

Steag Energy Services (formerly ESA) has designed and provided overfire air systems to numerous industrial and power stoker boilers. Many older stokers are equipped with poorly designed or insufficient overfire air systems. Steag Energy Services's (formerly ESA) overfire air systems typically involve a low capital cost and result in significant NOx reductions.

Flue Gas Recirculation

Flue gas recirculation (FGR) can be a very cost-effective means of NOx emission reduction as well as a means of improving combustion performance by enabling better spatial optimization and combustion efficiency by reducing ID fan capacity. Steag Energy Services (formerly ESA) has designed and installed FGR systems of various types with great success. Steag Energy Services (formerly ESA) has used FGR as a carrier in ash re-injection applications promoting increased efficiency and firing stability. Steag Energy Services (formerly ESA) has also used FGR as a replacement for undergrate air to create staged combustion and improve spatial grate combustion.

METHANE de-NOx

This natural gas reburning process reduces NOx emissions and improves combustion performance of solid fuel-fired stoker combustors. By improving grate combustion, METHANE de-NOX (MdN) increases boiler efficiency and enhances combustion of problem fuels. A low-capital retrofit, MdN is adaptable to a wide range of industrial stoker applications.

The MdN Process

In a typical MdN system, natural gas and FGR are strategically injected above the grate creating an oxygen deficient zone where a significant portion of NOx precursors decompose and react, forming N2 rather than NOx. Overfire air (OFA) is introduced higher in the furnace, allowing sufficient residence time for completion of reburn reactions and creating a burnout zone for the remaining combustibles in the flue gas. The schematic to the right depicts the MdN applied to a hog-fuel stoker boiler.

Benefits

The benefits of METHANE de-NOX vary somewhat depending on the application. The following are typical:

• Reduce NOx emissions by 50-70%.
• NO increasing undesirable emissions.
• No need for post combustion NOx controls.
• Reduce excess air.
• Increase thermal efficiency.
• Reduce CO2, SOx, H-Cs, particulates.
• Increased waste fuel firing capacity.
• Improved combustion of hard-to-burn fuels.
• Reduced gas usage in waste fuel stokers.
• Easy, low capital cost of retrofit.
• No need for downstream NOx controls.
• Improved load dispatch

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