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Boiler

The Noxtech® technology can be applied to utility, industrial, and waste-to-energy boilers. NOx emissions are reduced by gas-phase reactions at temperatures of 1400-1550° F using urea or ammonia. The flue gas temperature is controlled by a unique fuel injection system or grid. The fuel and chemical are introduced using a grid of injection nozzles within the convective section (the required temperature and residence time is available) of a boiler or a separate cavity can be constructed to accommodate the temperature and residence time required by the Noxtech System. Using no catalytic surfaces, only 150-200 milliseconds of residence time is needed in existing boiler cavities to reduce NOx by 90% or more with less than 5 ppm NH3 slip. This control of NH3 slip is expected to prevent the condensation of trace solids (ammonium bisulfate), which can foul air preheaters or produce visible stack plumes.

The gas-phase reactions do not depend on catalytic surfaces, which can foul and degrade with use. The reaction temperature is controlled reliably with as little as 50-100° F of flue gas heating. This temperature control greatly decreases CO, unburned hydrocarbons, and particulate matter. The flue gas heating may replace as much as 3% of the boiler fuel which increases furnace O2 by about 0.6%. The higher furnace O2 has been found to reduce ash LOI, while equivalent combustion in the cavity maintains normal stack O2 levels. The existing steam reheater, economizer, and air preheater recover the heat released in the convective section, so the Noxtech® process does not decrease the boiler efficiency or load rating.

A Noxtech® injection grid is installed within existing cavities between banks of heat exchange tubes. Fuel and urea or ammonia is injected into a flue gas mixer creating a homogenous lean reaction zone. The reaction zone requires only 150-250 milliseconds of residence time in a cavity with a maximum normal operating temperature of 1,400-1,500° F. The Noxtech® fuel injection grid can control reaction temperature automatically as boiler load fluctuates. Since the Noxtech® System controls temperature, emissions of NOx are reduced at the same location regardless of boiler load.

As the inlet gas flow rate and temperature decrease at lower boiler loads, the Noxtech® system maintains an optimum temperature for NOx reduction by controlling the fuel injection. The urea or ammonia injection is controlled to maintain NOx emissions compliance.

The Noxtech® system can provide the end user with the following benefits:

Bullet  90% or more NOx reduction to stack gas levels below 50 ppm
Bullet  Less than 5 ppm NH3 slip at maximum NOx reduction levels 90%+
Bullet  Concurrent reductions in CO, hydrocarbons, and ash LOI
Bullet  No reduction in boiler efficiency or load rating
Bullet  Minimum downtime for retrofitting boiler with injection grid
Bullet  No catalyst to replace or clean provides major reduction in operating costs/maintenance

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