Resource Recovery Facility: Emissions Data

Opacity | Carbon monoxide | Hydrogen chloride | Sulfur dioxide | Nitrogen oxides | Health effects

Nitrogen Oxides (NOx)

Nitrogen oxides, or NOx, is the generic term for a group of highly reactive gases that contain nitrogen and oxygen in varying amounts.

NOx is produced by two mechanisms: fuel NOx and thermal NOx. Fuel NOx is formed by the oxidation of nitrogen present in the waste at typical operating temperatures of combustion facilities. Thermal NOx is formed by exposing the nitrogen present in the combustion air to high combustion temperatures (generally higher than 2000 degrees F).

At the Resource Recovery Facility, NOx is controlled using a Selective Noncatalytic Reduction (SNCR) process, whereby aqueous ammonia is injected into the flue gas through the furnace walls. In this process, ammonia chemically combines with NOx to form nitrogen (N₂) and water (H₂O), which is released through the stack into the outside air.

In 2008-2009, the County modified the furnaces to include LN™ technology which modifies the balance of air and temperature distribution in the furnace to reduce NOx generation by half. With this technology and the SNCR progress, the units can limit annual NOx concentrations to 90 ppmv.

NOx is one of the major pollutants responsible for generating ground-level ozone. The permitted emission limit for NOx is 180 ppmv, averaged over a 24-hour period.

Ammonia injection must be carefully controlled to keep the stack emissions just below the permitted level. If excess ammonia is injected, it may combine with chlorine in the waste stream to form ammonium chloride. This would cause a visible plume, in violation of the permit limit for opacity.

Emissions monitoring data indicates that the NOx levels, on average, have been controlled to 90 ppmv, compared to the permitted emission limit of 180 ppmv.

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