There are four general methods for limiting particulate emissions from waste combustors

  • Limiting the ash content of the waste feed via source control or selection.

  • Designing and operating the primary combustion chamber to minimize fly-ash carryover.

  • Designing and operating the combustion chamber(s) in accordance with good combustion practice to minimize soot formation.

  • Using well-designed and well-operated fine-particle APCDs.

Source control of ash-producing waste constituents is an obvious method to reduce particulate emission, but it is impractical for most waste combustors. However, some incinerators and boilers burning liquid hazardous waste are able to meet particulate matter emission limits by stringent source selection alone.

The first three methods listed above are effective in reducing particle loadings in the combustion gas but are generally not sufficient by themselves to meet current and proposed maximum-available-control-technology (MACT) emission standards for particulate matter. Add-on particulate control is expected to be needed to meet the proposed MACT standards for waste incinerators.

Fine-particle control devices are in three general categories: filtration collectors, including primary fabric filters (baghouses); electrostatic collectors, including dry and wet electrostatic precipitators (ESPs) and ionizing wet scrubbers; and wet inertial-impaction collectors, including venturi scrubbers and advanced designs that use flux-force condensation-enhancement techniques.

Acid Gases

Acid gases are flue-gas constituents that form acids when they combine with water vapor, condense, or dissolve in water. Acid gases include NOx, SOx, HCl, hydrogen bromide, hydrogen fluoride, and hydrogen iodide. HCl and SO2 are often present in uncontrolled flue-gas streams in concentrations ranging from several hundred to several thousand parts-per-million-by-volume. The concentrations of NOx, hydrogen fluoride, and sulfur trioxide are typically below several hundred parts-per-million-by-volume. Free halogens such as chlorine, bromine, and iodine can also be produced at low concentrations from combustion of wastes that contain compounds of those elements.

Emissions of SO2, HCl, and the other halogen acids can only be controlled through the use of add-on APCDs, which have been previously described in this chapter.

There are two sources of NOx from incineration (and other combustion) processes, commonly referred to as thermal NOx and fuel NOx. Thermal NOx is formed by the reaction of nitrogen and oxygen in the combustion air. Its forma-

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