TechnicallySpeaking
Calculating Air Emission Rates May Save You from Potential Fines
Carbon monoxide (CO) emissions from operating combustion equipment can trigger state air permitting and annual emission reporting requirements that may drive up costs for owners of landfills and publicly owned treatment works (POTW). Flares, commonly used at landfills and POTWs, burn landfill gas and digester gas generated at the plants, and often owners may not be aware that the pollution exceeds regulatory thresholds. Fines, increased public scrutiny and extra time generating and submitting reports may result from violating state regulations.
Each state enforces different thresholds, and the regulatory agency holds the owners and operators responsible for calculating plant emissions to determine regulatory obligations.
Emissions from wastewater treatment systems and solids handling operations generally do not exceed regulatory thresholds, despite their potential to generate the most public scrutiny; however, a POTW larger than about 80 MGD or one that generates a large contribution from a volatile organic compound (VOC) source, such as a chemical manufacturer or refinery, may generate emissions significant to register beyond state regulations.
Microturbines and reciprocating engines frequently used at landfills and wastewater treatment plants generally produce lower carbon monoxide emissions than flares; however, emissions from other regulated pollutants such as nitrogen oxides register higher. Calculating the emissions of each regulated pollutant will help owners and operators comply with state regulations and help ensure efficient operation of landfills and POTWs.
States Vary In Permit Requirements
In Minnesota, a permit is required if potential emissions from a facility exceed 100 tons per year (ton/yr) CO. Using a U.S. Environmental Protection Agency emission factor and a 50-percent methane content, a 1,000 cubic foot per minute (cfm) flare has the potential to emit 100 ton/yr CO. Note that the threshold is based on potential emissions (i.e., the equipment capacity), not on the actual use of the equipment. Therefore, an infrequently used combustion unit can still trigger the need for a permit. Minnesota requires an annual emission report of any facility that needs a permit.
In Wisconsin, the permitting threshold is lower: 9.0 pounds CO per hour (there are some exceptions to this rule, see the Wisconsin Administrative Code NR 407.03). With emission assumptions similar to those used above, a 400 cfm flare could emit 9.0 lb/hr CO and require a permit. An annual emission report is required if actual emissions of CO exceed 10,000 pounds per year. This is equivalent to about 27 million cubic feet of gas burned (or about 51 cfm operated continuously). In Wisconsin, an annual emission report can be required of facilities that do not need a permit.
Colorado has even lower thresholds for permitting. Colorado is exempt from permitting combustion units that use gaseous fuel and have capacities less than 10 million BTU per hour. Assuming digester or landfill gas contains 560 BTU per cubic foot, a 300 cfm landfill or digester gas flare will need a permit.
Contact Tom Henning for more information on this subject.
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