Free Vent Through Flare or Selected LFG Wellheads
Many landfills operate a gas collection system to comply with state and federal solid waste requirements to prevent or mitigate landfill gas (LFG) migration beyond the facility property boundary but are not required to combust the LFG in a flare under air quality regulations. When such a landfill has declining methane content and gas flow that will no longer support combustion in a flare or an energy end-use, venting the LFG may be the option of last resort. Methane emissions will not be destroyed under this option except for methane oxidized under the cover. Venting can occur through the flare while still applying active vacuum and through individual LFG wellheads.
Greenhouse Gas (GHG) Mitigation Potential:
- Methane is not collected or destroyed.
- Some methane may be oxidized depending on cover type. For landfills without an active gas collection system, methane oxidation rates range from 10 percent in areas without final cover to 35 percent in areas with final cover.1
Criteria:
- Rural landfill without nearby neighbors to be affected by odor.
- Landfill with declining gas flow and methane content.
- Landfill does not have permit or other requirements to actively collect and combust gas.
Pros:
- For landfills venting through the flare, the active vacuum applied by the blower alleviates LFG migration/pressure concerns in and around the landfill to a greater extent than simply free venting through vents or wells.
- Nominal cost especially if no active vacuum is applied.
Cons:
- Possible odor issues.
- Achieves no GHG emission reductions.
Economic Considerations:
- Recurring operations and maintenance electricity costs to operate the blowers and apply vacuum to wellfield if active vacuum is applied.
- Minor savings in flare maintenance cost since no active flame (~$200/year for pilot fuel and avoided thermocouple replacement) and savings related to replacing logic controllers and data display systems should they be damaged by lightning.
References
1 U.S. EPA. Documentation For Greenhouse Gas Emission and Energy Factors Used in the Waste Reduction Model (WARM). Management Practices Chapters. November 2020. https://www.epa.gov/sites/default/files/2020-12/documents/warm_management_practices_v15_10-29-2020.pdf.