Emissions from Landfill Renewable Natural Gas (RNG) Plants in the Central USA
Summary:
The production of Renewable Natural Gas (RNG) from landfills has the potential to generate a useful resource while reducing methane and other gaseous landfill emissions; however, the net greenhouse gas (GHG) reductions achieved depend on many factors. The current study evaluated the losses inherent in gas handling and upgrading after collection from the landfill and prior to sales into existing natural gas pipelines.
Objectives:
- Quantify emissions of GHGs, primarily methane, and possibly other gas emissions species during the landfill gas (LFG) upgrading process
- Provide actionable information on the source of emissions and potential mitigation measures
- Estimate the GHG intensity of RNG due to emissions and combustion products.
Project Plan:
Visit several RNG facilities in the Central USA, ranging in capacity, and utilizing various processing methods to refine the collected LFG. Isolating RNG facilities from the landfill and collection system, identify and quantify all methane emissions using direct, downwind, and process measurements. Compare results to natural gas handling facilities of similar complexity such as gathering and treatment facilities.
Schedule:
Field campaign was completed in 2021.
Results:
Onsite, direct measurements, downwind tracer flux, and other test method (OTM) measurements were made at 9 renewable natural gas (RNG) plants located in the central US states of Kansas, Oklahoma, and Texas between 8/17/2021 and 9/10/2021. CH4 emissions originating between the inlet and outlet of each plant were quantified. Plant-level, throughput-normalized emissions (emission intensity) based on plant inlet CH4 flows, emission factors developed from measurements and observations, coupled with estimates for emissions from flaring and waste gas streams range from 0.4% to 5.7%. RNG plants without direct venting all show emission intensities less than 1%, while those that vent some portion of waste streams directly to atmosphere show emission intensities of 4-6%. Concurrent downwind measurements at two plants employing direct venting support modeled results, but indicate slightly higher emission intensities of 5-7%.
In aggregate, the 1.8% CH4 emission rate from the 9 plants, including the direct venting, is comparable to that of flaring (≈2%). If all 9 plants exhibited similar emissions as those without direct venting, CH4 rates would be approximately reduced by 2/3rds, to ≈0.6%. Considering total equivalent carbon emissions, expressed as CO2e, for the 9 plants studied, including direct venting at some of the plants, the RNG gas has approximately one half of the carbon intensity of natural gas. If direct venting of gas can be eliminated, resulting in a CH4 emission rate of 0.6% of methane handled, RNG gas has approximately one third the carbon intensity of the equivalent amount of natural gas.
Publications:
Final Report coming soon and will be posted on Mountain Scholar.
Funding Provided by:
