Purpose
One of the key reasons to implement manure anaerobic digestion (AD) to energy or an impermeable cover and flare (CF) system is to reduce greenhouse gas (GHG) emissions, especially methane (CH4), a potent GHG that makes up most of the US agricultural footprint. These systems that process or store manure, commonly liquid dairy or swine manure, are often referred to as biogas capture systems because they keep oxygen out and contain the manure gases that form primarily from the breakdown of organic matter by microorganisms. The biogas captured is then directed through collection pipes to a utilization system, where the goal is to convert the methane to the less potent carbon dioxide (CO2) via either combustion or electrochemical conversion. For AD systems, the biogas collected is consistent enough to burn or convert for useful energy. For CF systems, particularly those used in the Northeast and Upper Midwest, the biogas collected under the liquid manure storage cover is highly variable throughout the day and year, making it more suitable to flare the methane in the biogas rather than harvest energy. Biogas capture systems must be operated and maintained to avoid methane leaks and venting, particularly to realize their carbon reduction value that can often be monetized. Tools to easily identify point-source biogas losses, such as an optical gas imaging (OGI) camera, are still relatively costly for a bioenergy operation, however they can be used to periodically survey and conduct find it and fix it campaigns to repair and correct problems that may have gone unseen to the naked eye. The ability to better understand where and how biogas leaks and vents occur in AD and CF systems enables better design, operation, maintenance, and public confidence.
What Did We Do?
Twelve biogas capture systems operating on commercial dairy farms in NYS were surveyed once per quarter for at least a year for point-source methane losses using an optical gas imaging (OGI) camera (Teledyne FLIR GF77 uncooled) tuned to the infrared spectrum wavelength range (7 – 8.5 micrometers) where methane gas is absorbed. Any methane loss visualized with the OGI camera was recorded and its characteristics described and reported back to the farm or system owner. Other observations about the methane loss were recorded and losses were measured and/or quantified when feasible. The apparent size of the biogas loss was recorded, primarily by distinguishing between OGI visibility in “normal” camera mode versus “high sensitivity mode (HSM)”. Unique losses versus repeated (by visit) were tracked, indicating ease and motivation to correct the loss. Biogas vents were distinguished from biogas leaks, by characterizing a leak as an unknown or unintended biogas loss during normal operation. Biogas venting was considered loss that occurred by design during abnormal operating conditions, such as overpressure in the digester vessel that could not be immediately corrected with flaring excess biogas.
What Have We Learned?
This work is continuing through this year, and eight sites are completed so far. The results from those sites, that include four AD to energy systems (three electricity generation and one biomethane production) and four CF dairy manure storage systems, have generally highlighted that AD systems experience biogas venting more than biogas leaking whereas CF systems experience more leaking than venting. The number of unique biogas losses found was higher in CF systems than in AD systems, which may be due to their much larger biogas capture surface area that is also susceptible to damage from wind, wildlife, and thermal stress. Additionally, the biogas collection and flare struggle with variable biogas flow, quality, and operational robustness that results in lack of combustion during prolonged periods of the year. Another observation, which requires additional data collection from AD to biomethane systems to have confidence in, is that AD to electricity systems can result in biogas venting and/or unnoticed leaking when the biogas produced is greater than what the installed electric capacity can utilize. Additionally, most if not all AD to biomethane systems are instrumented to detect and measure biogas losses as part of their verification requirements for carbon market programs, making it less likely for losses to go unnoticed or unaddressed.
Future Plans
A methane loss detection protocol for both AD to energy systems and CF manure storage systems was developed by Cornell CALS PRO-DAIRY that has been improved during this project and will continue to evolve. Once the full 12 sites are completed, the protocol will be shared more broadly for reference, and best practices recommended for operations and maintenance to prevent, find, and correct biogas losses. Follow on work may include additional methane loss detection with total loss measurement of AD vessels and manure storage covers, to verify assumed loss rates used as defaults in GHG accounting.
Authors
Presenting & corresponding author
Lauren Ray, Sr. Extension Associate, Cornell University – PRO-DAIRY, LER25@cornell.edu
Additional authors
Jason P. Oliver, Dairy Environmental Systems Engineer, Cornell University PRO-DAIRY;
Peter Wright, Agricultural Engineer, Cornell University
Additional Information
https://cals.cornell.edu/pro-dairy/our-expertise/environmental-systems/climate-environment
Acknowledgements
This work is sponsored by the New York State Department of Agriculture and Markets. Special thanks to our collaborating dairy farms and biogas capture system operators.
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