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Quantifying Fugitive Methane Emissions From Gas Flares: WERF'S New Flare Efficiency Estimator

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Abstract:

A Flare efficiency estimator (FEE) is as part of a Water Environment Research Foundation (WERF) project U2R08 entitled “Methane Evolution from Wastewater Treatment and Conveyance” under WERF's Climate Change Program. The FEE is developed based on the work of the Flare Research Group at the University of Alberta (UOA) and it will help estimate the fugitive green house gas (CH4) emissions from the unprotected ‘candlestick’ flares for digester gas and landfill gas flares. WERF is planning to make the FEE available online for free for its subscribers as an online tool.

Details of the FEE are discussed in this paper including a brief overview of prior research on flares, WERF's approach for this research study, the calculation methodology, and a description of the user interface for the estimator tool. The FEE can be used to predict flaring efficiencies in variable operating conditions. Calculation method used for the FEE uses the gas composition, flare jet velocity, wind velocity and ambient temperature and pressure as some of the key input parameters.

The most widely accepted reference to estimate flaring efficiency, EPA's Emissions Factors and AP–42, recommends using a value between 98 to 100 percent (99 percent as a default) as flaring efficiency for the candlestick flares operating on landfill or digester gas. However, simply assuming 99 percent combustion efficiency can significantly underestimate the GHG emissions.

To demonstrate the use of the FEE to estimate fugitive GHG emissions, data from two wastewater treatment plants (WWTP), one from Georgia and another from Tennessee are presented as case studies. The FEE estimated flaring efficiencies of 94.5 percent and 96.6 percent for the WWTP in Georgia (80 mgd average daily flow) and the WWTP in Tennessee (100 mgd average daily flow), respectively. These lower efficiencies compared to the 99 percent flaring efficiency recommendations per EPA AP–42 amounted to approximately 522 MT CO2e/year and 488 MT CO2e/year of underreported GHG emissions for the WWTPs in Georgia and Tennessee, respectively.

Keywords: CH4; Candlestick Gas Flares; Digester Gas; Fugitive Emissions; Gas Flares; Greenhouse Gases; Landfill Gas; Methane; WERF

Document Type: Research Article

DOI: https://doi.org/10.2175/193864711802837057

Publication date: 2011-01-01

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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