Department of energy office of fossil energy
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120 refer to the same document. 265 Future versions of the Report will correct these duplicate citations. Sierra Club also calls out the citation for EPA, 2012c, although this is a correct reference that points to EPA’s documentation of New Source Performance Standards. (3) Coal Methane Data API and Concerned Citizens criticize the quality of data that DOE/NETL uses for coal extraction. In particular, API claims that coal mine methane emissions may be higher than the factors used by NETL. Concerned Citizens simply claim that NETL used a limited set of references to characterize coal mine emissions. Methane emissions from coal mines are based on data collected by EPA’s Coalbed Methane Outreach Program and have been organized by coal type and geography. Due to data limitations, the LCA GHG Report used this data as a proxy for emissions from foreign coal. This limitation is noted in the LCA GHG Report and is accounted for by uncertainty. 266 The bounds on coal methane uncertainty were informed by the variability in coal mine methane emissions between surface mines (subbituminous coal) and underground mines (bituminous coal) in the United States. The default parameters in NETL’s model represent subbituminous coal, which has lower coal mine methane emissions than bituminous coal (these parameters are specified in Table 5-3 of the LCA GHG Report). If coal mines in Europe and Asia emit methane at rates similar to the underground, bituminous coal mines in the United States, then the life cycle GHG emissions from coal power would increase. This increase in coal mine methane emissions would increase the life cycle GHG emissions of coal power by 8 percent (from 1,089 to 1,180 kg CO 2 e/MWh, using 100-year GWPs as stated in the IPCC Fifth Assessment Report). 265 U.S. Envtl. Prot. Agency, Greenhouse Gas Emissions Reporting from the Petroleum and Natural Gas Industry: Background Technical Support Document (2011), available at: https://www.epa.gov/sites/production/files/2015- 05/documents/subpart-w_tsd.pdf. 266 See, e.g., NETL, Life Cycle Analysis of Natural Gas Extraction and Power Generation. 121 This uncertainty is illustrated by Figure 6-16 in the LCA GHG Report. Again, even though changes to coal mine methane emissions change the GHG results of the LCA, they do not change the conclusions of the LCA. 5. Methane Leakage Rate Used in the LCA GHG Report a. Comments A number of commenters, including Sierra Club, Food & Water Watch, Americans Against Fracking et al., and Zimmerman and Associates, claim that the methane leakage rate used by NETL is too low. They assert that it does not match top-down (or aerial) measurements recently conducted in regions with natural gas activity, nor does it match the leakage rate in a recent analysis of wellhead casings in Pennsylvania. b. DOE/FE Analysis Recent studies lack consensus concerning the extent and rates of leakage from the upstream natural gas supply chain, with the leakage rates reported by these studies ranging from less than 1% to as high as 10%. 267 One reason for this broad range of leakage rates is the fact that different analysts use different boundaries (e.g., extraction only, extraction through processing, extraction through transmission, and extraction through distribution). Further, top- down measurements are taken over narrow time frames and limited geographic scopes that represent only a snapshot of operations. They do not necessarily represent long-term operations over a broad area. Another reason for this range of leakage rates is confusion between leaks and losses. Natural gas leaks include emissions from pneumatically controlled devices, valves, compressor seals, acid gas removal units, dehydrators, and flanges. These leaks are a mix of methane and 267 See NETL, Life Cycle Analysis of Natural Gas Extraction and Power Generation (Section 6.2.1) (identifying reports that include various leakage rates). 122 other hydrocarbons, and are a subset of total natural gas losses. Another type of loss includes flaring, which converts methane to CO 2 and thus reduces methane venting to the atmosphere. Similarly, the combustion of natural gas by reboilers in a natural gas processing plant or by compressors on a pipeline represents the loss of natural gas that is used to improve the purity of the gas itself and move it along the transmission network. NETL’s expected cradle-through-transmission leakage rate is 1.2%. In other words, the extraction, processing, and transmission of 1 kg of natural gas releases 0.012 kg of CH 4 to the atmosphere. In contrast, NETL’s expected loss rate from the same boundary is approximately 8%: for the delivery of 1 kg of natural gas via a transmission pipeline, 0.012 kg of CH 4 is released to the atmosphere, and 0.068 kg is flared by environmental controls or combusted for processing and transmission energy. Sierra Club compares NETL’s leakage rate to a 1.54% leakage rate derived from EPA’s 2013 GHG inventory. The two types of leakage rates (the 1.2% calculated by NETL’s life cycle model and the 1.54% implied by EPA’s 2013 inventory) are not directly comparable. LCAs and national inventories have different temporal boundaries. NETL’s leakage rate is a life cycle number based on a 30-year time frame; it levelizes the emissions from one-time well completion activities over a 30-year time frame of steady-state production. The leakage rate implied by EPA’s inventory represents 2011 industry activity; it captures the spike in completion emissions due to the atypically high number of wells that were completed that year. In other words, national inventories calculate all emissions that occur in a given year, while LCAs apportion all emissions that occur during a study period (e.g., 30 years) to a unit of production (e.g., 1 MWh of electricity generated). Both approaches are legitimate with respect to the unique goals of each type of analysis. Yüklə 353,3 Kb. Dostları ilə paylaş:
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