Synthesis of recent ground-level methane emission measurements from the U.S. natural gas supply chain

Transcription

1 Synthesis of recent ground-level methane emission measurements from the U.S. natural gas supply chain Presented by: Timothy J. Skone, P.E. National Academy of Sciences Workshop, Boulder, CO March 28, 2017 Solutions for Today Options for Tomorrow

2 Our Latest Publication This work represents a two year collaboration between NETL and EDF Littlefield, J. A., Marriott, J., Schivley, G. A., & Skone, T. J. (2017). Synthesis of recent ground-level methane emission measurements from the US natural gas supply chain. Journal of Cleaner Production. 2

3 Synthesis Combining data on a common basis is necessary for a fuller understanding Objective: Integrate new data to represent national supply chain CH 4 emissions Method: Use of NETL s natural gas life cycle model to translate and augment data for a complete LCA profile Key questions: - In what ways do the new data change our understanding of natural gas CH 4 emissions? - What are the top priorities for natural gas CH 4 emission reductions? - What are key opportunities for future research? 3

4 NETL s Life Cycle Natural Gas Model A framework for translating point-by-point emissions to a common basis Production G&P T&S Distribution Stage/Unit Process ID Unassigned (outside Barnett) 1 Unassigned (Barnett) 2 Completion 3 Chemical pumps 4 Equipment leaks 5 Pneumatics 6 Produced water tanks 7 Liq. Unloading (no plunger) 8 Liq. Unloading (plunger) 9 Compressor packing 10 Compressor exhaust 11 Dehydrator vents 12 Gathering facilities 13 Gathering pipelines 14 Processing facility 15 Processing fugitives 16 Transmission stations 17 Storage stations 18 Compressor exhaust 19 Pneumatics 20 Station venting 21 Other 22 Super-emitters 23 Mains 24 Service pipelines 25 Metering and regulating 26 Customer meters 27 Maintenance 28 Upsets 29 Production G&P T&S Distribution Large scale consumers (power plants) Small scale consumers (industrial, commercial, residential) Four natural gas supply chain stages Includes primary supply chain connectivity (shown here), as well as ancillary systems Default basis (i.e., functional unit) is 1 MJ of delivered natural gas Configured for delivered natural gas, which includes two types of consumers G&P Gathering and Processing, T&S Transmission and Storage

5 Probability Unassigned Methane Emissions A special case that represents translation and augmentation Unassigned = Total observed Known component Translation 14,200 kg CH 4 /hour of unassigned emissions from Barnett Region divided by 2.14 trillion cubic feet of annual production in Barnett Region Augmentation Extrapolation of unassigned emissions in Barnett Region to national level by using ratio of national-to-regional production CH 4 (kg/hr) 5

6 probability Uncertainty Characterization of uncertainty requires an understanding of what the input data actually represent, as well as a clearly defined study objective Known uncertainty - Retention of 95 confidence intervals from original studies - Linear extrapolation of unassigned emissions - No professional judgement or bounding of parameters Mean confidence intervals - Goal: characterize average natural gas, not a random unit of natural gas - Skewness affects central values, but distribution of averages is normal Population Average x 6

7 Unassigned (outside Barnett) Unassigned (Barnett) Completion Chemical Pumps Equipment Leaks Pneumatics Produced water tanks Liq. unloading (no plunger) Liq. unloading (plunger) Compressor packing Compressor exhaust Dehydrator vents Gathering facilities Gathering pipelines Processing facility Processing fugitives Transmission stations Storage stations Compressor exhaust Pneumatics Station venting Other Super-emitters Mains Service pipelines Metering & regulating Customer meters Maintenance Upsets g CH₄/MJ delivered NG Overall Result: 1.7% CH₄ life cycle emission rate Aside from total emission rates, results point to top emission reduction and research opportunities Measured Augmented Cumulative Emission Rate 1.23% 1.11% (0.22 g CH₄/MJ) (0.20 g CH₄/MJ) 0.70% (0.12 g CH₄/MJ) 1.57% (0.28 g CH₄/MJ) 1.65% (0.29 g CH₄/MJ) 2.2% 2.1% 2.0% 1.9% 1.8% 1.7% 1.6% 1.5% 1.4% 1.3% 1.2% 1.1% 1.0% 0.9% 0.8% 0.7% 0.6% 0.5% 0.4% 0.3% 0.2% 0.1% 0.0% CH₄ Emission Rate (g CH₄ emitted/g NG delivered) PRODUCTION GATHERING PROCESSING TRANSMISSION & STORAGE DISTRIBUTION 7

8 Additional Perspective Inventory perspective Synthesis result, U.S. annualized: 0.29 g CH 4 /MJ 7,349 Gg CH 4 /yr EPA 2016 Greenhouse Gas Inventory (GHGI) result for 2012 (after removing condensate tanks) is 6,716 Gg CH 4 /yr Synthesis result is 9% higher than GHGI because - Different data sources are used for production emission sources - Synthesis includes unassigned emissions Life cycle CO 2 e perspective Includes CO 2 and N 2 O in addition to CH Global Warming Potentials (GWP) 13.8 g CO 2 e/mj (100-yr GWP) and 28.6 g CO 2 e/mj (20-yr GWP) 8

9 Conclusions and Recommendations Emission reduction opportunities - Pneumatic devices widespread use in production and gathering stages - Unassigned emissions (observed, but not fully understood) - Gathering Systems (new to emissions inventories, but highly aggregated) Research opportunities - Improve activity data on pneumatic devices throughout supply chain - Identify drivers and regional variability for unassigned emissions - Disaggregate gathering emissions at the category level to individual system components 9

10 Acknowledgments DOE, Fossil Energy Christopher Freitas EDF Steven Hamburg, Drew Nelson, Ramon Alvarez, David Lyon, Daniel Zavala-Araiza Principal investigators David Allen, Anthony Marchese, Dan Zimmerle, and Brian Lamb 10

11 Contact Us Timothy J. Skone, P.E. Sr. Environmental Engineer Energy Systems Analysis Team (412) Joe Marriott Principal Engineer KeyLogic Systems (412) James Littlefield Senior Engineer KeyLogic Systems (412)

12 Translation and Augmentation Two types of operations required for this synthesis Translation to a Common Framework - Conversion of measured emissions to appropriate modeling parameters - Verification that reference flows of unit processes are consistent with intermediate supply chain flows - Modification of legacy modeling boundaries Augmentation - Identification of data gaps, non-edf field measurement data - Use of EPA Greenhouse Gas Inventory (GHGI) or extrapolation of other data sources, NETL natural gas modeling framework 12

13 Scope Specification of technological, temporal, and geographical boundaries Boundaries: Field production thru delivery to end-user Metric: CH₄ emissions per unit of delivered natural gas Timeframe: 2012 Geography: U.S. 13

14 EDF-sponsored Emission Measurements These measurement campaigns have provided us with new data on methane (CH 4 ) emissions from natural gas (NG) systems Field Measured Emission Sources - Completions - Chemical pumps - Equipment leaks - Pneumatic controllers - Liquids unloading (plunger) - Liquids unloading (no plunger) - Unassigned* - Gathering facilities - Processing facilities - Transmission stations - Storage stations - Pneumatics - Station venting - Super-emitters - Mains - Service pipelines - Metering and regulating Production Gathering & Processing Transmission & Storage Distribution Authors Allen et al. Marchese et al. Zimmerle et al. Lamb et al. Zavala-Araiza et al.* 14

15 Unit Processes Unit processes are the building blocks of a life cycle model Engineering calculations within each unit process that allows parameterization of system variables Key natural gas parameters include gas compositions at different points in the supply chain Calculations at this level ensure the scale of intermediate flows between supply chain steps NG in Unit Process: Component Characterization E NG = EF AF NG in = NG out + E NG Where, E NG = potential emission of natural gas (kg NG) EF = emission factor (kg NG/event) AF = activity factor (event count) NG in = natural gas from an upstream process (kg NG) NG out = natural gas to a downstream process (kg NG) E NG Unit Process: Gas Speciation and Flaring E CH4 = E NG C CH4 (1 F) Where, E CH4 = post flaring emission of CH 4 (kg) E NG = potential emission of natural gas (kg NG) NG out E CH4 C CH4 = CH 4 content of natural gas (% mass) F = share of potential emissions that are flared (%) 15