the US Natural Gas Infrastructure R Subramanian subucmuedu Scott Herndon Rob Roscioli Austin Mitchell Dan Zimmerle Anthony Marchese and Allen Robinson Funding data technical ID: 490624
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Slide1
Methane Emissions from
theUS Natural Gas Infrastructure
R Subramanian (subu@cmu.edu)Scott Herndon, Rob Roscioli, Austin Mitchell,Dan Zimmerle, Anthony Marchese, and Allen RobinsonSlide2
Funding, data, technical
input:
Environmental Defense FundKinder-MorganNiSourceTransCanadaDominionWilliamsEnableDowINGAAAnadarko
Access MidstreamSWNHessDCP*Slide3
Methane Emissions from Transmission and StorageSlide4
Transmission & Storage Sector
300,000 miles of pipelines~2000 compressor stationsOlder facilities often reciprocating compressorsPowered by gas reciprocating engines
Newer/larger units centrifugal compressorsDriven by gas turbinesSource: US EIA, http://www.eia.gov/state/maps.cfm?v=Natural%20GasSlide5
Top-down & bottom-up measurements at 45 compressor stations
Compressor Types
Category
Number
GHGRP reporters
Reciprocating
c
ompressors only
Centrifugal
compressor
only
Both
types
Sites with at least one
compressor running
Transmission37231221415Storage8 (10)27015Total45 (47)251921520
GHGRP reporters: facilities that emit over 25,000 MT-CO2e/year
Sixteen states, six partner companies, eleven weeks of parallel direct onsite and tracer flux
measurementsSlide6
Bottom-up: Direct Onsite Measurement of Methane EmissionsModeled on EPA GHGRP protocol, but more comprehensive
Leak detection with FLIR thermal imagingMeasure emissions with Hi-Flow, acoustic devices, turbine meters, bagsIssues:Accuracy of some techniques questionableSome leaks may not be detected due to adverse windNot all detected leaks are safely accessible
Time-consuming for comprehensive measurements and at larger sitesSlide7
“Top-Down” Downwind Dual Tracer Flux: Facility-Level Emission Rates
N2O
C2H2
CH
4Slide8
Onsite & Tracer Flux Data: Details
Reciprocating-only sites
Centrifugal-only sitesFacility-level CH4 Emissions (SCFM)Slide9
Direct Onsite vs Tracer Flux: Mostly AgreeSlide10
Onsite does not capture super-emitters
Super-emitters: Sites emitting over 300 SCFM methaneSlide11
GHGRP: NOP rod-packing venting not reported, OEL/connector emission factors lowSlide12
GHGRP emission factors not appropriate for engine exhaust methaneSlide13
The fat tail: super-emitters skew emissions distributions
Cumulative Fraction of Sites
Cumulative Methane Emissions (SCFM)Cumulative Fraction of TF Methane EmissionsSlide14
Processing Plant
Gathering Lines
Gathering Facility
Gathering pipelines were not measured as part of this study
Methane Emissions from Gathering and ProcessingSlide15
G&P Field Campaign
Tracer flux measurements at
16 processing plants
and
114 gathering facilities
(of Partner inventory of 28 & 738 facilities.)Slide16
G&P: Facility-Level Methane Emissions (kg/
hr
) & Loss Rate (% throughput)Mitchell, A.L.,
Zimmerle, D., Marchese, A.J., Robinson, A.L. et al. Measurements of Methane Emissions from Natural Gas Gathering Facilities and Processing Plants: Measurement Results.
Environ.
Sci. Technol
.,
49
(5) 3219-3227.
Median Loss Rate 0.42%
Gathering: 56 kg/
hr
/facility
Median Loss Rate 0.08%
Processing: 170 kg/
hr
/facilitySlide17
Mitchell
, A.L.,
Zimmerle, D., Marchese, A.J., Robinson, A.L. et al.
Measurements of Methane Emissions from Natural Gas Gathering Facilities and Processing Plants: Measurement Results. Environ. Sci
. Technol
.,
49
(5) 3219-3227.
25 facilities had methane loss rates > 1%
1%
9
% Emitter (660 kg/
hr
)
Mid-Size C/D Station (9.5
MMscfd
)
Three (3) 1150 HP
recipsNoticeable venting from PW TanksG&P: High-EmittersSlide18
9% Emitter (660 kg/
hr
)Mid-Size C/D Station (9.5
MMscfd) Three (3) 1150 HP
recips
Noticeable venting from PW Tanks
At 22
of the 114 sampled gathering facilities, substantial venting was observed from liquids storage
tanks
and the methane emissions from these gathering facilities was
3X compared to
facilities in which substantial
tank venting was
not
observed.
G&P: 9% emitterSlide19
Modeling Paper
Measurement Paper
From measurements to modeling
Field Campaign
Engineering Estimates
Study Onsite Estimate
Tracer Flux Measurement
GHGRP Result
Per Facility Comparison
National Model
Additional Data Sources
Additional Partner Meas.
GHGI
&
GHGRP
National ComparisonsSlide20
SummarySignificant new measurements of methane emissions from the T&S and G&P sectors
Tracer flux quantifies site-level methane emissionsIncludes* measurement of exhaust methaneQuantifies super-emittersMake EPA GHG Reporting Program comprehensiveInclude all major emission sources and sectorsUse updated emission factors, if not direct measurementsRemove the 25,000 MT-CO
2e reporting thresholdBetter identify and quantify super-emitters10% of sites => 50% of T&S emissions30% of sites => 80% of gathering emissionsSlide21
Questions?Email: subu@cmu.eduSlide22
EPA T&S methane inventory
Current:Emission factors: 1996 EPA/GRI (15 compressor stations) and 2010 ICF data
Activity factors: Pipeline miles scaled to 1990s survey, with some modificationsFuture?Can we use the GHGRP data from ~500 compressor stations?Slide23
Downwind tracer flux: Facility-level Methane Emission RatesLamb et al. (1995) used sulfur hexafluoride (SF
6) as tracerWe use nitrous oxide (N2O) and acetylene (C2
H2)Slide24
Tracer Flux: Method AssumptionsMethane and tracer(s) equivalently dispersedCheck correlation between methane and tracer(s)
Second tracer verifies assumptionAll methane sources at a site captured downwindDual tracers (up to 200m apart) encompass the siteNo other source of tracersUpwind and downwind transects with tracers off
Background-corrected methane from target siteUpwind transectsUse ethane as a signature for natural gas methaneSlide25
Ethane: Signature for natural gas emissions
Ethane lifetime ~2 months, compared to ~10 years for methanePlume dominated by natural gas ethane, not backgroundThe Aerodyne TILDAS provides mobile 1-Hz ethane measurements
Downwind Plume MeasurementsPartner-provided Gas CompositionSlide26
Tracer flux: From plume capture to methane emission rates
Uncertainty ±17% (dual tracer correlation) to ±34% (area plumes)
Methane (ppm)Ethane (ppb)
Acetylene (ppb)
N2
O (ppb)Slide27
Onsite Estimate vs Tracer Flux
1 standard ft3/min = 1.15 kg/hourSlide28
The EPA GHG Reporting Program
From 2011, mandates
reporting of CO2, CH4, N2O
Only facilities that emit over 25,000 MT-CO
2e (annualized)