Methane Emissions from T&S SectorDetailed Technical ReviewDaniel ZimmerleA. L. Robinson, L. L. Williams, T. L. Vaughn, A. J.Marchese,R. Subramanian, A.L. Mitchell, C. Quinn, G.P. Duggan, B.Willson, J.D. Opsomer, D. M. Martinez, S. Herndon2Study TeamFunding & Access PartnersStudy TeamSTUDY DESIGN & FIELDMEASUREMENT CAMPAIGN3Definitions•Transmission & Storage (T&S) sector of natural gassystem–All storage facilities in this study areundergroundnaturalgas storage facilities•Greenhouse Gas Inventory (GHGI)–EPA estimate of GHG emissions for USA•Greenhouse Gas Reporting Program(GHGRP)–EPA reporting program for GHG emissions–For T&S, facilities report iftotalGHG emission >25,000metric tons equivalentCO24Operational System BoundariesFull Transmission SystemColor coded by company. Transmission classification is inexact. Datafrom MapSearchTM, 2013Sample of System LayoutExtracted from Kinder Morgan system map, www.kindermorgan.comModeling PaperMeasurement PaperStudy DesignFieldCampaignEngineeringEstimatesStudy OnsiteEstimateTracer Flux MeasurementGHGRPResultPer FacilityComparisonNationalModelAdditionalData SourcesAdditionalPartner Meas.GHGI&GHGRPNationalComparisonsField Campaign Methodology•Paired downwind (tracer flux) and comprehensive onsite measurements–Dual tracer method (Aerodyne & Carnegie Mellon)–Onsite using combo of partner & contractor teamsfollowing same protocol•Selected from partner sites / national distribution9Field study:Subramanian, R., et. al.,Methane Emissions from Natural Gas Compressor Stations in the Transmission and Storage Sector:Measurements and Comparisons with the EPA Greenhouse Gas Reporting Program Protocol.Environmental Science &Technology(2015).Tracer methods paper:Roscioli, J. R., et. al,Measurements of methane emissions from natural gasgathering facilities and processing plants:measurement methods, Atmos. Meas. Tech. Discuss., 7, 12357-12406, doi:10.5194/amtd-7-12357-2014, 2014.T&S Field StudyPhase 1: Summer ‘13Phase 2: Fall ‘13On-site and downwind emissions @ 45 sites nationwideRandomly selected within sampling windows9 storage / 36 transmission / multiple operating modesPartners represent ≈56% ofinterstatenatural gas facilitiesMeasurement MethodsDual Tracer Gas MethodComprehensive OnComprehensive On--SiteSurvey12•Protocol Differences Relative to GHGRP (examples)–Measure in all compressor modes (NOP, NOD & OP)–Measure same components at storage & transmission facilities–Measure all seal vents–ID all leaks with IR camera & measure all–No portable acoustic meters–Did not measure intermittent pneumatic devicesField Measurements: Onsite ProtocolGHGRPCategoriesAdd’l Cat.StudyProtocolKey Field Study Result:Comparison Between MethodsTwo “super-emitter” facilities with >300 SCFM emission rateSeen by tracer methods butnot by on-site methodsRemaining sites:• Agreement between on-siteand tracer within experimentaluncertainty correlation• Operating engine type drivessignificant part of the emissionsConclusion:• Emissions can be modeledusing on-site measurementsifsuper-emitters are modeledexplicitlyDATA AND MODELS14Monte Carlo Model Example16Model InputsAll Partner SitesPartner Measured SitesSubmitted ToGHGRP Subpart WDrawing is representational only and is not scaled to match site countField MeasurementCampaignNon-PartnerSitesNon-PartnerSubmitted to GHGRPGHGRP-type DataDetailed Measurements922knownfacilities – 823 transmission & 99 underground storage1,279 measurements from field campaign1,013 measurements from other measurementsEIA dataunderground storage facility countFERC Form 2 data2ndtransmission facility countActivity (Census) Data for Model•Partner site details provided by partners•Non-partner sites:–Site configuration from GHGRP data–EIA data for underground storage facility count–FERC Form 2 data for transmission facility count•Omitted:–Pipelines–LNG–M&R–Add’l small categories17Emissions Data for Model•Field Data (1,279 measurements )•Additional measurement data (1,013 measurements)–Measurements from three partner companies–Measurements used same protocol as field campaign–All or nothing from each partner in each emission category•Blowdown data from partners•Methane in combustion exhaust:–Emissions measurements underlying AP-42–Additional exhaust measurements from partners18FacilityFacility--Specific Emissions DataSpecific Emissions Data(in addition to field & partner measurements)•Reported GHGRP data for 498 facilities–Partners provided data underlying submittedreports (262 facilities)•Facilities which were measured by partners,but not required to report to GHGRP (179facilities)19KEY FINDINGShttp://energyinstitute.colostate.edu/p/transmission-and-storage.htmlKey Findings•Statistically similar to GHGIDue to significantoffsetting factors in emission & activity categories•“Activity” estimates have big impact on emissionsestimatesFacility counts & equipment mix•Super-emittersBig impact but high uncertainty•GHGRP under-reports significantly due to reportingrequirements & some emissions factors21Overall Study ResultsNotes:•T&S GHGIGHGI estimate net of “voluntary reductions”•Model w/ Alt StationModel with alternative method of estimating transmission station count•Reported to GHGRP≈498 facilities in T&S that report to GHGRP22Results Compared to GHGIEmissions,Facility Count,Comp. Diff.Why?(major reasons)UsageDifference(esp transmission)More DataAvailable(transmission GHGRP)Offsetting Usage +Emissions Factors(esp transmission)Challenge of Activity Estimates•Facility Types:–GHGRP reported–Partner facilities–Non-Partner / Non-GHGRP•Study estimates:–Fewer transmission stationsthan GHGI–≈equal compressor power toGHGI–Slightly more undergroundstorage stations2420.3 GW [+25%/-18%] vs ≈19.5 GW382 [+9%/-9%] vs 3441,375 [+32%/-22%] vs 1799Two Types of Skewed Emissions ModelsAt device level•“Long tail” present in mostemissions distributions•Included in emission model foreach emission categoryAt facility level•“Super-emitters”- Exceptionalemissions measured by tracer but notcaptured by on-site measurements•Included for eachfacilityas extraemission categorySkewed Emissions Distributions•“Skewed” defined as: ≥30% of emission from 5% of measurements•All distributions > 90 measurementsskewed•All distributions < 40 measurementsnot skewed17 core emissionsmodels from study(excludes combustionmethane & superemitter models)Modeling SuperModeling Super--EmittersEmitters2700.050.10.150.20.250.30.3500.0050.010.0150.020.0250.03Frequency of Super-Emitter

Probability (-)Probability DistributionProbability from Field Measurement95% CIBig impact but highuncertainty:+103%/-63% transmission+153%/-83% storageField observation:2 of 45 facilities> 300 SCFM2 operating modesModel uncertainty of findinglarge emittersMean ≈ 4% of facilities foreach operating modeImpact of Skewed Emissions Models•At device level•“Long tail” present in mostemissions distributions•At facility level•“Super-emitters”- Exceptionalemissions measured by tracer but notcaptured by on-site measurementsLong tail in 11 emission categories:≈14-15% of total emissions36-39% of fugitive emissions23% of total emissions40% of total emissionsCompressor Types:One Large Driver of Facility Emissions29≈ Same estimated totalcompressor power29% CentrifugalMajority dry seals9% CentrifugalFew dry sealsNotes:•Based on activity data from partner &non-partner facilities•Uses baseline transmission facility countestimateStorage –GHGI/SME similar96% turbines orelectric drives98% ICenginesPneumatics•Mix of intermittent andcontinuous drives emission factor•May be seeing a shift from gasdriven to compressed air devices30239% of GHGILower emission factor morethan offset by increase indevice usage17% of GHGICombo of device mix,station count & usagechangesFacility TypeEmission Rate(Mg/device/yr)GHGI StudyTransmission 2.9 1.0Storage 2.7 2.1From GHGRP DataSeals•Study data shows smaller difference between wet anddry seals for centrifugal compressors–GHGI: Factor of 8 difference–Study: Factor of 3 difference•Impact on centrifugal compressor fugitives–GHGI: Wet = 1.6 X dry–Study: Wet = 1.7 X dry ... but for dry seal compressorsmuch larger portion is due to dry seal vents (22%) thanestimated in GHGI (8%)31Station Venting•Transmission:–GHGRP blowdowns (>50 scf)–From 617 facilities•Storage:–No GHGRP data–Transmission data weightedby compressor count32Station TypeVenting(Mg/station/yr)GHGI StudyTransmission Stations 72 57Storage Stations 72 43•Significantly more data than used for the GHGIEngine Exhaust•Emission model developed from AP-42 data + partnerdataNot measured in study•Study:–3.7 g/hr-hr based upon AP-42 + new data–1.6X higher than GHGI–Study >550X higher than GHGRP for lean-burn engines33EmissionsFactorVoluntaryReductionsNet EmissionsFactorGHGI 4.6 g/hp-hr 124 Gg 2.4 g/hp-hrGHGRP 0.09 g/hp-hrStudy 3.7 g/hp-hrComparison to GHGRP•Study:–260% [215% to 330%] ofreported emissions•Why?–Omitted emission sources(including super-emitters)–Combustion exhaust &other emission factors–Measurement methods34GHGRP DetailsGHGRP (Mg) SME (Mg)SME ConfidenceIntervalCategoryRatioDifference(SME - MRR)(Mg)Fraction ofTotalDifferencePrimary Origin ofDifference inEmissions Notes17,780 43,961[+81%/-31%]2.5 26,181 8.6% Emission FactorHigh & Low Continuous Bleed 7,387 13,152[+7%/-7%]1.8 5,765 1.9% Emission FactorIntermittent Bleed 4,312 4,312[+0%/0%]1.0 0 0.0% Not modeled 1762 762[+0%/0%]1.0 0 0.0% Not modeled 1Flares 0 0[+0%/0%]1.0 0 0.0% Not modeled 3Vent stack or dump valve 4,062 5,832[+18%/-18%]1.4 1,770 0.6% Meas. MethodBlowdown vent - NOP 11,730 18,281[+12%/-10%]1.6 6,551 2.2% Meas. MethodBlowdown vent - OP 9,480 17,077[+15%/-13%]1.8 7,597 2.5% Meas. MethodIsolation Valve - NOD 16,105 28,284[+22%/-19%]1.8 12,179 4.0% Meas. MethodRod Packing - NOP 0 44,407[+7%/-7%]- 44,407 14.6% GHGRP OmissionRod Packing - OP 42,994 35,701[+9%/-9%]0.8 -7,293 -2.4% OtherBlowdown vent - NOP 0 1,385[+74%/-45%]- 1,385 0.5% Meas. MethodBlowdown vent - OP 3,393 6,131[+25%/-19%]1.8 2,738 0.9% Meas. MethodDry Seal Vent - OP 0 4,814[+13%/-12%]- 4,814 1.6% GHGRP OmissionIsolation Valve - NOD 16,055 20,602[+7%/-7%]1.3 4,547 1.5% Meas. MethodWet Seal Vent - OP 4,580 11,651[+20%/-18%]2.5 7,071 2.3% OtherLean 2 Stroke 115 64,137[+4%/-4%]558 64,022 21.1% Emission FactorLean 4 Stroke 29 16,499[+13%/-12%]577 16,470 5.4% Emission FactorRich 4 Stroke 6 535[+19%/-17%]91 529 0.2% Emission FactorCombustion Turbine 221 889[+23%/-20%]4.0 667 0.2% Emission Factor51,250 55,744[+9%/-5%]1.1 4,494 1.5% GHGRP Omission 20 100,074[+128%/-80%]- 100,074 32.9% GHGRP Omission190,524 494,539[+26%/-17%]2.60 303,970 100.0%Notes123Tank flare emissions (both GHGRP and SME) are smaller than the precision of the model and display as zeroComponent Leaks, All GHGRP CategoriesComparison of Study Model Estimate to GHGRP for Sites With Measured Emissions (Lane 1 Reported & Lane2)Emission SourceIntermittent bleed pneumatics and wellhead components were modeled using GHGRP emission factors.SME estimate for blowdowns reflects a pass throughof transmission blowdowns and a per-facility estimate of storage blowdowns. Thestorage blowdowns are an omission from the GHGRP requirements.Total for Available Emissions DataStation Venting (Blowdowns)Super-EmitterCombustionMethaneCentrifugalCompressorVentingReciprocatingCompressorVentingTransmissionTanksPneumaticsWellhead Components35Additional Observations•Survey teams had a hard time distinguishingbetween “compressor component” and “noncompressor component” categories•Hi/low bleed pneumatic categories areambiguous at best – we use “continuous bleed”•We saw a difference inreportedemissionsbetween partner & non-partner facilities36Conclusions•Statistically similar to GHGI hides significantoffsetting differences embedded in:–Emissions factors–Facility & equipment utilization•Super-emitters must be modeled carefullyMoredata on large emitters needed•Significant challenges estimating “easy to get” datacounts of facilities & major equipment•GHGRP under-reports significantly due to reportingrequirements & some emissions factors37References•Link to paper•Web site•Prior Papers:38http://energyinstitute.colostate.edu/p/transmission-and-storage.htmlField study:Subramanian, R., et. al.,Methane Emissions from Natural Gas Compressor Stations in the Transmission and StorageSector: Measurements and Comparisons with the EPA Greenhouse Gas Reporting Program Protocol.Environ. Sci. Technol.2015, 49 (5), 3252–3261.Tracer methods paper:Roscioli, J. R., et. al,Measurements of methane emissions from natural gasgathering facilities and processing plants:measurement methods, Atmos. Meas. Tech. Discuss., 7, 12357-12406, 2014.Thank YouContactDan Zimmerledan.zimmerle@colostate.edu970-581-9945http://energyinstitute.colostate.edu/p/transmission-and-storage.html