Methane Emissions from T&S Se

Detailed Technical Review

Daniel Zimmerle

A. L. Robinson, L. L. Williams, T. L. Vaughn, A. J. March

R. Subramanian, A.L. Mitchell, C. Quinn, G.P. Duggan

Willson, J.D. Opsomer, D. M. Martinez, S. Herndon
Study Team

Study Team Funding & Access Partn
STUDY DESIGN & FIELD 

MEASUREMENT CAMPAIGN
Definitions

• Transmission & Storage (T&S) sector of natu

system – All storage facilities in this study are underground 

gas storage facilities

• Greenhouse Gas Inventory (GHGI) – EPA estimate of GHG emissions for USA• Greenhouse Gas Reporting Program (GHGR

– EPA reporting program for GHG emissions – For T&S, facilities report if total GHG emission >

metric tons equivalent CO2
Operational System Boundarie
Full Transmission System

Color coded by company. Transmission classification is inexact. Data from MapSearchTM, 2013
Sample of System Layout

Extracted from Kinder Morgan system map, www.kindermorgan.com
Measurement Paper Modeling Pap

Study Design

Field 

Campaign

Engineering 

Estimates

Study Onsite 

Estimate

Tracer Flux Measurement

GHGRP 

Result

Per Facility 

Comparison

National 

Model

A

Da

A

Pa

GHGI 

&

GHGRP

National Comparisons
Field Campaign Methodology

• Paired downwind (tracer flux) and comprehen

site measurements

– Dual tracer method (Aerodyne & Carnegie Mello– Onsite using combo of partner & contractor teams 

following same protocol

• Selected from partner sites / national distribut

Field study:

Subramanian, R., et. al., Methane Emissions from Natural Gas Compressor Stations in the Transmission and SMeasurements and Comparisons with the EPA Greenhouse Gas Reporting Program Protocol. Environmental S

Technology (2015).

Tracer methods paper:

Roscioli, J. R., et. al, Measurements of methane emissions from natural gas gathering facilities and processin

measurement methods, Atmos. Meas. Tech. Discuss., 7, 12357-12406, doi:10.5194/amtd-7-12357-2014, 201
T&S Field Study

Phase 1: Summer ‘13Phase 2: Fall ‘13

On-site and downwind emissions @ 45 sites nationwid

e

Randomly selected within sampling windows9 storage / 36 transmission / multiple operating modesPartners represent ≈56% of interstate natural gas facilities
Measurement Methods

Dual Tracer Gas Method Comprehensiv

Comprehensiv

Surve
• 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 devices

Field Measurements: Onsite Pro

GHGRP

Categories

Add’l Cat.

Study

Protocol
Key Field Study Result:

Comparison Between Method

Two “super-emitter” fac300 SCFM emission ra

Seen by tracer menot by on-site met

Remaining sites:• Agreement between 

and tracer within exuncertainty correlati

• Operating engine ty

significant part of th

Conclusion:• Emissions can be m

using on-site measusuper-emitters are mexplicitly
DATA AND MODELS
Monte Carlo Model Example
Model Inputs

All Partner Sites

Partner Measured Sites

Submitted To 

GHGRP Subpart W

Drawing is representational only and is not scaled to match site count

Field Measurement 

Campaign

Non-Partner 

Sites

Non-Partner

Submitted to GHGRP

922 known facilities – 823 transmission & 99 undergroun

1,279 measurements from field campaign1,013 measurements from other measurements EIA data  underground storage facility count

FERC Form 2 data  2nd transmission facility count
Activity (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 categories
Emissions Data for Model

• Field Data (1,279 measurements )• Additional measurement data (1,013 measure

– Measurements from three partner companies– Measurements used same protocol as field campa– All or nothing from each partner in each emission 

• Blowdown data from partners• Methane in combustion exhaust:

– Emissions measurements underlying AP-42– Additional exhaust measurements from partners
Facility- Facility-Specific Emissions Data Specific Emissions Data

(in addition to field & partner measurements)

• Reported GHGRP data for 498 facilities – Partners provided data underlying submitte

reports (262 facilities)

• Facilities which were measured by partn

but not required to report to GHGRP (1

facilities)
KEY FINDINGS

http://energyinstitute.colostate.edu/p/transmission-and-storage.h
Key Findings

• Statistically similar to GHGI  Due to signif

offsetting factors in emission & activity categ

• “Activity” estimates have big impact on emis

estimates  Facility counts & equipment mix

• Super-emitters  Big impact but high uncert

• GHGRP under-reports significantly due to rep

requirements & some emissions factors
Overall Study Results

Notes:

• T&S GHGI 

 GHGI estimate net of “voluntary reductions”

• Model w/ Alt Station 

 Model with alternative method of estimating transmission statio

• Reported to GHGRP 

 ≈498 facilities in T&S that report to GHGRP
Results Compared to GHGI

Emissions, 

Facility Count, 

Comp. Diff.

Why?

(major reasons)

Usage 

Difference

(esp transmission)

M

A

(trans

Offsetting Usage + 

Emissions Factors

(esp transmission)
Challenge of Activity Estimates

• Facility Types:

– GHGRP reported– Partner facilities– Non-Partner / Non-GHGRP

• Study estimates:

– Fewer transmission stations 

than GHGI

– ≈equal compressor power to 

GHGI 

– Slightly more underground 

storage stations





20.3 GW [+25%/-18%] v

382 [+9%/-9%] vs 344

1,375 [+32%/-22%] vs 1
Two Types of Skewed Emissions Mo

At device level• “Long tail” present in most 

emissions distributions

• Included in emission model for 

each emission category

At facility level• “Super-emitters”- Exc

emissions measured by captured by on-site me

• Included for each facil

emission category
Skewed Emissions Distributions

• “Skewed” defined as: ≥30% of emission from 5% of measurem• All distributions > 90 measurements skewed• All distributions < 40 measurements not skewed

17 core emissions models from study(excludes combustion methane & superemitter models)
Modeling Super- Modeling Super-Emitters Emitters

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

0

0.005

0.01

0.015

0.02

0.025

0.03

Frequency of Super-Emitter

Probability (-)

Probability DistributionProbability from Field Measurement95% CI

Big impauncerta+103%/+153%/

Field observation: 2 of 45 facilities > 300 SCFM2 operating modes

Model uncertainty of finding large emittersMean ≈ 4% of facilities for each operating mode
Impact of Skewed Emissions Mode

• At device level• “Long tail” present in most 

emissions distributions

• At facility level• “Super-emitters”- Exc

emissions measured by captured by on-site me

Long tail in 11 emission categories:≈14-15% of total emissions

36-39% of fugitive emiss23% of total emissions

40% of total emissions
Compressor Types: 

One Large Driver of Facility Emiss

≈ Sam

com

29% CentrifugalMajority dry seals9% CentrifugalFew dry seals

Notes:

• Based on activity data from partner & 

non-partner facilities

• Uses baseline transmission facility count 

estimate

Storage –

GHGI/SME similar

96% turbines or 

electric drives

98% IC 

engines
Pneumatics

• Mix of intermittent and 

continuous drives emission factor

• May be seeing a shift from gasdriven to compressed air devices

239% Lower than ofdevice 17% oCombo station change

Facility Type

E

(M

GH

Transmission 2

Storage 2

From GHGRP Data
Seals

• Study data shows smaller difference between 

dry 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 compre

much larger portion is due to dry seal vents (22%) estimated in GHGI (8%)
Station Venting

• Transmission: – GHGRP blowdowns (>50 scf) – From 617 facilities• Storage: – No GHGRP data – Transmission data weighted 

by compressor count

Station Type

(M

G

Transmission Stations 7Storage Stations 7

• Significantly more data than used for the GH
Engine Exhaust

• Emission model developed from AP-42 data + 

data  Not 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 e

Emissions 

Factor

Voluntary 

Reductions

Net Emissions 

Factor

GHGI 4.6 g/hp-hr 124 Gg 2.4 g/hp-hr

GHGRP 0.09 g/hp-hr

Study 3.7 g/hp-hr
Comparison to GHGRP

• Study: 

– 260% [215% to 330%] of 

reported emissions

• Why?

– Omitted emission sources 

(including super-emitters)

– Combustion exhaust & 

other emission factors

– Measurement methods
GHGRP Details

GHGRP (Mg) SME (Mg)

SME Confidence 

Interval

Category 

Ratio

Difference 

(SME - MRR) 

(Mg)

Fraction of 

Total 

Difference

PrimaDiffeEmiss

17,780 43,961 [+81%/-31%] 2.5 26,181 8.6% Emiss

High & Low Continuous Bleed 7,387 13,152 [+7%/-7%] 1.8 5,765 1.9% Emiss

Intermittent Bleed 4,312 4,312 [+0%/0%] 1.0 0 0.0% Not m

762 762 [+0%/0%] 1.0 0 0.0% Not m

Flares 0 0 [+0%/0%] 1.0 0 0.0% Not m

Vent stack or dump valve 4,062 5,832 [+18%/-18%] 1.4 1,770 0.6% Meas

Blowdown vent - NOP 11,730 18,281 [+12%/-10%] 1.6 6,551 2.2% Meas

Blowdown vent - OP 9,480 17,077 [+15%/-13%] 1.8 7,597 2.5% Meas

Isolation Valve - NOD 16,105 28,284 [+22%/-19%] 1.8 12,179 4.0% Meas

Rod Packing - NOP 0 44,407 [+7%/-7%] - 44,407 14.6% GHGR

Rod Packing - OP 42,994 35,701 [+9%/-9%] 0.8 -7,293 -2.4% Othe

Blowdown vent - NOP 0 1,385 [+74%/-45%] - 1,385 0.5% Meas

Blowdown vent - OP 3,393 6,131 [+25%/-19%] 1.8 2,738 0.9% Meas

Dry Seal Vent - OP 0 4,814 [+13%/-12%] - 4,814 1.6% GHGR

Isolation Valve - NOD 16,055 20,602 [+7%/-7%] 1.3 4,547 1.5% Meas

Wet Seal Vent - OP 4,580 11,651 [+20%/-18%] 2.5 7,071 2.3% Othe

Lean 2 Stroke 115 64,137 [+4%/-4%] 558 64,022 21.1% Emiss

Lean 4 Stroke 29 16,499 [+13%/-12%] 577 16,470 5.4% Emiss

Rich 4 Stroke 6 535 [+19%/-17%] 91 529 0.2% Emiss

Combustion Turbine 221 889 [+23%/-20%] 4.0 667 0.2% Emiss

51,250 55,744 [+9%/-5%] 1.1 4,494 1.5% GHGR

0 100,074 [+128%/-80%] - 100,074 32.9% GHGR

190,524 494,539 [+26%/-17%] 2.60 303,970 100.0%

Notes

123 Tank flare emissions (both GHGRP and SME) are smaller than the precision of the model and display as zero

Component Leaks, All GHGRP Categories

Comparison of Study Model Estimate to GHGRP for Sites With Measured Emissions (Lane 1 Reported & Lane 2)

Emission Source

Intermittent bleed pneumatics and wellhead components were modeled using GHGRP emission factors.SME estimate for blowdowns reflects a pass through of transmission blowdowns and a per-facility estimate of storage storage blowdowns are an omission from the GHGRP requirements.

Total for Available Emissions Data

Station Venting (Blowdowns)

Super-Emitter

Combustion 

Methane

Centrifugal 

Compressor 

Venting

Reciprocating 

Compressor 

Venting

Transmission 

Tanks

Pneumatics

Wellhead Components
Additional Observations

• Survey teams had a hard time distinguis

between “compressor component” and “

compressor component” categories

• Hi/low bleed pneumatic categories are 

ambiguous at best – we use “continuous 

• We saw a difference in reported emissio

between partner & non-partner facilities
Conclusions

• Statistically similar to GHGI hides significan

offsetting differences embedded in: – Emissions factors – Facility & equipment utilization

• Super-emitters must be modeled carefully  

data on large emitters needed

• Significant challenges estimating “easy to get

counts of facilities & major equipment

• GHGRP under-reports significantly due to rep

requirements & some emissions factors
References

• Link to paper• Web site• Prior Papers:

http://energyinstitute.colostate.edu/p/transmission-and-storage.html

Field study:

Subramanian, R., et. al., Methane Emissions from Natural Gas Compressor Stations in the TransmissioSector: Measurements and Comparisons with the EPA Greenhouse Gas Reporting Program Protocol. 

2015, 49 (5), 3252–3261.

Tracer methods paper:

Roscioli, J. R., et. al, Measurements of methane emissions from natural gas gathering facilities and p

measurement methods, Atmos. Meas. Tech. Discuss., 7, 12357-12406, 2014.
Thank You

Contact 

Dan Zimmerledan.zimmerle@colostate.edu970-581-9945

http://energyinstitute.colostate.edu/p/transmission-and-storage.html