# Attachment R

Compressors

Environmental Defense Fund

Ramón Alvarez, Robert Harriss, David Lyon

### Oil and Natural Gas Sector: Compressors

Peer Review Responses of Environmental Defense Fund

June 16, 2014

I. 

### E XECUTIVE 

### S UMMARY

• Compressors are collectively a substantial source o f methane emissions. Emissions from reciprocating and centrifugal compressors – in cluding emissions from seals and non-seal components – are significant.

o Emissions from compressor seals . Because Subpart W requires direct measurement of compressor emissions, it provides va luable estimates for both reciprocating and centrifugal seal emissions (thoug h likely conservative because it does not measure all operating modes). Based on thi s data, average emissions from reciprocating compressor rod-packing are likel y moderately higher than the emission factor used in EPA’s Annual Inventory. Ce ntrifugal compressor wet seal emissions are likely substantially higher than the EPA emission factor.

o Skewed distribution . Compressor emissions exhibit a highly-skewed or fat tail distribution, with about 20% of compressors produci ng approximately 80% of total rod packing and wet seal emissions.

o Non-seal emission. Non-seal emissions are an important component of ov erall compressor emissions. The ICF Report noted, for in stance, that non-seal, fugitive emissions from reciprocating compressors account fo r approximately 75% of

overall emissions from those sources.

o National Emissions . The best available data suggests that national em issions from compressors (all non-exhaust sources) are likely on the order of 2,000 Gg (2,000,000 metric tons) of methane, underscoring th at this is a substantial

emissions source relative to others in the inventor y.

• Compressor emissions can be effectively mitigated u sing readily-available, costeffective technologies. For both reciprocating and centrifugal compressors, mitigation technologies include both abatement and capture tec hnologies.

o Regular rod-packing replacement is an effective, lo w-cost way to mitigate emissions, which ICF projected would reduce emissio ns by 3.6 billion cubic feet (bcf) of methane (approximately 69,000 metric tons) at a cost of $6.11/mcf reduced. Rod-packing replacement can be optimized b y inspecting for excess seal emissions as part of a regular leak detection and r epair program, enhancing

control effectiveness.

o Rod-packing gas capture systems can have greater ef fectiveness than rod-packing replacement and, in many cases, result in beneficia l use of otherwise wasted gas.



### o Wet-seal degassing capture systems are feasible, re sult in substantial reductions, and are highly-cost effective. If broadly applied at centrifugal compressors notE NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

2 currently subject to the NSPS, ICF projected that s uch capture systems would reduce methane by 19.1 billion cubic feet (over 360 ,000 metric tons) while achieving net savings of $3.07/mcf of methane reduced.



### o LDAR and gas capture technologies can also effectiv ely mitigate non-seal compressor emissions.



### II. Q UANTIFYING THE 

### P ROBLEM OF 

### M ETHANE 

### & VOC L EAKS FROM



### C OMPRESSORS 

### (Q UESTIONS 

### 1, 2, 12)

At various points throughout EPA’s Compressor White Paper (“Compressor Paper”), 1 the agency presents component level emissions factors f or compressors (i.e., seal emissions), aggregate emissions factors for compressors (i.e., factors for wet seal centrifugal compressors and reciprocating compressors), and national emissi ons estimates for compressor emissions across segments. Each one of these emissions estim ates is important for different reasons. For instance, component level emissions factors provide an indication of the relative importance of different compressor emissions sources like vented seal emissions and leaks. These componentlevel factors also help identify technologies avail able to mitigate emissions described later in the paper. Aggregate compressor emissions factors and national emissions estimates, conversely, help to characterize the magnitude of emissions fro m compressors and the emissions reductions achievable by deploying various technologies.

Accordingly, Part II.A analyzes and critiques compr essor emissions factors, with particular emphasis on developing a clear understan ding of component-level emissions factors (seals, leaks, etc.) and identifying the gross-emit ter or fat-tail distribution that many compressor data sets exhibit. Part II.B analyzes and critique s national emissions estimates, with emphasis on recent findings from ICF indicating current invento ries may understate the number of large compressors in existence in the upstream segment. 2 Part II.C discusses forthcoming work.

We conclude that:

• Because Subpart W requires direct measurement of co mpressor emissions, it provides valuable estimates for both reciprocating and centr ifugal seal emissions (though likely conservative because it does not measure all operat ing modes). Based on this data, average emissions from reciprocating compressor rod-packing are likely moderately higher than the emission factor used in EPA’s Annual Inventory. Ce ntrifugal compressor wet seal emissions are likely substantially higher than the EPA emissi on factor.

1 EPA, Report for Oil and Natural Gas Sector Compres sors (2014) [hereinafter “Compressor Paper”], available at http://www.epa.gov/airquality/oilandgas/pdfs/201404 15compressors.pdf.

2 ICF International, Economic Analysis of Methane Emission Reduction Opp ortunities in the U.S. Onshore Oil and

Natural Gas Industries 3-7 (Mar. 2014) [hereinafter “ICF Cost Curve Repor t”], available at http://www.edf.org/sites/default/files/methane_ cos t_curve_report.pdf.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

3 • Non-seal emissions are an important component of ov erall compressor emissions. The ICF Report noted, for instance, that non-seal, fugitive emissions from reciprocating compressors account for approximately 75% of overall emissions from those sources.

• Compressor emissions exhibit a highly-skewed or fat tail distribution, with about 20% of compressors producing approximately 80% of total ro d packing and wet seal emissions.

• The best available data suggests that national emis sions from compressors (all non-exhaust sources) are likely on the order of 2 gigatons of m ethane, underscoring that this is a

substantial emissions source relative to others in the inventory.



### A. Analysis and Critique of Emissions Factors (Questio ns 1, 2)

We first provide our analysis of available data con cerning compressor seal emissions, noting the skewed distribution of these emissions. We then provide specific critiques on the

studies EPA cites.

1. Compressor Seal Emissions

The Compressor Paper summarizes previous work on co mpressor seal emissions, but the paper does not integrate the findings in a way that allows for easy comparison among sources. In this section, we describe why we believe Subpart W represents a particularly valuable data source for estimating seal emissions (though it lik ely underestimates these emissions); we synthesize data presented in the Compressor Paper a nd the referenced sources; and we discuss the distribution of compressor seal emissions – an important feature not addressed in EPA’s Compressor Paper.

Compressor seal emissions measurements reported in the EPA Greenhouse Gas Reporting Program (GHGRP Subpart W) are the most ro bust dataset available, due to the large number of direct measurements of compressor seal em issions (over 2,500 compressors were directly measured and reported in 2012). Notwithst anding these direct measurements, Subpart W very likely understates compressor seal emissions because it does not require reporting in every operating mode during which emissions can occ ur. Specifically, Subpart W requires rod packing emissions to be reported only in the "opera ting" mode, but both the GRI/EPA and

URS/UT 3 study show that rod packing emissions can be signi ficant while a compressor is pressurized, but idle (a “not-operating, pressurize d” mode) 4 and that transmission compressors spend 34% of their time in this mode. 5

3 URS Corp. et al., Natural Gas Industry Methane Emi ssion Factor Improvement Study (2011).

4 The URS/UT study also reported emissions from idle , depressurized compressors; GRI/EPA assumed such emissions would be negligible. URS/UT did not disc uss the cause emissions, but it is possible that th ey may originate from another component such a leaking iso lation valve.

5 The GRI/EPA study reported that Transmission compr essors are in operating mode 45% of the time, and 3 4% in the not-operating pressurized mode; they also indic ate that reciprocating compressors in processing ar e pressurized, but we could not find a distinction between operati ng and idle, not-operating modes.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

4 With this in mind, EPA GHGRP data can be used to de rive average emissions from compressor seals (both reciprocating and centrifuga l) that can be compared to other reported values ( see Tables 1-4 and discussion below). Tables 3 and 4 compare the compressor seal emissions reported by the various sources reviewed in the Compressor Paper. Estimates for rod packing emissions generally appear to agree to a gr eater extent than for wet seal emissions, though care must be taken when comparing these esti mates since they do not always represent the same thing. The main differences among estimat es are how operating hours in each operating mode are accounted for and whether an est imate includes emissions from non-seal

emissions sources:

• Operating Hours/Modes. As discussed above, reciprocating compressor rod packing emissions are only reported to Subpart W for the an nual hours that a compressor is in ”operating” mode (the same applies for centrifugal compressor wet seal emissions). As a result, rod packing emissions reported under Subpar t W represent a lower bound on total rod packing emissions from a compressor. The URS/U T study reported annual emissions assuming a compressor would be in the observed mode for all hours in the year. The GRI/EPA study accounted for hours in different oper ating modes for reciprocating compressors, as did all the other referenced studie s, which derive their estimates from

GRI/EPA.

• Seals vs. Non-Seal Emissions. All references except the GHG EI report emissions for compressor seals exclusive of other compressor emis sion sources. The GHG EI reports a single average emission factor for all compressor f ugitives; the GRI/EPA report indicated that the seal emissions are about 25% of total comp ressor emissions for reciprocating compressors and less than 5% for centrifugal compre ssors, though below, we describe why the centrifugal conclusion is flawed. 6

Table 3 shows that Subpart W data for rod packing e missions are lower than GRI/EPA estimates by 5% to 60%, depending on the sector. H owever, this difference may not persist if rod packing emissions from compressors in the not-o perating (idle-pressurized) mode were

included.

On the basis of GHGRP measurements, Table 4 strongl y suggests that the GRI/EPA estimates for centrifugal wet seal emissions are un derestimated – by as much as factors of 5 and 15 times for processing and transmission, respectiv ely (very few values are available for storage). The wet seal emissions data in the URS/U T study are somewhat higher than the GHGRP data, but support the conclusion that the GRI /EPA estimates for wet seal emissions are

too low.

The GHGRP data for centrifugal compressors indicate s that there are roughly equal numbers of compressors with wet seals and dry seals in the Transmission, Storage, and Processing segments, although the distribution vari es among segments. See Table 5. The percent of centrifugal compressors that have wet seals in t he GHGRP for these 3 segments is

6 See Compressor Paper at 12-13.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

5 intermediate to the values reported in the GHG EI ( 80%) and the API/ANGA report 7 (21% for processing only).

Data presented in the ICF report indicate that more large compressors are in use in the gathering segment, with emission factors comparable to the average rates for storage and processing compressors in the GHGRP. The URS/UT st udy provides actual measurements that are not quite as high as the ICF estimate, but much larger than the assumed value for production/gathering segment emissions in the GRI/E PA study, suggesting average emissions from this segment are indeed larger.

Table 1. Summaries of direct measurements reported under EPA GHGRP Subpart W for

Reciprocating Compressor Rod Packing Emissions in 2 012.

Reciprocating Compressor Rod Packing (2012) Compressors Mscfy CH4 Metric tons CH4 / yr

# Mean Median Mean Median

Transmission 851 1,247 367 24 7.1

Processing 1,269 882 160 17 3.1

Underground Storage 116 535 151 10 2.9

Table 2. Summaries of direct measurements reported under EPA GHGRP Subpart W 2012 Centrifugal Compressor Rod Packing Emissions - EPA GHGRP Subpart W

. Centrifugal Compressor Wet Seals (2012) Compressors Mscfy CH4 Metric tons CH4 / yr

# Mean Median Mean Median

Transmission 99 997 16 19 0.3
Processing 167 5,366 154 103 3.0

Underground Storage 5* 8,658* 14,074* 166* 270*
*Note: With emissions only reported for 5 storage c ompressors, we do not believe the values for this segment have statistical significance; they are pro vided here only for completeness.

7 Am. Petroleum Inst. & America’s Natural Gas Allian ce, Characterizing Pivotal Sources of Methane Emiss ions from Natural Gas Production: Summary and Analysis o f API and ANGA Survey Responses (2012).E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

6 Table 3. Summary of Reciprocating Compressor Rod P acking Emissions reported in EPA Compressor Paper.

Reciprocating Compressor Rod Packing Emissions mscfy CH4 (per compressor)

EPA GHG RP (Operating Mode Only) GRI/EP

A URS/U T (OP)* URS/U

T (NOP)* URS/U

T (NOD)* ICF NSPS GHG EI (whole

compressor - seal plus

non seal potential)
Processing 882 1,125 N/A N/A N/A 2,799 1,102 4,087

Transmission 1,247 1,307 5,201** 12,238† 29,602‡ 3, 801 1,282 5,550

Underground Storage 535 1,350 N/A N/A N/A 5,279 1,334 7,707

Gathering-Boosting N/A 9.5 241 N/A N/A 723 582 104-5,950 Production N/A N/A N/A N/A N/A 9.4
*Assumes compressor operating in this measured mode for the entire year; OP = Running (operating); NOP = Not Operating (Idle), Pressurized; NOD = Not Operating (Idle), Depressurized ** Recalculated from raw data in report to account for possible transcription errors in original repor t ( see attached spreadsheet). †This value becomes 8,741 if include 2 reported mea surements of zero. ‡This value was reported for operating compressors, but we believe that was an error. Their appendix indicates these emissions were from idle-depressuri zed compressors. We have reclassified these two

measurements as NOD.

Table 4. Summary of Centrifugal Compressor Wet Sea l Emissions reported in EPA Compressor Paper.

Cenrifugal Compressor Wet

Seal Emissions mscfy CH4 (per compressor)

EPA GHG RP (Operating Mode Only) GRI/EPA

† URS/UT (2011) ICF NSPS GHG EI (whole

compressor - seal plus non seal potential)
Processing 5,366 342 8,137* N/A 10,783 18,750

Transmission 997 248 N/A 5,959 18,331
Underground Storage 8,658** 189 N/A N/A 5,959 16,58 6

Gathering/Boosting N/A N/A N/A 12,000 N/A N/A
†See discussion below: it appears this factor does not capture vented emissions from seal oil degassin g * Assumes compressor operating in this measured mo de for the entire year. Value is reported to be an evaluative measurement, with potential measurement errors discussed; this value in original report

seems to be in error as it is inconsistent with the reported measurements (appears it should be ~8,800 ). **Note: only 5 storage compressors reported seal em issions, so this value has little statistical signi ficance.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

7 Table 5. Summary of Centrifugal Compressors Report ing to GHGRP Subpart W, by Seal Type.

Segment Wet Dry Unclassified Total Wet %

Processing 274 153 26 453 60%

Transmission 291 433 3 727 40%

Storage 23 16 1 40 58%

Total 588 602 30 1,220 48%

Finally, the distribution of reported compressor se al emissions is critical for identifying the most effective mix of technologies to reduce th ese emissions. The distributions of compressor seal emissions reported under Subpart W are highly skewed, with roughly 20% of compressors accounting for 80% or more of the total emissions from rod packing and wet seals.( see Figures 1 and 2). Accordingly, focusing on the h ighest emitting compressors and reducing their emissions to the level of the lowest emitting devices could produce significant reductions. Figures 1A and 1B illustrate the skew ed nature of the emissions distributions. For example, Figure 1B shows that rod packing emissions from the 20% highest emitting compressors at Processing Sites are greater than ab out 1,000 Mscfy, whereas 50% emit less than 160 Mscfy and the lowest emitting 20% emit less tha n 1 Mscfy. EPA’s Compressor Paper does not discuss these distributional issues, and we urg e the agency to incorporate and assess them going forward.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

8 Figure 1. Distributions of 2012 reciprocating comp ressor rod packing emissions

measurements reported under Subpart W

.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05Cumulative Probability

2012 Rod Packing Emissions (Mscf CH4 - log scale) A. Rod Packing Emissions - Cumulative Distribution F unction

Transmission

Processing

Underground Storage

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0fraction of cumulative emissions

fraction of compressors B. ~20% of Compressors Produce ~80% of Total Rod Pa cking Emissions

Transmission

Processing

Underground StorageE NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

9 Figure 2. Distributions of 2012 centrifugal compre ssor wet seal emissions measurements reported under Subpart W

.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05Cumulative Probability

2012 Wet Seal Emissions (Mscf CH4) A. Wet Seal Emissions - Cumulative Distribution Func tion

Transmission

Processing

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1fraction of cumulative emissions

fraction of compressors B. ~20% of Compressors Produce 80-95% of Total WEt Seal Emissions

Transmission

ProcessingE NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

10 2. Critique of the Compressor Paper's Summaries of Spe cific Studies

GRI/EPA . The values presented in Table 3-2 accurately ref lect the values in the GRI/EPA report. The Compressor Paper also correctl y summarizes the GRI/EPA assumption that annual per-seal reciprocating and centrifugal compressor emissions are similar; we hypothesize that this assumption may partially expl ain why GHGRP estimates of centrifugal compressor wet seal emissions are so much higher th an the GRI/EPA value. In addition, the

URS/UT at Section 1.3.3. examines this issue and co ncludes that the GRI/EPA estimate of the

wet seal emissions factor does not reflect the full suite of emissions. Specifically, the URS/UT report indicates that wet seal emissions have two c omponents: fugitives at the seal face and vented emissions from the circulating oil. The URS /UT report further indicates that the GRI/EPA study factor included only the fugitive com ponent, as the vented emissions from oil degassing were included as part of the station vent ing estimates. Finally, after reviewing available data in their Table 1-4, the URS/UT repor t concludes that only an estimate from the Natural Gas STAR program includes both the fugitive and vented component. The Natural Gas STAR emission factor of roughly 21,000-105,000 Mscf /year per seal, is even higher than the other estimates in our Table 4 and supports the con clusion that the GRI/EPA factor does not completely characterize wet seal emissions. We th us suggest that the GRI/EPA methodology for determining compressor level wet seal emissions improved and updated to reflect more fully

the extensive volume of emissions.

URS/UT . We have identified a number of weaknesses and po tential errors in Table 3-4 of the Compressor Paper, which should include several modifications to better reflect the measurements in the URS/UT report (presented in Tab les 3-3 and 3-4 of the URS/UT report). These are needed because there are apparent mismatc hes in the URS/UT report between the measurements classified in their Table 2-2, the mea surement results reported in Table B-3, and the resulting average values presented in their Tab le 3-4. We provide a spreadsheet that seeks to correct some of the apparent discrepancies, though additional consultation with URS/UT may be helpful to confirm whether these apparent discrepan cies are real, and update the summary tables as needed. In particular:

• The reported annual emissions factors should be cla rified to state that they are based on scaling up the measurements assuming operation in t he observed mode for all hours in the year.

• The Gathering/Boosting reciprocating compressor emi ssions data should be clarified to reflect the data was collected with the compressor in "run," or operating, mode.

• For Transmission compressors, the first entry for " Average Rod Packing - Idle + depressurized" should be for "Average Rod Packing - Idle + pressurized". Additionally, the reported average of 12,236 Mscfy appears to exc lude two zero values (measured, no emissions according to Table 2-2) for Site 2 recipr ocating compressors 1 and 2. Including these 2 measurements of zero emissions, r esults in an average of 8,741 Mscfy for 7 reciprocating compressors.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

11 • For Transmission compressors, the second entry for "Average Rod Packing" should be corrected to reflect that the 29,603 Mscfy value co rresponds to two measurements of emissions at Site 5, reciprocating compressors 6 an d 7 reported in Table B-3.

• For Transmission Compressors, the Table in the orig inal paper did not include 4 measurements of compressors in run mode (Site 4, re ciprocating compressors 2,4,6,8 which were measured according to Table 2-2 but ente red incorrectly into Table B-3). We suggest the WP add these results, which are "Averag e Rod Packing -Run Mode", 4 measurements, 5,201 Mscfy.

• The value for wet seal emissions seems to be in err or as it is inconsistent with the reported measurements (appears it should be ~8,800 - Table B-2 shows 12 measurements including one value of zero).

• The GRI/EPA value for wet seals should be 248 inste ad of 396, according to the GRI/EPA report.

GHGRP . As indicated in the Compressor Paper's summary o f the GRI/EPA and URS/UT study, reciprocating compressors can emit in the "idle and pressurized mode". Because this mode is missing from the GHGRP data, the GHGRP estimates of compressor rod packing

emissions underestimate actual emissions. The URS/ UT paper also reports rod packing emissions from the "idle-depressurized" mode (GRI/E PA assumed that these emissions would be negligible). The cause of these emissions should b e attributed to the appropriate source category (for example, the emissions measured from the rod p acking in the depressurized mode may come from a leaking isolation valve).

The information presented in Tables 3-5 and 3-6 of the Compressor Paper should be more clearly described. It appears that the reported em issions are total compressor emissions, not just seals. At a minimum, it would be helpful if the te xt and table headings describe what is included in the reported emission totals. Better would be t o report emissions by type, and then the sum totals. Such an analysis would provide a check on the GRI/EPA breakdown of seal vs. non-seal emissions. (Seal emissions were estimated to be ab out 25% of total compressors emissions for reciprocating compressors and less than 5% for cent rifugals.) 8 The Paper should also clarify that not all facilities report emissions to the GHGRP, s o the activity factors and emissions reported in

Tables 3-5 and 3-6 do not reflect national totals.

US GHG Inventory . As described in the ICF report ( see section 3.7), the compressor EFs

in the GHG EI contain both seal and non-seal emissi ons. ICF assumes the seal emissions are ~25% of the total compressor emissions in the invent ory; this is supported by the discussion of the GRI/EPA report in Section 31 that reciprocating seal emissions are 24-28% of total emissions from reciprocating compressors ( see, e.g., Table 4-18). The Compressor Paper discussion abo ut the GHG inventory needs to clearly indicate that th e emission factors in the GHG EI are aggregate compressor emissions - not just seals. T his clarification should also be made in Tables

3-8 and 3-9 to avoid confusion.

8 See Compressor Paper at 12-13.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

12 The last paragraph of Section 3-4 refers to "net 20 12 methane emissions" but the values presented appear to be potential emissions (which i s what the caption for Table 3-9 correctly indicates); table A-141 of the GHG EI shows net emi ssions are only reported for recip compressors - not for centrifugal. Thus it is impo ssible to determine total compressor seal emissions for each segment. However, reciprocating net totals are possible for all sectors except production from Table A-141.

A final general comment . We encourage EPA to ensure that all sources of e missions from compressors are analyzed, whether in the Compressor Paper or the Leaks Paper.



### B. Analysis and Critique of National Emissions Estimat es (Questions 1, 2)

EPA’s Compressor Paper also requests comment on nat ional estimates of compressor emissions, which provide an overall sense of the im portance of compressor emissions when compared to other significant sources. National es timates traditionally combine an emissions factor with an activity factor to establish overall national emissions. In the case of compressors, the emission factor in the national inventory inclu des not only seal emission (discussed in Part I.A, above), but also vented emissions blowdown ven t stacks, open-ended lines, and leaks from various components. Some of these additional compr essor emission sources are significant. For instance, the 1996 EPA/GRI data, ICF estimated that only about a quarter of total reciprocating compressor emissions come from rod-packing. Noneth eless, we focus here on the combined emissions factors for centrifugal and reciprocating compressors because nearly all of the emissions from these sources can be addressed by th e technologies we describe in Part III,

below.

The Compressor Paper presents several studies that touch on compressor activity factors and national emissions estimates. We highlight sev eral considerations relevant to national emissions, below:

• The ICF Report surveyed specific states and found t hat there were a greater number of larger compressors in upstream segments, leading to a 166% upward revision of compressor emission in the gathering sector.

• The GHGRP data can be used to provide an independen t estimate of the type of seals used in centrifugal compressors. As shown in Table 5, about 50% of all the centrifugal compressors in the Transmission, Storage and Proces sing segments that were reported to

the GHGRP have wet seals. This value is intermedia te to the values reported in the GHG EI (80%) and the API/ANGA report (21% - processing only).

Ultimately, the Greenhouse Gas Emissions Inventory provides a good benchmark for national compressor emissions and that source sugge sts that emissions are extensive (see Table 3-9 indicating emissions greater than 2,000 Gg CH4) . We note that the Inventory potential emission factors appear to be higher than would be consistent with the total compressor emissions factors derived from the GHGRP. Figure 3 shows the GHGRP (non-combustion) total emissions for 462 Transmission compressor stations, averaging 20,445 Mscf/yr. As notedE NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

13 earlier, however, the GHGRP data may not fully acco unt for all emissions such as rod packing in the not-operating, pressurized mode. In either cas e, available data suggests national emissions from compressors and compressor stations are an ext ensive source of emissions.

Figure 3. Subpart W Transmission and Storage Compr essor Station Emissions.



### C. Additional Studies (Question 12)

Colorado State University and Carnegie Mellon Unive rsity are leading two studies designed to characterize methane emissions from spe cific natural gas industry segments: one focuses on Transmission and Storage and the other o n Gathering and Processing. Both are part of the series catalyzed by EDF and are being done i n partnership with natural gas operators. Both studies will report emission measurements take n at representative facilities where compressors are a significant source of emissions a nd are on track to submit papers for publication in peer-reviewed scientific journals by late summer 2014.

Another project sponsored by EDF that focuses on em issions from oil and gas operations in the Barnett Shale will result in facility-level emission data from a limited number of

midstream and transmission facilities in the area. Papers summarizing the results of this work should be submitted for publication in peer-reviewe d scientific journals by late 2014. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

1.E-01 1.E+00 1.E+01 1.E+02 1.E+03cumulative probability

transmission facility emission rate (kg CH4 / hr)E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

14 

### III. M ITIGATION 

### T ECHNOLOGY 

### : E FFECTIVENESS 

### & C OST

EPA’s Compressor Paper presents a number of differe nt mitigation technologies, discusses the effectiveness of those technologies, and provides information on cost. Broadly speaking, the technologies EPA presents can be clas sified as either emissions avoidance (reciprocating rod-packing replacement and centrifu gal compressor dry seal retrofit) or emissions capture (rock packing venting capture and wet seal degassing capture). Part III.A of our response discusses reciprocating compressor mitigat ion technology, including both rod packing replacement and reciprocating compressor gas captur e. Part III.B discusses centrifugal compressor mitigation technology, with focus on wet seal degassing capture technologies and the charge questions EPA presents around this technolog y. These two sections respond generally to charge questions 4 and 5 and likewise include speci fic responses to questions 7, 8, 9, and 10. EPA has also requested comment on additional techno logies capable of reducing vented emissions at compressors (charge questions 3 and 6) , and in response, Part III.C discusses leak detection and repair (“LDAR”).

We conclude:

• Regular rod-packing replacement is an effective, lo w-cost way to mitigate emissions, which ICF projected would reduce emissions by 3.6 b illion cubic feet (bcf) of methane (approximately 69,000 metric tons) at a cost of $6. 11/mcf reduced. Rod-packing replacement can be optimized by inspecting for exce ss seal emissions as part of a regular leak detection and repair program, enhancing contro l effectiveness.

• Rod-packing gas capture systems can have greater ef fectiveness than rod-packing replacement and, in many cases, result in beneficia l use of otherwise wasted gas.

• Wet-seal degassing capture systems are feasible, re sult in substantial reductions and are highly-cost effective. If broadly applied at centr ifugal compressors not currently subject to the NSPS, ICF projected that such capture system s would reduce methane by 19.1 billion cubic feet (over 360,000 metric tons) while achieving net savings of $3.07/mcf of

methane reduced.

• LDAR and gas capture technologies can also effectiv ely mitigate non-seal compressor

emissions.



### A. Reciprocating Compressor Mitigation Technology; Eff ectiveness; and Cost (Charge Questions #4, 5)

This section addresses reciprocating compressor rod -packing mitigation technology, effectiveness, and cost, focusing on rod-packing re placement and also briefly discussing capturing of vented gas.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

15 1. Rod-Packing Replacement

EPA’s Compressor Paper describes how rod-packing re placement can mitigate emissions as well as the costs of replacing rod-packing. We note that rod-packing replacement costs are very low (on the order of $1,620 per cylinder, occu rring on average every four years 9 ) but otherwise do not have specific comments on EPA’s de scription of the technology or presentation of costs. Instead, we focus on mitigation potentia l and discuss the analysis EPA presents in the Compressor Paper (drawing from the TSD for NSPS OOO O 10 ). We also present an analysis from ICF’s Cost Curve Report, which is referenced i n the Compressor Paper but not fully characterized. Finally, we note the benefits an LD AR program could have in optimizing the cost-effectiveness of rod-packing replacement.

The ICF Cost-Curve Report provides a helpful descri ption of rod-packing emissions and the way in which replacing rod-packing can help mit igate emissions. Without fully recounting EPA’s discussion in the Compressor Paper, we emphas ize a few points key to determining the mitigation potential of this practice:

• EPA concludes that even newly-installed rod-packing emits methane, but these emissions increase over time as rod-packing wears out.

• Replacing rod packing can lower emissions by ensuri ng worn-out, higher-emitting seals are replaced with lower emitting seals. This is no t, however, a one-time action, and to be effective, rod-packing must be replace regularly ov er time (EPA suggests every 26,000 operating hours or approximately 3 years).

EPA estimated the effectiveness of rod-packing repl acement in the NSPS OOOO TSD for most segments by taking the average rod-packing emissions factor from the 1996 EPA / GRI study and subtracting the emissions factor for newl y-installed rod-packing, which EPA determined was 11.5 scf/h per seal. EPA performed this analysis focused on the likely impacts of rod-packing replacement at new compressors. The results are summarized in Table 4-1 on page 31 of the Compressor Paper, and for transmissi on sector reciprocating compressors, the analysis yields a control efficiency of approximate ly 80%.

IFC took a different approach to estimating the eff ectiveness of rod packing replacement. EPA’s Compressor Paper cites ICF’s assumed control effectiveness of 98% for timely rodpacking replacement, which appears in the appendix material of the report. In the body of the report, however, ICF makes more detailed assumption s with different results, summarized in Table 3-5 from the ICF report, reproduced below.

9 EPA, Natural Gas STAR Program, Lessons Learned: Reducing Methane Emissions from Co mpressor Rod Packing Systems (2006).

10 EPA, Technical Support Document for NSPS Subpart OOOO (2012).E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

16 In particular, ICF assumes that new rod-packing emi ts 11.5 scf/h (consistent with NSPS OOOO). ICF also adopts EPA’s average emissions fac tor for transmission compressor seals (57 scf/h) and assumes that, after 3 years, rod-packing emissions will increase linearly to this value, and, if not replaced, will continue to increase in a linear fashion every year beyond that. Finally, ICF assumes that rod-packing would be replaced ever y five years and takes the difference between three- and five-year replacements averaged over the course of 15 years as the per-year effectiveness of a replacement strategy.

Though different, both of these approaches provide helpful insights into the effectiveness of rod-packing replacement program. Similar to oth er regular maintenance programs like LDAR, the first time facilities undertake such prog rams, emissions reductions will likely be greater given that facilities may not have performe d these activities at regular intervals (or at all) in the past. After instituting a regular maintenan ce program, ongoing maintenance is critical to ensure emissions do not return to pre-program level s, though per-year reductions will be less than initial reductions given the established mitig ation baseline. Accordingly, EPA’s averagevalue based approach more closely approximates subs tantial reductions that could be expected from a first round of rod-packing replacement at ex isting compressor facilities, and ICF’s analysis assumes some baseline level of control and reductions that could be achieved in addition to that level, reflecting the effectiveness of ongo ing maintenance.

Though we discuss the importance of LDAR at compres sor stations more fully below, here, we note that regular LDAR at compressor stati ons can help optimize both the effectiveness and cost of rod-packing replacements. The rate of wear on cylinder rod-packing is not uniform, and, while regular replacement will yield benefits, a LDAR program will enhance these benefits in several important ways. First, it will allow op erators to perform regular maintenance – short of rod-packing replacement – that keeps rod-packing emissions as close to 11.5 scf/h as possible. Second, it will allow operators to pinpoint the tim e rod-packing must be replaced, whether before or after the 26,000 hours identified in NSPS OOOO. Finally, it will allow operators to more swiftly identify equipment failures that result in significant rod-packing emissions. This type of smart rod-packing replacement could, in principle, result in an effectiveness of close to 100%, assuming a smart approach could maintain emissions at levels close to 11.5 scf/h. These benefits are, of course, in addition to the ancillary benefi ts LDAR would have for reducing leaks from other components at compressor facilities.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

17 This type of smart rod-packing replacement program could also improve costs by allowing for less costly repairs, in lieu of replac ement, and leveraging rod-packing replacement costs when necessary. Moreover, in addition to con ventional LDAR approaches, there are several examples of flow-meter technologies that ca n inexpensively and accurately monitor rodpacking vents. For instance, Cook Compression of fers portable, inline, and insertion meters that can measure and track packing case vent flow w ith an accuracy of ±1% reading, ± 0.5% full

scale. 11 Hoerbiger also offers rod packing monitor kits th at can help operators determine when to change the packing. 12

Ultimately, we emphasize that there are real and si gnificant benefits to a regular rodpacking replacement program, though underscore that deploying LDAR alongside such a program will only enhance the effectiveness of rod packing replacement and potentially reduce the costs of such a program.

2. Rod-Packing Gas Recovery (Charge Question #9)

EPA’s Compressor Paper also presents information on the possibility of capturing gas from rod-packing vents that would otherwise be wast ed, focusing on one technology that would capture gas and reroute it back to the compressor f or beneficial use and another that would leverage existing capture infrastructure by connect ing to site vapor recovery units. As a threshold matter, we note that the gas capture syst ems described in the Compressor Paper are more effective at reducing emissions than rod packi ng replacements (which, even when newlyinstalled, leak methane). Also, these systems can capture vented emissions from other points at the compressor stations, so encourage beneficial us e of the vented gas and can have emission reduction benefits beyond those described in the Co mpressor Paper. Accordingly, we urge EPA to strongly consider these technologies.

Moreover, the two technologies EPA presents – VRUs and REM Technology’s capture system – are complementary and can potentially addr ess emissions at the vast majority of compressor sites. EPA’s Compressor Paper notes tha t the incremental costs of manifolding reciprocating compressor rod packing vents to an ex isting site VRU are small. In instances where a VRU isn’t present, however, adding a VRU al ong with needed additional compression could have significant cost impacts, but the REM te chnologies system provides an important alternative. Because the REM system reroutes vent gas to the compressor air intake, no additional compression is needed and the technology is therefore capable of capturing emissions where onsite compression and VRUs are unavailable. Accordingly, the gas capture technologies are capable of addressing substantial emissions fro m compressor stations, and we encourage EPA, when it considers the cost of these systems, t o assess them in light of the full suite of vented emissions sources they can address.

11 Sentrix TM Portable, Inline & Insertion Meters, Cook Compress ion, available at http://www.cookcompression.com/index.cfm/lev2/1869/ Sentrix%E2%84%A2.Gas.Flow.Measurement.

12 U.S. Dept. Of Energy, Methane Mitigation Workshop, http://www.arpa-e.energy.gov/sites/default/ files/documents/files/Methane_Mitigation_Workshop_M cCoy.pdf.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

18 In response to EPA’s charge question, we are not aw are of any technical limitations to installing this technology.



### B. Centrifugal Compressor Mitigation Technology; Effec tiveness; and Cost (Questions 4, 5, 7, 8, 9, 10)

EPA’s Compressor Paper also present centrifugal com pressor mitigation technologies, including dry seal retrofits and wet seal capture s ystems. The benefits of dry seal systems are manifest, and we agree with the Compressor Paper’s conclusion that, given these substantial

benefits and the small incremental costs of install ing dry seal systems, dry seals are preferable for new installations. Indeed, the ICF Report esti mates that 90% of new compressor installations are equipped with dry seals. Moreover, ICF estimat es that, even in retrofit applications with higher upfront costs, dry seal retrofits have a pay back period of 29 months.

In this section, however, we focus on wet seal capt ure systems, given their relatively

lower costs and the substantial emissions that come from these devices, as described in Part II,

above.

1. Wet Seal Degassing Capture

The ICF Cost-Curve Report has classified wet-seal g as capture technologies as one of the most significant emissions mitigation opportunities as well as one of the most cost-effective (with payback periods of 3 months and less dependin g on the size of the facility). The ICF Report provides and in-depth analysis of retrofitti ng wet seal systems, and EPA has appropriately characterized that analysis in the Compressor Paper . Here, we only emphasize that wet seal degassing capture systems are feasible in retrofit applications and that a variety of uses are available for the captured gas.

In addition, BP recently presented information at a Natural GasStar Technology Transfer Workshop, indicating that 100 centrifugal compresso rs it owns in Alaska operate using wet seal degassing technology, which achieves a 99% emission reduction and is extremely reliable (no failures in 30 years of operation). 13 Further, the technology has a payback period of l ess than a month, assuming a gas price of $3 mscf.

EDF has asked a consultant to perform further analy ses of system design and cost with several technology vendors and have learned that ca pture systems have been installed in retrofit applications. We are working to refine cost estima tes of a design similar to the BP system along with other possible designs.



### C. Importance of LDAR at Compressor Stations (Question 6)

EPA has requested comment on additional technologie s capable of achieving compressor reductions. In Part III.A, above, we described how leak detection and repair practices could help

13 BP, Centrifugal Compressor Wet Seal: Sea Oil Degas sing & Recovery (Feb. 11, 2014), http://www.epa.gov / outreach/gasstar/documents/workshops/denver-2014/Se al_Oil_Degassing.pdf.E NVIRONMENTAL D EFENSE F UND • J UNE 16, 2014

19 optimize rod-packing replacement. Though we discus s equipment leaks in a separate paper, here, we emphasize that LDAR at compressor stations can achieve substantial, additional reduction by minimizing equipment leaks and can do so in a very cost-effective fashion. Several reports have included data supporting these conclus ions:

• The ICF report found LDAR for compressor stations ( storage) to be cost effective, with potential methane reductions of 1.5 bcf per year at an annualized cost of -$4.5 million per year and initial capital costs of $2.8 million (-$3 .03/mcf methane reduced). The report also found LDAR for compressor stations (transmissi on) to be cost effective, with potential methane reductions of 2.8 bcf per year at an annualized cost of $7.7 million per year and initial capital costs of $5.3 million ($2. 79/mcf methane reduced). 14

• The Carbon Limits report found an average net prese nt value for performing an LDAR survey at a compressor station of $3,376, with aggr egate abatement costs of -$1.7/tCO2e in the production segment and -$8.3/tCO2e in the tr ansmission segment. 15

• The Clearstone II analysis found that methane leaks from gathering compressor stations averaged 97 tonnes per year per facility, resulting in $49,018 in lost gas value from the leaking components. 16



### D. Errata

1) In the Compressor Paper, there are two typos in the second paragraph of Section 3.7. The

Section numbers referenced should be 3.7.1 and 3.7. 2.

2) Table 3-5 in the Compressor Paper is incorrectly re ferred to as Table 3-4.

14 ICF Cost Curve Report at 4-4.

15 Carbon Limits, Quantifying Cost-effectiveness of Systematic Leak D etection and Repair Programs Using Infrared

Cameras at 17, 30 (Mar. 2014).

16 Clearstone Engineering, Cost-Effective Directed Inspection and Maintenance Control Opportunities at Five Gas Processing Plants and Upstream Gathering Compressor Stations and Well Sites at 28 (2006).