June 16, 2014 

U.S. Environmental Protection Agency 

Office of Air Quality Planning and Standards 

. 16666 Northchase Drive 

Houston, Texas 77060 

Submitted Via Email 

RE: White Paper on Methane and VOC Emissions from Compressors 

Exterran Energy Solutions, L.P. and EXLP Operating, LLC (collectively referred to herein as 

"Exterran") submit the following comments on the United States Environmental Protection Agency's 

("EPA's") April 2014 "Report for Oil and Natural Gas Sector Compressors" addressing potential 

methods to reduce methane and volatile organic compound emissions ("VOCs") from oil and natural gas 

sector compressors ("White Paper"). 1 

Exterran operates in approximately 30 countries, is a global market leader in full service natural gas 

compression services and is the largest contract compression company in the U.S. The engines Exterran 

utilizes globally to provide compression services range in size from under 200 horsepow~r ("HP") 

( ~41% of fleet) to over 1,600 HP ( ~4% of fleet). Approximately 66% of our compressors are less than 

500 HP. 

In the U.S., Exterran owns and operates a fleet of over 7,700 compression units driven by natural gasfired, spark-ignited, reciprocating internal combustion engines with an aggregate capacity of 

approximately 3,429,000 HP. These units are primarily used to service our customers' relatively remote, 

field production, gathering and processing operations. These compression applications are distinct from 

the compressors and engines used at natural gas pipelines, for example, which are typically much larger 

and part of a more significant infrastructure of equipment and personnel. 

Exterran has highlighted the contract service nature of its business because the benefits associated with 

methane capture are not realized by Exterran (or similarly situated service and equipment providers), 

given that title to the natural gas being compressed remains with the customer. In other words, 

compression companies such as Exterran would not derive an economic benefit from methane capture 

because they do not own the gas being compressed by their compression equipment. A compression 

company would likely incur the cost of any additional gas recovery requirements but would not receive 

any of the economic benefits. 

With that context in mind-notably the relatively small HP size of the engines in our fleet, the mostly 

remote, low infrastructure sectors of the natural gas industry in which we participate and the fact that we 

do not own the natural gas we process for our customers-Exterran believes that some of the methane 

1 References to "methane" throughout these comments are also intended to include VOCs unless otherwise stated. 
Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

control measures discussed in the White Paper are realistic and cost-effective even for small 

compressors. We note, however, that none of the studies in the White Paper included an emphasis on 

recommended emissions recovery practices for small compressors. For the reasons set forth below, we 

believe that other control measures would be prohibitively expensive and are not cost-effective, 

especially for compressors under 1,600 HP. We also believe that some of the data and information in 

the White Paper is either incorrect or unsubstantiated, especially as it relates to small compressors under 

1,600 HP. 

Overall, the White Paper supports the concept that leakage rates increase with larger compressors and 

higher operating pressures. Because we agree with these conclusions, Exterran believes that EPA 

should not adopt a one-size-fits-all approach to compressors. Rather, any future regulations pertaining 

to methane emissions from compressors should distinguish between large and small compressors 

because elaborate and costly emission mitigation techniques would not be economically justified for 

small production and gathering compressors-i.e., those under 1,600 HP and operating at lower 

pressures? If EPA deems that further regulation of compressors is necessary, any such future 

regulations should provide an exemption for small reciprocating compressors from costly and elaborate 

mitigation techniques that require anything more than replacing rod packing and checking piston rods 

every three (3) years. Continuing to use the current maintenance techniques and packing ring 

technologies while increasing the frequency of rod packing ring replacements is the optimal way to 

reduce methane emissions from small compressors rather than imposing any of the other emissions 

reduction alternatives described in the White Paper. 

Our comments first address the viable proposed methods of emissions reduction before addressing the 

methodologies Exterran views as non-viable. Finally, our comments address any charge questions that 

were not answered in the initial two sections of our comments. 

I. VIABLE PROPOSED METHODS FOR METHANE EMISSION REDUCTIONS 

With the qualifications and caveats provided throughout these comments-notably including those in 

Section III.1 of these comments related to the accuracy of the emissions factors-Exterran agrees that 

changing the compressor rod packing (i.e., the rings) more frequently would provide significant and 

economically justified reductions in methane emissions from the types of compressors owned by 

Exterran and in the applications Exterran predominantly deploys them. Exterran also supports the 

inspection of piston rods and replacement of excessively worn, damaged or defective piston rods, as 

more fully described and qualified below. 

A. Rod Packing Changes (i.e., Rings) 

The White Paper generally concludes that the current practice among industry is to replace the rod 

packing on compressors every four (4) years. In our view, the common practice in industry is to change 

out the rod packing every four to five ( 4-5) years. Although we have not independently validated the 

specific financial or emissions impact asserted in the White Paper to be tied to more frequent 

2 EPA, Oil and Natural Gas Sector Compressors: Report for Oil and Natural Gas Sector Compressors 26 (Apr. 2014). 

Exterran believes that it is appropriate to adopt 1,600 HP as a threshold to distinguish between small and large compressors 

as noted in the White Paper. 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

replacement of rod packing, Exterran agrees with the general assertion contained in the ICF Study3 and 

cited in the White Paper that replacing the rod packing every three (3) years-or approximately NSPS 

Subpart OOOO's 26,000 hours of operation (a standard that applies only to new reciprocating 

compressors in certain sectors of the natural gas industry)-would result in material emission 

reductions. Exterran believes at some point after three (3) years of use, degradation of the rings (and 

consequently the increase in emissions) is actually exponential rather than linear.4 For this reason, 

Exterran would support a requirement to replace the rod packing on all oil and gas compressorswhether large or small-every three (3) years. 

That said, Exterran also believes that any proposed regulation should be flexible enough to provide for 

improvements in technology that, for example, might encourage reciprocating compressor 

owners/operators to buy compressor rod packing rings that have a life expectancy beyond three (3) 

years, so long as such rings provide the same or better emissions retention as rings that currently have a 

life expectancy of three (3) years. On a related note, industry has not used bronze metallic rod packing 

rings referred to in White Paper Section 4.1.2 as the standard for many years now. PTFE5 plastics are 

the prevailing material used in packing rings, stemming from their ability to: (i) conform to the rod, (ii) 

seal effectively with virtually no wear-in period, and (iii) self-lubricate. 

Finally, EPA must recognize the distinction between replacing the rod packing rings and replacing the 

original equipment manufacturer's ("OEM's") packing system. Section 4.1.2 of the White Paper 

suggests that replacing the OEM's packing system is a viable option, but Exterran disagrees with this 

conclusion. Therefore, we have discussed this option as a non-viable alternative within Section II.C of 

these comments. 

B. Replacement ofthe Piston Rod 

The success of Exterran's contract compression services business depends in large measure on the 

reliability of the compression units Exterran utilizes to provide those services. Exterran's customer 

contracts typically call for a reduction in the relevant service fee if Exterran is not able to provide those 

services in excess of a negotiated percent of time each month, typically in the high 90% range. 

As such, Exterran and EPA are fully aligned when it comes to replacing piston rods if they are 

excessively worn, damaged or defective, as any failure or inefficiency in the operation of the rods can 

translate into inefficient operation or non-operation of the compressor package as a whole and, as a 

result, can negatively impact our provision of compression services to our customers. 

Accordingly, Exterran's regularly scheduled fleet inspection process includes both physically inspecting 

the piston rods and measuring them with a micrometer, dial indicator, or dial calipers for potentially 

non-visible wear or deformation. Exterran engages in this type of inspection whenever the rod packing 

is inspected and replaced. 

3 See, for example, page 3-12 of the "Economic Analysis of Methane Emission Reduction Opportunities in the U.S. Onshore 

Oil and Natural Gas Industries" dated March 2014, which was prepared for the Environmental Defense Fund by ICF 

International ("ICF Study"). 

4 See ICF Study at 3-14. 5 "Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The 

best known brand name ofPTFE is Teflon by DuPont Co." Wikipedia, http://en.wikipedia.org/wiki/Ptfe. 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

In cases where piston rods have been damaged due to wear or ring failure, it is Exterran's preference to 

replace the piston rod because this remedy is :fi·equently quicker, more reliable and more cost-effective, 

resulting in a longer lived piston rod relative to repairing the rod. 

Notwithstanding the foregoing, Exterran would not support a proposal to preemptively replace the piston 

rod on a defined interval, as durability can depend on the operating conditions and can vary from case to 

case. 

II. PROPOSED METHODS FOR METHANE EMISSION REDUCTIONS THAT ARE UNSUBSTANTIATED, NOT 

COST JUSTIFIED AND/OR NOT APPLICABLE 

In Section 4.0 of the White Paper ("Available Compressor Emissions Mitigation Techniques"), EPA 

mentions "refitting or realignment of the piston rod," capture of the rod packing emissions and the use of 

non-standard packing systems as potentially cost justified and applicable options to reduce emissions. 

For the reasons that follow, Exterran does not support the use of any of these options, at least as those 

methodologies would apply to a fleet and in compression applications similar to our own. 

A. "Refitting or Realignment of the Piston Rod" 

Exterran would like EPA to clarify the meaning of the concept of "refitting or realigmnent of the piston 

rod" referenced in Section4.1.1 ofthe White Paper. Ifthis phrase is intended to refer to the application 

of a new hardened surface such as tungsten carbide, then we agree this is a suitable method of repair if 

the general condition and straightness of the rod is sufficient for resurfacing. In this regard, note that 

Exterran's primary compression component supplier ion-nitride hardens the piston rods in the packing 

wear area rather than using tungsten carbide or chrome coating. However, as mentioned in Section I.B. 

of these comments, in many cases, replacement is faster and more cost-effective than repairing used 

piston rods. 

B. Capture of Emissions I Vapor Recovery 

While gas recovery by definition and in theory would reduce emissions, EPA's analysis of this potential 

reduction option: (i) involves equipment and technology that is not known by, has not been tested by and 

is not utilized by Exterran, the industry-leading contract compression service provider, (ii) relies on 

emission recovery data that is unrelated to rod packing emission recovery, (iii) does not appear to 

account for the potential collateral emission consequences of operating the gas recovery technology, and 

(iv) assumes an economic benefit that would not in many cases be realized by the party that would bear 

the cost of the gas capture technology. 

Untested and Unutilized Technology 

New technologies for capturing vent gas may be available, but the current use in the production and 

gathering segments is extremely limited in the experience of Exterran and the cost and safety 

performance ofthese systems is not commonly known as yet in the industry. 

To the best of our knowledge, we-the largest compression services company in the U.S.-have not 

ever utilized the REM Technology rod packing leak recovery system on any of our domestic fleet of 

over 7,700 compression units. During the comment period, Exterran attempted to obtain further 

information from REM Technology to facilitate responding to this aspect of the White Paper, but we did 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

not receive sufficient information before the time of submission of these comments to resolve our 

questions about the efficacy and safety of this system. 

Faulty Data 

Section 4.2.2 of the White Paper refers to a technique for recovering emissions from the compressor rod 

packing and cites a Natural Gas STAR PRO Fact Sheet titled "Install Automated Air/Fuel Ratio 

Controls" (U.S. EPA, 2011 c). Exterran would like to clarify that the referenced Fact Sheet addresses the 

ability to reduce methane emissions lost from the unburned fuel in the engine 's combustion process 

(through improved air/fuel ratio control). The Fact Sheet does not discuss gas recovered from the 

compressor's rod packing. Therefore, it is erroneous for the White Paper to conclude that the "reported 

average fuel gas savings of 78 thousand cubic feet per day (Mcfd) per engine with the gas recovery 

system installed" is based on any compressor rod leakage recovery. Given that these savings are not 

attributed to reductions in methane leaks from rod packings, the emission recovery estimates discussed 

in this section of the White Paper are over-inflated. 

Collateral Consequences 

The White Paper neglects to consider the unintended deleterious consequences of such recovery 

systems. These additional impacts and costs must also be considered in any justification analysis. In 

this case, EPA's analysis should additionally consider at least the following: (i) additional horsepower 

required to generate power for such a system and (ii) the additional emissions resulting from that power 

generation, natural gas leakage, or fuel combustion. 

Mismatch of Economic Benefit and Detriment 

The capture and use of rod packing gas is not an economic benefit to a contract compression services 

provider like Exterran because, among other things and as mentioned above, the gas is owned by 

Exterran's customer or a customer of Exterran's customer. Exterran and other like situated contract 

compression service and equipment providers merely take possession of the gas when tendered by the 

customer at the inlet flange of the compressor package. Contract compression service providers 

compress the gas from the inlet pressure to the prescribed outlet pressure, and then the gas is re-tendered 

to the customer at the outlet flange of the compressor package. Title to the gas throughout that short 

process is retained by the entity that held title to it when it entered the compressor-not Exterran or any 

other contract service provider who is providing contract compression services. 

When considering whether to utilize new equipment or processes, like the REM Technology system 

mentioned in the White Paper, Exterran's and our customers' primary concerns relate to understanding 

any safety and technological considerations. Assuming that any such unknowns associated with a gas 

capture system could be answered to our and our customers' satisfaction,6 the next question then is 

whether the value of any recovered methane would justify the cost to install, maintain, and operate the 

gas capture system. The cost of this equipment could be paid for in one of two ways: (1) either Exterran 

would have to purchase and install this equipment on its own equipment and then charge its customers 

for the vapor recovery units over time or (2) alternatively, the customer-who may or may not own 

compression assets of its own-would have to purchase and install that equipment for use with 

Exterran' s equipment. Exterran estimates that compression service providers own and operate 

6 These uncertainties are touched on below. 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

approximately 30% ofthe compressors operating in the oil and gas sector. Because compression service 

providers would not economically benefit from the installation of vapor recovery units, Exterran does 

not support the imposition of a requirement that compression services providers be required to purchase, 

install, or maintain such equipment. 

Conceptually, Exterran agrees that using an existing Vapor Recovery System could recover packing 

leakage. However, the majority of compression sites in the production and gathering sector do not 

currently have such a system. Exterran researched the availability of small on-board compressor-driven7 

vapor recovery unit ("VRU") systems used solely for the capture of vent gas and the cost per recovered 

standard cubic feet ("scf') of methane was not reasonable, even if we were to directly benefit from the 

value of the recovered hydrocarbons. For this reason, Exterran agrees with the White Paper's 

conclusion in Section 4.2.3 that "the installation of a VRU to only capture rod packing emissions may 

not be economically viable if an additional compressor system is required." 

Where the owner or operator of the facility has such a system in place, Exterran is willing to use that 

equipment to allow said owner or operator to capture vent gas, if requested by our customer. 

C. Use ofNon-Standard Rod Packing Systems 

The use of non-standard "low-emission" packing systems (i.e., beyond what is provided by the 

compressor OEM with standard offering) is not economically justified for production, gathering and 

boosting compressors. 

The reciprocating natural gas compression industry already has many effective systems for reducing rod 

packing leakage, including multi-ring systems and unique ring profiles. While effective, the cost for 

installing these systems is significant because a portion or all of the hardware must be replaced in 

addition to the replacement of the actual rings. Therefore, in our opinion, the cost of any such nonstandard rod packing systems would only be justified, if at all, for compressors with large rods operating 

in high pressure environments. 

III. RESPONSES TO CHARGE QUESTIONS 

1. Please comment on the national estimates of methane emissions and methane emission factors 

for vented compressor emissions presented in this paper. Please comment on the activity data 

and the methodologies used for calculating emission factors presented in this paper. 

Exterran Response: First, Exterran notes that the emission factors used to describe the leak rates 

fi·om reciprocating compressors and to calculate methane emissions estimates in the White Paper are 

contradictory and unsubstantiated in their use in these calculations. As a result, Exterran believes 

that the emission rates presented in several of the studies are overinflated, at least with respect to 

compressors used in the production, gathering and boosting segments. 

Table 3-2, which is presented in Section 3.1 of the White Paper,8 provides a Summary of 

Reciprocating and Centrifugal Compressor Seal Methane Emission Factors. Exterran questions the 

7 The reference here to "on-board" refers to the gas compression skid where the vent gas is compressed by a small positive 

displacement compressor. 

8 GRI/EP A Methane Emissions from the Natural Gas Industry, Volume 8: Equipment Leaks (hereinafter "GRI/EP A Study"). 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

assumption in this table regarding the "Number of Seals per Compressor" for reciprocating 

compressors in the "Natural Gas Production" segment. Exterran owns and operates over 7,700 

compression units in the U.S., primarily deployed in the production segment. Many of the units 

Exterran owns and operates are single cylinder or two cylinder units, not four. Therefore, Exterran's 

fleet is estimated to have 2.6 cylinders per production compressor. If the number of assumed seals 

per reciprocating compressor in the natural gas production segment is reduced to 2.6, the "Average 

Compressor Methane Emission Factor from Seals" in the ''Natural Gas Production" segment should 

also be adjusted downward by 35% (from 9.48 Mscflyear to 6.16 Mscf/year). Carrying this 

assumption further, the "Average Methane Emissions" for reciprocating compressors in the "Natural 

Gas Production" segment would then decline from 3,071 to 1,996 MT/year in Table 3-3.9 

Exterran also questions the summary ofthe 2014 GHG Inventory provided in Table 3-9.10 Page 18 

ofthe White Paper states the emission factors used in this section are from the GRIIEPA Study. The 

data summarized in Table 3-9 are based upon information provided in Table 3-8.11 However, Table 

3-8 states an emission factor of 263 to 312 scf!day per compressor for "small" reciprocating 

compressors. Converting this emission factor to Mscflyear results in a value of 115 Mscflyear per 

compression unitY In contrast, Table 3.3 states that the average Mscf!year for reciprocating 

compressors in natural gas production service is 9.48 Mscf!year. Therefore, it is unclear from the 

description provided in the White Paper how the analysis of the data 2014 GHG Inventory is based 

on the GRI/EP A Study when the results are so different. 13 It is important for the public to be able to 

meaningfully comment on these emission factors because they have the potential to directly impact 

the estimates that form the basis for justifying emission reduction methodologies. If EPA chooses to 

move forward with proposing a rule to reduce methane emissions from compressors, we would 

appreciate EPA providing a more detailed discussion regarding the basis for any numbers derived 

from data reported under the 2014 GHG Inventory and subject this information to further scrutiny, 

analysis and validation. 

One possible explanation for the discrepancies between these results is that the studies may have 

used different definitions for what constitutes ''production." In fact, it is unclear how different 

portions of the White Paper define "production," but it appears to be inconsistent between the studies 

cited. For example, footnote 1 on page 19 of the White Paper states that the GRIIEP A Study defines 

"small gathering compressors as compressors on the overhead lines from gas well separators and 

associated gas well separators" and "large" reciprocating compressors in the Production segment of 

Table 3-8 are defined as "compressors at large gathering compressor stations (stations with 8 

compressors or more)" (emphasis added). 14 Including gathering and boosting equipment in the 

"production" segment is inconsistent with EPA's definition of "onshore production" in the 

Mandatory Greenhouse Gas Reporting Rule. Given such inconsistencies, it is not surprising that the 

results of these studies vary greatly. The disparities lead us to speculate how EPA developed an 

9 Table 3-3 is entitled "Summary of GRI/EPA Methane Emissions from Reciprocating and Centrifugal Compressor Seals." 10 Table 3-9 is entitled "Summary of Natural Gas Sector Compressor Activity and Calculated Potential Methane Emissions." 

11 Table 3-8 is entitled "Natural Gas Sector Methane Emission Factors for Compressors." 

12 2.37 Msc£iyr-cyl x 4 cyl = 9.48 Msc£iyear/compressor. 

13 E.g., the emission factor for small compressors is ten times higher than the factor quoted in Table 3-3. Using the same 

methodology, the emission factor for large compressors is 600 times larger than the factor presented in Table 3-3. 

14 Exterran takes issue with this definition because it focuses on the number of compression units located at a particular site 

and ignores the fact that compressor sizes can vary widely in terms of horsepower. A compressor station with 8 compressors 

could actually have less horsepower than a compressor station with only 2 or 3 compressors. 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

emission factor that is substantially higher than the emission factor for gathering and boosting 

reciprocating compressors presented in other sections of the White Paper (e.g., the GRIIEP A Study 

and the URS/UT 2011 Study, both presented in Table 3-4). 

Exterran believes the emission factor for "small" reciprocating compressors is more accurately the 

9.48 Mscf/yr factor as presented in the GRIIEPA Study (while also accounting for the reduced 

emissions due to the lower number of cylinders per compressor in this industry segment, as earlier 

discussed). Utilizing the proper emissions factor significantly reduces the estimated quantity of 

methane emissions from the reported 35,930 compressors in the ''production" segment. 

Exterran also questions the emission factor provided in Table 3-8 for large compressors because the 

range of values provided-14,947 to 17,728 scf/day/compressor-is substantially larger than the 

emission factor for gathering and boosting reciprocating compressors presented in the GRIIEP A 

Study and even considerably higher than the "Average Methane Emission Factor" from the URS/UT 

Study, both presented in Table 3-4. 15 

It is further unclear whether the emissions calculated and presented in Table 3-9 reflect the 

erroneous assumption from the GRIIEP A Study that reciprocating compressors in natural gas 

production service have four (4) seals per compressor. If this estimate were carried through in the 

calculations used to develop the numbers in Table 3-9, those values should be reduced to reflect that 

the typical reciprocating compressor in production service generally has 2.6 seals per compressors 

(as discussed earlier in these comments). Therefore, Exterran questions the accuracy of the numbers 

presented in Section 3.1 of the White Paper and would not support using this data as the basis for 

imposing the requirement to install costly methane reduction technologies or configurations. 

Exterran also needs further information to be able to meaningfully comment on Section 3.7.1.1, 

Gathering and Boosting Segment. The first bullet in this section introduces, a "new methane 

emission factor'' for all gathering compressors of 1,980 scf/day. The second bullet under the 

heading "Reciprocating Compressors" states that the reciprocating compressor emission factor that 

was 2013 GHG Inventory "was updated to distinguish compressor seal emissions versus compressor 

fugitives .... " However, Exterran is unable to determine the origin of EPA's conclusion that seals 

account for 25% of the emissions and non-seals account for 75%. No data or calculations are 

provided to verify that this assumption is correct. The accuracy of this value is important because 

the focus of the White Paper is to gather accurate information regarding emissions from seals. 

Additionally, it is unclear whether the White Paper is missing a section or if there are typos in the 

cross-references provided in Section 3.7. For example, Section 3.7.1.2 refers to Section 3.8.1.1 of 

the White Paper. However, no such section exists. Similarly, Section 3. 7 .1.4 of the White Paper 

also refers to this non-existent section of the White Paper. Therefore, if EPA relies on this 

information in the future, it would be helpful for EPA to clarify these references by providing further 

information and citations to explain how it has updated the emission factors for reciprocating 

compressors. 

Finally, Exterran notes that it is extremely important for EPA to avoid reaching sweeping 

conclusions based on limited data from limited studies that were not intended to have broad industry 

15 Table 3-4 is entitled "Sampling Results for Reciprocating and Centrifugal Compressor Seals." 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

applicability. Additionally, as alluded to above, technology does tend to improve over time, so EPA 

should avoid rigid mandates that result in either the stifling of technological progress or a preference 

for one OEM product or technology to the disadvantage of others. Different technologies may 

provide better results under the variable operating conditions present in an oil and gas field 

application. 

2. Did this paper appropriately characterize the different studies and data sources that quantify 

vented emissions from compressors in the oil and gas sector? 

Exterran Response: While we do not believe the White Paper mischaracterized the different studies 

and data, we do believe that in some cases the data were misconstrued, misinterpreted and/or 

misapplied. We have discussed these instances in further detail in our comments above. 

3. Did this paper capture the full range of technologies available to reduce vented emissions from 

reciprocating compressors and wet seal centrifugal compressors at oil and gas facilities? In 

particular, are there other options for reducing emissions at existing reciprocating or 

centrifugal compressors? For example, EPA is aware of "low emissions packing" for 

reciprocating compressors but has no detailed information on this technology. 

Exterran Response: The White Paper covered all technologies Exterran is aware of to reduce vented 

emissions from reciprocating compressors at oil and gas facilities. Our comments above provided a 

discussion of"low emission packing" technology for reciprocating compressors. 

4. Did this paper appropriately characterize the emissions reductions achievable from the 

emissions mitigation technologies discussed for reciprocating compressors and wet seal 

centrifugal compressors? 

Exterran Response: As discussed earlier in our comments, Exterran believes that the emission 

mitigation technologies for reciprocating compressors were not clearly presented in terms of 

effectiveness, cost-benefit, safety and proven technology. In particular, Exterran questions the 

accuracy of the discussion presented in Section 4.1.2, which states that ''Newly installed packing 

average emissions were assumed to be 11.5 cubic feet per hour per cylinder (U.S. EPA, 2006a)." In 

contrast, the data in Table 3-10 of the White Paper states that for production compressors the 

methane emission factor is 0.271 scf/hour per cylinder. Therefore, according to the White Paper, 

new packing leaks significantly more than old packing (11.5 scflhour versus 0.271 scf/hour). This 

conclusion does not make sense, particularly if it is intended to be representative of compressors of 

all sizes. The White Paper does not clarify whether this assumption is reflective of emissions from 

larger compressors operating in higher pressure applications, which do not typically operate in the 

production segment. If EPA deems that further regulation of compressors is necessary, any such 

future regulations should provide an exemption for small reciprocating compressors16 from costly 

and elaborate mitigation techniques that require anything more than replacing rod packing and 

checking piston rods every three (3) years. 

16 The term "small compressor" as used in Exterran's comments is meant to indicate those with less than 1,600 HP. This 

definition is adopted from Section 3. 7 .1.1 of the White Paper, which distinguished between "small" and "large" gathering 

and boosting compression based on a 1,600 HP threshold. 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

In addition to our comments provided above, Exterran would like to reiterate that any cost savings 

associated with recovering additional methane from small reciprocating production compressors 

would be minimal for several reasons: (1) small compressors have less throughput and, therefore, 

less emissions, (2) they tend to operate in lower pressure service, which results in less potential 

emissions, and (3) the primary cost to replace rod packing is from the cost of the labor, which is 

generally a fixed cost and does not change significantly depending on whether the rod packing is 

being changed on a small or a large compressor. Therefore, it will be more cost effective and 

beneficial for any future rulemaking, if any, to focus on emissions from large reciprocating 

compressors. 

See the rest of our comments, above, for further discussion of gaps in the White Paper regarding 

reciprocating compressors. 

5. Did this paper appropriately characterize the capital and operating costs for the technologies 

discussed for reduction of vented emissions from reciprocating compressors and wet seal 

centrifugal compressors? 

Exterran Response: The White Paper was ambiguous regarding capital and operating costs for 

technologies involving reciprocating compressors. Furthermore, much of the data that was 

referenced in the White Paper is obsolete given that the gas market has undergone considerable 

improvements in the nearly twenty (20) years since the GRI/EP A Study was published. 17 Moreover, 

the White Paper does not acknowledge that a large percentage of compression operations and 

equipment is owned and operated by service contractors. As discussed above, such service providers 

do not own or have a financial interest in the gas that is compressed using their own equipment. 

Therefore, it is inaccurate for the White Paper to assume or conclude that the value of reducing 

methane emissions will necessarily benefit those who may incur additional expenses associated with 

increased maintenance or capital expenditures for compressors. 

Exterran does not own or utilize any centrifugal compressors. 

6. If there are emissions mitigation options for reciprocating and centrifugal compressors that 

were not discussed in this paper, please comment on the pros and cons of those options. Please 

discuss the efficacy, cost and feasibly for both new and existing compressors. 

Exterran Response: The existing emissions mitigation options that Exterran is aware of for 

reciprocating compressors are discussed earlier in these comments, including our analysis of the 

viability of each. Exterran does not own or utilize any centrifugal compressors. 

7. Are there technical limitations that make the replacement of wet seals with dry seals 

impractical at certain existing centrifugal compressors? 

Exterran Response: Exterran does not own or utilize any centrifugal compressors. 

17 See, e.g., Section l.A of our comments (explaining that industry has not used bronze metallic rod packing rings for many 

years now). 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

8. Are there technical reasons why an operator would use a wet seal centrifugal compressor 

without a gas recovery system? 

Exterran Response: Exterran does not own or utilize any centrifugal compressors. 

9. Are there technical limitations that make the installation of gas capture systems at certain 

reciprocating compressors impractical? 

Exterran Response: As discussed earlier in these comments, there are clear technical, commercial 

and safety limitations with gas capture systems that render them impractical in circumstances 

generally applicable to Exterran's fleet. In particular, Exterran does not believe there is a sufficient 

benefit to justify the cost of installation of gas capture systems on small production and gathering 

reciprocating compressors-i.e., those under 1,600 HP and operating at lower pressures. Rather, 

Exterran believes it would be more cost effective to require small reciprocating compressors to 

replace their rod packing every three (3) years and to inspect the rod piston whenever the rod 

packing is replaced to detennine if the rod piston should also be replaced. 

10. Please comment on the prevalence of the different emission mitigation options in the field. 

Exterran Response: Please refer to our earlier comments. 

11. Given the substantial benefits of dry seal systems (e.g., lower emissions, less maintenance, and 

higher efficiency), are you aware of situations where new wet seal centrifugal compressors are 

being installed in the field? If so, are there specific applications that require wet seal 

compressors? 

Exterran Response: Exterran does not own or utilize any centrifugal compressors. 

12. Are there ongoing or planned studies that will substantially improve the current 

understanding of vented VOC and methane emissions from reciprocating and centrifugal 

compressors and available techniques for increased product recovery and emissions 

reductions? 

Exterran Response: Exterran is currently unaware of any ongoing or planned studies of that nature. 

IV. SUMMARY AND CONCLUSIONS 

In summary, Exterran agrees with the conclusion in the White Paper that larger compressors operating at 

higher pressures produce more emissions. For this reason, Exterran believes that elaborate and costly 

emission mitigation techniques are not appropriate for small reciprocating compressors under 1,600 HP. 

The minimal emissions from rod packing on small reciprocating compressors can be effectively and 

cost-efficiently reduced by replacing that packing every three (3) years and by inspecting the rod piston 

for excessive wear when the rod packing is replaced. Additional measures beyond these steps are not 

cost justified for small compressors. 

Exterran appreciates EPA's willingness to share its thoughts and current understandings regarding the 

methane emissions from compressors. Our comments provided above are reflective of the limited time 

provided to review the studies presented in the Compressor White Paper. With additional time, Exterran 

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Exterran's Comments 

White Paper on Methane and VOC Emissions from Compressors 

can further refine its analysis and delve deeper into aspects that we have merely touched on in these 

comments. As with prior engine and compressor-related emissions undertakings, Exterran would be 

happy to meet with and further discuss these important matters with EPA staff. 

Thank you for the opportunity to comment. In the event that EPA concludes that regulation of 

compressor emissions is warranted, we look forward to having the opportunity to work with EPA to 

develop regulations and guidelines that are economically and environmentally sound. If EPA has any 

questions or would like further information about any of these comments, I can be reached at 281-836-

7000. 

Respectfully, 

Mike Wasson 

Director, Fleet Services 

I 

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