June 16, 2014

U.S. Environmental ProtectionAgency Office ofAir QualityPlanning 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%** offleet) to over 1,600 HP (**~4%** offleet). Approximately 66% ofour compressors are less than 500 HP. In the U.S., Exterran owns and operates a fleet ofover 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 primarilyused to service our customers' relativelyremote, 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 ofa more significant infrastructure ofequipment and personnel. Exterran has highlighted the contract service nature ofits 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 ofany additional gas recovery requirements but would not receive any ofthe economicbenefits. With that context in mind-notably the relatively small HP size ofthe engines in our fleet, the mostly remote, low infrastructure sectors ofthe 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 ofthe methane

1References to "methane" throughout these comments are also intended to include VOCs unless otherwise stated.Exterran's Comments WhitePaper onMethane andVOC Emissions from Compressors 

### control measures discussed in the White Paper are realistic and cost-effective even for small compressors. We note, however, that none ofthe 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 ofthe data and information in the White Paper is either incorrect orunsubstantiated, especially as itrelates 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 economicallyjustified 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 ofrod packing ring replacements is the optimal way to reduce methane emissions from small compressors rather than imposing any ofthe other emissions reduction alternatives described intheWhite Paper. Our 

### comments first address the viable proposed methods ofemissions reduction before addressing the methodologies Exterran views as non-viable. Finally, our comments address any charge questions that were not answered inthe initial two sections ofour comments. I. VIABLEPROPOSEDMETHODS FORMETHANEEMISSIONREDUCTIONS 

### With the qualifications and caveats provided throughout these comments-notably including those in Section III.1 ofthese comments related to the accuracy ofthe 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 ofpiston 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 ourview, the common practice in industryis 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). Exterranbelieves thatitis appropriate to adopt 1,600 HP as a threshold to distinguishbetween small and large compressors as noted inthe White Paper. -2-Exterran's Comments White Paper onMethane and VOC Emissions from Compressors 

### replacement ofrod 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 ofuse, degradation ofthe 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 compressorswhetherlarge or small-everythree (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 orbetter emissions retention as rings that currentlyhave a life expectancy ofthree (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 theprevailingmaterial used inpacking rings, stemming from their ability to: (i) conform to the rod, (ii) seal effectivelywith virtuallyno wear-inperiod, 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 ofthePiston 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 areduction in the relevant service fee ifExterran is not able to provide those services in excess ofanegotiatedpercent oftime 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 ofthe rods can translate into inefficient operation or non-operation ofthe compressor package as a whole and, as a result, can negativelyimpact ourprovision ofcompression services to our customers. Accordingly, Exterran's regularly scheduled fleet inspectionprocess includes bothphysicallyinspecting 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 ofinspection whenever the rod packing is inspected and replaced.

3 See, for example, page 3-12 ofthe "Economic Analysis ofMethane EmissionReduction Opportunities inthe U.S. Onshore Oil and Natural Gas Industries" dated March 2014, which was prepared for the Environmental Defense FundbyICF International ("ICF Study"). 4See ICF Study at 3-14. 5 "Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer oftetrafluoroethylene thathas numerous applications. The bestknownbrand name ofPTFEis TeflonbyDuPont Co." Wikipedia, http://en.wikipedia.org/wiki/Ptfe. -3-Exterran's Comments White Paperon 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 livedpiston rodrelative to repairing the rod. Notwithstandingthe foregoing, Exterran would not support aproposal to preemptivelyreplace the piston rod on a defined interval, as durability can depend on the operating conditions and can vary from case to case. II. PROPOSEDMETHODSFORMETHANEEMISSIONREDUCTIONS THATARE UNSUBSTANTIATED, NOT COSTJUSTIFIEDAND/ORNOTAPPLICABLE In Section 4.0 of the White Paper ("Available Compressor Emissions Mitigation Techniques"), EPA mentions "refitting orrealignment ofthe pistonrod," capture ofthe rod packing emissions and theuse of non-standard packing systems as potentially costjustified and applicable options to reduce emissions. For the reasons that follow, Exterran does not support the use ofany ofthese options, at least as those methodologies would applyto a fleet and in compression applications similarto our own. A. "Refitting orRealignment ofthe PistonRod" Exterran would like EPA to clarify the meaning ofthe concept of"refitting or realigmnent ofthe piston rod" referenced in Section4.1.1 oftheWhite Paper. Ifthis phrase is intended to refer to the application ofa new hardened surface such as tungsten carbide, then we agree this is a suitable method ofrepair if the general condition and straightness ofthe 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 pistonrods. B. Capture ofEmissions I Vapor Recovery While gas recoverybydefinition and in theory would reduce emissions, EPA's analysis ofthis potential reduction option: (i) involves equipment and technologythatis notknownby, has notbeen testedbyand 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 ofoperating the gas recovery technology, and (iv) assumes an economic benefit that would not inmany cases berealized bythe party that would bear the cost ofthe gas capturetechnology. Untested andUnutilized 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 commonlyknown as yet inthe 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 ofour 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 ofthe White Paper, but we did
-4-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 ofthis system. FaultyData Section 4.2.2 ofthe White Paper refers to a technique for recovering emissions from the compressorrod packing and cites a Natural Gas STAR PRO Fact Sheet titled "Install Automated Air/Fuel Ratio Controls" (U.S. EPA, 2011c). Exterranwould liketo clarifythatthe 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 recoveredfrom the compressor's rodpacking. Therefore, itis 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 inmethane leaks from rod packings, the emission recovery estimates discussed inthis sectionoftheWhite 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 anyjustification 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 thatpower generation, natural gas leakage, orfuel combustion. Mismatch ofEconomicBenefitand Detriment The capture and use ofrod 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 ofthe gas when tendered by the customer at the inlet flange of the compressor package. Contract compression service providers compress the gas from theinletpressureto theprescribed outletpressure, and then the gas is re-tendered to the customer at the outlet flange ofthe compressor package. Title to the gas throughout that short process is retainedbythe entity that held title to itwhen it entered the compressor-notExterran or any othercontract serviceproviderwho 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 ofany recovered methane wouldjustifythe cost to install, maintain, and operate the gas capture system. The cost ofthis equipment couldbepaid for in one oftwo 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 Theseuncertainties are touched onbelow. -5-Exterran's Comments White Paper on Methane and VOC Emissions from Compressors approximately 30% ofthecompressors operating in the oil and gas sector. Because compression service providers would not economically benefit from the installation ofvapor recovery units, Exterran does not support the imposition ofarequirement that compression services providers berequired 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 currentlyhave such a system. Exterranresearched the availability ofsmall on-board compressor-driven7 vapor recovery unit ("VRU") systems used solely for the capture ofvent gas and the cost perrecovered standard cubic feet ("scf') ofmethane was not reasonable, even ifwe 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 ofa VRU to only capture rod packing emissions may notbeeconomicallyviable ifan additional compressor systemis required." Where the owner or operator ofthe facility has such a system in place, Exterran is willing to use that equipment to allow said owner oroperator to capture vent gas, ifrequestedbyour customer. C. Use ofNon-StandardRod 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 economicallyjustified for production, gathering and boosting compressors. Thereciprocating natural gas compression industry alreadyhas 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 onlybejustified, ifat all, for compressors with large rods operating inhighpressure environments. 

### III.RESPONSES TO CHARGE QUESTIONS 1. Please comment on the national estimates ofmethane emissions and methane emission factors for vented compressor emissions presented in this paper. Please comment on the activity data andthe methodologies used for calculating emission factors presentedinthis 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 ofthe studies are overinflated, at least with respect to compressors used intheproduction, 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

7Thereference here to "on-board" refers to the gas compression skid where the vent gas is compressed by a small positive displacement compressor. 8 GRI/EPA Methane Emissions from the Natural Gas Industry, Volume 8: EquipmentLeaks (hereinafter "GRI/EPA Study"). -6-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 ofthe units Exterran owns and operates are single cylinder ortwo cylinderunits, not four. Therefore, Exterran's fleet is estimated to have 2.6 cylinders per production compressor. Ifthe number ofassumed 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 "AverageMethane Emissions" for reciprocating compressors inthe "Natural Gas Production" segmentwould then decline from 3,071 to 1,996 MT/yearinTable 3-3.9 Exterran also questions the summary ofthe 2014 GHG Inventoryprovided in Table 3-9. 10 Page 18 oftheWhite Paper states the emission factors used inthis 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 ofthe data 2014 GHG Inventory is based onthe GRI/EPA Studywhentheresults are so different. 13 Itis important for thepublicto be ableto meaningfully comment on these emission factors because they have the potential to directly impact the estimates that form thebasis forjustifyingemissionreduction methodologies. IfEPA 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 oftheWhitePaperdefine "production,"but it appears to beinconsistentbetweenthe studies cited. Forexample, footnote 1onpage 19 ofthe White Paper states that the GRIIEPA Studydefines "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, itis not surprisingthat the results ofthese studies vary greatly. The disparities lead us to speculate how EPA developed an

9 Table 3-3 is entitled "SummaryofGRI/EPAMethane Emissions from Reciprocating and Centrifugal Compressor Seals." 10 Table 3-9 is entitled "SummaryofNatural Gas SectorCompressorActivity and CalculatedPotentialMethaneEmissions." 11 Table 3-8 is entitled "Natural Gas SectorMethaneEmissionFactors for Compressors." 12 2.37 Msc£iyr-cyl x 4 cyl = 9.48 Msc£iyear/compressor. 13 E.g., the emissionfactor for small compressors is tentimes higherthanthe factor quoted inTable 3-3. Using the same methodology, the emission factor for large compressors is 600 times largerthan the factorpresentedinTable 3-3. 14 Exterrantakes issue withthis definitionbecause itfocuses onthe number ofcompressionunits located ata particular site andignores the fact that compressor sizes canvarywidely interms ofhorsepower. A compressor stationwith 8 compressors could actually have less horsepowerthan a compressorstationwith only2 or 3 compressors. -7-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 ofthe White Paper (e.g., the GRIIEPA Study and the URS/UT 2011 Study, bothpresented inTable 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 ofcylinders per compressor in this industry segment, as earlier discussed). Utilizing the proper emissions factor significantly reduces the estimated quantity of methane emissions from thereported 35,930 compressors inthe ''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 GRIIEPA Study and even considerablyhigher than the "Average Methane Emission Factor" from the URS/UT Study,bothpresentedinTable 3-4. 15 It is further unclear whether the emissions calculated and presented in Table 3-9 reflect the erroneous assumption from the GRIIEPA Study that reciprocating compressors in natural gas production service have four (4) seals per compressor. Ifthis estimate were carried through in the calculations used to develop thenumbers in Table 3-9, those values should bereduced to reflectthat the typical reciprocating compressor in production service generally has 2.6 seals per compressors (as discussed earlierinthese comments). Therefore, Exterran questions the accuracy ofthe numbers presented in Section 3.1 ofthe White Paper and would not support using this data as the basis for imposingtherequirementto install costlymethanereductiontechnologies 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 ofEPA'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 ofthis value is important because the focus ofthe WhitePaperis to gather accurate informationregarding emissions from seals. Additionally, it is unclear whether the White Paper is missing a section or ifthere 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 ofthe White Paper also refers to this non-existent section of the White Paper. Therefore, if EPA relies on this information inthe future, it would behelpful for EPA to clarifythesereferences byproviding 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 havebroad industry

15 Table 3-4 is entitled "SamplingResults for Reciprocating and Centrifugal Compressor Seals." -8-

### Exterran's Comments WhitePaperon Methane andVOC Emissions from Compressors applicability. Additionally, as alluded to above, technology does tend to improve overtime, so EPA should avoid rigid mandates thatresult in eitherthe stifling oftechnological 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 inthe oil and gas sector?
Exterran Response: While we do notbelieve the White Papermischaracterized the different studies and data, we do believe that in some cases the data were misconstrued, misinterpreted and/or misapplied. Wehave discussed theseinstances infurther detail inourcomments above. 

### 3. Didthis paper capture thefull range oftechnologies 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 reciprocatingcompressors buthas no detailedinformationonthis technology.
Exterran Response: TheWhitePapercovered all technologies Exterran is aware ofto reduce vented emissions from reciprocating compressors at oil and gas facilities. Our comments above provided a discussion of"lowemissionpacking"technologyforreciprocating 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 ofthe discussion presented in Section 4.1.2, which states that ''Newly installed packing average emissions were assumed to be 11.5 cubic feet perhourper 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, particularlyifitis intended to be representative ofcompressors of all sizes. The White Paper does not clarify whether this assumption is reflective ofemissions from larger compressors operating in higher pressure applications, which do not typically operate in the production segment. IfEPA deems that further regulation ofcompressors is necessary, any such future regulations should provide an exemption for small reciprocating compressors 16 from costly and elaborate mitigation techniques that require anything more than replacing rod packing and checkingpistonrods everythree (3) years.

16 The term "small compressor" as used inExterran's comments is meantto indicate those withless than 1,600 HP. This definitionis adoptedfrom Section3.7.1.1 oftheWhite Paper, which distinguishedbetween "small" and "large" gathering andboosting compressionbased ona 1,600 HP threshold. -9-Exterran's Comments White Paperon Methane andVOC 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 ofthe 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 ofour 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/EPA Study was published. 17 Moreover, the White Paper does not acknowledge that a large percentage of compression operations and equipment is owned and operatedbyservice contractors. As discussed above, such serviceproviders 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 ofreducing methane emissions will necessarilybenefit those who mayincur additional expenses associated with increased maintenance or capital expenditures for compressors. Exterran does not own orutilize any centrifugal compressors. 6. Ifthere are emissions mitigation options for reciprocating and centrifugal compressors that were not discussed in this paper, please comment on the pros and cons ofthose options. Please discuss the efficacy, cost andfeasibly for bothnew 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 viabilityofeach. Exterran does not own orutilize any centrifugal compressors. 7. Are there technical limitations that make the replacement of wet seals with dry seals impractical atcertainexistingcentrifugalcompressors? Exterran Response: Exterran does not own orutilize any centrifugal compressors.

17 See, e.g., Section l.A ofour comments (explaining that industryhas notusedbronze metallic rod packing rings for many years now). -10-

### Exterran's Comments WhitePaperon Methane andVOCEmissions 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 orutilize 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 notbelieve there is a sufficient benefit tojustify the cost ofinstallation ofgas 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 packingisreplacedto detennineiftherodpiston should alsobereplaced. 

### 10. Please commentontheprevalence ofthe differentemission mitigation options inthefield.
ExterranResponse: Pleasereferto ourearlier comments. 

### 11. Given the substantial benefits ofdry seal systems (e.g., lower emissions, less maintenance, and higher efficiency), are you aware ofsituations where new wet seal centrifugal compressors are being installed in the field? If 

### so, are there specific applications that require wet seal compressors?
ExterranResponse: Exterran does not ownorutilize 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?
ExterranResponse: Exterranis currentlyunaware ofanyongoing orplanned studies ofthatnature. 

### IV. SUMMARYAND CONCLUSIONS In summary, Exterran agrees withthe conclusionintheWhitePaperthatlarger 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-efficientlyreduced byreplacing that packing every three (3) years and byinspecting the rod piston for excessive wear when the rod packing is replaced. Additional measures beyond these steps are not costjustifiedfor 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 ofthe limited time provided to review the studies presentedinthe CompressorWhite Paper. With additional time, Exterran

-11-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 happyto meetwith and further discuss theseimportantmatters 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. IfEPA has any questions or would like further information about any ofthese comments, I canbereached at 281-836- 7000. Respectfully,

MikeWasson Director, Fleet Services



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