Matthew Todd

Regulatory and Scientific Affairs

1220 L Street, NW Washington, DC 20005

- 4070 USA Telephone: 202

- 682

- 8 319 Fax: 202

- 682

- 8031 Email: ToddM@api.org www.api.org

June 13 , 2014

Mr. Chris Frantz US EPA 109 T.W. Alexander Drive Mail Code: #143

- 05 Research Triangle Park, NC 27709

Re: EPA VOC /Methane White Paper on Oil and Natural Gas Sector Compressors

Dear Mr. Frantz :

The American Petroleum Institute (API) appreciates the opportunity to provide feedback on EPA’s White Papers on Methane and Volatile Organic Compound (VOC) Emissions in the Oil and Natural Gas Sector. On April 15, 2014, EPA released, for external peer review, white papers that focus on technical issues covering emissions and mitigation techniques targeting methane and VOCs from five separate emission sources. As noted in the Obama Administration ’s Strategy to Reduce Methane Emissions, EPA will use the papers, along with the input from the peer reviewers and the public, to determine how to best pursue additional reductions from these sources. As described below, API does not believe additional

met hane controls should be required at this time.

API represents over 590 oil and natural gas companies, leaders of a technology

- driven industry that supplies most of America’s energy, supports more than 9.8 million jobs and 8 percent of the U.S.

economy, a nd, since 2000, has invested nearly $2 trillion in U.S. capital projects to advance all forms of energy, including alternatives. Many of our members will be directly impacted by any policy decisions that may arise from this effort regardless of whether it informs either regulatory action by the federal government or states

.

API provide d technical feedback and expertise throughout the de velopment of the New Source Performance Standard (NSPS) Subpart OOOO rule

. Each source addressed by the white papers w as

c onsidered for regulation during th e development of the NSPS and EPA, ultimately, chose not to regulate them

. While our understanding of emissions from oil and gas production continues to evolve, the fundamental merits of requiring additional regulatory control of these sources is un changed

. A s such
, API continues to believe that no addition al regulation of oil and gas produ ction sources is

necess ary prior to the full implementation of the NSPS OOOO rule and a subsequent evaluation of
emissions

.Page 2

Considering the potential for significant impact on our members that may arise from any policy decision stemming from the white papers
, API has developed significant technical comments (see attached) to address a number of technical inaccuracies about the sources and the conclusions that have been
drawn. Barring significant revision, API believes that the current white papers are simply insuff icient to inform sound policy decisions and that simply posting comments on the current version will not result in an informed process . As such , API recommends the EPA take the following steps:

 R evise the white papers to correct any fundamental flaws or i naccuracies that were identified in response to peer review and stakeholder comment (e.g., improved source description s , improved understanding of emission quantification , misconceptions about emission mitigation options )

 Develop a response to comments doc ument that clearly identify the changes the EPA makes to the revised white papers and explains the Agency’s rationale for those changes

 Identify emission studies in progress that will better inform EPA’s understanding of these source
emissions and await th e pending study reports

In recent years, there have been significant swings in the national emission estimates from oil and gas production sources, including those covered by the white papers, which indicate a necessity to continue collecting data to impr ove our understanding. Much of this learning will come from improved reporting under Subpart W of EPA’s Greenhouse Gas Reporting Program as well as current studies and others planned in the coming years, which involve taking direct measurements of the sour ces. EPA and industry would both be well served by allowing these studies to inform policy.

Again, we appreciate the work by EPA to initiate these white papers and the opportunity to provide feedback on this effort. API and its members are dedicated to working with EPA to improve our collective understanding of these emissions and providing the technical operator experience that’s
needed to do so. Recognizing the potential for these white papers to inform not only EPA but other government agency policy d ecisions, w e request the opportunity to provide additional feedback to the Agency in response to any of our comments in advance. Furthermore, we again offer our experience and expertise as EPA moves into the policy evaluation phase of this effort.

Sincerely, /s/

Matthew Todd

Cc: Peter Tsirigotis, EPA David Cozzie, EPA

Bruce Moore , EPA

# Comments on

Oil and Natural Gas Sector Compressors

By EPA Office of Air Quality Planning and Standards

June 2014

Prepared by

The American Petroleum Institute (API)API Comments on Submitted to EPA

Oil & Natural Gas Sector Compressors June 1 3 , 2014



## Contents

A. Introduction

................................ ................................ ................................ ................................ .......... 4

B. Process Descriptions

................................ ................................ ................................ ............................. 5

C. Emissions Data and Emissions Estimates

................................ ................................ .............................. 5

D. Available Compressor Emissions Mitigation Techniques

................................ ................................ .... 10

E. Summary

................................ ................................ ................................ ................................ ............. 16

F. Charge Questions

................................ ................................ ................................ ................................ 16API Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

2 

## Executive Summary

The U.S. Environmental Protection Agency (EPA) has developed a draft document titled Oil and Natural
Gas Sector Compressors (referred to as “the White Paper”) to, as stated in the Preface, seek input and solidi fy its understanding of the methane and volatile organic compounds (VOCs) emissions from

compressors in this industry sector. The American Petroleum Institute (API) here by submits its input and comments in this document.

These comments generally follow the Table of Contents for the Compressors White Paper so that the reader can more readily associate them with the White Paper. This review mostly addresses reciprocating compressors. Additional answers to charge questions ar e only made if not previously
covered in comments.

In general, the White Paper simply reports emissions information and control technologies reported in various studies or papers without a meaningful critique or analysis of the data and recommendations

pr ovided in those studies/papers. These comments provide some of the needed critique. Following are the main findings from API’s review of the White Paper.

 The White Paper should specifically note that the only emissions study which sampled a significant nu mber of reciprocating compressors at oil and gas sites (1996 GRI/EPA) showed low vent rates from compressors located at oil and gas production sites. This result makes technological sense due to a combination of much lower cylinder suction pressures, small er piston rod diameters, and higher speed ( rpm s) for compressors located at oil and gas sites. All of these parameters, most importantly lower suction pressures, contribute to lower vent rates from compressor rod packing from compressors at oil and gas pro duction sites compared to compressors located at gathering and booster stations, gas processing plants, and transmission
stations.

 The White Paper should note that the 2011 URS/UT study provi ded no measurements or
emissions factors for the small reciproc ating compressors located at oil and gas production sites. The White Paper correctly points out that the 2011 URS/UT centrifugal wet seal measurements are suspect and not useful due to technical complications during measurements.

 Going forward, EPA should rely on the GHGRP data as the primary source of measured emissions data and compare that data with existing emissions studies, such as the 1996 GRI/EPA study, and other wet seal emissions estimates from subsequent EPA Paper s. EPA should use the 2012, 2013 and later data to develop emissions factors for compressors in processing and other downstream applications based on a select number of variables such as compressor operating pressures, compressor frames (piston rod size), speed, etc. The GHGRP already u ses emission factors for compressors in production, which is an appropriate approach (see discussion in the first bullet above).

 The most important takeaway from the 2012 API/ANGA study, as mentioned in the White Paper , is that the percentage of centrifug al compressors in all sectors of the industry that areAPI Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

3 equipped with wet seals is much lower than the 80% assumed by EPA for the U.S. GHG Inventory . The API/ANGA data suggests only 21% wet seals in U.S. service. Initial review of 2011 and 2012 GHGRP Subpar t W d ata for the transmission sector suggests a range of 3 5

- 5 0 % (the
U.S. GHG I nventory assumes 90% wet seals for this segment)

.

 The White Paper failed to mention the most important information from Table 6

- 7 in the July
2011 TSD for the Subpart OOOO proposed rule , which is the VOC and methane control cost effectiveness data in $/ton. In short, the cost effectiveness for midstream sectors (i.e., processing, gathering & boosting) was less than $1,000 per ton of VOC, and EPA determined this to be suffic ient to include a Subpart OOOO requirement to replace rod packing every 26,000 hours for gas process ing and gathering compression. The cost effectiveness for th e production sector, even with cost of methane saved considered, was extremely high at approxim ately $56,000/ton of VOC and $16,000/ton of methane. Downstream sectors (transmission and storage) were excluded due to VOC cost effectiveness of $2,800 per ton or higher, and minimal
VOC reductions.

 The White Paper reports results from the 2014 ICF/EDF cost/benefit analysis of rod packing replacement (every 3 years instead of every 5 years) as providing a payback of seven months ; however, the White Paper does not explain, or critique, the assumptions used by ICF in their cost/benefit analysis. In their c ost/benefit analysis, ICF assumes a linear increase in vent rates for three years, from 11.5 scf/yr

- cylinder to 57 scf/yr

- cylinder, followed by an unspecified percentage linear increase for two years. This technique is a misuse of the 57 scf/hr/cylinder

av erage emissions factor for compressors in the gas processing and transmission sectors obtained from the 1996 GRI/EPA study. The 57 scf/yr

- cylinder factor is a statistical average from a large measured data set which, theoretically, should include emissions from rod packing at various years of life, from almost new to close to end of life. This average emissions factor should be applied in a cost/benefit analysis in the method used by EPA in the TSD for Subpart
OOOO. In addition, it is inappropriate to pres ume linear vent range changes unless it is substantiated with real data. Vent rate changes over time due to wear are not likely to be linear.

 Any future EPA discussion of rod packing replacement cost effectiveness for the oil and gas production sector sho uld consider, as mentioned on page 3

- 13 of the 2014 ICF/EDF Paper , (1) the remote location of these compressors, (2) that many of the compressors are leased rather than owned, and, most importantly, (3) that there is typically not a back

- up compressor for use during downtime ; therefore, one or more wells must be shut

- in to replace rod packing on a
compressor if replacement is done at intervals separate from other major maintenance. Therefore, the cost of lost production must be included in any future cost/b enefit analysis for rod packing replacement for reciprocating compressors in the production sector. Alternatives to prescribed maintenance intervals, such as condition based maintenance where vent rates are monitored over time, should be considered.API Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

4 

## A. Intr oduction

Th e American Petroleum Association (API) appreciates the opportunity to present th is set of comments

on EPA’s pre

- dissemination draft Oil and Natural Gas Sector Compressors
, Report for Oil and Natural Gas
Sector Compressor (U.S. EPA 2014, subseque ntly referred to in this document as “the EPA White Paper”
, or “the White Paper” )

. The White Paper mentions that “over half of new oil wells drilled co

- produce natural gas.” The term “co

produce natural gas” is a recently coined and inaccurate term unknown to industry and never before used to describe one of the three types of wells: oil wells (which may produce associated gas), natural gas wells, and natural gas condensate wells (which produce both natural gas and liquid condensate).

In the Introduction , the White Paper groups compressors into four sectors: (1) oil and gas production ( gathering and boosting), (2) processing, (3) transmission, and (4) storage. Some of the other sections group compressors into five sectors by separating “oil and gas production” from “gathering and boosting”. Five sectors are required because reciprocating compressors located at oil and gas production sites, such as gas lift compressors, flash gas compressors, and small gathering compressors, typically operate at a range of pressures much lower than those at gathering and boosting stations and are typically smaller frame compressors.

Compressors at production sites typically operate with the following cylinder suction pressures as low as 1 to 5 psig (1 st stage of flash gas compressors on low pressure towers), 15 to 100 psig (1 st and 2 nd stages of flash gas compressors and gas lift compressors), and 50 to 250 psig (1 st and 2 nd stages for gathering compressors). Final stage discharge pressures can be as high as 2,000 psig for gas lift compressors, but for the other compressors are typically in the range of 200 to 1,000 psig. Gathering and boosting station compressors typically operate with 1 st stage cylinder suction pressures in the range of 150 to 500 psig and final stage discharge pressures of 500 to 1,500 psig. Cylinder suction and discharge pressure, primar ily suction pressure , is the driving force behind rod packing leaks; therefore, a lower cylinder suction pressure significantly reduces the potential leakage rate. (See page 9, CPI

- Mechanical Packing Design and Theory of Operation, attached

. ) Also, recip rocating compressors at production sites will typically have less capacity and power requirements than those at gathering and booster stations. Compressors at production sites are typically driven by a gas

- fired engine rated at 40

- 500 horsepower, while a c ompressor at a gathering or boosting station will typically be driven by a gas

- fired engine rated at 500 to 3,500 horsepower.

Therefore, the compressors at production sites are typically of a smaller frame size and driven by smaller engines with higher rp m (1,400 to 1,800 rpm) versus (800 to 1,200 rpm). These smaller compressor frames have piston rods that are smaller than the larger frame compressors (1.5

- 2 inches in diameter versus 2

– 3.5 inches in diameter). This reduces the effective area available for gas to leak past compressor seals
, thereby reducing the potential leakage rate. In addition, rod packing leakage is generally considered slightly less at higher speeds (rpm). This combination of lower cylinder suction pressures (primarily), smaller pi ston rod diameters, and higher compressor rpm supports the lowAPI Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

5 measured vent rates from rod packing presented in the White Paper for reciprocating compressors at oil and gas production sites.

The White Paper appropriately makes a distinction between “ven ted emissions” from compressor seals, the topic of the paper, and “leak emissions” from various compressor components, which are covered under another White Paper. An exception is for the U.S. GHG Inventory discussion (see comments in Section 3.4). The Whi te Paper’s focus is primarily on emissions from rod packing vents and wet seals as it should be. It is appropriate to address o ther emissions (which may pass through vents ) from leaking

compressor components in the Equipment Leaks White Paper.

API also recommends revisions to compressor definitions. For this white paper and existing and future
EPA regulatory definitions , we suggest a more accurate definition of a reciprocating compressor:

Reciprocating compressor means a positive

- displacement machine in which the compressing and displacing element is a piston having a reciprocating motion within a cylinder. The pressure increase is achieved by reducing the volume of a fixed amount of gas.

W e also suggest a more accurate definition of a centrifu gal compressor:

Centrifugal compressor means a dynamic machine in which one or more rotating impellers, usually shrouded on the sides, accelerate the flow of natural gas. The main gas flow is radial. The pressure increase is achieved by converting kinetic energy to static energy.



## B. Process Descriptions

The information provided in this White Paper is generally a high level overview. In the interest of clarity for policy makers and the public, EPA should provide a dditional detail in the process descriptions. Additional information is available in the literature and public domain, including in documents posted on the EPA Natural Gas Star website. The White Paper should note that reciprocating compressors may also be powered by elec tric motors.



## C. Emissions Data and Emissions Estimates

In general, the studies/p apers listed in Table 3

- 1 represent the most prominent documents available on emissions and emissions factors for compressors. However, the “Emissions Data” column of Table 3

- 1

s hould have noted the difference between “studies”, which provide original or additional “emissions data”, versus “ p apers”, which just use existing emissions data for some purpose. M ost of the emissions data cited in the studies/papers listed in Table 3

- 1 o riginates from the 1996 GRI/EPA study and is not original or new emissions data. In particular, Table 3

- 1 mislabels the 2014 ICF/EDF paper as a study ; however
, this paper is not a study because most of the information is simply compiled from earlier
studie s and references, including material from the Natural Gas Star website . Also , the White Paper should have provided a more detailed assessment/critique of each of the studies/papers cited andAPI Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

6 mentioned that the papers do not necessarily present the emission s data in the same manner. If EPA did not intend to analyze the studies / papers, at a minimum
, the “emissions” from the different references should have been tabulated to facilitate compar ison.

1.1 GRI/EPA Methane Emissions from the Natural Gas Industry, Vo lume 8: Equipment Leaks (GRI/EPA, 1996a)

Though dated, this emissions study is currently the most reliable regarding reciprocating and centrifugal compressors. This is especially true for reciprocating compressors at oil and gas production sites as the
GRI /EPA study measured emissions for a significant number of compressors. While Subpart W reporting provides alternative data, to date that compressor data has not been adequately compi l ed or analyzed. Other studies have a very small number or no rod packing vent measurements. The White Paper should note that emissions and emissions factors for reciprocating and centrifugal compressors in the gas processing, transmission, and storage sectors should be supplemented and upgraded with the vast amount of informat ion being collected under Subpart W

– i.e., three years of data, that include s measurements for processing, transmission and storage sources, have been submitted to date . (See Section 3.3)

1.2 Natural Gas Industry Methane Emission Factor Improvement Study, Final Report (URS/UT, 2011)

The White Paper should note that the URS/UT study provided no measurements or emissions factors for the small reciprocating compressors located at oil and gas production sites. The White Paper does show in Table 3

- 4 that the sam ple size for reciprocating compressors at gas gathering and booster stations in the URS/UT study is very limited (15 measurements) and for gas transmission reciprocating compressors is even more limited (7 measurements of which only 2 were in operating mod e); however, the White Paper should have stated that this means those particular emission s factors are statistically invalid and serve solely as example data for comparison to other data in the literature

. In addition, the URS/UT study did not indicate whi ch measurement techniques (e.g

. , Hi Volume Sampler, Enclosed Rotary Vane Anemometer, or Hand

- held Wire Anemometer ) , were used for these particular compressor seal measurements. The URS/UT study recommended that, for future studies, protocols should be
deve loped for the anemometer techniques, which suggests that there were possible issues with those

measurements.

The White Paper correctly points out that the URS/UT centrifugal wet seal measurements are suspect and not useful due to technical complications d uring measurements , one of which was whether the correct seal oil degassing vent(s) were measured during the study due to the complexity of the seal gas degassing systems.

1.3 Greenhouse Gas Report ing Program (U.S. EPA, 2013)

In Table 3

- 5, the White Paper sho ws that the 2012 greenhouse gas emissions reporting for Subpart W Natural Gas Systems provided data for 2,149 reciprocating compressors in the gas processing sector (54% direct measurement), 2,008 reciprocating compressors in the gas transmission sector (6 0% directAPI Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

7 measurement), and 309 reciprocating compressors in the storage sector (79% direct measurement). However, the White Paper fails to explain just how significant this vast amount of data is or how EPA plans to use the data to develop emissions facto rs for reciprocating compressors based on thousands of measured data points, rather than the single or double digit measurement sample sizes of previous
studies. The expansive GHGRP data are more representative of actual industry operations than data

extra polated from a few data points in various studies; however, EPA will need to apply appropriate quality assurance and quality control (QA/QC) to this data. Going forward, EPA should rely on the GHGRP data as the primary source of measured emissions data and compare that data with previous emissions studies, such as the 1996 GRI/EPA study, and other wet seal emissions estimates from subsequent EPA Papers. EPA should use the available data (i.e., three years of data have been submitted to date, starting with 2 011 data submittals in 2012) and additional data (e.g., 2014 data to be submitted by March 31, 2015) to develop emission s factors for reciprocating compressors based on a select number of variables such as compressor operating pressures, compressor frames (piston rod size), speed, etc. These same comments apply to the vast amount of measured emissions data collected for centrifugal compressors in Table 3

- 6.

While the White Paper presents the total methane emissions for reciprocating compressors in each ind ustry sector, it fails to make any attempt to d el ve into the data to at least provide an average emissions factor for each sector (for each operating mode) that could be compared to emissions factors from other studies

– including the “compressor

- level” em ission factor used of the U.S. GHG I nventory

. For example, the data is not broken down into emissions from rod packing vents while operating, or in pressurized standby, or for emissions from blowdown vent leaks. EPA could have easily used gas composition d ata from the 1996 GRI/EPA study, or from the U.S. GHG Inventory , or some other reasonable gas composition assumption, to arrive at an average gas molecular weight and methane composition for each industry sector. This, along with the measured methane emiss ions data and number of compressors, could be used to arrive at average emissions factors for each operating mode for each industry sector reporting. For now, emissions factors per cylinder could be estimated using the 1996 GRI/EPA data on number of cylind ers per compressor for each sector. These average emissions factors would be very useful for comparison with previous studies and as data for future assessment of cost/benefit analysis for potential regulations or suggested control technologies. A better understanding of the data is also needed to more clearly identify data gaps that remain or conflicting information (e.g., comparisons between the U.S. GHG I nventory (primarily based on the original GRI/EPA study) and Subpart W reported data.

1.4 Inventory of U.S. Greenhouse Gas Emissions and S inks: 1990

– 2012 (U.S. EPA, 2014)

The White Paper should have noted that the emissions factors from the 1996 GRI/EPA study shown in
Table 3

- 8, that were used for reciprocating and centrifugal compressors emissions in the 2012 U.S. GHG Inventory, include emissions from all sources associated with the compressors; including open

- ended lines, pressure relief valves, blowdown open

- ended lines, compressors seals, and miscellaneous (cylinder valve covers and fuel valves). It i s important for common nomenclature to be used and to delineate which “emission sources” are included for various reports. For example, as discussed above, itAPI Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

8 is appropriate for this White Paper to focus on rod packing venting from reciprocating compresso rs while compressor

- related leaks (e.g., unit isolation valve leakage) are covered under the Equipment Leaks White Paper. The U.S. GHG I nventory and other documents include other compressor

- related “leaks” within the emissions estimates / emission factors and various papers may not consistently address how emissions are presented. For example, depending on the industry segment and compressor type, emission factors used for the U.S. GHG Inventory are from different studies, including the 1996 GRI/EPA Study . The emission factors are a composite of different sources (e.g., rod packing venting in operating mode, isolation valve leakage in shutdown mode) that consider the emissions source and typical annual operating time for the related operating mode. API d id not revisit these emissions factors to de

- couple the different emission sources, but the emission factors include compressor emissions covered by this White Paper (e.g., rod packing) as well as leak sources. For Subpart W reporting, potential sources s uch as isolation valve leakage (shutdown mode) and blowdown valve leakage (operating mode) are included with compressor reporting, but i t is our understanding that for these white papers leaks are intended to be addressed in the Leaks White Paper. The pap er needs to explain these complicating factors. Without explanation or a warning of potential inconsistencies , a reader may confuse the emissions factors in Table 3

- 8 as just representing emissions from rod packing venting since those emissions are previo usly discussed and are the main focus of the White Paper. Therefore, EPA should specifically state which emissions factors in Table 3

- 8 include other compressor emissions sources along with the rod packing vent emissions.

As noted above, a tabular compar ison of emissions for at least some of the cited studies / papers should have been included. For example, based on an initial review of 2011 and 2012 data for select segments, comparison of GHGRP Subpart W reported emissions and emissions from the U.S. GH G I nventory would show significant disparities for some source types and segments. While a subset of facilities (i.e., those exceeding the emissions threshold) report for Subpart W, that difference alone does not account for significant disparities. For example, centrifugal compressor emissions in the GHGRP are lower by over an order of magnitude compared to the U.S. GHG I nventory estimate. This type of comparison is necessary to identify data gaps. Additional analysis is then needed to attempt to under stand the differences, or accept that additional effort is needed to discern the differences. Without a fundamental understanding of these emission issues, it is premature to formulate conclusions or assess mitigation implications.

1.5 Development of the NSP S for Oil and Natural Gas Production (U.S. EPA, 2011b and U.S. EPA, 2012b)

The White Paper accurately presents the emissions factors and the VOC and methane emissions obtained from the 1996 GRI/EPA study that were used in the TSD for NSPS Subpart OOOO. How ever, the White Paper should have noted that the emissions factor of 25.9 scf/hr

- cylinder used for reciprocating compressors in the gathering and boosting sector is arguably too high. This factor was taken from the 2006 Clearstone Engineering study and was reported as a “blended” factor for both gathering and boosting
, and gas processing sectors. The Clearstone study did not indicate how many, if any, of the measurements were made on compressors in the gathering and boosting sector, but the inclusion ofAPI Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

9 mea surements from the gas processing sector would likely bias the emissions factor high for the gathering and boosting sector.

1.6 Characterizing Pivotal Methane Emissions from the Oil and Natural Gas Sector, (API / ANGA, 2012)

The most important takeaway from this study, as mentioned in the White Paper, is that the percentage of centrifugal compressors in all sectors of the industry that are equipped with wet seals is much lower than the 80% assumed by EPA for the U.S. GHG Inventory . The API/ANGA data suggests only 21% wet seals in U.S. service. Data from the GHG reporting for Subpart W suggests a range of 3 5

- 5 0 % . There are some differences in the first two reporting years and for different segments, but the GHGRP data consistently shows a much smaller relative population than assumed by EPA in the U.S. GHG I nventory

. In addition, the disparity in activity data alone does not account for differences between the U.S EPA GHG Inventory and Subpart W reports for centrifugal compressors . For example, EPA uses compr essor

c ount as the activity data in the U.S. GHG Inventory. Thus, Subpart W data can be normalized into a simple emission factor (i.e., total Subpart W centrifugal compressor emissions divided by total Subpart W centrifugal compressor count) and scaled us ing the U.S. GHG Inventory compressor count for comparison of “national” estimates

. For example, a n initial review of 2011 data for the transmission segment shows that Subpart W centrifugal compressor emissions scaled up to a national estimate (using the compressor count from the U.S. GHG Inventory) are 20 times lower than the U.S. GHG Inventory
estimate. At this time, the reason for this significant disparity i s not clear. As noted above, better understanding of emissions issues, and how this translat es to U.S. GHG I nventory implications, is needed to understand the relative significance of different sources.

1 .7 Economic Analysis of Methane Emission Reduction Opportunities in the U.S. Onshore Oil and Natural Gas Industries (ICF International, 2014)

In general, this paper lacks the clarity and transparency for the public to understand how many of the calculations and suggested answers were arrived at. While this paper acknowledges that emission mitigation cost and performance are highly site

- specific and variable , it nevertheless presents only estimated average values and generally does not address ranges of emission mitigation costs and performance, or parameters impacting costs and performance. The paper identifies its list of the largest emitting sources, and then introduces costs and reductions from a single mitigation approach for each. Clearly, there is more than one technology or practice available in many cases. The paper generally relies on existing information (e.g., fro m the Natu ral Gas Star program), but in some cases introduce s new projections (e.g., for activity data or equipment counts) to estimate reductions and costs

. While the paper has not been thoroughly scrutinized by API , a curs ory review provides e xamples where the

pa per makes assumptions that are incomplete and sometimes incorrect and that indicate a limited understanding of oil and gas operations or uses gross indicators (e.g., miles of pipe) to formulate activity data projections.API Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

10 Two simple examples are provide d :

 T he paper uses unit counts to estimate reciprocating engine and turbine emissions but does not appear to consider size implications on fuel use or emissions (e.g., average size for rich burn engine population is likely smaller than lean burn engines; turbines are likely larger than reciprocating engines);

 T he paper estimates that 85% of transmission compressor stations report under Subpart W, and inaccuracy is evident based on a quick review of Subpart W data available from EPA
, and a rudimentary understanding of the transmission compressor segment or U.S. GHG Inventory activity data

. In 2012, 4 6 2 transmission compressor station s reported under Subpart W, while the transmission facility count for the U

. S. GHG I nventory i s 1, 799

– or 26% reporting under Subpart W compared to 85% estimated in the ICF paper

. These limited examples raise questions about the overall efficacy of the paper and the numerous assumptions used for the emission, reduction, and cost calculations.



## D. Available C ompressor Emissions Mitigation Techniques

In general, the White Paper identifies the known effective and relevant emissions mitigation technologies. However, the paper fails to mention or describe a “Conditions

- based Rod Packing Maintenance Program” as an alternative to mandatory replacement of rod packing on a pre

- determined interval such as 26,000 hours.

4.1 Reciprocating Compressor

– Rod Packing Replacement

4.1.1 Description

The White Paper should make a distinction between “rod packing replacement” an d “rod packing maintenance.” It is not always necessary to replace all rod packing components to restore performance; therefore, the prescriptive nature of the term “replacement” can result in the wasteful discard of functioning components and equipment, a nd may preclude innovations in rod packing design or materials by manufacturers and rod packing maintenance methods by operators. For instance, suppose a rod packing manufacturer develops a better design or finds a new material that allows more effective

e missions control for years longer than conventional rod packing, but at a substantial increase in initial cost of the packing. With a mandatory time interval for rod packing “replacement”, an operator has no incentive to use the more expensive packing with improved emissions control. Nor do operators have an incentive to institute innovative rod packing maintenance programs. Therefore, the White Paper should state that any existing or future discussion of regulations regarding rod packing should use the term “maintenance” rather than “replacement.”

As mentioned in the White Paper, rod packing maintenance is inherent to industry operations. However, the White Paper fails to mention rod packing maintenance/replacement control techniques other than a
mandat ory rod packing replacement at a set time interval. A more cost

- effective technique, which someAPI Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

11 operators were previously using before Subpart OOOO or continue to use for units not subject to Subpart OOOO , is what could be described as a “Conditions

- based Rod Packing Maintenance Program.” For instance, some operators periodically measure rod packing vent rate to provide a warning of excessive rod packing leakage and repair/replace the rod packing based on vent rate increases, which can result in rod packin g maintenance within a time frame that may be earlier or longer than 26,000 hours.

An example of this approach is found in the Natural Gas STAR lessons learned document “Reducing Methane Emissions from Compressor Rod Packing System ( http://www.epa.gov/gasstar/documents/ll_rodpack.pdf ). Using this technique, rod packing gas venting is periodically monitored and the value of the incremental leaked gas (relative to post

maintenance/replacemen t leak rates) is compared to the discounted rod packing maintenance/replacement cost. When the incremental lost gas value exceeds the maintenance/replacement cost, the rod packing maintenance/replacement is cost

- effective and performed. This approach is on e way to define the condition that triggers maintenance. Another option is to set the maintenance/replacement decision based on a defined leak rate or increase in leak rate
over time . This could be based on a predetermined cost effectiveness determinatio n or historical data that shows a certain vent rate (or relative increase) is indicative of wear that warrants maintenance . One of the advantages of such a program is that as natural gas prices increase, the program acknowledges the increased value of the gas for a maintenance/replacement determination.

4.1.2 Effectiveness

The White Paper notes the use of an emissions factor of 11.5 scf/hr per cylinder for newly installed rod packing that was ob tained from EPA Natural Gas STAR presentations. We have not fo und any documentation by EPA Natural Gas STAR supporting this emissions factor; however, we also do not have a better emissions factor to suggest for a generic set of rod packing since, as mentioned above, there are many variables that can affect the poten tial leakage rate from a reciprocating compressor.

The VOC and methane emissions reductions for the gathering and boosting sector shown in Table 4

- 1 are arguably too high since they are based on an average emissions factor of 25.9 scf/hr

- cylinder based

on the 2006 Clearstone Engineering study. (See comment in Section 3.5 ).

4.1.3 Cost of Controls

The White Paper correctly explains that the Technical Support Document ( TSD ) for the Subpart OOOO proposed rule used a cost estimate of $1,620 per cylinder to r eplace rod packing ( per EPA Natural Gas STAR), applied the GRI/EPA data for number of cylinders for compressors in each sector, and assumed that rod packing was typically replaced at a 4 year interval for all sectors (per EPA Natural Gas STAR).
The White P aper makes an error in Table 4

- 2, which extracts data from Table 6

- 7 in the TSD for Subpart OOOO. The dollar amounts shown under the column “Gas Savings for Equipment Life per Compressor” are actually the dollar amounts of “Annual Cost per Compressor ($/co mpressor

- year)

– Without Savings”
from Table 6

- 7 in the TSD for Subpart OOOO.API Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

12 The White Paper failed to mention the most important information from Table 6

- 7 in the Subpart OOOO TSD, which is the VOC and methane control cost effectiveness data in $/ton. In short, the cost
effectiveness for midstream operations, including gas processing and gathering & boosting, was less than $1,000 per ton of VOC. EPA determined that this warranted includ ing a Subpart OOOO requirement to replace rod packing every 26,000 hours for processing and gathering . The cost effectiveness for the production sector, even with cost of methane saved considered, was extremely high at approximately $56,000/ton of VOC and $16,000/ton of methane and EPA co ncluded that Subpart OOOO control was not warranted for production compressors

. Downstream operations (transmission, storage) were excluded from Subpart OOOO due to VOC cost effectiveness of $2,800 per ton or higher
and minimal VOC reductions.

The White Paper reports results from the 2014 ICF/EDF cost/benefit analysis of rod packing replacement (3 years instead of every 5 years) as providing a payback of seven months ; however, the White Paper does not explain, or critique, the assumptions used b y ICF for their cost/benefit analysis. ICF uses an estimated cost for replacing rod packing of $5,000 per cylinder, which we agree is more accurate than the EPA cost of $1,620 per cylinder. However, ICF assumes an emissions factor of 57 scf/h

- cylinder,
whi ch is the emissions factor for the processing and transmission sectors in the TSD for Subpart OOOO (based on 1996 GRI/EPA data). In their analysis, ICF assumes a linear increase in methane emissions from 11.5 scf/yr

- cylinder (new) to 57 scf/yr

- cylinder (70 % increase/yr for 3 years) and a linear increase from 57 scf/hr/cylinder out to 5 years. This “failure mode” may not apply for rod packing wear and it is inappropriate to assume linear increases in vent rate unless that assumption is supported with real

w orld data.

In addition, ICF fails to clearly state whether the same 70% rate of increase is used for the final 2 years, or if a higher rate of linear increase was assumed. If 70%/year is assumed, then the final vent rate would be 165 scf/hr

- cylinder, or 660 scf/hr for a compressor with 4 cylinders. This assumption of a linear increase for three years, from 11.5 scf/yr

- cylinder to 57 scf/yr

- cylinder, followed by an unspecified percentage linear increase for two years, represents a misuse of an average emis sions factor. The 57 scf/yr

- cylinder factor is a statistical average from a large measured data set which, theoretically, should include emissions from rod packing at various years of life, from almost new to close to end of life; therefore, the average e missions factor should be applied in a cost/benefit analysis in the method used by EPA in the TSD for Subpart OOOO.

The White Paper should explain the variability and sensitivity of replacement cost analysis, given the limitations of the assumptions used by ICF. Many of the assumptions used by ICF are questionable, and
in some cases incorrect. Given the incorrect and questionable assumptions made by ICF in their rod packing replacement cost analysis, the White Paper should have pointed out these questiona ble assumptions, and that the ICF analysis is not a correct or informative analysis, especially for reciprocating compressors in the production sector.

Any future EPA discussion of rod packing replacement cost effectiveness for the oil and gas production

s ector should consider the following circumstances as mentioned on page 3

- 13 of the 2014 ICF/EDF Paper :API Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

13 (1) the remote location of these compressors, (2) that many of the compressors are leased rather than owned, and, most importantly, (3) that there is typically not a back

- up compressor for use during downtime and one or more wells must be shut

- in to replace rod packing on a compressor, if replacement is done at intervals separate from other major maintenance.

Therefore, the cost of lost production must be included in any future cost/benefit analysis for rod packing replacement for reciprocating compressors in the production sector. As discussed elsewhere in these comments, the analysis should also consider that smaller compressors and lower pressures typically resu lt in lower vent rates for units in production.

4.2 Reciprocating Compressor

– Gas Recovery

The use of a vapor recovery unit or units ( VRU ) to collect rod packing vent emissions can be very complex , especially when multiple compressors are involved

. Therefore, t he White Paper should note that any cost/benefit analysis and safety review would need to be performed by an individual operator
on a site

- specific case by case basis.

API does not have cost data for the REM Technology. However, the White Pape r should note that the REM technology not only requires a vented vapor recovery and injection system, but also requires a specialized fuel/air ratio control system for at least one compressor engine using the vented gas in order to handle the highly variab le vent rates and high Btu content of the vented gas. Applicability of this technology would also require a site

- specific analysis that would require a case by case cost/benefit analysis and safety review. Case

- specific analysis would need to consider sa fety risks and compatibility of the recovered gas with the fuel gas.

4.3 Centrifugal Compressor

– Dry Seals

This section generally compares dry seals with wet seals, but is titled “Dry Seals”. The White Paper should have clearly described that informatio n and analysis presented is associated with reductions based on a comparison between wet and dry seals. As discussed below, there is uncertainty regarding centrifugal compressor emissions, especially wet seal emissions, and discrepancies in emission estim ates will affect the analysis of emission reduction effectiveness and cost effectiveness. For example, Subpart W reporting indicates centrifugal compressor methane emissions much lower than the U .S . GHG
I nventory estimate. In fact, the emissions comparis on to the U.S. GHG I nventory from this source appears to be more disparate (on a relative basis) than any other Subpart W source.

4.3.1 Description

API generally agrees with the description of dry seals, but the White Paper should more clearly indicate that performance implications (e.g., “Dry seals reduce emissions...”) are based on comparison to wet seal systems that include vent emission from oil degassing.API Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

14 In addition, it is evident that dry seals are standard for new centrifugal units as wet seal technology has been replaced. For example, the primary manufacturer of industrial scale turbines that are frequently used in compression service uses dry seals for new turbines , and this has been t he case for a decade or longer . For affected segments, Subpart OOOO also motivates operators to install dry seal unit s , which are exempt from Subpart OOOO (while wet seal units are subject to Subpart OOOO). Introductory text in the centrifugal compressor section should have described the current status of dry seal and wet seal configurations for centrifugal compressors

.

4.3.2 Effectiveness

The effectiveness d escription is based on older data from the GRI/EPA study and some more recent
information from EPA data on centrifugal compressor emissions. Additional detail should be included on the emission reduction calculations presented in Table 4

- 3. In addition, the effectiveness section does not discuss significant disparities in emissions reported for Subpa rt W. The Subpart W data indicates a lower population of wet seal units than the U.S. GHG I nventory. For example, the U.S. GHG
I nventory estimates the wet seal units comprise 80% of the total inventory, including 73% for gas processing, 91% for transmiss ion, and 71% for storage. An initial review of Subpart W for the transmission segment indicates less than 40% of centrifugal units reported for 2011 included wet seals with a marginally higher number reported for 2012

– these levels are much lower than th e 91% prevalence estimated for this segment in the U.S. GHG I nventory.

In addition, Subpart W requires measurement of wet seal vent rates for processing, transmission and storage. Although the population of wet seal degassing vent measurements is lower th an other

compressor

- related measurements, an initial review for 2011 and 2012 reporting indicates there are

over 150 measurements of wet seal oil degassing vents in operating mode . The White Paper should
have considered these data , or at least the general implications.

The Subpart W reported data for 2011 indicates centrifugal compressor emissions that are over a factor of 20 times lower than the U.S. GHG In ventory estimate. This is due in part to a subset of sources reporting. However, the U.S. GHG I n ventory estimate uses activity data based on compressor count, and Subpart W data could be reviewed to identify the apparent unit

- level emission factor (i.e., total emissions divided by total units). A detailed analysis has not been completed but an initi al estimate from a subset of data indicates a difference of more than an order of magnitude.

Clearly, there is significant uncertainty regarding emissions from centrifugal compressors; thus there is significant uncertainty regarding the emission reductions that can be realized. The reason for the differences between the U.S. GHG I nventory and Subpart W reporting must be determined, as there appears to be a significant data gap for emissions and reductions availab le from centrifugal

compressors. Since new u nits that are installed will include dry seals, it may be reasonable to conclude
that this emissions source warrants limited attention.API Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

15 4.3.3 Cost of Controls

API is not aware of the prevalence of replacing wet seals with dry seals for existing turbines , but this does not appear to be a common practice. Similarly, cost data was not gathered, but the costs presented in Table 4

- 4 appear questionable. For example, annual O&M costs in Table 4

- 4 for wet seals

are higher than the $75,000 capital cost for replacement

. A nnual O&M costs appear to be over

estimated and capital costs appear to be under

- estimated . The ICF costs presented in the same section, but not in the table, show capital costs and O&M costs that are very different than the costs in Table 4

- 4, with ICF capital costs over 5 times higher (i.e., $400,000) and operating costs 5 times lower than the
Table 4

- 4 costs

. A cost estimate was not available, but c apital cost for replacing wet seals with dry seals is well in excess of the $75,000 cost in Table 4

- 4, and possibly in excess of the estimate from ICF. Turbine manufacturers should be contacted to confirm costs. In addition, it appears that the costs are based on three different years. Differences in reported costs are not highlighted or expl ained . The White Paper credibility is questionable if such disparities are not understood , explained, and/ or corrected. As noted above, there is uncertainty regarding emission levels (based on recent Subpart W reporting) and if emissions are over

- estimat ed, than the associated savings based on natural gas costs are also over

- estimated. If EPA continues to be interest ed in wet seal emissions, the many data gaps related to emissions and costs must be addressed prior to justifying regulatory changes

.

4.4 And 4.5 Centrifugal Compressor

– Wet s eal s with a flare or gas recovery for use

Sections 4.4 and 4.5 of the White Paper discuss capturing wet seal degassing vent emissions and either using the recovered gas or sending the gas to flare. As noted above, exi sting information from the U.S.
GHG I nventory is not consistent with emission reporting for Subpart W. Until the emissions are better understood (i.e., the differences are explained and the current best estimate is defined), estimates of
reductions in Tab les 4

- 5 and 4

- 7 cannot be trusted. The tables would appear to significantly over

estimate reductions if recent Subpart W measurements are more indicative of current operations. As an example, the White Paper emission factor in Table 3

- 8 for wet seal cent rifugal compressors is 51,370 SCF per compressor per day. For a compressor operating 30% of the time, this equates to 5.6 million annual SCF. Initial review of a subset of reporting turbines in 2011 shows 68 wet seal vent measurements from a population of over 500 centrif ugal compressors, including 186 with wet seals. Subpart W presents annual emissions, and the average vent rate for these 68 units was 560,000 SCF

– or an order of magnitude lower than the estimate based on the U.S. GHG I nventory emission factor. The basi s for this discrepancy is not clear at this point. If current emissions are more consistent with this average value from Subpart W data, then emission reductions would be over

- estimated by a factor of
10.

Until disparities in available information on em issions are addressed, presentation s of reductions or costs (that include savings from recovered gas) are inappropriate. It is essential to address data gaps on wet seal emissions before any further consideration of whether wet seal emission reductions sh ould be pursued. Since wet seal technology is not likely in new installations, there may be other data gaps that are more important to address.API Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

16 Thus, several questions posed in the White Paper regarding challenges with reducing degassing vent
emissions ar e premature because emissions first need to be understood. If mitigation is assessed at a later date, recovery and use (or flaring) of wet seal emissions should consider the case

- specific nature of the analysis, as site conditions would likely effect cost s. At some sites, a vapor recovery system may be a very complex undertaking and introduce safety risks. Factors to consider include the availability of a current vapor recovery system (and flare), site

- specific emissions and typical unit utilization, and issues, including safety, associated with system design and the end point for usage (e.g., system pressures
, compatibility with fuel gas ).



## E. Summary

No specific comments.



## F. Charge Questions

1. Please comment on the national estimates of methane emissions a nd 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.
2. Did this paper appropriately characterize the d ifferent studies and data sources that quantify vented emissions from compressors in the oil and gas sector?
3. Did this paper capture the full range of technologies available to reduce vented emissions from reciprocating compressors and wet seal centrifu gal compressors at oil and gas facilities? In particular, are there other options for reducing emissions at existing reciprocating or centrifugal compressors? For example, the EPA is aware of “low emissions packing” for reciprocating compressors but has no detailed information on this technology.
There is little mention of maintenance practices that can impact reciprocating compressor rod packing life. Lubrication has significant impact on rod packing, i.e.

- proper rate, type, pre and post lube, and lubri cation based on compressed gas composition. Routine r od packing monitoring by operations & maintenance personnel or automated monitoring techniques and systems are available. Low emission packing will likely work well in some applications, if fully evaluated and designed properly on a case

- by

- case basis.

4. Did this paper appropriately characterize the emissions reductions achievable from the emissions mitigation technologies discussed for reciprocating compressors and wet seal centrifugal compresso rs?
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?

As a whole, the control cost s cited in the report seem to be low.API Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

17 With regards to reciprocating compressor rod packing replacement , the estimated cost to replace the packing rings for a reciprocating compressor included in the White P aper is $1,620 per cylinder and it is unclear what makes u p this cost, i.e. materials, labor, etc. An estimated cost of $5,000 per cylinder , as cited in the 2014 ICF/EDF paper is likely more representative, especially if there are any packing case and rod repairs associated with the replacement. The $1,620 per c ylinder packing ring replacement cost seems to be based on 2006 dollars. It is not clear if any attempt was made to bring cost to a current year value, i.e.

– 2006 dollars escalated to 2014. Also, it is not clear whether the cost presented in the paper i s based on the compressor already being down and isolated for maintenance. If so, the cost included in the paper likely represents the incremental cost of replacing reciprocating compressor rod packing. There is no indication of whether the packing case and compressor rod required maintenance, but the cost stated for rod packing replacement does not appear to cover this.

Two options are discuss ed for reciprocating compressor rod packing vent gas recovery: REM Technology and a Vapor Recovery Unit (VRU) system. In 2012, an API member received a quote for installing a REM technology SlipStream Control System at an onshore gas plant. The January 2012 proposal was $50,000 and this did not repres ent the total project cost which would have likely been $60,000. The technology is sound when applied correctly, but , for this project, the payout on fuel savings alone was too long to the company’s economic thresholds. The cost of a VRU Gas Recovery sys tem would be significantly higher than shown in the white paper because the paper does not appear to address any of the cost s associated with controls and safeguards.

6. If there are emissions mitigation options for reciprocating and centrifugal compres sors 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.
7. Are there technical limitations that make the replacement of wet sea ls with dry seals impractical at certain existing centrifugal compressors?
8. Are there technical reasons why an operator would use a wet seal centrifugal compressor without a gas recovery system?

9. Are there technical limitations that make the installa tion of gas capture systems at certain reciprocating compressors impractical?
With regards to the REM Technology, if the compressed gas quality is substantially different than the fuel gas, it can be a concern, especially in situations where the compresse d gas is sour. In situations where the compressed gas is sour gas, there are additional safety, environmental, and equipment reliability concerns that have to be addressed and mitigated before this type of system can be utilized.

With regards to the VRU system, the very low pressure on reciprocating compressor distance pieces, typically inches of water, makes routing these emissions to a VRU infeasible unless the VRU is located in the immediate vicinity of the compressor. The required controls and safegua rds must be given serious evaluation. Specific areas of concern are: minimizing any pressure buildup in the compressor distance piece, avoiding getting air into the VRU system, alternate route for vapors/emissions when VRU goes down, and the potential cro ss contamination of compressing multiple gases. If the emissions are to be routed to a flare system, the controls and safeguardsAPI Comments on Submitted to EPA

Oil and Natural Gas Sector Compressors June 1 3 , 2014

18 required for routing the stream to a VRU would also be required. There are also concerns with backflow, overpressure, contami nation, and introduction of air during flaring events.

10. Please comment on the prevalence of the different emission mitigation options in the field.
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 appl ications that require wet seal 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?

As mentioned above, 40 CFR 98 Subpart W requires facilities in the oil and gas industry to test compressor rod packing emissions annually. The current emissions information gathered during this testin g should improve the understanding of vented emissions from these compressors.