U.S. Environmental Protection Agency 

Mail Code: C404-02 

109 T. W. Alexander Drive 

Research Triangle Park, NC 27711 

Re: GCA Comments on the Oil and Natural Gas Sector Compressors White Paper 

To Whom it May Concern: 

The Gas Compressor Association (GCA) is a trade organization for the natural gas compression industry. 

Our member companies manufacture and package natural gas compressor packages and related 

components. The products our member companies manufacture, sell and often operate are utilized 

throughout the oil and gas industry to fill the energy needs of our nation. The GCA would like to provide 

comments on four main topics in regards to the Oil and Natural Gas Sector Compressors White Paper: 

1. Proactive rod packing replacement on compressors not located at wellheads is protective 

for the environment without being excessively cost prohibitive. Predominant rod 

packing technology has resulted in lower leak rates, and newer piston rod designs 

improve expected life without the necessity for further material specification. 

Furthermore, there should be allowances for "low emission" or improved rod packings 

that would have less leakage to the atmosphere for an extended period of time. 

2. It is not cost effective to require the installation of a gas recovery system or VRU solely 

for the capture and control of rod packing emissions. Furthermore, equipment 

necessary to route compressor rod packing emissions at a field site would result in an 

increase in natural gas emissions, offsetting any improvements from said capture of the 

rod packing emissions. Additionally, cost savings from captured natural gas are not 

realized by the companies leasing and maintaining the compressors. 

3. Some of the studies involved incorporate faulty or misleading assumptions that do not 

correlate with compressors operating at remote field sites in the Oil and Natural Gas 

sector. 

4. The definition of centrifugal compressor should be referenced from preexisting 

regulations to improve clarity and consistency between rules. 
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leak rates, and newer piston rod designs improve expected life without the necessity for further material specification. Furthermore, there should be allowances for "low emission" 

or improved rod packings that would have less leakage to 

the atmosphere for an extended period of time. 

Reciprocating compressor rod packings were formally addressed under 40 CFR 60 

Subpart 0000. Certain applications were excluded from the rule, and the GCA believes that 

these exclusions are worthwhile, per our knowledge of the industry and the arguments 

presented in the supporting Technical Support Documents (TSDs) referenced in the White 

Paper. Specifically, compressors located at a wellsite or an adjacent wellsite are not affected 

facilities under the rule. Compressors located at wellsites have several characterstics that justify 

exclusion. The vast majority of leakage on a compressor rod packing is between the packing and 

the rod. Compressors located at wellsites tend to be smaller than compressors used in other 

applications, both in rod diameter and the number ofthrows (rods). As a result, there is less 

surface contact area to leak. For example, a typical 200 horsepower 3 stage compressor located 

at a wellsite would have two rods that have a diameter of 1.25 inches. A larger compressor in 

transmission service would typically have 4 or 6 rods that have a diameter of 2" or larger1, 

resulting in a leakage path that is 3 to 6 times that of the smaller compressor. Furthermore, 

wellsite compressors tend to have lower pressures in the first stage cylinder. Therefore, the 

leakage across the packing is less with the lower pressure differential. 

The white paper published by the EPA refers to newer non-metallic rod packing 

materials such as Teflon® or PTFE (Polytetrafluoroethylene). Non-metallic rings such as PTFE 

have been the dominant rod packing material for decades, and the GCA estimates that over 95% 

of rod packings in use are already made from such non-metallic materials. The design of the rod 

packings, including the arrangement and design of the rings, vary by manufacturer, and there 

are some newer designs that may have reduced emissions and extended service life, according 

to available sales literature. The technology behind these newer designs evolved, like most 

1 "Larger" as used is consistent with the EPA White Paper that references a 1,600 horsepower threshold. This 

1,600 horsepower threshold originated in the 1996 EPA/GRI study. 

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designs (both current and future) in any future rulemaking effort. 

There were some comments in the White Paper on pages 30 and 32 regarding the 

piston rods themselves and processes such as chroming or coating with tungsten carbide to 

lessen the wear on the rod. These types of coatings, though, are not common, do not 

necessarily improve packing sealing and rod life, and are only necessary in special applications. 

Newer piston rod designs and materials (without special coatings) have improved the expected 

life of piston rods, and further material specification by a regulatory agency is unwarranted. 

Rods are often removed to change the rod packing and are subsequently inspected for surface 

finish and condition during rod packing maintenance activities. Because there is a significant 

amount of labor and downtime associated with removing the rods again at a later date, they are 

changed or repaired as necessary (due to the long rod life expectancy and high variability in gas 

conditions) at that time. It would not be practical to implement a regulatory life limit, as it would 

only result in unnecessary expense with little to no benefit. 

There is very little data that the GCA could find regarding rod packing wear over the life 

of the rod packing, specifically as it relates to increases (if any) of emissions over time. The 

limited amount of data that exists has a great deal of variability in it, and much of the data was 

collected to test the performance of specific designs relative to each other in a unique 

circumstance. Great caution should be exercised to not draw erroneous conclusions based on 

limited data from an extremely small population that was not intended to cover a wide range of 

operating conditions. As mentioned above, technology does evolve, but the EPA should not 

favor one brand or type of technology to the detriment of others that may provide superior 

results in any of the various potential operating conditions that could be present in an Oil and 

Gas field application. 

Comment 2: It is not cost effective to require the installation 

of a gas recovery system or VRU solely for the capture and 

control of rod packing emissions. Furthermore, equipment 

necessary to route compressor rod packing emissions at a 

field site would result in an increase in natural gas emissions, 

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The EPA mentions two methods of emissions reduction for reciprocating compressors. 

The first is the REM Technology, Inc, SlipStream® system, which is a highly specialized 

application, very costly, and not widely used in the Oil and Natural Gas compression industry. 

There are some challenges associated with the system, such as the safety hazard of mixing air and 

fuel in the air inlet system for which it was not designed and engine stability due to the varying 

BTU of the additional fuel source. In order to ensure proper engine operation, a highly 

sophisticated engine control system would also be required to account for the variability of the 

fuel sources. This additional equipment creates the need for an additional expense. The REM 

system will also be difficult to apply to smaller horsepower packages due to the limited physical 

space available on the package. A vast number of valves, flow meters, and filters are required for 

operation. It should be noted that the application of the REM system was subsidized by a $2.4 

Million dollar grant, and the economics included credits for reduction in greenhouse gasses in 

Alberta, Canada. Furthermore, all of the installations were done on 600 to 1000 horsepower 

engines. These economics are not representative of the oil and gas industry in the United States, 

and the limited horsepower range and engine types does not prove viability of this product for 

widespread use. 

The second system mentioned is a Vapor Recovery Unit (VRU). The use ofVRU 

systems to capture rod packing emissions is not common either and would rarely if ever be 

considered cost effective. The biggest challenge is that most of the VRU systems are electric 

driven, and the majority of the sources are remote with no access to the power grid. There is an 

option for a natural gas driven VRU, but this will negate any gains in emissions reductions by the 

system. If a VRU is akeady on a site, the packing vents could be piped in. However, most of the 

VRUs are located near storage tanks which are traditionally placed a significant distance away 

from gas compressors. It is very possible that existing systems would be undersized to overcome 

the losses due to this extra piping, thus requiring an additional pneumatic device to push the 

captured rod packing emissions through the closed vent system. 

In a situation where contract compression service companies or rental companies are 

providing the compressor packages (both of which are represented by the GCA membership), 

most of the cost of these systems are born by our member companies, not the producers. 

However, it is the producers who benefit from the capture of said natural gas. Thus, the assumed 

additional revenue from capturing these leaks cannot be broadly applied in determining the cost 

effectiveness of various control options. 

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The GRIIEPA study from 1996 that is referenced in Table 3-2 of the Compressor White 

Paper bases its assumptions of emissions from the natural gas production segment on the idea that 

there are 4 seals per compressor. As the study references leak rates per seal, this number is very 

important in determining the emissions from the natural gas production segment and the 

compressors therein. However, based on the information of the member companies in the GCA 

and the respective equipment they operate in the field, this number of seals per compressor 

significantly overestimates the emissions from this industry segment. A majority of the 

compressors in the natural gas production segment are less than 500 HP, where nearly all 

(99.95%) of compressors will have two seals, not four. Even with larger compressors, a number 

of these are also equipped with two seals (or throws), not four. Our member companies estimate 

that the average number of seals per compressor across their fleets operating in the natural gas 

production segment is actually 2.6. This fact would thus reduce the estimated emissions from this 

industry segment by about 35%. For compressors< 500 HP, the reduction would be roughly 

50%. These facts therefore support the assertion that this industry segment should remain 

excluded from further regulation, as discussed above and in the TSDs published for 40 CFR 60 

Subpart 0000. 

The emission levels reported in the 2014 GHG Inventory are reportedly based on the 

1996 GRIIEPA study, but the numbers don't align. The 2014 GHG Inventory reports that 

average emissions from small compressors are 286.59 scfd/compressor and 16,269.75 

scfd/compressor for large compressors (Table A-125, Annex 3). However, the GRIIEPA study 

reports that emissions from small production compressors are 12.09- 267.57 scfd/compressor and 

15,195.07 scfd/compressor for large compressors (Tables 5-2 and 5-3), while processing segment 

compressors are 11,203.29 scfd/compressor (Table 5-5). These 2014 GHG Inventory and 

GRIIEPA numbers appear to include emissions from all compressor emissions (i.e., blowdowns, 

equipment leaks, miscellaneous, and compressor seals), so it is misleading and should be 

evaluated properly when determining the cost effectiveness of regulation on compressor seals. 

Rod packing replacement for compressor seal leaks will not impact the majority of compressor 

emissions, as compressor seal leaks typically comprise less than 25% of the total emissions from 

a compressor, according to the 1996 GRIIEPA study. 

In section 4.2.1, the White Paper references REM Technology and average fuel gas 

savings from installation of a "gas recovery system". However, the Fact Sheet referenced 

discusses Air/Fuel Ratio Controls, not a gas recovery system used to capture compressor seal 

leaks. Furthermore, the fuel gas savings referenced are from improved operation of the engine 

and have no correlation to the compressor or the effectiveness of the compressor rod packings. 

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remote areas that are typically much smaller and operating under lower pressures. Thus, the fuel 

gas savings potentially associated with the installation of this AFRC do not apply in a discussion 

about compressor rod packing controls. 

Comment 4: The definition of centrifugal compressor should 

be referenced from preexisting regulations to improve 

clarity and consistency between rules. 

In the White Paper, the EPA defmes a centrifugal compressor as "Any machine for 

raising the pressure of a natural gas by drawing in low pressure natural gas and discharging 

significantly higher pressure natural gas by means of mechanical rotating vanes or impellers". 

This definition is broad and could inadvertently include compressors that do not operate the same 

as typically regulated centrifugal compressors. When evaluating centrifugal compressors, it is 

important that EPA maintain a consistent definition of the applicable source. Therefore, the GCA 

instead would suggest referencing the existing definition of centrifugal compressor in NSPS 

0000, to avoid unnecessary ambiguity. That definition reads, "Any machine for raising the 

pressure of a natural gas by drawing in low pressure natural gas and discharging significantly 

higher pressure natural gas by means of mechanical rotating vanes or impellers. Screw, sliding 

vane, and liquid ring compressors are not centrifugal compressors." 

Summary 

The GCA wishes to thank the EPA for the opportunity to make the preceding comments and for its 

thoughtful consideration of the same. If you have any questions regarding this submittal please contact the 

GCA via our management company (NACM) at 972-518-0019 or Erin Badough, Environmental 

Committee Chairman, at 281-836-7514. 

Sincerely, 

~(_ 

____ _____ 

Erin Badough, PE 

Environmental Committee Chairman, Gas Compressor Association 

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