June 13, 2014 

Roberto Morales 

US Environmental Protection Agency 

Office of Air Quality Planning and Standards 

Mail Code: C404-02 

109 T.W. Alexander Drive 

Research Triangle Park, NC 27711 

Re: Williams Response and Comments to 

Methane I VOC Emissions and Mitigation Techniques in 

Report for Oil and Natural Gas Sector Compressors, Review Panel, April 2014 

U.S EPA Office of Air Quality Planning and Standards (OAQPS) 

Dear Mr. Morales: 

The Williams Companies (Williams) is submitting this correspondence to the U.S. Environmental 

Protection Agency (EPA) regarding methane and volatile organic compound emissions and mitigation 

techniques for compressors in EPA's, Report for Oil and Natural Gas Sector Compressors/ Review Panel/ 

April2014. 

In April, 2014, EPA solicited technical comments and additional information from reviewers on five 

white papers covering methane and volatile organic compounds (VOCs) emissions from compressors, 

hydraulically-fractured wells, leaks, liquids unloading, and pneumatic devices. Williams' response for 

compressors is presented in this letter; a separate letter has been submitted to EPA for pneumatic 

devices. 

Williams reports greenhouse gas (GHG) emissions for 60 natural gas transmission, 48 gathering, 16 

natural gas processing, 1 petrochemical, and 2 underground storage facilities across the United States. 

These, and other smaller Williams' facilities that are currently below reporting thresholds, could be 

.impacted by future EPA rulemaking on methane and VOC reductions. Williams has demonstrated, and 

continues to demonstrate, its commitment and cooperation toward reducing greenhouse gas (GHG) 

emissions by identifying and prioritizing GHG sources, implementing GHG monitoring programs, and 

working with industry groups such as Interstate Natural Gas Association of America (INGAA), Gas 

Processors Association, and the American Petroleum Institute (API). Williams recognizes the 

importance of this issue and shares EPA and the Administration's intention to reduce these emissions. In 

order for that effort to achieve our mutual objectives, a strong, science-based approach must be applied 

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presented in Section I below. Additional comments from Williams

 experts regarding the content of the 

EPA report are presented in Section II. 

I. WILLIAMS RESPONSE TO EPA CHARGE QUESTIONS 

Question 1: 

Please comment on the national estimates of 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. 

Answer: 

Reciprocating and Centrifugal Compressors 

Williams believes the various national estimates of methane emission factors for compressors are 

improving with time as reporters and researchers gain more experience in data collection, 

instrumentation, and monitoring. 

Williams encourages EPA and others to incorporate actual wet seal measurements, rod packing 

measurements, blowdown vent measurements, and operation-mode hours into emission factors for 

reciprocating and centrifugal compressors. This data is being collected on an annual basis by owneroperators and is reported in EPA's annual Greenhouse Gas Reporting Program (GHGRP}. 

Question 2: 

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

emissions from compressors in the oil and gas sector? 

Answer: 

Reciprocating and Centrifugal Compressors 

Based on Williams review, it appears that EPA has accurately summarized methane emission factors 

from the referenced previous studies. It would be helpful if EPA would provide a summary table of 

emission factors from the studies, expressed in common units, so that readers could compare results. 

Question 3: 

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

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

are there other options for reducing emissions at existing reciprocating or centrifugal compressors? For 

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At this time, Williams is not aware of emissions-reducing technologies for reciprocating compressors 

other than the ones cited by EPA in the white paper. With respect to the low emissions packing systems 

referred to by EPA in its question, this technology has been in existence for some time and information 

is available from numerous low emissions packing system manufacturers. Low emissions packing (LEP) 

systems employ advanced materials of construction, un-segmented rings, tighter tolerances and 

smoother packing cup surfaces in an effort to achieve lower methane and VOC emissions. Williams has 

conducted limited testing on LEP systems with mixed results. 

The primary disadvantage of LEP systems is they can only be installed when the piston rod is removed 

from the compressor. Rod removal is infrequent, generally occurring during major compressor 

overhauls. For this reason, worn rod-packing rings would likely be replaced with conventional rod 

packing rings and not LEP systems during most rod-packing change-outs. When major compressor 

overhauls are performed, use of LEP systems could be evaluated. 

Centrifugal Compressors 

At this time, Williams is not aware of emissions-reducing technologies for wet seal centrifugal 

compressors other than the ones cited by EPA. 

Question 4: 

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

mitigation technologies discussed for reduction of vented emissions from reciprocating compressors and 

wet seal compressors? 

Answer: 

Centrifugal Compressors and Reciprocating Compressors 

Williams believes that EPA's estimated emissions from centrifugal and reciprocating compressors are 

too high. If we are correct, achievable emissions reductions, and their associated cost savings, are 

overestimated. 

Also, in Table 4-4 under Transmission I Storage, annual natural gas savings is reported by EPA as "zero". 

For purposes of the evaluation, cost savings should not be dependent on who owns the gas. If so, 

"zero" natural gas savings could be purported at some processing plants where the gas is owned by the 

producer and the processor charges the producer a processing fee. 

Question 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 compressors? 

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Rod Packing Replacement Cost 

Based on Williams' experience, cost estimates by Natural Gas STAR, the TSD for Subpart 0000 

Rulemaking, and ICF International to replace rod packing systems in reciprocating compressors is 

underestimated. In Section 4.1.3, EPA cited a cost of $1,620 per cylinder according to a Natural Gas 

STAR Lessons Learned document published in 2006. Based on this cost, ICF International estimated a 

replacement cost of $4,050 and $5,346 per compressor for Processing and Transmission, respectively. 

For good packing with low leak rates, the current cost for Williams is approximately $2,300 I cylinder for 

materials and $500 I cylinder for labor. Most compressors have at least four cylinders, so the estimated 

cost is approximately $11,200 (or more) per compressor. This cost excludes the cost of the blow-down 

gas and start-up purge gas associated with the rod packing replacement. 

Piping to a Vapor Recovery Unit 

The cost of $2,000 given in Section 4.2.3 for planning and installing additional piping from a 

reciprocating compressor to an existing vapor recovery unit (VRU) is underestimated. Depending on the 

proximity of the compressor to the VRU, Williams estimates that the cost of design and drawings, 

materials, labor, and required weld x-rays, would be at least $7,500 for an ({average installation". 

Centrifugal Compressors 

Section 4.3: Dry Seals 

The differential capital cost between dry gas and wet seal configurations on new compressors appears 

to be reasonable. The capital cost for replacing wet seals with dry seals also appears reasonable. The 

actual replacement cost will vary greatly with compressor model. 

Operating cost savings are questionable as the differential gas leakage rates presented in Table 4-3 do 

not align well with Williams' experience. Williams' wet seal compressors typically are configured with 

gas recovery to process suction, and observed leakage rates for this configuration are generally lower 

than reported in this paper. A second analysis by EPA to evaluate conversion from wet seal with gas 

recovery to dry seal is warranted. 

Also, in Table 4-4 the value of natural gas savings should not be reported as$ 0 for transmission/storage 

applications just because the operator does not own the gas. The worth of the gas should be reflected in 

the table. 

Section 4.4: Wet Seals to Flare 

As noted previously, the described configuration with no gas recovery to process suction is highly 

unusual in Williams' experience. Therefore, it is not possible to comment on leakage rate reductions. 

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p

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efficacy, cost and feasibility for both new and existing compressors. 

Answer: 

Reciprocating Compressors 

Monitoring Program for Rod Packing Replacement 

Any future EPA regulations on rod packing replacement for existing reciprocating compressors (i.e. 

installed before the Quad 0 effective date of February 15, 2012) should be based on a monitoring 

program, and not on a mandatory periodic replacement schedule. Williams employs a dynamic 

compressor cylinder analysis on a quarterly schedule to analyze performance which identifies rod 

packing leakage. 

The following operations, monitoring, and maintenance-related practices are suggested by Williams as 

effective emissions mitigation options for reciprocating compressors. 

Lubrication of Packing I Packing Material 

Proper selection of the lubricant oil, and routine monitoring of the lubrication rate will help mitigate 

methane and VOC emissions in the rod packing case. Proper lubrication is required to effect a good seal 

between the packing material and piston rod. Good lubrication also prevents overheating of the piston 

rod and associated (premature) wear of the rod packing material. Lube rate monitoring is done 

proactively by Williams using electronic equipment. 

Piston Rod Coatings 

EPA notes in Section 4.1.2 that "Compressor rods can also be coated with chrome or tungsten carbide to 

reduce wear and extend the life of the piston rod." Williams does not support the use of rod coatings 

because the coatings prevent the detection of cracks in the piston rod which is critical to ensuring safe 

operation of the compressor. 

Piston Rod Smoothness 

Monitoring of piston rod smoothness is an effective mitigation measure against methane emissions. If 

the rod is too smooth, the lubricant does not stick to the rod; if the rod is too rough, the packing wears 

out. Inspection and testing of the rod smoothness (RA) can be conducted during major maintenance 

events when the rod is removed. 

Compressor Block Valve Packing Replacement 

Annual monitoring and replacement of compressor blowdown and isolation block valve packing glands 

{when warranted) is an effective emissions methane mitigation measure. At facilities subject to Subpart 

W of the federal Greenhouse Gas Reporting Rule, emissions from compressor blowdown vents are 

monitored annually during the equipment leak and compressor monitoring survey. 

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certain existing centrifugal compressors. 

Answer: 

Yes; dry gas seal replacement is not offered on some older models of centrifugal compressors due to 

technical limitations. 

Question 8: 

Are there technical reasons why an operator would use a wet seal centrifugal compressor without a gas 

recovery system? 

Answer: 

Williams is not aware of any technical reasons why it would not be possible to use a gas recovery system 

on a wet seal compressor. 

Question 9: 

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

compressors impractical? 

Answer: 

No. However, the cost of installing a vapor recovery unit (or flare) where one does not exist (e.g. at a 

compressor station) is a control cost that should be evaluated by EPA as part of its analysis when 

evaluating the range of options for cost-effectively reducing methane emissions. The installation of 

VRUs or flares at smaller compressor stations may be cost prohibitive at smaller facilities. 

Question 10: 

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

Answer: 

Reciprocating Compressors 

Replacement of rod packing and replacement of blowdown vent valve packing are prevalent in the field 

and are viable, realistic options for reducing methane emissions from reciprocating compressors. Vapor 

recovery of reciprocating compressor emissions is prevalent where there are VRUs or flares. Most older 

compressor stations do not have VRUs, thermal oxidizers or flares; their installation is more prevalent at 

newer compressor stations. Vapor recovery and flaring (combustion) of rod packing emissions, 

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Question 11: 

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

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

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

Answer: 

No. Williams no longer installs wet seal centrifugal compressors. 

II. ADDITIONAL WILLIAMS COMMENTS 

Williams offers the following additional comments for EPA's consideration regarding the technical 

content of the compressor white paper. Williams' intent is to provide useful information that will: {1) 

help EPA's understanding of compressor operations; and {2) allow EPA to more fully evaluate the range 

of options for cost-effectively cutting methane emissions. 

Reciprocating Compressors 

1. Page 3, Third Paragraph 

Suggest the following revision (in italics) when defining a reciprocating compressor: 

A piece of equipment that increases the pressure of a process gas by positive 

displacement, converting rotational motion of the crankshaft to linear motion of 

one or more cylinder pistons. 

2. Page 4, 1st Paragraph under Section 2.1 

Recommend the following addition when describing the operation of a reciprocating compressors 

(in italics): 

In a reciprocating compressor, natural gas enters the suction manifold, and then flows into a 

compression cylinder where it is compressed by a piston driven in a reciprocating motion by the 

crankshaft powered by an internal combustion engine or electric motor. 

3. Page 4, Last Paragraph 

Suggest the following modification (in italics) with respect to rod packing leakage: 

Over the operating life of the compressor, the rings become worn and the packing will begin to 

wear resulting in higher leak rates. Emissions from packing systems originate from one 

component/ the packing case. Leaks may occur between the packing case and nose gasket/ and from the seal rings and packing cups inside the packing case. Typically/ gases leaked from the 

packing case are vented or flared. 

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Williams is not familiar with the fuel saver system referenced by EPA (below in italics) that would 

result in an idle, partially pressurized compressor. 

Different emission rates were calculated for the different operating modes of the compressor 

(GRI/EPA, 1996bL and were as follows; 

• Operating and pressurized; 

• Idle and fully pressurized; 

• Idle and partially pressurized using a fuel saver system (reciprocating compressors only); 

• Idle and depressurized. 

6. Page 31, First Paragraph 

In the last sentence, EPA assumed 11.5 cubic feet per hour per cylinder for newly installed rod 

packing for cost development purposes. Williams believes this is high. According to Ariel, a 

manufacturer of rod packing, leak rates for new rod packing range between 6 and 12 scfm. 

Centrifugal Compressors 

1. General Comment #1 

It seems that the white paper only considers field measurements for dry gas seal vent flows and not 

design values from the seal vendors. Future consideration of design values would be useful. 

2. General Comment #2 

Data were not presented in consistent units throughout the report; reporting units were different in 

virtually every table. 

3. General Comment #3 

It may be useful to normalize methane emissions data by compressor capacity and evaluate the 

results. Centrifugal compressors are often larger than reciprocating compressors. Failing to 

normalize the data by equipment capacity ignores the effect of larger natural gas volumes handled 

by larger compressors. 

4. General Comment #4 

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Williams' fleet. This makes a great difference in leakage rate. 

6. Page 7, Figure 2-3 

This depiction of a dry seal is significantly different than the typical configuration on Williams' fleet 

of centrifugal compressors (mostly Solar and Dresser Rand}. Figure 1.C-8 (shown below} from API 

617 is more representative. The important difference is that natural gas is expected only from the 

"Primary seal gas leakage" path, and not the "Secondary seal gas leakage" path. The "Separation 

gas" is usually air (sometimes nitrogen} and this leaks from the secondary vent. The natural gas on 

the inboard side of the secondary seal is at atmospheric pressure, so flow of natural gas across this 

seal is extremely low. 

Process Side 

7. Page 14, Third Bullet: 

Primary seal gas suppty 

Inner 

Ia by 

Primary seal gas leak.age 

Secondary seal gas leakage 

Primary sea! Secondary 

back~up 

seal 

Separahon seal 

1.C-8-Tandem Gas Seal 

Bearing Side 

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8. Page 36, Third Bullet: 

Power consumption for wet seal pumps varies with compressor size, but the SO -100 kW cited by 

EPA in the white paper seems unusually large. For reference, a 20 hp (1S kW) pump is adequate for 

typical Solar Turbine compressors in the S,OOO- 10,000 hp size. 

Williams believes that EPA's consideration of the above response and comments, and input from others 

in the natural gas industry, will help the Agency better understand options for cost-effectively reducing 

methane emissions. We believe that some data gaps still remain, and that filling these gaps with 

additional measurement data is necessary before EPA develops best practices, voluntary actions, and I 

or regulations regarding methane reductions. 

Williams appreciates the opportunity to provide comments regarding EPA's Report for Oil and Natural 

Gas Sector Compressors/ Review Panel/ April2014. Should you have questions regarding these 

comments, please contact me at (713) 21S-2134 or at glen.jasek@williams.com. 

Sincerely, 

Glen Jasel 

The Williams Companies, Inc. 

Director of Environmental Services 

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