Attachment S

Compressors 

John Cordaway Transcanada 

Corporation
Response to Oil and Gas Sector 

Compressor White Paper John Cordaway

6.0 CHARGE QUESTIONS FOR REVIEWERS

These responses are provided with a practical or operational point of view. Many 

well positioned groups and technical data providers will be responding to the 

charge questions. Some questions will not be fully commented given the 

questions are better addressed by those with a more qualified background in data 

compilation, assessment of study results, etc. 

It seems the quantification of compressor leaks is the end game or focus of the

EPA paper. Assuming that is the case, the following summary is offered as 

background to the response of the various charge questions. 

First and foremost, the GHGRP (Greenhouse Gas Reporting Program) was 

intended to provide an extensive overview or insight into the fugitive emission 

picture of several sectors within the oil and gas industry. It is highly 

recommended that EPA allow the process to work and begin the data mining 

process. The data mining process should include a partnership with industry 

sector professionals, advisors and industry trade groups to develop effective 

regulation. This would both enrich any subsequent requirements and serve to 

build agreement between operators and regulators.

This partnership would be a key step and will be the mechanism to effectively and 

correctly evaluate the best means to manage GHG’s from the oil and gas sector. 

The papers mentioned, and to some degree summarized by the EPA paper, 

provide information of areas to target emission reduction but those papers have 

not provided full background into explaining reasons for the differences in the 

reported fugitive measurements in the study papers. This context is critical for 

effective decisions. It is through partnership with industry that will allow the time 

to fully characterize and substantiate a cooperative go-forward direction to 

reduce GHG emissions. 

The partnership discussions will allow the ‘operational realities’ to be discussed 

and adequately considered. The time allowed in this comment period limited the 

opportunity to investigate and document the ‘operational realities’ but the 

partnership discussions could allow for this documentation to occur. Some 

‘operational realities’ are mentioned in the individual charge question responses. 

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Response to Oil and Gas Sector 

Compressor White Paper John Cordaway

It is also observed that many companies are already improving their GHG 

emission footprint due to the GHGRP. For example, operating companies have a 

desire to operate safely. If an emission source is identified and determined a 

safety concern, they will be addressed. When it comes to reciprocating 

compressor packing, operating companies routinely perform reciprocating 

compressor packing replacement. It is in the best interest of the operating 

companies to install the best packing so that the activity is not prematurely 

repeated! It is also critical to note that all companies actively manage their GHG 

emission footprint as emissions released directly relate to a loss of product to be 

marketed. Methane is NOT considered a waste product by industry. 

Lastly, a few operational realities that should be discussed and understood in the 

joint EPA/Industry discussions: 

• Understand the total impact of ‘simple’ actions like modifying vents. 

• Understand the degree of ‘typical’ compressor designs before making broad 

assertions of prevalence.

• Understand unintended repercussions of installing and operating mitigation 

actions. 

• A prime example, and need to conduct joint discussions, is to understand 

the impact of wet seals.

o What is the real prevalence of wet seals in the industry? 

o What were the wet seal reading sample sizes in the various studies 

and the characterization of all wet seals from the very limited sample 

size?

o Further, the wet seal vents are typically sized by the manufacturer to 

be 1 or 1 1⁄2 “ inches in diameter. It is understood large volumes of 

gas can be emitted but if the manufacture sizes a vent line that small, 

the likelihood of wet seals being a high emitter is low. 

The intended point here is to emphasize the need to truly understand the data 

prior to correctly characterize the results from the many studies. 

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

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

activity data and the methodologies used for calculating emission factors presented in 

this paper.

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Response to Oil and Gas Sector 

Compressor White Paper John Cordaway

Response to Question 1. 

I have limited knowledge in this area and therefore will not provide a 

response. 

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

quantify vented emissions from compressors in the oil and gas sector? 

Response to Question 2. 

The paper did provide a reasonable list of the key industry studies and the 

results. What would have been beneficial is a characterization of the study

results from the view of the EPA. What is needed is to characterize or 

explain the reason for key differences in the results of each paper. For 

example, the time span of the different studies can affect the ‘apparent’ 

results. The type of material of construction or component design changes

may have changed from one study to the next and therefore could be the 

source for the varying readings. The key differences in the studies must be 

understood before comparing the results to other studies. When comparing 

studies, there are countless data quality considerations that if not 

addressed, will provide a mischaracterization. For example, sample size, 

component construction or type, etc. 

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

from reciprocating compressors and wet seal centrifugal compressors at oil and gas 

facilities? In particular, are there other options for reducing emissions at existing

reciprocating or centrifugal compressors? For example, the EPA is aware of “low emissions 

packing” for reciprocating compressors but has no detailed information on this technology.

 

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Response to Oil and Gas Sector 

Compressor White Paper John Cordaway

Response to Question 3. 

Companies are incentivized to reduce fugitive emissions and many have 

conducted various internal or operational studies on, for example, Low 

Emissions Packing. (LEP) LEP is an area of promise that has seen some very 

positive results in reducing fugitive emissions. The operational reality is LEP 

may not be promising in all sectors or situations. Operational realities may 

call for different packing to operate in different gas quality environments. For 

example, some gas streams have a bit more dirt or entrained liquids that 

must be addressed with different types of packing. As companies further 

review and understand the GHGRP results, operators will more fully 

understand and the improvements needed to support the LEP operation, 

machining of the packing cups, maintaining proper packing clearances, and 

understanding compressor rod qualities leading to extending reciprocating 

packing operational life. 

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

the emissions mitigation technologies discussed for reciprocating compressors and 

wet seal centrifugal compressors?

Response to Question 4. 

Overall, the paper does not appropriately characterize the reductions. 

The results are snap shots of various studies performed for various 

reasons and various goals. The take away should be that the papers are 

directing the focus of additional detailed study. For example, some 

companies understand how to properly repair and/or install 

reciprocating compressor packing. If studies were conducted with a goal 

to determine the best reciprocating packing solution, a different result 

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Response to Oil and Gas Sector 

Compressor White Paper John Cordaway

would likely occur when compared to the reductions characterized in the 

paper. 

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?

Response to Question 5. 

The operating costs referenced in the paper are an order of magnitude low. 

In today’s operational environment, the cost to modify an existing facilities 

design is quite high. Additional cost considerations include: 

Something as ‘simple’ as conducting a design review requires a large 

amount of manpower. Securing a company design engineer to review 

existing drawings to verify equipment, site visits are required, as-built 

drawings from a draftsman, procurement of pipe, valves and fittings, etc. 

are all additional cost considerations for many ‘simple’ vent modifications. 

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

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

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

compressors.

Response to Question 6. 

I am not aware of other mitigation options. 

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

seals impractical at certain existing centrifugal compressors?

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Response to Oil and Gas Sector 

Compressor White Paper John Cordaway

Response to Question 7. 

Yes. Given the technical limitation is the focus of the question and 

therefore cost will not be mentioned, the lead drivers are likely 

availability of very clean gas or electrical power. For example, some 

installations are limited by availability of power to drive an air 

compressor for the dry seals. In other situations, the gas quality 

(presence of micro solids or entrained liquids) can be low enough that 

filtration cannot be relied on to provide 100% clean gas to the dry 

seal. A seal failure is very costly and never timely. Theoretically, one 

could say that if enough money was spent on the filtration, the proper 

quality can be achieved but such is not known and therefore this 

statement would not be a reasonable response. The risk to shutting 

in production and suffering contractual implications is also a resulting 

impact that is an operational reality. Even with dual filtration 

systems, an operator will be challenged to determine the risk of 

shutting a unit down and stopping production. In remote or offshore 

applications, this would be extremely difficult to address. 

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

compressor without a gas recovery system?

Response to Question 8.

Potentially, yes. 

1. There must be a lower pressure source for the wet seal gas to be 

routed and used. 

2. If the lower pressure gas source can potentially introduce a higher 

pressure on the wet seal vent, the seal may no operate properly. Today, 

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Response to Oil and Gas Sector 

Compressor White Paper John Cordaway

Operators can be resistant to deal with that type of issue. Technically, the 

issue can probably be resolved but will require quite a few dollars to 

address. 

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

certain reciprocating compressors impractical?

Response to Question 9.

Yes. Some limitations include:

• A fuel burning source of lower pressure gas must be available. 

• As the gas is captured, time must be available for the amount of 

trapped gas to ‘bleed’ into the lower pressure fuel source. Time is not 

always available. Example: Many facility safety requirements state a 

facility must provide pressure relief within a certain time frame. 

• Gas capture ‘venturi tubes’ may not be technically limiting but could 

have a high operation cost due to the loss of the driving gas. 

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

Response to Question 10. 

Many companies employ or utilize Low Emissions Packing. Since LEP is 

considered an emission mitigation option, it is suggested that operators 

implement this option, but in varying degrees. Personal knowledge has observed

the success of LEP but this technology should be further and properly documented

for broader understanding. 

Additionally, many companies already have unit blow down recovery systems. 

Effectiveness of the blow down systems can be influenced by the daily operation 

of the unit, other equipment on site and other issues. Quantification of the 

recovered gas can at times be challenging given wide variance of operation. 

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Response to Oil and Gas Sector 

Compressor White Paper John Cordaway

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? 

Response to Question 11. 

It is not known if a general industry philosophy exists where wet seals are 

replaced by dry seals. Given the extreme high cost of the dry seals and the 

potential to require other facility modifications to support the dry seals, it is 

unlikely any operator much less a general philosophy exists to replace the 

wet seals. If an existing engine/compressor unit is equipped with wet seals 

and is overhauled, the general philosophy is to return the unit with the wet 

seals. As previously stated, there may be times operation conditions suggest 

a need to keep wet seals in service. If a new unit is purchased and installed, 

dry seals are likely the choice. 

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?

Response to Question 12. 

Efforts to data mine the GHGRP information are underway by the various oil and 

gas trade groups who are better suited to respond to this question. 

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