Attachment U

Compressors

Gary Reeves

Pioneer Natural Resources
6.0 CHARGE QUESTIONS FOR REVIEWERS 

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. 

• The methodologies used for measuring the emissions are the same as are generally used in the industry 

for measuring this type of emissions. I am not sure how representative the sample is. Where both low 

speed and high speed compressors sampled? Was the sample representative of different manufacturers 

and sizes of compressors?

• Did the sample capture data for compressors of various ages? The condition of the packing and other 

components has an effect on the ability of the packing to seal. Newer compressor rods are normally 

manufactured with a hardened surface.

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

from compressors in the oil and gas sector?

• Yes

• Did they investigate why the rates for production compressors are so much lower that all the rest?

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.

• Low emission packing is available from multiple manufacturers and has been utilized for several years 

now. I know of at least one field test that was performed and I am sure the manufacturer will be glad to 

share the data.

• As the emphasis on reducing compressor seal emissions increases new technology will be developed. 

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

technologies discussed for reciprocating compressors and wet seal centrifugal compressors?

• Yes

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? 

• The wet seal to dry seal conversion for centrifugal compressors was just the price difference between the 

two if you bought a new machine. The cost of conversion would be higher when you take into account 

the cost of modifying the case and installing a seal gas system.

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. 

• None that I am aware of but I am sure that as the need arises they will be developed.

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

existing centrifugal compressors? 
• Yes, there is more to it than just pulling out wet seals and installing dry seals. The compressor case has to 

be machined/modified to accommodate the dry seals. This may not be possible for some models of 

compressor cases.

• Possible changes to rotor dynamics which could cause issues. Wet seals tend to act as a dampener.

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

recovery system? 

• None that I am aware of.

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

compressors impractical?

• If you are capturing the gas for engine fuel, compressing high BTU rich gas and using pipeline quality gas 

for fuel there could issues that the blended gas is too rich for some engines to operate properly.

• Premixing fuel into the inlet air could possible cause issues with a dry low NOx engine emission control 

system.

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

• At the present time the only systems that I have seen are where they were required to meet VOC 

permitting requirements

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?

• Not that I am aware of.

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? 

• Not that I am aware of.