Attachment Q

Compressors

David Allen

University of Texas at Austin
Comments on

Oil and Natural Gas Sector Compressors

Draft dated April, 2014

Submitted to:

Carrie Richardson Fry

Research Triangle Institute

Submitted by:

David Allen

June 16, 2014

Overview

I have reviewed the draft white paper titled “Oil and Natural Gas Sector Compressors” prepared 

by the U.S. EPA Office of Air Quality Planning and Standards (OAQPS), dated April 2014. My 

responses to charge questions are summarized in the following pages. I have only commented in 

areas of expertise. Since the white paper focuses on compressor seals, and my expertise in the 

area of compressor seals is limited, my comments on this white paper are limited, particularly 

compared to my comments on other white papers released in parallel with white paper on

compressor seals. 
Responses to charge questions

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. 

Response: In the white paper, a variety of emission factor unit systems are used. While these 

may reflect the diversity of units used in the studies that are cited, some attempt at intercomparison would be useful. For example, the emissions factor for wet seal centrifugal 

transmission compressors reported in Table 3-8 (50,222 scf/day/compressor) could be compared 

to the emissions reported in Table 3-4 (8,137 Mscf/yr/compressor). This comparison would be a 

relatively straightforward conversion of units. For other emission factors where, for example, 

rod packing emissions are in some cases reported by cylinder and in other cases by compressor, 

the comparison is far more confusing and it is not clear how the data were interpreted. 

For activity factors, it is not clear why some data were not used. For example, in a companion 

white paper titled “Oil and Natural Gas Sector Leaks”, data from a study conducted by the City 

of Fort Worth are summarized. While the focus of this white paper on compressors may be on 

emissions from seals, rather than from other sources, data from the Fort Worth study would be 

useful in establishing counts of compressors. (ERG and Sage Environmental Consulting, LP. 

2011. City of Fort Worth Natural Gas Air Quality Study, Final Report. Prepared for the City of 

Fort Worth, Texas. July 13, 2011. http://fortworthtexas.gov/gaswells/default.aspx?id=87074)

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: See response to Question 1.

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. 

Response: No response – this question is outside the scope of my expertise.

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: No response – this question is outside the scope of my expertise.
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: No response – this question is outside the scope of my expertise.

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: No response – this question is outside the scope of my expertise.

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

impractical at certain existing centrifugal compressors? 

Response: No response – this question is outside the scope of my expertise.

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

without a gas recovery system? 

Response: No response – this question is outside the scope of my expertise.

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

reciprocating compressors impractical? 

Response: No response – this question is outside the scope of my expertise.

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

Response: No response – this question is outside the scope of my expertise.

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: No response – this question is outside the scope of my expertise.

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: There are a number of joint Environmental Defense Fund/Industry studies underway 

that will report emissions from the natural gas supply chain, including emissions from 

compressors. Publication of these studies is anticipated over the coming year.