# Attachment T

Compressors

Ned Jerabek

New Mexico Environmental Department

### OIL AND NATURAL GAS SECTOR COMPRESSORS

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.

COMMENT: I found it difficult to understand the emission factor calculation methodology. As there is a very large differen ce in the emission factors for r eciprocating and centrifugal compressors it seems logical that the emission factors would have been developed independently and applied independently instead of using the component method which “uses average emission factors for reciprocating and centrifugal compressor seals and the average number of reciprocating and centrifugal compressors per fa cility to estimate the average facility emissions

. ” The ICF study commissioned by EDF showed a 166% increase compared to the emissions calculations based on the EPA/GRI 1996 study. One concludes whatever the deficiencies of either study at a minimum

methan e emissions are at least as large as represented from the emission factors derived from the EPA/GRI 1996 study. Furthermore, as an air quality permitting manager from 1997 through 2013, I witnessed significant growth and expansion in the oil and gas produ cing and processing sectors such that I believe the updates and revisions made in the ICF study are appropriate and more representative. This conclusion is also supported by the URS/UT 2011 study.

2. Did this paper appropriately characterize the differen t studies and data sources that quantify vented emissions from compressors in the oil and gas sector?

COMMENT: Yes, I think the studies and data sources were appropriately characterized, and perhaps

that was the mos t workable approach, but it would be more accurate and easier to follow if we had an analysis that quantified vented emissions unique to each compressor type.

3. Did this paper capture the full range of technologies available to reduce vented emissions from reciprocating compres sors 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 reciprocat ing compressors but has no detailed information on this technology.

COMMENT: The technologies discussed in the paper are low

- tech easy to understand, and easy to see the value of capturing the vented methane emissions and routing them either back to the pr ocess or using them as a fuel on site. This is hard to argue against and sounds very much like a MACT

floor baseline. The fact that the estimated payback periods are relatively short further strengthens the argument for immediate implementation. If there a re other technologies out there, short of replacing the entire compressor, they are likely to be more technical and therefore more expensive and result in higher maintenance costs. These compressors live in very harsh environments and therefore the more

lo w

- tech the solution the higher the probability that they will be reliable

, long lived and well within the capabilities of existing maintenance personnel

.4. Did this paper appropriately characterize the emissions reductions achievable from the emissions mitigation technologies discussed for reciprocating compressors and we t seal centrifugal compressors?

COMMENT: Yes, the fact that the emission reduction strategies are comparable to existing mitigation technologies already in practice suggests they are ac hievable. For example, ducting the emissions to a Vapor Recovery Unit (VRU) is very similar to ducting Glycol Dehydrator emissions to a VRU, and therefore it is reasonable to expect the same recovery efficiency.

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?

COMMENT: Industry leads tha t I interviewed believe there are significant ope rating costs for labor, installation, and ongoing maintenance that were under

- represented. They point out that labor costs eighteen years ago (1996 study) were much less than they are now. They also pointed out that much

of the installation work will likel y be contracted out and there will be significant costs in transportation and per diem because the contractors are traveling to extremely remote locations

. Section 4.1.2, Economic Rod Packing Replacement , states that “In some cases, the economic

threshold for replacement can be as low as 30 scfh of gas leakage.” Industry representatives believe it

is at least 3 times that. They also stated that coating the compressor rods with chrome or tungsten would be cost prohibitive. It should be pointed out that whil e they found fault with some of the

details , they agreed there are opportunities for both resource conservation and cost savings.

6. If there are emissions mitigation options for reciprocating and centrifugal compressors that were not discussed in this p aper, please comment on the pros and cons of those options. Please discuss the efficacy, cost and feasibly for both new and existing compressors.

COMMENT: I am not aware of other emission mitigation options.

7. Are there technical limitations that make t he replacement of wet seals with dry seals impractical at certain existing centrifugal compressors?

COMMENT: I did get one comment whereby they thought that extremely large centrifugal compressors using wet seals benefitted from the oil lubrication thereby decreasing wear, but this reasoning is refuted by the very detailed explanation of how dry seals function i n section 4.3.1.

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

COMMENT: I did not receive any comments to that effect. Given the fact that tables 3

- 8, 3

- 10, and

3

- 11 clearly show that the wet seal centrifugal compressor affords the greatest recovery opportunity

for vented methane and the estimated payback period represented in section 4.5.3 for recovery systems is less than a year it would appear to be a win/win investment for indu stry.

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

COMMENT: Not necessarily technical limitations , but it is my understanding that reciprocating compressors are of ten used in the field gathering system , natural gas production sector, where you have both low pressure and low gas volume. In that scenario a gas capture system would haveminimal value. This appears to be supported by table 3

- 2 which lists an “Average Co mpressor Methane Emission Factor from Seals” at 9.48 Mscf/yr for reciprocating compressors in natural gas production. This is further supported by the discussion following table 3

- 3 which points out that the

methane emissions from these units “...include emi ssions from compressor blowdowns, starter gas, and miscellaneous equipment associated with the compressor. Methane emissions from reciprocating compressor seals represent approximately 29% of the total emissions from reciprocating compressors. Note that th e Eastern U.S. natural gas production did not include methane emissions from compressor seals in the reciprocating compressor emission factor, only emissio ns from associated equipment ...” I conclude this is not a good investment of monetary resources given the fact that the Processing, Transmission, and Storage sectors on average have reciprocating emissions that are 31 times greater than the Production sector.

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

COMMENT: I called five environmental managers in the oil and gas industry . The ir comments are
as follows:

For high pressure compression in the processing sector wet seal centrifugal compressors are favored because they believe the oil lubrication reduces wear. Of much greater concern is the liquids dump valve jamming open and blowing gas to the atmosphere as o pposed to capturing gas from a wet oil seal system . They believe the emissions from wet seals are minimal. The overall opinion was that

there are a lot more wet seal compressors out there than dry seal compressors which refutes the conclusions in the API/ANGA study. Very little compressor emissions mitigation is being implemented in the field because they have better opportunities to mitigate emission s on other components at the facility that giv e them a greater return on their investment. Again, by far the biggest source of methane emissions is from the liquids dump valve, either do to jamming from build up or improper programing governing their opera tion (i.e. set points).

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?

COMMENT: As noted above in number 10 and follow up research, there are hybrid wet seal centrifugal compressors that have emissions comparable to dry seal systems. It was also industries position that there is not a significant advantage bo th mechanical and in maintenance of d ry seal centrifugal compressors when used for high compression loads.

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 redu ctions

COMMENT: I assume that to be a certainty. In order for local air agencies to implement new regulation to control VOC and methane emissions they will

, by necessity

, partner with industry and create workshop trainin g programs to improve general under standing of how the emissions are emitted and how they are reasonably mitigated and controlled.