## Attachment V

Pneumatic Devices

David Allen

University of Texas at Austin

### Comments on



## Oil and Natural Gas Sector Pneumatic Devices

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 “O il and Natural Gas Sector Pneumatic Devices” prepared by the U.S. EPA Office of Air Qua lity Planning and Standards (OAQPS), dated April 2014. I have concentrated my review on my areas of expertise. My comments identify additional

sources of data and describe so me important features of the av ailable data. The review is organized into two sections: res ponses to the charge que stions for reviewers that appear in the white paper, and additional specific co mments, organized by page number.Responses to charge questions

1. Did this paper appropriately characterize the di fferent studies and data sources that quantify emissions from pneumatic controllers and pneumatic pumps in the oil and gas sector?

Response: Table 2-1 summarizes the data that I am aware of, that were ava ilable at the time of the white paper was written, with one exception. That exception is the data on pneumatic pumps reported in Allen et al. (PNAS, 110, 17768-17773, re ferred to as Allen, et al. 2013 in this review). Allen et al. (2013) report emissions fr om 62 pneumatic chemical injection pumps in the Gulf Coast and Mid-Continent regions (see page s S-29 and S-30 in Supporting Information). Average emissions were reported as 0.204±0.089 sc f whole gas per minute (12.2 scf whole gas per pump per hour), and as 0.192±0.085 scf methane per minute (11.5 scf methane per pump per hour, 276 scf methane per pump per day). These aver age emission rates reporte d by Allen, et al. (2013) are within the relatively narrow range of values reported in Tabl e 2-14 of the white paper (244-289 scf methane per pump per day). Allen, et al. (2013) also repor t statistically higher emissions for the 21 pu mps on which emission measurements were made in the Gulf Coast (0.506±0.209 scf whole gas per pump per hour), com pared to the 41 pumps on which emission

measurements were made in the Mid-Contin ent Coast (0.050±0.014 scf whole gas per pump per hour). This regional difference is not reflected in the em ission factors presented in Table 2-14 of the white paper. Allen, et al. (2013, Supporting In formation pages S-29 to S-30) were not able to determine, from the data collected, the reasons for the regional differen ces in emissions. As noted by the authors: “A number of hypotheses were examined to atte mpt to explain the differences in emissions. Volume of liquid pumped was not a good predic tor of emissions. Well head and separator pressure were considered since the pumps must overcome these pressures to drive liquid flow. These variables also were not good pr edictors of emissions. Company specific practices were also considered. While roughly 90% of the samples came from two companies, one from each region,” .. “a total of 6 companies pr ovided data, 3 in the Gulf Coast and 3 in the Midcontinent, and for al l of these companies the same regional differences (Gulf Coast emis sions > Midcontinent) were observed. Mean values of emissions, by company, were sim ilar in each of the regions.”

In addition to the work on pneumatic pumps by A llen, et al. (2013), there are a number of studies currently underway investigatin g emissions from pneumatic d evices, particularly pneumatic controllers. Publication of these studies in the scientific literature is expected later this year.

2. Please discuss explanations for the wide range of emission rate s that have been observed in direct measurement studies of pneumatic c ontroller emissions (e .g., Allen et al., 2013 and Prasino 2013). Are these differences driven purely by the design of the m onitored controllers or are there operational characteristics, such as supply pressure, that play a crucial role in determining emissions?

Response: A defining characteristic of the data reported by Allen, et al. (2013) is that a relatively small subset of pneumatic controllers domi nates total emissions. Of the 305 emission measurements for pneumatic controllers on natu ral gas production sites, 41% with emissions greater than 6 scf/h accounted for 90% of emissions. Twenty pe rcent of devices had emissionsgreater than 17 scf/h. While th e average emissions were 11.2 sc f whole gas/h per device, the median value was 4.5 scf/hr. All of these characte rizations of the data are consistent with a data set dominated by extreme values, sometimes re ferred to as a “fat tail” distribution. The distribution of emissions per devi ce, sorted by emission rate, for the Allen et al. (2013) data set,

is shown below.

Data set on emissions from pneuma tic controllers from Allen, et al. (2013), sorted by emission

rate

Since average values of emission rates are dominated by the “hi ghest emitting” devices, it is important to examine the characteristics of the “highest emitting” devices. These “highest emitting” controllers are not necessarily the same as EPA’s “high continuous bleed” pneumatics as defined in the Greenhouse Gas Reporting Rule (GHGRP) (Code of Federal Regulations,, Title 40 Protection of the Environment, Chapter 98 Mandatory Greenhouse Gas Reporting, 2014). High continuous bleed controllers are designed to emit at a continuous high rate. The highest emitting controllers are simply the controllers actually emitting at a large rate, regardless of their service or design type; thes e controllers can have hi gh emissions because of factors, other than design, rela ted to maintenance, malfunction, or defect. In fact, Allen, et al. (2013) note that none of the controllers measured in their work were identified as high bleed by

the site owners.

Allen, et al. (2013) have made pub licly available the data on indivi dual controller measurements reported in their work. The data are available on a study web site maintained at the University of Texas ( http://dept.ceer.utexa s.edu/methane/study ). The data on indivi dual controllers include information on the region in which the measur ement was made (AP = Appalachian; GC = Gulf Coast; MC = Mid-Continent; RM = Rocky Mountain), the characteristics of the wells on the site, the owner of the site on which the measurements were made (identified by randomly selected letters), and a classification of the controller as low bleed, high bl eed, intermittent, or unclassified. This information can be used to id entify additional characteri stics of the “highest emitting” devices. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00DevicePercentileinMeasuredPopulation(%)

Whole Gas Emissions Rate Measurement (scf/h)Shown in the Figure below are device emission rate s, sorted by region, operator and controller type. The “highest emitting” devices (here defined as emi ssions greater t han 17 scf/h (5.4 g/min), the highest 20% of the measurements) o ccur in all regions except the Rocky Mountains, for multiple operators, and for all device types that were meas ured (intermittent, low bleed and unclassified).

Data set on emissions from pneuma tic controllers from Allen, et al. (2013), sorted by region in which the measurement was made (AP = Appalachi an; GC = Gulf Coast; MC = Mid-Continent; RM = Rocky Mountain), the owner of the site on wh ich the measurements were made (identified by randomly selected letters), and a classificati on of the controller as low bleed, high bleed (none reported), intermittent, or unclassified. region / Host

AP GC MC RM

DHNQW F L RW FNS L R 0 5 10 15 20 25 30 35 40

Average

type

int

low

un ~20% of

devices

with

highest

emissions3. Did this paper capture the full range of tec hnologies available to reduce emissions from pneumatic controllers and pneumatic pumps oil and gas facilities?

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

4. Please comment on the pros and cons of the di fferent emission reduction technologies. Please discuss efficacy, cost and feasibility for both new and existing pneumatics.

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

5. Please comment on the prevalence of the diffe rent emission contro l technologies and the different types of pneumatics in the field. What pa rticular activities requ ire high bleed pneumatic controllers and how prevalent are they in the field?

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

6. What are the barriers to installing instrument air systems for conver ting natural gas-driven pneumatic pumps and pneumatic controllers to air-driven pumps and controllers?

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

7. Are there situations where it may be infeasible to use air driven pumps and controllers in place of natural gas-driven pumps and c ontrollers even where it is feasible to install an instrument air system?

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

8. Did this paper correctly characterize the limita tions of electric-powered pneumatic controllers and pneumatic pumps? Are these electric devices appl icable to a broader ra nge of the oil and gas sector than this paper suggests?

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

9. Are there ongoing or planned studies that will substantially improve the current understanding of VOC and methane emissions from pneumatic controllers and pneumatic pumps and available techniques for increased product reco very and emissions reductions?

Response: Some methane emission data can be used to estimate VOC emissions. Allen et al. (2013) report gas composition data for each pneum atic controller on which measurements were made. The composition data are available in the dat a archives at the study web site maintained at the University of Texas ( http://dept.ceer.utexas.edu/methane/study ). Thus, while not explicitly reported, the methane emission data supplied by A llen, et al. (2013) can be used to calculate VOC emission rates. Zavala, et al. (Env ironmental Science & Technology, 48, 5314–5321, 2014) use these data to estimate VO C emission rates for controlle rs. An average VOC emission rate of 0.17 Mg/yr VOC for a controller with 1.77 Mg/yr methane emissions was estimated basedon gas compositions in the Barnett Shale.

There are also number of studies currently unde rway investigating emissions from pneumatic devices, particularly pneumatic controllers. Pu blication of these studies in the scientific literature is expected later this year.

Specific Comments

Page 4: The white paper states that “Similar designs [of pneumat ic controllers] will have similar steady-state rates when operated unde r similar conditions” This may be true under limited circumstances, but is not generally true . For example, two identical intermittent vent controllers in level control applications on separ ators, operating in on-off service (completely opening and shutting a valve as necessary) may ha ve very different emission rates if the amount of liquids being processed by th e separators is different. Diffe rent liquid flow rates would lead to different frequencies of actua tion, and likely different emissions. This is just one example of how similar designs of controlle rs may have different rates of emi ssion. Empirically, these types of differences can be observed in data set pu blished by the Prasino Group for controllers in British Columbia and Alberta (Prasino Group, Final Report for determining bleed rates for pneumatic devices in British Columbia. Report to British Columbia Ministry of Environment, December 2013). They report highly skewed (“fat-tail”) distributions for many controllers, even when the data are sorted by application (e.g., le vel control) and device manufacturer and design.

Page 8: As noted in the white paper, the Canadian Petroleum Association (CPA) categorized controllers in on/off service and in throttling service. It is not clear how these categories can be mapped onto the EPA emission categories of in termittent, low continuous bleed and high

continuous bleed devices. Thr oughout the literature on emissions from pneumatic controllers, there is inconsistency and confus ion in terminology used in ca tegorizing controllers. This inconsistency limits the extent to wh ich studies can be compared.

Page 40: Table 3-1 (and page 50): The white paper stat es “Instrumentation in poor condition typically bleeds 5 to 10 scfh more than represen tative conditions”. The data reported by Allen et al. (2013), and summarized in this review, sh ow some controllers ha ve emission rates much higher than 5 to 10 scf/h above the standar d emission factor for the device.

Page 44. The white paper provides estimates of monetary savings of reducing natural gas emissions from pneumatics in th e transmission sector. The data re ported by Allen, et al. (2013) can be used to generate similar estimates in th e production sector. Specifically, for the data set reported by Allen, et al. (2013), devices with more than 6 sc f/h of emissions had average emission rates of 24.5 scf/h, and would releas e approximately 215,000 standar d cubic feet per year of natural gas. That natural gas woul d have a value of $2,600 over 3 years, assuming a value of $4 per thousand scf of gas. Reducing th e emissions these devices from their current level to less than 6 scfh would reduce total emi ssions from these pneuma tic controllers by an average of 160,000 standard cubic feet pe r device per year ($640/yr).Page 56. The white paper states that “recent emission estimates for pneumatic controllers have focused on methane emissions and not VOC emi ssions” Allen et al. (2013) report whole gas emission rates for each pneumatic controller, an d report gas composition for each controller on which measurements were made. The composition data are available in the data archives at the study web site maintained at the University of Texas ( http://dept.ceer.utexas.edu/methane/study ). Thus, while not explicitly reported, the data supp lied by Allen, et al. ( 2013) can be used to calculate VOC emission rates. Zavala, et al. (Environmental Science & Technology, 48 , 5314– 5321, 2014) use these data to estimate a VOC emissi on rate for pneumatic d evices in the Barnett Shale, as noted earlier in this review. Zavala, et al., also calculate average VOC emissions of 0.19 Mg/yr for pneumatic chemical injection pump s with methane emissions of 1.94 Mg/yr (see Supporting Information in Zavala, et al., 2014).

Page 56. The white paper states that “emissions c an vary depending on sector (e.g., production, transmission, or storage) and the type of contro ller”. These are import ant factors, but many other factors can also be important.

Page 58. For the Allen, et al (2013) reference, in addition to citing the material published by the Proceedings of the National Academy of Sciences (which is open access), the white paper should cite the study web site, which provides supplementary data. ( http://dept.ceer.utexas.edu/methane/study ).