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 “Oil and Natural Gas Sector Pneumatic Devices” 

prepared by the U.S. EPA Office of Air Quality 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 some important features of the available data. The review is 

organized into two sections: responses to the charge questions for reviewers that appear in the 

white paper, and additional specific comments, organized by page number. 
Responses to charge questions

1. Did this paper appropriately characterize the different 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 available 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, referred to as Allen, et al. 2013 in this 

review). Allen et al. (2013) report emissions from 62 pneumatic chemical injection pumps in the 

Gulf Coast and Mid-Continent regions (see pages S-29 and S-30 in Supporting Information). 

Average emissions were reported as 0.204±0.089 scf 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 average emission rates reported by Allen, et al. 

(2013) are within the relatively narrow range of values reported in Table 2-14 of the white paper 

(244-289 scf methane per pump per day). Allen, et al. (2013) also report statistically higher 

emissions for the 21 pumps on which emission measurements were made in the Gulf Coast 

(0.506±0.209 scf whole gas per pump per hour), compared to the 41 pumps on which emission 

measurements were made in the Mid-Continent Coast (0.050±0.014 scf whole gas per pump per 

hour). This regional difference is not reflected in the emission factors presented in Table 2-14 of 

the white paper. Allen, et al. (2013, Supporting Information pages S-29 to S-30) were not able to 

determine, from the data collected, the reasons for the regional differences in emissions. As 

noted by the authors: 

“A number of hypotheses were examined to attempt to explain the differences in emissions. 

Volume of liquid pumped was not a good predictor 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 predictors 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 provided data, 3 in the Gulf 

Coast and 3 in the Midcontinent, and for all of these companies the same regional 

differences (Gulf Coast emissions > Midcontinent) were observed. Mean values of 

emissions, by company, were similar in each of the regions.” 

In addition to the work on pneumatic pumps by Allen, et al. (2013), there are a number of studies 

currently underway investigating emissions from pneumatic devices, 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 rates that have been observed in 

direct measurement studies of pneumatic controller emissions (e.g., Allen et al., 2013 and 

Prasino 2013). Are these differences driven purely by the design of the monitored 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 dominates total emissions. Of the 305 emission 

measurements for pneumatic controllers on natural gas production sites, 41% with emissions 

greater than 6 scf/h accounted for 90% of emissions. Twenty percent of devices had emissions 
greater than 17 scf/h. While the average emissions were 11.2 scf whole gas/h per device, the 

median value was 4.5 scf/hr. All of these characterizations of the data are consistent with a data 

set dominated by extreme values, sometimes referred to as a “fat tail” distribution. The 

distribution of emissions per device, sorted by emission rate, for the Allen et al. (2013) data set, 

is shown below. 

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

rate 

Since average values of emission rates are dominated by the “highest 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; these controllers can have high emissions because of 

factors, other than design, related 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 publicly available the data on individual controller measurements 

reported in their work. The data are available on a study web site maintained at the University 

of Texas (http://dept.ceer.utexas.edu/methane/study ). The data on individual controllers include 

information on the region in which the measurement 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 bleed, intermittent, or 

unclassified. This information can be used to identify additional characteristics of the “highest 

emitting” devices. 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

Device Percentile in Measured

Population(%)

Whole Gas Emissions Rate Measurement (scf/h)
Shown in the Figure below are device emission rates, sorted by region, operator and controller 

type. The “highest emitting” devices (here defined as emissions greater than 17 scf/h (5.4 

g/min), the highest 20% of the measurements) occur in all regions except the Rocky Mountains, 

for multiple operators, and for all device types that were measured (intermittent, low bleed and 

unclassified). 

Data set on emissions from pneumatic controllers from Allen, et al. (2013), sorted by region in 

which the measurement was made (AP = Appalachian; GC = Gulf Coast; MC = Mid-Continent; 

RM = Rocky Mountain), 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 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

emissions
3. Did this paper capture the full range of technologies 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 different 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 different emission control technologies and the 

different types of pneumatics in the field. What particular activities require 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 converting 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 controllers 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 limitations of electric-powered pneumatic controllers 

and pneumatic pumps? Are these electric devices applicable to a broader range 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 recovery 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 pneumatic 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 methane emission data supplied 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 VOC emission rates for controllers. An average VOC emission 

rate of 0.17 Mg/yr VOC for a controller with 1.77 Mg/yr methane emissions was estimated based 
on gas compositions in the Barnett Shale. 

There are also number of studies currently underway investigating emissions from pneumatic 

devices, particularly pneumatic controllers. Publication of these studies in the scientific 

literature is expected later this year.

Specific Comments 

Page 4: The white paper states that “Similar designs [of pneumatic controllers] will have 

similar steady-state rates when operated under 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 separators, operating in on-off service (completely 

opening and shutting a valve as necessary) may have very different emission rates if the amount 

of liquids being processed by the separators is different. Different liquid flow rates would lead 

to different frequencies of actuation, and likely different emissions. This is just one example of 

how similar designs of controllers may have different rates of emission. Empirically, these types 

of differences can be observed in data set published 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., level 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 intermittent, low continuous bleed and high 

continuous bleed devices. Throughout the literature on emissions from pneumatic controllers, 

there is inconsistency and confusion in terminology used in categorizing controllers. This 

inconsistency limits the extent to which studies can be compared. 

Page 40: Table 3-1 (and page 50): The white paper states “Instrumentation in poor condition 

typically bleeds 5 to 10 scfh more than representative conditions”. The data reported by Allen 

et al. (2013), and summarized in this review, show some controllers have emission rates much 

higher than 5 to 10 scf/h above the standard emission factor for the device. 

Page 44. The white paper provides estimates of monetary savings of reducing natural gas 

emissions from pneumatics in the transmission sector. The data reported by Allen, et al. (2013) 

can be used to generate similar estimates in the production sector. Specifically, for the data set 

reported by Allen, et al. (2013), devices with more than 6 scf/h of emissions had average 

emission rates of 24.5 scf/h, and would release approximately 215,000 standard cubic feet per 

year of natural gas. That natural gas would have a value of $2,600 over 3 years, assuming a 

value of $4 per thousand scf of gas. Reducing the emissions these devices from their current 

level to less than 6 scfh would reduce total emissions from these pneumatic controllers by an 

average of 160,000 standard cubic feet per 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 emissions” Allen et al. (2013) report whole gas 

emission rates for each pneumatic controller, and 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 supplied 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 emission rate for pneumatic devices 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 pumps with methane emissions of 1.94 Mg/yr (see 

Supporting Information in Zavala, et al., 2014). 

Page 56. The white paper states that “emissions can vary depending on sector (e.g., production, 

transmission, or storage) and the type of controller”. These are important 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 ).