Lessons
Learned
NaturalGas
EPA POLLUTION PREVENTER
£XX4
From Natural Gas STAR Partners
g
•a
DIRECTED INSPECTION AND MAINTENANCE AT GAS
PROCESSING PLANTS AND BOOSTER STATIONS
Executive Summary
Natural gas processing plants and their associated compressor booster stations emit an estimated 36 billion
cubic feet (Bcf) of methane annually. More than 24 Bcf of total methane losses from gas plants are fugitive emis-
sions from leaking compressors and other equipment components such as valves, connectors, seals, and open-
ended lines. Implementing a directed inspection and maintenance (DI&M) program is a proven, cost-effective way
to detect, measure, prioritize, and repair equipment leaks to reduce methane emissions.
A DI&M program begins with a baseline survey to identify and quantify leaks. Repairs are then made to only the
leaking components that are cost-effective to fix, based on criteria such as repair cost, expected life of the repair,
and payback period. Subsequent surveys are designed based on data from previous surveys, allowing operators
to concentrate on the components that are most likely to leak and are profitable to repair. Baseline surveys of
Natural Gas STAR partners' gas processing facilities found that the majority of fugitive methane emissions are
from a relatively small number of leaking components. Valves are the largest source (30 percent), followed by
connectors (24 percent), and compressor seals (23 percent). The remaining 23 percent of methane losses are
primarily from open-ended lines, crankcase vents, pressure relief devices, and pump seals.
Natural Gas STAR processing partners have reported significant savings and methane emissions reductions by
implementing DI&M. A four-plant pilot study conducted by EPA and the Gas Technology Institute (GTI) demon-
strated that instituting a DI&M program at gas processing facilities could reduce methane emissions by up to 96
percent and save up to $164,000 per plant.
Leak Source
Fugitive Methane
Emissions from
Gas Processing
Plants and
Booster Stations
Fugitive
Methane
Emissions
45,000 to
1 28,000 Mcf/yr
per gas plant
Method for
Reducing
Methane Loss
Directed
Inspection &
Maintenance
Potential
Emissions
Reduction
Up to 96 percent;
average 77
percent
Typical Implementation
Cost
$14,000 to $50,000 for
leak screening and
measurement; $39,000 to
$78,000 for repairs
Typical Partner
Savings (at $3/Mcf)
$58,000 to $164,000/yr
per gas plant
This is one of a series of Lessons Learned Summaries developed by EPA in cooperation with the natural gas industry on superior
applications of Natural Gas STAR Program Best Management Practices (BMPs) and Partner Reported Opportunities (PROs).
-------
Introduction
Technology
Background
Fugitive emissions from equipment leaks account for more than 80 percent
of annual natural gas losses from gas processing plants and booster sta-
tions. Emissions from continuous vents, combustion equipment, and flare
systems contribute to the remaining 20 percent of gas losses and methane
emissions. Natural Gas STAR partners have demonstrated that a DI&M pro-
gram can profitably eliminate as much as 96 percent of gas losses and a
corresponding 80 percent of methane emissions from equipment leaks. This
Lessons Learned study describes the practices and technologies that can
be used to successfully implement a DI&M program.
DI&M programs begin with a comprehensive baseline survey in which equip-
ment components are screened to identify the leaking components. The
mass emissions rates from the leaking components are measured, repair
costs are estimated, and the repair payback period is calculated for each
leak. Both the leak and repair cost data obtained from the baseline survey
are then used to guide subsequent surveys, allowing operators to focus on
components that are most likely to leak and are profitable to repair.
The following sections describe various leak screening and measurement tech-
niques that can be employed as part of a DI&M program at gas processing
plants and booster stations.
Leak Screening Techniques
Leak screening in a DI&M program may include all components in a com-
prehensive baseline survey, or may be focused instead on gas processing
plant components that are likely to develop significant methane leaks.
Several leak screening techniques can be used:
* Soap Bubble Screening is a fast, easy, and very low-cost method to
screen for leaks. Soap bubble screening involves spraying a soap solu-
tion on small, accessible components such as threaded unions, piping
connections, plugs, and flanges. Soaping is effective for locating loose
fittings and connections, which can be tightened on the spot to fix the
leak, and for quickly checking the tightness of a repair. Many methane
emissions sources that are cost-effective to locate, measure, and fix are
generally larger than the small leaks likely to be found by soaping.
However, because soap screening is rapid and of negligible cost, it can
easily be incorporated into routine maintenance procedures.
* Electronic Screening using small hand-held gas detectors or "sniffing"
devices provides another fast and convenient way to detect accessible
leaks. Electronic gas detectors have catalytic sensors designed to
detect the presence of specific gases. Depending on the sensitivity of
-------
Exhibit 1. Toxic Vapor Analyzer
Source: Thermo Environmental Instruments Inc
the instrument, detecting leaks
in areas with elevated ambient
concentrations of hydrocarbon
gas can be difficult. Electronic
gas detectors can be used on
larger openings that cannot be
screened by soaping.
Organic Vapor Analyzers
(OVAs) and Toxic Vapor
Analyzers (TVAs) are portable
hydrocarbon detectors that can
also be used to quantify leaks.
An OVA is a flame ionization
detector (FID), which measures
concentration of organic vapors over a range of 9 to 10,000 parts per mil-
lion (ppm). A TVA is a combination device containing both an FID and a
photoionization detector (PID), which can measure organic vapors at con-
centrations exceeding 10,000 ppm. Exhibit 1 shows a typical TVA, con-
sisting of a probe attached to a portable analytical instrument. TVAs and
OVAs measure the concentration of methane in the area around a leak.
Screening is accomplished by placing the probe inlet at the opening
where leakage can occur. Concentration measurements are observed as
the probe is slowly moved along the interface or opening, until a maxi-
mum concentration reading is obtained. The maximum concentration is
recorded as the leak screening value. Screening with TVAs is somewhat
slow, approximately 40 com-
ponents per hour, and the
instruments require frequent
calibration. In larger facilities
TVAs are commonly used for
volatile organic compound
(VOC) leak screening, so these
instruments may be readily
available to screen for methane
leaks.
Acoustic Leak Detection
uses portable acoustic screen-
ing devices designed to detect
the acoustic signal that results
when pressurized gas escapes
through an orifice. As gas moves from a high-pressure to a low-pressure
environment across a leak opening, turbulent flow produces an acoustic
Exhibit 2. Acoustic Leak
Detection
Source: Physical Acoustics Corp.
-------
signal, which is detected by a hand-held sensor or probe, and read as
intensity increments on a meter. Although acoustic detectors do not
measure leak rates, they provide a relative indication of leak size—a high
intensity or "loud" signal corresponds to a greater leak rate. Acoustic
screening devices are designed to detect either high frequency or low
frequency signals.
High Frequency Acoustic Detection is best applied in noisy environ-
ments where the leaking components are accessible to a handheld sen-
sor. As shown in Exhibit 2, the acoustic sensor is placed directly on the
equipment orifice to detect the signal. Acoustic sensors are particularly
useful for detecting leaking valves where the line vent is inaccessible,
such as blowdown valves and pressure relief devices connected to ele-
vated vent stacks. Alternatively, Ultrasound Leak Detection is an
acoustic screening method that detects airborne ultrasonic signals in the
frequency range of 20 kHz to 100 kHz. Ultrasound detectors are
equipped with a hand-held acoustic probe that is aimed from a distance
at the potential leak source. Ultrasound detection is directional, making it
possible to pinpoint the location of leaks from distances as great as 100
feet. Although ultrasound detection may be sensitive to background
noise, this technique is useful for identifying gas leaks at inaccessible
equipment components.
Leak Measurement Techniques
An important component of a DI&M program is measurement of the mass
emissions rate or leak volume of identified leaks, so that manpower and
resources are allocated only to the significant leaks that are cost-effective to
repair. Four measurement techniques are commonly used:
* Toxic Vapor Analyzers (TVAs) can be used to estimate mass leak rate.
Concentration measurements in ppm are converted to mass emissions
estimates by means of correlation equations. A major drawback to TVAs
for methane leak measurement is that the correlation equations are typi-
cally not site-specific. The mass leak rates predicted by general TVA
correlation equations have been shown to deviate from actual leak rates
by as much as three or four orders of magnitude. Similarly, a study con-
ducted jointly by Natural Gas STAR partners, EPA, the Gas Research
Institute (GRI—now GTI, the Gas Technology Institute), and the
American Gas Association (AGA) found that measured concentration
thresholds, or "cut-off" values, such as 10,000 ppm or 100,000 ppm are
ineffective for determining which methane leaks are cost-effective to fix.
Because the use of general TVA correlation equations can increase
measurement inaccuracy, the development and use of site-specific cor-
relations will be more effective in determining actual leak rates.
-------
Exhibit 3. Leak Measurement
Using a High Volume Sampler
Source: Oil & Gas Journal, May 21, 2001
Bagging Techniques are commonly used to measure mass emissions
from equipment leaks. The leaking component or leak opening is
enclosed in a "bag" or tent. An inert carrier gas such as nitrogen is
conveyed through the bag at a known flow rate. Once the carrier gas
attains equilibrium, a gas sample is collected from the bag and the
methane concentration of the sample is measured. The mass emis-
sions rate is calculated from the measured methane concentration of
the bag sample and the flow rate of the carrier gas. Leak rate meas-
urement using bagging techniques is a fairly accurate (within ± 10 to
15 percent) but slow process (only two or three samples per hour).
Although bagging techniques
are useful for direct measure-
ment of larger leaks, bagging
may not be possible for
equipment components that
are inaccessible, unusually
shaped, or very large.
High Volume Samplers cap-
ture all of the emissions from a
leaking component to accu-
rately quantify leak emissions
rates. Exhibit 3 shows leak
measurement using a high volume sampler. Leak emissions, plus a large
volume sample of the air around the leaking component, are pulled into
the instrument through a vacuum sampling hose. High volume samplers
are equipped with dual hydrocarbon detectors that measure the con-
centration of hydrocarbon gas in the captured sample, as well as the
ambient hydrocarbon gas concentration. Sample measurements are
corrected for the ambient hydrocarbon concentration, and a mass leak
rate is calculated by multiplying the flow rate of the measured sample by
the difference between the ambient gas concentration and the gas con-
centration in the measured sample. Methane emissions are obtained by
calibrating the hydrocarbon detectors to a range of concentrations of
methane-in-air.
High volume samplers are equipped with special attachments designed
to ensure complete emissions capture and to prevent interference from
other nearby emissions sources. High volume samplers measure leak
rates up to 8 cubic feet per minute (scfm), a rate equivalent to 11.5
thousand cubic feet (Mcf) per day. Leak rates greater than 8 scfm must
be measured using bagging techniques or flow meters. Two operators
can measure 30 components per hour using a high volume sampler,
compared with two to three measurements per hour using bagging
techniques.
-------
Decision
Process
* Rotameters and other flow meters are used to measure extremely large
leaks that would overwhelm other instruments. Flow meters typically
channel gas flow from a leak source through a calibrated tube. The flow
lifts a "float bob" within the tube, indicating the leak rate. Because
rotameters are bulky, these instruments work best for open-ended lines
and compressor seals, where the entire flow can be channeled through
the meter. Rotameters and other flow metering devices can supplement
surveys made using TVAs, bagging, or high volume samplers.
Exhibit 4 summarizes the application and usage, effectiveness, and approxi-
mate cost of the leak screening and measurement techniques described
above.
Exhibit 4: Screening and Measurement Techniques
Instrument/Technique
Soap Solution
Electronic Gas
Detectors
Acoustic Detectors/
Ultrasound Detectors
TVA (flame ionization
detector)
Bagging
High Volume
Sampler
Rotameter
Application and Usage
Small point sources,
such as connectors.
Flanges, vents, large gaps,
and open-ended lines.
All components. Larger
leaks, pressured gas, and
inaccessible components.
All components.
Most accessible
components.
Most accessible
components (leak rate
<11.5Mcfd).
Very large leaks.
Effectiveness
Screening only.
Screening only.
Screening only.
Best for
screening only.
Measurement
requires site-
specific leak
size correlations.
Measurement
only; time-
consuming.
Screening and
measurement.
Measurement
only.
Approximate
Capital Cost
Under $100
Under $1,000
$1,000-$20,000
(depends on
instrument
sensitivity, size,
associated
equipment)
Under $10,000
(depends on
instrument
sensitivity/size)
Under $10,000
(depends on sample
analysis cost)
> $10,000
Under $1,000
A DI&M program is conducted in four steps: (1) conduct a baseline survey;
(2) record the results and identify candidates for cost-effective repair; (3)
analyze the data, make the repairs, and estimate methane savings; and (4)
develop a survey plan for future inspections and follow-up monitoring of
leak-prone equipment.
-------
Step 1: Conduct Baseline Survey. A DI&M program typically begins with
baseline screening to identify leaking components. As leaking components
are located, accurate leak rate measurements are obtained using bagging
techniques, a high volume sampler, or TVA surveys that have site-specific
concentration correlations. Partners have found that leak measurement
using a high volume sampler is cost-effective, fast, and accurate.
Prior to conducting a baseline survey, gas plant operators may not have
accurate counts of their equipment components. Initial estimates of equip-
ment components have been shown to be 40 percent lower than the actual
component counts developed during a baseline survey. The number of
equipment components depends upon the size and complexity of the facili-
ty. Baseline leak screening conducted by EPA and GRI at four gas process-
ing plants found that the physical component counts ranged from approxi-
mately 14,200 components at the smallest facility to more than 56,400
components at the largest facility surveyed.
The cost of a complete baseline screening
using a high volume sampler is approximately
$1.00 per component, or approximately
$15,000 to $20,000 for a medium-size gas $1'°° per component
Rule-of-Thumb
Initial baseline survey cost =
plant (in 2000 dollars). Partners have found that
the cost of follow-up surveys in an ongoing DI&M program are 25 percent to
40 percent less than the initial survey. Subsequent surveys focus only on the
components that are likely to leak and are cost-effective to repair. For some
gas plant components, leak screening and measurement may be best
accomplished during a regularly scheduled DI&M survey program. For other
components, simple and rapid leak screening can be seamlessly incorporat-
ed into ongoing routine operation and maintenance procedures. Some oper-
ators train maintenance staff to conduct leak surveys, while others hire out-
side consultants to conduct the baseline survey.
Step 2: Record Results and Identify Candidates for Repair. Leak meas-
urements collected in Step 1 must be evaluated to pinpoint the leaking plant
components that are cost-effective to repair. Leaks are prioritized by compar-
ing the value of the natural gas lost with the estimated cost in parts, labor,
and equipment downtime to fix the leak. Some leaks can be fixed on the
spot by simply tightening a connection. Other repairs are more complicated
and require equipment downtime or new parts. For these repairs, operators
may choose to attach identification markers, so that the leaks can be fixed
later, if warranted by the repair costs. Some large leaks might be found on
equipment normally scheduled for routine maintenance, in which case the
-------
maintenance schedule may be
advanced to repair the leak at
no additional cost.
As leaks are identified and
measured, operators should
Decision Steps for DI&M
1. Conduct baseline survey.
2. Record results and identify candidates for
repair.
3. Analyze data and estimate savings.
record the baseline leak data ,n , ,, _..„.,
4. Develop a survey plan for future DI&M.
so that future surveys can
focus on the most significant
leaking components. Easy repairs should be completed on the spot, as soon
as the leaks are found. Others leaks might be tagged for later attention. The
results of the DI&M survey can be tracked using any convenient method or
format. The information that plant operators may choose to collect include:
* An identifier for each leaking component.
* The component type (for example, blowdown OEL, 3-inch valve).
* The measured leak rate.
* The survey date.
* The estimated annual gas loss.
* The estimated repair cost.
This information will direct subsequent emissions surveys, prioritize future
repairs, and track the methane savings and cost-effectiveness of the DI&M
program.
Baseline surveys conducted on more than 100,000 equipment components
at four partner-operated gas processing plants found that only 3 percent of
equipment components were leaking. However, these leaking components
contributed 82 percent of total methane emissions from the four plants, a
total of more than 265 million cubic feet (MMcf) per year. Results indicate
that components subject to vibration, high use, or temperature cycles are
the most leak-prone.
Exhibit 5 shows average methane emissions measured from leaking gas
plant equipment components, as well as the average leak repair costs for
the various components. Exhibit 5 can be used to identify which gas plant
equipment leaks are likely to be cost-effective to find and fix. For example,
many of the largest leaks may be associated with compressors, but these
leaks tend to be the most costly to repair. Leaking connectors, on the other
hand, are inexpensive to repair. Exhibit 5 suggests that other equipment
components such as flanges, valves, and open-ended lines may offer cost-
effective opportunities to reduce fugitive emissions.
Step 3: Analyze Data and Estimate Savings. By comparing the estimated
repair cost to the measured leak rate, a determination can be made whether
the leak is cost-effective to repair. Cost-effective repair is a critical part of a
-------
Exhibit 5: Average Methane Emissions Factors and Repair Costs for
Selected Gas Processing Plant Components
Component
Description
Compressor
Blowdown
Open-Ended
Line (DEL)
Starter DEL
Site
Blowdown
DEL
Other DEL
Compressor
Seal
Valve
Pressure
Relief Valve
Cylinder
Valve Cover;
Fuel Valve
Connection
Flange
Gas Plant Non-
Compressor
(Mcf/yr/component)
—
742
43
—
25
3.9
6.7
88.2
Reciprocating
Compressor
(Mcf/yr/component)
1,417
1,341
—
1,440
—
308
127
—
89.7
Centrifugal
Compressor
(Mcf/yr/component)
2,887
1,341
—
485
—
—
63.4
—
115
Average
Repair Cost ($)
$5,000
—
$75
$65
$2,000
$130
$150
$125
$25
$150
Source: Methane emissions factors represent weighted average of measured fugitive emis-
sions reported in two studies: U.S. EPA, Gas Research Institute (now the Gas Technology
Institute), and Radian Intl., 1996, Methane Emissions from the Natural Gas Industry,
Volume 8: Equipment Leaks; and Gas Technology Institute and Clearstone Engineering,
2002, Identification and Evaluation of Opportunities to Reduce Methane Losses at Four Gas
Processing Plants. Repair cost data are in 2000 dollars from GTI/Clearstone study.
Note: Methane emissions factors are adjusted to account for the average volume percent of
methane in the natural gas, which is 87 percent. Similarly, emissions factors are also
adjusted to account for 1 1 percent of compressors that are routed to a flare, plus the frac-
tion of compressors that do not use natural gas starters.
successful DI&M program because the greatest savings are achieved by tar-
geting only those leaks that are profitable to repair.
A survey of equipment leaks and estimated repair costs at four gas plants
found that for a payback of 6 months or less, 78 percent of leaking compo-
nents were cost-effective to repair. In addition, 92 percent of leak repairs
were found to payback in less than 1 year, and 94.5 percent of leaks paid
back in less than 4 years.
Exhibit 6 provides an example of the gas savings that would be possible by
fixing the 10 largest leaks at a single gas plant. This exhibit illustrates the
straightforward calculation that should be made for each measured leak to
determine which leaks are cost-effective to repair.
-------
Exhibit 6. Example of Potential Gas Savings from Fixing the Ten Largest
Leaks at a Single Gas Processing Plant
Component Description
Plug valve (leakage at
bottom of valve body)
Union on fuel gas line
Threaded connection
Plug valve on flare line
Governor
Distance piece on
recompressor cylinder
Open-ended line
Union on fuel gas line
Compressor seals
Gate valve
Total
Gas Savings
(Mcf/yr)
4,214
4,052
3,482
3,030
2,572
2,550
2,320
2,204
1,928
1,576
27,928
Value of Gas
Saved at $3.00/
Mcf ($/yr)
$12,642
$12,156
$10,446
$9,090
$7,716
$7,650
$6,960
$6,612
$5,784
$4,728
$83,784
Repair Cost
($)
$200
$100
$10
$200
$200
$2,000
$60
$100
$2,000
$60
$4,930
Payback Period
5-6 days
3-4 days
Immediate
8 days
1 0 days
3 months
3-4 days
5-6 days
4 months
4-5 days
21 days
Natural Gas STAR partners have found that an effective way to analyze
baseline survey results is to create a table listing all leaks, with their associat-
ed repair cost, expected gas savings, and expected life of the repair. Using
this information, economic criteria such as net present value or payback
period can be easily calculated for each leak repair. Partners can then
decide which leaking components are economic to repair.
Exhibits 7 and 8 illustrate the type of analysis that can be completed to
determine the relative profitability of DI&M for selected types of gas plant
components. The cost data, component counts, and average component
emissions factors are based on the data obtained from a pilot study of DI&M
at four gas processing plants. Exhibit 7 illustrates the cost basis for the initial
baseline survey and repair of leaking connectors, pressure relief valves,
open-ended lines (OEL), and other valves. Exhibit 8 uses the cost bases
shown in Exhibit 7 for an economic analysis of DI&M for the selected equip-
ment components.
10
-------
Exhibit 7 : Cost Basis for Cash Flow Analysis of DI&M for Selected Gas
Processing Plant Components
Type of Component
Connections
Pressure
Relief Valve
DEL
Other Valves
Compressor-
Related
Non-Compressor
Related
Connections Total
Compressor-
Related
Non-Compressor
Related
Pressure Relief
Valve Total
Compressor
Slowdown DEL
Compressor
Starter DEL
Site Slowdown
DEL
Other DEL—
Non-Compressor
Related
DEL Total
Compressor-
Related
Non-Compressor
Related
Valve Total
Number of
Components
per Gas
Plant
2135
7664
9799
13
48
61
15
15
1
171
202
309
1825
2134
Estimated
Survey
Cost
$2,135
$7,664
$9,799
$13
$48
$61
$15
$15
$1
$171
$202
$309
$1 ,825
$2,134
Assume
3%
Leaking
64
230
294
1
1
2
1
1
1
5
8
9
55
64
Estimated
Repair
Cost
($/Comp.)
$5
$-
$150
$150
$5,000
$1 ,000
$75
$65
$175
$130
Total
Repair
Cost
$320
$0
$150
$150
$5,000
$1,000
$75
$325
$1 ,575
$7,150
Total Cost to
Find & Fix
$2,455
$7,664
$10,119
$163
$198
$361
$5,015
$1,015
$76
$496
$6,602
$1 ,884
$8,975
$10,859
Assumptions: Cost data and component counts from 2000 GTI/Clearstone study. Cost for non-compressor
connection repair assumes that repair is made on the spot by tightening the connection.
Exhibit 8 shows that DI&M is most cost-effective for components such as
open-ended lines and compressor-related pressure relief valves. These com-
ponents are relatively easy to locate, screen, and measure, and have the
potential for significant gas savings. Compressor and non-compressor relat-
ed connections can also be cost-effective to repair. Potential economic ben-
efit from these components, however, may be constrained due to small
average leak rates and higher "find and fix" costs associated with a larger
number of connections. Economic benefits are maximized when "on-the-
spot" repairs, such as tightening a loose fitting, can be performed. For "other
valves," the benefits of a DI&M program depend on the size of the leak, the
potential gas savings, and the repair cost. Exhibit 8 suggests that DI&M is
cost-effective for leaking valves associated with compressors, but may not
be economic for other valves with smaller average leak rates, unless the leak
11
-------
survey and repairs can be incorporated into routine maintenance proce-
dures.
Exhibit 8: Example Economic Analysis of DI&M for Selected Gas
Processing Plant Components
Type of Component
Connections
Pressure
Relief Valve
DEL
Other Valves
Compressor-
Related
Non-
Compressor
Related
Connections
Total
Compressor-
Related
Non-
Compressor
Related
Pressure Relief
Valve Total
Compressor
Slowdown
DEL
Compressor
Starter DEL
Site
Slowdown
DEL
Other DEL—
Non-
Compressor
Related
DEL Total
Compressor-
Related
Non-
Compressor
Related
Valve Total
Total
Cost to
Find&
Fix
$2,455
$7,664
$10,119
$163
$198
$361
$5,015
$1,015
$76
$496
$6,602
$1 ,884
$8,975
$10,859
Gas
Savings
(Mcf/
Comp./Yr)
6.7
6.7
6.7
308
3.9
2,152
1,341
742
43
95
25
Total
Annual
Gas
Savings
(Mcf)
429
1,540
1,970
308
4
312
2,152
1,341
742
215
4,450
855
1,375
2,230
Value
of Gas
Saved
($3.007
Mcf)
$1,287
$4,621
$5,909
$924
$12
$936
$6,456
$4,023
$2,226
$645
$13,350
$2,565
$4,125
$6,690
Cash
Flow
Year!
($1,168)
($3,043)
($4,210)
$761
($186)
$575
$1,441
$3,008
$2,150
$149
$6,748
$681
($4,850)
($4,169)
Cash
Flow
Year 2
$1,287
$4,621
$5,909
$924
$12
$936
$6,456
$4,023
$2,226
645
$13,350
$2,565
$4,125
$6,690
NPV
$2
$1,053
$1,056
$1,455
($160)
$1,296
$6,646
$6,059
$3,794
$669
$17,168
$2,739
($1,000)
$1,739
Payback
Period
(Years)
1.9
1.6
1.7
0.2
16.9
0.4
0.8
0.3
0.3
0.8
0.5
0.7
2.2
1.6
Assumptions: Average repair life is two years. Emissions data represent weighted average component
emissions from EPA/GRI/Radian study and GTI/Clearstone study. NPV discount rate = 10%.
Step 4: Develop a Survey Plan for Future DI&M. The final step in a DI&M
program is to develop a survey plan that uses the results of the initial base-
line survey to direct future inspection and maintenance practices. An effec-
tive DI&M survey plan should include the following elements:
12
-------
Estimated
Savings
* A list of components to be screened and tested, as well as the equip-
ment components to be excluded from the survey.
* Leak screening and measurement tools and procedures for collecting,
recording, and accessing DI&M data.
* A schedule for leak screening and measurement.
* Economic guidelines for leak repair.
* Results and analysis of previous inspection and maintenance efforts,
which will direct the next DI&M survey.
Operators should develop a DI&M survey schedule that achieves maximum
cost-effective methane savings yet also suits the unique characteristics and
operations of their facility. Some partners schedule DI&M surveys based on
the anticipated life of repairs made during the previous survey. Other part-
ners base the frequency of follow-up surveys on company maintenance
cycles or the availability of resources. Since a DI&M program is flexible, if
subsequent surveys show numerous large or recurring leaks, the operator
can increase the frequency of the DI&M follow-up surveys. Follow-up sur-
veys may focus on components repaired during previous surveys, or on the
classes of components identified as most likely to leak. Over time, operators
can continue to fine-tune the scope and frequency of surveys as leak pat-
terns emerge.
The potential gas savings from implementing a DI&M program will vary
depending upon the age and size of the facility, the number and types of
components included in the DI&M program, and operating characteristics of
the facility. Natural Gas STAR partners have found that the initial expense of
a baseline survey is quickly recovered in gas savings. The following are two
examples of the potential savings from a DI&M program. The first example is
a joint EPA/GTI pilot study that looked at four gas plants, and the second is
a study conducted by Natural Gas STAR partner, Dynegy Inc.
Pilot Study of DI&M at Four Gas Processing Plants
Four partner-operated gas plants were selected for a joint EPA/GTI pilot
study of directed inspection and maintenance practices. The facilities ranged
in age from 20 to 50 years. Plant throughput ranged from 60 MMcfd to 210
MMcfd. Leak screening was conducted by soaping and portable hydrocar-
bon gas detectors. Leaking components were tagged and leak rates were
measured using a high volume gas sampler. Exhibit 9 illustrates the estimat-
ed annual volume of natural gas lost as fugitive emissions and the potential
savings for these four plants from implementing DI&M. Some of the key find-
ings of the study include:
13
-------
* The cost of the initial baseline survey in each pilot plant was estimated to
be approximately $1.00 per component, or $15,000 to $20,000 per gas
plant.
* Valves, connectors, compressor seals, and open-ended lines con-
tributed the majority of fugitive methane emissions.
* Less than 3 percent of components were found to be leaking.
* Of all the leaks identified at the individual plants, 50 to 96 were cost-
effective to repair.
* Repair costs ranged from negligible to $5,000, depending on the type of
component and the nature of the repair. Most of the repairs were esti-
mated to have a repair life of two years.
Exhibit 9. Estimated Potential Savings from DI&M at Four Gas
Processing Gas Processing Plants, Pilot Study
Site
1
2
3
4
Total
Site
Fugitive
Emissions
(Mcfd)
123
207
352
211
893
Annual
Volume
of Gas
Lost
(Mcf/yr)
44,895
75,555
128,480
77,015
325,945
Value of
Lost Gas
at $37
Mcf ($/yr)
$134,685
$226,665
$385,440
$231,045
$977,835
% Emissions
Cost-
Effective
to Repair
90%
95%
50%
96%
77%
Baseline
Survey
Cost ($)
$16,050
$14,424
$56,463
$14,168
$101,105
Total Repair
Cost ($)
$44,725
$39,300
$77,900
$43,450
$205,375
Net
Savings
$3/Mcf
($/yr)
$60,442
$161,608
$58,357
$164,185
$444,592
Dynegy Study
Natural Gas STAR partner, Dynegy Inc., conducted a pilot DI&M study at
two gas processing plants. Both plants are large (greater than 50 MMscfd
gas throughput) and approximately 35 years old. One plant processes sweet
gas; the other is a sour-gas processing facility. Leak screening was conduct-
ed using soap bubble tests, portable hydrocarbon detectors, and an ultra-
sound detector. Leak measurement was conducted using a high volume
sampler, and bagging and rotameter measurements for leak rates that
exceeded the upper limit of the high volume sampler. For each identified
leak, cost-effective opportunities to reduce methane emissions were identi-
fied by comparing the cost of repair or equipment replacement with the
value of the gas that would be saved in one year. Exhibit 10 summarizes the
results of this study.
14
-------
Lessons
Learned
Exhibit 10. One Partner's Experience—Dynegy DI&M Pilot Study
Cost of initial baseline survey
Total components surveyed in two plants
Total leaking components
% of leaking components repaired
Total annual methane emissions reductions
Annual savings (at $3/Mcf)
Follow-up surveys planned (based on expected
life of equipment repairs)
$35,000 ($15,000-$20,000 per plant)
30,208
1,156(3.8%)
80% at one facility; 90% at the other
100,OOOMcf/year
$300,000/year
Once every 3 years
DI&M is a proven management practice for cost-effective reduction of
methane emissions. Recent implementation of DI&M at four partner-operat-
ed gas processing plants indicate that DI&M programs have the potential to
significantly reduce methane emissions from the gas processing sector. The
principal lessons learned from Natural Gas STAR partners are:
* The costs of the initial baseline survey can be recovered in gas savings
during the first year. The cost of subsequent surveys can be reduced by
focusing the survey efforts on those components that were identified
through earlier studies as the most likely to leak.
* Partners estimate that the cost of follow-up surveys will be 25 percent to
40 percent less because subsequent surveys will focus only on the
equipment components that are likely to leak and are profitable to repair.
* No two gas processing plants are alike. Opportunities for cost-effective
gas savings will vary widely depending upon such factors as the age
and size of the facility, types of plant components, and the operating
time since the last major plant maintenance.
* A combination of screening and measurement devices can be used to
obtain accurate leak data. A high volume gas sampler is an effective tool
for identifying and quantifying leaks.
* A DI&M program should target the five categories of equipment compo-
nents that contribute to the majority of methane losses: block valves,
control valves, connectors, compressor seals, and open-ended lines.
* If possible, partners should repair the most severe leaks first. Typically
only a few leaking components are responsible for the majority of fugitive
methane emissions.
* Repair costs for components such as valves, flanges, connections, and
open-ended lines are likely to be determined by the size of the compo-
nent, with repairs to large components costing more than repairs to
small components.
-------
* Repair of minor leaks can be incorporated into regular maintenance
practices. Repairs that require shutting down a system may be under-
taken during the next scheduled outage.
* Institute a "quick-fix" step that involves making simple repairs to simple
problems (e.g., loose stem packing, valve not fully closed) during the
survey process.
* Screening or measuring leaking components after repairs are made con-
firms the effectiveness of the repair. Soap bubble screening is a quick
way to check the effectiveness of a repair. Post-repair measurements
with a high volume sampler allow the gas savings to be quantified and
recorded.
* Record methane emissions reductions for each gas processing plant
and/or booster station and include annualized reductions in Natural Gas
STAR Program reports.
Ananthakrishna, S. and Henderson, C., 2002, Cost-effective Emissions
Reductions Through Leak Detection, and Repair, Hydrocarbon Processing,
May 2002.
Clearstone Engineering, 2002, Identification and Evaluation of Opportunities
to Reduce Methane Losses at Four Gas Processing Plants, internal report
prepared under U.S. EPA Grant No. 827754-01 -0 for Gas Technology
Institute, Des Plaines, IL.
Connolly, Jan, Toxic Vapor Analyzers, personal communication.
Frederick, J., Phillips, M., Smith, G.R., Henderson, C., Carlisle, B., 2000,
Reducing Methane Emissions Through Cost-Effective Management
Practices, Oil & Gas Journal, August 28, 2000.
Gas Technology Institute (formerly the Gas Research Institute), personal
communication.
Henderson, Carolyn, U.S. EPA Natural Gas STAR Program, personal com-
munication.
Henderson, C., Panek, J., Smith, M., Picard, D., 2001, Gas-Plant Tests
Reveal Cost-Effective Inspection and Maintenance Practices, Oil & Gas
Journal, May 21, 2001.
Howard, Touche, Indaco Air Quality Services, Inc., personal communication.
McMillan, L.W. and Henderson, C., 1999, Cost-Effectively Reduce Emissions
for Natural Gas Processing, Hydrocarbon Processing, October 1999.
16
-------
Mohr, Gary, UE Systems Inc., personal communication.
Phillips, M. and Lott, R., 1999, Emissions Reductions Can Be Cost-Effective,
Pipeline and Gas Journal, October 1999.
Radian International, 1996, Methane Emissions from the Natural Gas
Industry, Volume 2, Technical Report, Report No. GRI-94/0257.1, Gas
Technology Institute (formerly Gas Research Institute), Chicago, IL.
Radian International, 1996, Methane Emissions from the Natural Gas
Industry, Volumes, Equipment Leaks, Report No. GRI-94/0257.1, Gas
Technology Institute (formerly Gas Research Institute), Chicago, IL.
Tamutus, Terry, Physical Acoustics Corporation, personal communication.
Tingley, Kevin, U.S. EPA Natural Gas STAR Program, personal communication.
17
-------
&EPA
United States
Environmental Protection Agency
Air and Radiation (6202J)
1200 Pennsylvania Ave., NW
Washington, DC 20460
EPA430-B-03-018
October 2003
------- |