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 ------- |