Gathering Station Module: Measurement Protocol

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1 Gathering Station Module: Measurement Protocol Authors: Dan Zimmerle and Anthony Marchese, Colorado State University Laurie Williams, Fort Lewis College Matthew Harrison, AECOM STATUS: Final Special Note The attached document is the protocol utilized for the study, and was developed prior to field campaign. With the exception of grammatical corrections, the protocol is included intact as it was utilized for the field study, with one exception: 1) Notes have been added where significant deviations from the field plan occurred during operations. These are discussed in more details in the main body of the report. 1.0 Overview This document provides an overview of the field measurement plan for onsite facility level measurements at gathering compressor stations (a.k.a. Gathering and booster stations) in the RPSEA target basin. The overall goal of the RPSEA project is to reconcile aircraft mass balance and facility-based emissions estimates at the facility and sub-basin level. Separate measurement protocols will be utilized for each O&G sector included in the study transmission compressor facilities (downwind measurements only); Gathering facilities (onsite and downwind measurements); distribution facilities (onsite measurements); distribution and gathering pipelines (onsite measurements); and production (onsite and downwind measurements). This document provides an overview of the methane emission measurement collection and conduct of field teams. The specific objective of the gathering system field measurements is to: Quantify total facility-level methane emissions from representative facilities within the Booster and Gathering network, including but not limited to compressor stations, dehydrators, onsite gas treatment activities, and combinations thereof. We shall achieve the project objective by making measurements of methane emissions on a number of partner facilities using source level measurement techniques and controlled dual tracer-flux techniques, (see separate document Booster and Gathering Module: Tracer Flux Ratio Protocol). A fundamental aspect of the project is to pair the two measurement techniques at multiple sites, allowing a comparison of the measurement techniques and, potentially, a better estimate of measurement uncertainty. To the greatest extent possible, measurements will also be conducted contemporaneously with aircraft overflights to emphasize the spatial and temporal alignment between facility-based ground-level measurements and aircraft measurement and mass balance methods, including some aerial sampling at a facility level. Each team in the group will operate, measure and consolidate results independently for each facility measured, maintaining the integrity and independence of the paired measurements. For a small number of facilities, both downwind measurement teams along with a direct measurement team will be made contemporaneously, allowing a comparison of the measurement techniques and, potentially, a better estimate of measurement uncertainty. Contemporaneous measurements are defined as measurements made on the same day with no significant changes in equipment state occurring between the two measurements. 1 P a g e

2 2.0 Measurement Techniques The project will utilize two different, independent measurement methods to estimate methane emissions from booster and gathering facilities: Onsite and Tracer-flux Ratio. These measurements will be made contemporaneous to the greatest extent possible. When possible, measurements will also be coordinated with contemporaneous facility-scale measurements utilizing aircraft methods (not discussed herein). Given temporal variations in emissions, performing same day tracer-flux and onsite measurements is a critical aspect of the study design. Although same day measurements are not truly simultaneous because of the nature of the two measurement techniques (tracer flux provides a snapshot of the facility level emissions at an instant in time while onsite survey often take a day or more to quantify every leak), it should help reduce the effects of changes in operations on the emissions and allow more direct comparison of two independent facility-level emission estimates. Observers will also note any changes in operations and other parameters that might influence emissions during the measurement period. Same day measurements will require coordination between different survey teams. The tracer-flux ratio measurements will be performed by Aerodyne Research, Inc. Onsite measurements will be performed by AECOM. For SWN facilities, AECOM will work in conjunction with a SWN LDAR team to speed up detection and measurement activities. Hereafter, the measurement team, whether AECOM alone or AECOM + SWN teams, will be identified as measurement team. In this section we provide a brief overview of the onsite and tracer-flux techniques and how they will be utilized during the project. 2.1 Onsite measurements and observations Onsite measurements will be performed by a measurement team. The measurement team will conduct comprehensive leak surveys followed by direct measurement of accessible fugitive and vented methane emissions (non-combustion) at natural gas booster/gathering sites in the project sub-basin, between 9/28/15 and 10/16/15. Leak surveys will be performed using a FLIR GasFindIR thermal optical gas imaging (OGI) camera or equivalent. The leak surveys will comprise of a walk around at each site, and inside each building with a potential for gas emissions. A leak is defined as an image of a plume in the OGI camera screen. Emission rates for leaks observed by the OGI camera will be measured primarily with a Bacharach Hi Flow sampler (Hi Flow) except in cases where the vented flow rate exceeds the Hi Flow instrument s upper limit (approximately 8 scfm). In such cases, the vented emission rate will be measured using an alternate approach such as a calibrated bag. Note: In practice, some measurements exceeded the Hi Flow instrument s upper limit, and special measures were taken in modeling to account for these errors. See study publications. Potential emission sources for inclusion of the onsite measurement plan include normal packed and sealed surface equipment leak emissions, such as emissions from flanges, screwed connectors, valve packings, pressure relief valve seats, and open-ended lines. Since large compressors exist at eachgathering station, compressor fugitive emissions will be measured, including the emissions from the unique compressor equipment leak sources such as rod packing vents, blowdown line open ended line (OEL) vents, and starter line OEL vents. Understanding these vents, and tracing these vent lines, will be accomplished with the 2 P a g e

3 assistance of the participant company escort. It is anticipated that access to some of these vents will require elevated manlift access. Emissions from pneumatic controller loops on the site will be measured. Note: During field campaign, it was observed that the actuation frequency of pneumatic controllers was so infrequent that it was not practical to measure them with the resources available. The team will also examine any storage tanks to determine if any emissions are coming from those systems. No measurements are planned for combustion sources, such as compressor engine exhaust, flares, nor dehydrator reboilers (though no dehys are expected at these gathering sites). Note: This was an incorrect assumption during planning. Many of the gathering stations were equipped with dehydrators, and these were measured as documented in study publications. Compressor engine exhaust is known to contain methane, but data from participant company stack tests already performed will be combined with fuel use data collected for that day, to allow an estimate of emissions from engine exhaust. Dehydration system data will include their size, circulation rate, etc. will be collected so that their contribution to the site emission rate can be reasonably estimated. Some gathering compressor stations may be so large that they cannot be measured in one day. In those cases, subsets of the station will be measured (one of a set of identical compressor trains, for example), so that the station can be completed in one day. Leak surveys for compressor sites, will be performed using an Optical Gas Imaging camera such as the methane-tuned FLIR GasFindIR thermal gas imaging camera. The leak survey will comprise of a walk around at each site by a trained camera operator. Emission rates for leaks observed by the OGI camera will be measured primarily with a Bacharach Hi Flow sampler. Pneumatic controller emissions may be measured with an inline flow meter (Fox Flow meter, model #FT2A), or in some cases with a Hi Flow sampler. In cases where the in line flow meter is used, it will be inserted into the power gas supply line to the pneumatic controller, after the partner company escort has temporarily shut off the power gas supply. Once the meter is inserted, the partner company escort will restore flow of power gas to the pneumatic device, and the device will be allowed to operate several minutes without data recording. Data recording will then begin and last for as long as possible while on site. AECOM plans to have 4 such meters, so that 4 pneumatic devices could be read simultaneously. In the case of tanks, the tank top vents, hatches, and pressure relief valves will be scanned by the OGI camera. If emissions are observed, but appear to be small enough to safely measure by Hi Flow, then the team will deploy the Hi Flow sampler. In some cases, access by manlift will be required. If leaks appear to be too large to safely or effectively deploy the sampler, then the downwind teams will be called in to see if they can separate the tanks emissions out as a unique and separately quantified source. If the OTM33A team is unable to do so, the Aerodyne tracer team may be called to perform this task. With the permission from the partner company, digital photographs will be taken of all significantly large or atypical emissions sources and any other sources where photographs would be helpful when analyzing 3 P a g e

4 or reporting the measurement results. Electronic data recorded on the thermal imaging camera and Hi Flow sampler will be backed up before leaving the test sites. As emission sources are observed, the measurement team will qualitatively evaluate each source to estimate an emission rate. Following observation, the measurement team will measure methane emissions from observed emission points within each facility, in order of estimated emission rate. Emission sources that cannot be accessed safely from the ground will be measured if a bucket truck or manlift is available. If an emission sources cannot be measured due to location or other safety issue, the presence of the emission source will be noted in the team s logs, and will be modeled by other means during subsequent analysis. Methane emissions from combustion sources (e.g., compressors, flares, heaters, etc.) will not be measured, however their presence on site will be noted, and data collected. The measurement team will deploy team with at least 3 persons to each test site. One team member will conduct leak detection using the OGI camera, another team member will measure observed leak rates, and the third team member will document the results and ancillary data pertaining to the site and specific leak sources. The onsite team will be accompanied by one CSU observer. Responsibilities of the onsite observer include documenting the site configuration and state of the site during measurement. Noted items will include: 1) Compressor configuration: For each compressor Type of prime movers (make, model, hp), type of seal (wet or dry for centrifugal compressors), vent configuration, the presence of emission control equipment, operating mode, fuel use. 2) Listing of major yard equipment, including dehydrators, condensate tanks, separators, station blowdown events, pig launchers/receivers, gas treatment, etc. 3) Pressure source for pneumatics gas or compressed air. If gas pneumatics, list brand, models, function, location and operating mode (intermittent, low bleed, high bleed), if that can be determined. 4) Significant partner company equipment (e.g. pig launchers) outside the fence line and within visual range. 5) General description of the immediate, visible surroundings of the facility fenceline to be confirmed by partner company operations personnel (at least the first meters), especially any unusual equipment or facilities near the site. 6) Any unusual configurations, any operations that result in maintenance blowdowns during the day of measurement, etc. The on-site observer will also maintain a log of observations as long as either the on-site or tracer team is conducting measurements. The log should note: The status of operating equipment (compressors, engines, standby generators, line pressures, etc.) on at least an hourly basis. If possible, exact start and stop times should be noted in the log. 4 P a g e

5 The operation of intermittent vents, dump valves or other venting operations during the measurement period. If possible exact start and stop times will be recorded. If there is a change in operation status (e.g. compressor start or stop), document sequence of events (e.g. venting) that occur associated with this change in status. Visual and auditory observation and documentation of any noticeable emissions. Site to site differences in operations. Observed leaks will not be repaired, unless the leak presents a safety concern, until after other measurements (tracer, OTM.aerial???) have been completed. It is requested that the partner companies allow the observer to utilize a digital camera on site to record photographic evidence. These photos will not contain any identifying marks which could be utilized to track the photograph to the site where the photograph was taken. Photographs will only be utilized as an internal memory aid during subsequent data analysis and not publically released. 2.2 Tracer-flux ratio Quantifying facility level emissions utilizing a tracer flux ratio is a well-established technique that was developed to quantify the aggregate, facility-level emissions of methane (or other species) from large complex facilities with multiple leak points. It has been demonstrated to accurately quantify the total emissions from natural gas sites (Lamb et al., 1995; Shorter et al. 1997) and landfills (Czepiel et al. 1996). It was used as part of the GRI/EPA methane leakage study in the early 90s. For gathering compressor stations these measurements will be made by one field team (Aerodyne Research). The tracer-flux ratio technique is described in detail in the Tracer-Flux Ratio Protocol document. Briefly, this technique involves releasing two or three tracer gases at a site at a known flow rate. The concentrations of these tracers and the target analyte (methane) are measured downwind of the site. The measured downwind ratios of methane to the tracer gases, in combination with the known tracer release rate, are used to determine the facility-level methane emission rate. Interpreting the data does not require modeling pollutant dispersion - that complexity is captured by the tracers. Key assumptions of the method are 1) the target analyte and tracers undergo equivalent dispersion; 2) there are no unintentional sources of the tracer; and 3) that background-corrected methane concentrations are only due to emissions from the target site. These assumptions are discussed in more detail in the Tracer Flux Ratio Protocol document. The tracer measurement team will work with site personnel to explain and optimize the location of the tracer gas release points. A common plan is to have the N 2O and C 2H 2 release points feet apart from each other. The N 2O is normally placed close to the (expected) main leak sources, while the C 2H 2 tracer is placed some distance away. The goal is to keep the two tracers close together without losing coverage of yard piping, pig launchers, separator tanks and similar equipment. 5 P a g e

6 July Aug Sept Oct Final Report 3.0 Site selection See Screening and Guided Measurement Protocol document for details on screening method and site selection process. 4.0 Onsite Equipment FLIR GasFindIR thermal optical imaging camera Opcal EyeCgas thermal optical imaging camera Bacharach High flow sampler Fox FT2 meters and data systems Digital camera Notebook computer In addition to onsite measurement equipment, the tracer flux measurement teams will also deploy tracer release apparatus at the facility, as noted above. 5.0 Measurement Planning In advance of on-site measurements, CSU has provided a specific data request to study partners to determine which emission sources at the study sites require advanced planning to be adequately tested. 6.0 Proposed Measurement Timeline The measurements will be made during a 3 week measurement campaign beginning on Monday, September 21, 2015 and ending Saturday, October 10, Task Preparation of protocols Review and approval of measurement protocols by RL, TRC, Other? Site selection X X Set up site-access contracts X X Field Measurements X X 7.0 References Czepiel, P. M., Mosher, Shorter, J. H., McManus, J. B., Kolb, C. E., Allwine, E., Lamb, B. K. and Harriss, R.C., Landfill Methane Emissions Measured by Static Enclosures and Atmospheric Tracer Methods, J. Geophys. Res. 101, 16,711-16,719, 1996 Lamb, B., Shorter, J. H., McManus, J. B., Kolb, C. E., Mosher, B. W., Harriss, Allwine, E. J., Blaha, D., Siverson, R., Howard, T., Lott, R. A., Siverson, R., Westberg, H., and Zimmerman, P., Development of Atmospheric Tracer Methods to Measure Methane Emissions from Natural Gas Facilities and Urban Areas, Environ. Sci. Technol., 29, , P a g e

7 Scheutz, C; Samuelsson, J; Fredenslund, A.M.; and Kjeldsen, P. (2011). Quantification of multiple methane emission sources at landfills using a double tracer technique. Waste Management, 31: Shorter, J. H., McManus, J. B., Kolb, C. E., Allwine, E. J., Lamb, B. K., Mosher, B.W., Harriss, R. C., Partchatka, V., Fisher, H., Harris, G. W., Crutzen, P. J. and Karbach, H. J., Methane Emission Measurements in Urban Areas in Eastern Germany, J. Atmos. Chem. 24, , Shorter, J. H., McManus, J. B., Kolb, C. E., Allwine, E. J., Siverson, R., Lamb, B. K., Mosher, B. W., Harriss, R. C., Howard, T. and Lott, R. A., Collection of Leakage Statistics in the Natural Gas System by Tracer Methods, Environ. Sci. Technol., 31, , P a g e