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Home My WebLink AboutDAQ-2024-010549Pneumatic Controller Emission Factor Update (2024) The Utah Division of Air Quality (UDAQ) is continuously working to improve the oil and gas emissions inventory. An improved emissions inventory leads to better modeling, pollution controls, and helps UDAQ with emission reduction strategies in non-attainment areas such as the Uinta Basin. At this time, UDAQ believes it is appropriate to update the pneumatic controller emission factors to improve the inventory. The basis for the currently used factors is the Environmental Protection Agency’s (EPA) November 8, 2010, 40 CFR Part 98, Subpart W, (Subpart W)1 which is part of the Greenhouse Gas Reporting Program (GHGRP) rules. This provided the whole gas emission factors for pneumatic controllers. In EPA’s “Oil and Natural Gas Sector: Standards of Performance for Crude Oil and Natural Gas Production, Transmission, and Distribution”2, the Volatile Organic Compound (VOC) factors can be found for high-bleed, intermittent, and low-bleed pneumatic controllers. Figure 1. GHGRP with initial VOC conversion method (0.0208 ton CH4/Mcf CH4 conversion factor in footnote b to table 5-2 and 0.278 ton VOC/ton CH4 from Section 5.2.2 of EPA’s “Oil and Natural Gas Sector: Standards of Performance for Crude Oil and Natural Gas Production, Transmission, and Distribution” document). Pneumatic Controller Type Whole Gas Factor (std ft3/device/hr) VOC Factor (tons/device/yr) Low Bleed Continuous Bleed 1.39 0.072 High Bleed Continuous Bleed 37.3 1.92 Intermittent Bleed 13.5 0.698 Figure 2. The equation for calculating the pneumatic controllers as part of the GHGRP Where: Es,i = Annual total volumetric GHG emissions at standard conditions in standard cubic feet per year from natural gas pneumatic device vents, of types “t” (continuous high bleed, continuous low bleed, intermittent bleed), for GHGi. Countt = Total number of natural gas pneumatic devices of type “t” (continuous high bleed, continuous low bleed, intermittent bleed) as determined in paragraph (a)(1) or (a)(2) of this section. EFt = Population emission factors for natural gas pneumatic device vents (in standard cubic feet per hour per 1 https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-98/subpart-W 2 https://nepis.epa.gov/Exe/ZyNET.exe/P100CHTC.TXT?ZyActionD=ZyDocument&Client=EPA&Index=2011+Thru+201 5&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=& QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data %5C11thru15%5CTxt%5C00000000%5CP100CHTC.txt&User=ANONYMOUS&Password=anonymous&SortMethod= h%7C- &MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeek Page=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&See kPage=x&ZyPURL device) of each type “t” listed in Tables W–1A, W–3B, and W–4B to this subpart for onshore petroleum and natural gas production, onshore natural gas transmission compression, and underground natural gas storage facilities, respectively. Onshore petroleum and natural gas gathering and boosting facilities must use the population emission factors listed in Table W–1A to this subpart. GHGi = For onshore petroleum and natural gas production facilities, onshore petroleum and natural gas gathering and boosting facilities, onshore natural gas transmission compression facilities, and underground natural gas storage facilities, concentration of GHGi, CH4 or CO2, in produced natural gas or processed natural gas for each facility as specified in paragraphs (u)(2)(i), (iii), and (iv) of this section. In 2017, UDAQ updated the intermittent pneumatic controller whole gas bleed rate from 13.5 std ft3/device/hr to 1.72 std ft3/device/hr. In the document titled “UDAQ Response to EPA Comments on Changing the Intermittent Pneumatic Controller Emission Factor for the Utah Air Agencies 2014 Emissions Inventory”3, the intermittent bleed whole gas emission factor was updated. Figure 3. 2017 Updated Intermittent Bleed Factor (still using VOC conversion method described in Figure 1) Pneumatic Controller Type Whole Gas Factor (std ft3/device/hr) VOC Factor (tons/device/yr) Low Bleed Continuous Bleed 1.39 0.072 High Bleed Continuous Bleed 37.3 1.92 Intermittent Bleed 1.72 0.086 In 2020, the Uinta Basin Composition Study (UBCS)4 was published. In 2020 (revised 2022) the Uinta Basin VOC Composition Study Impacts on the 2017 Oil and Gas Emissions Inventory5 was released. Based on the Uinta Basin Composition study, the emission factors for pneumatic controllers were updated. The whole gas bleed rates remained the same but the VOC to whole gas ratio was updated. This update increased the VOC emissions by 41% for each pneumatic controller type. Figure 4. 2020 Updated Factors Based on the UBCS Pneumatic Controller Type Whole Gas Factor (std ft3/device/hr) VOC Factor (tons/device/yr) Low Bleed Continuous Bleed 1.39 0.10 High Bleed Continuous Bleed 37.3 2.71 Intermittent Bleed 1.72 0.12 In 2023, an oil and gas emissions inventory consultant brought up an issue with using EPA’s “Oil and Natural Gas Sector: Standards of Performance for Crude Oil and Natural Gas Production, Transmission, and Distribution” document due to a potential misuse of a standard cubic feet (scf)- methane (CH4)/hour (hr) use instead of scf-whole gas/hr. Additionally, when reviewing the Subpart W-based emission factor equation, the CH4 scf/Whole Gas scf ratio was not well defined and did not make mathematical or 3 https://documents.deq.utah.gov/air-quality/planning/technical-analysis/research/oil-and-gas/DAQ-2017- 011497.pdf 4 https://documents.deq.utah.gov/air-quality/planning/technical-analysis/DAQ-2020-004826.pdf 5 https://lf-public.deq.utah.gov/WebLink/DocView.aspx?id=386291&repo=Public&searchid=53e7d8a0-56bc-4ab4- a42d-ae8863add414&cr=1 chemical sense as the calculation implied that there was more CH4 in whole gas than whole gas (the ratio appeared to be 1.02 CH4 scf/Whole Gas scf). When this potential issue was brought to the attention of EPA, EPA suggested using Equation 51 (Figure 5) from the Eastern Research Group’s (ERG) 2020 Nonpoint Oil and Gas Emission Estimation Tool Version 1.36 that was prepared for EPA. Using this new equation would eliminate the prior CH4/whole gas ratio issue, and also allow UDAQ to use Uinta Basin-specific atmospheric pressure and temperature as well as the molecular weight of the gas. Figure 5. Equation 51 from ERG’s 2020 Nonpoint Oil and Gas Emission Estimation Tool Version 1.3 UDAQ will continue to use the whole gas intermittent bleed rate based on the 2017 “UDAQ Response to EPA Comments on Changing the Intermittent Pneumatic Controller Emission Factor for the Utah Air Agencies 2014 Emissions Inventory”7. With the new equation and data from the Uinta Basin Composition Study, UDAQ can also make site-specific emission factors based on whether a facility is primarily an oil or gas production facility. In the UBCS, there is a notable difference in the VOC/whole gas composition when comparing oil and gas facilities. When separating the emission factors, emissions from gas facilities decreased while oil facilities increased. Having separate factors for oil and gas facilities will improve emissions allocations, enhance modeling, and help target emissions reductions more accurately. The new emission factors based on ERG’s method along with separating emission factors by production type and their relative impacts are listed in Figure 6. 6 https://www.epa.gov/system/files/documents/2024-02/2020-nonpoint-oil-and-gas-emission-estimation-tool- v1_3.pdf 7 https://documents.deq.utah.gov/air-quality/planning/technical-analysis/research/oil-and-gas/DAQ-2017- 011497.pdf Figure 6. 2024 New Pneumatic Controller Factors and Impact Pneumatic Controller Type Whole Gas Factor UBCS VOC Factor New VOC Factor New Factor % Increase/Decrease (std ft3/device/hr) (tons/device/yr) (tons/device/yr) Low Bleed Continuous Bleed Gas Facility 1.39 0.102 0.04 -62% Low Bleed Continuous Bleed Oil Facility 1.39 0.102 0.11 5% High Bleed Continuous Bleed Gas Facility 37.3 2.708 1.04 -61% High Bleed Continuous Bleed Oil Facility 37.3 2.708 2.86 6% Intermittent Bleed Gas Facility 1.72 0.121 0.005 -96% Intermittent Bleed Oil Facility 1.72 0.121 0.13 9% Ultimately, the purpose of adopting these new emission factors is to help better quantify our emissions inventory. These factors may be used to adjust previous/future inventories and submittals to the NEI (National Emissions Inventory).