Gas Technology Institute (GTI), with project partners AECOM, GHD Services, Inc., and Washington State University will improve the characterization of methane emissions from the natural gas distribution system. The project will focus on emissions from industrial meters in the natural gas distribution system, differences between vintage and new plastic pipelines, and gather data to compare steel and cast iron pipelines with and without plastic liners. The project team will conduct an unprecedented assembly of existing and new field data on methane leaks that will feed advanced statistical methods to offer a new perspective on methane emissions, the metrics/categories used to estimate emissions, and techniques used to curb those emissions.
Gas Technology Institute, Des Plaines, IL 60018
To meet the Nation’s Climate Action Plan goal of reducing emissions 40–45% below 2012 levels by 2025 requires a comprehensive understanding of the emissions profile from the entire natural gas infrastructure to enable cost-effective and efficient identification and control of methane emissions. This project will contribute to one piece of the research needed to provide input into a cohesive strategy for greenhouse gas reduction. The EPA Greenhouse Gas Inventory (GHGI) estimates are used to drive environmental policy and regulations at the federal level, which directly impacts individual natural gas customers, rate payers. By reducing uncertainty and improving the characterization of methane emissions from the gas industry, appropriate regulations will be made, the cost of compliance will be reduced, and the savings will be passed on to the rate payers.
The research will have a significant impact on the national estimates of methane emissions from the natural gas industry. It is intended that the improved Emissions Factors and activity data will be incorporated into EPA’s annual GHGI. The proposed project will also identify specific metrics to be tracked at a company level so operators can prioritize the repair of their non-hazardous leaks to maximize the reduction of methane emissions. Studies have shown fat-tailed emissions can be responsible for up to 50% of total emissions. By identifying these leaks, operators can more efficiently reduce the environmental impacts of their system. The results from the study will also improve the activity data estimates for specific sources such as industrial meters and distribution pipelines. This can help individual companies develop targeted leak repair programs for non-hazardous leaks to optimize emissions reductions. Specifically, the data collected on emissions from cast iron and unprotected steel with plastic liners will help determine if this is an effective practice for reducing leaks. It could then be made into practice in the field and possibly support the creation of a different classification for this type of pipeline to promote the use of these liners as a method of reducing emissions. A reduction in leaks also improves safety for customers and the public.
The project included 10 planned weeks of industrial meter measurements in all 6 regions nationally along with 3 weeks of revisiting already sampled meters. Overall, GTI visited over 400 individual industrial meter sets and revisited approximately 100, conducting detailed leak surveys and component counts. During seven of the sampling weeks, GTI focused on maximizing the number of sites visited, only quantifying leaks that indicated 45% lower explosive limit (LEL) concentration or higher. For three of the sampling weeks, GTI quantified every leak that presented at 100 ppm or higher to better understand all leaks coming from this category.
A total of 24,670 components were examined across six regions for six types of industrial/commercial meter sets (Rotary, Turbine, Diaphragm, Orifice, Ultrasonic, and Regulating Equipment), across ten different companies and at a mix of various types of industrial and commercial facilities within the sector. Of the components scanned, 1,474 components had a leak indication above 100 ppm, resulting in emission rate quantifications for 458 individual components nationwide. Emission rate data distributions for individual components were right-skewed and heavy-tailed, indicating that a small subset of leaks was driving overall emissions from this category. Caps, meters, and regulators had the highest mean emission factors (EF) for all component types.
The current EF used in the GHGI for a combined nationwide industrial/commercial meter category is 9.7 kg CH4 meter-1 yr-1. The data from this study indicated that this nationwide value may be closer to 78.9 kg CH4 meter-1 yr-1. Also, there were differences in EFs calculated for each of the six geographical regions indicating that EFs would be more representative if delineated by region. Turbine meters were emitting larger amounts of CH4 than rotary and diaphragm meters (indicated by the higher EF), and significant differences were observed in EFs calculated for industrial facilities and commercial facilities. It is therefore recommended that regional EFs be separated by industrial and commercial and then by region and main meter set types (turbine, diaphragm, rotary). The data revealed that industrial/commercial meters included heavy-tailed emitters that caused significant impact on emission rates and thus EFs. Addressing these “heavy-tailed” emitters (top 10% of leaks) presents an important opportunity for emission reductions and EF reductions for Natural Gas (NG) distribution companies.
Ten three-to-five-day field sampling campaigns were conducted in five of the six geographical regions across the U.S. to study potential differences between CH4 emissions from buried modern and vintage plastic pipe. Field sampling was conducted using a Hi Flow sampler and surface enclosure, with vintage plastic pipe defined and categorized as being installed prior to 1986 and modern plastic pipe as installed after 1986. The team screened 339 potential underground leak sites with emission rates quantified from 186 of the sites. Of these 186 quantified leaks, GTI was able to verify that 103 leaks were located on either modern or vintage plastic pipe, with 45 leaks measured on modern plastic pipe and 58 measured on vintage pipe.
Field data was used to develop mean leak rate comparisons for both modern and vintage plastic pipe, delineated by region. After removal of one vintage pipe emission rate outlier, mean emission rates for the two types of pipe were similar, with modern plastic having a mean emission rate of 40.9 ± 83.2 g h-1 and vintage plastic having a mean emission rate of 48.7 ± 78.4 g h-1. Therefore, this data (although limited) suggests that differences in leak rates between modern and vintage plastic pipe are insignificant. However, the limited sample size and/or removal of one outlier data point for vintage plastic pipe could indicate that either heavy-tailed emissions are more prevalent in vintage plastic pipe or outliers for the modern plastic pipe were undetected due to the small sample size. GTI conducted one field campaign to survey 10,031 feet of cast iron and steel mains lined with cured-in-place-plastic liners and did not locate any leaks on the specific segments of plastic lined pipe. The lack of leaks on these segments, coupled with few or no leaks in partner companies records of leaks on these types of pipe, has caused GTI (with the approval of DOE) to shift focus away from these types of pipe for this project.