Assessing fugitive emissions of CH4 from high-pressure gas pipelines in the UK

Ian M Boothroyd,Sam Almond,Fred Worrall,Rosemary K Davies,Richard J Davies

doi:10.1016/j.scitotenv.2018.02.240

Ian M Boothroyd, Sam Almond + Show 3 more

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https://doi.org/10.1016/j.scitotenv.2018.02.240

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Abstract

Natural gas pipelines are an important source of fugitive methane emissions in lifecycle greenhouse gas assessments but limited monitoring has taken place of UK pipelines to quantify fugitive emissions. This study investigated methane emissions from the UK high-pressure pipeline system (National Transmission System - NTS) for natural gas pipelines. Mobile surveys of CH4 emissions were conducted across four areas in the UK, with routes bisecting high-pressure pipelines (with a maximum operating pressure of 85bar) and separate control routes away from the pipelines. A manual survey of soil gas measurements was also conducted along one of the high-pressure pipelines using a tunable diode laser. For the pipeline routes, there were 26 peaks above 2.1ppmv CH4 at 0.23peaks/km, compared with 12 peaks at 0.11peaks/km on control routes. Three distinct thermogenic emissions were identified on the basis of the isotopic signal from these elevated concentrations with a peak rate of 0.03peaks/km. A further three thermogenic emissions on pipeline routes were associated with pipeline infrastructure. Methane fluxes from control routes were statistically significantly lower than the fluxes measured on pipeline routes, with an overall pipeline flux of 627 (241–1123 interquartile range) tonnes CH4/km/yr. Soil gas CH4 measurements indicated a total flux of 62.6ktCH4/yr, which equates to 2.9% of total annual CH4 emissions in the UK. We recommend further monitoring of the UK natural gas pipeline network, with assessments of transmission and distribution stations, and distribution pipelines necessary.

Highlights

IntroductionIncorporated within life-cycle assessments are transmission and distribution losses, including infrastructure such as pipelines and compressor stations that pressurize natural gas for transport along pipelines
This comparison is undertaken with available studies on leaks from pipelines but distribution pipelines in cities compared with high-pressure pipelines in predominantly rural areas must be considered to be limited as they do not operate under the same pressure
It is difficult to place the results of this study in context for transmission systems, in terms of UK emissions given that most studies focus upon USA city mains and service distribution systems that operate at lower pressure and often comprise different construction materials

Summary

Introduction

Incorporated within life-cycle assessments are transmission and distribution losses, including infrastructure such as pipelines and compressor stations that pressurize natural gas for transport along pipelines. Weber and Clavin (2012) downgraded the Howarth et al (2011) loss rate to 0.8–2.2% for transmission only but cited the same concerns of the above studies; Stephenson et al (2011) calculated fugitive emissions using facilitylevel factors for transmission pipeline from the 2009 API Compendium (API, 2009) and found a loss rate for transmission pipelines of 0.066% over 1440 km transportation distance. While life-cycle emissions inventories provide insights into fugitive emissions of CH4 across the oil and gas sector, it is important to quantify losses based upon observations from monitoring data including components of the transmission and distribution system

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