Life Cycle Greenhouse Gas Emissions of Conventional and Coal Seam Gas LNG

Abstract

Abstract As the world moves towards cleaner forms of energy worldwide, gas will have an increasingly important role to play in the future energy mix. From this perspective, there has been growing interest in the relative greenhouse gas (GHG) intensities of a range of fossil fuels, and how various forms of LNG compare to not only coal, but also to renewables and nuclear across their life cycles. These issues are important for energy and GHG policy, especially with developments in carbon pricing. However, until recently there has been little information on the life cycle GHG emissions from Australian fossil fuel exports. This paper helps to complete the picture. Using a wide range of available data from government submissions by industry and the authors’ own project experience, life cycle GHG emissions estimates were developed for LNG derived from conventional natural gas sourced from Western Australia's North West Shelf and Queensland coal seam gas (CSG). A comprehensive assessment of GHG emissions was made for upstream operations, LNG production, transport, regasification, and end-user combustion for electricity generation (assumed to be in China). These life cycle emission estimates were compared to life cycle emissions for Australian black coal exported to China and used to generate electricity. Comparisons were also made with renewables and nuclear. The results show that the life cycle GHG intensity (tCO2-e/MWh) of electricity sent out is highly sensitive to the thermal efficiency of the end-use combustion technology. For most comparison scenarios, natural gas-fired power generation is less GHG intensive than black coal-fired power generation. The differences range from 17% to 56% less intensive for a variety of plant efficiencies. In some cases, coal was marginally less GHG intensive when comparing open-cycle gas technology with ultra-supercritical coal combustion. LNG derived from CSG was also found to be more GHG intensive than conventional gas. Modelling of upstream methane fugitive emission scenarios from CSG (using 100-year and 20-year methane Global Warming Potentials) had little impact on the life cycle GHG intensity rankings, such is the dominance of end-use combustion. When exported to China for electricity production, LNG was found to be 22–36 more GHG intensive than wind and concentrated solar thermal (CST) power and 13–21 times more GHG intensive than nuclear power