(701b) Decarbonizing Natural Gas Sector: Natural Gas/Hydrogen Blends and Synthetic Gas Production Pathways

Natural gas (NG) is widely used across all energy sectors. Combustion of fossil NG leads to significant greenhouse gas (GHG) emissions. It is estimated that NG was responsible for approximately 30% of the total U.S. GHG emissions in 2021. Replacing NG with cleaner alternatives, such as hydrogen (H₂) produced from renewable or low-carbon sources, could have substantial impacts on decarbonizing U.S. energy sectors. While H₂ can play an important role in such decarbonization, the infrastructure for H₂ transportation is costly in the early markets and is yet to be fully developed. One promising option to decarbonize the NG supply chain and mitigate the lack of hydrogen delivery infrastructure is to inject clean H₂ into the NG pipeline networks to deliver a blended NG/H₂ gas. In this work, we conducted a quantitative analysis to estimate life cycle GHG emissions associated with delivering blended gas in an existing NG transmission pipeline. While a significant reduction in life cycle GHG emissions can be achieved when delivering the same NG baseline volume throughput of blended gas but at a reduced energy flow, maintaining the energy throughput will likely limit the maximum life cycle emissions reduction to about 6% as the H₂ blending ratio will likely be constrained to approximately 30 mol% due to pipeline operating limitations. Further reduction in GHG emissions of gas blend while maintaining energy throughput would likely require modification of the NG pipeline infrastructure. Alternative to use of H₂ for blending with NG, H₂ may be used to produce synthetic natura gas (SNG) utilizing captured CO₂, thus bypassing the infrastructure hurdles associated with gas blending. In this study, we developed an engineering model of SNG production at an industrial scale to investigate its levelized cost and life cycle GHG emissions. Depending on the CO₂ supply chain, the levelized cost of SNG is estimated to be in the range of $45–76 per million British thermal units (mmBtu) on a higher heating value basis. SNG can also reduce life cycle GHG emissions by 52–88% compared with fossil NG.