Evaluating potential risk of clathrate hydrate formation for the transport of hydrogen-natural gas blends through pipelines

Hydrogen-natural gas blends (HNGB) transport through pipelines is a promising way of economic H2 transport, utilizing the already established pipeline networks. While H2 penetrates the pipeline metal surfaces, limiting its concentration to 20 % can prevent the risk of brittleness. Under typical operating conditions of HNGB transport, clathrate hydrates, crystalline solids of water and gas, would form and cover pipe surfaces, causing large pressure drops and thus considerably reducing the transport efficiency. Although the moisture is primarily removed, it tends to accumulate in the bent or curved sections of pipelines upon intermittent operation based on field experiences. Here, to assess hydrate formation risk in HNGB transport, phase equilibrium conditions of HNGB hydrates were measured by adding 10 % or 20 % H2 into a synthetic model natural gas (CH4 97 %/C3H8 3 %). Adding H2 decreases hydrate formation temperatures by ∼1.5 K, but HNGB hydrates can still form when moisture is present. Adding 15 wt% NaCl decreases hydrate formation temperatures by 7.7 K, implying significant prevention considering typical HNGB transport operating conditions. The excellent reliability of measured data was demonstrated by thermodynamic consistency analysis. Our results will be essential for design of efficient HNGB transport processes and deriving optimal strategies for successful HNGB pipeline operations.