An Investigation into the Volumetric Flow Rate Requirement of Hydrogen Transportation in Existing Natural Gas Pipelines and Its Safety Implications

Abstract

As an alternative to the construction of new infrastructure, repurposing existing natural gas pipelines for hydrogen transportation has been identified as a low-cost strategy for substituting natural gas with hydrogen in the wake of the energy transition. In line with that, a 342 km, 36″ natural gas pipeline was used in this study to simulate some technical implications of delivering the same amount of energy with different blends of natural gas and hydrogen, and with 100% hydrogen. Preliminary findings from the study confirmed that a three-fold increase in volumetric flow rate would be required of hydrogen to deliver an equivalent amount of energy as natural gas. The effects of flowing hydrogen at this rate in an existing natural gas pipeline on two flow parameters (the compressibility factor and the velocity gradient) which are crucial to the safety of the pipeline were investigated. The compressibility factor behaviour revealed the presence of a wide range of values as the proportions of hydrogen and natural gas in the blends changed, signifying disparate flow behaviours and consequent varying flow challenges. The velocity profiles showed that hydrogen can be transported in natural gas pipelines via blending with natural gas by up to 40% of hydrogen in the blend without exceeding the erosional velocity limits of the pipeline. However, when the proportion of hydrogen reached 60%, the erosional velocity limit was reached at 290 km, so that beyond this distance, the pipeline would be subject to internal erosion. The use of compressor stations was shown to be effective in remedying this challenge. This study provides more insights into the volumetric and safety considerations of adopting existing natural gas pipelines for the transportation of hydrogen and blends of hydrogen and natural gas.

The role of ammonia as an alternative fuel by mixing it into natural gas and satisfying the gas quality requirements

“…By mixing ammonia into NG, the compression factor, LHV, and WI are reduced. The compression factor is an important parameter in the flow of gases through pipes, where a too big variation in the compressibility factor can be a challenge for the media flowing in the pipeline 49 . When ammonia was added into the different NG compositions, the change in compression factor was minor and it is not a concern for the investigated cases.…”

“…The compression factor is an important parameter in the flow of gases through pipes, where a too big variation in the compressibility factor can be a challenge for the media flowing in the pipeline. 49 When ammonia was added into the different NG compositions, the change in compression factor was minor and it is not a concern for the investigated cases. Instead, the decrease in the LHV with addition of ammonia can be a concern, since a bigger volume flow is needed to keep the same energy content as the original gas.…”

Ensuring natural gas infrastructure is suitable for hydrogen service

“…Simulations of velocity profiles in blended HCNG fuels have revealed that hydrogen may be safely blended up to 40% by volume. Once the hydrogen content increases above 40%, the erosional velocity limit is met for most pipeline materials and transportation of blended fuel above this concentration can become unsafe for most applications 36 . The gas compressibility factor ( z ), which changes based on the percentage of H 2 in the HCNG blended fuel, is also relevant.…”

Hydrogen Blending into Natural Gas Pipeline Infrastructure: Review of the State of Technology

“…Previous literature has extensively examined the performance impacts of injecting hydrogen into the natural gas transmission pipelines (Schouten 2004;Blacharski et al 2016;Witkowski et al 2018;Zabrzeski et al 2019;Kuczyński et al 2019;Abbas et al 2021). Just as mixture thermodynamic and transport properties discussed in Section 2 change with increasing blends of hydrogen, so do pipeline operating conditions.…”

“…Erosional velocity also increases for less-dense gas mixtures; as a result, this velocity is not approached in constant volume flow rate scenarios where hydrogen content increases (American Society of Mechanical Engineers 2019). This constraint may be relevant for maintaining energy delivery via increasing gas flow rates, because increased pressure drop along the pipeline will lead to increased gas velocities (Abbas et al 2021). Erosional velocity constraints may also be relevant for constant pressure drop operation, because the increase in volumetric flow rate with hydrogen concentration for constant pressure drop scenarios seen in Bainier and Kurz (2019) could only be achieved via an increase in flow velocity.…”