Since hydrogen produces no carbon dioxide when burned, it is the current focus of considerable attention for reducing greenhouse gas emissions. One of the most difficult issues that arises from the widespread use of hydrogen is the transportation of hydrogen to end-user markets. Utilizing the United States’ vast network of existing natural gas pipelines has obvious appeal. In fact, the U.S. Department of Energy is interested in this possibility and has requested proposals for funding the necessary research to allow hydrogen to be transported as mixtures in natural gas pipelines.

Adding hydrogen to natural gas in pipelines will have many effects that need to be addressed such as material selection/hydrogen content to avoid hydrogen embrittlement, design of compressors for hydrogen mixture combustion, efficient separation of hydrogen/natural gas mixtures, and changes in pipeline operations.

This paper is focused on the changes that will occur for steady-state and transient pipeline operations. First, the estimation of density, is addressed via comparison of the predictions of typical cubic equations of state, AGA8, and the latest high-accuracy equations of state to experimental data. Second, steady-state pipeline operations are considered, focusing on the effect of increasing hydrogen on capacity, compression requirements, and heat transfer. Finally, the effect of increasing hydrogen content on the transient operations of packing and unpacking is considered.

Introduction and Background

Given the extensive, existing pipeline network in the U.S., there is definitely an opportunity to transport hydrogen. However, the addition of hydrogen to natural gas feed poses several uncertainties in terms of technical feasibility. Three questions are of interest:

1. What is the most appropriate Equation of State (EoS) that can model gas feed with high hydrogen content and what are the differences between different models?

2. What is the effect of hydrogen on capacity and compression requirements?

3. What is the effect of increasing hydrogen content on line pack (volume of gas in the pipeline at any given time) during transient events?

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