Abstract

Gas Transport System Operators (TSO1) are considering injecting hydrogen gas in their networks. Blending hydrogen into the existing natural gas pipeline network appears to be a strategy for storing and delivering renewable energy to markets [1], [2],[3].

In comparison to methane, hydrogen gas (dihydrogen or molecular hydrogen) has a higher mass calorific value than methane gas. Because of this property, molecular hydrogen is appreciated for space shuttle engines. A second property is that hydrogen gas has a lower mass density than methane gas. The result of the second property is that the volume calorific value is in favor of methane gas. The list of differences between methane and hydrogen is long. In the relevant range of pressures and temperatures, the Joule-Thomson coefficient has a different sign for hydrogen and methane, and the compressibility factor has the opposite trend when the gas is compressed. The dynamic viscosity is also significantly different, and finally, heat capacity, isentropic exponent, and the thermal conductivity are also different.

What are the impacts of these hydrogen characteristics on the transport capacity and its efficiency in the case of blending in a gas transport network?

The first part of the paper is a review of the differences in characteristics between Hydrogen Gas and a Typical Natural Gas in Europe and their impact on the gas flow performance in a pipeline network equipped with compressors.

The second part of the paper is dedicated to pipe segments. And in the third part, compressor stations are introduced between each pipe segment. At each step, an analysis of a mixed gas from one hundred per cent pure natural gas to one hundred per cent pure hydrogen is done.

The paper provides some results for 10 %, 40 %, and 100 % of hydrogen blending in an international pipeline. The study shows that the energy quantity transported at the same pressure ratio is reduced respectively by 4 %, 14 %, and 15 to 20 %, and energy requirement for compression increases respectively by 7 %, 30 %, and 210 % (i.e. it more than triples). To transport the same quantity of energy in a network, assuming the resizing to the same level of optimizations, the energy requirement increases by 11 %, 52 %, and 280 %. In other words, it takes 4 times the energy to transport a given amount of energy if the gas is pure hydrogen than it takes if the gas is pure natural gas.

The paper does not address the issue of equipment or material, it only compares the influence of hydrogen gas on the network capacity and the transport efficiency. This paper doesn’t take into account the limits of the equipment. All equipment is considered as compatible with any load of hydrogen blending.

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