Hydrogen is one of most promising solution for the energy transition. It can be produced through hydrolysis using excess of electricity from renewable sources. In a short-term approach, European gas operators foresee to inject part of produced hydrogen in existing natural gas network. Expected blending volumes between 10%-20% in volume in the next decade looks reasonable when looking at the technical and normative limitations.
When blending hydrogen with natural gas in the existing transmission network, physicochemical properties of the gas mixture is affected. At constant transported standard volume flows, natural gas blended with hydrogen generates less pressure drop in pipeline due to reduced friction. Consequently, existing compression equipment can cope with new mixture without any modification. In addition, though hydrogen is more difficult to compress, the compressor duty is further reduced as hydrogen content increases.
However, energy capacity per volume of hydrogen is much lower than the natural gas. When hydrogen is injected, transported volumes should be increased in order to keep the same available energy capacity at the pipeline output. In such case, it has been observed that existing compressor station can cope with hydrogen content up to 5% volume, using speed and power design margins. Above, compression equipment should be replaced.
Injection of hydrogen in existing natural gas network raises other challenges. Compatibility of hydrogen with materials used in the machine must be investigated carefully. As most of compressor stations in Europe are equipped with integrated oil free motor driven centrifugal compressors, material compatibility investigations must cover also the magnetic bearings and the motor components, as they are in direct contact with the process gas. In absence of evidence of compatibility, it is suggested to perform some experimental validations.