Abstract
Renewable electricity can be converted into hydrogen via electrolysis also known as power-to-H2 (P2H), which, when injected in the gas network pipelines provides a potential solution for the storage and transport of this green energy. Because of the variable renewable electricity production, the electricity end-user’s demand for “power when required”, distribution, and transmission power grid constrains the availability of renewable energy for P2H can be difficult to predict. The evaluation of any potential P2H investment while taking into account this consideration, should also examine the effects of incorporating the produced green hydrogen in the gas network. Parameters, including pipeline pressure drop, flowrate, velocity, and, most importantly, composition and calorific content, are crucial for gas network management. A simplified representation of the Irish gas transmission network is created and used as a case study to investigate the impact on gas network operation, of hydrogen generated from curtailed wind power. The variability in wind speed and gas network demands that occur over a 24 h period and with network location are all incorporated into a case study to determine how the inclusion of green hydrogen will affect gas network parameters. This work demonstrates that when using only curtailed renewable electricity during a period with excess renewable power generation, despite using multiple injection points, significant variation in gas quality can occur in the gas network. Hydrogen concentrations of up to 15.8% occur, which exceed the recommended permitted limits for the blending of hydrogen in a natural gas network. These results highlight the importance of modelling both the gas and electricity systems when investigating any potential P2H installation. It is concluded that, for gas networks that decarbonise through the inclusion of blended hydrogen, active management of gas quality is required for all but the smallest of installations.
Highlights
The challenge of reducing Green House Gas (GHG) emissions is a growing global concern as average global temperature continue to rise
The lowest pressure occurred at the maximum demand node and was 45 Barg when only natural gas flowed in pipelines, while, with a 17% hydrogen concentration, the pressure reduced to 42 Barg
The results that are presented in this study demonstrate that, in a well designed natural gas network, the direct blending of green hydrogen is possible without any gas network issues, but consideration must be given to end users down stream of the hydrogen injection
Summary
The challenge of reducing Green House Gas (GHG) emissions is a growing global concern as average global temperature continue to rise. Increasing human consumption patterns, recent wild fires, as well as nearly 90% of the global energy share coming from fossil fuels, can be counted as the major reasons for global GHG emissions, increasing by 11% in the last two decades [1,2]. There is a shift towards Natural Gas (NG), while this is partially due to NG having the lowest carbon emissions, it is primarily due to developments in the shale gas Energies 2020, 13, 6047; doi:10.3390/en13226047 www.mdpi.com/journal/energies. The current contribution of NG to electricity generation in the world is 22%, while, in the EU, this figure is 19% [4]. Like Singapore, 95% of the electricity is generated from NG, while, in Ireland, 50% of the annual electricity is produced by NG and on occasions it can supply up to
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