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Mixing and Transporting H2 through the natural Gas Network
Ajah, A.N.; Weeda, M.; Meerwaldt, H.B
Gepubliceerd door: Publicatie datum:
ECN Waterstof en Schoon Fossiel 25-2-2010
ECN publicatienummer: Publicatie type:
ECN-E--10-026 ECN rapport
Aantal pagina's: Volledige tekst:
70  Niet beschikbaar.

Hydrogen is a future energy carrier that has great potential for addressing many practical problems associated with attaining a sustainable, competitive and secure energy future for the European Union. Hydrogen can be produced from many different energy sources including fossil fuels with carbon capture and storage as well as renewables and nuclear power. The problem is how to deliver the required quantity cost-effectively in order to kick-start wider demand and application. This would involve, for example, the use of hydrogen in fuel cells and other technologies to meet transport needs without reliance on imported oil, whilst avoiding problems with air quality and depletion of primary energy resources. One of the delivery options that can be considered is the mixing and transporting of hydrogen using the extensively existing natural gas grids within the European Union (EU). In this regard, significant progress can be made by using the natural gas network as a transitional stage in the creation of the full Hydrogen energy economy. In order to do this, it is necessary to test all critical components of this transitional stage. Such testing is a central feature of the NATURALHY project (Contract No. 502661), which is being funded by the Directorate-General for Research under the 6th Framework Programme of the European Commission. Using a systematic and co-ordinated approach, the NATURALHY project contributes by "preparing for the hydrogen energy economy by using the existing natural gas system as a catalyst". The NATURALHY project involves a European consortium of 39 partners and consists of 8 Work Packages. Work Package 1 (WP1) concerns Life Cycle and Socio-Economic Assessment of mixing and transporting hydrogen using the existing natural gas grid, of which this report is an integral part.

For determining how efficiently and effectively the overall primary energy resource and the total greenhouse gas emissions are minimised by this delivery mode(s), a source-to-user model has been developed in WP1. The model identifies and characterises the complete chain of activities ranging from exploration of primary energy sources to end use of hydrogen. Using this model, the impacts on greenhouse gas emissions and primary energy resource consumption associated with injecting and transporting hydrogen through the natural gas grid have been evaluated and compared with other delivery options.

The other delivery options considered were using a dedicated pipeline for the compressed hydrogen delivery, using trucks in the delivery of hydrogen in compressed form and also using trucks in the delivery of hydrogen in liquid form. Also in the analysis, various hydrogen production routes were considered and included - natural gas with carbon capture and storage (CCS), coal with CCS, nuclear power, wind power and biomass energy. Apart from the production route, the mix of these routes also plays an important role in the primary energy use and emissions. In the light of this, different scenarios of production mix (adapted from the EU HyWays project on hydrogen road-mapping) were used in the analysis. The production mixes basically differ in the share of the renewables and/or fossil based production routes in the total EU hydrogen supply and were developed within the HyWays project.

The difference between the delivery options is that while others emphasise transportation using only hydrogen-dedicated systems, the NATURALHY project concerns injecting and transporting hydrogen, using the natural gas grid with the possibility of extracting it downstream. In this case, where to inject and where to extract the H2 that will minimise primary energy use and emissions becomes an issue. In the analysis of the optimal injection and extraction points (which was conducted using the Dutch natural gas grid as a representative grid), it was concluded that the regional transport line is the optimal point for the injection and extraction of hydrogen. Various separation technologies – membranes, pressure swing absorption (PSA), etc., were considered for the extraction of the injected hydrogen. Based on an assessment of the separation technology, it is concluded that a system consisting of a state-of-the-art polymer membrane unit followed by a PSA unit shows the best outlook for extraction of hydrogen in terms of energy use. In any case, whichever separation technology is used, it is not possible to recover all the hydrogen contained in the natural gas/hydrogen mixture stream.

The overall impact of injecting and transporting hydrogen using the natural gas system on the primary energy use and greenhouse gas emissions not only varies by the choice of injection and extraction points, or the way the hydrogen is produced, but also by the penetration rate of H2 end use application as well as the spatial and temporal domain being considered. The end-use application considered in the impact analysis is hydrogen fuel cell vehicles. In the analysis, assumed penetration rate was again adapted from the HyWays project, and a temporal domain spanning 2010 to 2050 was assumed with the spatial domain being the wider EU. Overall primary energy use and emission reductions associated with producing hydrogen (using a given production -mix), injecting and transporting (though the existing natural gas system as well as other transport modes) it to the consumers (for mobile end use application) is analysed.

The Well-to-Wheels (WtW) primary energy use involved for the case of injecting and transporting hydrogen using the natural gas system is highest compared to the other transport modes. This can be explained from the fact that not all hydrogen can be extracted from the mixture. The remaining hydrogen is not counted as loss, as the calorific value of the hydrogen can still be used. However, the conversion losses associated with production of the remaining hydrogen would not have occurred if it was not necessary for the pure hydrogen to be extracted from the mixture. Therefore, the conversion losses, and all other upstream losses, are all attributed to the pure hydrogen extracted from the grid, thus leading to high overall primary energy use. A highest primary energy use increment of approximately 80% (relative to the reference case ) is reached in year 2050 for the case of transporting hydrogen using the existing natural gas grid.

At the same time, the results show that, not withstanding its higher primary energy use, the case of using the existing natural grid in the transport of H2 for mobile applications has the greatest emission reduction potential, and amounts to a WtW emission (equivalent carbon dioxide; eq. CO2) reduction of approximately 85% compared to the reference scenario. Again, emission reduction potential can be explained from the fact that not all hydrogen can be extracted from the grid. The remaining part replaces natural gas as a fuel and will lead to CO2 emission reduction for the natural gas application downstream in the grid, for example, in a residential boiler, at subsequently low CO2 emission factors of the hydrogen. However, the CO2 emission reduction for the natural gas application only materialises because it was necessary for the pure hydrogen to be extracted from the grid. Therefore, the CO2 emission effect is attributed to the pure hydrogen stream that is used for the hydrogen vehicles. This may lead to great emission reduction potentials if hydrogen is largely produced from renewable sources.

Also, using the assumption that hydrogen vehicles would penetrate the EU-market substantially in the time frame 2020-2050, an alternative production-mix (renewable path production mix) was simulated. The result shows that the emission reduction and primary energy use are most sensitive to the production mix considered. With the most optimistic renewable hydrogen production mix, the results show a WtW greenhouse gas emission reduction (in eq. CO2) of about 88% compared to the reference scenario in 2050. This represents a WtW eq. CO2 reduction of about 3% by 2050, compared to the base case. Also, in terms of primary energy use, the alternative production mix (renewable path production mix) shows a 61% reduction of the primary energy use (in comparison to the base case) could be achieved in 2050 for the case of mixing and transporting H2 using the existing natural grid.

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