The natural gas grid could provide the key to unlock the long talked-about potential of the hydrogen economy says Henri Winand.
With fuel cell vehicles now on the forecourts, hydrogen is being enthusiastically promoted as a clean, efficient and sustainable energy source.
As we journey towards a society where it forms a major part of the energy landscape across a wide range of sectors, alternative methods of delivering hydrogen to a variety of users are being explored. Sceptics of hydrogen technology often point to the lack of existing infrastructure as a major barrier to the adoption of hydrogen as a fuel adoption and in one sense they are right: it is a challenge that needs to be addressed.
A viable hydrogen infrastructure requires that hydrogen be delivered from where it's produced to the point of end-use, such as a dispenser at a refuelling station or a stationary power generator.
Blending hydrogen into the existing natural gas pipeline network has been proposed as an effective means of delivery. Using the existing system to transport mixtures of natural gas and hydrogen would offer the possibility of accommodating significant volumes of hydrogen. It also represents a unique opportunity to connect hydrogen producers and end users with relatively little significant additional investment in infrastructure.
This approach negates the high cost of implementing a purpose built hydrogen pipeline infrastructure – estimated to be several thousand billion Euros – by utilising existing assets. Hydrogen blended in this way can also be used to bulk out natural gas supplies in conventional gas to power operations with the potential to significantly improve efficiency.
From an environmental perspective, adding hydrogen to natural gas could significantly reduce greenhouse gas emissions, though only if the hydrogen is produced from low-carbon energy sources, for example by spare capacity from renewables, bio-waste or fossil resources with carbon capture and storage (CCS).
Work on making the transition possible has actually been ongoing for some time now. It was more than five years ago that the NATURALHY-project, a pan-European effort supported by member states, business and academia, demonstrated the viability of mixing hydrogen with natural gas. The project’s aim was to provide the natural gas industry and pipeline operators with the necessary information to enable the sector to accommodate hydrogen in the existing natural gas grid. According to Energy Storage Europe, the proportion of hydrogen that could be blended with natural gas in modern grids is as high as 15% in the midterm. In the United States, a report commissioned by the US Department of Energy on blending hydrogen into natural gas pipelines found that the concept was a viable long term solution:
“Blending hydrogen into natural gas pipeline networks at low concentrations has the potential to increase output from renewable energy production facilities in the near term. In the longer term, blending may provide an economic means of hydrogen delivery when the hydrogen is injected upstream and then extracted downstream for use in fuel cell electric vehicles (FCEVs) or stationary fuel cells.”
Unfortunately, because the physical and chemical properties of hydrogen differ significantly from those of natural gas, it is not possible to simply exchange natural gas for hydrogen in the existing natural gas system. One limiting factor is the durability of existing pipelines. Some metal pipes can degrade when they are exposed to hydrogen over long periods, particularly with hydrogen in high concentrations and at high pressures. The effect is highly dependent on the type of steel and must be assessed on a case-by-case basis. Making the necessary modifications to strengthen pipelines would be costly, but they pale in comparison to constructing an entirely new network.
The US Department of Energy highlights three primary downstream gas-separation technologies that could be used to isolate hydrogen from mixtures in natural gas pipelines: pressure swing adsorption (PSA), membrane separation, and electrochemical hydrogen separation (EHS, or hydrogen pumping). The best extraction method depends on the blend of hydrogen in the pipeline.
Higher concentrations bring the cost of extraction down under pressurised conditions, though they are still on the high end or above what would be considered competitive for the FCEV market. At pressure reduction facilities, they fall even further. As the report outlines: “the pressure drop is synergistic with hydrogen separation”. The lack of a pressure drop requires uneconomically large amounts of compression energy and compressor capital to reinject hydrogen-depleted gas back into a pipeline.
But extraction from the grid is not strictly necessary either. Hydrogen can be used to bulk out natural gas and can be burned along with it at a power station. Hydrogen is carbon free, therefore emissions at that plant will be lower and, because it burns at a higher temperature, the gas turbine runs hotter and is therefore more efficient.
Japan is in the process of constructing 100 hydrogen filling stations alongside the main roads connecting four of its biggest cities, according to the Financial Times. Germany is aiming for 400 stations by 2025. One option being explored is the capacity to generate hydrogen at the refuelling station, using wind or solar power, to dispense the gas at source. The downstream infrastructure for hydrogen is expanding quickly, so upstream capacity must develop rapidly too.
As an industry we must explore all avenues for delivering an efficient hydrogen infrastructure. The research has been conducted to demonstrate feasibility; we must now turn that into practical solutions. Henri Winand, chief executive, Intelligent Energy