After many years of talk but no action, significant steps are finally being taken toward realizing a hydrogen-based energy ecosystem.
One such effort involves leveraging existing natural gas transmission infrastructure as a highway on which decarbonization concepts can gain velocity.
A veritable rainbow of renewable hydrogen sources is being aggressively explored in search of the scale and efficiency needed to reduce—or even reverse—the carbon intensity of other feedstocks and energy sources.
But the transportation of pure hydrogen presents a serious problem.
Liquifying it for transport is expensive and energy intensive, and the extremely low temperatures required make it difficult to do at a small scale.
Natural gas pipeline systems—the product of a century of innovation and investment—present an attractive option for connecting distributed hydrogen production with end users by blending it with existing natural gas flows.
We are primarily speaking of blue and green shades of hydrogen that have a very low carbon intensity since, to play a meaningful role in decarbonization, the hydrogen must be produced using a low carbon energy source.
We are keenly aware of the “studies” showing that the carbon impact of a Tesla run on coal-based power has an unfavorable footprint compared to an equivalent ICE vehicle.
The Evil ‘E’
Embrittlement is another nemesis of hydrogen transportation.
It refers to mechanical damage caused by the penetration of hydrogen molecules into metal (notably steel), causing a loss of ductility and tensile strength.
The smaller size of the hydrogen molecule relative to methane molecules severely limits operators’ ability to transmit H2 in older natural gas pipelines at meaningful concentrations.
Experiments conducted with hydrogen concentrations as low as 5% have shown that older pipelines have a much greater propensity to crack or fail.
At 15-20% hydrogen concentration, even recently installed pipelines show signs of rapid deterioration.
Multiple approaches are being considered to retrofit coatings to existing pipes and reduce the potential impact of this evil ‘E’.
For large-scale infrastructure—and especially buried pipelines—this means identifying functional, cost-effective coatings and delivery methods that can operate at near-ambient conditions without requiring heat to cure them.
Several polymers developed for the food packaging industry offer the right combination of low cost and low gas permeability, including ethylene vinyl alcohol (EVOH), polyvinylidene chloride (PVDC), and polyvinyl alcohol (PVA).
Among these, the most promising is PVA, a water-soluble synthetic resin used widely in paints. It exhibits very low gas permeability and coatings can be fabricated using a solution casting method with water as the solvent.
However, PVA is also a potent wastewater pollutant, so any large-scale application would need to be carefully designed and controlled.
Leak Detection
Methane leaks are a significant contributor to greenhouse gas emissions because methane is about 25-times more potent at trapping heat than carbon dioxide.
Even a minor pipeline leak could reverse the carbon intensity benefits of blending low carbon hydrogen into the natural gas stream.
And hydrogen leaks can be even harder to identify.
Detecting and remediating leaks from natural gas infrastructure is therefore an area of continuing focus and improvement.
Conventional approaches to pipeline monitoring use SCADA systems to provide inputs for volumetric and mass balance calculations that report flowrate-based leakage.
Many pipeline operators are upgrading to fiber optic or acoustic sensors capable of direct leak detection and localization.
The sensitivity of this approach is an order of magnitude better than using conventional sensors and mass balance calculations.
Infrared and thermal imaging equipment is also being used to monitor for leaks at production well sites and processing facilities, such as compression stations.
Speaking of Compression
The impact of hydrogen blending on compressors is another area of intense study.
On a BTU per pound basis, hydrogen exhibits about 2.5 times the energy density of methane. So, burning one pound of hydrogen delivers 2.5 times the energy compared to burning one pound of natural gas.
But, because hydrogen is much less dense than methane, it takes approximately 3 times the volume of hydrogen to deliver the same amount of energy.
So, for a pipeline operator to deliver the same “bang for the buck”, it must either increase its operating pressure or increase the volumetric flowrate (or a combination of both).
This effect gets worse in proportion to the amount of hydrogen that has been blended into the natural gas.
This leads to serious concerns about reductions in compressor operating efficiency and longevity, and how those relate to the blend ratio, pipeline pressure, and temperature.
Burning Hydrogen Blended Natural Gas
Can a hydrogen-natural gas blend be used as a drop-in substitute for natural gas?
Gas-fired power generation experiments using small- and medium-sized units have shown promising results, as has using the blend in industrial and home boilers.
At the Canadian Hydrogen Convention, held in Edmonton, we heard of a larger-scale experiment that delivered 20% hydrogen / 80% natural gas to 2,200 households.
Half of the homes received upgraded burner tips while the other half used unmodified, recent appliances.
At the time of reporting, there were no reports of negative consequences for either group, though the results were preliminary and based on relatively limited data.
Similar long-term experiments run with 5-15% hydrogen blends indicated no need for any changes to existing burners or appliances technology.
Taken in aggregate, these initial results suggest that hydrogen-natural gas blends can be used in existing applications without significant repercussions.
In Conclusion
Trillions of dollars have already been invested around the globe to develop natural gas pipeline networks.
There are over 200,000 miles of pipeline in the US, and another 50,000 miles in Canada alone.
This is an enormous infrastructure base upon which to build the hydrogen economy as part of an energy transition.
However, it’s not a slam-dunk solution and a combination of care, proactive intervention, and equipment upgrades will be needed to enable the widespread transportation of hydrogen via this pathway.
At Trellis, we support all possible paths to decarbonization, while supporting the mutual goals of net-zero on the carbon side and energy justice on the social side.
Distributed generation of RNG and hydrogen provide opportunities to reduce the carbon intensity of natural gas, and sharing conventional transportation infrastructure provides an attractive way of bringing that low carbon energy to market.
Improved measurement technologies connected to existing SCADA and operational systems—including energy management systems, such as Trellis—will allow for better overall system management and superior outcomes for all.
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