Faced by global climate change, countries and industries around the world are looking to de-carbonize their energy sources. Hydrogen – the smallest chemical element on our planet – is seen by many as holding the key to a sustainable future. This journal contacted Deepak Bawa, Director of Project Development with New Fortress Energy, to glean his observations on the potential role of hydrogen.
By David Sear
At room temperature and pressure, hydrogen is an odorless, colorless gas. However, there are references in articles and journals that associate hydrogen with a color, such as grey, blue, or green. This has nothing to do with added dyes; instead the colors indicate the perceived environmental credentials of the gas. Grey hydrogen, for example, is mainly produced by reforming natural gas, a process which releases unwanted carbon dioxide into the atmosphere. If, as part of that production process the carbon dioxide emissions are captured and stored, then the hydrogen is said to be blue. An alternative production technique for hydrogen is electrolysis of water. If that electrolysis is achieved using emission-free electricity, and is generated by wind farms or solar parks, then the hydrogen is said to be green as no carbon dioxide is released during production. It is the blue and green forms of hydrogen that could therefore contribute to sustainable societies. “Right now we are in the middle of an energy transition, and in this process I believe that hydrogen will play a crucial role,” opened Mr. Bawa. “Hydrogen has long been used as a raw material in chemicals and refining; now many people see its potential as a clean fuel for both aviation, general transportation, as well as power generation, and heating.” In an ideal world, societies might wish to immediately switch to green hydrogen. However, given the need to first develop a green hydrogen infrastructure, and second, the state of the existing hydrogen production facilities, Mr. Bawa suggests a more balanced approach is called for.
“Of the three forms of hydrogen, blue is the most balanced option. Blue hydrogen can give us the energy source we need, at a realistic price, whilst avoiding the carbon emissions associated with grey hydrogen. Green hydrogen is, for the immediate future, still too expensive. That is why we need blue hydrogen in this energy transition.”
Worldwide, natural gas is of course used extensively as an energy source by both industry and households. It is praised by many for being a clean burning fuel although it does release carbon dioxide into the atmosphere during combustion. Mr. Bawa therefore sees blue hydrogen as an ideal way to improve the environmental credentials of natural gas. “As we have captured the carbon during production, blue hydrogen could, for example, be mixed into the natural gas that is fed into our homes and factories to lower overall carbon dioxide emissions. In countries such as the UK this has already been successfully implemented.”
Blue hydrogen can also be used to fuel power plants. “In Ohio, for example, we are working with Long Ridge Energy Terminal to convert their 485 MW combined-cycle power plant to run on carbon-free hydrogen. The plan is to introduce up to 20% hydrogen into the gas stream by the end of 2021, and to slowly increase that to 100% hydrogen. It is for this reason that I say that blue hydrogen and natural gas complement each other perfectly. I expect both will retain their existing roles during the next ten to twenty years.”
When asked about challenges to the further introduction of blue hydrogen, Mr. Bawa first considered the financial aspects of carbon sequestration. “Capturing and sequestering carbon dioxide currently costs roughly $65-70 USD per ton, yet the carbon tax credit paid for doing so is just $50 USD per ton. Hence the biggest challenge right now is helping companies balance their books. If the carbon tax credit were a little higher that would certainly motivate the big hydrogen producers to install carbon capture systems.”
He gives a practical example of a hydrogen plant producing 50 metric tons per day. “Such a facility would have to spend $10-12 million USD to install carbon capture equipment. What incentive do they have to do that if the carbon tax credit paid out is too low for them to at least recoup their costs? In order to motivate these types of companies, two things have to happen – first, the carbon tax credit has to go up, and second, we have to further work on the technological side. Right now the amine technology is the best route to capture carbon, at least during the pre-combustion phase. Yet there is still a large amount of work to be done to reach the goal of 100% carbon capture, especially during the actual combustion phase.”
An additional hurdle, continues Mr. Bawa, is the time required to obtain the necessary permits. “Right now, in the USA, it can take up to 24 months for a company to hear if they can go ahead and build a carbon sequestration facility. If you are planning a greenfield development that is easy enough to factor in, but if you are looking to upgrade an existing plant you do not want to have to wait that long.”
Materials Considerations in Hydrogen Systems (Gases & Liquids)
Generally acceptable materials for compressed hydrogen gas include austenitic stainless steels, aluminum alloys, copper, and copper alloys.
• Nickel and most nickel alloys should not be used, as they are subject to severe hydrogen embrittlement.
• Gray, ductile, and malleable cast irons should not be used for hydrogen service.
• Designers of high-pressure hydrogen storage vessels and piping systems should understand the effect of hydrogen exposure to materials (e.g., hydrogen embrittlement) in order to make appropriate material selections. Note that certain surface finishing techniques (e.g., electro-polishing) and welding may introduce hydrogen into a metal, resulting in accelerated embrittlement.
• Ideally, testing (i.e., direct exposure of the material to hydrogen) and analysis should be done to assure that the material will perform as expected at planned operating conditions as well as worst case conditions.
• Material selection for liquid hydrogen service should be based on mechanical properties at the low temperature (e.g., yield and tensile strength, impact strength). Industry typically uses the Charpy impact test to determine the amount of energy absorbed by a material during fracture, which is a measure of the material’s toughness.
• Some materials change from ductile to brittle behavior as their temperature is lowered, and this can occur at temperatures much higher than cryogenic temperatures.
• Materials exhibiting low-temperature embrittlement should not be used for cryogenic service.
• The large temperature difference between ambient and cryogenic conditions (300° F or more) results in significant thermal contraction of most materials, which should be accommodated for in designs for cryogenic service.
Hoses in Hydrogen Applications
The transfer and dispensing of hydrogen is a delicate process which requires the use of specialized hoses. To account for the varying pressures of gaseous hydrogen, wire or textile reinforced hoses are used that comply with standards set for the dispensing of hydrogen up to 70 MPa nominal working pressure with a typical temperature range of -40˚C to 65˚C. The ISO 19880-5:2019 standard, specifically, provides information on the safety requirements for the material, design, manufacture, and testing of gaseous hydrogen hose and hose assemblies for hydrogen fueling stations.
More generally, as hydrogen molecules are very small and compressed at a high pressure, the hoses used to convey it must be made of particular materials and have a high pressure rating. A plastic material suited for containing hydrogen gas is therefore typically is used for the inner layer of hydrogen hoses. For the reinforcement layer, steel wire with impressive tensile strength is wound in 4 to 6 tiers to form a layer that endures the high pressure of hydrogen gas. Further, the optimization of material and winding pattern of steel wire also produces both strength to endure high pressure and flexibility for usability.
Government policies can do much to stimulate both blue and green hydrogen, believes Mr. Bawa. “Take the state of California, where officials recently announced the phase-out of cars running on gasoline or diesel by 2035. That is a huge opportunity and is one example of a market where hydrogen cars can be more successful. Right now the price for hydrogen fuel is $14-15 USD per kg. If we can bring that down to around $5 USD per kilo then people really will have an economical as well as an environmental motive to buy a hydrogen car.”
In his final reflection on the industry, Mr. Bawa stated again how convinced he is of the potential for blue and green hydrogen. “Worldwide, there is a real and significant interest in hydrogen, with plans announced and engineering well underway. I expect that blue hydrogen will take the lion’s share of the market in the immediate future simply because it is more affordable. However, the price of green hydrogen will drop following technological advances in production as well as in the generation of renewable electricity. Fortunately, the transition from blue to green hydrogen will be straightforward. A consumer who buys a hydrogen car will not notice any difference in performance if he switches from blue to green hydrogen. Both will give the performance he needs, without releasing harmful carbon into the environment.”