SUPPLY CHAIN DYNAMICS IN OPTIMAL CHOICE OF HYDROGEN CARRIER

Several options are being evaluated for long distance transport including compressed hydrogen (C-H2), liquid hydrogen (L-H2), ammonia (NH3) and liquid organic hydrogen carriers (LOHCs).

LOHCs store hydrogen in molecules via covalent bonds. They differ from carriers such as ammonia and methanol in that their sole purpose is to transport hydrogen, and the dehydrogenated carrier is usually liquid.

Their primary advantage is that little boil-off occurs, so hydrogen losses during transport are small. After transportation, the hydrogen is released via an endothermic reaction, and the LOHC is returned to the point of production. Ideally, LOHCs are non-toxic and have similar properties to crude oil-based liquids such as diesel and gasoline so they can potentially use existing ship and terminal infrastructure with little modification.

No one carrier has emerged as the best choice, partly because the different model parameters and assumptions set by the various studies makes direct comparisons difficult and partly because of the uniqueness of potential supply chains they have targeted.

Grand ambitions

Saudi Arabia aims to be the world’s largest hydrogen supplier. The nation’s large natural gas reserves enable it to produce blue hydrogen via natural gas reforming, with the CO2 byproduct captured.

Last year, Aramco demonstrated the production and shipment of blue ammonia from Saudi Arabia to Japan. Explaining the focus on ammonia, a spokesperson for Aramco said: “Ammonia is one of the leading hydrogen carrier candidates. It is a widely and internationally traded commodity. The production and global distribution networks are in place. In addition, SABIC – in which Aramco owns a majority stake – is one of the major producers and suppliers in the global ammonia market. Due to these reasons, ammonia is the hydrogen carrier of choice for Aramco.”

The Japan demonstration spanned the full value chain including the conversion of hydrocarbons to hydrogen and then ammonia, the capture of associated CO2 emissions and the shipment of the blue ammonia to Japan for use in power plants. 30 tons of CO2 was captured during the process and designated for use in methanol production at SABIC’s Ibn-Sina facility, and another 20 tons was used for enhanced oil recovery at Aramco’s Uthmaniyah field.

Saudi Arabia has already signed hydrogen-related MoUs with the UK, Germany and South Korea, and the world’s first large scale green hydrogen plant is currently under construction in the new clean-energy-powered megacity of NEOM on Saudi Arabia’s Red Sea coast.

C-H2 simplicity

Australia has also announced plans to be a world leader in the supply of hydrogen, and the nation is partnering green exports with green industry at home.

A study undertaken by Australian-based Global Energy Ventures (GEV) evaluated exporting green hydrogen volumes of 50,000; 200,000; and 400,000 tonnes per annum, to market distances of 2,000; 4,000; and 6,000 nautical miles. Production of these volumes would require very large-scale renewable energy generation, such as the Asian Renewable Energy Hub located in the Pilbara region of Western Australia, one of the world’s top 10 renewable energy projects. Here, solar and wind power will be used to generate cheap clean energy that will enable new and expanded mines, downstream mineral processing and large-scale production of green hydrogen products for domestic and export markets.

GEV’s scoping study highlighted that compression is an integral component in the design and engineering of C-H2, L-H2 and NH3 supply chains, with L-H2 and NH3 also compressing the gaseous hydrogen prior to their respective transport processes. The company has determined that its compressed hydrogen supply chain will be competitive at distances up to 4,500 nautical miles and very competitive for distances of up to 2,000 nautical miles. GEV has therefore resolved to focus on export projects located in the mid-west of Western Australia (Geraldton) across to Queensland (Brisbane) with target markets being Singapore, Japan and South Korea.

GEV’s analysis assumed a stable and continuous base load supply of green hydrogen for export. This was viewed as challenging in reality, given both solar and wind have variable and volatile daily generation profiles. C-H2 was seen as the solution, as it had the ability to “load follow” such profiles, whereas L-H2 and NH3 could not. Additionally, says GEV, the development of a C-H2 supply chain benefits from being a simple and energy efficient process along with having minimal technical barriers for commercialisation in the next five years.

Like Aramco, another critical benefit of the chosen carrier for GEV is its synergies with the company’s existing business, with the application and equipment required for compression in the C-H2 supply chain the same as its CNG Optimum supply chain for natural gas. The one exception is its new C-H2 ship design. However, this potential barrier has now been removed, because ABS granted approval for the ship’s cargo containment system in March this year based on a cargo capacity of 2,000 tonnes of hydrogen stored in two onboard 20-metre diameter tanks at 250 bar and at ambient temperature.

Using waste heat

Liquefaction is currently energy-intensive, consuming up to 45% of the energy stored as hydrogen, and resulting in further energy losses due to the boil-off gas generated. However, for new and large-scale facilities this value could drop to roughly 18%.

Researchers at the Technical University of Hamburg studied the energy consumption and costs of transporting hydrogen from Algeria to Germany, including its subsequent local distribution, and their analysis showed that L-H2 had the highest production costs.

The researchers concluded that transport distance and the way heat is supplied to dehydrogenate the LOHCs were most important for their relative cost-effectiveness compared to C-H2 or L-H2. If waste heat was used, dibenzyl toluene or toluene were advantageous, and LOHCs were generally favoured for long distance transport.

Methanol had the highest hydrogenation costs of the LOHC options examined and also involved the recurring purchase of CO2, although it was the cheapest to transport. Methanol’s low heating demand during dehydrogenation and its high storage capacity makes it advantageous for long-distance transport.

For short distances, transporting C-H2 by pipelines lowered costs. However, the researchers found that no specific transportation chain was superior under all circumstances.

Separating hydrogen at its final destination

Researchers at Germany’s Fraunhofer-Gesellschaft have developed membrane technology for the energy-efficient and economic separation of hydrogen from natural gas. The technology makes it possible for the two substances to be routed through the national natural gas grid together and then isolated from one another at their final destination.

The membrane is an ultra-thin layer of carbon deposited on porous, ceramic substrates. The pores in the carbon are less than a nanometre in diameter. During the separation process, hydrogen and natural gas are pushed through tubular modules. The smaller hydrogen molecules are forced through the pores in the membrane and reach the other side in gaseous form; the larger methane molecules are held back. This gives 80% pure hydrogen, and the residual natural gas is filtered out in a second separation step to achieve a purity of over 90 percent.

Hydrogen of this purity can be used for various applications including steel production. In high-temperature furnaces, it replaces carbon in the process of reducing iron ore to iron, making an important contribution to cutting CO2 emissions. Hydrogen is also an attractive option for the climate-friendly energy supply to buildings. When combusted, hydrogen generates power and heat, the only by-product is water. Combined heat and power systems, for example, could supply clean power and heat energy to individual building complexes.

Big consumers

The EU and Japan are expected to be major hydrogen users, and they are therefore the subject of a number of supply chain studies. A study of the feasibility of hydrogen exports from Norway to Rotterdam and Japan conducted by researchers at SINTEF in Norway and the Institute of Applied Energy in Japan compared L-H2 and NH3 as carriers. In this case, hydrogen was produced predominately by natural gas reforming, with around 10 percent produced by electrolysis using renewable power.

L-H2 was found to be more energy efficient than NH3 if cracking of the NH3 was required at the destination country. It also had a smaller CO2 footprint. The levelized cost of hydrogen delivered to Rotterdam was also lower for L-H2. For the longer distance to Japan, the costs were similar.

The energy efficiency of L-H2 was largely determined by the loss of energy during hydrogen production. This was followed by losses as boil-off gas, which would be used for the transport ship’s propulsion. Ultimately, the amount of delivered L-H2 would be 14% higher in Rotterdam than Tokyo.

For NH3, the largest loss of energy also occurred during production and was greater than for L-H2. The second largest energy loss occurred during cracking, a process that requires heat and electricity for the reaction and purification.

Point-to-point analysis shows no clear winner

Focusing on transport cost and efficiency rather than end-user applications, a study by researchers at the German Aerospace Center modelled the large-scale point-to-point transport of hydrogen from Australia to Japan where the hydrogen was carried as L-H2 or via the LOHCs methyl cyclohexane or hydrogenated dibenzyl toluene.

Under the scenarios modelled, L-H2 had the highest investment costs, mainly attributed to the high cost associated with liquefaction in Australia, although LH2 has a technical advantage because the energy demanding step (liquefaction) is at the point of energy abundance, says lead researcher Dr Moritz Raab. The ships used on the L-H2 pathway would also be more expensive than those that transport LOHCs by a factor of roughly three if L-H2 ships are as expensive as LNG ships, as they require cryogenic storage technology. However, L-H2 had the highest transport efficiency, so it was advantageous when hydrogen production costs were relatively high and only required low-grade thermal energy at the destination to be returned to gaseous form for use.

The dibenzyl toluene pathway was found to be the cheapest option due to lower investment costs, even though energy (in the case of Japan: LNG) was required at the destination for dehydrogenation. Both LOHCs had technical disadvantages due to the need to manage unwanted byproducts during hydrogenation and dehydrogenation. The use of methyl cyclohexane was additionally disadvantaged by the need to manage its high vapour pressure.

The ability to scale up production of the LOHCs to accommodate future hydrogen demand comes down to the saying: “Where there’s a will there’s a way,” says Raab. “The annual production capacity of toluene was 30 million tons in 2018, with 0.16 million tons required in our evaluation. Dibenzyl toluene has been used as a heat transfer oil in the chemical industry for a long time, and upscaling the production capacity seems feasible.”

The researchers’ techno-economic assessment of large-scale hydrogen transportation had some uncertainties especially regarding future technology development, says Raab, but it gives a good basis for comparing the different pathways. “At this level of accuracy, the cost comparison doesn’t show a clear winner. LOHCs in general have the drawbacks that they require energy and at the point of destination but have the advantage that further distribution might have fewer losses than a L-H2 trailer transport.” He says that some people might have thought that the advantage of LOHCs over L-H2 would be much more prominent.

Hundreds of projects, billions of dollars

Even though the choice of optimal hydrogen carrier is not necessarily clean-cut, a Hydrogen Council report demonstrates massive global investment in hydrogen supply chains. Hydrogen Insights 2021: A Perspective on Hydrogen Investment, Deployment and Cost Competitiveness, developed in collaboration with McKinsey & Company, states that, as of early 2021, over 30 countries have released hydrogen roadmaps, and governments worldwide have committed public funding in support of decarbonisation through hydrogen technologies.

Over 220 large-scale projects have been announced along the value chain, with 85% located in Europe, Asia and Australia. These include large-scale industrial usage, transport applications, integrated hydrogen economy, infrastructure and giga-scale production projects. If all announced projects come to fruition, total investments will reach more than $300 billion in spending by 2030. Of this investment $80 billion can currently be considered mature.

The Hydrogen Council says the report confirms that – from a total cost of ownership perspective – hydrogen can become the most competitive low-carbon solution in more than 20 applications by 2030, including long haul trucking, shipping and steel. Deployment through clusters with strong off-takers will help suppliers share both investments and risks while establishing positive reinforcing loops. Three cluster types are already gaining traction: industrial centres that support refining, power generation and fertiliser and steel production; export hubs in resource-rich countries; and port areas for fuel bunkering, port logistics and transportation.