By Baroruchi Mishra, Group Chief Executive Officer, Nauvata Energy Transition Enterprise Private Limited
India is looking towards harnessing hydrogen as the new potential for economic growth and betting big on green hydrogen production. However, several technological and economic nuances need to be kept in mind while ensuring proper transportation of hydrogen. For instance, the gravimetric energy density (by weight) is highest for hydrogen – 1 kg of hydrogen contains as much energy as approximately 2.1 kg of natural gas. However, its volumetric energy density of 325 British thermal units/standard cubic feet (btu/scf) is three times less than that of natural gas, which is 1,000 btu/scf. All transportation mechanisms to connect the manufacturing locations to demand sites have to deal with this issue, besides addressing cost and safety concerns. Industry deploys various physical and chemical processes to increase the volumetric energy density and for safe transport of hydrogen. These processes are discussed in detail in this article…
Physical processes
Pipeline transportation of compressed hydrogen: For distances of up to 2,000 km, pipeline transportation offers distinct cost benefits. Credible estimates put the cost of pipeline transportation of pure hydrogen (for 1,000 km) at $0.15-$0.35 per kg by 2030, from the current around $1.5 per kg for 1,000 tonnes per day hydrogen transportation. This includes both capex and opex costs.
While some countries such as the US and some European countries have already created hydrogen pipeline networks, others (Australia, Canada, Japan, China, South Korea, Russia and the Middle eastern countries) have firm plans for creating/expanding their hydrogen pipeline. Countries like the Netherlands, the UK, Germany and Japan aim to repurpose the existing natural gas pipelines, besides constructing dedicated pipelines for hydrogen. However, India does not figure in this list. Hopefully, it will soon find a place. There is no harm in commencing a fitness-for-service assessment of some sections of GAIL’s cross-country pipelines for this purpose, if such assessments are not already being undertaken. This will create options for hydrogen transportation through the hythane (blending) route.
Pipeline transportation of hydrogen up to economically viable limits of around 2,000 km is most promising from the perspective of continuity, bulk handling and simplicity of process. However, safety, especially with the key risk of hydrogen embrittlement and cost, are key concerns that need to be dealt with.
Blending – hythane (hydrogen and methane): Blending with natural gas in existing pipelines is an established way of substituting some percentage fossil fuel molecules with hydrogen, without compromising the heating value needed for complete combustion by the end users. Hythane stays within the wobbe index range (an indicator of interchangeability of fuel gases for burners used in various services such as gas turbines) for 5-10 per cent blend of hydrogen in natural gas.
In India, NTPC’s Kawas township’s gas network has been blending approximately 2-4 per cent hydrogen since January 2023. The Petroleum and Natural Gas Regulatory Board allows 5 per cent blending of green hydrogen with piped natural gas. It believes hydrogen blending could be scaled up phase-wise to reach 20 per cent.
The blending recommendations (or in most instances, recommendations for repurposing of gas pipelines) need revision with new correlations for evaluating the transient flow properties of the blend, which, in technical terms, is known as flow-assurance. The evaluation of issues related to diffusion, permeation, segregated flow and hydrogen embrittlement effects on the steel grade needs to follow a structured process. Finally, it is significant to mention that hythane transportation costs change by less than 0.5 per cent with an increase in hydrogen content from 1 per cent to 15 per cent by volume. So, if compression capacities allow, hydrogen volumes are available and safety is taken care of, blending could be the cheapest and fastest way of using hydrogen to reduce fossil fuel use in many domestic and commercial applications.
Compressed cryo-hydrogen (CcH2): Pressurised tanks are another option for storage and transportation of batches of hydrogen. CcH2 is essentially the concept of storing liquefied hydrogen (LH2) at 700 bar pressure in high pressure tanks. While still under development, some car manufacturers such as Toyota have used the concept for their hydrogen fuel cells in cars like Mirae. This is not yet a bulk transportation concept. Standard road transportation of compressed hydrogen or LH2 is by tube trailers. A typical tube trailer could transport 300-600 kg of hydrogen at 230-300 bar pressures. Liquid hydrogen trailers with cryogenic tanks can transport up to 3,500 kg of LH2. For transportation of hydrogen under high pressures, tanks are made of composite material such as carbon fibre with non-metallic lining (Type 3 and Type 4 Tanks). The costs of transportation through these means are significantly higher than others. Depending upon the fuel being used by transportation trucks and considering the volumes being transported, a typical cost range could be $7-12 per kg.
LH2 and ship transport: In February 2022, the Suiso Frontier became the first ship that has undertaken an ocean voyage from Australia to Japan with liquefied hydrogen. It has a capacity of 1,250 cubic metres of LH2 at 253 degrees Celsius in its storage tanks. Liquefaction is an energy-intensive process (around 14 kWh per kg LH2). It consumes 33 per cent of LH2’s own energy content (this figure is 10 per cent for LNG). Boil of gas losses (1-5 per cent per day) is the other concern. Regarding the high boil of gas losses, it needs to be understood that ortho-hydrogen is thermodynamically unstable and spontaneously converts into para-hydrogen in cryogenic environment. This is an exothermic process – the heat released is one of the reasons for the high boil-off of hydrogen from tanks.
Further, the cost of LH2 shipment continues to be a key bottleneck. The shipping cost estimates are at approximately $1 to $2.5 per mmbtu – from Australia to Tokyo Bay or Yanbu to Tokyo Bay. This is two to four times higher than that for LNG. Moreover, LH2 ships have to be constructed, which will be a significant capex commitment in case this route is adopted.
Chemical processes
Chemical bonding of elements/compounds/metals with hydrogen creates a hydrogen vector. The chemical bonds are broken at the demand site, releasing free hydrogen for use.
Ammonia: Green ammonia manufactured through the Haber-Bosch process by combining nitrogen and hydrogen is a proven technology for hydrogen storage and transportation due to its high hydrogen content by weight and the stable liquid that it can be converted to, under moderate pressure and temperature conditions. At the destination, ammonia is converted back into hydrogen through a catalytic process. However, the conversion back into hydrogen or decomposition or cracking is not highly efficient. Innovation in catalysts and process design, which can improve the conversion back to hydrogen, will be key to its success.
Depending upon the distance, the cost of ammonia shipment varies from $0.032 per kg (distance of over 6,000 km) to $0.087 per kg (shipping distance over 17,000 km). This cost of ammonia transport in terms of stoichiometric equivalent hydrogen would be $0.23 per kg and $0.5 per kg respectively. Even with the cost of conversion back to hydrogen being in the range of $0.2 to $0.35 per kg hydrogen for 100 tonnes per day (tpd) to 10,000 tpd hydrogen range, this comes out significantly lower than the transportation cost of liquid hydrogen. In addition, the high capex of building LH2 ships is avoided.
Liquid organic hydrogen carriers (LOHC): LOHCs are fast emerging as a potent hydrogen vector. Through specific chemical reactions that can be carried out at relatively mild conditions, LOHCs can reversibly bond with hydrogen molecules. The ease of hydrogenation and dehydrogenation allows them to store and release hydrogen without extremes of pressure and temperature. LOHCs are reused after dehydrogenation, albeit with some losses and degradation over a period and hence, there is a need for replacement after a stipulated number of cycles. Given the wide range of vectors considered under LOHC, the cost estimates for use of LOHCs as well as the cycling rates vary. At a high level, the cost compares very well with ammonia as a carrier of hydrogen. If used for small volumes/distances, the transportation cost could be actually lower than that for ammonia transport.
Metal hydrides (MHx): MHx as a hydrogen carrier hold significant promise. They can store and release hydrogen with ease. MHx-forming alloys and hydrogen, when merged together at the stipulated temperature and pressure conditions, lead to absorption of hydrogen within the MHx matrix. This hydrogen-rich MHx material is transported to hydrogen-demand locations by trucks, trains, or ships. At the destination, the MHx is heated to release the hydrogen. The depleted MHx is cycled back to the production site for rehydrogenation. More data is needed to understand the costs of MHx use as a hydrogen vector. At the current projected costs, this vector appears to be a viable option comparable with the ammonia vector.
The way forward
It is pertinent to mention that a lot needs to be done on the standards and regulations front for various modes of transportation. It is a no brainer that a robust storage and transportation ecosystem for hydrogen is key to a safe hydrogen economy. A clear set of guidelines, standards and regulations that are in sync with international standards will reduce risks in all modes of hydrogen storage and transportation to As Low As Reasonably Practicable. This will be the key to success.
Going forward, India needs to catch up with the rest of the world on research and development efforts to reduce costs. Reduction in specific transportation costs can happen through innovations in energy consumption for various transportation modes. Replication and standardisation of specifications of equipment will reduce equipment costs. Furthermore, scale will be key to cost reduction. Eventually, with scale, a global supply chain will emerge, which will bring in competition and further cost reduction.
