[C Tech Now] Liquefied Hydrogen 'Straight Path' or Ammonia 'Detour': Hydrogen Economy at a Crossroads

How Should Hydrogen Storage and Transportation Be Managed?

On the 8th, IGE, a subsidiary of SK E&S, held a completion ceremony for a liquefied hydrogen plant in Seo-gu, Incheon. This facility is the world's largest single plant, capable of producing 30,000 tons of liquefied hydrogen annually. It liquefies hydrogen using by-product hydrogen in gas form produced at the SK Incheon Petrochemical plant.

In the first half of this year, Hyosung Hydrogen, under the Hyosung Group, plans to operate a liquefied hydrogen plant (5,200 tons annually) in Ulsan. Earlier in January this year, Doosan Enerbility completed a liquefied hydrogen plant with a capacity of 1,700 tons in Changwon. Combining these three companies, domestic production of liquefied hydrogen will reach 36,900 tons annually. The liquefied hydrogen produced in this way is mainly expected to be used for transportation such as hydrogen cars and hydrogen buses.

On the other hand, the government will launch the world's first Clean Hydrogen Power Supply (CHPS) bidding market in June this year. It will recruit companies to participate in co-firing power generation that mixes hydrogen or ammonia recognized as clean hydrogen with coal or liquefied natural gas (LNG). Companies preparing for clean hydrogen power bidding are mostly considering importing clean hydrogen produced overseas in the form of ammonia. The government recognizes hydrogen converted into ammonia as 'clean ammonia.' It is anticipated that ammonia will serve as a stepping stone toward a hydrogen society.

"Transporting hydrogen is like moving Styrofoam"

‘How to store and transport hydrogen’ is one of the biggest challenges to overcome along with ‘how to produce hydrogen’ to advance toward a hydrogen economy. Storage and transportation technologies are the key connecting links in the hydrogen ecosystem. Securing means to economically and safely move hydrogen is a core issue.

So far, practical solutions that have emerged include liquefying hydrogen or converting it into ammonia. Additionally, research is being conducted on Liquid Organic Hydrogen Carrier (LOHC) technology.

The difficulty in storing and transporting hydrogen stems from its characteristics. Although hydrogen is gaining attention as a future clean energy source, it is not only difficult to produce but also challenging to store and transport. Hydrogen is the lightest substance in the world. Its energy density per unit volume is 0.5 to 2.5 kWh/ℓ, which is very low compared to other fuels such as methanol (about 4.5 kWh/ℓ) and gasoline/diesel (9 to 10 kWh/ℓ). Transporting hydrogen in its gaseous form is often compared to ‘loading Styrofoam onto a truck and moving it.’

In the energy industry, the means of transporting hydrogen are called hydrogen carriers. Hydrogen carriers are classified into physical carriers (compressed hydrogen, liquefied hydrogen) and chemical carriers (ammonia, LOHC) depending on the conversion method. Until now, compression methods compressing hydrogen to 200?700 bar have been widely used.

Liquefied hydrogen: well-known benefits but lacking foundation

Liquefied hydrogen is attracting attention as the next-generation hydrogen storage method. When hydrogen is cooled to its boiling point of minus 253 degrees Celsius, it becomes liquid, called liquefied hydrogen. Liquefied hydrogen reduces the volume to 1/800 compared to gaseous hydrogen. In other words, it means that 800 times more hydrogen can be stored in the same storage space. This increases transportation volume and reduces transportation costs. In actual transport, a high-pressure hydrogen trailer transports about 3,000 m³ per trip, whereas liquefied hydrogen can transport up to 36,000 m³ at once, which is 12 times more.

Compared to other carriers, liquefied hydrogen has the advantage of being ready for immediate use after transport. Liquefied hydrogen refueling stations occupy less space than gaseous hydrogen stations. Above all, the biggest advantage is safety. Unlike gaseous hydrogen that must be compressed at high pressure, liquefied hydrogen is cooled to cryogenic temperatures and stored and transported at near atmospheric pressure, reducing the risk of explosion.

However, the technological barrier to liquefying hydrogen at cryogenic temperatures is high, and domestic companies still rely on overseas technology. Globally, liquefied hydrogen plant technology is almost monopolized by three companies: Air Liquide of France, Linde of Germany, and Air Products of the United States. In Korea, SK E&S and Doosan have built or are building liquefied hydrogen plants with Air Liquide, and Hyosung is doing so with Linde.

It is still not easy to import liquefied hydrogen produced overseas into Korea. Importing liquefied hydrogen requires the development of liquefied hydrogen carriers, receiving terminals, and large-capacity storage tanks. The three Korean shipbuilders?HD Hyundai Heavy Industries, Samsung Heavy Industries, and Hanwha Ocean?are developing liquefied hydrogen carriers. HD Hyundai Heavy Industries recently announced plans to develop a large liquefied hydrogen carrier commercially viable by 2030.

Can ammonia save humanity twice?

With the liquefied hydrogen production and transportation ecosystem not yet complete, ammonia (NH3) is being discussed as a practical way to import hydrogen produced overseas into Korea. Ammonia can be produced by combining one nitrogen (N) atom and three hydrogen (H) atoms using a technology called the ‘Haber-Bosch process.’

In 1789, British economist Thomas Malthus predicted in his book 'An Essay on the Principle of Population' that population growth would outpace food production, eventually leading humanity to famine. However, German chemist Fritz Haber discovered a method to synthesize ammonia artificially from atmospheric nitrogen, producing nitrogen fertilizer (the nitrogen fixation method), which dramatically increased food production. Since then, ammonia has been regarded as a representative substance that saved humanity.

Ammonia can be liquefied at about minus 33 degrees Celsius, close to room temperature, and is easy to transport, so a significant amount is traded internationally even today. Globally, ammonia export and import ports and infrastructure are well established.

As of 2020, there are 38 export terminals and 88 import terminals worldwide, with six capable of handling both imports and exports simultaneously. Korea has import terminals with storage facilities in Incheon (15,000 tons), Yeosu (50,000 tons), and Ulsan (93,000 tons). The three domestic shipbuilders are also manufacturing ultra-large ammonia carriers.

Ammonia is gaining attention as a hydrogen carrier because existing infrastructure can be effectively utilized to economically store and transport hydrogen. The hydrogen storage capacity per volume of ammonia is about 120 kgH2/m³, which is about twice that of liquefied hydrogen (70 kgH2/m³), another advantage.

However, the problem is that ammonia must undergo a ‘cracking’ process to be converted back into hydrogen. Cracking ammonia requires catalysts at temperatures above about 400 degrees Celsius, consuming significant energy and cost. Extracting high-purity hydrogen through cracking is also challenging. Korea currently lacks commercial-scale cracking facilities. Lotte Fine Chemical and Wonik Materials are conducting demonstration projects.

Domestically, instead of converting ammonia back to hydrogen, plans are underway to use ammonia for ‘co-firing power generation,’ mixing it with coal or liquefied natural gas (LNG). Co-firing power generation will eventually transition to full combustion power generation using only ammonia or hydrogen as fuel. This is why ammonia is seen as a stepping stone toward a hydrogen society.

Looks like water but it's hydrogen? ... LOHC

Recently, research on LOHC technology has been actively progressing. This method stores and transports hydrogen by bonding it with liquid organic compounds. LOHC containing hydrogen looks like transparent water externally. The hydrogen storage capacity per volume is about 45 kgH2/m³. Using LOHC, large amounts of hydrogen can be transported in a small volume of liquid at ambient temperature and pressure.

At the point of use, hydrogen is separated again from the organic compounds for use. The organic compounds can be reused 200 to 300 times in this way. Toluene is a representative substance used. Separating hydrogen from LOHC requires about 300 degrees Celsius of thermal energy. LOHC technology is currently at the demonstration stage in Japan, the United States, and Europe, and active research is underway in Korea at government-funded research institutes and universities.