Liquid Hydrogen – A choice for Efficient Energy Storage and Transport – Stargate Hydrogen
In the ever-growing quest for cleaner, more sustainable energy solutions, hydrogen has emerged as a frontrunner. As industries and nations seek to reduce their carbon footprints, hydrogen offers a promising alternative. However, hydrogen in its gaseous state presents challenges regarding storage and transportation. Read more about hydrogen storage here.
In some cases, transforming gaseous hydrogen into a liquid is the solution. But why should we liquefy hydrogen, and what are the pros and cons of this process? In this article, we explore the science, applications, risks, and advantages of liquid hydrogen, providing key insights for professionals working in research, development, and procurement.
Main Takeaways of the article:
- Liquid hydrogen offers higher energy density and is easier to transport and store compared to gaseous hydrogen.
- Liquefaction is very energy-intensive and so far increases the cost of hydrogen beyond what is economically viable but ongoing research aims to improve its efficiency.
- Risks include cryogenic burns, hydrogen embrittlement, and flammability, but with the right safety measures, these can be managed.
- Key applications include space exploration, fuel cells, and industrial, and renewable energy storage.
Why Turn Gasous Hydrogen into Liquid Hydrogen?
The main reason to turn hydrogen into a liquid is simple: Efficiency. In its gaseous state, hydrogen has a low energy density, which makes it difficult to store and transport in large volumes. Liquefying it compresses the hydrogen, significantly reducing its volume—by a factor of about 800 times.
Dr. Rainer Küngas, Stargate’s Hydrogen CTO, explains :
Hydrogen gas is incredibly light,
” From a purely energy-density point of view, if you’re trying to store it at scale, you’re either dealing with extremely large tanks or compressing it to high pressures. By turning hydrogen into a liquid, you make it far more compact and easier to transport over long distances. But there are other aspects that need to be considered, such as the energy consumption of liquefaction. In some cases, it makes more sense to convert H2 into ammonia or CH4 for transportation purposes, because these chemicals are easier and cheaper to transport ”
Advantages of Liquid Hydrogen
- Higher Energy Density: In its liquid form, hydrogen offers a much higher energy density compared to its gaseous state. This means more energy can be stored in smaller spaces.
- Efficient Transportation: Hydrogen in its gaseous state requires high-pressure containers for transportation, which are both expensive and complex. Liquid hydrogen, on the other hand, can be moved more easily via cryogenic tanks. In terms of logistics, liquid hydrogen is far more practical for long-distance transportation.
- Long-Term Storage: Another advantage is that liquid hydrogen can be stored for longer periods without the constant need for high-pressure containment. This makes it suitable for applications where storage duration is crucial, such as energy backup systems.
Disadvantages of Liquid Hydrogen
While liquid hydrogen presents clear advantages in terms of density and storage, but, it comes with its own set of drawbacks:
Energy-Intensive Process: Liquefying hydrogen is not easy. The process consumes a substantial amount of energy—nearly 30% of the energy contained in the hydrogen itself.
As Dr. Rainer Küngas, points out,
The energy required to cool hydrogen to its liquid state is significant. We need to balance this energy cost with the overall benefits of liquid hydrogen for transport and storage.
Specialized Storage Requirements: Storing liquid hydrogen requires cryogenic tanks capable of maintaining temperatures as low as -253°C. These tanks are expensive and require advanced technology to ensure the hydrogen remains in a liquid state. “The challenge isn’t just cooling the hydrogen down; it’s keeping it at that temperature for extended periods,” says Dr. Rainer Küngas.
Evaporation Losses: Even with the best cryogenic storage systems, some amount of hydrogen will inevitably evaporate over time. This gradual loss must be factored into the overall efficiency and cost of using liquid hydrogen. However, the losses are smaller compared to gaseous pressurised hydrogen storage.
How to Turn Hydrogen into a Liquid
The process of turning hydrogen into a liquid is known as cryogenic liquefaction, and it is no small feat. Here’s how it works:
- Gas Collection: The process begins with hydrogen gas, typically produced through methods like electrolysis, which splits water into hydrogen and oxygen, or through natural gas reforming.
- Compression: The hydrogen gas is compressed in stages to prepare it for cooling. Compression alone isn’t enough to liquefy hydrogen but is a critical step in reducing the overall energy required for cooling.
- Cooling to Cryogenic Temperatures: Hydrogen gas needs to be cooled to -253°C to become a liquid. This requires specialized cooling equipment capable of reaching cryogenic temperatures. A series of compressors and heat exchangers are needed to bring the temperature down to the point where the hydrogen transitions from a gas to a liquid.
- Storage in Cryogenic Tanks: Once liquefied, the hydrogen is stored in specially designed cryogenic tanks. These tanks not only keep the hydrogen at its required temperature but are also built to prevent evaporation and leakage. The energy required to maintain these tanks is a factor in the overall efficiency of using liquid hydrogen.
Risks of Turning Hydrogen into a Liquid
While the pros and cons of liquid hydrogen are clear, it’s important to understand the risks involved in handling it. Safety is a top priority, especially when dealing with a substance as volatile as hydrogen.
- Cryogenic Burns: One of the most immediate risks is the extreme cold of liquid hydrogen. At temperatures of -253°C, direct contact can cause severe cryogenic burns. Handling liquid hydrogen requires specialized equipment and protocols to ensure safety. Any contact with skin or regular materials can lead to severe damage.
- Hydrogen Embrittlement: Another risk associated with liquid hydrogen is hydrogen embrittlement, a phenomenon where metals exposed to hydrogen become brittle and prone to cracking. This is particularly problematic for storage tanks, pipelines, and other infrastructure. Hydrogen embrittlement can cause unexpected failures in materials, so it’s crucial that we use metals and alloys specifically designed to resist this effect.
- Flammability and Explosion Risk: Hydrogen is highly flammable, and its low ignition energy makes it easy to ignite in the presence of air. When dealing with liquid hydrogen, even a small leak can pose a significant risk. Hydrogen burns in the air with an invisible flame, making it harder to detect. Safety measures are critical to ensure that any leaks are immediately addressed.
- Pressure Build-Up in Storage: Over time, even the best cryogenic storage tanks will allow some evaporation of liquid hydrogen, leading to a pressure build-up. Without proper safety measures, this pressure could lead to a dangerous situation. That’s why storage systems must include pressure release mechanisms to avoid potential explosions.
Where Can Liquid Hydrogen Be Used?
The applications for liquid hydrogen are vast and growing as industries seek cleaner energy solutions.
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- Space Exploration: Liquid hydrogen has been used in space missions for decades as rocket fuel. Its high energy density and efficient combustion make it ideal for powering spacecraft. NASA has long relied on liquid hydrogen to propel its rockets into space.
- Fuel Cells for Vehicles: Hydrogen-powered vehicles are becoming more common, especially in the form of fuel cells. Fuel cells convert hydrogen into electricity to power electric motors, with water vapor being the only byproduct. Liquid hydrogen offers a promising alternative to traditional fuels in transportation, especially for heavy-duty vehicles like buses and trucks where large volumes of fuel is required.
- Industrial Applications: Liquid hydrogen is used in various industrial processes, from refining metals to producing ammonia for fertilizers. It’s also a critical component in some chemical reactions, making it an essential resource for many industries.
- Power Generation and Energy Storage: Perhaps one of the most exciting applications of liquid hydrogen is in the field of energy storage. Excess electricity generated from renewable sources like solar and wind can be used to produce hydrogen, which is then liquefied and stored. When electricity demand spikes, the hydrogen can be re-converted into electricity. Liquid hydrogen can play a major role in stabilizing energy grids and supporting renewable energy efforts.
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Liquid Hydrogen – A choice for Efficient Energy Storage and Transport – Stargate Hydrogen, source
