Classification by hydrogen storage pressure

Classification by hydrogen storage pressure

The mass density of hydrogen gas increases as the pressure increases. It increases rapidly in the range of 30-40 MPa, but the change becomes minimal when the pressure exceeds 70 MPa. Therefore, hydrogen storage tanks should operate at pressures between 30-70 MPa. High-pressure hydrogen storage tanks in hydrogen fuel cell vehicles typically come in two pressure ratings: 35 MPa and 70 MPa.

Both Type III and Type IV tanks come in different pressure ratings. Type III tanks are available in 35 MPa and 70 MPa variants, while Type IV tanks can also be classified into high-pressure and low-pressure versions. However, the advantages of Type IV tanks are more pronounced at high pressures. If the application only requires low-pressure storage, Type III tanks might be more cost-effective and advantageous in terms of long-term use. Therefore, most companies focus their research and development efforts on 70 MPa Type IV tanks, as these are better suited for high-pressure applications.

Liquid storage and transport containers are devices designed for the storage and transportation of liquid substances, typically liquid or liquefied gases. These containers are engineered to withstand high pressures and low temperatures, ensuring the safe storage and conveyance of liquids. Here are some common types of liquid storage and transport containers:

Liquid Gas Cylinders (Liquefied Gas Cylinders): These containers are utilized for the storage and transportation of liquid gases, such as liquid oxygen, liquid nitrogen, and liquid hydrogen. They often feature a double-wall design, comprising an inner wall to maintain gas liquefaction and an outer wall to preserve low temperatures and ensure safety.

Liquid Fuel Storage Tanks: These containers are employed for the storage of liquid fuels, including liquefied natural gas (LNG) or liquefied petroleum gas (LPG). They play essential roles in applications like natural gas transport, LNG refueling stations, and household gas storage.

Liquid Gas Transport ISO Containers: These ISO containers are employed for the large-scale transportation of liquid gases, such as LNG. They are typically designed with high levels of insulation to maintain the required temperature and pressure conditions during long-distance transit.

Liquid Hydrogen Storage Tanks: Liquid hydrogen storage tanks are used to store and transport liquid hydrogen, particularly in applications like fuel cell vehicles and hydrogen energy systems.

The design and material selection for these liquid storage and transport containers take into account the safety and efficiency requirements under high-pressure and low-temperature conditions. They are integral in various industrial, energy, and transportation applications, ensuring the secure storage and effective conveyance of liquid substances.

Linde Kryotechnik, a subsidiary of Linde, is one of the few companies in the world with the capability to design and construct large-scale cryogenic systems for the liquefaction of helium and hydrogen. Linde provides cryogenic standard tanks for liquid nitrogen, liquid argon, liquid oxygen, liquid carbon dioxide, liquid hydrogen, liquefied natural gas (LNG), and liquid nitrous oxide. These tanks have capacities ranging from 3,000 liters to 450,000 liters, with standard operating pressures of 18 MPa, 22 MPa, or 36 MPa. Each tank is vacuum-insulated and can be installed vertically or horizontally for transportation. The internal containers and piping are made of stainless steel to ensure cleanliness, and the outer shell is coated with special materials to enhance insulation performance.

At room temperature, a 100-liter tank can store 4.1 kg of hydrogen gas, requiring a pressure of 75 MPa. However, when the hydrogen gas temperature drops to 77 K, the same amount of hydrogen gas stored in a 100-liter tank only exerts a pressure of 15 MPa. Linde uses low-temperature liquid pumps with discharge pressures ranging from 35 to 90 MPa and flow rates exceeding 1000 Nm3/h.

Lawrence Livermore National Laboratory in California, USA, has developed a new high-pressure cryogenic tank with an outer shell length of 129 cm and a diameter of 58 cm. The inner liner of this hydrogen storage tank is made of aluminum, while the external layer is wrapped in carbon fiber. The protective outer layer consists of highly reflective metallized plastic and stainless steel, and a vacuum exists between the hydrogen storage tank and the protective layer. Existing cryogenic tanks can only maintain the medium without volatilization for 2-4 days, but tests on hybrid vehicles equipped with the newly developed high-pressure cryogenic hydrogen tank have shown that it can effectively reduce hydrogen vaporization and maintain hydrogen for 6 days without volatilization.

Japanese companies have also invested heavily in research and development to address critical technical challenges in the field of liquid hydrogen storage and transportation, with many of their products entering practical testing phases. For example, Japanese companies have developed large liquid hydrogen storage and transport tanks that ensure high strength through vacuum exhaust design while achieving high thermal resistance.

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