Explanation of hydrogen storage cylinders and their classification and application

Explanation of hydrogen storage cylinders and their classification and application

High-pressure gaseous hydrogen storage has the advantages of fast hydrogen filling and discharging speeds, as well as a simple container structure, making it the primary method for hydrogen storage at the current stage. Hydrogen storage pressure vessels are also known as high-pressure hydrogen storage cylinders (tanks). In general, there is no special distinction made, and in the industry, hydrogen storage cylinders and tanks are often used interchangeably.

A hydrogen storage cylinder is a container used for storing hydrogen gas and is applied in various scenarios where hydrogen is used. This report primarily analyzes the demand for hydrogen storage cylinders in the upstream and downstream markets of the hydrogen fuel cell industry chain.

According to the analysis of the upstream and downstream markets of the hydrogen fuel cell vehicle industry, hydrogen storage cylinders are primarily used in three areas:

1.Vehicle Hydrogen Storage Cylinders: These are used for storing hydrogen on board hydrogen fuel cell vehicles.

2.Hydrogen Refueling Stations (Hydrogen Mother Stations) Hydrogen Storage Cylinders: These cylinders are used at hydrogen refueling stations to store and dispense hydrogen for fueling vehicles.

3.Hydrogen Storage Cylinders for Transportation Equipment: These cylinders are used in various forms of transportation equipment, such as trucks or other vehicles that require hydrogen for their operation.

These three segments represent key applications of hydrogen storage cylinders within the hydrogen fuel cell industry ecosystem.

Based on the materials used in their production and their manufacturing methods for safety, gas cylinders are generally classified into four types:

Type I cylinder: These are metallic gas cylinders.

Type II cylinder: These are metal-lined composite cylinders with a fiber-wrapped hoop.

Type III cylinder: These are metal-lined composite cylinders with a full fiber wrap.

Type IV cylinder: These are non-metallic composite cylinders with a full fiber wrap.

These classifications are important for understanding the construction and safety features of gas cylinders, which can vary depending on the type and materials used in their manufacture.

Metal hydrogen storage cylinders, typically made from high-performance materials like steel, have limitations in terms of their pressure resistance. In the early days, steel cylinders were limited to storage pressures of 12 to 15 MPa, with a hydrogen gas mass density of less than 1.6%. Increasing the thickness of the storage tank can increase the hydrogen storage pressure to some extent but reduces the tank's volume. For example, at 70 MPa, the maximum volume is only 300 liters, and the hydrogen gas mass remains low.

Since these tanks are often made from high-strength seamless steel pipes with spun closures, as material strength increases, they become more sensitive to hydrogen embrittlement. Hydrogen embrittlement occurs when hydrogen dissolved in steel forms hydrogen molecules, leading to stress concentration that exceeds the steel's ultimate strength and results in tiny cracks within the steel, also known as hydrogen-induced cracking or "white spots." This increases the risk of failure.

Additionally, because metal hydrogen storage steel cylinders are single-layer structures, they cannot be continuously monitored for safety in real-time. As a result, these tanks are only suitable for stationary and low-capacity hydrogen storage and cannot meet the requirements for vehicular systems, where safety and real-time monitoring are crucial.

With the development of hydrogen technology, there has been an increasing demand for high-pressure hydrogen storage technology with higher container capacity. Metal-lined fiber-wrapped tanks have gradually gained popularity in this context. These tanks feature a metal liner made of stainless steel or aluminum alloy to contain and seal the hydrogen gas, while a fiber-reinforced layer serves as the pressure-bearing layer, allowing for hydrogen storage pressures of up to 40 MPa.

The advantage of using a metal liner is that it can be relatively thin since it doesn't bear the primary pressure load. This significantly reduces the weight of the storage tank. Moreover, the use of a multi-layer structure not only prevents corrosion of the internal metal layer but also creates sealed spaces between layers, enabling real-time monitoring of the tank's safety status.

Due to its relatively lower cost and higher hydrogen storage density, metal-lined fiber-wrapped tanks are often used for large-volume hydrogen storage applications. They offer a good balance between structural integrity and hydrogen storage capacity, making them suitable for various hydrogen storage needs in the growing hydrogen energy industry.

To further reduce the weight of storage tanks, people have turned to lightweight composite fiber-wrapped tanks that use plastic with a certain level of stiffness to replace metal. These tanks typically consist of three layers: a plastic liner, a fiber-reinforced layer, and a protective layer.

Plastic Liner: The plastic liner not only helps maintain the shape of the tank but also serves as a mold for the fiber wrapping. Plastic liners have advantages such as superior impact resistance compared to metal, excellent air-tightness, corrosion resistance, high-temperature resistance, high strength, and toughness.

Fiber-Reinforced Layer: This layer provides the tank with structural integrity and strength. It is responsible for bearing the pressure of the stored hydrogen.

Protective Layer: The protective layer helps shield the tank from external factors that could potentially damage it.

The use of lightweight composite fiber-wrapped tanks significantly reduces the tank's weight, typically around 50% of the weight of an equivalent-capacity steel cylinder. As a result, these tanks are highly competitive in vehicle hydrogen storage systems.

To further enhance the lightweight characteristics of these tanks, three optimization methods have been proposed:

Enhanced Hoop Wrapping: Reinforcing the hoop wrapping of the tank's cylindrical section to reduce the number of wrapping layers.

High-Angle Spiral Wrapping at Edges: Using a high-angle spiral wrapping technique at the tank's edges to reduce the fiber usage.

Low-Angle Spiral Wrapping at the Bottom: Employing a low-angle spiral wrapping method at the tank's bottom to reduce the number of wrapping layers and fiber usage by 40%.

These optimization techniques contribute to making the tanks even lighter while maintaining their structural integrity and safety.

Type I and Type II have low hydrogen storage density and are susceptible to hydrogen embrittlement issues, which makes them less commonly used for vehicular hydrogen storage.

Type I:
Low hydrogen storage density.
Poor safety performance.
Heavy in weight.
This type has the most mature technology and was used early in the development of hydrogen storage.
Limited applications in passenger cars and trucks using Compressed Natural Gas (CNG).

Type II:
One side of the inner liner is made of steel.
Utilizes a process involving the spiral wrapping of glass fiber or carbon fiber.
Primarily used in the transportation sector for CNG vehicle cylinders.
A small number of Type II cylinders are used in the storage and transportation market.
Manufacturing standards for CNG vehicle cylinders include GB24160 and various enterprise standards.
While Type I and Type II hydrogen storage cylinders have been used in certain applications, their limitations in terms of low hydrogen storage density and safety concerns have led to the development and adoption of more advanced hydrogen storage technologies like Type III and Type IV cylinders, which offer better performance and safety for hydrogen-powered vehicles.

Type III and Type IV hydrogen storage cylinders are two different types of pressure vessels used for storing hydrogen gas, and they have some differences in terms of materials, manufacturing processes, and applications.

Type III Hydrogen Cylinder:

Materials: Type III cylinders are typically made of steel or aluminum for the inner liner and then use carbon fiber or glass fiber full-winding technology for the protective layer.
Applications: Type III hydrogen cylinders are mainly used in lightweight CNG (compressed natural gas) vehicles, hydrogen fuel cell vehicles, hydrogen fuel drones, and other markets.
Standards: The domestic standard for automotive hydrogen cylinders is "Vehicle Compressed Hydrogen Aluminum Liner Carbon Fiber Full-Winding Cylinder" GB/T 35544-2017.

Type IV Hydrogen Cylinder:
Materials: Type IV cylinders typically have a plastic inner liner, and the inner liner material complies with relevant standards. They also use carbon fiber or glass fiber full-winding technology to reinforce protection.
Applications: Type IV hydrogen cylinders are more common in the international market, but they are not widely used in the domestic market in China, and there are no relevant standards.
Both of these types of hydrogen storage cylinders offer advantages such as lightweight construction and increased hydrogen storage density, making them suitable for applications like fuel cell vehicles. The choice between these two types of cylinders depends on specific application requirements and regional standards. Both Type III and Type IV cylinders are widely used in the field of on-board hydrogen storage, but the selection of the appropriate type depends on the specific project and requirements."

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