hydrogen storage tanks
17 October 2024Hydrogen is the most abundant element in nature, constituting about 75% of the matter in the universe. However, the abundance of molecular hydrogen on Earth is quite low, while the abundance of hydrogen in combined forms is very high.Therefore, hydrogen needs to be produced through water splitting or other chemical reactions. Once generated, hydrogen must be stored and transported to the end users. Thus, hydrogen storage and transportation serve as the bridge between hydrogen sources and users, playing an irreplaceable role in the development of hydrogen energy.
Due to its very low density of just 0.0899 g/L, hydrogen has excellent combustion properties, igniting quickly with low energy requirements and a wide flammable range when mixed with air. This poses challenges for hydrogen storage and transportation, primarily focusing on ensuring safety and improving efficiency.
Hydrogen must undergo various storage and transportation processes from the hydrogen production facility to the end users. The transportation methods for hydrogen can be categorized based on its state: gaseous hydrogen (GH2) delivery, liquid hydrogen (LH2) delivery, and transportation using other hydrogen carriers.
In applications with lower hydrogen demand and dispersed users, hydrogen is typically stored and transported in high-pressure gaseous form. As early as the early 20th century, seamless steel gas cylinders were used for hydrogen storage and transportation. By the 1970s, the industry began to notice the occurrence of hydrogen embrittlement, leading to the introduction of aluminum cylinders. However, these were much more expensive than steel cylinders and had a lower storage capacity.
To increase the working pressure and reduce costs, metal cylinders started using a circumferential winding process. With the advancement of aerospace and military technologies, full-wrapped cylinders were developed by the 1980s. Due to their lightweight nature, these full-wrapped cylinders were used for mobile or portable applications, such as vehicle-mounted fuel cylinders. Today, fully wrapped composite gas cylinders, including Type III and Type IV cylinders, are used for hydrogen storage and transportation.
Hydrogen storage cylinders can be categorized based on their materials and structures as follows:
Type I Cylinder: Made entirely of metallic materials as pressure vessels.
Type II Cylinder: Features a thin-walled metal liner as the pressure vessel, with the body wrapped in fiber-reinforced composite materials.
Type III Cylinder: Has a thin-walled metal liner as the pressure vessel, with the entire body wrapped in fiber-reinforced composite materials.
Type IV Cylinder: Composed of a polymer engineering plastic liner, fully wrapped in fiber-reinforced composite materials, and equipped with a metal valve installation sleeve.
Currently, high-pressure hydrogen storage and transportation products mainly include industrial steel cylinders, cylinder bundles, long tube trailers, fixed storage containers, and onboard storage containers. Industrial cylinder bundles and long tube trailers can serve both as transportation and temporary storage solutions. Fixed storage containers are typically installed at stations as hydrogen cylinder groups, which can belong to different cylinder types based on their structure.
In addition to the various forms of cylinders used for hydrogen storage and transportation, two traditional chemical container structures are also utilized: layered pressure vessels and steel tape-wound pressure vessels. Currently, a wide variety of cylinder forms are predominantly used for hydrogen storage equipment.
1.Industrial Hydrogen Gas Cylinder Bundle
At present, gas cylinders used for storing and transporting industrial hydrogen are usually designed and manufactured in accordance with the requirements of GB5099 "Seamless Steel Gas Cylinders". The volume range of a single industrial hydrogen gas cylinder is 0.4-80L, and the nominal working pressure is divided into three levels: 15, 20, and 30MPa. The temperature requirement for the use of the cylinder is -20~60 ℃. At present, steel cylinders with a specification of 40L and a working pressure of 15MPa are widely used in the market, with a hydrogen storage capacity of about 0.5kg at room temperature. To increase hydrogen storage capacity, industrial hydrogen storage container bundles are usually made from multiple gas cylinders, consisting of 9-20 hydrogen gas cylinders, with a total hydrogen storage capacity of approximately 3-10kg. Mainly for general industrial or laboratory use hydrogen.
Industrial hydrogen gas cylinders are divided into five types based on their forming structures (a, b, c, d, e). Type A cylinders have a single mouth and a concave bottom; B-type bottles have a single mouth and a convex bottom with a base; The C-type bottle has a single mouth and a convex bottom without a base; The D-type bottle has a single mouth and an H-shaped base; The E-type bottle has a double bottle mouth structure.
For the material requirements of industrial steel cylinders used for storing and transporting hydrogen, they must be materials recognized by relevant national departments, and high-quality manganese steel, chromium aluminum steel, or other alloy steel should be selected. Its chemical composition should comply with the relevant provisions of the national standard GB222. The material should have good impact performance, carbon steel materials should be treated with normalizing, and alloy steel materials should be treated with quenching and tempering. The hydrostatic test pressure of the steel cylinder is 1.5 times the nominal working pressure, and the allowable pressure shall not exceed 0.8 times the hydrostatic test pressure.
2.Hydrogen Long Tube Trailer
The hydrogen long tube trailer that we usually refer to can actually be divided into two types of products. One type is an independent hydrogen long tube trailer. Assembled from several high-pressure gas cylinders in a fixed frame, equipped with corresponding pipelines, valves, and safety devices. The entire installation is on a dedicated semi-trailer chassis, used for transporting high-pressure hydrogen gas. This independent hydrogen long tube trailer, as a special vehicle, needs to comply with the requirements of the Ministry of Industry and Information Technology's "Announcement on Road Motor Vehicle Production Enterprises and Products" regarding market access management for vehicle production enterprises and products, and can only be put on the market for sale after approval of the vehicle announcement. Equipped with a dedicated tractor head, hydrogen can be transported.
Another type is not strictly a hydrogen long tube trailer, but is composed of a dedicated vehicle chassis and a mobile pressure vessel for storing and transporting hydrogen gas. The mobile pressure vessel is a bundle type container that integrates multiple large volume seamless high-pressure gas cylinders through supporting and fixing devices, and is combined with pipelines, valves, safety accessories, instruments, etc. to transport hydrogen gas. It can be easily placed or removed on the dedicated semi-trailer chassis. This product requires an independent certificate of conformity and supervision inspection certificate for mobile pressure vessels. The following two products are collectively referred to as hydrogen long tube trailers.
Long tube trailer is currently the most common hydrogen storage and transportation method used in the global hydrogen energy industry. It is currently the most mature and commercialized hydrogen storage and transportation product in terms of technology. The cost of transporting hydrogen with a long tube trailer increases with distance and is generally suitable for hydrogen transportation within 300 kilometers. Currently, 6-12 large volume seamless steel bladder gas cylinders are commonly installed on long tube trailers used in China, with the main types being Type I and Type II cylinders. The body of Type I cylinder is a seamless large capacity steel gas cylinder, with a single cylinder capacity of up to 3700 liters. The long tube trailer cylinder body composed of Type II bottles is a seamless steel large volume gas cylinder with a glass fiber or carbon fiber structure wrapped around the outer circumference of the inner liner. The maximum single cylinder capacity can reach 4200 liters. The transportation efficiency and economy of a long tube trailer depend on the amount of hydrogen it can load. At present, the working pressure of conventional hydrogen long tube trailers in China is mainly 20MPa. The main specifications and hydrogen loading capacity of long tube trailers are shown in the table below.
3.Station Hydrogen Storage Container
For hydrogen refueling stations, currently in China, hydrogen fuel is mainly provided to fuel cell vehicles in the form of high-pressure gaseous hydrogen gas. The refueling pressure of hydrogen refueling stations is usually divided into two levels: 35MPa and 70MPa. Correspondingly, the working pressure of hydrogen storage devices in hydrogen refueling stations is usually divided into two levels: 45MPa and 90MPa. For hydrogen storage pressure vessels used in hydrogen refueling stations with a design pressure greater than 40MPa, a design temperature not lower than -40 ℃ and not higher than 85 ℃, and a storage medium of hydrogen fuel for vehicles, in addition to meeting the relevant technical requirements of TSG21, they should also comply with the provisions of TCATSI05003-2020 "Technical Requirements for Hydrogen Storage Pressure Vessels in Hydrogen Refueling Stations".
The hydrogen storage container for hydrogen refueling stations, composed of seamless large volume steel cylinders, can be easily combined into a cascade station hydrogen storage system with three pressure levels of "low, medium, and high" according to different cylinder ratios. Under the action of the station sequence control panel, high-pressure hydrogen gas is provided to the hydrogen refueling machine in stages, which can greatly improve the utilization rate of the station hydrogen storage cylinder group and reduce the energy consumption of the compressor in the hydrogen refueling station.
For different hydrogen storage containers, their hydrogen storage capacity can be calculated based on the water volume of the container and the density of hydrogen gas at different ambient temperatures. The table below shows the density of hydrogen gas at different working pressures and ambient temperatures, which can be used as a reference for users to calculate the hydrogen storage capacity of corresponding long tube trailers or fixed hydrogen storage containers.
When storing hydrogen, in order to ensure the safety of high-pressure vessels, the materials used must be hydrogen friendly materials that meet the requirements, and factors such as the microstructure and mechanical properties of the materials, usage conditions, stress levels, and the influence of manufacturing processes on hydrogen embrittlement must be comprehensively considered. The commonly used hydrogen contacting materials are chromium aluminum steel or austenitic stainless steel, with grades such as 4130X, 30CrMo, or S31603.
For 4130X and 30CrMo materials, the chemical composition requirement is C ≤ 0.35% P≤0.015%、S≤0.008%。 After heat treatment, the mechanical properties of the material should meet the requirements of tensile strength Rm ≤ 880MPa in air, yield ratio ≤ 0.86, elongation at break (A) ≥ 20%, average impact absorption energy KV2 ≥ 47J of three standard specimens at -40 ℃, lateral expansion value LE ≥ 0.53mm, ratio of tensile strength in hydrogen and air, and ratio of maximum total elongation at break ≥ 0.9. For S31603 material, its chemical composition requires nickel content Ni ≥ 12%, nickel equivalent Nieq ≥ 28.5%, its mechanical properties require a cross-sectional shrinkage rate of ≥ 70% in air, and the ratio of cross-sectional shrinkage rates in hydrogen and air is not less than 0.9.
4.Vehicle Mounted Hydrogen Supply System
In addition to the storage and transportation of hydrogen at the hydrogen production end, specialized storage equipment is also required at the usage end, especially for on-board hydrogen supply systems represented by fuel cell vehicle applications. The volume and weight of car mounted gas cylinders are limited by the installation scenario. It has special requirements for charging. Therefore, lightweight, high pressure, high hydrogen storage mass ratio, and long lifespan requirements are the characteristics of onboard hydrogen storage systems.
At present, domestic fuel cell vehicles are mainly commercial vehicles, and the main on-board hydrogen supply system used is a system composed mainly of Type III bottles with a working pressure of 35MPa. Among them, the bottle group system with a single bottle capacity of 140 liters has been the mainstream product in the market in the past few years, accounting for over 85%. Starting from 2021, the gas cylinders of the Type III cylinder car mounted hydrogen supply system are gradually developing towards larger capacities such as 165 liters, 260 liters, 320 liters, and 385 liters.
With the tilt of national industrial policies towards fuel cell commercial vehicles and heavy-duty trucks, the onboard hydrogen supply system has evolved from the initial 3-bottle system for logistics light trucks to 4-bottle, 6-bottle, 8-bottle, and other systems.
Type III hydrogen cylinders for vehicles are designed, produced, and inspected in accordance with the national standard GB/T35544 "Compressed Hydrogen Gas Cylinders with Aluminum Inner Cylinders and Fiber Wrapped Cylinders for Vehicles". Suitable for refillable hydrogen cylinders with a nominal working pressure not exceeding 70MPa, a water volume not exceeding 450 liters, and a working temperature not lower than -40 ℃ and not higher than 85 ℃. Type III hydrogen cylinders can be divided into T-type cylinders and S-type cylinders according to their structural forms. The T-shaped bottle has a single mouth and convex bottom structure, while the S-shaped bottle has an open end structure at both ends. As shown in the following figure:
According to different work pressures, Type III bottles are divided into Class A and Class B. A-class hydrogen cylinders are gas cylinders with a nominal working pressure of less than or equal to 35MPa. The water volume of A-class cylinders is not more than 450 liters, with a design cycle of 11000 times and a design service life of 15 years. B-class gas cylinders are gas cylinders with a nominal working pressure greater than 35MPa, a nominal water volume of no more than 230 liters, a design cycle of 7500 times, and a design service life of 10 years. When the service life of two types of gas cylinders has not reached the design service life, but the filling cycle has reached the design cycle number, they should be scrapped.
The inner liner of Type III gas cylinders is generally made of 6061 aluminum alloy material. The inner liner can be formed from aluminum alloy sheets, pipes, or rods. The chemical composition of the material shall be retested according to GB/T7999 or GB/T20975. The aluminum alloy liner should be a seamless gas cylinder, and different cold forming methods should be used for different aluminum alloy profiles, such as extrusion, cold stretching, stamping, spinning, etc. The aluminum alloy liner should not be welded into shape.
Continuous untwisted carbon fiber should be used as the load-bearing fiber, and mixed fibers should not be used. Fiberglass can be used as a layer to prevent galvanic corrosion or as an outer surface protective layer.
At present, the domestic on-board hydrogen storage systems mainly use 35MPa Type III bottles, with a mass hydrogen storage density of less than 5%. There are also a small number of 70MPa Type III bottle systems on the market, but the increase in wall thickness and working pressure has not had a significant positive impact on the improvement of hydrogen storage density. Therefore, it is currently mainly used in commercial vehicles, and for small passenger cars, due to the influence of the volume and hydrogen storage density of Type III bottles, it is not suitable for fuel cell passenger cars in China.
In the international market, vehicle mounted hydrogen storage systems mainly use Type IV bottles as hydrogen storage containers. Under the same outer diameter, volume, and working pressure, Type IV bottles have the advantages of lower cost, lighter weight, and higher hydrogen storage density compared to Type III. At present, China's Type IV bottles are still in the stage of product development, and relevant standards and regulations are not yet perfect. At present, there is only one group standard, T/CATSI02007-2020 "Compressed Hydrogen Plastic Inner Cylinder Carbon Fiber Fully Wrapped Gas Cylinder for Vehicles", released in 2020.
5.Safety Requirements for Hydrogen Storage and Transportation Process
Hydrogen is a colorless, odorless, flammable, and explosive gas. Hydrogen contains a mixture of oxygen, chlorine, carbon monoxide, and air, which poses an explosion hazard. Due to the low ignition point and high explosive energy of hydrogen, strict safety precautions must be taken during production and storage. The production, use, and storage of hydrogen should comply with the relevant provisions of GB4962 "Regulations on the Management of Hazardous Chemicals" and "Regulations on the Safety Supervision of Special Equipment".
Before repairing or handling hydrogen pipelines, equipment, and gas cylinders, it is necessary to replace the hydrogen content in the container and auxiliary pipelines with inert gas to meet safety requirements before carrying out other related maintenance work.
When hydrogen gas leaks or is rapidly discharged from the nozzle of a gas cylinder, static sparks can be generated due to high-speed friction of the gas. Therefore, when bottled hydrogen gas leaves the factory, it should be ensured that there is no leakage from the nozzle and valve of the cylinder, and the bottle cap should be tightened. When using bottled hydrogen, the bottle valve should be slowly opened.
Bottled hydrogen should be stored in a place without an open source of fire, away from heat sources and oxidants, and in a well ventilated area. The construction, electrical, fire-resistant, and explosion-proof requirements of the hydrogen cylinder warehouse should comply with relevant regulations.
At present, the development of the domestic hydrogen energy industry is in the initial exploration stage of cost reduction and efficiency improvement, technological innovation, and collaborative promotion. The synergistic effect of the upstream and downstream of the hydrogen energy industry chain has not yet been fully demonstrated. When can the cost of fuel cell vehicles decrease? When can the core technology issues of hydrogen energy be overcome? The question of when hydrogen energy applications can truly be implemented is gradually becoming apparent......