[ gas cooling ]
Types of compressed hydrogen gas cylinder
The construction of compressed gas cylinders is categorised as Type 1 , 2 , 3 , 4 or 5 . The most common type of industrial gas cylinder is a Type 1 cylinder . It is of an all-metal construction , essentially meaning that it is made from an alloy of either steel or aluminium . The typical working pressure of such cylinders is in the range of 200 to 300 bar .
Type 1 cylinders are manufactured from metal . Type 1 steel cylinders filled to a pressure of around 300 bar are used for intermediate-pressure hydrogen storage at refuelling stations .
A Type 2 cylinder builds on the Type 1 construction and adds a hoop-wrap of a composite material around the metal cylinder . A hoop wrap , also referred to as a body wrap , covers the vertical wall of the cylinder but does not enclose the heel nor the shoulder . Type 2 cylinders filled to a pressure of around 1,000 bar are used for high-pressure hydrogen storage at refuelling stations .
Type 3 cylinders are similar to Type 2 , but the composite wrap covers the entire metal cylinder . Type 3 cylinders are generally constructed with an aluminium alloy body with a glass fibre , Kevlar ® , or carbon fibre composite wrap . When using an aluminium alloy liner and carbon fibre composite full-body wrap , the operating pressure of a Type 3 cylinder is generally 350 or 700 bar – the standard pressures for onboard hydrogen storage on trucks and buses or passenger cars .
Type 4 cylinders are of a similar construction to the Type 3 design . However , the liner is plastic , not metal . Generally , a thermosetting carbon fibre composite material is used as the wrap . The liner is generally made from polyethylene or polyamide . Where carbon fibre composite is used , the working pressure of a Type 4 cylinder can be up to 1,000 bar for static storage of compressed hydrogen gas or 700 bar where the cylinder is used to store hydrogen on a vehicle . A disadvantage of many established Type 4 hydrogen gas cylinders is that the liner is a thermoplastic material , and the wrap is a thermosetting polymer . The adhesion between the two is not perfect , and a residual pressure of around 20 bar is required in the cylinder to avoid the liner from collapsing and separating from the outer composite layer .
Type 5 cylinders are of a composite construction , without an internal liner . They have only rarely been used for aerospace and defence applications . A potential advantage of a Type 5 cylinder is that the issues of the liner separating from the outer composite layer can be avoided . This would allow the full content of the cylinder to be used , which makes storage more efficient . It would also potentially allow a vacuum to be pulled on the cylinder to enable rigorous cleaning to maintain the best possible purity of hydrogen .
Hydrogen Tech World | Issue 16 | June 2024 47