5 tips to ensure hydrogen plant safety
1. Select the correct compressed hydrogen storage tanks
Hydrogen can either be stored as a gas or a liquid. The former requires high-pressure tanks (100-1,000 bar or 1,400-14,500 psi), while the latter requires cryogenic temperatures. In this article, we focus on compressed hydrogen gas.
To guarantee optimal hydrogen plant safety, it is crucial to use tanks built with the proper materials.
Depending on the volume and pressure, one of four types of pressure vessels should be used for storing compressed hydrogen.
- Type I
These metal tanks are usually made of steel or aluminum. They can withstand an estimated maximum pressure of 175 bar (aluminum) to 200 bar (steel). Type 1 tanks are cheap to produce but weigh a lot because they consist entirely of metal. They are used for storing hydrogen in liquid and gaseous form.
- Type II
These metal tanks are made of aluminum but feature filament windings around the metal cylinder. These can consist of glass fiber/aramid or carbon fiber. Depending on the material, they can withstand a maximum pressure of up to 299 bars.
Type II tanks weigh less and are stronger but also more expensive.
- Type III
Consisting of composite materials with a metal liner, these tanks can withstand even higher pressure. For example, an aluminum/aramid tank can withstand pressure of up to 438 bar. An aluminum/carbon composite, on the other hand, can even withstand pressures of up to 700 bar. As a result, they are also more expensive.
- Type IV
These tanks feature no metal. They are made entirely of carbon fiber with a polymer liner. They can withstand a maximum pressure of 700 bars even though they weigh less than other types. The downside is that the use of a lot of carbon fiber also makes them more expensive.
2. Select the right materials
Hydrogen has a detrimental effect on the mechanical properties of all materials. For example, it can cause metal to become brittle. This, in turn, can result in a loss of tensile strength, ductility and fracture toughness and lead to accelerated fatigue crack growth.
The degree of this deterioration depends on the material, the pressure and temperature of the hydrogen and the mechanical load. This means that some materials are better than others.
Ideally, the materials should be tested to ensure they perform under the expected operating conditions.
If that is not possible, here are some materials that are commonly used:
- Austenitic stainless steel
- Aluminum alloys
- Low-alloy ferritic steels
- C-Mn ferritic steels
- Copper alloys
On the other hand, the following materials should be avoided:
- High strength ferritic and martensitic steels
- Gray, malleable, and ductile cast irons
- Nickel alloys
- Titanium alloys
3. Select the optimal location to set up hydrogen storage tanks
When it comes to hydrogen plant safety, it is not only important to choose the right storage vessel but also the optimal location to set it up.
While it is possible to store small hydrogen cylinders indoors, that is not recommended for larger volumes.
Outdoor storage is safer overall and even required for storing large hydrogen volumes since this allows the gas to dissipate easily in case of hydrogen accidental leaks.
Here are some characteristics of an optimal location for storing compressed hydrogen.
-Good ventilation to prevent hydrogen accumulation
-Set up at a safe distance from structures and ventilation intakes
-Protected from vehicular traffic or falling objects
-No direct sunlight and ambient temperature should not exceed 52°C (~126°F)
-Protected from unauthorized access
5 characteristics of an optimal location for storing compressed hydrogen.
- Good ventilation to prevent hydrogen accumulation
- Set up at a safe distance from structures and ventilation intakes
- Protected from vehicular traffic or falling objects
- No direct sunlight and ambient temperature should not exceed 52°C (~126°F)
- Protected from unauthorized access
4. Prevent hydrogen gas from building up in a container or enclosure
As noted above, ventilation is extremely important when working with hydrogen.
It ensures that the gas dissipates quickly and cannot form a potentially flammable mix with the oxygen in the air.
Because hydrogen is so light, this buildup is certainly to occur near the ceiling of a room or enclosure.
This must be considered when designing these facilities.
Meaning this implies there needs to be proper high space ventilation, detection, and control measures.
In addition, because a hydrogen leak can never be ruled out, it is also important to install flame and/or gas detectors and, ideally, a fire suppression system.
When H2 is release in an air environment, the gas will immediately go up, and this with a speed of 10m/s. So it’s simply a must to detect H2 concentration at the highest point of the room. And also there you need to foresee ventilation of the room: the air is to be extracted from the room at the highest point. If you put the detector at a lower point in the room, the part of the room above the detector will be filled first with a too high concentration of hydrogen, before you detect the gas. Same for ventilation. If you bring in air from the top and evacuate at a lower level, you will simply not evacuate H2. The ventilation flow is to be from the bottom to the top.
During normal operation, ventilation is not very high. Only when you detect gas at the top of the room, you immediately have to extract a massive amount of air (gas mixture). New buildings for the construction of H2 trucks (and they are also filled inside that building), can install a gas detector near the roof (more than 10 m height), and when gas is detected, the roof simply opens.
5. Prevent hydrogen leaks
Leaks are a major problem for operations using hydrogen since this is such a small element and they are responsible for a large share of incidents.
One way to prevent them from occurring is to install leak detectors, which should be maintained and tested periodically. In any case, leak tests should be conducted routinely, including operational checks for valves.
Two popular test methods are the use of soap bubble solution or a hand-held hydrogen detector. In addition to regular tests, plant operators should also check for leaks every time the joints are reassembled. Furthermore, the system’s connections should be inspected for signs of corrosion, erosion, cracking, bulging, blistering, or any other form of deterioration.