Safety analysis of hydrogen for fuel cell vehicles

Safety analysis of hydrogen for fuel cell vehicles

Hydrogen energy, as a clean, efficient, safe and sustainable new energy, is regarded as the cleanest energy with the greatest development potential in the 21st century and is the strategic energy development direction.

1. Is hydrogen safe?

The safety performance is no less than that of common fuels and can meet application requirements.

The characteristics of hydrogen are analyzed as follows.

The leakage rate of hydrogen is faster than that of common fuels, but the total leakage energy is not high.

Hydrogen has a high diffusion coefficient and buoyancy, and the concentration can be quickly reduced when leaking.

The explosion limit range of hydrogen is wide, but the explosion energy is very low and does not produce thick smoke and haze.

Hydrogen embrittlement can cause metal embrittlement cracks, which can be avoided by selecting appropriate materials for protection.

2. Is the storage and transportation of hydrogen safe?

Mainly transported by gas hydrogen trailers, with perfect safety measures from filling to storage and transportation.

The main ways of transporting hydrogen are: gas hydrogen trailer transportation (tube trailer), gas hydrogen pipeline transportation (pipeline) and liquid hydrogen tanker transportation (liquid truck). From the current demand of hydrogen stations for transportation distance (<500km, 200km is appropriate) and transportation scale (10 tons/day), the best way to transport hydrogen is still the gas hydrogen trailer.

The operation process of the gas hydrogen trailer system is as follows:

The empty gas hydrogen trailer is filled with hydrogen at the centralized hydrogen production plant until it is fully loaded, and then the vehicle drives to the hydrogen station, directly unloads the tubular storage container on the vehicle as the storage equipment of the hydrogen station, and picks up the "empty" tubular container originally located at the hydrogen station and transports it back to the centralized production plant to start a new round of loading.

Hydrogen filling method
In order to compress 7kPa hydrogen at room temperature to 35MPa or even higher in multiple steps for filling with hydrogen long tube vehicles, the entire hydrogen filling  process is very complicated, including compressors, canning systems and other links have corresponding safety measures.

3. Are fuel cell vehicles safe?
The design is complete and provides all-round protection, and the actual operation is safe and effective.

3.1 

On-board hydrogen supply system: design and materials work together to achieve multiple guarantees for hydrogen safety

The on board hydrogen supply system is an important part of fuel cell vehicles. Its main function is to provide hydrogen with stable pressure for the fuel cell system, and its safety measures are mainly based on prevention and monitoring.

From the perspective of technical design: the on-board hydrogen supply system is mainly composed of high-pressure hydrogen storage bottles, filling ports, one-way valves, safety valves, overflow valves, pressure reducing valves, solenoid valves, thermal thrombus, pressure and temperature sensors, and hydrogen pipelines. It not only has functions such as over-temperature protection, low-pressure alarm, over-pressure protection, and over-current protection, but also takes into account collision safety and hydrogen leakage control.

From the perspective of component manufacturing: hydrogen bottles and system pipelines used to store hydrogen have high requirements due to hydrogen embrittlement  and other reasons. Choosing appropriate materials and protective structures is crucial to the safety of the hydrogen storage system.
Hydrogen storage bottle material: Aluminum alloy liner carbon fiber high-pressure hydrogen storage bottle, light weight, high hydrogen storage density, excellent toughness and impact resistance;

Hydrogen storage tank protection: adopts an integral design, the entire frame integrates the hydrogen tank into the frame assembly through 3 crossbeams and 2 longitudinal beams to ensure that the dynamic displacement of the high-pressure hydrogen storage bottle will not be too large during the collision to avoid breakage;
Hydrogen system pipeline: Most of the hydrogen pipelines are made of 316 stainless steel, which has outstanding tensile properties, fatigue properties and old crack  extension properties in hydrogen, and good hydrogen embrittlement resistance;

Gas pipe design: The direction of hydrogen discharge from the gas pipe is along the front and rear direction of the bottom of the vehicle, which can protect the cabin from  being affected by the flame.

3.2 Fuel cell vehicle: With strict performance testing and close hydrogen monitoring system
Diverse safety tests can ensure the safety and consistency of fuel cell vehicles when they leave the factory: In addition to ensuring the safety of the on-board hydrogen system, relevant safety tests are applied in the development of fuel cell vehicle power systems. Fuel cell vehicles must undergo multiple safety tests before leaving the factory.

4. Is the vehicle still safe in the face of accidents and extreme situations?

Hydrogen storage bottles are not easy to burst when penetrated by fire, and hydrogen leakage in a confined space is unlikely to cause an explosion. 

Hydrogen safety
There are many practical tests on the safety of hydrogen storage bottles under various conditions. The safety of hydrogen energy is very guaranteed under hydrogen  storage and use technology.

5. Is the hydrogen refueling infrastructure safe?
There are relevant technical specifications to guide, and accelerate the improvement of the industry standard system.

Hydrogen refueling stations are an important part of building a future fuel cell vehicle network.

The safety design of hydrogen refueling stations needs to establish corresponding technical specifications based on the equipment composition and hydrogen refueling mode of the hydrogen refueling station itself. More than 10 countries in the world have formulated hydrogen refueling station regulations, including Japan, the United States, and the United Kingdom. my country also promulgated the "Technical Specifications for Hydrogen Refueling Stations" (GB50516-2010) in 2010. The standards and requirements therein mainly refer to the standards of hydrogen production stations, combined with the original "Building Design Fire Protection Code", which jointly guide the construction of domestic hydrogen refueling stations.
Hydrogen filling device safety: The filling gun is locked by the electromagnetic mechanism after being connected to the gas filling port of the vehicle, and its safety is  comparable to that of the charging connector of an electric vehicle. The pipeline solenoid valve can effectively prevent gas from entering the battery when filling the gas cylinder.
Overall: Due to the rapid diffusion of hydrogen, even if a leak occurs, it will mainly diffuse vertically and will not spread to the surrounding areas. And in the case of a flammable gas cloud being ignited and exploded, as long as the layout of the facilities in the station complies with the safety distance regulations and the explosion-proof wall is reasonably set up, it can ensure that the scope and impact of the accident are within a limited range, indicating that the construction specifications of the hydrogen filling station are reasonable and effective, and can ensure its overall safety.