Hydrogen will play an important role in making our transport more sustainable. Passenger cars with a hydrogen gas fuel cell are already on the market and the infrastructure of service stations is increasing. A possible disadvantage of hydrogen gas, however, is its large volume. Hydrogen gas filling stations must therefore have extensive storage facilities and refueling a vehicle with hydrogen gas takes quite some doing.
In particular in vehicles with large fuel tanks, such as buses, hydrogen gas is therefore not the most optimal sustainable energy alternative. Countries such as Korea, which highly prioritizes CO₂-neutral public transport, are therefore fully committed to the use of liquid hydrogen. Passenger car manufacturers have also been working for years on vehicles that can run on cryogenic hydrogen. One of the challenges they faced was devising a solution for the so-called boil-off gas (BOG).
Release excess hydrogen
Hydrogen liquefies at a temperature of -253 ° C and liquid hydrogen is therefore also referred to as cryogenic hydrogen. However, once in a vehicle's fuel tank, the ice-cold liquid hydrogen irrevocably heats up due to the ambient temperature. Particularly when the vehicle is stationary for a longer period of time, this can increase the pressure in the fuel tank to dangerous levels. This makes it necessary to be able to release some of the excess hydrogen in gaseous form.
Car manufacturer BMW has been pioneering cryogenic hydrogen cars for decades and turned to Kiwa to solve the BOG problem. Kiwa developed a unique safety system for this that uses a state-of-the-art catalytic burner. This system detects the occurrence of boil-off at an early stage and then safely blows off excess hydrogen, after which it is discharged as water through the exhaust. The Kiwa system does not consume electricity, can be used in both high and low ambient temperatures and is suitable for use on cryogenic hydrogen tanks with a pressure of 0.5 to 50 MPa.
Kiwa's boil-off safety system for liquid hydrogen vehicles has been successfully used by BMW in both the BMW Hydrogen 7 (which burns liquid hydrogen in a bi-fuel combustion engine) and the Hydrogen 5 GT (which provides a fuel cell with cryo-compressed hydrogen gas).