High Pressure Gas Generation Unit (HPGU) and Leak Test Module (LTM)
System Layout with Key Features
High Pressure Gas Generation and Recovery Methods
The high pressure generation unit (HPGU) is housed within a bespoke ISO shipping container.
The HPGU charges a hydrogen fuel tank to the test pressure of either 350bar or 700bar with a tracer gas mix of 5% helium and 95% nitrogen, (saving on gas costs of using 100% Helium) for use in the leak test module (LTM).
The HPGU receives the tracer gas mix, which is stored at low pressure, around 10barg, in the low pressure recovery vessel before being compressed to 350barg and stored.
Some of this 350barg gas is compressed to 900barg and stored. This compressed gas is used to fill the hydrogen fuel tank being tested within plant by sending the gas to the LTM enclosure. First the fuel tank is filled from the 350barg storage to an intermediary pressure, then the fill finished from the 1000barg storage to top up the fuel tank to the test pressure. For the larger volumes and test pressure of 700bar, a third fuel stage where the hydrogen fuel tank is filled directly is included.
Once the test sequence is completed within the leak test module, the hydrogen fuel tank is defueled via the recovery storage. The system can reuse the gas from the tested fuel tank.
A chiller unit which is used in tandem with the heat exchanger cools the tracer gas at various stages of the test process.
The leak test module (LTM) tests the leak tightness of the hydrogen fuel tank via the use of a mass spectrometer.
The hydrogen fuel tank is loaded into the leak test chamber and connects to the test gas line coming from the high pressure generation unit (HPGU). The fuel tank is then filled with the tracer gas to the test pressure from the HPGU, whilst the test chamber is evacuated by the vacuum pumps.
A nitrogen purge of the test chamber occurs at a low vacuum removing any background contamination from the chamber. Once at vacuum, the mass spectrometer detects any helium which may be leaking from the hydrogen fuel tank. Once the test cycle is completed, the test gas in the fuel tank is returned to the HPGU. The fuel tank is then removed from the test chamber prior to the next fuel tank being loaded for the test cycle to be repeated on a new fuel tank.
A preliminary test is carried out by filling a specific amount of tracer gas into the test chamber whilst no fuel tank is present to ensure the mass spectrometer is working as intended and calibrated to the correct range. The calibrated leak test uses low pressure gas from the HPGU.
The leak test module is housed within its own safety interlocked enclosure.