Warm flushing & first fill

Every new hydrogen tank starts its life full of the wrong gas.

Type IV MEGCs leave the factory pressurised with nitrogen — around 20 bar of it. Before a tank can carry hydrogen, that nitrogen has to go. How you remove it determines what the job costs, how long it takes, and whether the tank comes through the process undamaged.

The wrong way is cheap equipment and expensive gas. Conventional cold flushing dilutes the nitrogen through wide pressure cycles, typically 20–60 bar, burning through hydrogen with every round. It works. It is also wasteful — and hydrogen is not a gas you want to waste.

Our way is warm. At Kløfta, we flush at 0.2–3 bar in a controlled sequence of pressure cycles, using heated hydrogen from our own biohydrogen production. The physics are simple: when the cylinder is conditioned above 25 °C, the internal pressure can safely be taken down to near-atmospheric levels, and each cycle removes far more nitrogen per kilogram of hydrogen spent. The result is 90 % lower hydrogen consumption than the cold method — roughly 800 kg of hydrogen saved per flush on a 45 ft high cube container.

Why 25 °C matters. The polymer liner in a Type IV cylinder only tolerates atmospheric pressure when the tank is warm. Release the pressure cold, and the liner can be permanently damaged. Temperature is not a comfort setting here; it is a structural requirement. That is why the work happens in our ATEX-approved indoor hall — held above 25 °C year-round, Norwegian winter included. The flush gas itself is combusted flamelessly into water and heat, and the heat goes straight back into the hall. Nothing is vented, nothing is wasted.

Then we fill — and prove it. After flushing, the tank gets its first fill of hydrogen at 99.97 % purity. Every delivery is verified by gas analysis and leaves with a certificate of analysis documenting less than 300 ppm total impurities, plus ADR transport documents and safety data sheets, collected on My Page.

The practicalities. 20 and 30 ft containers take 4 working days; 40 and 45 ft take 5. You can read about our first week of warm flushing at Kløfta. Send an enquiry and we confirm your schedule — normally within one working day.