Tanks for the Hydrogen

A cryogenic pressure vessel developed and installed in an experimental hybrid vehicle can hold liquid hydrogen for six days without venting any of the fuel.

Unlike conventional liquid hydrogen (LH2) tanks in prototype cars, the pressure vessel developed by the California-based Lawrence Livermore National Laboratory (LLNL) research team was parked for six days without venting evaporated hydrogen vapour.

LH2 tanks hold super-cold liquid hydrogen at around -420oF. Like water boiling in a tea kettle, pressure builds as heat from the environment warms the hydrogen inside.

Current automotive LH2 tanks must vent evaporated hydrogen vapour after being parked three to four days, even when using the best thermal insulation available (200 times less conductive than Styrofoam insulation).

In recent testing of its prototype hydrogen tank onboard a liquid hydrogen powered hybrid, LLNL’s tank demonstrated a thermal endurance of six days and the potential for as much as 15 days, helping resolve a key challenge facing LH2 vehicles.

Today’s automotive LH2 tanks operate at low pressure (2-10 atmospheres). The LLNL cryogenic capable pressure vessel is much stronger, and can operate at hydrogen pressures of up to 350 atmospheres, which is similar to scuba tanks.

The high-pressure means that a vehicle’s thermal endurance improves as the tank is emptied, and is able to hold hydrogen fuel indefinitely when it is about one-third full.

LLNL’s Salvador Aceves (left) and Tim Ross check out the on-board hydrogen storage tank that powers a prototype hybrid vehicle.

Last year, an LLNL experimental hybrid vehicle demonstrated the longest driving distance on a single tank of hydrogen (650 miles).

The Livermore work, sponsored by the US Department of Energy’s (DOE’s) Office of Energy Efficiency and Renewable Energy, is part of the DOE’s National Hydrogen Storage Project to demonstrate advanced hydrogen-storage materials and designs.