Sandia Labs looks to the liquid hydrogen filling stations of the future
Hydrogen-powered vehicles are here, but we're still a long way from having widespread infrastructure to support them. In anticipation of the hydrogen economy of the future, Sandia National Laboratories (SNL) is working on software models that will help hydrogen refueling stations switch from hydrogen gas to liquid hydrogen while implementing new, easier to follow safety standards.
As an alternative to gasoline and diesel, hydrogen has a lot going for it. It can not only be burned directly in properly designed engines, but it can also power fuel cells for hybrid vehicles. It's the most abundant element in the universe, leaves behind only water as an emission, can be dispensed as fast as conventional fuels and, with the right adjustments, can be handled and transported like natural gas.
The problem is that hydrogen isn't a very dense fuel source – especially in a gaseous state – and there are still very few hydrogen filling stations, with most of those in the United States concentrated in San Francisco, Los Angeles, and San Diego. Worse, the current designs for stations allow for only one pump and not much hydrogen stored on site.
With an increasing number of hydrogen cars expected to be built in the near future to join the estimated 5,000 already on US roads today, a more widespread and efficient hydrogen infrastructure will be needed. To provide this, SNL and the largest American hydrogen retailer, First Element, have entered into a Cooperative Research and Development Agreement to find ways to better use liquid hydrogen, which is much denser than hydrogen gas, so more can be stored in one place.
However, liquid hydrogen has to be kept at a temperature below -253° C (-423° F) and that causes all sorts of headaches. Not the least of these is that the current US National Fire Protection Association safety codes are decades out of date when it comes to handling liquid hydrogen.
Using a new software package, SNL is developing models to help it better understand how liquid hydrogen behaves, especially in cases of leaks. Unlike hydrogen gas, liquid hydrogen is so cold that it freezes the air around it when it escapes, which means it's hard to determine how a leak works, how much hydrogen is in the air, and how far away from a leak the combustion sources are. These are things that need to be solved before large numbers of hydrogen fueling points are established in built up areas with dense populations.
The new SNL models look at how hydrogen and oxygen interact in gaseous and liquid states. Since oxygen has a much higher boiling point, one element will warm as the other liquefies, and vice versa, so the computer model assumes a zone of initial hydrogen and air mixing that is far enough from the leak that the mixture is warm enough to accurately model. This allowed the SNL team a better understanding of how far from a leak will show a flammable concentration.
According to SNL, this modeling will provide First Element with an inexpensive scientific basis for designing and gaining local permits for the 12 fueling stations the company is planning to build in California. In addition, it will help in writing new fire safety codes that are performance based rather than prescriptive. That is, instead of laying out in painful detail how to meet safety standards, the codes will determine what a safe station will look like and it will be up to the supplier to meet those requirements.
The claim is that this will make it easier to build more stations in different states as well as encourage the wider application of hydrogen as an energy source in both the domestic and industrial spheres.
"Our mission has always been to foster the adoption of these cars, ensuring better air quality and energy security," says Tim Brown, COO of First Element Fuel. "That is the part of the project that will live on beyond the particular stations we're building right now."