Hydrogen fueled vehicles, such as Toyota's FCV and Hyundai's Tuscon Fuel Cell, face a chicken or egg predicament: consumers are rightfully hesitant to invest in such vehicles if they don't have a convenient way to refuel them, and energy companies don't want to cough up dollars for costly infrastructure without significant numbers of such vehicles on the road. But a study by researchers at Sandia National Laboratories says that more existing gas stations in California could readily integrate hydrogen fuel than previously thought.
The fundamental safeguards for the generation, installation, storage, piping, use and handling of hydrogen in compressed gas or cryogenic liquid form are covered by the National Fire Protection Association (NFPA) hydrogen technologies code. Under the previous code requirements established in 2005, no existing gasoline stations could readily accept hydrogen.
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However, this code was developed for flammable gases in an industrial setting and not hydrogen fuel at a fueling station, which poses different risks. In response to this, a new code, known as NFPA 2, was published in 2011.
Focusing on California, which already has the largest number of hydrogen fueling stations of any US state, the Sandia study determined that, based on the current code, 14 of the 70 commercial gasoline station examined could readily accept hydrogen fuel, while another 17 could do so with property expansions.
These findings relate to separation distances outlined in the NFPA 2 code that are based on Sandia's research into the physical behavior of hydrogen and risks associated with the fuel. The code defines the required distances between fueling infrastructure – including fuel dispensers, air intakes and tanks and storage equipment – and public streets, parking, on-site convenience stores and perimeter lines around the site.
According to Chris San Marchi, manager of Sandia’s hydrogen and metallurgy science group, due to the separation distances outlined in the code, many small gas station lots will not be able to be properly configured to accept hydrogen fuel.
"Certain smaller gas stations, especially those in cities, have unusual shapes that aren’t going to accommodate the right separation distances," San Marchi said.
However, he says that there is the possibility of developing risk mitigations that would allow wider deployment of hydrogen fueling stations. This will be the next focus for Sandia. Because the current code covers both gaseous and liquid hydrogen, Sandia is in the process of examining the potential to shorten separation distances for storage of the latter at fueling stations.
Liquid hydrogen is more attractive to site operators as it takes up less space than gaseous hydrogen, however, the low temperatures required for liquid hydrogen systems do pose additional challenges for small sites.
"We need to do more experimental and modeling work to understand and evaluate the science and physics of liquid hydrogen," said San Marchi. "By evaluating the risks quantitatively, we believe we can shorten the separation distances required in the code for liquid hydrogen just as we did with gaseous hydrogen. That could then lead to even more fueling stations that can accept hydrogen and support the continued growth of the fuel-cell electric vehicle market."
The study was conducted as part of Sandia's hydrogen safety, codes and standards program, which is funded by the Department of Energy's Fuel Cell Technologies Office and is tasked with providing the technical basis for developing and revising safety codes and standards for hydrogen infrastructure, including the NFPA 2 code.
"We’re comfortable with the risks of natural gas in our homes and under our streets," San Marchi says. "We want to be just as confident of the safety of hydrogen in our fuel tanks and on our street corners. Whether you are filling your car with gasoline, compressed natural gas or hydrogen fuel, the fueling facility first of all must be designed and operated with safety in mind."
The Sandia study can be downloaded here (PDF).
Source: Sandia Labs