Hydrogen and Fuel Cells - Transportation and Distribution
Transportation of hydrogen for industrial use has been ongoing since the early part of this century. As demand for gasoline and heating oil became greater, the need for hydrogen to process these fuels also increased, as did use in making carbon dioxide. Storage methods initially consisted of gaseous hydrogen held in steel cylinders, pressurized up to 2,000 pounds per square inch (PSI). After many years of successful use, steel hydrogen tanks show no sign of corrosion or degradation of any kind, as hydrogen is not caustic or toxic. More recently, storage tanks have been reinforced with composite carbon fibers, making them ten times stronger than steel, greatly enhancing the safety with which gaseous hydrogen can be handled. Roy McAlister, writing for Natural Science magazine, states that these composite fiber tanks can "readily resist the impact of a 100-MPH collision, an attack with a .357 magnum pistol, or a bonfire test in which the tank's surface reaches 1,500 degrees Fahrenheit."
In the 1990's, most conventional transportation of hydrogen takes place with hydrogen in the form of a cryogenic or super-cooled liquid. Hydrogen becomes a liquid at temperatures below -423 degrees Fahrenheit, requiring a complex and energy intensive process consisting of treatment with liquid nitrogen and a sequence of compressors. Once liquefied, the space requirements for storage are greatly reduced, although proper insulation must be assured to keep the liquid hydrogen from boiling off, as it will quickly evaporate if temperatures rise. Stored in large pressurized tanks, the liquid hydrogen can then be transported by ship, barge, train or truck.
Safety issues surrounding conventional storage and transportation of hydrogen focus on the flammability and explosive qualities of gaseous hydrogen, as any accident involving the exposure of liquid hydrogen to the environment means evaporation into a gaseous state. The possibility also exists of a leak in piping or industrial equipment, presenting problems of detection and fire suppression. As hydrogen ignites in air in very low concentrations, and ignition can be instigated by something as simple and commonplace as a static electric spark, these potential problems must be monitored very carefully.
NASA has worked in concert with the International Standards Organization and the U.S. Department of Energy to establish world wide codes and standards for the safe handling of hydrogen. As the largest consumer of liquid hydrogen, NASA has also led the way toward greater safety by sharing some of its technological developments with industry. This includes enhanced ability to detect hydrogen leaks and fires, which pose a tremendous but hidden threat, as hydrogen burns producing no visible flames. Discussions continue as to whether an odorant should be added to hydrogen gas, as it is to the natural gas we use in out homes so we can smell a gas leak, or whether more work needs to be done on sensing equipment for leak detection.
Pipelines carrying natural gas are also capable of delivering hydrogen gas, and these two gases can even be transported together and separated at the point of use. Natural gas, labeled chemically as methane, has a greater density than hydrogen, which means it takes three times the volume of hydrogen to equal the energy in a given amount of natural gas. But at its lower density, hydrogen can be pumped through a pipeline at three times the flow rate of methane, balancing a delicate energy equation. An extensive network of natural gas pipelines have been efficiently delivering natural gas from the fields where it is collected to the refineries where it is processed for many years, and from those refineries to millions of homes in the U.S. and abroad, demonstrating that this type of transportation is safe and dependable. As long as industrial codes and safety standards are stringently followed, the same should be true of transporting hydrogen.
Another factor to be examined when considering pipeline delivery of hydrogen gas in a municipal energy setting is the efficiency with which the energy can be transported from its point of origin to the consumer. Delivery of electric power from large power plants over high voltage power lines has a certain energy loss factored in, increasing its cost. With efficient pipeline delivery of hydrogen gas, a well-maintained system at our present level of technical ability can give the consumer equal or greater value for their energy dollar, as more of the energy put in to the system actually reaches the customer.