Storage and Transport of Hydrogen as a Potential Fuel

Gaseous hydrogen can be piped as is natural gas, with preference for plastic pipe to avoid questions of hydrogen embrittlement of steel. Large volume storage of hydrogen (as is presently the case for natural gas) may be possible in favorable geological underground formations. Caverns presently sought for storing or “sequestering” unwanted CO2 underground may conceivably also prove [115] useful alternatively for storage of hydrogen gas or as large pressure vessels to store energy, if fitted with compressors and exhaust turbines to generate electricity.

Liquid hydrogen requires the low temperature of 20.3 K. Liquid hydrogen has high energy density per unit mass, but on a volume basis the energy density is about a factor 4 less than gasoline or diesel fuel. Storage tanks for liquid hydrogen, which are vacuum vessels with “superinsulation” in the form of 30-300 layers of aluminized mylar, are available in a variety of sizes, including 1001 and 1901. These tanks accommodate hydrogen liquid at atmospheric pressure, without internal refriger­ation and have losses in the range of 1% per day, decreasing with increasing tank volume. A line of sedans has been developed and tested by manufacturer BMW that use such liquid storage tanks, the gas powering internal combustion engines.

The schematic in Figure 9.6 [116] of a proposed process cools hydrogen at atmospheric pressure in a series of three heat exchangers, each heat exchanger block being cooled by expansion ofa mixture ofneon and helium gas. The proposed cycle would require only one pass of hydrogen through the system, while existing cycles require multiple passes to liquefy all the gas. The energy and capital expenses in liquefaction are not negligible. Commercial liquefaction schemes usually involve compression of the hydrogen gas.

Tank trucks are on the highway transporting liquid helium, and other high-value cryogenic liquids including liquid oxygen and liquid nitrogen. Liquid natural gas is

Storage and Transport of Hydrogen as a Potential Fuel

Figure 9.6 Possible single-pass low-pressure hydrogen liquefaction cycle, proposed [116] by Gas Equipment Engineering Corp. In this diagram, the resistor-like symbols are heat exchangers, and the cooling occurs as the He-Ne gas mixture, initially pressurized, is allowed to expand.

transported on a larger scale by ship and railroad tank car. On a large scale, hydrogen transport as a liquid is economic for some applications.

On the smaller scale, to replace the gas tank of an automobile, liquid storage may be a less viable option, since the fuel would disappear over relatively short storage times. At present, the most common hydrogen storage is in a high-pressure tank.

9.7

Updated: October 27, 2015 — 12:10 pm