Environmental Engineering Reference
In-Depth Information
Automaker Honda in 2008 [114] released its hydrogen-fuel cell powered sedan, the
FCX. This vehicle has a 280 mile range, using pressurized hydrogen. Pressurized
hydrogen is available only in a few places, for example, at $5/kg at a series of stations
in California. This auto is expensive, largely owing to the cost of the fuel cell. It
accelerates rapidly and can reach 100 mph. The manufacturer is said to have a
production line available, which it can run when the infrastructure of hydrogen
stations expands. At the moment, the manufacturer is leasing these cars at a low
introductory rate. This car has a fuel cell the size of a desktop PC that weighs about
150 pounds and has a power rating of 100 kW (134 hp, at 746W/hp). It is anticipated
that the cost of the fuel cell unit will fall, so that the cost of producing the car will fall
from several hundred thousand dollars to below $100 000. The manufacturer says
that the car is ef
cient, equivalent of 74 miles a gallon of gas. Other manufacturers
sell cars that simply burn hydrogen gas in an internal combustion engine, an
expedient that loses the efficiency inherent to the fuel cell/electric motor combina-
tion, and ignores the release of carbon dioxide.
9.6
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 CO
2
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 100 l and 190 l. These tanks
accommodate hydrogen liquid at atmospheric pressure, without internal refriger-
ation 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 of a mixture of neon 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
