Environmental Engineering Reference
Hydrogen-enriched natural gas buses are expected to meet the
California Air Resources Board's transit emissions requirements. They
also pave the way for a hydrogen infrastructure that can support fuel cells
for transportation. The use of hydrogen powered buses and infrastructure
facilities conforms with the goals of the California Fuel Cell Partnership,
the U.S. Department of Energy, the U.S. Department of Transportation,
and the U.S. Environmental Protection Agency.
UniTrans is the host and operator of the clean fleet and the refueling
facility. The Yolo County Transportation District will operate the project
buses serving Sacramento, including the Sacramento International
Airport. UC Davis is the technical lead for design and evaluation. NRG
Technologies, Inc., is modifying the natural gas buses to operate on a
mixture of compressed natural gas (CNG) and hydrogen.
A commercial CNG bus with a John Deere 8.1 liter engine will undergo
modifications to the engine for operation on a mixture of 30% hydrogen and
70% natural gas by volume. This is expected to reduce emissions of NO x
substantially without a significant reduction in engine power.
Freightliner and the U.S. Department of Energy Advanced Vehicles
Program are exploring using fuel cell auxiliary power units (APUs) in lieu of
main engine idling in their vehicles. The truck auxiliary power application
may offer a viable near-term market for small (1- 5-kW) fuel cells.
It is estimated that idling uses 9,090 gallons of fuel over five years
for an average late model truck that idles 6 hours per day, 303 days
per year. The fuel cost over this five-year period could be $35-40,000 in
addition to preventative maintenance and engine overhauls. Idling is also
estimated to contribute 1 to 3 tons of nitrogen oxide emissions and 40 to
120 tons of carbon dioxide over a five-year period. Fuel cell APUs in lieu of
idling could greatly reduce truck fuel consumption, pollution emissions,
greenhouse gas emissions, and trucking costs.
At Forschungszeutrum Julich GmbH in Julich, Germany, scientists
developed an in-line reformer to oxidize carbon-containing fuel impurities
in a liquid state instead of a gaseous state. By reforming in a liquid, a
fuel cell avoids the energy losses associated with reforming fuels in gas.
Compared to pure gaseous oxygen, liquids are easier to store and handle.
Oxidized impurities in the fuel are also adsorbed and oxidized by
the reactor which has U.S. Patent 6,068,943. Suitable oxygen-containing
compounds include peroxo monosulfuric acid, a peroxide of the alkali
or alkaline earth metals in an acid solution. These oxygen-containing
compounds can be catalytically decomposed to release oxygen. Liquid