Synthetic Fuels with Advanced Engines or Hydrogen and Fuel Cells as a Medium-Term Solution?
11 September 2006
The transportation sector may find that synthetic fuels combined with next-generation advanced compression-ignition engines are more cost- and energy-efficient than using refinery-produced hydrogen to power fuel-cell vehicles in the medium term, suggests Thomas Rostrup-Nielsen of Haldor Topsoe. Topsoe is one of the world’s leading catalyst companies.
He made the remarks during a plenary address to a symposium on hydrogen production at the 232nd National Meeting of the American Chemical Society in San Francisco.
Although the long-term goal is the development of systems for the cost-effective production of hydrogen from renewable resources, he noted, in the present—and likely into the medium-term—steam reforming of hydrocarbons is still the most cost- and energy-efficient process even with carbon capture and sequestration factored in.
Carbon capture and sequestration basically doubles the cost of hydrogen produced via steam methane reforming, according to figures Rostrup-Nielsen showed—and its cost still comes in below other hydrogen production methods at this point in their development.
Although the financial costs are much higher, hydrogen production from non-fossil sources offers much lower overall GHG emissions.
Advances in the large-scale refinery production of hydrogen via steam reforming using gaseous hydrocarbon feedstocks (methane, refinery off-gases, LPG, and so on) have become increasingly efficient, with current processes requiring about 2.98 Gcal of energy for each 1,000 normal cubic meters of hydrogen produced.
Theoretically, the lowest consumption required—from stoichiometry—would be about 2.81 Gcal (when using liquefied hydrogen). Thus, current advanced reforming processes consume about 6% more energy thant the theoretical minimum, according to Rostrup-Nielsen.
As a result, he said, the cost of hydrogen at the refinery gate is approximately equivalent to that of gasoline. It’s the other factors downstream from the refinery—such as transportation and distribution—that push the cost of hydrogen to 3-4 times that of gasoline.
While distributed reforming to produce hydrogen—at a filling station, for example—could address some of those additional costs, it also would open up other challenges. Carbon capture and sequestration would be difficult to perform economically with distributed production, Rostrup-Nielsen noted. Even assuming the carbon capture was cost-effective, there then would arise the issue of what to do with the carbon dioxide and how to transport it.
Yet even with the efficiency of centralized hydrogen production, synthetic fuels combined with coming advanced combustion engines and powertrains could end up with a well-to-wheels energy efficiency comparable to that of using hydrogen produced via steam reforming in a refinery and a fuel cell, he said.
With advances in existing engine technologies, and using existing infrastructure, one could consider whether it is a good idea in the interim to go [for distributed production of hydrogen]. Use the money saved [by opting for synfuels and advanced engines] for developing hydrogen production from renewable energy sources. It’s an interesting set of tradeoffs.
It is important that one does not pursue hydrogen as a matter of religion but as an educated decision.—Thomas Rostrup-Nielsen
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