“On average, when one removes the water, biomass fuels such as wood and hay have a ratio of 40 carbon atoms to four hydrogen,” he said.
“Coal typically has about 8 Cs for each 4 H. Gasoline and jet fuel average about 2 C for each 4 H. Methane burns only one carbon for each four hydrogens – one-fortieth the ratio of wood.”
Ausubel and his colleagues plotted the history of fuel in terms of the ratio of carbon to hydrogen and found a strong trend towards decarbonisation with carbon losing market share to hydrogen much as horses lose market share to cars or typewriters lose to word processors.
“The slow process to get from 90% C to 90% H in the fuel mix should take about 300 years and culminate about 2100,” Ausubel told the conference. “Some decades have lagged and some accelerated but the inexorable decline of carbon seems clear.”
This trend is driven by the ever-increasing need for spatial density of energy consumption by the end-user, that is the energy consumed per square metre, especially in urban areas.
“Fuels must conform to what the end-user will accept and constraints become more stringent as spatial density of consumption rises,” he said.
“Rich, dense cities accept happily on electricity and gases, now methane and later nuclear and hydrogen. These are the fuels that reach consumers easily through pervasive infrastructure grid, rights to the burner tip in your kitchen.”
Growing consumer demand would drive economies of scale that would make gas and ultimately hydrogen more efficient and cost-effective, he said.
“Economies of scale are a juggernaut over the long run,” he said.
This drive to greater efficiencies would see the development of gas-fired zero-emission power plants (ZEPPs) in the near-to-medium term.
Based on very rapidly spinning turbines, ZEPPs will operate at very pressures and very high temperatures.
“This delivers very high efficiency and allows the revolutionary shrinking of power plants,” Ausubel said.
This would reduce power plants’ environmental footprint, and operating at very high pressures would keep carbon dioxide in a liquid form for easy extraction and easy sequestration, he said.
Clean Energy Systems in California is currently working on a ZEPP and such facilities would be cheaper, cleaner and more viable than so-called “clean coal” plants, according to Ausubel.
“There’s a lot of interest in trying to preserve the coal industry but as an engineer I want to begin with a clean feedstock,” he said.
“My own view is that these efforts won’t succeed.”
While coal emits sulphur, mercury and cadmium in addition to carbon dioxide, methane is very clean to being with.
“Clean coal is very hard,” he said. “We will be left with mounds of hazardous materials.”
