Last week Houston investment banker and peak oil prognosticator Matt Simmons popped a plan to use wind, the generated electricity and air to manufacture ammonia. Then just use it to fuel cars. The price to start up is “only” $25 billion plus a new generation of cars for consumers to buy. Is ammonia, NH3, remotely practical?
Lets compare with first fossil petroleum, at less than $5 per barrel in the Middle East to more than $50 from oil sands and some offshore production, petroleum products sell profitably at prices that consumers can pay and keep a reasonably healthy economy intact. It’s the major source for now and subject to risk for pricing in the future, which risks the whole of the world’s economy.
Next would be biomass sources as in methanol and ethanol. Both are, or can be used with existing consumer products in fuel mixes, the infrastructure is already partly in place and the carbon cycle is current, using airborne CO2 and returning it for reuse. Light alcohols are undeniably energy positive, although much calculation gives wide variations. Light alcohols also are candidates for Direct Alcohol Fuel Cells that should offer simple and cheap means to get from fuel to electricity to motion.
Hydrogen, liquefied or stored as a gas, could be burned in internal combustion engines with little engine modification, but quite large portable and stationary storage costs are required. Hydrogen must also be ‘made,’ requiring energy and capital, for water electrolysis and then cryogenic storage or very high-pressure vessels or media to hold the hydrogen that use energy to function.
Ammonia then is interesting as it is a storage media with the ability to be both burned or used in a fuel cell. Ammonia holds 18% hydrogen by mass, more than cryogenically formed liquid hydrogen, and far beyond what sensible compression technology allows in comparable volumes. Is easy to store and stable. But:
Ammonia is a noxious, caustic vapor at room temperature requiring pressure and cooling to past 8 atmospheres for liquid containment at less energy by volume than ethanol or methanol. The hydrogen can be freed from ammonia as needed by catalysis at 500º C or simply be burned. Yet burning usually leaves 20% unburned and produces nitrous oxides, problems that technology should fix and exploit handily given time and resources.
There are more interesting pathways. The Danish Technical University is developing a system called “Amminex.” Amminex is an ammonia-based solid-state hydrogen storage solution: a tablet that can be held in your hand. The tablet is a metal ammine complex that stores 9.1% hydrogen by weight in the form of ammonia absorbed efficiently in magnesium chloride: Mg(NH3)6Cl2. The storage is completely reversible, and by adding an ammonia decomposition catalyst, hydrogen can be delivered at temperatures below 347º C (656º F). The tablets can be recharged with additional ammonia. The team is finding that the kinetics of ammonia adsorption and desorption with the metal ammine complexes are reversible and fast, and that the complex is simple to manufacture and easy to handle.
A company called U3K has patented technology (USPTO 7,140,187) (the u3kenergy.com link has lapsed) can convert urea (in a white solid form) to either ammonia or hydrogen for delivery to internal combustion engines and fuel cells in stationary or mobile applications. U3K’s system can provide internal combustion engines with ammonia or fuel cells with hydrogen “on demand.”
U3K’s claimed urea advantages are it is non-toxic, clean burning, non-explosive, and is more economical than refined petroleum products. Urea can fit into the existing liquid based fueling infrastructure. Existing engines can be retrofit cheaply. The capital cost of urea fueling stations is significantly less than the cost of existing gasoline stations. With current urea manufacturing technology, urea has a “well to wheel” efficiency that exceeds gasoline. And urea can be stored as a solid or a liquid.
So far we know that H2 can be effectively stored using alcohols, ammonia and to be complete, natural gas methane. From a system perspective methane is entrenched, both for fuel in homes, cars and electricity generation. Light alcohols are gradually becoming competitive without supports from government. Ammonia is still far underdeveloped.
For burning or oxidizing ammonia is at a disadvantage. But when considered from a fuel cell perspective ammonia has advantages. For systems development, ammonia might have a powerful role in stranded or isolated wind or solar installations as the concentration level is superior. Electrolysis can be comparatively efficient from a financial perspective when the cost of transmission lines is considered. Flowing ammonia vapor or liquid might be a low cost way to move stored energy in hydrogen.
At the use end all the fuels must be one means or another be stripped of the carbon or nitrogen atoms and in some fuels oxygen for the fuel cells to use the hydrogen. This step is where the crux of the competition may lie. Last year saw a paper in Science magazine reveal an alternative to stripping out the oxygen that might work across alcohols and for air batteries. Further checking shows that paths are being blazed to strip the hydrogen off fuels both in a process step and during the operation of some fuel cell designs. Lab units seem expensive, but with material development, commercial scale, and fuel price considerations, all of the light carbon based and ammonia fuels look like contenders.
Ammonia has an incredible advantage, the energy source could be free sunlight or dirt-cheap solar or wind. The alcohols need land surface area. Straight hydrogen is a devil to handle and contain. Methane is abundant now, but over time as more use is made of it the price will rise.
The key in ammonia and its disadvantage is the lack of any carbon, which adds to the energy content. There is little expectation that ammonia as a combustion motor fuel will make a market for itself on the merits. For fuel cell use the field is still pretty wide open, but the bio-based alcohols head start has made great strides.
From an electrical power generator to ammonia then on to fueling power generation ammonia makes sense. But can the economic case be made until fuel cell progress promotes demand?
The answer is ammonia can be a viable fuel. The next question is will the research and development make economic competitiveness possible.