Ammonia Fuel—The Other Hydrogen Future
By Larry Bruce, Joe McClintock and John Holbrook
America’s approach to the transformational challenge of Peak Oil has resembled nothing so much as a Keystone Kops two-reeler. Not since Jimmy Carter has an administration demonstrated a commitment commensurate to the challenge, perhaps because President Carter was sent packing back to Georgia with his cardigans after an attempt to rouse Americans from their blissful dreams of a future where Exxon and Mobil would ensure that no one would have to line up for gasoline ever again. Thirty years later, we are just one Category Four hurricane in the wrong place or a Strait of Hormuz terrorist attack away from waiting in long lines to buy fuel we can no longer afford for the SUVs we no longer love. Recent events in Nashville suggest that even imagined shortages will have the same results. We need a rational approach to energy transition, and nothing exemplifies the lack of a comprehensive energy policy as much as the magical-time-machine thinking involved in the promise of a "hydrogen future."
To appreciate this policy void, we have to clearly understand where we are right now. Cheap and plentiful petroleum has defined almost every aspect of our modern economy: from automobile-dependent McMansion suburbs, to mega-box retailing of cheap Asian consumer goods, to petrochemical-based agriculture, we are addicted to the concept of a single energy source. For the last century that single energy source has been petroleum—light, sweet, cheap crude oil. Hydrogen offers the hope of a single vehicle energy source, which is a key element of its appeal. The reality is that we are faced with a transition to a multi-source energy future.
The real problem in transitioning to a new comprehensive energy system is a power source for individual transportation. Electricity generation has many options, including coal (cleaner—we hope), natural gas, hydropower, nuclear energy, and, increasingly, renewable sources such as wind and solar. In the case of transportation, the options for replacing gasoline and diesel fuel are severely limited. Electric vehicles have a limited range. Liquid fuels can be produced from coal although the investment cost is high and this approach generates significant carbon dioxide emissions. Plant-derived liquid fuels such as ethanol and bio-diesel can be domestically produced and offer the benefit of being carbon neutral when consumed, yet what is less clear is the total cost and carbon balance when fossil fuels are used in farming, transportation, and processing these "clean" bio-fuels. In addition, the diversion of food crops such as corn and soy beans to fuel production impacts the world food supply and may lead to political unrest.
Gaseous fuels, mainly natural gas and hydrogen, are also candidates for transportation fuels. Natural gas and hydrogen may be stored in a vehicle as cryogenic liquids or as high pressure gasses. The complexity and energy cost of cryogenic liquids has made them unpopular in transportation applications, so high pressure storage has been the choice. High pressure storage requires a heavy, expensive container and does not provide much driving range. Despite this, high pressure hydrogen fueling stations are being built, and California has plans for a Hydrogen Highway that will run the length of the state.
Now that America is awakening to the prospect that our energy system is under fire and possibly nearing collapse, hydrogen is being promoted as the magic bullet. It’s the clean, carbon-free answer to the question, "What single energy source will replace petroleum?" But hydrogen energy infrastructure is decades away, a fact admitted by even its most vocal proponents, as they attempt to address the key challenges of a fuel with an extremely low volumetric energy density and the propensity to escape every vessel and effort to contain it. Those promoting a hydrogen future (a group which includes every major oil and coal company) fail to mention that the most prevalent feedstock for their "clean" fuel is natural gas or coal, or that the process [what process?] generates massive amounts of carbon dioxide which will need to be sequestered. So much for the promise of clean hydrogen energy.
It may indeed be the case that pure hydrogen will be one of the many solutions that can be harnessed to rescue us from our current reliance on imported oil. There is much promise in today’s research. But the technical challenges facing pure hydrogen today in economic production, storage, and transport put that piece of the puzzle years in the future—and we need answers right now.
What if this vision of a distant hydrogen energy future ignores a critical reality: that an alternative approach to hydrogen fuel is available immediately; that with minimal modifications we could convert the bulk of our gasoline and diesel internal combustion engines to an existing hydrogen based fuel, eliminating carbon emissions and reducing our dependence on foreign oil; that a proven technology exists to produce this hydrogen based fuel without carbon dioxide emissions; and that new and more efficient synthesis is already in coming online? What if we do not need to wait for the hydrogen future of the year 2030? What if our hydrogen future is within our grasp right now?
The one pollution free, hydrogen-based renewable fuel we could begin using today on a large scale is anhydrous ammonia, one of the most commonly synthesized chemical compounds on the planet. Anhydrous ammonia is already used worldwide as fertilizer for its nitrogen content, and delivered by a well-established and safe infrastructure. Due to its hydrogen content, anhydrous ammonia (NH3) can be used in both gas and diesel internal combustion engines with minor modifications, can be used in direct ammonia fuel cells, and can provide hydrogen feedstock for standard hydrogen fuel cells.
Ammonia fuel is a more effective hydrogen fuel than pure hydrogen. It is a molecule composed of one atom of nitrogen and three atoms of hydrogen. It has similar physical characteristics to propane: it is a gas at normal temperatures and atmospheric pressure but becomes liquid at slightly higher pressure. NH3’s ability to become a liquid at moderate pressure allows ammonia to store considerably more hydrogen per unit volume than compressed hydrogen, and 50 percent more than cryogenic liquid hydrogen. Anhydrous ammonia delivers 4.5 times more energy per liter than pure gaseous hydrogen at 5000 psi. In addition to providing a practical means to store and transport hydrogen, ammonia can be burned directly in internal combustion engines and direct-ammonia fuel cells—today.
Ammonia fuel offers an easy solution to one of the greatest challenges facing an energy system based on renewables. What do you do when the wind doesn't blow and the sun doesn't shine? Plans currently under discussion include pumped hydro or storing compressed air in underground caverns to drive turbines. With ammonia fuel synthesis equipment co-located with wind and solar facilities, power produced in excess of grid demand can be used to generate ammonia fuel, which can be easily stored on site. When the wind fails or the sun goes down, that stored energy can be harvested by using ammonia fuel to generate continuous, reliable power that is completely carbon free.
Ammonia has been synthesized for nearly a century using the Haber-Bosch process, which combines hydrogen and nitrogen. Although the hydrogen for the process is normally derived by reforming a fossil fuel, such as natural gas, hydrogen can also be produced without using carbon based fossil fuels by the electolytic splitting of water using any source of electricity, including hydropower, wind and solar cell power, or nuclear power. This is where the renewable angle comes in. There are several "wind-to-ammonia" demonstration projects underway across North America. These projects largely use "stranded" wind resources (wind resources that are not near electric transmission lines) to produce ammonia for use as fertilizer or fuel. The goal is to refine the process so that, as the cost of fossil fuel stock for ammonia such as natural gas increases, renewable production of ammonia can be brought online rapidly to replace it.
At the same time, improved technologies are coming on-line including lower cost electrolyzers and an approach called solid-state ammonia synthesis (SSAS), which makes ammonia without making hydrogen as an interim step. In particular, SSAS promises to reduce the electric energy required to produce ammonia from water and air by 35 to 50 percent, and to lower the capital costs as well. Using these advanced technologies, ammonia can be produced from renewable and nuclear electric power for a cost cheaper than today’s gasoline and diesel fuel, and without a trace of greenhouse gases. Even with the existing electrolyzer and Haber-Bosch process, ammonia is cost competitive with gasoline retailing at prices above $3 per gallon, and can only become more economically attractive as oil prices rise and/or the cost of ammonia production falls due to improving technology or economies of scale.
Ammonia has a long and successful history as a substitute for petroleum based fuels. In 1935 the firm of Ammonia Casale, Ltd. received a patent for a system to burn a mixture of ammonia and hydrogen in internal combustion engines. During World War II, because of a severe shortage of diesel fuel in Belgium, municipal busses were operated using a mixture of coal gas and ammonia which was readily available. The Department of Defense also studied ammonia as a potential fuel in the 1960s on the Energy Depot Program, since it could be manufactured from water, air, and electricity. The concept was that a portable nuclear reactor that could drive a generator to produce electricity and ammonia, could be manufactured to fuel vehicles. The NASA/Air Force X-15 Rocket Plane was powered by ammonia, and ammonia fueled engines are in operation right now, demonstrating the viability of this fuel source.
Of course, ammonia is not without its challenges. Ammonia is an inhalation hazard and must be handled with respect. But, the world ammonia industry produces and delivers 130 million tons a year with an exemplary safety record. About 20 million tons of ammonia is consumed in the U.S. annually, largely as fertilizer, and delivered by truck, rail, barge, and 3,000 miles of small-diameter, underground carbon steel pipeline in the U.S. agricultural heartland. Ammonia is not classified as a flammable liquid by the DOT, and does not have the fire and explosion hazard of gasoline, natural gas, propane, or hydrogen. Although hazardous when inhaled, it is lighter than air and disperses into the atmosphere when released, and without residual harmful effects. Ammonia is not a greenhouse gas, and does not attack the ozone layer.
For ammonia to be in wide use as a transportation fuel, design standards for on-board ammonia fuel tanks must be established as well as procedures for ammonia transfer from storage to vehicle tanks, however much of this work is already in place. Although propane-powered personal vehicles are not a staple of the American road, they are relatively common overseas, and the technical challenges are almost identical. If an Australian can pump propane into his utility vehicle and drive away, an American can refuel with ammonia.
The best features of ammonia are those it shares with hydrogen: it can be used both in internal combustion engines and in fuel cells, it produces no greenhouse gasses on combustion, and it can be produced from a wide variety of renewable energy resources.
If hydrogen is the answer to the energy challenge of peak oil, then there is absolutely no reason to wait. The better hydrogen future is ready right now with proven technology, from production and distribution to storage and engine modification. An aggressive program to use wind and solar power to generate this carbon-free fuel can create a sea of change in our energy policy. Ammonia fuel is not the one single answer to peak oil, because there is no single answer. But as an existing implementable strategy to cut greenhouse gases, reduce reliance on fossil fuels, and create new green collar jobs, ammonia is the stepping stone to the hydrogen future that up until now seemed decades away.
Larry Bruce is an international consultant in strategic planning and enterprise development and Marketing Director of StrandedWind.org. Joe McClintock is a physicist investigating alternative fuels. John Holbrook is Director of AmmPower LLC and Chairman of the Ammonia Fuel Network.