The future of transportation fuels is a very important topic and is the subject of a significant amount of debate. Electric vehicle (EV) proponents believe that extensive displacement of liquid fuels will occur as battery costs come down and performance increases. Drop-in fuels are currently (2016) being targeted by the U.S. DOE as promising fossil fuel replacements. Hydrogen fuel cell vehicles are favored by several major automobile manufacturers and are currently being delivered to California markets. Methanol, ethanol, DME, butanol, renewable diesel and other alternative fuels have proponents as well.
The overused phrase “all of the above” is very applicable when referring to primary energy sources (e.g. wind, solar, biomass, nuclear, coal, natural gas, etc.) since the dependence on any one of these sources to supply all of our energy needs would not be an optimal situation. Standardizing on one optimal liquid transportation fuel, however, could have huge economic, environmental and efficiency benefits including: 1) Storage and delivery infrastructure costs could be minimized, 2) engine and fuel cell efficiencies could be optimized for a single fuel, 3) air emissions and negative environmental impacts could be minimized, 4) regulatory/compliance costs could be significantly reduced, 5) engine and fuel cell life-cycle-costs could be minimized due to mass production and standardized design, and 6) health and safety issues could be standardized and widely accepted.
Any analysis to help identify the most optimal alternative fuel should begin with a logical, comprehensive set of desired characteristics. The following criteria were used to help identify the fuel closest to an “ideal” liquid alternative transportation fuel.
Production flexibility – i.e. the ability to be produced from all primary energy sources (e.g. solar, nuclear, wind, biomass, OTEC, natural gas with CCS, coal with CCS, etc,). Another highly desirable characteristic is that the production of the fuel be a relatively simple process with a wide range of scalability.
Affordability. This involves infrastructure costs, production CapX and OpX costs, efficiency and other considerations. The fuel should be cost competitive with gasoline and diesel fuel.
End use flexibility – suitable for use in spark ignition engines, compression ignition engines, combustion turbines, fuel cells, etc.
High engine/fuel cell efficiency potential - the single most important characteristic for high efficiency SI engines is octane rating. A high octane rating allows the use of high engine compression ratios and therefore highly efficient engines. A closely related issue in SI engines is resistance to pre-ignition. High efficiency fuel cell operation is also important.
Having additional non-fuel uses of significant benefit to society. E.g.– fertilizer, renewable energy storage, chemical precursor, refrigerant, hydrogen source, household cleaner, etc. One example is ethanol which can be used as a fuel, a solvent, to produce polyethylene and as a beverage.
NH3 (aka “The Other Hydrogen”) rises above other alternative fuel candidates based on the criteria listed above. Simply stated, NH3 is the most cost-effective, energy dense means of storing and delivering hydrogen. It has excellent environmental performance, extremely high engine efficiency potential, production flexibility characteristics second to none, universal end use potential, and a decades-long, proven, acceptable safety record. The fact that NH3 also serves as the most cost-effective means of delivering nitrogen fertilizer provides enormous additional benefits, especially to developing countries. NH3 is an efficient, environmentally friendly refrigerant, an excellent household cleaner, is an efficient medium for long-term storage of intermittent renewable energy and a versatile chemical precursor. No other alternative fuel can deliver the comprehensive benefits associated with NH3.
NH3 can be produced using natural gas, coal, biomass, wind, solar, hydro, OTEC, wind, wave, nuclear energy and all other primary energy sources. One of the most promising methods of storing and transporting stranded renewable energy utilizes NH3 as the storage medium.
NH3 is primarily produced from coal and natural gas at the present time and is normally cost-competitive with gasoline and diesel fuel on a gallon of gasoline equivalent (GGE) basis. Infrastructure costs for NH3 are low and are similar to propane infrastructure costs.
NH3 produced from renewable electricity such as wind or solar PV, assuming an electrical energy cost of 5 cents/kWh (including CapX and OpX costs) and an electrical consumption of 7000 to 9000 kWh/ton, the cost per ton of ammonia produced would be $350 to $450/ton. This corresponds to a gallon of gasoline equivalent (GGE) cost of $2.45 - $3.15/GGE.
NH3 is the second most transported chemical in the world and has a huge, world-wide storage and delivery infrastructure already in place. Infrastructure costs are relatively low and very similar to propane at low storage volumes (<4 ton or ~1500 gallon). At larger storage volumes (30 - 30,000 ton), ammonia can be stored at atmospheric pressure as a refrigerated liquid. It is transported as a refrigerated liquid in ocean-going ships as well. The existing, low-cost storage and delivery infrastructure provides a very valuable advantage to NH3 fuel.
The use of NH3 in gas turbines, spark ignition engines, compression ignition engines, gas burners and fuel cells has been demonstrated. Although NH3 has a relatively slow flame-spread-speed and high ignition energy, it can easily be partially cracked to produce a mixture of hydrogen and ammonia, which then combusts with characteristics very similar to natural gas (but carbon free!).
High efficiency, affordable cost and low emissions are key metrics associated with optimized internal combustion engines, combustion turbines and fuel cells. The high octane rating and tunable resistance to pre-ignition allow NH3 to be used in the highest compression (and therefore highest efficiency) engines capable of being designed.
NH3 is commonly a naturally occurring chemical and also a common man-made chemical. It is not a known carcinogen, not a greenhouse gas, has an ozone depletion number of zero.
NH3 production requires only two widely available raw materials: air (nitrogen) and hydrogen. An iron-based catalyst is used making catalyst availability a non-issue. Any and all primary energy source(s) (e.g. wind, solar, biomass, nuclear energy, OTEC, wave, coal, natural gas, etc.) can be used to produce NH3 and providing an opportunity for unlimited, sustainable production.
NH3 would provide developing countries with an opportunity to create a robust, sustainable local economy and greatly enhance the likelihood of developing an export economy as well. One relatively simple industrial facility producing NH3 can provide fuel for transportation and dispatchable electrical generation, fertilizer for local food production, an environmentally friendly refrigerant for space cooling and food storage freezers, an environmentally friendly disinfectant/cleaner, and a precursor for many other chemicals.
The investment required for a NH3 refinery is relatively low, providing an attractive option for developing countries to drastically improve their standard of living and to spur opportunities for additional economic development.
Two highly-credible safety studies have been completed to establish the comparative risks of NH3 verses propane and gasoline in transportation fuel applications. The studies entitled, “Safety assessment of ammonia as a transport fuel” (RISO, 2005) and “Comparative Quantitative Risk Analysis of Motor Gasoline, LPG, and Anhydrous Ammonia As An Automotive Fuel” (Quest Consultants Inc., 2009). The conclusion of both reports was that NH3 would not present any unacceptable safety risks and in fact would be safer than propane in transportation fuel applications.
Unlike some technology areas where “all of the above” has significant advantages, there are tremendous advantages associated with choosing a single, optimized, liquid transportation fuel. The cost, efficiency and environmental benefits associated with choosing an optimized liquid transportation fuel are enormous and merit serious consideration.
NH3 most closely meets the criteria for an ideal liquid transportation fuel. It is the most efficient and cost-effective means of delivering hydrogen and has an extensive world-wide delivery system already in place. Using currently available catalytic controls, NH3 emissions can be even cleaner than hydrogen engine emissions. While NH3 can effectively be produced using biomass, it can also be produced from all other primary energy sources including wind, solar, nuclear, natural gas, OTEC, etc. NH3 can be used in fuel cells, gasoline engines, diesel engines, gas turbines and gas burners.
Developing countries could create extensive, robust agricultural and energy economies based on NH3 production facilities in a sustainable, environmentally-friendly fashion. Competitive energy prices and robust agricultural economies would provide the basis for nearly limitless additional economic development opportunities.
Impressive federal programs in Japan and numerous patents field by Toyota combined with significant R&D efforts in the U.S., Canada and Europe are providing exciting momentum for the NH3 fuel movement. It is time to acknowledge the show-stopping deficiencies associated with the usual alternative fuel “suspects” and move forward with the closest thing to an ideal fuel, NH3.