CONTRIBUTED PAPER The Dual-Fuel Strategy: An Energy Transition Plan The transition from fossil to renewable and nuclear energy sources is enabled by developing liquid renewable fuels. Electric power and electrochemical energy conversion have central roles. By William L. Ahlgren ABSTRACT | Depletion of easily accessible petroleum reserves renewable fuels and relies on the force of free enterprise to has created unstable oil supply and price, opening the create a postpetroleum civilization powered by a zero-net- opportunity to replace oil as an energy source with other fossil carbon energy system. The strategy enables global carbon sources and ultimately with renewable and perhaps nuclear emissions to be reduced significantly early in the transition, sources. The dual-fuel strategy is a plan to facilitate the transi- perhapsbyasmuchasanorderofmagnitudeby2030,with tion from fossil to renewable sources by first replacing fossil zero-emissions perhaps as early as 2050. with renewable fuels. It stipulates that all energy sources (fossil, renewable, and nuclear) will be most efficiently mone- KEYWORDS | Alternative fuel; ammonia; ammonia fuel; carbo- tized by conversion to three primary energy vectors: electric fuel; carbon emissions; coal-to-liquid; electric power; electro- power and two liquid renewable fuels, all compatible with chemical energy conversion; energy chain; energy policy; existing infrastructure. One member of a dual-fuel pair is energy strategy; energy vector; fuel; gas-to-liquid; greenhouse nitrogen-based, for example, ammonia, and the other is gases; hydrogen; hydrogen economy; methanol; methanol fuel; carbon-based, for example, methanol. The two are comple- nitrofuel; postpetroleum; renewable fuel; sustainable energy; mentary: ammonia is carbon-free, but has high relative toxicity, synthetic fuel while methanol has low relative toxicity, but contains carbon. Unlike hydrogen (a gas), these liquid fuels are compatible with existing infrastructure with only modest modification. Alter- CONTENTS natives to ammonia are liquid ammoniates; alternatives to methanol include ethanol, dimethyl ether, and higher alcohols, and alkanes. The two renewable fuels may be called nitrofuel I. Introduction II. Summary and carbofuel to avoid prejudice as to their exact composition. III. Energy supply chain Renewable fuels are derived from air, and because nitrogen is A. Processes 2000 times more abundant in air than is carbon dioxide, B. Source, vector, infrastructure nitrofuel will be most efficiently produced and at least cost; it C. Fossil sources are not fossil fuels will therefore be used whenever possible. In some applications, however, the additional cost of producing carbon-based fuel IV. Fuel is crucial will be justified by ease of handling. A small number of appli- V. Economic inertia cations require high energy density fuel; these will be served by A. Liquid fuel and the legacy infrastructure B. Market feedback a secondary carbon-based fuel vector, derived from primary VI. Renewable fuels carbofuel at further cost. The dual-fuel strategy is market- A. Candidate substances driven. It identifies the sources of competitive advantage for B. Air capture C. Cost and use factors set market shares D. Production processes Manuscript received August 29, 2011; accepted March 15, 2012. Date of publication E. Photosynthesis July 10, 2012; date of current version October 16, 2012. The author is with the Electrical Engineering Department, California Polytechnic State F. The problem with hydrogen University, San Luis Obispo, CA 93407-0355 USA (e-mail: [email protected]). G. The benefits of ammonia and methanol Digital Object Identifier: 10.1109/JPROC.2012.2192469 VII. Complementary fuels 0018-9219/$31.00 Ó2012 IEEE Vol. 100, No. 11, November 2012 | Proceedings of the IEEE 3001 Ahlgren: The Dual-Fuel Strategy: An Energy Transition Plan VIII. Nitrofuel and carbofuel XVIII. Environmental and health and safety hazards IX. The dual-fuel strategy A. Methanol safety and spill remediation X. Source neutrality B. Comparative risk analysis is needed A. Dual-fuel energy triangle C. Nitrogen oxides B. Electrochemical converter and related D. Ammonia toxicity terminology E. Fire and explosion safety advantage C. Scenario based on efficient electrochem- XIX. Business model ical conversion A. Sources of competitive advantage D. Photochemical and thermochemical B. Half-price goal alternatives C. Triggering the energy transition E. Source-neutral fuels empower renewable D. Near-term projects sources 1. Marine propulsion XI. Efficient electrochemical conversion 2. Railway locomotives A. Conversion efficiency 3. Road transport local fleets B. Disruptive technology 4. Mid-scale energy hubs C. Photochemical and thermochemical alter- 5. Base-load electric power natives E. Role of the DFX XII. Non-fuel storage XX. Conclusion A. Round-trip efficiency B. Batteries as energy vectors Appendix A: U.S. energy use structure C. Fuel production as energy storage Appendix B: Literature of ammonia and methanol as fuel D. Distributed generation and energy hubs Appendix C: Enhanced gas recovery and mineral E. Energy from remote regions carbonation XIII. Natural gas as a transition source Appendix D: Fuel carbon intensity A. Which comes first? Appendix E: Properties of fuels B. Stranded natural gas Appendix F: Relative fume point C. Prerequisites Appendix G: Risks of complexity, advantage of simplicity D. DFX: the Dual-Fuel Exchange Appendix H: Divers’ solution and related mixtures XIV. Carbon emission Nomenclature A. Centralized CO generation enables 2 Acknowledgement CCSS References B. Examples of CCSS Author biography 1. Enhanced gas recovery 2. Mineral carbonation 3. Carbon-nitrogen displacement C. Near term order-of-magnitude reduction I. INTRODUCTION in CO2 emissions With the depletion of easily extractable petroleum re- XV. Fuel design serves, oil supply and price have become unstable, creating A. Carbon-free substances an opportunity to replace oil with other fossil sources and B. Carbon-containing substances ultimately with renewable and perhaps nuclear sources. C. Mixtures and blended fuels The dual-fuel strategy is a plan to facilitate the transition D. Perspective on renewable fuels from fossil to renewable energy.1 It is summarized in XVI. Ammonia/nitrofuel Section II. In subsequent sections, the ideas behind the A. Base-load electric power and industrial plan are elaborated. Although this essay concerns energy process heat strategy, no mention is made of conservation. Here at the B. Peaking power, distributed generation, beginning let it be acknowledged that energy conservation and transportation is the first and foremost component of any future global C. Environmental and safety advantages energy strategy. Given that energy conservation is of first D. Pipes vs. wires and liquids vs. gases importance, and is taken as far as possible, what else is to E. Monetizing stranded gas, solving the LNG be done? That is the question addressed in this essay. problem, and enabling carbon capture 1Here (and subsequently) we often use Brenewable[ as shorthand for XVII. Methanol/carbofuel Brenewable and perhaps nuclear.[ Nuclear fission energy faces a difficult A. Easy replacement for gasoline campaign to re-establish itself as a viable energy source. Nuclear fusion is B. Ethanol and DME yet to be demonstrated. Still, either or both might become important, even dominant, as a future energy source. The dual-fuel strategy enables both C. Higher alcohols and alkanes renewable and nuclear sources; we sometimes drop the phrase Band D. Cost vs. range perhaps nuclear[ only because it is tiresome to repeat it. 3002 Proceedings of the IEEE | Vol. 100, No. 11, November 2012 Ahlgren: The Dual-Fuel Strategy: An Energy Transition Plan Manyoftheideaspresentedherehavealonghistory. essay is to do so. At the same time, the validity of these As early as 1967 Leon Green, Jr., writing in Science maga- concerns must be acknowledged. Ammonia is a hazardous zine [1], formulated a concept for the large-scale use of substance, and NOx is found in the exhaust of ammonia ammonia as fuel. He observed: combustion processes. We argue that ammonia can never- theless be safely used as fuel if it is not required to serve all BThe long-term consequences of the greenhouse purposes. We outline a planVthe dual-fuel strategyVthat effect due to CO2 buildup in the atmosphere are of supplements ammonia with a complementary substance, serious concern. ... Toremovetheoffendingele- methanol, well known as an alternative fuel. Ammonia and ments(carbonandsulfur)fromthefuelpriorto methanol each has strength that compensates the other’s combustion is a much more efficient and less expen- weakness: ammonia is carbon-free, but has high relative siveprocedurethantryingtocleanupthecombus- toxicity;2 methanol has low relative toxicity, but contains tion products. ... Outlined below is a concept for carbon.Theirusetogetheryieldsagood(notperfect) energy generation in which the fossil fuels are not solution for liquid renewable fuel, which we assert to be burned directly but serve as raw materials for the sine qua non for a post-petroleum global energy system. synthesis of a clean fuel... This clean fuel is Further, we note that ammonia and methanol are but one ammonia. ... In commercial high-tonnage produc- example of such a dual-fuel pair. Other, better pairs might tion of ammonia, natural gas is used as raw material be found, and must be sought. What we reject is hydrogen. for steam reforming to generate hydrogen for the