19-09-2014, 11:03 AM
HYDROGEN: FUEL FOR FUTURE
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ABSTRACT
This report assesses the potential of hydrogen fuel to serve as an economically viable fuel alternative to oil and natural gas. Hydrogen’s physical properties are first reviewed with special attention to how they are advantageous and disadvantageous in hydrogen combustion and fuel cell propulsion systems. This analysis determines the primary shortcomings of the existing hydrogen economy, including limited, inefficient, and often environmentally detrimental production methods; insufficient delivery infrastructure; prohibitive costs; low energy density in storage applications; and problems associated with hydrogen vehicles themselves. These existing obstacles are weighed against new technologies and potential solutions to evaluate the future of hydrogen in the transportation sector.
Today, virtually all commercial trucks are powered by diesel fuel, while private cars are fueled by gasoline. While these petroleum-based fossil fuels have served society well for many years, their supply is limited, and their use creates pollution that contributes to poor air quality in many areas. Supported by National Energy Policy, a new generation of technologies is currently being developed that allow the use of hydrogen as a fuel to power cars and trucks.
Hydrogen is the most abundant element in our universe. In addition to being a component of all living things, hydrogen and oxygen together make up water, which covers 70 percent of the earth. In its pure form, hydrogen is a gas at normal temperatures and pressures; it is the lightest gas (even lighter than helium), with only 7 percent of the density of air. If you get it cold enough (-423 °F), gaseous hydrogen will liquefy, and it can be transported and stored in this form.
There is virtually no “free” hydrogen on earth—all of it is combined with other elements (mostly oxygen or carbon) in other substances. Every molecule of water contains two hydrogen atoms and one oxygen atom. Hydrocarbon fuels such as coal, gasoline, diesel, and natural gas also contain hydrogen. In the case of gasoline and diesel fuel, there are approximately two hydrogen atoms for every carbon atom, while natural gas contains four hydrogen atoms for every carbon atom. To be used as a fuel, hydrogen is typically separated from either water (via electrolysis) or from a hydrocarbon fuel (via reforming).
Introduction
With gasoline at the pump growing ever more expensive and greenhouse gas emissions an increasingly more worrisome environmental concern, finding a stable and environmentally friendly energy option has forced its way into the American and global agenda. Transportation, accounts for 29.2% of primary energy use and 33.9% of carbon dioxide emissions in the U.S. (according to 2001 figures), with the vast majority of emissions the result of the combustion of oil derivatives. The transportation sector represents not only a sizeable portion of energy consumption, but with technological advancement, a promising area for potential pollution reductions.1 Current projections
forecast that primary energy emissions of greenhouse gases and other air pollutants will continue to rise over the next 100 years from increased demand, especially from the developing world. Thus, in order to prevent potential environmental catastrophe without curbing demand, a viable fuel substitute is essential. Numerous potential alternative fuels have been proposed, including reformulated gasoline, biodiesel, methanol, ethanol, synthetic liquids (such as dimethyl ether produced from coal and natural gas), compressed natural gas, and hydrogen.2 Of these fuel
sources, hydrogen appears to be on the forefront of the current administration’s agenda, as made evident in a speech delivered by President Bush at the National Building Museum in Washington, D.C., in February 2003: “Cars that will run on hydrogen fuel produce only water, not exhaust fumes.
Eliminating pollution from cars will obviously make our air healthier. Hydrogen power will dramatically reduce greenhouse gas emissions, helping this nation take the lead when it comes to tackling the long-term challenges of global climate change.”
This paper explores the economic feasibility and potential of hydrogen to serve as a competitive fuel option. We will first consider the advantages and disadvantages hydrogen offers as a fuel source based on its physical properties, and review how those properties may be employed to power a vehicle either in a hydrogen fuel cell or internal combustion engine. In order for hydrogen to be considered a viable option, there must be sufficient production and delivery infrastructure, and hydrogen must be supplied at a reasonable price so that the operating cost of a hydrogen vehicle on a cost per distance basis is competitive with the cost of operating a gasoline vehicle. Thus, it is necessary to assess the adequacy of current infrastructure, consider how this infrastructure must be
expanded and at what investment cost, and estimate at what price this infrastructure will be able to deliver hydrogen to the consumer. Finally, existing and new vehicle and storage technologies will be evaluated focusing on propinquity to commercial availability, fuel economy, and operation cost in order to assess the capability of a hydrogen car to compete in the transportation sector.
PROPERTIES OF HYDROGEN
Hydrogen is the most abundant element in our universe. In addition to being a component of all living things hydrogen and oxygen together make up water, which covers 70 percent of the earth. In its pure form, a hydrogen molecule is composed of two hydrogen atoms (H2) and is a gas at normal temperatures and pressures. It is the lightest gas (even lighter than helium) with only 7 percent of the density of air. If you get it cold enough (–423 °F), gaseous hydrogen will liquefy, and it can be transported and stored in this form.
There is virtually no “free” hydrogen on earth; all of it is combined with other elements (mostly oxygen or carbon) in other substances. Every molecule of water contains two hydrogen atoms and one oxygen atom. Hydrocarbon fuels such as coal, gasoline, diesel, and natural gas also contain hydrogen. In the case of gasoline and diesel fuel, there are approximately two hydrogen atoms for every carbon atom, while natural gas contains four hydrogen atoms for every carbon atom.
In order to directly use hydrogen as a fuel (whether in a fuel cell or in an internal combustion engine), it must be separated from these other elements. The hydrogen fuel used in vehicles is either derived from water (by electrolysis) or from a gaseous or liquid hydrocarbon fuel (by reforming). After being separated it must be stored—first at the fuel station and then on the vehicle. Some fuel stations include liquid hydrogen storage, but on the vehicle, hydrogen is usually stored as a gas at high pressure. It is also possible to store a liquid fuel (gasoline, diesel, and methanol) onboard a vehicle and then use an onboard reformer to separate the hydrogen just before it is used in the fuel cell engine. While this requires additional equipment on the vehicle, it removes the need for high-pressure gas storage.
s chapter provides an overview of the properties of both gaseous and liquid hydrogen that are necessary to understand how hydrogen differs from more familiar motor fuels, such as gasoline and diesel fuel, and what is required to handle and use it safely. While there are risks, hydrogen can be as safe, or safer, than diesel and other fuels when vehicles and fuel stations are designed and operated properly. All fuels require particular design and handling practices based on their properties, and all present certain hazards when mishandled. Understanding the properties of hydrogen is necessary to understanding what is required to use it safely.
Building on the discussion of hydrogen properties, this chapter also provides an overview of the general principles that govern safe design and use of hydrogen fuel. These principles inform the design and operating guidelines presented in chapters 3 through
Conclusions
Judging from these analyses hydrogen is not yet at a point of technical or economic viability. It is unlikely that consumers will be eager to pay more for a hydrogen vehicle that is ultimately more expensive to operate than a gasoline vehicle on a per-mile basis. Without demand for hydrogen end-use technologies, there will be no infrastructure development, and without increases in the production and delivery capacity of hydrogen, there will be no cost reductions and therefore no further increases in demand. Moreover, a hydrogen vehicle would only be in the realm of commercial practicality when powered by hydrogen produced through reforming; hydrogen produced from electrolysis pushes the hydrogen vehicle even farther from pecuniary sensibility.
Thus, at present switching the transportation sector to hydrogen may not even help to reduce emissions of carbon and other pollutants. With all of these setbacks, is hydrogen doomed to fail as an alternative fuel? Not necessarily. Economics alone is unlikely to lead to a switch to hydrogen, but
a not altogether unreasonable mix of progressive actions and uncontrollable global developments could. As the availability of energy sources becomes increasingly squeezed, the price of gasoline could rise to a point where paying five, six, even seven dollars for a kilogram of hydrogen may not be unreasonable. After all, gasoline prices only ten years ago were half of what they are now.63 Further development of hydrogen sequestration may potentially be able to make hydrogen reformation cheaper and if the Department of Energy is successful in its endeavors, the cost of electrolysis may be considerably reduced. Technologically, fuel efficient hydrogen vehicles exist, and despite negligible demand, car manufacturers continue to produce increasingly more innovative and efficient fuel cells. While continued research is still necessary the obstacles once posed by hydrogen safety and storage also do not seem insurmountable. Because tailpipe emissions are virtually zero when hydrogen is burned or chemically reacted, it certainly has enormous potential to effect substantial and indispensable environmental benefits and improve air quality if it is produced with an environmental conscience. The success of hydrogen fuel is dependent on such a wide variety of factors, including the size, type, and geographic density of demand; local energy prices and availability; the cost of primary resources needed as production inputs; the price of fuel substitutes; and the availability of hydrogen vehicles, that for now it is important to focus on short-term goals including the continued development of vehicle and production technologies, and increasing cost reductions. It is possible that hydrogen may have faster growth in developing countries that have little existing energy infrastructure or in isolated areas of the globe that are entirely dependent on the price of imported oil. For the time being, however, it is safe to say that hydrogen’s development as a mainstream alternative fuel in the U.S. will be slow and its ultimate success reliant on a strong political will.