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Fueling the Cells PUBLIC ACCESS

Clean-running Vehicles Can Convert Hydrogen Into Electricity. The Question is, How are we Going to Get the Hydrogen?

[+] Author Notes

Associate Editor

Mechanical Engineering 121(12), 46-49 (Dec 01, 1999) (4 pages) doi:10.1115/1.1999-DEC-1

This article focuses on how scientists, environmentalists, industrialists, and engineers are slowly beginning to agree that energy for the 21st century is going to come from hydrogen. The fuel cell, itself an invention that dates back more than 150 years, will be partly responsible for this change. Among the fossil fuels, petroleum and natural gas are considered primary contenders to provide a source of mobile hydrogen. They have higher ratios of hydrogen to carbon dioxide when compared to coal. Coal, with 50 percent hydrogen, may simply be too rich in carbon dioxide to provide an attractive source of fuel-cell energy. New demand for stationary fuel cells would then bring about a reduction in their costs through mass-production efficiencies. Although the price of fuel cells might not rival that of internal combustion engines, fuel cell pricing could fall enough to make them practical in tomorrow's super-efficient cars. A hydrogen infrastructure would follow as fuel cell vehicles caught on.

A hundred years ago, people predicting what life was going to be like in the 20th century warned of more wars, and droughts, and famines. Some expected that agricultural advances would help feed the world. Others awaited refrigerated foods and wireless telegraphy. Many even envisioned the car replacing the horse.

Few, it seems, foresaw the position that automobiles would come to occupy in the foreground of our landscape. No one predicted how the then-insignificant auto, by encouraging a thirst for mobility that could be quenched by fossil fuels, would be accused of helping to warm the globe.

Our ability to see the future has probably not advanced much in the past hundred years. What follows here must be considered in that light. Nevertheless, scientists, environmentalists, industrialists, and engineers are slowly beginning to agree that energy for the 21st century is going to come from hydrogen. The days of fossil fuels may be waning.

The fuel cell, itself an invention that dates back more than 150 years, will be partly responsible for this change. Because the device does not burn its fuel, but rather, catalyzes it, the fuel cell is regarded as a way to abate humanity's carbon dioxide contribution to the atmosphere. Anyone interested in energy generation, transportation, or the health of the planet is attempting to plan, innovate, or influence how this technology will arrive.

That is not to say that the fuel cell is here for certain. There remain any number of technological hurdles to jump over before fuel cells replace the internal combustion engine as the prime mover for our cars. For one thing, though fuel cell prices have descended drastically from their space-age levels, they are still much higher per kilowatt than the price of internal combustion engines. Yet, efficiency from mass production is expected to reduce fuelcell costs even more. And fuel-cell cars are looming on the horizon: DaimlerChrysler, to cite but one example, has promised production fuelcell vehicles by 2004.

Electricity generated by wind turbines like this 275-kW prototype operating at the National Wind Technology Center near Golden, Colo., will provide a carbon dioxide-free source of hydrogen for. fuel-cell vehicles. Wind-generating capacity in 1998 was just under 10,000 MW worldwide.

Grahic Jump LocationElectricity generated by wind turbines like this 275-kW prototype operating at the National Wind Technology Center near Golden, Colo., will provide a carbon dioxide-free source of hydrogen for. fuel-cell vehicles. Wind-generating capacity in 1998 was just under 10,000 MW worldwide.

It is energy for the fuel cell that has opened the greatest debate. Just where is this hydrogen supposed to come from? How is it going to be stored? How is it going to be transported? Delivered? How will the public perception of hydrogen's danger have to change for it to gain acceptance?

Research into these questions follows many paths. Investigators working on energy storage, for example, are uncovering radical approaches such as carbon nanotubes or metal hydrides for holding hydrogen. A breakthrough could bring about a hydrogen economy faster than anyone expects.

Yet there are those who say that a transitional fuel is what is needed to propel us toward a hydrogen economy. Gasoline or methanol, converted into hydrogen, could take advantage of existing production and infrastructure to provide fuel-cell vehicles, when they arrive on the scene in the next few years, with a ready source of hydrogen.

The promise of the fuel cell is a car with zero emissions. Hydrogen, nature's most abundant element, does not stay long in a pure state, but combines readily with other atoms. Before it can be used as a fuel, hydrogen must be separated from its chemical bonds. The energy needed to crack those bonds can come from any of four sources: fossil, nuclear, solar, or geothermal.

When fuels scientists and engineers talk of investigating energy sources "from well to wheel," they mean that an entire production cycle must be examined for any carbon dioxide contributions to the atmosphere. For a fuel cell vehicle to be truly emissions-free, the hydrogen for the fuel cell must itself come by way of a source that produces no emissions.

Among the fossil fuels, petroleum and natural gas are considered primary contenders to provide a source of mobile hydrogen. They have higher ratios of hydrogen to carbon dioxide when compared to coal. Coal, with 50 percent hydrogen, may simply be too rich in carbon dioxide to provide an attractive source of fuel-cell energy. Oil does better than coal, at 67 percent hydrogen. Natural gas, at 80 percent hydrogen, does better still.

Renewable sources of primary energy-solar and geothermal-can provide hydrogen without producing carbon dioxide. Photovoltaic cells, for example, make electricity directly from sunlight, which can then be used to strip hydrogen from water. Wind power, another form of solar energy, can make hydrogen as well without producing carbon dioxide.

Everyone, though, agrees that hydrogen is tough to store and low in energy density. It is also expensive to make and suffers from image problems related to safety and the public memory of two powerfully graphic disasters: the Hindenburg and the Challenger.

Stored as a gas, hydrogen requires more tank volume than do liquid fuels for the same amount of mileage.

Stored as a liquid, hydrogen requires cryogenic systems to keep it cold. One of the reasons that so much demonstration work in hydrogen-powered vehicles has focused on buses is because they generally run fixed routes. An airport bus need not carry a tremendous volume of hydrogen to effectively deliver passengers within the confines of an airport circuit. Refueling stations for buses, located strategically along a fixed route, add only a few minutes for a stop that is easily incorporated into a bus's regular schedule. Buses that do travel long distances between fueling stops can carry larger tanks.

At the Telonicher Marine Lab in Trinidad, Calif., the nation's first solar hydrogen-fuel cell system built by Schatz Energy Research Center serves as a research and demonstration facility. A 7 -kW electrolyzer can make 20 standard liters of hydrogen a minute, storing it in three 500-gallon tanks at 100 psi.

Grahic Jump LocationAt the Telonicher Marine Lab in Trinidad, Calif., the nation's first solar hydrogen-fuel cell system built by Schatz Energy Research Center serves as a research and demonstration facility. A 7 -kW electrolyzer can make 20 standard liters of hydrogen a minute, storing it in three 500-gallon tanks at 100 psi.

Hydrogen storage on an auto is more difficult. A car does not allow much room for hydrogen tanks. And a car needs a reasonable driving range between fill-ups. Hence, methanol and gasoline are attractive hydrogen carriers: Both are liquid at ambient temperatures. Gasoline is already carted around today in millions of cars; methanol, derived from natural gas; could be carried likewise.

These fuels, however, must be reformed into hydrogen before they can be consumed by a fuel cell. On-board methanol reforming seems to be closer to practical realization than gasoline reforming. Indeed, many automakers are planning to structure their first fuel-cell vehicles around methanol reformer technology.

On-board reformers have their own drawbacks. One objection to such devices is the cost and complexity they add to a vehicle. Another difficulty is the time lag that reformers introduce between a driver's demand for power and a vehicle's response. Troubling, too, is the warmup period that reformers require, which could be as long as one minute every time the car is started. Critics say the public will never accept such performance restrictions.

Arguments against on-board reformers suggest the option of situating reformers at filling stations. There, they could operate continuously. Size restrictions and performance limitations would not be nearly as pressing as they are for on-board reformers. The whole debate, however, returns to the question of on-board storage.

Talk of stationary reformers brings into focus another segment of the fuel-cell discussion. Fixed reformers could make use of established delivery systems for gasoline. Studies have shown that methanol distribution could be phased into the current gasoline infrastructure without prohibitive expense. Such attributes render gasoline and methanol desirable transitional fuels until we can sidle up to a full hydrogen economy.

One of gasoline's biggest advantages as a hydrogen carrier is its already mature infrastructure. The transportation, the codes for safe handling, and the public's familiarity with the fuel all make gasoline a good choice for transitional ease. But looming large over this optimistic picture are two flaws. Gasoline's high ratio of carbon dioxide to hydrogen weakens its desirability as a source of fuel-cell hydrogen. And gasoline, as it is supplied today, may be too laden with additives to make a hydrogen pure enough so it would not poison a fuel cell. Gasoline, it turns out, might have to be reformulated anyway.

This past summer, Epyx Corp. of Cambridge, Mass., reported a successful demonstration of its fuel cell processor using synthetic fuel supplied by Syntroleum of Tulsa, Okla., and a fuel cell stack from Plug Power of Latham, N.Y The test, conducted under a Department of Energy program, showed that a synthetic liquid fuel, which can be dispensed from standard gas pumps, was capable of providing a fuel cell with a source of hydrogen that is free of catalyst poisons such as sulfur, metals, and aromatics. Work continues on refining and shrinking the processor technology.

Methanol does better than gasoline from the perspective of carbon dioxide. Like hydrogen, though, it lacks infrastructure. However, there aren't nearly the economic obstructions facing a methanol infrastructure that seem so ready to bog down one of hydrogen.

Concern does surround methanol's toxicity. Recent reports about the fuel additive MTBE (methyl tertiary-butylether, a methanol derivative used to oxygenate gasoline) migrating into the ground water supply has led California to begin its phaseout. Greg Dolan, communications director for the American M ethanol Institute, said that methanol, if you drink it, is slightly more toxic than gasoline. It is harder to ignite than gasoline, it burns slower, and it gives off only one-fifth the heat of a gasoline fire.

Researchers are developing direct methanol fuel cells capable of bypassing external reformers altogether. Such devices might be available by 2010.

Hydrogen is not extracted from the ground. Instead, producers must divorce hydrogen from the chemical bonds that it forms with other elements. Today, the hydrogen industry makes its product for industrial customers chiefly through steam reforming of natural gas. Such reforming could generate enough hydrogen to power fuel cell vehicles for about 100 years, the estimated reserve of natural gas.

Natural gas has a well-developed infrastructure. Indeed, before the sudden interest in fuel cells, natural gas vehicles were touted as appropriate responses for the need to reduce emissions. They still have supporters who see natural gas vehicles as an immediately practical approach to reducing the carbon dioxide burden. Internal combustion engines, with little modification, run well using natural gas. Buses, in an assortment of demonstration projects, have been burning natural gas for years.

But it is the burning itself that makes for the greatest concern. Although igniting natural gas in internal combustion engines may reduce carbon dioxide emissions, it will not eliminate them, as a hydrogen-based energy economy promises to do.

How do we achieve such an economy? Advocates of hydrogen say it ultimately will be produced using renewable resources. By serving as a storage medium, hydrogen can answer a principal objection to renewable sources: that they are available only intermittently. But photovoltaic panels and wind turbines make up only a small, though rapidly expanding, percentage of the existing generating capacity. How are we to produce hydrogen in the near future?

John Turner, a researcher at the National Renewable Energy Laboratory in Golden, Colo., suggested that in the short term the most appropriate step in transitioning to a hydrogen economy would be to build stationary reformers at existing natural gas filling stations. Such reformers would not have to meet size restrictions that onboard reformers do. Plus , because on-site reformers would operate more of the time, and serve many customers instead of a single, lone automobile, a greater number of users could keep down equipment costs.

Of course, stationary reformers could convert gasoline into hydrogen, too. Natural gas, however, contains a higher percentage of hydrogen and a lower percentage of carbon dioxide compared to other fuels. It makes sense to start as high up the scale as we can, especially considering that the infrastructure is already in place for natural gas delivery. Still, the question of on-board hydrogen storage remains.

Some advocates of natural gas point out that the same pipelines used to move that product could eventually deliver hydrogen. That turns out to be only partly true, however. Newer pipelines that never carried hydrogen-rich "town gas" might fall victims to hydrogen embrittlement.

A prototype personal fuel appliance under development at Stuart Energy of Toronto could make hydrogen for as many as five cars parked at home.

Grahic Jump LocationA prototype personal fuel appliance under development at Stuart Energy of Toronto could make hydrogen for as many as five cars parked at home.

Shell Hydrogen has teamed up with Daimler Chrysler, Ballard, and Norsk Hydro to experiment with a closed hydrogen economy in Iceland. Although the exact pattern of the experiment is awaiting definition, and is expected to be announced early in the coming year, talk has centered around converting Iceland's large fishing boat fleet to hydrogen, and then powering its automotive and transit vehicles in the same manner. Iceland has vast geothermal energy sources, so using them to generate hydrogen makes good economic sense.

Phillip Baxley, a manager at Shell Hydrogen in Houston, speaking about the Iceland project during a recent fuel cell conference, said, "The purpose there is to understand on the ground how you would use renewable resources to build a hydrogen economy-an entire hydrogen economy rather than just a fueling station." Even though Shell's hydrogen division amounts to a mere sliver of a corporation dedicated to the discovery, production, and delivery of oil, its interest in fuel cells casts a revealing look at the activity taking place at every major automobile and petroleum producer today. Hydrogen burns with an invisible flame, but the way in which it has heated things up is plain to see.

The systems required to deliver clean hydrogen fuel to a mass of hydrogen-powered vehicles will be enormous, and will require great sums of money to make them work. But there may be another approach that avoids the frightening prospect of pouring money into the ground.

Amory Lovins, director of research at the Rocky Mountain Institute in Golden, Colo., has been promoting superlight, superefficient automobiles for several years. Indeed, many ideas he has written about are coming true, as the members of the government's Partnership for a New Generation of Vehicles program (GM, Ford, and DaimlerChrysler) make good on their promises of 80-mpg five-passenger sedans. Lovins said that high-efficiency vehicles are particularly suited to hydrogen power. An efficient car uses less fuel, and a fuel-cell car has better efficiency than one powered by an internal combustion engine. Add these two benefits, and a vehicle emerges that easily stores enough hydrogen for a long cruise, in a tank that fits comfortably on board. And such a tank has already been developed at Lawrence Livermore National Laboratories in Livermore, Calif.

But the real gestalt shift occurs when you stop looking at the hydrogen infrastructure needed to support fuel-cell vehicles as an isolated issue. Buildings consume two-thirds of the energy in this country. Start by putting fuel cells in buildings, Lovins said, and hydrogen-powered cars will surely follow.

Installed initially in buildings that are connected to congested electrical grids, a fuel cell costing several thousand dollars per kilowatt could provide electricity by catalyzing hydrogen reformed from the building's natural gas supply. This source of reliable, high-quality electricity would encourage the abandonment of uninterruptible power supplies. It would also generate a supply of 70°C water, the fuel cell's exhaust, for heating and other building services such as cooling and dehumidifying.

Lovins said that new demand for stationary fuel cells would then bring about a reduction in their costs through mass-production efficiencies. Although the price of fuel cells might not rival that of internal combustion engines, fuel cell pricing could fall enough to make them practical in tomorrow's super-efficient cars. A hydrogen infrastructure would follow as fuel cell vehicles caught on.

The idea of a hydrogen economy is not new. In the early 1970s, as concern rose over limited supplies of fossil fuels, the American Gas Association commissioned the Institute of Gas Technology to study the feasibility of a system of hydrogen production, transmission, distribution, and use on a nationwide scale. At the time, the idea of global warming was still off in the future. The environment was not the motivation for looking into a hydrogen economy. Oil was.

And it still is. Environmental issues aside, we simply may not have a 100-year supply of oil. Some experts are saying that world oil production could peak in the first or second decades of the coming century. That's 10 to 20 years from now. After production •peaks, oil's price will continue to rise unless demand slackens. The world's oil will never actually run dry; it will simply become more expensive to extract, until, eventually, it becomes too costly to burn.

This time around it is entirely possible that we will switch our economy over to a new fuel. With global warming a dominant issue, with oil supplies headed for extinction, and with fuel cells, renewable energies, and automobiles making great strides in efficiency, one might be tempted to take a guess at what life will be like in the next hundred years. Did anyone mention hydrogen?

Copyright © 1999 by ASME
Topics: Hydrogen , Fuel cells
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