meeting report
Fuel Cell Progress Reported at the 41st Power Sources Conference
Philadelphia, PA USA
- Consulting Engineer
Seattle, Washington
The intensity of current fuel cell development programs was confirmed by successes reported by authors of 27 technical papers presented at the 41st Power Sources Conference that was held in June in Philadelphia, Pennsylvania. Around 600 people attended and 44 companies exhibited their products. A total of 147 presentations were made there. In the text that follows we review the important developments that were described in fuel cell related papers at this conference. We first note the slow development of fuel cells in the past, and then cite the sudden and important new need for developing fuel cells, based on new electrochemistry, and the consequent recent successes that resulted from intense development effort that was supported by many agencies.
Sir William Grove, the father of fuel cell development, started working on fuel cells in 1839, using his own money and contributed platinum. Subsequent development progressed slowly. In 1939 Allis Chalmers built a fuel cell powered tractor, which was exhibited at farm fairs and ended in the Smithsonian Institution’s museum. In 1967 a fuel cell energy-conversion efficiency of 45% was being achieved. The Electric Power Research Institute of the U.S. Department of Energy and several utilities in 1983 supported the development of a 4.8MW fuel cell power plant that was installed by Consolidated Edison at a station on Manhattan Island. The sponsors spent $22.5 million on its development. The project was eventually abandoned because it could not compete with combined-cycle steam power plants that can now convert fuel energy to electric power with 60% efficiency.
The need for electric power in a manned space flight to the moon created a development program for a power source in which compressed hydrogen and oxygen in tanks supplied fuel and oxidizer to fuel cells. These cells that contained precious-metal catalysts successfully fulfilled mission power requirements. However, these fuel cells were so costly that they could not compete with other sources of earth-surface power.
Military Need for Fuel Cell Power Motivates Research and Development
Newly available technology in communications and sensing has produced weapons that can be commanded to go after a moving target and can even be redirected after they are launched. The launched weapon can sense targets from their optical or thermal radiation, or even from their acoustic sound emissions. For example, the exact location of a soldier acknowledging a telephoned command can be precisely detected from his hand-held wireless telephone’s electromagnetic emission. An engine that powers his radar and radio can be detected from either its acoustic noise or the thermal radiation from its exhaust gases. A missile can carry a sensor that guides it to the engine to destroy the engine and nearby personnel.
For soldiers this new environment has produced a requirement for quiet and reliable power sources that don’t need a truck for towing them to the moving battlefront. Batteries are available, but a soldier may have to perform battle-related tasks other than keeping his battery charged. Furthermore, a 120V 60Hz outlet may not be available at his battle position for plugging in the battery charger he carries on his back.
The bandwidth requirements of new lightweight electronic apparatus demand more power than lightweight batteries can supply. Therefore, fuel cell technology is being developed to provide a power source for the individual soldier, sensors, communication equipment, and other U.S. Army applications.
A fuel cell power source that gets its energy from a commonly available military fuel is the obvious power source for the soldier, command posts, and even military vehicles. This need has resulted in an intense research program that has utilized government laboratories, university research laboratories, and the research-and-development facilities in companies in the United States and in other nations around the world. This intense research, plus non-military development, produced 16 of the 27 fuel cell related papers that were presented at the 41st Power Sources Conference.
Hydrogen Production with Reformers and PEM Cells
Fuel cells can be a convenient source of electric power for soldier-carried equipment as well as other needs of military activity in remote regions. Carrying hydrogen gas for fuel cells is not practical, so hydrogen needs to be extracted from petroleum fuels by reformers that also release non-hydrogen gases. These gases must be separated from the hydrogen produced by the reformer. The efficient proton-membrane (PEM) fuel cell deteriorates when supplied impure hydrogen.
Mukund Karannjikar summarized the advantages and problems in fueling PEM cells with hydrogen from petroleum reformers (1). The hydrogen extracted from the hydrogen-containing liquid by heating it over catalysts produces a hydrogen gas that contains vapors and gases that can quickly end the useful life of the membrane in the PEM cell. Figure 1 shows the filters and absorbers that extract the contaminants from the produced hydrogen that is then delivered to the PEM fuel cell. PEM fuel cells that can be scaled down to small size without sacrificing performance are suitable for applications ranging from microwatts to hundreds of kilowatts. Their noise level is low, in comparison to engines. They release pure water as a byproduct, and can be refueled rather than recharged or discarded. PEM fuel cells are preferred in applications like mobile power generation units, man-portable power generators, and on-board power generation for vehicle propulsion.
The steps in producing pure hydrogen from JP4 fuel are outlined in Figure 1. The liquid fuel is boiled to produce a vapor that is split into its chemical components, and compressed. The first reactor is the steam reformer for JP8 fuel. The reformer’s output flows into a post reformer. Then after H 2 S removal the reformate flows into high-temperature water-gas shift and low-temperature water-shift reactors, followed by preferential oxidation of CO in a reactor. The reformate then flows through a carbon dioxide removal absorption tower that has continuous circulation of alkaline absorbent. The reformate finally flows through a fuel filter to remove trace quantities of all gases other than hydrogen before entering the fuel cell.
The steam reforming of JP8 at 900°C and atmospheric pressure over the commercial catalyst gives reformate with a composition of 60 to 65% H 2 , 18 to 22% of CO 2 , 8 to 12% of CO, 5 to 12% of C 1 -C 3 , and around 60 parts per million of H 2 S. Post reformation reduces the light hydrocarbons to below detection limits.
PEM fuel cells require pure hydrogen fuel, and hydrocarbon reforming is the best way of extracting hydrogen from methane, methanol, ethanol, gasoline, and diesel fuel. Diesel and JP8 have advantages over other fuels in their high energy density, safe handling, and logistics.
Karanjikar concluded that with additional process integration, mainly energy, the fuel processor can become an attractive means of hydrogen generation.
Factors in Overall Efficiency
Power plant performance is measured in terms of heat rate, expressed as the higher value of the fuel consumed in generating 1kWh of electric power of electricity (2). A 100% efficient fuel cell would need only 3412Btu of fuel per kWh generated. The best U.S. steam plant in 1983 had a heat rate of 8987 Btu per kWh. The United Technology 4.8MW fuel cell power plant built for Tokyo Electric at that time had a heat rate of 9600Btu per kWh. The year 2001 Mitsubishi Industries model MPCP(M501H) combined-cycle electric power plant delivers 403,000kW with a heat rate of 5689Btu per kWh, with an efficiency of 60% (3).
The energy released when hydrogen and oxygen combine in combustion is 1.48 volts if water is the output of the fuel cell, and 1.23 volts if it is steam. Neither voltage can be achieved because of the irreversibility of the electrode process, activation polarization, and concentration or activity gradient in the electrodes.
Power on Demand Fuel Cell Systems
A soldier in today’s battle environment must have a quickly available and dependable source of electric power for needs ranging from communication with his commander to launching a rocket that demolishes a missile that is headed to his location. Shailesh Shah described a new “Hydrogen on Demand” technology that enables fuel cartridges for both battery replacement and battery charging applications from 20 to 300 watts(4).
The main barrier to the implementation of hydrogen fuel cell technology for portable power applications is the lack of a practical method of storing hydrogen in a small container. Compressed hydrogen is practical for small devices only if it is stored at a pressure like 10,000 pounds per square inch (psi). Hydrogen from compressed gas is dry, and it can dry out PEM fuel cell membranes unless it is wetted. Metal hydrides are inefficient in terms of weight, and require unique recharging facilities. On-board reforming of methanol requires a reactor that operates at over 200°F, plus a power supply. On the other hand, chemical hydrides, which release hydrogen when wetted with water, have significant advantages. An example reaction is:
NaBH 4 + 2H 2 O --> catalyst --> NaBO 2 + 4H 2
This hydrogen source has the following advantages:
• Regulating the contact of the SBH fuel solution with the catalyst controls hydrogen generation.
• The hydrogen is humidified and free from catalyst poisons like CO and S that are associated with hydrogen produced from hydrocarbons or methanol reformation.
• The cost of energy with a PEM/HODTM system is 20% of the cost of energy from alkaline batteries.
• The reaction is exothermic and therefore requires no parasitic energy to produce hydrogen. In contrast, methanol reformation consumes almost 30% of the stored methanol to provide the energy to make hydrogen.
Millennium Cell Inc. has demonstrated the potentialities of the Hydrogen on Demand technology with a prototype that is similar to the system that they are developing for a 30-watt 72-hour mission with an energy density, including a fuel cell, of over 450Wh/kg. Development of dry sodium borohydride fuel technology will enable the cartridge to deliver 1100Wh/Kg if on-site water is used. The demonstration prototype ran on a hydrogen supply pressure of 5 to 10psig, and supported a 20W load.
Figure 1. Hydrogen produced from petroleum is filtered before being delivered to a PEM fuel cell.
U.S. Army Searches for Rugged Fuel Cells for Trench Warfare
A fuel cell power source can meet the new battleground requirement of not emitting heat and electromagnetic radiation that an enemy can use to detect its location. However, the fuel cell must also perform in the extreme hot and cold temperatures that exceed the requirements of fuel cells that are met by fuel cells designed for other present-day applications. Durability and reliability are strict requirements, and in this service the fuel cell will almost never be operating on a flat surface and be perfectly upright.
Elizabeth Bostic described a unique program, developed by the U.S. Army Communications Electronics RD&E Center (CERDC), for acquiring a fuel cell that meets the requirements of reliable operation in a battlefield environment (5). Requirements were identified for these three fuel applications:
Soldier and sensor power (under 100 watts)
Stand-alone battery charging (100 to 500 watts)
Auxiliary power units (500 watts to 10kW)
The CERDC then developed the requirements for these applications and invited foreign vendors to supply “near production” systems that could be evaluated for rapid transition into units that would meet field requirements. The goal in testing the low-power systems was to compare the power quality, energy density, and overall performance to that of standard military batteries. Performance of the higher power systems was compared against data for the tactically quiet generator sets in the field today. The units that were subsequently adopted for testing are listed inFigure 2.
Bostic described the results of testing two SFC A25 units that had been leased from Smart Fuel Cell (SFC) AG which is based in Brunnthal-Nord, Germany. The system weighed 22 pounds and was 18.25” by 6.5” by 12.25” in size. A unit was run for a full 8-hour day at ambient temperature (20°C to 25°C) on three different occasions. The fuel consumptions and efficiencies, based on the lower heating value of methanol, are inFigure 3.
At higher temperatures the unit began producing shutdowns at 35°C. At 45°C the system would not carry a load. The system did not start or operate at +15°C. The tests did show the load durations at which the A25 fuel-cell system would weigh less than batteries (Figure 4).
Bostic concluded that current fuel cell technology has not advanced to the point where effective and reliable operation in military environments and conditions is feasible. In order for fuel cell technology to make real strides in commercialization and substantial use in the military, the focus must be placed on developing ruggedized complete systems that operate consistently and reliably on the battlefield.
PEM Fuel Cells for U.S. Army’s
“Silent Watch” Combat Vehicles
On March 1, the U.S. Army created a new organization that intends to become the world leader in military research, development, and engineering. It is the U.S. Army Research, Development and Engineering Command (RDECOM), headquartered at Aberdeen Proving Ground, Maryland. The command seeks out and develops the latest technology to provide the most advanced weapons, communications, clothing, food, and vehicles.
An increasingly important combat vehicle application is a tactical mode of operation that requires meeting stringent acoustic and infrared levels. Enemy forces can often hear vehicle engines and portable power generators well before establishing visual contact. They can then strike the army’s assets without warning. Therefore, “Silent Watch” configurations currently use the vehicle’s batteries to power large communications and situation-awareness electronic equipment in the vehicle cabin. However, these batteries cannot be used for extended periods of time, like over one hour. Fuel cells, with low operational signatures and improved efficiency, may provide the army a solution for Silent Watch applications. Therefore RDECOM joined IdaTech to fabricate and integrate a 2kW liquid-fuel cell auxiliary power unit on a C3OTM-vehicle test bed to enhance its Silent Watch capabilities. IdaTech had previously developed fuel cell modules that ranged from 1 to 50kW. Rene Dubois from IdaTech described the results from a six-month timeline for building the fuel cell and integrating it on the vehicle (6).
The 2kW fuel cell system had to operate on approved fuels and could not weigh over 260 pounds. IdaTech chose its 1kW FCS-1200 methanol system as a backbone for the C3OTM 2kW APU. With modifications of the fuel reformer and balance-of-plant sections, the Mobile Power Plant (MPP) unit was ready for test in four months. The MPP consists of two 1kW fuel cells, developed by Ballard Inc., and an IdaTech methanol steam reformer.
The methanol-water fuel is pumped into the fuel reformer where the fuel is vaporized and sent through a catalytic reforming bed. There the vapors react over the catalyst to form hydrogen and carbon dioxide gas, plus small amounts of trace molecules such as carbon monoxide. The gases go to a selective membrane that lets the small hydrogen molecule penetrate, and rejects the larger carbon-based molecules and other residual trace elements. The exhaust stream goes to a burner that heats the reformer and vaporizes the incoming fuel. The hydrogen goes to the PEM stacks that produce the output power. The balance-of-plant includes power electronics, sensors, electronics, control boards, and heaters for freeze prevention in cold weather.
The MPP was connected to a 24-volt DC bus inside the vehicle’s cabin. Also connected to the bus was a 24-volt lead-acid battery. During normal Silent Watch operation the battery supplied power to the communication and electronic equipment on the vehicle, and the MPP kept the battery charged.
Acoustics-test results for the Silent Watch vehicle with its engine running, and with engine not running, are summarized inFigure 5. At 50 feet from the vehicle the fuel cell system’s acoustic signature could not be discerned from ambient noise. Follow-on testing will subject the vehicle to various environments, including dust, wind, rain, snow, excessive vibration and shock, sub-freezing temperatures, and low humidity.
One of the remaining challenges is the need to operate on military fuel. Under the military’s one-fuel policy, all fueled military systems must operate on logistic fuels such as JP-I and diesel fuel.
U.S. Navy 625kW Ship Service Fuel Cell
Generator and Power for Underwater Vehicles
The U.S. Navy had recognized by 1997 the potential benefits of fuel cell power on shipboard. It then started with the development of a conceptual 2.5MW power plant which could operate with naval logistics fuel that contained up to 1% sulfur by weight. Preliminary design and systems analyses included determining the optimum fuel cell stack, its support system, plus power conditioning alternatives for meeting shipboard voltage requirements. Denise Chen described the results of this work and the selection for development of a 500kW integrated logistics-fuel processor and a 625kW molten-carbonate fuel cell generator for construction and test (7). Anthony Nickens described plans for demonstrating the performance of the 625kW molten-carbonate fuel cell generator (8). After the completion of testing in 2005, the module may be installed aboard a ship for an at-sea demonstration.
The 625kW molten carbonate fuel cell generator includes dual regenerable hydrogen-sulfide sorbent reactors, and a pre-former that generates sulfur free, methane-rich, reformate, plus two molten carbonate fuel cell stacks (Figure 6). The reformate gas stream is suitable for internal reforming in the commercial-product based fuel cells. This system will be land-base tested at the Naval Surface Warfare Center, Philadelphia, in 2005.
The parallel program for designing and testing a 500kW integrated fuel processor and a proton exchange membrane for fuel cell application is proceeding under the supervision of SOFCO Electrochemical Fuel Systems, with engineering and test facilities provided by the Idaho National Engineering and Environmental Laboratory. The fuel processor includes an autothermal reformer, dual regenerable desulfurizers, and carbon monoxide reduction reactors. The process is completely integrated and includes dual turbo compressors, a steam generator, heat recovery, and fully automatic controls.
Propelling U.S. Navy’s Underwater Vehicles with Semi Fuel Cell Power
An unmanned underwater vehicle after launch has no connection to a supporting power source. It must therefore carry a power source that delivers required power during its specified mission duration. Battery power sources have been used in the past, but a battery requires frequent checking and testing to assure that it can deliver the mission’s required energy. Electrochemical energy is preferred over internal combustion engines because it is quiet, and battery and fuel cell power sources can be recharged with minimum expense and downtime.
Charles J. Patrissi described the U.S. Navy investigations of alternatives for supplying propulsion power for underwater vehicles (9). He observed that energy density is a critical enabler for autonomous systems such as unmanned underwater vehicles (UUV). With no energy lifeline, UUV mission time depends on the energy stored on board the vehicle. Electrochemical energy is favored over internal-combustion power because it is quiet, and with batteries and fuel cells the power source can be recharged with minimum expense and downtime. Safety is a significant issue. As more energetic electrochemical couples are being explored and developed, special procedures are being written to ensure that they are safe to carry on U.S. Navy vessels.
Lithium-seawater batteries have demonstrated high current density, even above the 300mA/cm2 needed in high-power torpedoes. Challenges emanated from the high reactivity of lithium with water and the resulting hydrogen evolution. The Naval Undersea Warfare Center (NUWC) is presently developing Mg-H 2 O 2 -SFC (semi-fuel-cells) which have a high potential for energy density on a systems basis, low per-run cost, and safe operation. Recently Mg is being replaced in an effort to obtain a higher SFC voltage and specific energy.
High cell voltage (3V) and specific energies of 668 to 725Wh/kg have been measured in experiments. Lithium efficiency is limited to approximately 55% by corrosion in the aqueous hydroxide electrolyte. The resulting hydrogen gas is a concern for maintaining the stealth of underwater vehicles. One alternative may be to use the hydrogen to power a PEM fuel cell with oxygen provided from the H 2 O 2 being used for the SFC. Corrosion inhibitors will be investigated for increasing Li efficiency and SFC energy density. Polarization experiments show that SFC voltage will decrease rapidly if the critical current density is exceeded. However, power production resumes quickly if current is decreased. Safety with respect to the hydrogen gas will be part of future studies. Other researchers have shown how electrochemical operation could be turned off without continuous evolution of hydrogen by purging the anode compartment with an inert atmosphere or liquid. These investigations show that the Li- H 2 O 2 and SFC operating parameters must be optimized and closely controlled to meet UUV energy and power requirements.
Conclusion
Fuel cells, lithium-ion batteries and other batteries were topics of many other papers that were presented at the 41st Power Sources Conference. Rather than summarize all the 27 fuel cell papers, I chose to summarize those that showed clearly that fuel cell performance is improving, its useful lifetime is growing, and many new applications are developing. It is also obvious that intense and well-funded research effort is directed toward making fuel cells a practical and economical power source. Fuel-cell powered and hybrid vehicles can become an efficient substitute for vehicles powered by petroleum-based fuels after the world’s petroleum production begins to diminish in 2005.
More fuel cell data can be found in the “Proceedings of the 41st Power Sources Conference,” available from Palisades Convention Management, 411 Lafayette St., Suite 201, New York, NY 10003.
References
1. Karanjikar, Mukund, and associates, “Logistic Fuel to Hydrogen – Fuel Processing using Microfibrous Entrapped Catalysts and Sorbents for PEM Fuel Cell,” pages 231 to 234.
2. Oman, H., “Cells That Make Power from Fuels,”Energy Systems Engineering Handbook,” Prentice Hall Inc., 1986, page 227.
3. 2001-2002 GTW Handbook, “Industry Price Levels, Combined Cycle Power Plants,” page 37.
4. Shah, Shailesh and associates, “Advancements in Hydrogen on Demand TM Fuel Systems for Military and Consumer Electronic Devices,” pages 247 to 251”.
5. Bostic, Elizabeth and associates, “The U.S. Army Foreign Comparative Test Fuel Cell Program,” pages 267 to 370.
6. Dubois, Rene, and Sifer, Nicholas Xavier, “Multi-Fuel Type PEM Fuel Cell Systems for Military APU Applications,” pages 371 to 374.
7. Chen, Denise, and associates, “Integrated Logistic Fuel Processor for PEM Fuel Cell Application,” pages 235 to 238.
8. Nickens, Anthony, and associates, “Molten Carbonate Fuel Cell Generator for Ship Service Applications,” pages 363 to 366.
9. Patrissi, Charles J. and associates, “Investigating a Li-H 2 O 2 Semi Fuel Cell with a Microfibrous Cathode as a Power Source for Unmanned Underwater Vehicles,” pages 420 to 423.
FCT Program units being tested
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