Sheral L. Arbuckle
Supervisor, EV Infrastructure
TH!NK Technologies, Ford Motor Company,15050 Commerce Drive North,Dearborn, MI 48120
E-mail Address: [email protected]
The new frontier for Zero Emissions Vehicles (ZEVs) is the fuel cell powered electric vehicle (FCEV). A variety of fuels can be used to fuel FCEVs, including hydrogen (gaseous or liquid), natural gas, methanol, diesel, gasoline and other alternative chemistries. This broad spectrum of fuel options compounds the challenges and complexity of the refueling infrastructure. Furthermore, at the present stage of FCEV development, industry stakeholders feel it is too early to declare one of these fuel options as the ‘fuel of choice.’ The given, however, is that proton exchange membrane (PEM) fuel cells require hydrogen. This hydrogen can be supplied directly from onboard storage tanks (direct hydrogen) or it can be produced onboard the vehicle from more readily available fuels. This paper will explore the challenges and strategies needed to establish safe, reliable and affordable direct hydrogen refueling infrastructure.
Is Hydrogen Safe?
Hydrogen is the most abundant, naturally occurring element in the universe. It can be produced from a variety of feedstocks using thermal, electrolytic or photochemical processes. Examples of processes currently being explored to produce what is being called ‘the new energy source for the 21st Century’ include:
· Reforming of petroleum based feedstocks such as natural gas, coal, diesel, and gasoline.
· Production from biomass or municipal solid waste (MSW).
· Electrolysis of water molecules to form hydrogen and oxygen using electricity from the existing power grid or from renewable energy sources such as solar, wind, geothermal, hydro or photochemical.
This lightweight, buoyant and highly diffusive hydrogen molecule packed with energy can be produced domestically, and it is not a finite resource. Hydrogen has been used in large quantities as a gaseous feedstock in the petroleum refining, chemical, petrochemical and synthetic fuels industries for the past fifty (50) years. In industrial applications, it is primarily produced from steam methane reforming of natural gas with the majority used as captive feedstock for on-site processes (for example, ammonia production and petroleum refining). The remainder is mostly produced by industrial gas manufacturers (Air Products, PraxAir, BOC, etc.) at central locations and shipped to customers.
The safety record of hydrogen has been excellent.1 It is worth noting that this excellent safety history is attributed to standards and codes that were developed to manage potential hazards so that severe damage to surrounding buildings and personnel would be highly unlikely. Hence, the approach is to distance hydrogen production facilities from any flammable or electrical source, and to provide a means of escape in the event of leakage.
Hydrogen’s long history of safe use is not apparent to the general public since its primary use is in industrial applications. Industrial accidents with hydrogen have been few over these past 50 years. Two significant incidents are cited in the “Sourcebook for Hydrogen Applications (1997)”: 1) the May 6, 1937 Hindenburg zeppelin fire which resulted in fatalities; and 2) an August, 1972 incident where a NASA tractor-trailer with 16,000 gallons of liquid hydrogen was broad-sided by an automobile that ran a red light in Tallahassee, Florida. The two drivers were injured. The most recent incident, that is probably still fresh in our minds, is the Challenger explosion caused by defective ‘O’-rings. These incidents reinforce the need to develop robust, reliable designs; implement rigorous and thorough safety procedures; and provide safeguards against human errors. Lessons learned from each of these incidents have resulted in improved, more robust designs, tighter safety checks and added personnel training.
Why the eagerness to proliferate the use of hydrogen as an alternative energy source or as an alternative fuel for automotive applications? A recent report published by the Office of U.S. Senator Harry Reid (Nevada) listed ten reasons why a hydrogen energy economy should be pursued in the United States.2
• Global Advancement:The U.S. must remain competitive in this technology.
• National Security: The U.S. can be energy self-sufficient.
• Jobs : Thousands of new jobs could be created with a new hydrogen-based economy.
• Supply: Hydrogen is ‘renewable’ and, therefore, unlimited.
• Clean Air: Hydrogen combustion emits no pollution; only water vapor.
• Deficit: The U.S. could reduce the billions of dollars currently spent to subsidize oil exploration.
· Clean Water: Hydrogen use reduces the occurrences of huge oil spills.
· Wilderness: Hydrogen production leaves no environmental scars.
· Health: There is less smog and other pollutants caused by today’s gasoline fueled vehicles’exhaust; hydrogen is clean
· Economy: The U.S. trade balance could realize a reduction in the estimated billions spent weekly on oil imports.
The move into this new era, where hydrogen will be as familiar to everyday consumers as gasoline is today, requires initiatives that will ensure its safe and efficient use. These initiatives are discussed below.
Standards, Codes and Regulations for Hydrogen as an Automotive Fuel
The planned introduction this year of demonstration fuel cell electric vehicles by theCalifornia Fuel Cell Project (CaFCP) has spawned a number of initiatives to address safety (design and user), performance, emissions and fuel economy of FCEVs, as well as design and safety of the refueling infrastructure.
Standards groups and Ad Hoc committees are being formed to address these safety and regulatory issues of hydrogen’s use as an automotive fuel. Five major areas of focus are:
· Onboard (vehicle) fuel storage
· Vehicle systems design and safety controls
· Hydrogen generation, handling and storage (off-board)
· Refueling infrastructure and vehicle interface
· Standards, codes and regulations (for example: fire, building, mechanical, electrical, plumbing, etc., codes)
The negative safety perception of hydrogen must be overcome to promote its use as an automotive fuel. This will require in-depth reviews of existing codes to ascertain whether new codes are required or if existing codes need to be modified. Agencies involved in both hydrogen-fueled vehicles and refueling infrastructure standards, codes and regulations development are summarized in Table 1.
The California Energy Commission recently released a draft document in April 2000 on “Regulations for Hydrogen Fueled Vehicles in California” which stated: “According to the California Highway Patrol, there is no California Vehicle Code Section or Title 13, California Code of Regulations that governs or regulates the installation of hydrogen gas for the propulsion of motor vehicles.”3 One area of concern for infrastructure is the risk of home garage hazards. Cars stored in closed-in areas (home garages and underground parking structures) must be safeguarded against confinement due to the possibility of hydrogen leakage. The Author recommends that a detailed study be conducted to examine relevant safety measures and recommend appropriate actions.
The initiatives outlined above, and others that are sure to come with the introduction of demonstration FCEVs, should proceed post-haste to ensure that designs, construction and use of hydrogen refueling infrastructure is safe.
Gaseous or Liquid Hydrogen
Direct hydrogen refueling is probably the easiest to implement of all the alternatives being studied for hydrogen PEM fuel cell vehicles. The trade-off, however, is more costly refueling infrastructure. There have been many detailed studies conducted by Directed Technologies, Inc. on initial investment and operating cost advantages of direct hydrogen fueling for FCEVs versus methanol, propane and gasoline, particularly in the early phases of FCEV deployment. Methods of supplying hydrogen for direct hydrogen refueling are: 1) deliver directly to the end-user as liquid or high pressure gas, or 2) produce gaseous hydrogen on-site using natural gas reformers or electrolyzers. Refueling infrastructure options for compressed gaseous hydrogen and cryogenic liquid hydrogen will now be explored.
Hydrogen is the lightest weight element of the Periodic Table. It is odorless, tasteless, and colorless (which makes it difficult to detect), and it is non-toxic. Its flammability range is 4% to 74% concentrations in air (by volume) and it has a low ignition temperature at lean and rich mixtures in air (one cause of concern with using hydrogen as an automotive fuel). Hydrogen’s minimum ignition energy is one-tenth of gasoline, making it easier to ignite. However, this low ignition energy applies only to fuel concentrations of 25% - 30% (by volume) in air. On the other hand, gaseous hydrogen has a much higher minimum self-ignition temperature than gasoline. It is most similar to gaseous fuels already being used in automobiles. It is now the ‘fuel of choice’ for early demonstration vehicles.
Liquid hydrogen (LH2) has an extremely low boiling point (-2530C,-4230C) and can cause burns when in contact with the skin and eyes. Inhaling liquid hydrogen vapors in confined areas can result in asphyxiation. It has a high rate of boil-off and if mixed with air (oxygen) in the right quantity, could result in ignition and even detonation. Liquid hydrogen fuel must be kept at ultra-low temperatures; thus, onboard equipment (fuel storage tank, hoses, fuel pumps, etc.) must be insulated and capable of withstanding liquid hydrogen’s low temperature and poor lubricating properties. Boil-off can result in significant losses during everyday use, and small liquid cryogenic tanks (less than 1600 gallons) are not readily available. The one advantage of liquid hydrogen is that more mass can be stored onboard (versus gaseous hydrogen) in the same volume.
A brief comparison of safety, onboard storage capacity and costs of gaseous versus liquid hydrogen follow:
Safety. Gaseous hydrogen is easier to store and safe for dispensing, even at higher pressures. Most fuel uses of hydrogen today are in the gaseous form. Although liquid hydrogen is at much lower pressures, exposure to liquid hydrogen could result in burns to the skin and eyes.
Onboard Storage. The lower density of gaseous hydrogen requires that it be compressed to pack more mass in a specified volume. Refueling infrastructure equipment being constructed today will include both 3600 psi and 5000 psi refueling capability. Liquid hydrogen refueling is at much lower pressures (70 psi 100 psi), and two to four times more weight can be stored onboard than gaseous for the same volume.
Costs. Studies by Directed Technologies, Inc. show that the delivered (to the vehicle) price of hydrogen must be in the $3 per kilogram range to be competitive with gasoline retail prices today. Gaseous hydrogen from large-scale production facilities used as ‘captive fuel’ costs about $0.70 per kilogram ($0.32 per pound). This cost is more than quadrupled when equipment and operating costs are added for delivering, compressing and dispensing. A more economical option is to generate hydrogen on-site either by reforming of natural gas or by electrolysis using off-peak electricity.
Costs to the customer of hydrogen delivered to the vehicle for various alternatives are shown in Figure 1. The cost of hydrogen at early low volumes is most cost effective using electrolyzers at vehicle quantities less than 100 units. Steam methane reformers become the hydrogen generator choice at vehicle quantities of 100 to 10,000 units. When vehicle levels reach 100,000 units or more, centralized dispensing stations with trucked in liquid hydrogen and on-site steam methane reforming could offer more economical solutions for hydrogen refueling.
Equipment availability and capital costs are also issues for hydrogen refueling infrastructure. Table 2 compares capital cost of various gaseous hydrogen refueling infrastructure alternatives which use various means of hydrogen generation, i.e., trucked-in liquid hydrogen, steam methane reformers, partial oxidation (POX) methane reformers, and electrolyzers.
Steam methane reformers and partial oxidation methane reformers are commercially available today and are mainly custom-built for large industrial customers. However, smaller sizes needed for early FCEV deployment are still under development. A small-scale steam methane reformer (SMR) is not commercially available today, but the cost of such a unit is projected to be about $250,000 in production quantities of 1,000 units. Today’s cost of a 600 scf/hour POX methane reformer is approximately $225,000.
Electrolyzers are available today in small-scale units. An efficient, small-scale electrolyzer (600 scf/hour) could provide gaseous hydrogen at $2.00 to $4.00 per kilogram ($1.00 to $2.00 per pound) delivered during early, low volume FCEV deployment. The estimated cost of a small-scale electrolyzer is projected to be $150,000 today. Several electrolyzer manufacturers are developing even smaller units (home units) for refueling one vehicle overnight. These home units are projected to cost under $5,000 at production volumes of 100,000+ units long term.
Hydrogen refueling stations being built today use trucked-in liquid for gaseous refueling. Liquid hydrogen plants are sparsely scattered in North America (see Fig. 2). Delivered liquid hydrogen purchased from existing plants and shipped by cryogenic tanker to a dispensing station is estimated to cost $1.68 per kilogram ($0.80 per pound) plus $0.50 per kilogram for transportation. When factoring in the cost of the dispensing station and operating costs, the cost of liquid hydrogen rises dramatically as the number of vehicles supported decreases and could reach $6.00 - $7.00 per kilogram ($3.00 to $4.00 per pound) for stations supporting only 100 vehicles. If only 10 vehicles are supported, the cost per kilogram for liquid hydrogen could be as much as $35 to $50 ($18 - $25 per pound). Another alternative being examined is trucked-in liquid hydrogen and using the boil-off at 5000 psi to refuel FCEVs. Cost analysis for this alternative is under review.
Though not discussed in great detail in this paper, another technology being explored is metal hydride storage of hydrogen. These systems have the potential of offering higher storage density and a greater degree of safety since the hydrogen molecule is not free but is bonded to the metal hydride. However, they need to achieve elevated temperatures to liberate the stored hydrogen. Lower temperature hydrides are costly and provide insufficient storage capacity. The infrastructure requirements for these systems will certainly be unique compared to those discussed above. Energy Conversion Devices and Texaco recently announced a Project to continue development of this technology for fuel cell vehicle applications. This development effort is expected to take at least another five (5) years before commercial feasibility is demonstrated.
On-site generation of gaseous hydrogen offers the best solution for early low volume FCEV deployment from a safety, cost and implementation readiness standpoint. The economics point to the need for small-scale, efficient and affordable on-site appliances that can generate high purity hydrogen to support 5 - 10 vehicles for early fleet customers. Electrolyzers appear to be the most economically feasible and readily available alternative for early low FCEV volumes and would probably offer the best long-term solution for retail customers (at home refueling). Methane reformers could also be used in fleet applications for increased hydrogen production rates, reduced greenhouse gas emissions (versus gasoline, methanol and electrolyzers), and lower energy costs (versus electrolyzers).
What’s Available Today?
Several demonstration refueling stations that have been in operation for several years and have shown promising results are briefly discussed here.
Chicago Transit Authority Hydrogen Bus Project - In 1997, Air Products, Ballard Power Systems, Inc. and the Chicago Transit Authority teamed up to demonstrate the feasibility and benefits of hydrogen as a fuel for public transit buses. This program included three full-size buses, powered by Ballard fuel cells that operated on a regular route in the greater Chicago area. A commercial fueling station was built to deliver hydrogen at 3600 psi to the cylinder mounted on the roof of the bus. The station included liquid hydrogen storage, a compressor station that delivered 3600 psi hydrogen to high pressure storage tanks and finally to a refueling dispenser. The station was designed to refuel a bus in about 15 minutes (actual average was 25 minutes). With a single refuel, the average bus was expected to travel 250 miles. It was recently announced that the two-year program was concluded with successful results. The three buses logged more than 5,000 hours in revenue service and covered over 30,000 miles.
British Columbia Transit Authority Fuel Cell Bus Program - Three fuel cell powered buses began operations at the Coast Mountain Bus Company in Vancouver, Canada for a two-year demonstration program to assess the viability of fuel cell technology in actual revenue service. Ballard supplied the hydrogen refueling station, which includes a Stuart electrolyzer that produces 2500 scf/hour of hydrogen at 3600 psi. This unit is capable of refueling 30 buses. Hydrogen is generated overnight using off-peak electricity and stored in buffer tanks. The electrolyzer has been successfully operating for over a year, and there have been no problems with fuel supply. Trained Transit Authority personnel refuel the buses. Refueling time when buffer tanks are full ranges from 2.5 hours for the first bus, up to 10 hours for the third bus. The major issue identified to date is the high cost of the fuel supply due to high cost of electricity used to generate hydrogen.
Ford’s Hydrogen Refueling Station - Ford Research Lab commissioned its gaseous hydrogen refueling station in February 1999. This facility is capable of supplying 200 scf/hour of hydrogen at 3600 psi and 5000 psi. The facility will eventually include both gaseous and liquid hydrogen refueling capability. Two liquid dispensing systems are planned: a Messer-Griesheim system and a Linde system. Presently, only the Messer-Griesheim system is installed and operational. The station was designed and built by Air Products and is leased to Ford.
California Fuel Cell Project Hydrogen Refueling Station - A facility similar in design to the Ford facility is currently under construction in Sacramento to support the California Fuel Cell Project vehicles. This facility will be capable of refueling 17 vehicles per day with gaseous hydrogen at 3600 psi and 5000 psi.
Creating A Hydrogen Refueling Infrastructure
Industry experts agree that a phased deployment strategy tied to FCEV volumes in a few selected cities is the most practical way to grow the hydrogen refueling infrastructure. This phased deployment will also facilitate development of a standardized system of mechanical and communications interfaces such that any gaseous fueled FCEV can refuel at any of these sites. The challenges and approach are briefly discussed here.Standardized Interface
WEH of Germany is supplying prototypes of the mechanical interface, i.e., nozzle and receptacle, for 3600 psi and 5000 psi for the gaseous fueled vehicles to be delivered to the California Fuel Cell Project demonstration program. WEH has designed the hydrogen nozzle/receptacle (or coupler) to:
· Prevent a compressed natural gas (CNG) or similar nozzle from connecting to a vehicle with a hydrogen receptacle.
· Prevent a hydrogen nozzle from connecting to a CNG or other alternative fueled vehicle with similar interfaces.
· Allow a 3600 psi nozzle to connect to a 5000 psi hydrogen vehicle receptacle.
· Prevent a 5000 psi nozzle from connecting to a 3600 psi hydrogen fueled vehicle receptacle, avoiding over-pressure or over-temperature issues.
Other mechanical interface issues that will be addressed during standards development
· Prevention of hydrogen leakage during connecting and disconnecting.
· Orientation of the vehicle receptacle to ensure safe connection and ease-of-use.
· Validation of hardware durability and reliability.
· Providing defueling capability to allow for evacuation of the onboard tank for shipping and long-term storage.
· Developing certification tests and procedures, and identifying the appropriate certification agency.
Vehicle to Reueling Station Communications
Hydrogen fuel cell vehicles are presently being designed to ensure safe refueling. Before refueling can begin, the following steps must be completed: 1) major vehicle electrical systems must be shut down; 2) the vehicle must go through a series of safety verification checks to ensure that it is ‘OK’ to refuel; and 3) both the vehicle and station must be electrically grounded. There should also be a means of communicating to the dispenser the actual onboard fuel tank temperature and pressure to avoid over-pressure and over-temperature conditions during ‘fast fills.’
At present, the communications link is a separate electrical connection that provides two-way communication from the vehicle to the refueling dispenser. This requires a customer to make a separate and distinct connection in addition to the nozzle/receptacle connection. Design and development are underway to simplify the refueling process to make it as easy as refueling a gasoline vehicle. Efforts must be focused on making the refueling process safe and user-friendly.
Modular Hydrogen Refueling Stations
As discussed earlier, small-scale on-site hydrogen generators have merit in supporting the early low volumes of FCEVs. The current hydrogen infrastructure strategy is to build centralized industrial type refueling stations that have large liquid storage capacity on-site to service a few vehicles. The proposed bridging strategy for refueling limited numbers of vehicles scattered across the nation is a modular skid unit that is capable of refueling 5 - 10 vehicles daily and that can be easily installed at a fleet customer’s site.
Modular skid refueling stations should be designed to fit into a standard ocean container. This skid will include all the other components required to deliver hydrogen to the vehicle at its design pressure (compressor, storage or buffer tanks, and dispenser). This package concept is shown in Figure 3.
This fully integrated modular skid design would allow use of any of the three methods of producing hydrogen (steam methane reformers, partial oxidation or autothermal reformers, and electrolyzers). Longer term, when FCEVs number 10,000+ and are deployed in more areas of the U. S., hydrogen refueling infrastructure could utilize the existing natural gas pipeline and the electric power grid and may even be as near as your neighborhood gasoline service station.
There are major challenges ahead to provide safe, reliable, affordable, and readily accessible hydrogen refueling infrastructure. These include:
· Developing and/or modifying standards, codes and regulations for hydrogen use as an automotive fuel.
· Standardizing the mechanical interface and communications protocol to ensure safe and reliable refueling for any automobile.
· Developing and validating hardware for robustness and compatibility with all automakers’ FCEVs.
· Adopting a strategy that provides more affordable equipment during early low volumeFCEV deployment that is flexible and portable.
The support of industry stakeholders to adhere to a rational, phased deployment strategy, consistent with FCEV deployment, will minimize costs during early market introduction of FCEVs, reduce obsolescence and facilitate the development of a common hydrogen refueling infrastructure.
1. Hydrogen Research Institute and National Renewable Energy Laboratory, Sourcebook for Hydrogen Applications, 1998, pp. 90-91.
2. Office of U.S. Senator Harry Reid (Nevada), “Why Hydrogen,” 1999.
3. Blackburn, Bill (CEC), “Draft Document: Regulations for Hydrogen-Fueled Vehicles inCalifornia,” April 2000 [draft report to California Energy Commission]
· Directed Technologies, Inc. (Consultant to Ford Motor Company), Direct-Hydrogen-Fueled Proton-Exchange-Membrane Fuel Cell System For Transportation Applications: Hydrogen Infrastructure Report, July 1997 [ Report to DOE ]
· Hydrogen Burner Technology, Inc., Developing Stationary Hydrogen Refueling Stations: Siting, Concepts and Current Plans, December 8, 1999 [ report ] BD