Hydrogen Refueling Stations

An inside look at the components and equipment for this new fuel

By Brad Smith Jr., P.E.

Hydrogen has been used industrially for over half a century within manufacturing processes ranging from refining to metal to food and electronics. The methods and practices developed to produce and handle hydrogen safely at industrial scale are today being downscaled to provide systems for fueling vehicles at service stations and other venues.

Those familiar with the use of compressed natural gas (CNG) or propane for vehicle fuel will find similarities in many of the elements used in hydrogen-refueling stations (HRS). There are some interesting differences, however. It is worth understanding basic HRS configurations before delving into the specific components that are common to many stations.

Hydrogen Refueling Station Configurations
The traditional gasoline refueling station consists of below-ground gasoline storage, piping and gasoline dispensers placed under a canopy structure. Gasoline storage capacity varies, but a common gasoline volume stored might be 30,000 gallons. This traditional configuration may support 8 to 16 fueling positions and be able to refuel upwards of 1,500 cars per day, assuming 20 gallons per refueling.

Shell Hydrogen’s Washington, D.C., station, operating daily since 2004, was not only the first retail HRS in the United States, but it also features the unique application of below-grade storage of liquid hydrogen. This multi-fuel service station dispenses gasoline, diesel and hydrogen, a menu that will become more common to other stations in the years to come.

This is a good point at which to mention vehicle efficiency and, hold on, kilograms! A typical gasoline vehicle uses gasoline at under 20 percent efficiency. A fuel cell vehicle (FCV) can travel two to three times farther on one kilogram of hydrogen than a typical gasoline car does on one gallon of gasoline since the FCV efficiency is 40 percent and higher depending upon the particular vehicle design. Conveniently enough, one gallon of gasoline contains roughly the same energy content as one kilogram of hydrogen. This handy comparison allows for an easy understanding of the efficiencies of hydrogen fuel cell vs. gasoline vehicles. Yes, kilograms are metric and yes, standard cubic feet can be used instead; however, it is much simpler to begin thinking about hydrogen in kilograms rather than in hundreds or thousands of standard cubic feet. The industry expectation is that consumers will pick this up quite easily.

The hydrogen dispenser utilizes familiar components such as hoses, nozzles and hose breakaways—all designed for pressurized gaseous hydrogen service. Hydrogen dispensers have an electronic interface, which enables the vehicle driver to refuel in a self-serve fashion.

So what does efficiency have to do with HRS configurations? It means that for a similarly capable station serving gasoline, the equivalent hydrogen station would only need to “store” half to one-third of the same “energy,” but with hydrogen it doesn’t all have to be physically stored. More on that later.

Hydrogen stations can follow the traditional gasoline model using below-ground storage. Currently, however, only liquid hydrogen is “not-so-routinely” placed below grade, while compressed gaseous hydrogen is stored above ground. Other configurations available to the HRS developer include the generation of hydrogen on site, connection to a hydrogen pipeline (similar to CNG stations) and variations in between that may feature self-contained mobile systems (on wheels), overhead installation on special canopies and below-grade vaulted systems. There is much more variety in HRS installations than in traditional gasoline stations.

Station Components
Components and equipment utilized in HRS installations have a long history of safe use, typically in industrial and commercial non-fueling applications. The most common and familiar elements involve stainless steel piping or tubing, hydrogen-specific valves, steel storage vessels, hydrogen compressors and vaporizers if liquid hydrogen is involved. Most off-the-shelf items for industrial use are at times a bit oversized for an HRS, but otherwise it is the same equipment and proven technology.

Even the more specialized equipment items that might be utilized have a long history of proven use. These items include hydrogen generators, dispensers, detectors, sensors and control systems. Again, the common modification is a downscaling to be suitable for HRS applications.

Hydrogen generators typically include natural gas reformers and water electrolyzers to produce hydrogen on-site, eliminating fuel deliveries and reducing on-site storage requirements. Industrial volumes of hydrogen are most commonly manufactured using natural gas reformation technology, and these systems, downsized, are also utilized at HRS installations and involve connection to natural gas supply, water and power sources. Electrolyzers generate hydrogen using water and electricity and also are downsized for HRS purposes. Today’s demonstration-scale HRS hydrogen generators are very small, ranging in output from dozens of kilograms per day to a few hundred.

Dispensers for compressed hydrogen gas are very similar to those used for CNG dispensing, although hydrogen dispensers have become more sophisticated as gas pressures have increased beyond CNG’s typical 3,600 psig. Hydrogen dispensing pressures are commonly 5,000 psig and most recently 10,000 psig. The dispenser utilizes familiar components such as hoses, nozzles and hose breakaways—all designed for pressurized gaseous hydrogen service. Today’s hydrogen dispensers typically have an electronic interface, which enables the vehicle driver to refuel in a self-serve fashion.

Liquid hydrogen dispensers serve vehicles that store liquid hydrogen on board the vehicle. These dispensers and nozzles are very specialized and since most automakers are producing vehicles with gaseous hydrogen storage, are not common today.

Liquid hydrogen storage at an HRS is a more common feature than liquid hydrogen dispensing. This is because liquid hydrogen occupies much less volume than gaseous hydrogen and therefore it is the hydrogen state-of-choice for trucking hydrogen, providing improved economics vs. gaseous trucking. The same technology used in liquid hydrogen trailers is applied to ground and below-grade stationary storage vessels or tanks. Since liquid hydrogen is a cryogenic fluid (–435ºF), it requires insulated storage similar to a thermos where double-walled, vacuum-jacketed tanks and piping are utilized.

Regardless of whether the HRS generates hydrogen on site, connects to a hydrogen pipeline (several industrial pipelines exist today) or receives deliveries of liquid or gaseous hydrogen, the station does require a capability to store compressed gaseous hydrogen. If liquid hydrogen is delivered via a tanker truck, the fluid is either vaporized and then compressed or cryo-compressed using specially designed cryogenic compressors that enable much of the resulting gaseous hydrogen to be directly dispensed without intermediate gaseous-state storage. This is a good feature that helps minimize required on-site gaseous storage.

Gaseous storage vessels are typically American Society of Mechanical Engineers (ASME) steel vessels resembling large steel pipes (e.g., 20-inch diameter), about 20 feet long and sealed at both ends. Unfortunately, and similarly a challenge on the vehicle, compressed hydrogen takes up more volume than desired even at pressures of 10,000 psig. Therefore, HRS developers work to minimize gas storage requirements and look to new codes, such as from ASME and the National Fire Protection Association (NFPA), to facilitate the use of composite (non-steel) vessels in HRS applications (currently limited to vehicle applications). Using lighter-weight vessels with larger internal volumes helps by reducing footprint demands and opening up additional configurations such as overhead placement.

Specialized nozzle delivers hydrogen to the vehicle.

Hydrogen compressors are available in smaller versions of industrial models and include either multiple-stage reciprocating, hydraulic or diaphragm-type systems. Output capacities of these compressors range from several kilograms per hour to a kilogram per minute, at pressures ranging from 7,000 psig to 13,000 psig. Compression systems will evolve over time to provide greater flexibility and performance as the hydrogen transportation industry grows.

Codes/Standards
There is a significant amount of effort within many domestic and international code and standard development bodies to complete the writing and publication of documents to facilitate the routine development of HRS worldwide. Several areas have been referenced or adopted from existing industrial codes and standards, though many new areas have been and are being developed.

Some key areas of focus involve specifications related to hydrogen fuel quality and efforts targeting reduction of offset or setback distances from hydrogen equipment and surrounding activity or structures. Setback distances being utilized today are based mostly upon industrial-type applications and when applied to HRS applications, the effective footprint of the hydrogen system eliminates being able to use many existing gasoline stations due to limited site area. Studies and tests are focusing on risk assessments that can help fine-tune setbacks to a more commercially viable level.

Hydrogen fuel quality is being addressed to determine exactly which contaminants have negative impacts on the fuel cell membrane and which ones can be tolerated. Currently, hydrogen quality dispensed to vehicles targets meeting or exceeding 99.99 percent; however, the standard test methods to establish quality are yet to be documented, which involves the American Society of Test Methods.

Technology Development
As codes and standards continue to be defined, there is a strong focus on ensuring these are written in a performance-based manner, rather than prescriptive, to ensure that new technologies have a way to be incorporated into commercial use as easily as possible.

One example of new technology development pertains to hydrogen quality analysis and monitoring to enable an HRS operator to know the fuel quality real-time before dispensing to vehicles. This type of analysis is typically conducted in laboratories, but today there are efforts underway to produce equipment that can effectively and affordably be placed in the relatively severe environment of an HRS.

There are new developments within the developing hydrogen transportation sector that address vehicles, HRS, pipelines, manufacturing, composite storage and related uses. In fact, today’s equipment may appear a bit dated just five years from now, given the state of progress and international investment activity.

ONLINE EXCLUSIVE Air Products is the world’s largest supplier of merchant hydrogen and has built over 65 fueling stations in 12 countries. In “Hydrogen Power,” a special report provided to The PEI Journal, Ed Kiczek, senior business development manager at Air Products Hydrogen Energy Group, explores the complex set of issues surrounding the dispensing of hydrogen fuel at the consumer level. Not surprisingly, safety and cost are paramount issues that must be resolved.

Timelines
The average consumer may not see an HRS until sometime late in the next decade, and then it may be a limited experience for certain markets. The U.S. Department of Energy has a research target date of 2015 to determine a “go/no-go” decision regarding FCV commercialization, which its current research and development efforts are aiming to answer. Beyond this date, expectations are that by 2020 there likely will be several thousand FCVs on the road in the United States and a corresponding fueling infrastructure will support this fleet.

The pace of adoption of FCVs in the United States and elsewhere will be related to the costs of other alternatives for personal mobility. FCVs and hydrogen fuel must compete with the other choices consumers have, and while the hurdle for hydrogen appears quite high, those involved in the race are developing very long legs.

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The PEI Journal • Second Quarter 2008 • Volume 2, No. 2 • Contents are Copyright © Data Key Communications, Inc.
All rights reserved. • Nothing may be reproduced in whole or part without written permission of the publisher.