The global shift to use of vehicles powered by fuels other than gasoline, like natural gas and hydrogen, has spurred substantial growth in the manufacture of pressure vessels. Pressure vessels are used to store fuel in a car or truck (15 to 150 liters in volume), akin to a gas tank for a combustion-type engine, or for bulk storage applications. The largest market is for smaller on-vehicle tanks, which are classified into types:
CNG Type I: All-metal construction, generally steel.
CNG Type II: Mostly metal with some fiber overwrap in the hoop direction, mostly steel or aluminum with a glass fiber composite; the metal vessel and composite materials share approximately equal structural loading.
CNG Type III: Metal liner with full composite overwrap, generally aluminum, with a carbon fiber composite; the composite materials carry the structural loads.
CNG Type IV: An all-composite polymer liner — typically high-density polyethylene (HDPE) — with carbon fiber or hybrid carbon/glass fiber composite; the composite materials carry all the structural loads.
Each vessel type has its benefits and liabilities. Type I vessels are the least expensive, with estimated production costs of roughly $5 per liter of volume. The metalworking skills and equipment needed to produce them are widely available internationally. To their detriment, Type I vessels also are the heaviest, weighing approximately 3.0 lb/liter (1.4 kg/liter). By comparison, Type II vessels cost about 50 percent more to manufacture but can reduce the weight of the storage containers by 30 to 40 percent. Type III and Type IV vessels take the weight savings even further, weighing between 0.75 and 1.0 lb/liter (0.3 and 0.45 kg/liter). The cost of Type III and Type IV vessels, however, is roughly two times greater than Type II vessels and 3.5 times greater than the all-metal Type I tanks.
A fifth, all-composite, linerless Type V tank has been the pressure vessel industry’s Holy Grail for years. Recently, one company, Composites Technology Development Inc. (CTD, Lafayette, Colo.), successfully designed, tested and built such a tank for a real-world application.
Built in cooperation with the U.S. Air Force Research Laboratory (Wright-Patterson AFB, Ohio) and the University of Texas (Austin, Texas), it was installed on the FASTRAC 1 (Formation Autonomy Spacecraft with Thrust, Relnav, Attitude and Crosslink) satellite, The 1.9L tank was approximately 6 inches (152 mm) in diameter, 7 to 8 inches (178 to 203 mm) in length and weighed only about 0.44 lb (0.2 kg). The tank was filament-wound with T700 carbon fiber supplied by Toray Carbon Fibers America Inc. (Flower Mound, Texas) wet out with CTD’s proprietary KIBOKO toughened epoxy resin. It had an operational pressure of 200 psi, a proof pressure of 1,000 psi, with a burst pressure between 2,000 and 2,500 psi. The tank was used to store argon gas as a component of the satellite’s micro-discharge plasma thruster.
Elsewhere, Eldib Engineering & Research Inc. (Berkeley Heights, N.J.) released a market study on growth of demand of carbon fibers in reinforced vessels designed to store high-pressure hydrogen. The market study was carried out by a team of researchers headed by Dr. I. Andrew Eldib, president of Eldib Engineering and Research Inc. Eldib Engineering & Research (EE&R) has determined that carbon fibers are, and will remain, a key enabler of hydrogen fuel cell commercialization. According to the Eldib study, the growth of demand of carbon fibers will rise quickly this decade. Estimated that demand will reach or slightly exceed 7,000 metric tonnes (15.43 million lb) per year by 2020. The primary end-use segment will be automobiles (70 percent), followed by buses (18 percent) and in-transit /refueling storage (10 percent). Materials handling vehicles will compromise about 2 percent of the demand in 2020.
The Eldib study identifies seven major producers of carbon fiber wound high-pressure hydrogen vessels. These companies include Dynetek Industries (Calgary, Alberta, Canada), Faber Industrie SpA (Cividale del Friuli, Italy); Lincoln Composites of Lincoln, Neb.; Luxfer Gas Cylinders of Riverside, Calif.; Quantum Technologies (Irvine, Calif.); Sleegers Machining & Fabricating Inc. of London, Ontario (Canada); and Worthington Industries of Columbus, Ohio.
The segment promises to place increasing demand on carbon fiber manufacturers for product to construct Type III and IV vessels. Accordiing to market analyst Lucintel Growth Opportunities in Global Composites Cylinder Market 2011- 2016: Trends, Forecast and Market Share Analysis, the composites cylinder market is expected to grow at a compounded annual growth rate (CAGR) of 13.8 percent, and the end product market is expected to surpass $1 billion (USD) by 2016.
Most composite pressure vessels are manufactured via filament winding, which can be relatively time consuming. As a result, research has focused on production methods with shorter cycle times.
3M (St. Paul, Minn.) and Chesapeake Energy Corp. (Oklahoma City, Okla.) on Feb. 21 announced an agreement to collaborate in designing, manufacturing and marketing a broad portfolio of compressed natural gas (CNG) tanks (photo, right). Chesapeake has pledged an initial $10 million (USD) toward design and certification services and market-development support, and most importantly, it has made a commitment to use the new tanks as it converts its corporate fleet to CNG. 3M has engaged pressure-vessel specialist Hypercomp Engineering Inc. (Brigham City, Utah) for the design and certification of the tanks. 3M, however, will manufacture the commercial tanks and focus its capital on all future operations and production. 3M expects tanks to be available in the fourth quarter of 2012.
Meanwhile, GASTANK Sweden AB (Piteå, Sweden) announced on March 5 that it has developed new “zero permeation” high-pressure CNG cylinders for motor vehicles. The cylinders meet the stringent ECE R110 regulation governing the use of Type IV high-pressure CNG tanks for motor vehicles, yet they are reportedly cost-competitive with legacy materials. The inner liner is made with Akulon (polyamide 6) Fuel Lock from DSM Composite Resins (Geleen, The Netherlands) and HiPer-tex high-performance glass fiber from 3B-the fibreglass co. (Battice, Belgium). Reprotedly, Akulon Fuel Lock not only shows a permeation factor at least 150 times lower than high-density polyethylene [HDPE], it also significantly limits creep under extreme temperatures at the cylinder’s neck thanks to a 50°C higher temperature resistance than HDPE. In addition, the ability to withstand higher temperatures allows a faster curing time of the composite material
In other pressure vessel news, SGL Group – The Carbon Co. (Wiesbaden, Germany) announced on March 16 that it has been selected by The Linde Group (Munich, Germany), a world-leading gases and engineering company, to be the exclusive carbon fiber supplier for its Linde Gases division’s new GENIE line of gas cylinders that reportedly represents a “significant and revolutionary step” away from traditional steel cylinders. The lightweight GENIE cylinders are said to hold more gas and have excellent portability. They also incorporate extensive new features, including built-in “digital intelligence,” unique regulators and a range of accessories that, according to The Linde Group, “significantly enhance functionality and user experience.” The vessel’s steel liner is filament wound with SGL’s own SIGRAFIL C50 T024 EPY carbon fiber, then the cured tank is encased within a recyclable HDPE jacket. Reportedly the first gas cylinder of this type to reach market
In a field dominated by the filament winding process, Bayer MaterialScience LLC (Pittsburgh, Pa.) reported that a resin transfer molding (RTM) manufacturing process combined with a customizable polyurethane composite can produce pressure vessels faster . Bayer’s RTM/polyurethane process reportedly cycles in less than 20 minutes and finished vessels exhibit better damage tolerance. Profile Composites (Sidney, British Columbia, Canada) is the lead on the project, with funding from the U.S. Department of Energy (DoE) and the U.S. Department of Transportation. Project support is provided by A&P Technology (Cincinnati, Ohio), Canada’s National Center for Manufacturing Sciences, Parker Hannifin and Toray Carbon Fibers America (Flower Mound, Texas). The RTM process deploys a completely dry one-piece fiber mat or mesh to wrap the mandrel or mold, followed by a brief, one-shot resin injection process.
The technology is being demonstrated for vessels with capacities ranging from 7.5 to 40 liters. Potential applications include use in automotive and aerospace vehicles that require high-pressure hydraulic fluid and pneumatic gas storage. Profile is seeking to meet performance and certification standards on the road to commercialization