High-pressure gas storage vessels represent one of the biggest and fastest-growing markets for advanced composites. Although they are used in self-contained breathing apparatuses and provide oxygen and gas storage on aerospace vehicles, the primary end-markets for composite-reinforced pressure vessels are bulk transportation of compressed natural gas (CNG) products and fuel storage in passenger cars, buses and trucks with powertrains dependent on CNG and hydrogen alternatives to gasoline and diesel.
Demand for these alternative fuels is growing, in large part because the extraction of natural gas from shale reserves has contributed to lower prices in North America and parts of Europe. In the North American market, for example, the cost of natural-gas fuels currently runs about 40% less than diesel, per diesel gallon equivalent. In addition, increasingly stringent emissions regulations, including the European Union’s Euro 6 Standard, which became effective earlier this year, are making diesel-powered buses and commercial vehicles more expensive for operators. Impending regulations are improving the marketability not only of CNG but also of hydrogen — after a period of relative dormancy — for fuel-cell powered vehicles.
Five years ago, the world’s natural gas-powered vehicles (NGVs) — cars, trucks, buses, and fork-lift vehicles — numbered about 10 million units. By 2023, the NGV population could be more than 65 million. Based on strong demand in locales as diverse and far flung as Argentina, Brazil, China, India, Iran, Italy and Pakistan, NGV vehicle deliveries could reach nearly 11 million per year by 2023. The vast majority (94%) of these NGVs are expected to be equipped with high-pressure (200+ bar) fuel storage systems.
Although past promises about the marketability of pressure vessels for hydrogen (H2) storage in automobile fuel-cell powered drivetrains were received with well-deserved skepticism, 13 automotive OEMs have fielded FCV demonstrators and test fleets. The number of new-build FCVs was up to 4000 in 2014 and, according to market researcher Chris Red, president of Composites Forecasts and Consulting (Mesa, AZ, US), it is plausible that annual production could climb to approximately 200,000 vehicles per year by 2023. This would create sizeable demand for high-pressure hydrogen storage tanks. Further, demand for much larger vessels, for use in over-the-road and water transport of gases in bulk, is growing.
In 2016, Red predicts that annual production could approach 12.5 million pressure vessels, and delivery of more than 150 million pressure vessels is forecast between 2014 and 2023. (See Red's full report by clicking "Pressure vessels for alternative fuels, 2014-2023" under "Editor's Picks," at top right.) Over that time, vessel fabricators will need to procure approximately 752,400 MT of raw materials to support composite vessel production volumes — worth more than US$12 billion, including about US$5.8 billion in carbon fibers. To keep up with demand, carbon fiber manufacturers will likely need to produce an additional 30,000 MT of fiber. And vessel manufacturers will almost certainly need to step up production levels. That means increased automation. One machinery supplier, MIKROSAM (Prilep, Macedonia), reports that it has already delivered an automated line which produces 500,000 high-quality, filament-wound liquid propane gas (LPG) tanks/yr and is assembling a fully automated line, which will deliver compressed natural gas (CNG) tanks that can withstand pressures of 250 bar vs. 20 bar for LPG tanks, at the rate of 50,000/yr. These systems encompass automated liner handling, fast filament winding with patented automatic fiber cut and restart and quick-clean resin bath, energy efficient curing oven, quality assurance testing and state-of-the art quality control and data acquisition, all managed from an easy-to-use control system.
A potential market breakthrough is a Type IV pressure vessel (82.5 MPa pressure rating) designed to solve problems with existing designs for hydrogen (H2) fuel tanks intended for proliferating fuel-cell vehicle (FCV) fleets. Current Type IV designs — high-density polyethylene (HDPE) or rubber liners fully overwrapped with carbon fiber/epoxy — pose end-of-life recycling problems (i.e., the epoxy) in Europe. Type III designs can be used, but their metal liners tend to absorb H2, risking hydrogen embrittlement and galvanic corrosion. (See an explanation of vessel types in "Pressure vessel tank types" under "Editor's Picks".)
A consortium of UK-based companies called Hydrogen – Optimisation of Storage and Transfer (HOST), funded in part by the UK Technology Strategy Board, is in the latter stages of developing a monolithic filament wound thermoplastic Type IV tank. The carbon fiber/polyoxymethylene (POM, or acetal) construction is headed for testing and development of a turnkey robotic manufacturing process and a real-world demonstration on an FCV. (Read more about the HOST Type IV H2 fuel tank in “Thermoplastic composite pressure vessels for FCVs” under “Editor’s Picks”).