ASNE Day 2016 - Technical Paper Session 1 : Wednesday, March 2, 2016 1400-1545
DEMATL & Energy Storage
Authors: Thierry Carriere, Mitchell Hageman, and Mike Tomlinson
Title: Development and Testing of a Safety Enclosure for High Density Energy Storage Devices
The weight, volume and storage capacity benefits of current and future high energy density storage systems make them attractive options to complete far-reaching and ambitious future missions. Both dormant and operational hazards associated with heat, fire, release of toxic materials and pressurized explosions are major concerns when these energy storage systems are installed in the same areas which are populated by personnel, sensitive equipment or vital structures. Safe packaging of these devices has lagged and as a result, a few significant events have taken place, highlighting the need for better tools to manage and control a possible uncontrolled release of stored energy. ADA Technologies is developing and testing a new, rugged, ultra-safe enclosure designed to withstand fire and explosion risks associated with large-format lithium-ion batteries. The enclosure combines the properties of several low-cost, lightweight and off-the-shelf materials in a laminate structure in a design capable to channel and contain released energy and protect nearby equipment and personnel. Further improving the safety of the enclosure and the surroundings is the inclusion of a pressure relief vent.
Existing battery hard cases composed of nickel-coated steel or aluminum do not provide the required level of thermal and overpressure protection. Truly rugged enclosures are generally designed to protect their contents, for example telecommunication equipment, from wind, rain, fire and impact originating externally. In such scenarios, different primary objectives have led to a wide variety of enclosure designs. Typical construction would use stainless steel (16 and 14 gauge) or aluminum for durable outdoor use. These rugged enclosures constitute a reasonable baseline but are not designed for a fire or explosion taking place inside the cabinet and therefore have no pressure rating. Doors and access panels would be blown out in the case of even a minor internal explosion. In addition, they tend to be bulky and heavy. The ADA enclosure design uses an engineered, laminate structure approach combining the design philosophy of traditional, rugged electrical enclosures with explosion protection best design practices. This approach is resulting in a solution meeting the enclosure requirements without the need to develop any new, costly and unproven material.
The final laminate structure was selected based on the performance of 6”x6” laminate samples in a flame exposure test, its weight, and thickness. The flame exposure test used a Meeker propane burner to supply a constant 1000°C to one side of the sample while the opposite side was monitored for temperature increase. At the conclusion of the test, the best laminate sample registered an external surface temperature directly opposed to the flame of under 120°C after 30 minutes and for a sample under ½” thick. This preferred laminate wall structure was then implemented into a roughly 1/4 scale, complete enclosure for demonstration and abuse testing purposes. The walls utilizing the innovative insulating laminate were fabricated and mounted on a standard industrial enclosure frame (19” rack architecture).
The second key safety feature of the enclosure is its pressure relief mechanism. Because lithium ion battery can explode and ignite, it was necessary to characterize a notional worst case scenario, in particular in terms of overpressure and explosion strength. Battery fires have been extensively studied by several outfits including the FAA Technical Center, Sandia National Laboratories, Exponent, FM Global and others. However little if any pressure data has been published. ADA Technologies made measurements in two explosion vessels of different volumes (10.5 gal and 1.9 gal) to demonstrate that the worst case explosion would develop in a sealed container or enclosure with a low packing factor. The high free volume inside the volume would provide a large quantity of oxygen for stoichiometric fuel/air mixtures, which upon ignition, could prove devastating. The design study resulted in the key conclusion that highly packed enclosures are desirable to limit oxygen availability and mitigate the risk of severe explosions should the battery pack malfunction and fail. Unique pressure data was acquired in this development project and informed the design of the pressure relief vent. The vent was oversized in the first enclosure built by ADA as a precaution. Further testing confirmed that future enclosures will not need such high surface area burst discs and smaller pressure relief valves will be used instead.
ADA Technologies has designed and built a 1/4 scale safety enclosure for shipboard high energy density devices. The design was informed by flame exposure tests, battery explosion tests, and optimized for low weight and high internal volume. It is scalable, and full-scale enclosures (84”x27”x44”) based on the same technology are being built in 2016. They will provide complete safety and allow the confident deployment of new, large-format lithium ion battery marine packs on board ships.
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