In many different industries, nitrogen is used in liquid form; in this state, it has the maximum cooling capacity. To remain liquid, however, the cryogenic liquid must be stored at -196°C. If it heats up, it loses its liquid form.
Which storage methods keep liquid nitrogen at its required temperature for as long as possible? In this blog, we examine liquid nitrogen storage. We look at safety and insulation, and we’ll outline the infrastructures Demaco offers for liquid nitrogen.
The importance of safe liquid nitrogen storage
As with all other liquid gases, secure storage is essential for producing, preserving, and applying liquid nitrogen. These are the main reasons why liquid nitrogen users invest in cryogenic vacuum-insulated storage tanks and associated vacuum-insulated cryogenic infrastructures:
Safety risks
Liquid nitrogen storage comes with several safety risks:
- A first risk is pressure build-up in the tank or container and the subsequent danger of explosion. If the cryogenic liquid heats up due to poor insulation, it becomes gaseous. One liter of liquid nitrogen increases about 694 times in volume when it becomes gaseous at room temperature and atmospheric pressure. If a tank or closed storage vessel is used for liquid nitrogen, there will not be enough storage capacity to contain the gas. The gas must, therefore, be vented to prevent excess pressure build-up and possible explosions.
- A second safety risk in the application of liquid nitrogen is asphyxiation due to oxygen displacement in poorly ventilated spaces. When liquid nitrogen evaporates, it rapidly expands, causing oxygen levels in the ambient air to drop at record speed. Without prior warning, this can lead to loss of consciousness or suffocation.
- Finally, insufficient insulation and defective storage tanks can cause extreme cold leaks. This can cause oxygen in the air to condensate into liquid oxygen. Liquid oxygen is a powerful oxidizer, which increases the flammability of materials. This can cause a fire or explosion.
Economic loss
A leaking or poorly insulated liquid nitrogen storage tank or dewar is not only dangerous but also financially unfavorable. If an infrastructure leaks or the insulation is inadequate, liquid nitrogen loss can be as high as tens of liters per day. If the storage tank is large, this may not be noticeable, but there will soon be nothing left when smaller containers are used.
Impure gas and stable gas supply
Most applications that use liquid nitrogen depend on high-grade cryogenic liquid. Examples include refrigeration systems in the food industry and cryopreservation applications. When the liquid exceeds its boiling point, gas bubbles will form, which can cause problems with the application’s operation and performance. Every cryogenic application needs high-quality liquid nitrogen (cooling capacity) and will not function optimally on a mixture of liquid and gas.
Liquid nitrogen storage equipment
How to store liquid nitrogen? To reduce the risks described above, safety and insulation are crucial for storing liquid nitrogen. However, the best way for the cryogenic liquid to be stored depends on its purpose. These are the most well-known liquid nitrogen storage devices:
Liquid nitrogen (bulk) tank
Large-scale liquid nitrogen storage uses cryogenic storage tanks. These tanks, ranging from hundreds to thousands of liters, are optimized for long-term storage with minimal heat up, rendering boil-off losses of often less than 0.05% of contents per day. They are also highly resistant to changing external conditions and extreme internal cold and are equipped with the very best insulation.
Most storage tanks are made of predominantly stainless steel and feature quality-improving techniques to vent gases. They also feature overpressure safety valves and equipment to monitor pressure and liquid levels. For control purposes, huge tanks are occasionally equipped with ladders and access systems to allow easy operation and control of each component.
Liquid nitrogen container
Storage containers are used to store liquid nitrogen on a smaller scale. Storage containers come in virtually endless shapes and sizes. From small, portable dewars (1-15 liters), which are placed in laboratories, to larger mobile containers for transport or local storage at hospitals or food producers (up to 400 liters).
As well as in size, storage containers also vary in shape and material. They may, for example, be made of aluminum or stainless steel, but they have one thing in common: insulation is vital. Vacuum insulation is often used in combination with aluminum foil and glass paper to minimize heat intrusion.
Liquid nitrogen dewar
One specific type of cryogenic storage container is the dewar, named after James Dewar, the scientist who developed the technology in the 19th century. Dewar containers are designed to store and transport smaller quantities of cryogenic liquids. They, therefore, often contain a few liters of liquid nitrogen, although dewars with space for dozens or even hundreds of liters are also available.
Dewars are almost always cylindrical, with a tapered neck to prevent heat intrusion and with that evaporation. As with any liquid nitrogen storage method, insulation is paramount for dewars. Dewars are often made of stainless steel, with an insulation method similar to that of other cryogenic systems: vacuum insulation with a layer of aluminum foil and glass paper.
Because of their enormous versatility, dewars are used in many different industries. In the medical industry, they are used to carry small amounts of liquid nitrogen for treatments. Dewars are also widely used in research laboratories and the food industry. Ever since the 19th century, the dewar has been popular, and will undoubtedly remain to be.
Vacuum insulation
As described earlier, vacuum insulation is essential for safely storing and transporting cryogenic liquids at extremely low temperatures. How exactly does this technology work?
Vacuum insulation is a technique that uses a double-walled structure with a vacuum in between the walls to minimize heat transfer through convection. Drawing out the air between the inner and outer walls creates a vacuum that provides an effective barrier against external heat and internal cold. This ensures that the cryogenic gases within the system are less likely to boil and consequently retain their liquid form longer.
The insulation rating of a vacuum-insulated system is significantly higher than that of systems using traditional insulation materials. In fact, vacuum insulates as much as 8 to 25 times better than other commonly used materials, such as PIR/PUR foam or Armaflex. Add in multilayer insulation materials such as aluminum foil and glass paper, and practically all heat will be kept out of the system.
Demaco's liquid nitrogen infrastructures
Demaco specializes, among other structures, in developing advanced cryogenic infrastructures for liquid nitrogen. Our expertise includes designing and constructing vacuum-insulated piping (VIP), phase separators, filling stations, cooling trays, and much more. All of our systems are designed to meet the specific requirements of various industries, such as healthcare, the food industry, and scientific research. At Demaco, we strive not only to meet the needs of our customers, but we also continue to raise the bar in cryogenic technology. It’s all about Cryogenius!
Would you like to know more about Demaco’s vacuum-insulated and quality improvement products? Please feel free to contact us or browse through our products and projects for more information.
