4 Advice to Choose a Liquid Oxygen Dewar

Cryogenic tanks are an essential part for many industries, as they are a key element to store certain gases crucial for diverse processes. In light of such importance, we take a look at the different possibilities in the current cryogenic tanks market and provide 4 key questions to answer before acquiring a cryogenic container.

If you want to learn more, please visit our website.

Use and utility of cryogenic tanks

Cryogenic tanks are a type of industrial storage tank ideal for situations where large quantities of gas need to be stored in liquid form.

They are the right solution to store substances such as Liquid Oxygen, Liquid Nitrogen, Argon, C02, LNG, LPG, Liquid Hydrogen, etc, all of which must be stored at very low temperatures in order to maintain their properties. Thus, it’s common to hear of a cryogenic oxygen tank, a LNG cryogenic tank, and so forth.

As more and more industries require the gases mentioned above, demand for cryogenic tanks keeps growing and is projected to grow at a higher rate than 5% CAGR between and . 

The main characteristics of an adequate cryogenic storage tank include:

• They’re versatile, provide an optimal internal distribution and thus optimize resources. They allow for the installation of a centralised network for the optimal distribution of the different cryogenic gases used, so that there is no gas return to the plant
• Improved loading process through the use of vaporisers, so that the liquid gas passes directly from the production plant to the user, avoiding sudden movements and improving stability and safety.
• Higher purity than other storage systems, as the gas remains isolated in a hermetically sealed tank so that the possibility of contamination with any external agents is minimized.
• Because they’re hermetically sealed, they remain stable and thus are safer than other storage alternatives. Also, as the cylinder transfer within the facilities is avoided, unnecessary risks aren’t taken.

Related content: Cryogenic dewar: tips for a safe, optimized storage

Types of cryogenic tanks

The structure for cryogenic tanks is made of three parts:

• An inner vessel made of stainless steel and designed to withstand very low temperatures.
• An outer vessel made of carbon steel. In order to guarantee cryogenic temperatures and safety, these two vessels are insulated from each other by a combination of materials that provide such insulation.
• In addition to these two containers, a cryogenic storage tank is also equipped with a pressure regulation system, which is specifically designed to ensure that the cryogenic tank always operates at a constant pressure. At the same time, this pressure is set with the user’s needs in mind.

While cryogenic tanks have this basic structure in common, it’s possible to distinguish between two types of cryogenic container: 

• Flat-bottom cryogenic tanks, such as the flat-bottomed tanks Cryospain has recently installed in the USA.
• Large vacuum-insulated cryogenic pressure vessels, such as the new vacuum insulated vessels Cryospain has generated in collaboration with IDESA, which allow for large-scale cryogenic storage.

How to choose a cryogenic container?

Depending on the substance to be stored

When choosing cryogenic tanks, companies must consider what substances they need to store, and communicate it to the tanks manufacturer. 

Different substances will require a different tank shape and design, so that it perfectly adapts to the cryogenic liquid it will need to store. 

Some common substances that require a cryogenic container include: 

• LIN (liquid nitrogen) 
• LOX (Liquid Oxygen) 
• LAR (Liquid Argon) 
• CO2 (Carbon Dioxide) 
• LNG (Liquefied Natural Gas)
• LHe (Liquid Helium)
• LH2 (Liquid Hydrogen)
• LPG ( Liquefied Petroleum Gas) 
• Liquid Ethylene

Depending on the size

Different companies will be in need of different tank sizes, depending on their substance demand and use, among other factors. At Cryospain we are specialized in tanks for large quantities >500 m3

Depending on the material

Stainless steel and carbon steel are the main two materials for building cryogenic tanks. At the same time, different insulating materials can be used: from cellular glass, to rockwool and expanded perlite. Thus, each project must be studied separately, in order to ensure the right materials are used. 

Other considerations

Other criteria to pick the right cryogenic tanks can include: 

• The need to comply with national and/or international regulations.
• The geographical location where the tanks will be installed. For instance, seismic criteria must be considered. The difficulty to access the are might also present a challenge, like it did when Cryospain built a flat-bottom cryogenic tank in Santa Cruz, Bolivia.

Keep reading: Everything you need to know when choosing cryogenic tanks for gas storage

At Cryospain we develop custom flat-bottom cryogenic tanks, as well as large vacuum-insulated cryogenic pressure vessels, all according to our clients’ needs as well as international and local regulations.

If you want to learn more, please visit our website SERLNG.

We are in charge of designing these cryogenic tanks from the first sketches  through to construction and commissioning, coordinating our design, engineering and production teams. 

In order to take into account our clients’ needs and to guarantee a smooth implementation, we provide a careful design process through computer-aided systems, which provide virtual simulations of the future cryogenic tanks.

Atmospheric-Pressure Storage and Transport Dewars

Dewars are used for sample storage, transport of cryogens from source-to-point of use, and temporary benchtop storage of cryogens for immersion of samples and flasks.

Under no circumstances should cryogens be stored or transported in a container that is not designed specifically for cryogenic storage or transport.  Insulated beverage containers, glass labware, and other non-approved vessel are not designed to vent properly or to withstand cryogenic temperatures and must not be used.

Pressurized Cryogen Dewars

Cryogenic liquids such as liquid nitrogen and argon are dispensed from pressurized dewars that vary in capacity between 60 and 265 liters.  These large, pressurized dewars can be used for dispensing liquid cryogens, but can also be used when high volumes of gas are required for lab processes. 

The equipment described below is a common type of liquid nitrogen dewar used on Penn’s campus.  For information about pressurized dewars for other cryogenic liquids, contact EHRS.

Liquid nitrogen service is provided to the labs in one of the two ways described below.

Liquid-nitrogen fill station on campus

• The pressurized dewar is owned by the laboratory or department, and is refilled by trained staff on campus.
• The dewars owned by Penn labs or departments must be sent to a gas vendor for inspection and maintenance whenever the equipment shows signs of malfunction or damage.  Contact EHRS for more information about dewar inspections and repair.

Gas-supply companies

• Full dewars are delivered to the building or laboratory by the gas supplier.
• The laboratory does not own the dewar.  The contract is for the liquid nitrogen product.
• Dewars from gas suppliers may not be refilled at Penn liquid nitrogen fill stations.

Pressure settings

Industry-standard pressure settings for liquid nitrogen dewars classify them as Low Pressure, Medium Pressure, or High Pressure depending on the operating pressure of the dewar.  The pressure rating for the safety relief vent are generally set by the manufacturer as follows:

Low Pressure 22 psig Medium Pressure 230 psig High Pressure 350 psig

Low-pressure dewars are used for liquid withdrawal.  Medium and high-pressure dewars are used for gas withdrawal.  Dispensing liquid from a medium or high-pressure dewar is not recommended as it may cause splashing and/or transfer-line whip and increases the risk of exposure and cryogenic burns.  Only low-pressure dewars may be used for dispensing liquid nitrogen.

Low-Pressure Cryogen Dewars

Low-pressure dewars are used for supplying cryogenic liquid only.  Pressure-relief valve setting: 22 psi

In a low-pressure liquid nitrogen dewar, the pressure inside the vessel is maintained through the normal heat-leak of the cylinder.  As the liquid warms, it evaporates and expands to almost 700 times its liquid volume, which increases the pressure inside the vessel.  When the pressure reaches 22 psi, it will automatically vent through the pressure relief valve.  If the relief valve fails, the emergency rupture disk will vent the excess pressure so that the cylinder does not fail.

Medium and High-Pressure Cryogen Dewars

Medium and high-pressure dewars are used for supplying gas. Pressure-relief valve setting: 230 psi and 350 psi

Medium and high-pressure dewars are used for delivery of gas.  The two types of dewars function very similarly but differ in the amount of liquid cryogen they can contain.  The gas delivery pressure is not the same as the vessel’s operating pressure.  Delivery pressure must be controlled using a separate regulator connected to the gas-use fitting.

Medium and high-pressure tanks increase internal pressure by means of a vaporizer coil in vacuum insulated outer jacket of the dewar.  When the pressure build valve is opened, liquid enters the coil and is warmed, evaporating and expanding to gas.

When the internal pressure of the cylinder reaches the pressure-relief set point (230 psi for medium-pressure, 350 psi for high-pressure), the relief valve will open and vent gas to reduce the pressure.  If the relief valve fails, the emergency rupture disk will vent the excess pressure so that the cylinder does not fail.

Consult the equipment manufacturer’s operating manual for the recommended pressure settings and flow rates for your equipment.  If flow rates are too high, the gas from the dewar will be very cold and may result in excessive ice accumulation on the dewar’s controls and valves and damage to the attached equipment.

Contact us to discuss your requirements of Liquid Oxygen Dewar. Our experienced sales team can help you identify the options that best suit your needs.