Liquid Oxygen and its Uses - Nature

AN article or product regarded as a scientific curiosity by one generation not infrequently becomes a commonplace of the next. The vacuum flask used by Dewar to preserve very cold liquids at normal pressure has become a household necessity for retaining the temperature of warm liquids, and, under modern mass-production methods, the glass flask is now obtainable at a remarkably low price. The metal vacuum vessel, with charcoal in connexion with the vacuous envelope, is less widely known. It is not suitable for the retention of hot liquids; but by reason of its relative robustness and of the large sizes in which it can be made, it is preferable to the glass form for the storage and transport of liquid oxygen or liquid air. Without question, the introduction of the metal vessel has rendered possible such expansion in the commercial and scientific uses of liquid oxygen as is now slowly proceeding. That the importance of the metal vacuum bottle is fully realised, becomes clear upon a perusal of the recently published Report of the Oxygen Research Committee.1 Quite 90 per cent, of the Report is devoted to the manner of construction of these vessels, to the mode of testing them, to the evacuation of the envelopes, and to certain ancillary but vital problems, particularly those concerned with the behaviour of gas-adsorbents (activated charcoals, colloidal silica, etc.) at liquid-air temperature. Though the general reader may regret the absence from the Report of information” respecting both the manufacture of oxygen and the specific uses to which the liquid is put, the Committee has decided wisely in limiting its survey to the aspect of its subject which its members have experimentally studied.

Please visit our website for more information on this topic.

Medical grade CO2 has 99.99% purity rating. Both Beverage and Food grade CO2 both have a 99.95% purity rating. Industrial CO2 has a 99.90% purity rating. The other .09 – 1% is made up of impurities such as hydrocarbons or nitrogen. The slight difference between Industrial-grade CO2 and Food grade CO2 is the type of test that are done to qualify CO2 as Beverage gas compared to Industrial-grade. Food grade CO2 is in fact Beverage grade CO2, they are equivalent. Its all about the purity of the gas. All CO2 is made the same (to the best of our knowledge). Its all about how the CO2 is stored, handled and transferred. The FDA has put compliance laws on Food aka Beverage grade CO2, making distributers store the gas in specific tanks just for Food or Beverage grade. Food grade CO2 is pure enough for human consumption based on FDA compliance. Food-Grade, anything (in the US) means special requirements on transport and handling, which implies more expense. So even though the same plant may produce it, the pipes leaving the plant have to be Food grade, the tanks the product goes into have to be Food grade. The non-food grade version will go through less expensive /less-maintained/less-cleaned pipes and into similarly treated containers. Medical grade CO2 is not reasonable to get for consumption purposes.

When talking about cylinders we must first consider high pressure vs. low pressure. HPA (High Pressure Air) tanks are pressurized up to the tank’s rating of psi or psi (Pounds per Square Inch). The pressure is then regulated through the tank’s regulator down to 850psi (High Output) or 450psi (Low Output). High pressure vessels are generally referred to as tanks, whereas Low pressure containers are generally referred to as dewars. Many people use the word “dewar” to describe a “liquid cylinder”, and vice versa. There are some key differences and they come in a wide variety of options.

While dewars might seem complicated at first, in reality they’re safe and easy to use once you understand the basics. If you’re interested in talking with an expert about how liquid CO2 trimming and sifting can radically improve efficiencies at your operation, contact us today to talk to one of our post-harvest processing experts.

We will now focus on Liquid Cylinder operations
for use with The Original Resinator.

When utilizing The Original Resinator in a commercial application, CO2 Cylinders similar to the Liquid Cylinders pictured above are very popular. This is do to the nature of large volume production needs, cost savings and convenience. Typically there are three valve handles, a pressure gauge, and a CO2 level indicator located on the top of the Liquid CO2 Tank. These valves handles should be labeled as Gas/Vent, Liquid, and Pressure Builder. We only use the Liquid supply to operate The Original Resinator. We will cover each of these below.

Before we dive into the tank valves we will briefly review the two types of outlets found on Liquid Cylinders, the CGA-622 and the CGA-320 outlets. Tanks outfitted with a CGA-622 or a female end, will need a CO2 liquid cylinder adapter, an essential component for hooking up your Resinator to a low-pressure liquid cylinder. If your cylinder has a CGA-322 outlet then your Resinator coil assembly included with your machine purchase is all you will need.

The top of a liquid cylinder tank – a standard CO2 source for Resinator machines – can be a confusing sight at first. Each outlet and valve serve a particular purpose, so each are important to understand. Since each outlet and valve should be clearly labeled, let’s zero in on the most critical one for a Resinator machine: the Liquid outlet. This is the source of our liquid supply of CO2. This outlet is the one you’ll use for all Resinator machines, but it’s important to know that you may need a particular CO2 tank adapter to hook up to the outlet properly. (Adapter not provided with Resinator purchase.) Until recently, Dewar/Liquid Cylinder tanks came standard with liquid CO2 outlets called a CGA-320, allowing you to then attach a hose between the outlet and Resinator machine. That’s changed. Liquid cylinder tanks are now coming standard with a female CGA-622 outlet, and therefore require a new CO2 tank withdrawal adapter, the CGA-622 x 320, to fit properly to a hose. If your liquid cylinder has a CGA-622 this Liquid Dewar adapter is now a necessary part of a secure setup so that your machine functions properly. It’s a minor change, but it’s important to make sure that you’re using the correct fitting when dealing with liquids and gases at such pressures.

Link to SERLNG

*CGA-622 X 320 Liquid Cylinder withdrawal adaptor.
(Pictured below and available through our online store.)

Once you have identified the Liquid valve and are using withdrawal adapter (if necessary), it’s time to attach the hose. The CO2 supply hose is threaded onto the valve outlet, being sure to use the appropriate sealing washer, and tightening to mitigate any leaks. Being that the Resinator is not a closed loop system, a few CO2 leaks are nominal. Although leaks will contribute to raised CO2 levels, which should always be monitored. When ready to operate the Resinator, open the Liquid valve fully by turning counter clockwise. The pressure builder is a very important component in achieving the proper Resinator operating pressure. We can monitor this operating pressure by observing the pressure gauge located on the top of the Liquid CO2 Tank. Ideally the operating pressure of the Liquid CO2 Tank is 330-350 psi. This is achieved by opening the pressure builder valve prior to operating the Resinator.

Notes:

• The relief valve may hiss for pop if the pressure build beyond the relief valve rating and this is normal.
• The Liquid CO2 Tank is equipped with a pressure relief valve that is fixed to open at 350 psi. (Be sure to get a 350 psi tank.) The pressure relief valve is in place to ensure the internal Liquid CO2 Tank pressure does not exceed 350 psi. As you approach the ideal operating pressure the relief valve may open slightly and release CO2 gas. Although this is sometimes noisy this is no cause for alarm, simply close the pressure builder valve by turning clockwise.
• A tank with a dent or dig may not work as good.
• You must make sure the pressure build is on 300- 350 range.
• TECH TIP: Building the pressure to the proper level may take up to an hour, so it is suggested that the Pressure Builder valve be fully opened one to three hours before use.
• Never use the gas side, purge tank before liquid use.
• Tanks are extremely heavy and a tank dolly is recommended when moving.

Know Your Gauges and Valves

Tell help you see the forest from the trees, take a look a the diagram below to become familiar with the important parts of your liquid cylinders. Be sure to get request

Economizer Circuit

If you don’t use the a cylinder for several days, pressure will continue to rise at a rate of apox. 30 psi per day because a small amount of heat will leak into the inner tank. This heat vaporizes a small amount of liquid and causes the pressure to slowly rise. The pressure may build up to the design of your Pressure Control Valve. The valve will then open and vent gas to the atmosphere. To minimize losses from this venting, the cylinders have an Economizer Circuit. The Economizer Circuit comes into action when the pressure reaches psi setting. At this point, the regulator allows gas from the top of the tank to flow through the internal vaporizer out of the Gas-use Valve to the target system. This reduces pressure in the inner tank and minimizes losses from venting. When pressure normalizes, the Economizer Regulator closes and the cylinder then deliveries gas by drawing liquid through the Vaporizer Circuit. The Economizer Regulator should have a set pressure 15 psi higher than the Pressure Building Regulator.

Pressure Gauge

The Pressure Gauge is probably the one you will look at first and refer to most frequently. This gauge indicates gas pressure inside the inner tank. Since cryogenic liquids are actually liquefied gases, pressure within the tank will constantly increase as the laws of physics transform the cold liquid into warmer gas. Fortunately, this pressure will help you withdraw the liquid or gas from your cylinder. But for most applications, the pressure inside the tank must be artificially maintained. A Pressure Building Circuit can automatically do that.

Opening the Pressure Building Valve located at the top of the tank takes liquid from a line that runs from the bottom of the inner tank, and passes it through the Pressure Building Coil attached to the inside wall of the outer tank. As liquid passes through the Coil, it is vaporized by the heat of the outer tank. The resulting gas is fed through the Pressure Building Valve and Pressure Building Regulator, into the inner tank causing the pressure to rise. We recommend operating your cylinder at 350psi to avoid any clogging/freezing issues while under operation with your Resinator.

Want more information on Liquid Oxygen Dewar? Feel free to contact us.