Chemical and petrochemical nitrogen gas blanketing
When storing gases and liquids created in the food processing, pharmaceutical, chemical, and petrochemical industries, blanketing with an inert gas is advised. This is because it helps avoid the risk of fire. Often high-purity nitrogen (N2) is used for blanketing due to its very low oxygen (O2) content and its low weight. It’s important that as much O2 is removed as possible.
Essentially, the space between the stored gases or liquids and the leftover tank volume is filled with a non-flammable gas - such as N2. The goal is to push as much O2 out as possible.
The reason for this is that when O2 content in a storage tank is over 16%, it becomes a fire risk. It's also worth mentioning that the stored gases and liquids will have their own O2 concentration.
Keeping all this in mind, high-purity (99.999%) N2 is recommended for gas blanketing. This makes it easy to keep the total O2 inside a storage tank in a safe range. To achieve this, it's recommended to use an on-site pressure swing adsorption (PSA) nitrogen generator. You can read more about this in our related article [link].
Other benefits of gas blanketing
Aside from reducing the risk of fire, N2 gas blanketing has other benefits. Since O2 is what many life forms need to survive, it can allow microorganisms and other undesired contaminants to grow inside a storage tank. Also, O2 can lead to water vapor (moisture), causing rust and corrosion.
Due to oxygen’s negative impact on quality control, it’s important to remove as much as possible. N2 blanketing ensures the stored gas or liquid remains in the same state as when it was first produced. Therefore, it protects a company’s products and its reputation. In addition, using N2 can improve working conditions. This is because it’s good for process safety and protecting personnel. That said, it’s important to use clean, high-purity blanket gas.
Optimal blanketing conditions & types
In the introduction we mentioned using an N2 generator capable of producing high-purity gas. To produce this, clean, dry compressed air is needed. This is because a generator takes air and separates O2 from N2. As a result, it’s important to use the right dryers, filters, and other air treatment equipment before N2 is generated. This is especially important for sensitive applications that impact human life.
Once you have clean, high-purity N2, the blanketing process can begin. This involves tank padding and de-padding. Padding ensures that the vapor pressure is below a certain level so the blanketing gas can flow and displace the O2. With de-padding, the excess gas is allowed to flow out of the tank. When blanketing, three methods are used: continuous purge, pressure control, and concentration control.
Types of blanketing
Continuous purge uses a constant flow of N2, and therefore has high consumption rates. Pressure control responds to the levels inside the tank to ensure there’s minimal space between the stored gas or liquid and the tank. This is done with a gas regulator. With this, it's important to consider the fire triangle, where equilibrium needs to be maintained between fuel, O2, and an ignition source. A blanket gas regulator keeps this in check by letting out any excess gas.
Lastly, concentration control blanketing relies on feedback from an O2 analyzer to cycle an N2 generator on or off. This is an economical approach and ensures O2 is kept below the acceptable limit. By contrast, continuous purge has no control device. While continuous purge is easier by comparison, it requires a larger N2 supply than concentration control or pressure control blanketing. This is where on-site N2 generation can come in handy.
Considerations for the chemical and petrochemical industries
While this article generally speaks about gas blanketing, it's worth focusing on the chemical and petrochemical industries. Since both can create hazardous products, there's certain protocols that need to be followed. You'll want to follow local and national regulations on this, particularly regarding the storage vessel, handling, and signage used.
When choosing the right vessel, it should easily and safely store the chemical. Not all containers are compatible with every chemical and petrochemical, so it's important to pay attention to this. The container should also be clearly marked, so its contents won’t be confused for something that can be consumed.
The container should also be completely sealed, without any risk of leakage. The last thing you want is for gas to escape and O2 to enter, after the chemical or petrochemical was properly blanketed. With this, you'll want to maintain a proper temperature. This is particularly relevant with organic products.
Refrigeration is usually recommended to keep the chemical or petrochemical from both freezing or heating up too much. The latter can lead to expansion and vapors to escape. Of course, you should consult best practices related to your industry for optimal conditions.
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We hope this article provides a good overview on gas blanketing and what to consider when working with chemicals and petrochemicals. As always, you can reach out to our team to learn more about the topics covered. We're happy to provide an overview of how we can best meet your needs, including N2 generation solutions. Contact us today.