When sourcing your nitrogen supply, it's common to choose industrial gas bottle delivery. However, there's more efficient alternatives, mostly notably on-site production with a PSA or membrane generator. This article covers various options, while emphasizing the benefits of each.
The first choice mentioned is purchasing nitrogen bottles from an off-site production facility. This process is very straightforward. You order the desired nitrogen quantity for your application, and the supplier delivers it in big heavy bottles.
N2O2, generated by a cryogenic nitrogen plant, is converted into a gas and bottled under very high pressure (300 bar). As a result, a lot of nitrogen gas is stored in a relatively small bottle. However, in order to withstand the high pressure, the containers are quite bulky, adding weight.
After use, these bottles are placed in a rack, where they are stored for pickup - requiring additional storage.
Advantages:
● An easy solution for facilities with a low nitrogen consumption.
● Provides readily available nitrogen for peak flows.
● Simple installation.
Disadvantages:
● Due to the size and weight of bottles, transportation is not environmentally friendly.
● Working pressure must be greater than bottle pressure. If not, nitrogen is wasted.
● Relatively high price due to production and shipment costs.
● Special bottle rack switching system required to avoid workflow interruptions.
● Safety concerns (heavy steel handling, high pressure).
● Creates dependency on nitrogen suppliers.
● Not suitable for high gas consumption.
A second option involving a third party is to install a liquid nitrogen storage tank that's periodically filled by a gas company. These tanks can either be rented from the supplier or purchased. Additionally, an evaporator is required for gaseous nitrogen use.
An evaporator transforms liquid nitrogen into nitrogen gas. Just like bottled nitrogen, transportation is required for liquid nitrogen supply. However, in this case, it's delivered by a thermally insulated tank truck. The liquid nitrogen is then pumped from the truck into the insulated storage tank.
It is also possible to order liquid nitrogen in smaller cans for situations with low consumption. These small tanks are known as dewars. Also, just like bottled nitrogen, liquid nitrogen is produced by a cryogenic nitrogen plant.
Advantages:
● Provides readily available nitrogen for peak flows.
● Generally more cost-effective than bottled nitrogen.
● Capacity adjustments are easy to match changing nitrogen demands.
Disadvantages:
● Tank insulation isn't perfect. Liquid gas can heat up and evaporate, known as boil-off losses.*
● Long term contracts with gas companies are common (usually 5-7 years).
● Additional setup required including a special foundation and evaporator.
● Not environmentally friendly.
● Safety concerns (liquid nitrogen is -196 °C, there is a frostbite risk when working with liquid nitrogen).
● Evaporator can freeze up when your nitrogen consumption is higher than nominal or when it’s cold outside.
*Boil-off losses are waste. Whenever you use less nitrogen than the tank's capacity, pressure rises causing boil-off losses. If no gas is consumed at all, this waste is as high as 1% of the tank's remaining volume, per day. To counteract these losses, filling up the tank regularly is required (typically once a week).
Related to liquid nitrogen delivery is on-site cryo production. When your consumption is extremely high, a gas company might install a small cryogenic nitrogen plant. This is the same type of generator used to create nitrogen that's transported in bottles and tank trucks. You can read more about cryogenic nitrogen generators in the linked article.
Opposed to the previous methods of purchasing and receiving nitrogen, generating your own does not involve the cryogenic process. As a result, both membrane or Pressure Swing Adsorption (PSA) nitrogen generators don't require extreme temperatures. These types of equipment separate air into their components through other means.
Although PSA and membrane are two very different technologies, they both require a stream of compressed air to work. Also, since these two generators don't use cryo, the resulting gas composition is not the same.
Cryogenic nitrogen has a fixed, high purity level. The nitrogen purity of commercially available generators is adjustable to match your preferences. It's worth noting that achieving the same purity level as cryo-generated nitrogen is inefficient with PSA and membrane generators.
With these machines, higher purity requires more power, resulting in increased operational costs. That being said, PSA and membrane generator purity levels are sufficient for most applications. And users can lower their cost per unit of nitrogen by producing the right purity for their application instead of the highest. You can read more about nitrogen purity here.
Advantages:
● Usually, generating your own nitrogen is the most cost-effective.
● Purity can be set accordingly. Energy expenses depend on your desired level.
● No dependency on gas suppliers.
● Stable gas price.
● Safe option.
● No waste.
● Most environmentally friendly option.
Disadvantages:
● Special measures required for peak flows (e.g. buffer tank, high pressure buffer tank, liquid gas buffer).
● Less adaptable to changing nitrogen demands than liquid or bottled delivery.
● Requires additional maintenance.
Take a Closer Look at PSA and Membrane Generators
21 April, 2022
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