On-Site Nitrogen Generation for Modified Atmospheric Packaging
In the food and beverage industry, the moment a product leaves the production line, the clock starts ticking down to when that product will no longer be viable for sale or consumption. To combat the clock, modified atmospheric packaging (MAP) techniques are used to help maintain product freshness and increase shelf life. Nitrogen is the most cost effective, efficient and widely used industry solution for a company’s packaging needs—whether it is for manufacturing cheese, coffee, dried snack foods, or fresh and ready-to-eat (RTE) foods. MAP also helps to decrease chances of contamination or spoiling, keeping products on the market for longer and ultimately increasing the reach of distribution (Figure 1).
Figure 1: When the proper nitrogen purity is used, modified atmospheric packaging can greatly increase a product’s shelf life.
The vast majority of manufacturers purchase nitrogen gas through bulk delivery. However, there is a better, more sustainable option: To become self-sufficient, manufacturers can produce their own nitrogen gas with an on-site nitrogen generator. This not only eliminates the ongoing costs associated with bulk delivery and storage, but it is also significantly safer.
If a business is not already producing its own nitrogen, there are mainly three ways of supplying nitrogen to a facility: cylinders, dewars and bulk liquid tanks. Beyond the costs of having these supplies delivered, each of these approaches has additional costs and safety considerations.
Cylinders for Nitrogen Supply
High-pressure cylinders are the most expensive form of bulk gas supply, and there are many hidden costs associated with their usage.
- Safety: High-pressure cylinders are dangerous if they are knocked over or mishandled. Direct supervision is required when they are moved to or from storage. Even when empty, the cylinders are very heavy, and can cause injuries if they fall. Furthermore, changing high-pressure lines can be hazardous if not done properly, and turning lines on when they are not secured properly can lead to explosive results.
- Nitrogen Waste: It is physically impossible to get every cubic foot of gas out of a cylinder due to progressively falling pressures and the accumulation of impurities. So when a business returns “empty” cylinders to a gas company, they are effectively giving around 10 percent of the gas back.
- Product Damage/Loss: If operators are not monitoring gas supply levels and forget to switch tanks in the middle of a run, then products can be damaged or entirely lost. Running without nitrogen renders the same results. This is a rather large liability, and often requires additional systems to monitor. Failure to do so can result in massive costs.
- Rental Costs: Many companies may also be paying rental charges for cylinders or tanks. Businesses should be cognizant of contracts in order to avoid additional rental fees.
- Added Costs for Logistics: If a business operates in a remote area or outside the gas supplier’s main route, they will probably be familiar with the issues created by untimely supply. It often results in delayed production or having to turn down new business altogether.
The Downside to Dewars
Another common solution for supplying bulk nitrogen is to have liquid delivered directly to a facility. The gas is usually stored in dewars, large stainless steel tanks with a volume of liquid nitrogen in them. They share all of the aforementioned issues with gas cylinders, in addition to one particularly unique concern: off-gassing. Off-gassing is a problem common to all types of gaseous liquid storage, as liquid nitrogen is constantly being converted to gas. Consequently, the gas leaks from the dewars. Therefore, if a company is not constantly using their supply, it is slowly being wasted.
Bulk Storage Tanks For Nitrogen Supply
While companies don’t have to worry as much about operator liability or workplace safety, bulk storage tanks have their own set of hidden costs.
- Off-Gassing: Just like dewars, off-gassing is also a major problem with tanks.
- Installation/Rental Costs: Bulk tanks can be pretty big (on average, they range from 10 to 50 feet in height, occupying 25 to 100 square feet) and have to be installed outside the facility, meaning they require a fair amount of square footage. Also, there are monthly payments for equipment rental and upkeep. Lastly, depending on the extent of a company’s needs, bulk delivery charges may apply.
- Long Contracts: Bulk suppliers will often tie businesses into multi-year contracts (on average 5 to 10 years) and will prosecute for early withdrawal, subsequently limiting a company’s ability to find better deals or solutions.
Switching to On-Site Nitrogen Generation
Ultimately, the main justification for switching from bulk supply to on-site nitrogen generation is return on investment. However, this can seem quite complicated, as gas costs are subject to a host of variables, which can vary from state to state. Performing a cost analysis demonstrates how quickly returns can be made, and subsequently re-invested into the business. While the scope of each project will vary based on business needs, some typical examples of bulk supply costs that an average business could relate to are provided in Figure 2.
Figure 2: Although gas costs vary from state to state and projects differ in scope, this chart provides typical ROIs for switching from bulk supply to on-site nitrogen generation.
As Figure 2 demonstrates, deliveries, rental costs and hazmat charges contribute a great deal towards annual costs. Furthermore, the upfront charges of gas cylinder or dewar supply doesn’t take into consideration any additional costs related to labor, storage and potential product wastage when nitrogen supplies run out. With on-site nitrogen generation, there is an opportunity to repurpose such potential losses into operational improvements, such as building more production lines, upgrading existing equipment or even hiring/training employees.
Demystifying On-Site Nitrogen Gas Generators
Nitrogen generators are nothing new: However, general awareness within manufacturing has been quite low, and as a result, on-site nitrogen generators have not yet reached a high level of market penetration. In addition, the technology involved has advanced significantly in recent years, and most perceptions of nitrogen generation are out of date.
For the food and beverage sector, the main technology used for nitrogen generation is pressure swing adsorption (PSA), and it works in a relatively simple way. Each generator consists of carbon molecular sieve (CMS) material packed into dual pressure vessels. Compressed air is fed into these vessels, and due to molecular size, the sieve adsorbs the oxygen, while allowing nitrogen to pass through. As oxygen builds up in the vessels, it is purged through a cycle of compression and decompression (hence, pressure swing adsorption).
Nitrogen generators come in numerous shapes and sizes, but they all require compressed air to operate. A fully self-contained system includes an air compressor, filtration and drying systems that feed into the nitrogen generator. However, investment in much of this may not be necessary, as the generator can be set up to run from existing compressed air systems. In terms of flow rates, the nitrogen generation system includes a generator and a buffer tank. As the generator is cycling, the buffer tank ensures that nitrogen flow rates are never impacted downstream.
Figure 3: Self-contained nitrogen generation systems include an air compressor, filtration, and drying systems that feed into the nitrogen generator.
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Proper Compressed Air Purification for Nitrogen Generation
Compressed air quality is critical for proper operation of an on-site nitrogen generator. For instance, the Peak Industrial i-Flow nitrogen generator requires compressed air meeting the ISO 8573-1:2010 Class 1.2.1 specification (as seen in Figure 4). This means that prior to entering the generator, compressed air must be filtered by a two-stage filtration system to remove nearly all particulates, along with a carbon filter to remove any oil vapor. This specification also requires air to be dried down to a -40°F dew point with a desiccant dryer. As long as there is clean, dry compressed air being provided to the generator, it can effectively operate without supervision. However, not meeting these specifications may lead to decreased equipment life span and reduced performance.
Figure 4: On-site nitrogen generators from Peak Industrial need compressed air that meets ISO 8573-1:2010 Class 1.2.1 specifications.
Key Nitrogen Specifications: Flow Rate, Purity and Pressure
In order to develop a nitrogen generation system for a business, there are three specification points that are required: flow rate, purity and pressure. In simpler terms, the end user needs to know how much nitrogen is used, what level of purity is required, and the delivery pressure required downstream.
Within the food and beverages industry, most applications are low pressure (sub 100 psig, or close to atmospheric), and require purity levels between 99 and 99.99 percent (as shown in Figure 1). Packaging equipment will regulate the gas pressure suitable to its own operation, and purity requirements will depend on the product type (on average 99.9 percent will suffice—the higher the purity requirement, the greater the quantity of compressed air needed, consequently increasing the costs). Flow rates will also vary depending on the equipment and production requirements. To establish what is needed, consulting with the packaging equipment manufacturer is usually the best place to start.
Installation, Infrastructure and Distribution
Installation space and infrastructure vary when comparing different nitrogen generator manufacturers. In the past, with the likes of twin tower nitrogen generators requiring greater than 20-foot ceilings, size alone would have turned a company away from considering the technology. However, the size of units has changed dramatically over time.
Peak Industrial’s i-Flow generators are under 6 feet in height, and are modular in design, meaning they can be expanded with additional CMS columns or built with multiple units working in parallel (Figure 5). This allows flexibility for growth at low costs and integration without major alterations to workspace. Also, in most cases, there will be no special requirements in terms of infrastructure or distribution of nitrogen gas from a generator (i.e. it will use existing distribution lines), and no special material will be required outside of a company’s specifications.
Figure 5: Peak Industrial i-Flow nitrogen generators are modular, and a system can use multiple units working in parallel.
Why Investing in On-Site Nitrogen Generation Makes Sense
The information covered in this article helps demonstrate that on-site nitrogen generators are the most cost effective and sustainable method of providing nitrogen for a manufacturing facility. They can deliver any level of flow, pressure and purity. While the initial capital investment may be slightly higher than bulk delivery, the investment would pay for itself within 6 to 18 months (on average). Such an investment not only minimizes the impact of ongoing supply costs on a company’s bottom line, but it also helps take steps toward self-sufficiency.
To read more about Nitrogen Generation, please visit www.airbestpractices.com/technology/air-treatment.