Industrial Utility Efficiency    

Nitrogen Generation in the Metal Industry

Manufacturers in the metal processing industry are always looking for the most cost-efficient and effective solutions to their process. At many plants, lasers are employed for cutting metals like steel and aluminum. These laser cutters often utilize nitrogen to eliminate moisture and oxygen from certain parts of the process. In the past, bulk storage systems have been used to house nitrogen on-site at the manufacturing plants, but this method of storage can result in a significant loss in revenue when all is said and done. So, what is the solution for plant owners? The answer begins with in-house nitrogen generation systems.

First, it is important to explore the use of nitrogen in these processes in order to understand the effects of and differences between bulk storage systems and nitrogen generation systems. Factory lasers use nitrogen right at the cutting point on the metal because the high temperatures used in the process can often cause oxidation. When oxidation occurs, the metal pieces being cut can be damaged, as can the tooling creating the cut. Structural damage or inaccurate cuts can make parts weak and render them useless. The use of nitrogen at the point of contact from laser to metal removes oxygen from the cutting area and helps cool the die as it cuts, thus preventing oxidation. This prevention improves the quality of the final products, produces less scrap metal and cuts back on the reworking of pieces.

 

Bulk Storage Systems

The first way that manufacturers can go about bringing nitrogen to the injection point on the laser is fairly simple in its execution. A typical bulk storage system consists of a tank, a vaporizer and controls. There are other types of bulk storage, but this is one of the most common systems. A supply of liquid nitrogen is housed in a large tower or tank located in the facility and nitrogen gas is pulled directly from this supply. The typical flow path for these units starts at the bulk tank and runs into an ambient air vaporizer. From there the nitrogen enters the piping and flows through regulators, depending on system design, and then goes out to process.                                                                                                                                                                                                                                                                                                                                                                                                                                  

Nitrogen Generation Systems

Nitrogen generation systems are a unique way to provide a sustainable approach to supplying nitrogen in metal manufacturing and many other industries. There are two types of nitrogen generators: a pressure swing absorption (PSA) and a membrane. A PSA system uses a carbon molecular sieve to adsorb oxygen under high pressure while allowing the nitrogen to pass through. A membrane uses hollow, porous fibers to separate the N2 molecules from the other molecules present in oxygen.

A typical nitrogen generation system for a laser cutting application will have the following components: nitrogen generator, storage tanks, high-pressure booster and high-pressure storage cylinders. Most laser cutting applications will require a PSA generator to accomplish the desired flow rates and purities. Laser cutting applications require high flow rates and high pressures, which is why all nitrogen generator systems are designed to fill 6, 12, 18 or 24 packs of bottles with nitrogen gas instead of delivering the gas directly into the application. When designed and sized correctly, these systems run efficiently and require very little monitoring.

Nitrogen generation systems utilize compressed air—a process that obviously begins with a compressor. The compressor pulls air from the surrounding atmosphere, at which point it passes through a high-efficiency coalescing filter and a dryer. This filter and dryer will remove oil, water and particulates that could damage the generation system. If the system in question is a PSA generator, after moving through the filter the dried air will make its way to an additional pre-filter before entering the nitrogen generator. After the generator, the nitrogen is delivered into the high-pressure booster where it is boosted to 2,500psi or 5,000psi depending on the system design. Once the nitrogen has reached the high pressure it is delivered to the pack of cylinders where it is stored until needed. At any point when the nitrogen is needed, it passes through a regulator that is set to the desired pressure for the application and piped to the laser cutter.

Nitrogen generator

A nitrogen generation system utilizes compressed air to generate nitrogen on-site.

Advantages, Disadvantages and Maintenance

The list of advantages that accompany using a nitrogen generation system as opposed to a bulk storage system is long and promising. As it is currently, the manufacturing industry sits somewhere around a 50/50 split of plants that use one or the other. There are a few reasons for this, one being that a nitrogen generation system is a big cost to a manufacturer upfront. Investing hundreds of thousands of dollars on a piece of equipment always seems like bargaining for an ROI that makes the expense worthwhile. Though a return on investment is relative to what application the generation system is being used for, manufacturers can sometimes see payback as early as six months after implementation.

A large portion of the savings come from the fact that the system is being bought outright, and a plant owner is not beholden to a multi-year contract from a nitrogen supplier. This cuts a number of costs including rental fees, annual supplier costs and delivery fees. Relying on an outside supplier for nitrogen can also mean conflicts in delivery scheduling. Most manufacturers run their laser cutter a minimum of twice a day and if they find themselves at the end of their supply of nitrogen before their next scheduled delivery, they have no other option than to wait. Downtime for these laser cutters can result in a large chunk of revenue loss. With nitrogen generation systems, however, the supply of air is never gone and its availability does not rely on an outside, third party.

Another chunk of savings comes from the prevention of head loss from a waste of nitrogen that occurs when using a bulk storage system. Because a generation system can be turned on and off, it is only used when necessary and can produce only the specific amount of nitrogen needed; This saves on and essentially eliminates the waste of gas. When using bulk storage systems, the purity of nitrogen being pumped into an application will almost always be near 99.998%. At first glance, that seems like an advantage but if a process does not require that level of purity then the system is not running as efficiently as possible. This is part of the reason why bulk systems seem more cost-efficient upfront but fall behind in the long run. Most nitrogen generation systems allow the user to set their own purity rate that can be tailored to what is required for their process.

Because it is absolutely critical to deliver clean, dry air to the nitrogen generator, the system is equipped with multiple filters and components that will ensure this happens. These elements are designed to remove water, oil and other contaminates and must be maintained in order to get the best life expectancy from the system as a whole. A properly cared for generation system can stay in place for 15+ years. The proper preventative maintenance that accompanies a nitrogen generation system will typically run a manufacturer around a couple thousand dollars per year, depending on their application. Pre-filters usually need maintenance every six months to a year, and the filters within the nitrogen generator will need changing every six months. The generator itself will require maintenance once every year, and the pre-filters in the desiccant dryers should be changed every six months to a year. The booster compressor is most often run on an hourly-based servicing schedule. Like the compressor, the maintenance of all elements in the system could increase or decrease in frequency from these benchmarks depending on the process they are being used for.

 

Making the Switch

The average transition from bulk storage to nitrogen generation typically takes six months to year or longer for most manufacturers. The first step facility operators need to make in the transition is figuring out when the contract with their nitrogen suppliers ends. Once that is determined, a complete report of their system requirements is essential. Some important factors to consider are the purity, flowrate (SCFH) and delivery pressure required in the process. Once manufacturers have this information they should reach out to a nitrogen generator supplier and work with them to quote a system that meets their needs. During this quoting process, suppliers will most likely give several quotes ranging in price, benefits and lead time. It is important to fully understand each supplier’s design because there is still a wide range of variables in these systems that can affect longevity, service and the manufacturing process as a whole.

 

About the Author

Patrick Hyland is a Technical Specialist who specializes in Filtration for Valin Corporation, a leading technical solutions provider for the technology, energy, life sciences, natural resources and transportation industries. Valin offers personalized order management, on-site field support, comprehensive training and applied expert engineering services utilizing automation, fluid management, precision measurement, process heating, filtration and fluid power products.

 

For more information, please visit www.valin.com.

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