Questions about nitrogen
and oxygen generation today.

Your own nitrogen or oxygen PSA (Pressure Swing Adsorption) generator.

Start with your costs and the price increases you keep having to swallow. Consider the efficiency of your current supply: How big a factor is transport? Energy? Safety? Look at the next big technological challenge you face: Will traditional supply channels help you get there faster, more reliably, with the efficiency you need?

There are specific actions you must take to make the switch, particularly when ending a bulk liquid industrial gas supply agreement. Through years of experience with companies saddled with burdensome contracts, we’ve clarified the steps you need to follow—and the pitfalls to avoid. Click here for important advice.

There’s one sure way. How large a check does your company write for nitrogen or oxygen each month? How much do you use each month? Compare the two and see how much you’re overpaying.

Ninety-three percent of your cost is power and fuel for transport.

Non-Cryogenic nitrogen and oxygen generators do not emit pollutants or hazardous waste. They simply take in compressed air, then dry and filter it and return the unwanted air components back to the atmosphere cleaner than before. When compared to hauled-in cryogenic liquid nitrogen and oxygen, onsite generated gas uses considerably less power to manufacture in addition to saving fuel and energy costs in transportation.

It really depends on your application and preference. Just from a capital cost standpoint, membranes are approximately 30% more expensive than PSA systems. They require more power than PSAs when operating at nitrogen purities of 98% and higher. PSAs are more robust and less sensitive to hot and cold ambient conditions. Membranes require 160 to 200 psig of compressed air for an efficient nitrogen separation to take place. On the other hand, PSAs require a much lower air pressure to achieve an efficient separation. Therefore, membranes will result in a higher outlet nitrogen pressure than PSA systems. PSAs generally operate longer with less maintenance costs.

Membranes have fewer moving parts, but membranes begin to age and degrade over a relatively short period of time. Replacement of membrane modules, represent a significant capital cost to the buyer. The biggest advantage of membrane systems is their inherent lightweight and small footprint.

The carbon molecular sieve material used in Gas Systems Corporation's PSA units is extruded from carbonized coconut shells and represents a very hard and durable form of carbon with an exceptionally high propensity for separating compressed air into pure nitrogen product.

The CMS material literally has an indefinite life. And like membrane fibers, it too requires protection from compressor oil carry-over. The filtration system in both the PSA and membrane unit is designed to prevent hydrocarbons from coming in contact with the CMS material and membrane fibers. Following the recommended filter changes as prescribed in the Owner's Manual is key to a long and productive life for both nitrogen generation systems.

The PSA system utilizes a programmable logic controller (PLC) located inside a NEMA 4 control enclosure to automatically control the operation of the nitrogen generator. This PLC consists of an 8k processor, power supply and I/O modules. The PLC performs all the controls and monitoring functions, including execution of the adsorption cycle. The PSA also has a built-in pressure switch and it monitors the nitrogen pressure. If no nitrogen is being used (or very little), the PSA will stop and go into standby mode. It will shut off the air inlet valve and nitrogen outlet valve so no air is used. The air compressor also has a pressure switch or sensor that monitors downstream air pressure and it too, goes into a standby mode when the air pressure begins to rise. If the air compressor remains in this mode for more than three minutes, the main compressor motor will automatically shut down and wait until the air pressure is lowered before turning back on. This feature represents a tremendous power savings advantage.

The membrane system is totally reliant upon pressure switches to control its on and off operation. The pressure switch is installed in the nitrogen product line inside the control cabinet. The pressure switch can be set to turn the unit off and on at desired product pressure levels.

A PSA nitrogen generator is a two-bed absorption system and therefore, has an interrupted air demand to the system when air is diverted from one bed to another. An air surge tank located downstream of the air compressor and upstream of the PSA unit is required in order to smooth out surges in air demand. Membrane systems on the other hand, have a smooth constant demand for air and, otherwise do not necessarily require an air receiver. However, Gas Systems Corporation highly recommends this vessel to accommodate air surges caused by starting and stopping the system.

Again, PSA systems require a nitrogen storage vessel in order to insure a smooth product delivery. Membrane systems do not require as large a nitrogen storage vessel, but is still recommended to prevent the system from starting and stopping frequently.

Gas Systems Corporation's offers a patented purity adjustable valve with up to three different purity settings. This three-position valve is pre-set at the factory and designed for the end user to change from one purity setting to another without any other adjustments to the PSA Generator. The system can be turned up or down to offer lower purity nitrogen at a higher flow rate or higher purity nitrogen at a lower flow rate.

Here's an example: An existing liquid nitrogen customer is using 3.6 million scf per month of LIN. A GSC engineer determines that the customer's continuous process (730 hrs/mo) can utilize 99.5% pure nitrogen product.

Note: Figures are for example only. Consult GSC for firm pricing.

The Industrial Gas supply agreements tend to be very one-sided in favor of the Industrial Gas Company. The term of this agreement is usually 5 to 7 years and renews automatically at the expiration date, unless canceled in writing with at least twelve (12) months prior to the contract anniversary date. A little known fact is that the letter of cancellation can be sent to the supplier at any time during the agreement. This prevents the possibility of the customer from missing the 12-month notification window. You can actually present the Industrial Gas Company with a cancel letter the date the agreement is signed.

Evaporated liquid oxygen purity is 99.5% to 99.9% pure. The average oxygen purity in an industrial high-pressure cylinder is typically 99%. The oxygen purity generated from a PSA generator is 95% +/-1%. The reason for this lower purity accounts for the fact that argon in the air does not get removed as efficiently as nitrogen. Therefore, argon makes up about 4-5 percent of the oxygen product. Ninety-nine percent purity can be achieved with an oxygen generator, but at a considerable higher cost. U.S. Pharmacopoeia (USP) sets the standard medical oxygen purity at 93%.

After the compressed air leaves the air dryer, it is filtered in a series of filtration stages. The first and second stages consist of two acetate type filters with a pore space of 0.1 and 0.01 micron. These filters are designed primarily to remove water and particulates in the compressed air. The third and final stage is an activated carbon filter designed to eliminate any residual oil or hydrocarbon from the air before it passes into the adsorption vessels.