PSA Nitrogen Generation Package

On Site Nitrogen by Pressure Swing

The SorbiTech PSA Nitrogen Generation Package produces nitrogen from compressed air on a pressure swing adsorption cycle. Twin carbon molecular sieve adsorbers run out of phase: one vessel adsorbs oxygen under pressure while nitrogen passes through to a buffer tank, the other vessel regenerates by depressurising to vent the captured oxygen. The cycle repeats every 60 to 120 seconds, giving a continuous flow at the purity the duty requires.

The package is delivered as a skid mounted unit with the compressor, the adsorbers, the buffer tank, and the controls integrated and pre commissioned by SorbiTech, ready to start producing nitrogen within hours of arrival on site.

Carbon Molecular Sieve and Kinetic Selectivity

Carbon molecular sieve separates oxygen and nitrogen by a difference in diffusion rate, not by a difference in equilibrium loading. The CMS pores are tuned so that oxygen, with a slightly smaller kinetic diameter, enters the pore network faster. Under the typical adsorption time of 60 seconds, oxygen is captured while most of the nitrogen passes through.

SorbiTech supplies the CMS for the SorbiTech package, with grade selection matched to the contracted purity and recovery. Adsorption pressure (7 to 10 barg), cycle time, and bed depth are tuned together to keep the kinetic separation factor above the value required.

Air Conditioning Front End

The CMS is intolerant of liquid water, oil, and particulate. The front end therefore includes refrigerated or membrane drying of the feed air to a pressure dew point of 3 °C or lower, a coalescing filter for liquid water and oil, and a particulate filter ahead of the adsorber inlet. Feed air is delivered at ISO 8573 class 1.4.1 or better.

A breach of any of those specifications shortens the CMS life. A correctly conditioned feed gives CMS service of seven to ten years before noticeable purity drift.

Selecting Purity, Flow, and Recovery

Three variables set the package size and the operating cost: contracted purity, peak flow, and nitrogen recovery from the feed air.

• Purity 95 to 99 percent: high recovery (40 to 50 percent), smaller CMS charge
• Purity 99.5 to 99.9 percent: moderate recovery (30 to 40 percent)
• Purity 99.999 percent: lower recovery (15 to 25 percent), deoxo polishing step required

A purity above what the duty needs forces a larger compressor and a larger sieve charge than required. SorbiTech sizes the package to the actual purity demanded by the downstream consumer, with a margin of 0.1 percent on the contract value.

Energy and Compressed Air Demand

Specific air consumption rises with purity: 2.5 to 3.5 Nm³ of air per Nm³ of nitrogen at 99 percent, 4 to 5 at 99.5 percent, and 7 to 10 at 99.999 percent. The compressor electrical load follows directly. SorbiTech matches the demand profile to the compressor turn down and to a buffer tank that absorbs short peaks without driving up the average load.

For a 24/7 consumer with stable demand, a single screw compressor with frequency drive runs at near constant load and gives the lowest specific electricity. For an intermittent demand, two parallel compressors with lead/lag control beat a single large machine.

Where It Is Used

Tank blanketing, vessel and pipeline purging, food and beverage packaging, laser cutting cover gas, electronics assembly, and inert atmospheres for thermal treatment. The duty is described under PSA nitrogen generation, and the sector treatment under industrial gas and air separation.

Maintenance Schedule and Sieve Changeout

Routine maintenance is filter changes every 4,000 hours, oil and coolant on the compressor at manufacturer interval, and a calibration check on the oxygen analyser every 12 months. The SorbiTech CMS is unloaded and replaced at seven to ten years, depending on feed air quality and on the cycle severity.

A planned changeout takes 48 to 72 hours per vessel with the package shut down. SorbiTech supplies the replacement CMS, the loading service, and the post changeout performance test on a contracted call out for sites that need to minimise downtime.

Lifecycle Economics Versus Delivered Gas

A SorbiTech on site PSA replaces delivered liquid nitrogen and cylinder gas with a capital plus electricity cost. For continuous demand above 50 Nm³/h, payback is typically under 24 months and lifetime cost of nitrogen falls by 50 to 70 percent. The package is delivered turnkey by SorbiTech with a single performance guarantee covering the CMS, the equipment, and the contracted purity, and a rental option is available for commissioning or bridging supply. SorbiTech delivers the PSA nitrogen package across the industrial gas sector for on site nitrogen generation, charged with the CMS N₂ grade.