How to Specify Nitrogen Generators for Chemical Manufacturing

Which figure should procurement use for compressor capacity: nitrogen demand, generator feed air or the combined inlet duty? Selecting nitrogen generators for chemical manufacturing starts with the process requirement, but the compressor must support the complete treatment and generation system.

Anglian Compressors, a Branch of Atlas Copco Compressors, has been sizing industrial compressed-air systems since 1977. We assess nitrogen purity, demand, pressure, feed-air quality and site conditions as one system rather than treating the generator as an isolated machine.

Define the Nitrogen Requirement Before Selecting Equipment

Start with the process, not a generator model. Chemical blanketing, vessel purging, product transfer and storage protection can impose different purity, pressure and flow requirements, even within the same production area.

Record the following for every nitrogen consumer:

• Required nitrogen purity or maximum permissible residual oxygen
• Normal, minimum and peak flow in a stated reference unit
• Pressure required at the point of use
• Operating pattern, including batch peaks and simultaneous demand
• Permitted recovery time after a peak
• Consequences of an interruption or off-specification supply
• Expected production changes over the equipment’s service life

Do not combine flows until their timing is understood. Three batch processes with identical peak demand do not necessarily require three times the generator capacity if their cycles cannot overlap. The opposite applies where an unplanned overlap would stop production.

If your team needs a technical explanation of the separation process before preparing the schedule, read how does a nitrogen generator work.

PSA or Membrane Generation?

Pressure swing adsorption, or PSA, passes compressed air through vessels containing Carbon Molecular Sieve (CMS). Oxygen is adsorbed while nitrogen continues to the outlet, then the vessels alternate between production and regeneration.

Membrane systems separate gases through selective permeation. They can suit duties where compact installation, continuous operation and a moderate purity requirement carry more weight than the higher nitrogen purities associated with PSA systems.

Selection Point	PSA Generator	Membrane Generator
Main specification driver	Higher nitrogen purity	Simpler continuous separation
Feed-air sensitivity	CMS requires tightly controlled air quality	Feed air still requires filtration and moisture control
Capacity assessment	Purity, inlet pressure and cycle conditions affect air factor	Purity and recovery setting affect feed-air demand
Typical design question	Can the compressor sustain every adsorption cycle?	Does the selected purity justify the associated air consumption?

Technology selection can change if different products require different purities. A single high-purity design point may waste compressed air during lower-purity production, while separate generation banks or controlled purity settings may give a better operating result. That decision needs the site’s demand profile.

Calculate the Complete Compressed-Air Duty

Compressor capacity must cover generator feed air, dryer purge air and every simultaneous ancillary demand at the required pressure.

The nitrogen flow is only the first input. Obtain the generator’s air factor at the specified nitrogen purity, inlet pressure and operating conditions. An air factor of 3.4, for example, means the generator requires 3.4 units of compressed air for each unit of nitrogen delivered under the stated rating conditions.

Convert Nitrogen Flow Into Compressor Duty

Use the following calculation:

`Generator feed air = required nitrogen flow × stated air factor`

Then calculate the compressor duty:

`Total compressor duty = generator feed air + dryer purge air + simultaneous ancillary demand`

Keep every value on the same reference basis. A normal cubic metre, standard cubic metre and compressor free air delivery figure are not automatically interchangeable. The equipment schedule should state the reference conditions used for every flow.

Why Dryer Purge Cannot Be Treated as Spare Capacity

A heatless desiccant dryer uses part of the dried compressed air to regenerate its desiccant bed. That purge flow is continuous during normal cycling and does not reach the nitrogen generator.

Specifying a compressor against the generator’s baseline feed requirement alone leaves the dryer competing for the same air. Header pressure then falls as nitrogen demand rises. The generator may remain operational while failing to deliver its specified purity, pressure or flow.

Margin should come from measured demand, control behaviour and the agreed expansion plan. Adding a blanket percentage cannot correct a missing dryer load or a calculation based on incompatible flow conditions.

Apply Environmental Derating to the Compressor and Generator

Catalogue capacity is not site capacity. Ambient temperature, altitude, ventilation, cooling-air recirculation and inlet pressure can affect the available compressor FAD and the generator’s nitrogen delivery.

Use the manufacturer’s correction tables for the proposed compressor, dryer and generator at the site’s worst credible operating condition. Apply those corrections separately because one general derating factor may not represent all three machines.

The plant-room assessment should also account for pressure losses through filters, dryers, receivers, valves and pipework. The generator requires its specified inlet pressure while delivering peak nitrogen flow, not merely when the plant is idle.

This is where logged site data earns its place. A pressure reading taken during a quiet maintenance shift will not expose a short production peak that empties the air receiver every afternoon.

Protect the CMS With the Correct Feed-Air Quality

Specify and verify ISO 8573-1:2010 Class 1:2:1 or Class 2:2:1 at the nitrogen generator inlet, according to the approved system design.

The three-part ISO 8573-1 classification describes particles, water and oil in that order. The required class must appear on the equipment schedule, commissioning plan and maintenance documentation. Writing “clean, dry air” leaves too much open to interpretation.

Oil aerosol, liquid condensate and atmospheric particles can permanently contaminate the CMS. A technical nitrogen generation guide (f.hubspotusercontent20.net) identifies compressor oil, water and particulates as threats to the molecular sieve. Once the bed is poisoned, changing a filter will not restore its separation performance.

The treatment train should be selected as a system. Depending on the approved specification, this may include bulk water separation, filtration, a desiccant dryer, final filtration and automatic condensate drains. An oil-free compressor does not remove atmospheric moisture or particles, so it does not eliminate downstream treatment.

Sites already experiencing wet-air faults should resolve those upstream issues before commissioning the generator. Otherwise, the new CMS bed becomes the most expensive contamination indicator in the plant room.

Plan the Installation Around Stable Pressure and Verifiable Purity

A workable layout needs more than an inlet and outlet connection. The compressor, treatment equipment, generator and receivers must operate as a controlled train.

The installation design should address:

• Compressor control: Confirm that the compressor can sustain total inlet duty without unstable load and unload cycling or prolonged pressure sag.
• Upstream storage: Size and position the air receiver to support generator cycling and short demand changes.
• Air treatment: Install filters, dryers and drains in the specified sequence with accessible isolation points.
• Nitrogen storage: Use the nitrogen receiver to smooth delivery and support short process peaks.
• Purity measurement: Fit an oxygen analyser at a representative point, with calibration access and defined alarm limits.
• Off-specification handling: Decide whether low-purity gas will be vented, isolated or prevented from reaching the process.
• Safe discharge: Assess ventilation and oxygen-depletion risk wherever nitrogen or oxygen-enriched waste gas can accumulate.
• Distribution pressure: Calculate pressure loss through the complete nitrogen main at peak flow.

For projects around Northamptonshire, our corby nitrogen generator service covers generator sizing, compressor selection, treatment and installation as one engineering package.

Commission Against the Process Duty

Commissioning should prove performance across the operating range, not record one stable reading after start-up. Test the system at minimum demand, normal production and the agreed peak condition.

Record generator inlet pressure, compressed-air flow, dryer operation, feed-air quality, nitrogen flow, delivery pressure and residual oxygen. Confirm alarm operation, off-specification diversion and recovery after a demand step. These readings become the baseline for maintenance and later fault diagnosis.

The handover pack should include equipment settings, analyser calibration records, treatment specifications, pressure-loss assumptions and the calculation used to select compressor FAD. If production changes, engineers can then see which assumption has moved.

Facilities in and around Kettering can use our kettering nitrogen generator support for site assessment, installation and commissioning.

Consider the Supply Model Alongside the Equipment

On-site generation is not the only procurement route. Production risk, capital approval, maintenance resources and changing demand can make rental or a supply agreement a better fit.

For projects where capital ownership is the sticking point, you can supply nitrogen without getting a generator outright. The technical specification still matters because the compressor, treatment system and generator must be matched regardless of the commercial arrangement.

Anglian Compressors can measure the existing compressed-air system, confirm the nitrogen duty and produce a specification covering compressor FAD, dryer purge, air quality, storage and controls. Speak to our team with your purity, flow, pressure, operating schedule and site-condition data, and we’ll size the complete system around the process it has to protect.