Editorials GB - Nitrogen for Food industry

A- A A+

Continuous aeration is widely applied nowadays in the bakery, dairy, confectionery and sometimes even meat and fish processing industry. In the continuous aeration process, compressed air which has been filtered for dust, oil and moisture is injected in a flow of pumpable food products. The mix of product with the air passes through a high shear mixing head, where the air is finely dispersed into the liquid to make a fine food foam, ready to be packed, deposited or extruded.

During the shelf-life, the (over 20%) oxygen in the air reacts with the fat in the food product and limits the shelf life of the finished product (rancidity of whipped butter, fat creams, chocolate and vegetable fat decoration creams). Also aerobic bacteria that may be in the food product can develop in the presence of oxygen. The compressed air has to be dried to a dew point of 2 °C to prevent damage to the sophisticated (massflow controlled) air dosing system. This requires an air dryer mounted in the air supply line to the aeration system.

Nitrogen

For all these reasons aeration with nitrogen is recommended; in many cases the food processing industry applies the more expensive nitrogen bottle instead of the air compressor to supply the continuous aeration system.

New developments in nitrogen separation from compressed air

Membrane technology has made the separation of nitrogen gas from compressed air possible. For this purpose the ‘NG-Compact’ generator was developed. With the gas separation membrane, it is possible to produce a nitrogen-rich mixture of up to 99.9% purity. The purity depends on the way in which the system has been adjusted. The membrane system starts working immediately, once the compressed air supply is connected or when the compressor is switched on. The nitrogen is immediately ready to be injected into the mixing head.

Fig 1: The hollow membrane fibres are clustered together in a tube.

Principle of operation

To separate air in an oxygen and a nitrogen enriched stream, the generators make use of hollow fiber membranes (figure 1). These membranes employ the principle of a selective permeation to separate gases. Each gas has a characteristic permeation rate that is a function of its stability to dissolve and diffuse through a membrane. This characteristic allows ‘fast’ gases such as oxygen, to be separated from ‘slow’ gases such as nitrogen.

To operate the nitrogen generators, you simply connect to the compressed airline at typical air pressures of 5 to 10 bar. You can use an existing compressed air system, or you can install a dedicated compressor, either lubricated or oil-free.

Compressed air passes through two coalescing filters to remove dust and oil. The air then enters the separators. As it passes through the bore of the hollow fibres, oxygen, water vapour and other ‘fast’ gases permeate rapidly through the membrane walls of the hollow fibres and are vented as an oxygen enriched gas stream. The nitrogen product, typically from 95 to 99.5% oxygen free, is drawn off at the opposite end of the separators at close to feed pressure. The system is designed to ensure precise control of nitrogen product quality.

You now have a super-dry nitrogen gas for your application

In all continuous aerating systems this nitrogen generator can be mounted inside the machine cabinet (figure 2). The total system is then connected to a compressed air supply line and the nitrogen is metered into your food product.

However, the nitrogen generator is also available as a separate module, so you can connect it easily in your compressed air line to your existing aerating system. The module is available in different sizes to accommodate the required quantity per hour of nitrogen for your application. In case of several aerating systems, you can apply one bigger unit to feed to all your individual aerating systems.

Summary
To improve on the shelf-life of your aerated product, injecting nitrogen into the mixing head of your continuous aerating system is to be recommended. For this purpose membrane technology has developed a nitrogen generator to separate nitrogen from compressed air.

The system offers these advantages:

  • The cheapest way to make your own nitrogen when and where you need it;
  • No wear nor maintenance since the nitrogen generators have no moving parts
  • small and compact construction makes it easy to install, even wall mounted or inside the cabinet of the Continuous aerating machine.
  • Moisture is removed from the nitrogen to a dew point of -50 °C;
  • No logistics problems as with nitrogen bottles;
  • Low cost and very quick pay-hack of your investment;
  • The nitrogen can also be used for other applications such as packing of different food products, production of wine, blanketing of fruit juices, edible oil, syrups, etc.

Nitrogen

Fig 2: The nitrogen generator can also be mounted inside the aerator

The Author
Robert Luiten has a BSc degree in Chemical Engineering. He has worked in the Food Processing industry since 1977 and particularly he has specialized in many aspects of continuous aeration processes in the dairy, bakery and confectionery industry.

Trefa Continu Aerating Systems B.V. - Trefa Continu Aerating Systems
Ligging
Beup