Gas Mixers for 2 or 3 Gasses
Gas mixtures in Modified Atmosphere Packaging (MAP)
Modified Atmosphere Packaging is a method of packaging food or other products, such as beverages or pharmaceuticals. This is done in a way that increases the shelf-life of the product and prolongs the product’s freshness and appearance.
Particular mixtures of gases are carefully selected depending on the product. Red meat, for example, requires elevated concentrations of oxygen in the modified atmosphere so that it can maintain its colour; other products are packaged in low-oxygen atmospheres to reduce the growth rate of microorganisms such as bacteria and moulds.
Typically the three main gases used in MAP are carbon dioxide (CO2), oxygen (O2) and nitrogen (N2). In all cases the gases used are approved for food product use. Gas mixers, sometimes called gas blenders, are used to create the appropriate gas mixture.
The importance of the gas mixers or gas blenders in Modified Atmosphere Packaging
For the MAP operator, it is vital that the gas mixer (gas blender) on the packaging line is of the appropriate capacity and that the sufficient gas volume is being delivered at the appropriate flow rate. This ensures that the mixture enters the package as is intended and is not diluted by the surrounding non-modified atmosphere.
Sufficient flow capacity of the gas mixer is therefore paramount and operators make a calculation on how many litres of gas mixture must be delivered by the gas mixer in a given time in order to achieve complete flushing.
Types of gas blender for MAP
In some cases, ready-blended mixtures are provided by the gas supplier so there is no need for gas mixers on site. However, an on-site gas blender device gives the operator more versatility and control over the mixtures to be delivered.
Mechanical gas mixer system
These are ‘traditional’ proportional gas mixers where the gas is blended mechanically within the mixing chamber of the gas mixer device. The gas mixers or gas blenders are equipped with a gas equaliser to ensure that the input gases are of the same pressure and the diameter of the gas mixer aperture is controlled to ensure the appropriate flow rate into the mixing chamber to deliver the correctly proportioned gas mixture.
Adjustments to the gas mixers are manual. One potential disadvantage of this gas mixer or gas blender system is that it requires a relatively high input pressure compared with the output pressure. So, for example, if an output pressure of 5 Bar is required from the gas flow mixer, it might be necessary to have an input pressure of, say, 9 or 10 Bar. If there is a sudden drop in pressure of one of the input gases into the mixer, it might take some time before the mixing is corrected at the output.
‘Intelligent’ electronic gas mixer system
MOCON Europe (Dansensor) has developed a state-of-the-art smart gas mixer, MAP Mix Provectus, which uses intelligent mass flow control sensors which actively monitor the flow of gas in each input line to the gas mixer, adjusting the flow as necessary to provide a consistent, pre-programmed output from the gas blender unit. Provectus has a number of key advantages over traditional mechanical gas mixers.
With the Provectus gas blender it is not necessary to equalise the pressure of the incoming gases, and there is much lower pressure loss for the output gas mixture. Typically an input pressure of only 6.5 or 7 Bar is needed to achieve an output pressure of 5 Bar. This can be important where nitrogen is being generated on site at relatively low pressure, for example. It also means the operator can achieve more value from gas bottles – the lower-pressure gas at the end of the bottle can still be used, minimising waste.
Also, if there is a sudden drop in pressure of one of the input gases to the gas mixer, within 50 to 100 milliseconds Provectus’s sensors detect this and alter the flow rate accordingly to maintain the correct output mixture from the gas blender system. This gas mixer is, therefore, far less susceptible to pressure changes.
The Provectus gas mixer has up to three input ports, allowing it to mix up to three gases; if only two gases are needed in the gas blender mixture, two ports can take the same gas, with the third port taking the second gas of the mixture to enable a higher maximum output from the gas mixer.
The Provectus gas blender has a remarkably small footprint for its outstanding maximum flow of 1500 litres per minute. Furthermore, up to three Provectus gas mixers can be bridged in parallel to deliver 4500 litres per minute.
For even greater regulator control and efficiency, the Provectus electronic gas mixer can be coupled with the MAP Check 3 on-line gas analyzer. The MAP Check 3 gas analyzer constantly monitors the composition of the gas at the flushing point and can send signals to the Provectus gas mixer to adjust the flow if the residual oxygen level is falling outside pre-programmed parameters.
Another important feature of the Provectus gas mixer is its high versatility. The operator can program the gas blender to accept a given gas for a specific inlet port. For example inlet 1 can be programmed for CO2 one day and for nitrogen the next day. This is in contrast to a traditional gas mixer, whose inlets are calibrated for a specific gas.
The Provectus gas mixer has a user-friendly touch screen for set-up and operation, and stores all relevant data in the gas mixer, which can be sent directly across a LAN, or else downloaded at the end of a packaging run. In this way, key traceability requirements can be met. The Provectus gas mixer system allows precise documentation of the mixtures that have been supplied.
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We can help ensure that you have a first-rate gas blender on your production line!