PET air compressor FAQ

Most of the costs associated with compressing air don’t show up on the price tag of the PET compressor or the booster air compressor. In fact, that initial investment makes up only a fraction of these expenses, which is why an important mistake to avoid is simply comparing the initial cost of new PET compressors when making a purchasing decision.

Instead, the operators of PET bottle production plants should always keep in mind something called the total cost of ownership. This term refers to all costs related to the high-pressure compressed air they need to keep their production running.

Specifically, in addition to the purchase price of the PET compressor, this means capital expenses for other equipment (tanks, piping and cooling systems) as well as building and installation costs. Then there are operational expenses, such as the energy the compression process consumes, maintenance expenses and the cost of service plans. Finally, and this is especially important for the PET bottle industry, you also have to factor in “risk reduction.” Essentially, this refers to the reliability of the system and whether it is likely to incur unexpected additional costs if it lets you down.

As noted above, the price tag of the compressor and the booster air compressor is one of the smaller parts of the total cost of ownership. You will spend much more money on energy. When looking at energy, keep in mind that these energy costs reflect the electricity consumption of the entire installation and not just the motor power or shaft power. The latter can be 20% lower.

In addition, investing more in quality equipment will allow you to realize big savings elsewhere. For example, Atlas Copco is the only provider which offers a booster that can be installed near the point of use. This eliminates the need for expensive high-pressure pipes that run from the compressor room to your PET bottle production equipment. Furthermore, you may not have to add sound insulation to your compressor room if you invest in a quiet unit.

Speaking of the compressor room, you may not even need one depending on the equipment you buy and the way you design your production facility, which obviously also offers huge potential savings.

When it comes to the production of PET bottles, risk reduction is of crucial importance. If you want to manufacture thousands of bottles per hour in continuous operation around the clock, you cannot afford any production shutdowns. That means you have to always be able to count on your equipment to deliver a top performance and a top product. 

Because compressing air consumes so much energy, sizing the compressed air equipment is very important. If the compressors or the air compressor boosters are too large, they will waste a lot of energy and money. If they are too small, they will not meet the rigorous demands of the production of PET bottles and the performance of your operation, and therefore your customer satisfaction, suffers.

Since a lot of different variables are involved, determining the air consumption and sizing the equipment is a real skill and, ideally, you would want to get the experts from your compressed air partner to help you. This not only applies to the compressor itself but also, for example, the air compressor receiver tank sizing. 

If you want to try your luck alone, here are some of the factors you have to take into account: First of all, you need to know your flow and pressure requirements.

While pressure is the amount of force required to perform a certain amount of work, flow refers to the compressor’s or booster’s ability to continue performing a task in a given time.

But that’s not all. In the PET bottle production sector, the products themselves also influence the required pressure, so that has to be factored in. Generally, more pressure is needed the thicker the walls of the bottles are, the more unusual their shape is and the bigger they are.

An expert will also look at the ambient conditions of your facility, such as the elevation above sea level, the ambient temperature and the humidity. In addition, the cooling system, PET compressor type and electrical infrastructure also affect the required pressure and therefore the size of the compressed air equipment you need.

Now you know which information you need to size your equipment, but how do you get it? Basically, to give you an idea of how much air you need, you can multiply the number of PET bottles you produce with the volume of each bottle and then with the blowing pressure of your blow molding machines.

However, if you want to optimize your energy consumption, then there are ways in which you can reduce your compressed air demand. For example, you can lower the pressure or recover some of the air so that it can be used for other tasks.

By taking full advantage of all strategies currently available and the right equipment, it is possible to reduce the air consumption from the calculation above by about half. This will result in substantial energy savings.

When using a reciprocating compressor, you will also need an air receiver. That is because these compressors use a low-pulsation type of compression (a piston compressor compresses air at a rate of 500 times per minute while a screw compressor can reach 10,000 or more of these “pulsations” per minute).

The slower pulsations of a reciprocating compressor deliver more air with each pulsation, which also means they release a greater force (this is why you might see the piping of a piston compressor vibrate but not that of a screw compressor). To counter this pulsation force, a receiver vessel is installed downstream from the compressor. The bigger these pulsation forces are, the bigger the receiver has to be.

Ideally, you should install it close to the location of the compressor to eliminate these pulsation forces as fast as possible.

And, of course, you also want to make sure that you get the air compressor receiver tank sizing just right.

The determining factor when it comes to pipe sizing is where you will put your air compressor booster. If it is installed in a compressor room, you need to span the distance to the point of use. If you have a low-noise and low-vibration booster that can be installed close to your blow molding machine, you will need a lot less piping.

Keep in mind that efficiency is key when it comes to high-pressure pipe sizing. Your piping must be able to withstand high pressure, which means it has to be made of a high-quality material. In most cases, that material is stainless steel, which makes these pipes very expensive. That means one of your goals in designing an efficient compressed air system should be to reduce the amount of the high-pressure pipes you have to install. 

When using reciprocating compressors, which vibrate more, you often need a special foundation. However, if you choose Atlas Copco’s piston booster with concrete base, that is not required.

Another issue is noise. If the equipment emits a lot of noise, then you can’t install it near the point of use and might even have to add sound insulation to make sure that noise emission standards are met.

This also means that, depending on which equipment you use, you will need a separate compressor room for your high-pressure machines, which takes up more space and costs more money. You can try to avoid this by using low-vibration, low-noise equipment, e.g. Atlas Copco boosters with a canopy that suppress sound. 

With traditional equipment, you have to choose a centralized approach, which means your compressor and/or booster are located in a compressor or utility room and the high-pressure air is transported to the point(s) of use from there.

In the case of production facilities for PET bottles, this isn’t ideal because it means having to install expensive high-pressure pipes. In addition, it’s also not efficient to use higher pressure air for applications that do not require it.

A fully decentralized approach, i.e. one with a high-pressure compressor is installed at every point of use, generally does not work. The investment costs would be too high and the energy efficiency too low. In addition, the equipment may not even be allowed to be installed at the point of use because of its high noise and vibration levels.

The optimal solution is a hybrid approach in which a low (medium)-pressure compressor is placed in the compressor room and sends air to a booster near the point of use. This booster then converts it into the high-pressure air that is needed for the production of PET bottles.

However, this only works if the booster is quiet enough.

Another way to increase the efficiency of the system is to use an energy-saving compressor or booster with variable speed drive (VSD) technology. VSD units adjust their motor speed to the air demand, generating energy savings of up to 20% compared to traditional fixed-speed units. With today’s energy prices, your savings quickly add up.

Finally, high-pressure compression with 4-stages is more energy efficient than a 3-stage unit. 4-stage compression allows for a more gradual compression with a lower compression ratio, resulting in a more energy-efficient compression. It’s pure physics (and you can’t beat physics!). In combination with our market-leading VSD technology, that means our 4-stage solution can handle lower air demands in the most reliable and efficient way. 

You have the option of using an air-cooled or water-cooled system. The latter is more common. Here, the amount of cooling water is dictated by the total BTU/h or HP, the conditions on site and the percentage of glycol the cooling water contains.

However, high-pressure air-cooled compressor solutions are available as well. So if you don’t have access to cooling water or prefer air cooling, Atlas Copco offers plug-and-play high-pressure air-cooled PET compressors as well.