Active magnetic bearings (AMB) have been used in large industrial machinery for decades. This technology has been proven over the years to be a highly reliable concept and has been used in applications where energy efficiency is an issue, or a high standard of the production process is required.
Challenges of the Centrifugal Compressor
Compressed air is one of the four utilities, together with electricity, water and heat. Industrial manufacturers do not have to produce the other three utilities, but compressed air is their responsibility. Centrifugal compressors or turbo compressors are dynamic types of compressors, which are used for the injection and compression of gases. Centrifugal compressors are widely used in industrial processes such as chemical, food processing, wastewater treatment, air-conditioning, heating & ventilation applications.
Centrifugal compressors are utilized to produce significant amounts of air and by their nature, they need a high rotational speed. Where speed is high there is always a challenge for bearings. This application area is lucrative for the active magnetic bearings as the impeller already operates without mechanical contact to the frame. Turbo compressors work 24/7 producing a huge amount of pressurized air.
Figure 1 Example of Turbo Compressor
Compressed air contaminated with oil in the food manufacturing process can be costly and dangerous. There are a variety of sources that can introduce oil into a compressed air system. Oil-lubricated compressors, which are prevalent in manufacturing facilities, use oil to seal, lubricate, and cool during the compression stage. Oil vapors can also be introduced from worn seals, o-rings, or compressors that are overheating and allowing vapors to escape through the system. Because oil is used so abundantly in the compressed air process, the potential for contamination is elevated. Contaminated compressed air systems can result in a decrease of productivity, loss of product, recalls, and even complete shutdown for system cleaning and re-validation.
When excess oil is present in the compressed air system, it has adverse effects on the machinery and the end products. The distribution system is also at risk as excess oil creates a nutrient-rich environment that is particularly suitable for microbiological growth and can cause damage to the distribution system or equipment. Food that is contaminated with oil will have a bad taste and odor and could affect the consumers’ health. Oil can also create a displeasing visual appearance to the product. Even food packaging manufacturers need to be aware of the effect that oil residue has on their products. If oil is deposited onto the food packaging, then it can transfer to the food product, which compromises its quality.
Many industries are continuously tightening requirements on the cleanness of the air to improve the process and products. The latest trend was to require oil-free air especially by companies active in the pharmaceutical, food, beverage, and paint segments to list a few. Also, the semiconductor industry would like to eliminate any possible foreign participles. All these areas can be addressed by turbo compressors with magnetic bearings.
With the help of active magnetic bearings, turbo compressor operates without the use of oil for lubrication, which reduces energy losses due to friction and the heat transfer efficiency of the system because no oil enters the other compressor components. Besides, it also eliminates the risk of end-product contamination. Furthermore, the oil-free centrifugal compressor also eliminates the need for oil maintenance, resulting in operations and maintenance savings.
Figure 2 Example of SpinDrive’s Active Magnetic Bearing
Benefits of using Active Magnetic Bearings in Turbo Compressors
Bearings play a critical role in turbo compressors. They not only support the load of the rotating shaft assembly but also mitigate the friction generated between the moving and stationary parts. The variable speed drive on the motor allows the turbo compressor to operate much more efficiently at partial loads than standard compressors, especially with AMBs. Additionally, active magnetic bearings allow turbo compressors to be protected from damage during the surge, extending compressor operational flexibility. AMBs can actively detect surge forces in centrifugal compressors and inject current to keep the shaft rotating in its axis.
Other AMB benefits also include:
- Sustainable production
- Less energy losses due to friction and higher process efficiency
- Lower electricity cost
- Reduce operational and total life cycle costs
- Cut off significant maintenance costs due to no oil use
- No risk of product oil contamination
- Quiet operation of turbo compressor
- Lightweight which allows for easier transportation and faster installation
- Minimize unnecessary failures and breakdowns
- Low startup draw: just a few amps required, which can reduce capacity/peak power requirements for a backup power source
Author: Dr. Nikita Uzhegov
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