Centrifugal air compressors have the characteristics of large single-machine flow and no oil in compressed air, but from the perspective of energy saving and reliability, centrifugal air compressors are not suitable for many fields. Users should consider the following issues before purchasing a centrifugal air compressor:
1. The speed is too high
Centrifugal air compressors use multi-oil pitch tilting pad sliding bearings. The speed of pinion and impeller is generally around 30,000 revolutions per minute. The requirements for lubricating oil and lubrication system are very strict. Any defect in the lubrication system can easily cause major accidents. .
The rotational speed of screw compressors is generally lower than 3,000 revolutions per minute. Rolling bearings are used to drive the circulation of lubricating oil with its own gas pressure, which has good tolerance to changes in lubricating oil quality.
2. High cost of backup machine
For production lines with high reliability requirements, backup air compressors must be installed. The flow rate of a single centrifugal air compressor is generally 100 cubic meters per minute to several hundred cubic meters per minute. To prepare a centrifugal air compressor is equivalent to purchasing one more large air compressor. An air compressor station with a gas production capacity of 200 cubic meters per minute must be equipped with a centrifuge of 200 cubic meters per minute, that is, the purchasing capacity reaches 400 cubic meters per minute. If the screw air compressor is used for three backups and one plan, the air compressor station with a gas production of 200 cubic meters per minute only needs to prepare one screw air compressor with a capacity of 70 cubic meters per minute, that is, the purchasing capacity is only 280 cubic meters per minute. Calculated based on the average market price of 10,000 yuan per cubic meter, an air compressor station with a gas output of 200 cubic meters per minute can save more than 1 million investment by using a screw machine than using a centrifuge.
3. The flow regulation method consumes high energy
The centrifugal air compressor cannot close the air inlet. When the gas consumption of the production line is reduced or the gas is temporarily not used, the gas produced by the centrifugal air compressor must be consumed by venting, and the energy consumption is huge.
The screw air compressor can suspend the air supply by closing the air inlet, and only consumes 30% of the rated power in the unloaded state. At the same time, some compressors can be shut down to adjust the gas production. Therefore, centrifugal air compressors should not be used for production lines whose gas consumption changes by more than 15%.
4. The standby machine takes a long time to start
For the production line, once the main air compressor fails, the standby machine must ensure immediate air supply, and the interval time is generally calculated in seconds. Screw air compressors can complete the start-up process in less than 15 seconds, while centrifugal air compressors take several minutes. Therefore, the use of a centrifuge as a standby machine often results in interruption of gas supply.
5. Inconvenient for heat recovery and utilization
Centrifugal air compressors basically adopt a water-cooled structure. If the temperature of the cooling water increases by more than 10 degrees, it is easy to cause scaling on the tube wall, so the waste heat of the centrifugal air compressor is difficult to recover.
90% of the input power of the screw air compressor is absorbed by the lubricating oil and converted into heat. The temperature of the lubricating oil in the oil separation tank is generally about 80 degrees. A special heat exchanger can be used to recover most of the heat, which can be used to produce more than 60 degrees. Hot water, or heating above 40 degrees, can meet the needs of ordinary enterprises for domestic hot water or winter heating, and can replace atmospheric pressure boilers.
6. Comparison of price and performance of different configurations
According to the total gas consumption of 110 cubic meters per minute, the gas pressure of 0.8MPa, and the average price of air compressors of 8,000 yuan per cubic meter:
The total price of two centrifugal air compressors (one open and one standby) is 1.76 million yuan, and each set of high-voltage switchgear, soft-start cabinet and after-cooler needs an additional 200,000 yuan, for a total of 2.16 million yuan;
The total price of three screw air compressors (open two and prepare one) is 1.344 million yuan, including switch cabinets and after-coolers.
In summary, centrifugal air compressors are suitable for use in the case of large gas consumption and small gas consumption fluctuations. Centrifugal air compressors still have certain advantages in terms of energy efficiency, maintenance costs, failure rate, and service life.