Ten considerations for choosing an air compressor

When building a compressed air system, in addition to the purchase cost, how to save high electricity expenses, extend the life of the air compressor, stabilize the air supply pressure, and reduce environmental noise and pollution? It has always been a problem that users are eagerly looking forward to solving. And how to correctly select the air compressor in the initial stage of installation plays a key factor. The ten considerations for selecting an air compressor are as follows:
1. Purpose of compressed air:
When purchasing an air compressor, most users rarely consider the use of compressed air, such as power transmission or instrumentation, equipment cooling and detection. The established pressure should be different. Many plant planners set up the same pressure from the beginning to replace use, resulting in waste of system power every year.
2. Pressure:
You should first understand the maximum and minimum operating pressures of each air end, plus the necessary pressure drop in the conveying pipeline and purification system and the pressure range of the air compressor loading / unloading to determine the rated exhaust pressure of the air compressor.
  Generally, the loss of pipeline is about 0.5 kg/cm². Compressed air usually needs to be processed by a cleaning system. The drying of heat exchange through the pipeline or the cleaning process through a filter will cause a pressure drop, which is about 0.3~ 0.5 kg/cm² (filter + dryer).
3. Air capacity:
Most users usually choose air compressors by "fixed horsepower". In fact, "fixed air capacity" is the more correct method. Users should select and configure different types and sizes of air compressors according to the off-peak demand air volume, and try to make the air consumption of each air consumption period consistent with the air compressor's exhaust volume. Then choose different types of air compressors according to the peak and off-peak load changes.
"Base load" uses centrifugal compressor or screw type compressor.
"Variable load" uses multiple screw type with frequency conversion type
"Instant load" uses a high compressed air compressor and a large air tank to homologize with it.
The following points should be considered in the selection of exhaust volume:
         (A) Current demand
         (B) Possible pipeline leakage
         (C) Future expansion plan
         (D) Used margin
4. Quality requirements:
Just as flushing water and drinking water require different treatments, compressed air must also be treated differently according to different air quality requirements. Usually we divide compressed air into process use (PA), instrument use (IA), breathing use (BA) and special process use (SPA). Usually according to ISO 8573-1 compressed air quality standards, different types and grades of dryers and precision filters are selected and configured. Too good quality wastes energy, and insufficient quality affects the manufacturing process, which must be carefully considered.
Air compressors can be divided into oil-injection air compressors and oil-free air compressors according to their different structures.
Oil-injection type: Anyone who must use lubricating oil to lubricate the inside of the body and the compression part is called oil-injection type. The compressed air produced contains a small amount of oil and gas. Although it contains a small amount of oil, it is still suitable for general industrial use.
Oil-free type: The oil-free parts are made of special self-lubricating materials, and the lubrication effect of the compression part can be achieved without lubricating oil. Therefore, there is no oil in the used air, which can meet the requirements of oil-free air in some industries. Applicable objects: precision industry, medical, food, semiconductor, coating and other industries.
Basically, the oil-injection type air compressor has the problem of waste oil, the problem of oil pollution, and the oil contained in the condensate water, which must be properly handled in accordance with the requirements of environmental protection regulations.
5. Control technology:
The earliest air compressors used "mechanical pressure switches" and "pneumatic controls" for solo machine On/Off control. In the 1980s, with the rise of PLC programmable controllers, there was the so-called "multi-machine sequential control", but they only staying on the electrical control of the air compressor itself, it was not until the late 1990s that air compressors entered the PC-Based "multi-machine interlocking control". Since 2000, "frequency conversion control" technology has also been surging. Technologies such as "multi-machine interlocking", "electronic control", "frequency conversion" and "remote monitoring" can effectively suppress the loss of system regulation and operation and the waste of unloading (saving electricity costs by 25-40%). The operating units are running close to full load, with stable air supply pressure (±0.1bar). Can achieve nearly 30% energy saving benefit from control.
6. Operational efficiency:
When the equipment is operated at the design point, the highest efficiency can be maintained, but the farther the design point is the lower the efficiency will be. Therefore, the correct air compressor is selected during planning, which can save a lot of operating costs in the future.
7. Installation and ventilation:
Compared with the manufacturing process and air-conditioning equipment, air compressors are relatively inexpensive, durable and less demanding. Therefore, it is often placed in the worst corners of the factory environment, and there are many phenomena such as oil leakage, air leakage, water leakage, high temperature, western sunlight, humidity, dust contamination, poor ventilation, and hot end circulation. In addition to unfavorable air compressor operation, it also has a certain degree of impact on energy saving. The size of the compressor room space, ventilation conditions, noise isolation, waste heat, waste water recycling, etc. all affect the use of energy. In addition, "centralized" has lower installation, maintenance and monitoring costs than "distributed", and can also reduce peripheral equipment investment.
8. Cooling method:
The cooling methods of air compressors are basically divided into two types: air cooling and water cooling. Unless the environment is special, air cooling is generally recommended below 200hp, and water cooling is recommended above 200hp. The air-cooled type does not require additional investment in cooling towers and water pumps, but it must have good ventilation; the water-cooled operating temperature is not affected by the environment, which is beneficial to the life of the air compressor, only the shortcomings of ice burst and blockage.
9. Power supply specifications:
Countries and regions in the world have different power supplies, different voltages, different frequencies, and different electrical regulations. When purchasing an air compressor, you must specify the voltage, frequency and number of phases used so that the manufacturer can correctly assemble the air compressor’s electrical control equipment. The voltage demand and the stability of the voltage drop must require that the motor used in the air compressor can be divided into single-phase or three-phase according to the power supply:
Single-phase: The usual voltages are 110V, 220V. For convenience and safety, 110V can be used under 1hp, 220V can be used above 1hp, and single-phase power supply is not suitable for 5hp or above.
Three-phase: usually used in larger horsepower models. Low voltage system (common 380V~460V), high voltage system (3kV~10kV) is recommended for the air compressor of 600hp
10. Maintenance:
In maintenance, we must focus on the hours of use of consumables and the original warranty requirements to avoid using low-priced and inferior products from other repairers. From an energy-saving standpoint, air compressor management is the primary consideration. The machine room should have proper maintenance space and necessary lifting facilities and access channels. Operators and maintenance personnel should also be given different energy-saving and maintenance professional training.
Data reference: Manual of energy saving technology for air compressor system, compiled and printed by the Energy Commission under the Ministry of Economic Affairs.