Basic Knowledge of Centrifugal Air Compressor

Basic knowledge of centrifugal compressor

Compressor power and pressure:

1. The shaft power of the compressor is the sum of the indicated power and the frictional power. The indicated power is the power directly consumed by compressing the gas, the frictional power is the power consumed to overcome mechanical friction, and the shaft power of the compressor is used to select the power of the driving motor.
2. pressure:1 bar=14.504 psi=0.1 Mpa=1 kg/cm2 =105pa

Application of gas compressor:

A gas compressor is a machine that compresses gas, increases gas pressure, or transports gas。

main purpose：

1）Gas delivery；

2）Power medium；

3）Refrigeration and gas separation

Types of gas compressors

1. According to the principle of action, it can be divided into：Volumetric and velocity based

• Positive displacement compressors rely on pistons that move back and forth in the cylinder or rotors that rotate to change the working volume, thereby reducing the volume of gas and increasing its pressure. The increase in pressure is achieved through direct gas volume compression。
• The speed compressor relies on the high-speed rotating impeller to increase the pressure and velocity of the gas, and then converts a portion of the gas velocity into gas pressure energy in the fixed element. That is, with the help of the high-speed rotating impeller, the gas molecules are first given a high velocity, and then the velocity is reduced in the diffuser to convert kinetic energy into pressure energy。

2. According to the pressure level classification, it can be divided into low-pressure compressors, with an outlet pressure of 2-0.98Mpa (gauge pressure); Medium pressure compressor, with an outlet pressure of 0.98-9.8 Mpa (gauge pressure); High pressure compressor, outlet pressure greater than 9.8 Mpa (gauge pressure)。
3. According to the type of compression medium, it can be divided into air compressors, nitrogen compressors, hydrogen compressors, oxygen compressors, gas compressors, etc

Advantages and disadvantages of centrifugal, screw, and piston compressors：

category	advantage	shortcoming
turbine	1. Simple structure, few vulnerable parts, low maintenance volume, and long operating cycle. 2. High rotational speed, high airflow velocity, small machine size, light weight, small footprint, low investment, safe and reliable operation. 3. Smooth operation, large displacement, and low vibration. 4. Gas is not easily contaminated by lubricating oil, 5. Easy to achieve automation control and scalability, 6. Has a flat performance curve and a wide range of smooth operation. 7. Long operating cycle	1. Poor operational adaptability, the driving motor should have a large power margin. 2. The airflow speed is high, the friction loss is large, and its efficiency is not as high as that of piston engines. 3. There is a surge phenomenon. 4. The noise is loud.
Fuel injection screw type	1. Reliable operation. 2. There are few vulnerable parts. 3. Low vibration and noise. 4. High efficiency. 5. Easy installation.	1. There is oil in the gas. 2. High operation and maintenance costs. 3. Narrow displacement and exhaust range, not suitable for large-scale production. 4. High material requirements.
piston-type	1. Wide range of exhaust pressure. 2. Low material requirements. 3. High thermal efficiency. 4. The adjustment of gas volume is not affected by changes in exhaust pressure. 5. The driver is simple	1. The structure is bulky, with many vulnerable parts, a large amount of maintenance work, and a short service life. 2. Uneven exhaust can easily cause pipeline vibration. 3. The unit experiences significant vibration. 4. The gas has a high oil content.

Structure of centrifugal compressor system:

1. The main components of a centrifugal air compressor include: 1) air filter, 2) compressor host, 3) unloading valve (vent valve), 4) coupling, 5) oil tank, 6) auxiliary oil pump, and 7) electrical system.
2. The main engine of a centrifugal air compressor includes: 1) inlet guide vanes, 2) gearbox, 3) first stage, 4) first stage intercooler, 5) second stage, 6) second stage intercooler, 7) third stage, 8) aftercooler, 9) check valve, 10) oil cooler, 11) main oil pump, 12) oil filter, 13) oil mist remover, 14) constant temperature bypass valve.
3. The lubricating oil system of the air compressor mainly includes: 1) oil tank, 2) oil filter screen, 3) oil heater, 4) oil mist remover, 5) main oil pump, 6) auxiliary oil pump, 7) oil cooler, 8) oil filter, and 9) constant temperature bypass valve.
4. The safety protection system of centrifugal air compressor mainly includes: 1) temperature protection system, such as alarm and interlock shutdown of intake temperature, oil temperature, bearing temperature at all levels; 2) Pressure protection systems, such as oil pressure, instrument control air source pressure, etc., alarm and interlock shutdown; 3) Mechanical protection, such as vibration alarms and interlocking shutdowns at all levels; 4) Anti surge protection.
5. The rotor of a centrifugal air compressor mainly consists of: 1) gear shaft, 2) impeller, and 3) fastening nut,

Functions and characteristics of centrifugal air compressor components:

1. The function of an oil filter is to remove dust and impurities from the oil
   The function of an air filter is to remove dust and impurities from the air, and the pressure difference alarm value of the air filter is 05 bar.
2. The function of the oil-gas separator is to separate the oil in the air and prevent it from escaping.
3. The function of the centrifuge oil mist remover is to absorb and filter the oil mist in the gearbox and return it to the oil tank, reducing oil loss and environmental pollution.
4. The function of an oil heater is to heat the oil in the oil tank to maintain it above the required minimum temperature.
5. The function of the constant temperature bypass valve (constant temperature control valve) is to mix the hot oil in the oil tank (oil separator) with the cold oil coming out of the oil cooler to ensure that the oil temperature at each lubrication point is as constant as possible。
6. The impeller adopts a backward tilting ternary flow impeller, which is manufactured and processed as a whole. Its materials include stainless steel 17-14 material or titanium alloy material, which is not easy to wear and can prevent the corrosion and wear of the impeller by gases and moisture contained in the air.
   • Adapt to different load changes to provide optimal operational efficiency。
   • Wide throttling range, most energy-efficient。
   • When the intake temperature or cooling water temperature increases, it has little effect on the rated flow rate。
   • The gear shaft adopts an ultra short shaft impeller rotor design, which minimizes the torque generated by the shaft and reduces vibration。
7. Centrifugal air compressor bearings: Each set of rotors adopts two sets of tilting multi disc pad self-aligning thrust sliding bearings, with characteristics：

Low noise, wide range of load variation, no life limit, high load capacity, low friction loss, automatic centering, good stability. The large gear bearing adopts a horizontal sliding bearing, which is easy to install and disassemble and maintain

9. Import guide vanes and unloading valves (vent valves) to achieve flow regulation of centrifugal air compressors.
10. Sealing: Both oil seals and gas seals use carbon ring assembly seals, which have good sealing effect and long service life
11. Imported guide vanes: Most use imported guide vanes, which reduce energy consumption by 9% compared to standard throttle valves under reduced load conditions. Imported guide vanes allow air to move in the direction of rotation of the first stage impeller, thereby reducing the energy required to meet performance parameters。
12. The cooler adopts a drawer style design for easy maintenance。

Precautions for use and maintenance:

1. The minimum and maximum intake temperatures of centrifugal compressors are -5 ℃ and 40 ℃, respectively, with slight differences in some special models.
2. The cooling water for the air compressor uses industrial cooling water The inlet water temperature should generally be controlled below 35 ℃.
3. The air compressor must be shut down and the power must be cut off before maintenance, and the pressure must be released before disassembling the pressure pipeline or container.
   Without permission from the pressure vessel department, welding or modification of pressure vessels is strictly prohibited.
4. During the first debugging of the air compressor and after each modification of the electrical connector, the rotation direction of the motor should be checked to prevent damage to the compressor.
5. After repairing the air compressor, tools, scattered parts, or other debris must not be left inside or on top of the machine, motor, and drive equipment. Before the official start, the unit must be turned and checked for flexible and reliable rotation.
6. In principle, high-voltage motors should not be started more than twice within one hour, and the time interval must be at least half an hour.
   When the air compressor is running, try to avoid emergency shutdown with load as much as possible. Only emergency shutdown can be carried out in accordance with the operating procedures
7. The main methods to reduce the oil temperature of centrifugal air compressors are: 1) lowering the cooling water temperature, 2) timely removing scale from the oil cooler, 3) increasing the cooling water volume and water pressure, 4) replacing deteriorated lubricating oil, 5) clearing pipeline faults and checking whether the temperature control valve is malfunctioning.
8. The anti reverse measures for centrifugal air compressors include: 1) closing the gate valve behind the air storage tank and opening the vent valve; 2) Check if the check valve is in place.