What Is a Centrifugal Compressor?

The increase of the air pressure in the centrifugal compressor is achieved by the impeller rotation and the pressure expansion of the diffuser. According to the level of exhaust pressure, it can be divided into three categories: centrifugal fans with wind pressure in the range of 10-15kPa or less; centrifugal blowers with wind pressure in the range of 15 ~ 350kPa; centrifugal compressors with wind pressure in 350kPa the above.

Centrifugal compressor

The increase of the air pressure in the centrifugal compressor is achieved by the impeller rotation and the pressure expansion of the diffuser. according to

Centrifugal compressor

Centrifugal compressor is a blade

The main components of a centrifugal compressor for compressing gas are a high-speed rotating impeller and a diffuser with a gradually increasing flow area. In short, the working principle of a centrifugal compressor is to perform work on the gas through the impeller. In the flow path of the impeller and the diffuser, the use of centrifugal pressure increase and deceleration and expansion effects converts mechanical energy into pressure energy of the gas of.

More generally, when the gas flows through the impeller of the centrifugal compressor, the impeller running at high speed makes the gas under the action of centrifugal force, on the one hand, the pressure is increased, and on the other hand, the speed is also greatly increased, that is, the centrifugal compressor The impeller first converts the mechanical energy of the prime mover into the static pressure energy and kinetic energy of the gas. After that, when the gas flows through the channel of the diffuser, the cross section of the flow channel gradually increases, the velocity of the gas molecules in the front decreases, and the gas molecules in the back continue to flow forward, so that most of the kinetic energy of the gas is converted into static pressure energy That is to further play a role in boosting pressure. Obviously, the impeller's work on the gas is the root cause of the increased pressure of the gas, and the amount of work performed by the impeller on the unit mass of gas in a unit time is closely related to the peripheral speed of the outer edge of the impeller. The greater the work done.

The reason why centrifugal compressors can obtain such a wide range of applications is mainly

1. Centrifugal compressors are not suitable for situations where the gas volume is too small and the pressure ratio is too high.

2. The stable working area of the centrifugal compressor is relatively narrow. Although its gas volume adjustment is more convenient, its economy is poor.

3. Centrifugal compressors are generally less efficient than piston compressors.

China has been able to manufacture centrifugal compressors in the 1950s. Since the early 1970s, it has mainly used petrochemical plants and large-scale fertilizer plants. Rich experience in use, and on the basis of digestion and absorption of imported technology, greatly enhanced its own research, design and manufacturing capabilities.

In centrifugal compressors, in order to reduce air leakage between the compressor rotor and the fixed element, a seal must be provided. Seals can be divided into four types according to their position: wheel cover seals, interstage seals, balance plate seals and (front, rear) shaft seals. The seal is usually a comb-shaped labyrinth seal. In addition, graphite ring seals, fixed sleeve liquid film seals, floating ring seals, and mechanical seals can also be used.

1 Different structure

From: mainly composed of two parts: rotor and stator

Screw: double rotor, body,

Centrifugal compressor bearing temperature rise

The working temperature of centrifugal compressor bearings is generally 45 ~ 50 , and the maximum temperature should not exceed 65 . Generally speaking, 65 is the alarm temperature, and 75 is the chain shutdown temperature. Causes of excessive bearing temperature are:

The gap between the bearing bush and the journal is too small.

The orifice diameter of the bearing lubricating oil inlet is small and the amount of oil is insufficient. The orifice diameter of the orifice should be appropriately increased;

(3) The oil inlet temperature is too high. The cooling water volume of the oil cooler should be adjusted;

Moisture or dirt in the oil are mixed and deteriorated, which affects the lubrication effect. The oil cooler should be checked to eliminate water leakage faults or replace with new oil;

Dirt enters the bearing and wears the bearing pads. Bearings and lubricating oil pipelines should be cleaned, and bushings should be scraped.

The bearing bush is broken, the bearing bush should be recast.

What is the "surge" of centrifugal compressor

Surge is an abnormal vibration that occurs when the turbine compressor's flow rate is reduced to a certain degree. Centrifugal compressors are a form of turbo compressors. Surge can be very harmful to centrifugal compressors.

When a centrifugal compressor surges, typical phenomena are:

The outlet pressure of the compressor initially increased, then decreased sharply, and showed periodic large fluctuations;

The flow of the compressor drops sharply and fluctuates greatly. In severe cases, even air is poured back into the suction pipe;

The current and power meter of the motor that is driving the compressor indicates instability and large fluctuations;

The machine generates strong vibrations and emits abnormal airflow noise.

Factors affecting the displacement of centrifugal compressors

There are many factors that affect the displacement of centrifugal compressors. In addition to the design, manufacture and installation, the factors that can affect the displacement of the compressor during operation are:

1. The air filter is blocked or the resistance is increased, which causes the suction pressure of the compressor to decrease. When the outlet pressure is constant, the compressor pressure ratio is increased. According to the compressor performance curve, when the pressure ratio increases, the displacement decreases;

2. The air separation equipment pipeline is blocked, the resistance is increased or the valve is faulty, which causes the compressor suction pressure to rise. In the case of constant suction pressure, the pressure ratio increases, resulting in a decrease in exhaust volume;

3. The compressor intercooler is blocked or the resistance is increased, which results in a reduction in the exhaust volume. However, there are differences in the blockage at different positions: if the air-side resistance of the cooler increases, only the internal resistance of the machine is increased, which reduces the compressor efficiency and the exhaust volume; Reduce, make the gas not cool well, which will affect the suction of the next stage and reduce the discharge of the compressor;

4, the seal is not good, causing gas leakage. include:

1. Endoleak, that is, channeling gas between levels. The compressed gas is returned and a second compression is performed. It will affect the working conditions at all levels, increase the pressure ratio of the low-pressure stage, and reduce the pressure ratio of the high-pressure stage.

2. Leakage, that is, leakage from the shaft end seal to the outside of the casing. Although the suction volume is unchanged, a part of the compressed gas leaks out, which naturally reduces the exhaust volume;

5. The cooler leaks. If the first stage leaks, because the water-side pressure is higher than the air-side pressure, the cooling water will enter the air-side passage and be further entrained by the airflow into the impeller and the diffuser. After a certain period of time, it will cause scaling and blockage, and reduce the air flow. If the second or third stage cooler leaks, because the air side pressure is higher than the water side, the compressed air will leak into the cooling water and run away, reducing the exhaust volume;

6. The frequency or voltage of the power grid drops, causing the speed of the motor and compressor to decrease, and the exhaust volume to decrease;

7. Increasing the intake temperature of any stage and decreasing the gas density will also reduce the intake volume.

Centrifugal compressor seal leak

Leaks at the wheel cover seals and interstage seals are internal leaks. Severe internal leakage will increase the energy loss of the compressor, reduce the stage efficiency and compressor efficiency, and reduce the displacement. However, the influence mechanism of the two is also different: the leakage of the wheel cover seal is to return the compressed gas to the impeller and then perform the second stage compression, which mainly increases the total power consumption of the stages; The blow-by gas between the stages will increase the low-pressure stage pressure ratio and decrease the high-pressure stage pressure ratio.

Although the severe leakage of the balance disk seal has little effect on the performance of the compressor, it has a great impact on the safe operation of the centrifugal compressor.

Leakage of the shaft seal is external leakage. Leakage is the leakage of gas from the seal to the outside of the cabinet. It goes without saying that severe external leakage will directly result in a reduction in the displacement of the compressor.

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