What is the working principle of magnetic levitation blower in detail?

Magnetic suspension blower is an efficient and energy-saving fluid machine that combines magnetic suspension bearing technology, high-speed permanent magnet synchronous motor technology and three-dimensional impeller pneumatic technology. Its core is to make the rotor completely out of mechanical contact through magnetic suspension force, and directly drive the impeller to rotate with high-speed motor to realize gas suction, compression and discharge. There is no mechanical friction and no need for lubricating oil in the whole process. Compared with traditional Roots and centrifugal blowers, it has the characteristics of high efficiency, low noise, low energy consumption and less maintenance. Its overall operation principle can be disassembled into three core parts: core support principle (magnetic bearing), power drive principle (high-speed permanent magnet motor) and fluid compression principle (centrifugal impeller), and combined with the coordinated regulation of closed-loop control system, the whole machine can run stably. The following is the detailed working mechanism and operation flow of each part.

First, the core support principle: contactless suspension of magnetic bearing (the core technology, different from traditional blower)

The rotor of magnetic suspension blower (impeller+motor rotor integrated structure) is completely supported by magnetic suspension bearing, which replaces the traditional ball bearing and sliding bearing, and eliminates mechanical friction from the root, which is the core reason for its energy saving and low noise. Magnetic bearing is mainly divided into radial magnetic bearing (supporting the radial direction of the rotor to prevent left-right/up-and-down deviation) and axial magnetic bearing (supporting the axial direction of the rotor to prevent back-and-forth movement), which cooperate to realize the full suspension of the rotor with six degrees of freedom, and the working principle is electromagnetic induction+closed-loop feedback control.

1. The foundation of suspension: the balance between electromagnetic attraction and rotor.

The stator side of the magnetic bearing is equipped with an electromagnetic coil, and the corresponding position on the rotor side is equipped with a magnetizer (such as ferromagnetic material). When the electromagnetic coil is energized with direct current, it will generate stable electromagnetic attraction and adsorb the magnetizer on the rotor side. By accurately controlling the current of the coil, the strength of electromagnetic attraction can be adjusted, so that the electromagnetic attraction received by the rotor can be dynamically balanced with its own gravity and centrifugal force in operation, and a constant air gap of 0.1~0.5mm can be maintained between the rotor and the bearing stator, thus realizing complete contactless suspension.

2. Precise control of suspension: closed-loop adjustment of displacement sensor and controller.

The suspension of the rotor is not a static balance, but a dynamic balance that changes with the speed and load in operation. The core depends on the real-time feedback regulation of the high-precision displacement sensor and the magnetic suspension controller;

The displacement sensor (accuracy up to μm) is installed on the stator side of the bearing, which detects the air gap distance between the rotor and the stator in real time and converts the displacement signal into an electrical signal and transmits it to the magnetic suspension controller.

If the rotor slightly deviates (the air gap becomes larger/smaller) due to speed change and airflow disturbance, the controller will immediately adjust the current of the electromagnetic coil according to the displacement signal: if the air gap becomes smaller, it will reduce the current (reduce the electromagnetic attraction and reset the rotor), and if the air gap becomes larger, it will increase the current (enhance the electromagnetic attraction and pull back the rotor);

The response time of the whole adjustment process is in millisecond level, which ensures that the rotor is always stably suspended in the design center position, without any mechanical contact, friction loss and lubricating oil consumption.

3. Emergency protection: the bottom role of the auxiliary bearing.

The magnetic suspension blower is equipped with mechanical auxiliary bearings (also called protective bearings, mostly made of graphite or ceramics). During normal operation, the auxiliary bearings have no contact with the rotor, and only play a role in sudden failures (such as power failure, magnetic suspension controller failure and displacement sensor failure) to catch the falling/deviating rotor, prevent the rotor from colliding with hard parts such as equipment shell and stator, protect the core components from being damaged, and gain time for equipment shutdown.

Second, the principle of power drive: the direct drive of high-speed permanent magnet synchronous motor.

Magnetic suspension blower adopts high-speed permanent magnet synchronous motor, and realizes the integrated design of motor rotor and centrifugal impeller (direct drive, without coupling, gear box and other transmission parts). The motor directly drives the impeller to rotate, eliminating the mechanical loss of traditional blower transmission parts, and the transmission efficiency is close to 100%, which is another core reason for its high efficiency and energy saving. The working principle of high-speed permanent magnet motor combines permanent magnet excitation and frequency conversion speed regulation technology.

1. Basic working principle of permanent magnet synchronous motor.

Stator side of the motor: Three-phase AC winding is installed. When the frequency-converted three-phase AC is applied, a rotating magnetic field will be generated (the rotation speed of the magnetic field is proportional to the frequency of AC);

Rotor side of motor: built-in high-performance permanent magnet (such as NdFeB permanent magnet, with strong magnetic force and high stability), without additional excitation current, the constant magnetic field generated by the permanent magnet will generate electromagnetic torque with the rotating magnetic field of the stator, driving the rotor to rotate synchronously with the rotating magnetic field, that is, "synchronous" operation.

2. Realization of high-speed operation: variable frequency speed regulation+polar logarithm optimization.

The impeller of the magnetic suspension blower needs to rotate at high speed (the conventional working speed is 15,000 ~ 40,000 r/min, which is much higher than that of the traditional motor) to realize efficient gas compression. The high-speed permanent magnet motor can run at high speed through two major designs:

Pole-logarithm optimization of motor: the formula of motor speed is

n=60f/p

(

n

Is the rotational speed,

f

For AC frequency,

p

For motor pole logarithm), pole logarithm

p

The smaller it is, the higher the rotation speed is. The high-speed permanent magnet motor of magnetic levitation blower mostly adopts two-pole design, which lays the foundation for high-speed rotation.

High-frequency variable frequency speed regulation: Equipped with a special high-speed frequency converter, it can convert power frequency alternating current (50Hz) into high-frequency alternating current (up to several hundred Hz). By adjusting the output frequency of the frequency converter, the rotating speed of the rotating magnetic field of the motor can be accurately controlled, and then the rotating speed of the rotor+impeller can be adjusted, so as to realize stepless adjustment of the flow and pressure of the blower (no throttle valve, baffle and other adjusting components are needed to reduce throttling loss).

3. Advantages of direct drive transmission

The rotor and impeller of the motor are integrated, and there are no intermediate transmission parts such as coupling and gear box, which avoids mechanical wear, vibration noise and transmission loss of traditional transmission (the transmission loss of traditional gear box can reach 5%~10%), simplifies the equipment structure and reduces the maintenance cost.

Principle of fluid compression: gas compression of three-dimensional flow centrifugal impeller

The gas compression link of magnetic suspension blower adopts centrifugal compression, and the core component is three-dimensional flow centrifugal impeller (impeller blades adopt three-dimensional flow pneumatic design, which is suitable for high-speed rotation and has higher pneumatic efficiency). By relying on the high-speed rotation of impeller, centrifugal force is generated to realize gas suction, acceleration, pressurization and discharge. The whole compression process is single-stage centrifugal compression (simple structure, suitable for high-speed direct drive), and the compression medium is mostly air (also suitable for inert gas). The working process is divided into

1. Suction stage: gas enters the impeller.

The air inlet of the blower is connected with an air filter (to filter dust and prevent abrasion of the impeller). When the impeller rotates at high speed, the center of the impeller (at the inlet) forms a negative pressure zone due to the rotation of the blades, and the outside atmosphere is sucked into the blade channel of the impeller through the air inlet under the action of atmospheric pressure.

2. Acceleration stage: gas gains kinetic energy.

The gas entering the blade channel is rapidly driven to rotate under the centrifugal force of the high-speed rotation of the impeller, and moves along the blade channel from the center of the impeller to the edge (outlet) of the impeller. In this process, the linear velocity of the gas is greatly improved, and a lot of kinetic energy (velocity energy) is obtained.

3. pressurization stage: kinetic energy is converted into pressure energy.

The gas moving at high speed enters the volute (diffuser) of the blower after being thrown from the edge of the impeller. The channel of the volute is designed as a gradually expanding type (the cross-sectional area gradually increases from the inlet to the outlet). According to the Bernoulli principle of fluid mechanics, the flow speed of the gas in the gradually expanding channel gradually decreases, kinetic energy is converted into pressure energy, and the pressure of the gas is greatly increased, thus achieving the core goal of compression.

4. Exhaust stage: high-pressure gas output

The pressurized high-pressure gas is discharged from the air outlet of the volute and enters the pipeline system to provide high-pressure gas sources for subsequent processes (such as sewage treatment aeration, pneumatic conveying, blast furnace blowing, photovoltaic hydrogen production pressurization, etc.); If the process needs stable pressure/flow, the impeller speed can be adjusted by frequency converter to realize stepless regulation and meet the requirements of different working conditions.

Supplement: Characteristics of centrifugal compression

Centrifugal compression of magnetic suspension blower is isothermal compression (the equipment is equipped with a cooling system to take away the heat generated in the compression process to prevent the gas temperature from being too high), with high compression efficiency, and single-stage compression can meet the medium and low pressure working conditions (outlet pressure is 0.04~0.15MPa (gauge pressure) and flow rate is 1 ~ 1000 m/min), which is suitable for the blowing demand of most industrial sites.

Four, the whole machine collaborative operation process (from start-up to stable work)

The core components of the magnetic levitation blower (magnetic levitation bearing, high-speed permanent magnet motor and three-dimensional flow impeller) are coordinated and controlled by the magnetic levitation controller, frequency converter and main controller, and the whole process automation from start-up, suspension, high-speed operation to shutdown is realized without manual intervention. The whole machine operation process is as follows:

1. Start-up stage: suspend first, then rotate (core principle, prevent mechanical friction)

After the equipment is electrified, the magnetic suspension controller is started first, the displacement sensor starts to detect the position of the rotor, and the electromagnetic coil is energized with initial current to generate electromagnetic attraction to suck the rotor from the auxiliary bearing, thus realizing stable suspension with six degrees of freedom until the rotor and stator maintain a constant air gap;

After detecting that the rotor is suspended stably, the magnetic suspension controller sends a start signal to the frequency converter, and the frequency converter starts to work, and low-frequency alternating current is applied to the stator winding of the high-speed permanent magnet motor, and the motor drives the rotor+impeller to rotate at a low speed (for example, below 5000r/min), and at this time, the rotor remains suspended without any contact.

2. Speed-up stage: stepless speed regulation to working speed.

According to the set parameters of the main controller (pressure/flow required by the process), the frequency converter gradually increases the output frequency, the motor speed increases synchronously, the impeller speed increases gradually, and the gas compression and pressure increase synchronously;

During the whole acceleration process, the magnetic suspension controller adjusts the current of the electromagnetic coil in real time to ensure the dynamic suspension stability of the rotor under high-speed rotation, and the displacement sensor continuously feeds back the rotor position to ensure the constant air gap.

3. Stable working stage: closed-loop regulation, adapting to changes in working conditions.

After the impeller reaches the rated working speed, the blower stably outputs high-pressure gas, and the main controller detects the pressure and flow of the air outlet in real time through the pressure sensor and the flow sensor;

If the process conditions change (for example, the pipeline resistance becomes larger, and the blast volume needs to be increased/decreased), the main controller will send an adjustment signal to the frequency converter, and the frequency converter will adjust the output frequency in real time, change the motor speed, and then adjust the gas pressure and flow rate to realize stepless regulation; At the same time, the magnetic bearing adjusts the electromagnetic attraction in real time with the change of speed to keep the rotor suspended stably.

During the working process, the cooling system (air cooling/water cooling) of the equipment works continuously, taking away the heat generated by the motor and the compression cavity, and ensuring the operation of all parts of the equipment within the rated temperature range.

4. Stop stage: slow down first, and then drop the shaft (contrary to start-up, to prevent mechanical impact).

After receiving the stop signal, the inverter gradually reduces the output frequency, the motor speed slowly decreases, and the compression of the impeller gradually decreases until the motor rotates at a low speed;

After the rotational speed drops to the set value (for example, below 3000r/min), the magnetic suspension controller gradually reduces the current of the electromagnetic coil, and the electromagnetic attraction slowly decreases. The rotor falls onto the auxiliary bearing smoothly under its own gravity, and then the magnetic suspension controller and the frequency converter are powered off, and the equipment stops, so there is no severe impact in the whole shaft falling process, which protects the auxiliary bearing and the rotor.

V. Operating characteristics corresponding to core technological advantages

The working principle of magnetic suspension blower determines that compared with traditional Roots blower and gearbox centrifugal blower, it has remarkable operating characteristics and is also the core advantage of its industrial application:

High efficiency and energy saving: no mechanical friction (magnetic bearing), no transmission loss (direct drive) and no throttling loss (stepless speed regulation), the comprehensive efficiency is 30%~50% higher than that of the traditional Roots blower, and the energy consumption is greatly reduced;

Low noise operation: no mechanical friction, no gear box meshing noise, the operation noise is only 70~85dB (far lower than the traditional roots blower's 95~110dB), and there is no need to make a separate soundproof room;

Maintenance-free: no lubricating oil (no contact of bearings), no vulnerable transmission parts, only need to replace the air filter regularly, and the maintenance cost is only 1/10 of that of traditional fans;

Convenient start/stop: fully automatic start/stop, no need for preheating and lubrication, short start/stop time, and frequent start/stop;

Stable operation: dynamic closed-loop control of magnetic bearing, high rotor operation accuracy, small vibration (vibration value ≤0.05mm/s) and long service life of equipment (design life is 15~20 years).

Vi. Applicable working conditions and industries

With the above advantages, the magnetic suspension blower is widely used in low-pressure and high-flow blast/pressurization conditions. Its core industries include: aeration in sewage treatment plants, desulfurization and denitrification in power industry, pneumatic conveying in cement industry, blast furnace blowing in steel industry, photovoltaic hydrogen production/fuel cell pressurization, gas conveying in chemical industry, municipal engineering sewage aeration, etc. It is the mainstream upgrade and replacement product of traditional blowers.