Causes of boiler fan damage and repair methods

Fans are widely used in many fields, especially during the operation of boilers. A fan is a type of mechanical machine that converts the mechanical energy of a motor into energy that can convey gas and provide energy to the gas. During the boiler's combustion process, the fan plays a balancing and ventilation role, continuously providing the necessary air inside the boiler and at the same time pushing smoke out of the boiler to ensure that the boiler's combustion takes place. Normal. In addition, it is one of the indispensable mechanical devices in all fields, with many types such as blowers, secondary fans, exhaust fans, material blowers, ash return fans, etc. However, during long-term continuous operation, fans may encounter harsh operating conditions, causing high failure rates.

boiler blower
Boiler fans must always operate in harsh conditions

For years, problems such as high error rates and low fan reliability have plagued the operations and maintenance staff of manufacturing plants. Common problems encountered during fan maintenance and operation include: fan wheel damage; fan vibration; failure of ball bearings; oil leakage of bearing housing, etc. Analyzing and diagnosing the cause of fan problems, applying scientific solutions to ensure efficient operation of the fan, meeting production requirements, is important.

I. Operating principle and main structure of the fan

The operating principle of the fan is to rely on the input structural energy to increase air pressure and transmit air, it is a type of machine. Dynamic fluid mechanics. The main performance parameters of the fan include flow, pressure, capacity and rotation speed, along with noise and vibration levels are also important indicators to evaluate fan performance. The fan is mainly composed of fan shell, impeller, suction door, sound absorber, inlet adjustment door, rotating group, coupling, ball bearing box, etc., which are rotated by an electric motor to rotate the fan blade. The operating principle of a centrifugal fan is similar to a turbine compressor, the only difference is that due to the low gas flow rate, the pressure variation is not large, usually there is no need to consider the variation in the compressibility of the gas, that is, consider the gas as an incompressible liquid. Centrifugal fans can be made into two types of clockwise and counterclockwise rotation. Viewed from the side of the electric motor, when the impeller rotates clockwise, it is called a clockwise centrifugal fan, when it rotates counterclockwise, it is called a rotary centrifugal fan. counterclockwise.

The fan parts
Fan parts in production

II. Analysis of common problems of boiler fans

According to the development of economic and social technology, with the rapid industrialization of society, many types of products High-tech products have convenient the production process and our lives. Boiler exhaust fans are one of those high-tech products. However, during use, problems cannot be avoided. Boiler fan problems can be divided into mechanical problems and performance problems. Mechanical failures of boiler fans include blade wear, mechanical vibration, lubrication system failure, bearing failure, etc. These incidents can have mild to serious effects on the stable operation of the boiler, even forcing the boiler to temporarily stop, causing great economic loss. As a main support device of the boiler, good or poor operation of the fan directly affects the operation of the boiler. Detailed analysis of boiler fan failure is useful to ensure safe and reliable operation of the boiler.

1. Analysis of the causes and remedies for blade abrasion problems

The causes of boiler fan blade abrasion problems are of many types, mainly including the following causes: The following reasons:

  • Not designing the working state to suit the operation of the boiler fan, the curve coming from the leading edge of the blade is not the same as the airflow direction of the wheel. fan, which creates an angle of attack for the air stream; Dust particles in the fan airflow cause wear at the blade inlet.
  • Install a cyclone dust removal device at the fan inlet, which effectively removes dust good, but if the dust removal device is not cleaned in time, the fan is easily contaminated by dust, the airflow generated by the boiler fan will push dust particles close to the blades, creating a function similar to a brush knife , improving the degree of blade wear; Besides, the weld seams or structural materials of the impeller blades do not reach a certain hardness. If the dust particles entering have a higher hardness, it will increase the speed of working wear.

For abrasion problems airfoil, the corrective measures are as follows:

  • First, strengthen the dust cleaning in the dust removal device, reduce the amount of dust in the exhaust gas from the boiler and collect dust in the device filtered at least once every 2 hours, which can reduce the degree of blade blade wear caused by dust;
  • Second, reduce the airflow resistance, keep the cutting edge of the blade The blades and airflow direction in the fan are consistent.
  • Third, improve the blades of the boiler fan, improve the life of the blades, after improvement, thick curved blades can be used Moreover, this can significantly increase the engine load, but can avoid equipment wear caused by dust, prolonging the life of the blade.
  • Fourth, it is possible to use materials with higher hardness, increasing the abrasion resistance of boiler fan blades.

2. High temperature of fan bearing

exhaust fan
Boiler exhaust fan after many troubleshooting times

During operation, the fan bearing may become hot due to abnormal temperature. According to actual analysis, the causes of high temperature of the fan bearing are due to bearing abnormalities, insufficient cooling time, poor lubrication performance, etc. During normal operation, the fan needs to use cooling water to cool the bearings. If not careful, it can easily cause the cooling water pipe to enter the heat exchanger, thereby causing temperature rise. temperature of the cooling water pipe, which affects the cooling effect of the bearing. In addition, after a long period of operation, the bearing may appear peeling, and the increased clearance will also cause an increase in the temperature of the bearing. To reduce friction between bearings, it is usually necessary to apply a amount of lubricating oil on the fan bearings. During operation, the bearings will consume a large amount of lubricating oil, once the bearings operate for a long time. Long periods of time will cause increased friction. In addition, during normal operation of the fan, some water will enter the fan device, the lubricating oil layer on the surface of the bearing will be destroyed by water, and the amount of lubricating oil will continuously decrease. Continuously with the destruction of the lubricating oil layer causes the temperature of the bearing to increase, and more seriously, it can be burned out.

Before solving the temperature problem of the fan bearing, Maintenance personnel can spin the bearing to hear the bearing sound and observe vibration, thereby identifying the underlying cause of the bearing's possible failure, which can speed up the problem's elimination. During normal operation of the fan, maintenance personnel can rely on a series of problems that appear on the bearings to take early preventive measures, such as checking the lubricating oil applied on the bearings, Always ensure that the lubricating oil is not damaged or contaminated. Only this way can ensure that the bearing can operate normally. Second, check the quality of the bearing to avoid aging and grinding. wear affects the operation of the bearings. Finally, attention must be paid to checking the cooling fan group to ensure that the operating condition of the fan group reaches standard requirements.

3. Loud fan noise

A problem with the dynamic balance of the fan or if the fan blades are damaged during operation can cause vibration. The fan is a centrifugal fan. mind, when operating it will make a very loud sound. Noise from boiler fans seriously affects the rest of surrounding residents, causing consequences for their health, so it is necessary to apply overall noise reduction measures.

Auxiliary measures to reduce dust can be strengthened to solve the problem of dust exceeding standards. The exhaust pipe of the fan through a long piece of metal pipe connected to the moisture filter, after removing large dust particles from the moisture filter, it is introduced into the noise reduction space, incorporating the combination technology of the pipe expansion and expansion chamber can reduce the air flow speed, causing small dust particles to accompany the water vapor in the smoke and low temperature, this dust particle will naturally fall, and also has the effect of cutting sound. When the low-speed air flow enters the noise reduction chamber after one expansion, the combination of the reduction tube and the sound absorption chamber with noise reduction materials can reduce the sound. The boiler fan can be used at a lower rotation speed, increase the size of the exhaust fan wheel, reduce the fan rotation speed, the fan pressure remains the same, the fan operates normally, achieving the goal of noise reduction , also use rectangular exit for fan exhaust cooling, increase the distance between boiler fan and resident building, reduce the influence of boiler fan on residents.

4. Oil leakage in bearing housing

The cause of oil leakage in the bearing housing can have several aspects: unreasonable seal design; the size of the seal structure is unreasonable; The gap running between the bottom edge of the seal and the rotating shaft is too large, which is also a cause of leakage; the use of ph materials improper chili; The differential pressure causes the seal to become hollow.

exhaust fan

Applicable measures: Design a reasonable seal structure, set up an anti-oil device and drainage hole, the seal should be set up on the shaft and the ring rotates with the shaft, not only can prevent oil from leaking out, but also can throw the lubricating oil near the head to the outside, so it can be guaranteed that the seal does not leak oil, at the same time The seal should be installed close to the shaft collar, but should not create friction with the outside of the pipe body, using a clearance between 0.05-0.10mm. At the same time, in the seal, open an outlet hole below the end of the seal, exporting the oil, exporting the oil from the seal, reducing the possibility of oil leakage.

Cause: This phenomenon mainly comes from the fan suddenly increasing during operation. This is because when the air enters the impeller, it will create a fixed angle with the working face of the impeller. Based on the principle of fluid mechanics, the gas in the impeller will create a moving vortex on the air surface. working of the fan blade, so the dust in the air due to the impact of the vortex will gradually settle on the non-working side of the fan blade. Airplane fan blades are susceptible to dust. When the amount of dust reaches a fixed volume, due to the centrifugal force of the impeller, part of the dust is blown out of the impeller, creating an uneven balance. of the fan wheel weight, thereby increasing fan vibration.

Remedy: In this case, usually just cleaning the dust on the fan blade can minimize fan vibration. . The usual handling method is to temporarily stop the machine and then open the fan inlet door to clean the dust on the fan wheel.

III. Conclusion

Under the continuous promotion of mechanical engineering level in Vietnam, fan performance and reliability are increasingly improved, but during operation continuously, many problems still exist. In addition to problems such as vibration, high temperature, oil leakage and corrosion wear, there are many other problems that occur, such as rotational fluctuations and loss of speed that cause blower failure. . Therefore, to ensure that the fan can operate safely and stably, maintenance personnel need to combine various trouble causes to repair fan problems, minimize the possibility of problems and serious incident.