Shanghai up Pa Ventilation Equipment Co., Ltd
We are mainly engaged in the production of fans, centrifugal fans, fan parts, boiler fans, axial fans and other products, axial fans due to high efficiency and low energy consumption is widely used. In actual operation, many power plants due to axial fan fan is particularly adjustable axial fan reliability is poor, frequent failure, resulting in power plant unplanned downtime or reduced load, affecting the unit power generation. In recent years, several power plants in Guangdong, such as the Pearl River Power Plant 4 × 300 MW, the South China Sea Power Plant 2 × 200 MW, Hengyun C plant 1 × 210 MW have occurred in the adjustable axial fan fan blade accident, Power plant repeated many times, seriously affecting the safety of the unit full. Therefore, it is very necessary and urgent to solve these problems and improve the reliability of axial fan operation in large thermal power plants.
Reliability concept of power station fan
The state of the reliability statistics of the power station is as follows:
The operating fan reliability can be described in the following two important parameters.
Where tSH - the number of hours of operation, refers to the number of hours the fan is running;
TUOH - unplanned outage hours, refers to the fan in the unplanned outage of the number of hours, also known as the number of hours of accident shutdown.
Before the 1990s, China's large-scale power plant boiler fan caused by unplanned downtime and non-planned download more frequently, according to statistics, in 125 MW, 200 MW, 300 MW and 600 MW units, according to the loss of the equivalent power plant downtime , Send, induced draft fan are ranked among the top 10 influencing factors, and the gap between developed countries.
After the 1990s, several major power plant fan factory equipment quality improved rapidly, for the actual situation of China's power plants, the introduction of foreign advanced technology, so that the power station fan is particularly adjustable blade axial fan reliability has been improved. For example, in 1997, a blower factory for its use of the introduction of technology production, in the 15 sets of 300 MW thermal power units used in the 28 rotor adjustable axial flow fan and 24 rotor adjustable axial fan for reliability Analysis, found that its operating rate has reached 99%. Other manufacturers of products, the reliability of a greater increase.
2 factors affecting the reliability of axial fans
2.1 Power station fan accident classification
Class 1 Accident: Fan failure caused by thermal power unit exit operation.
Class 2 Accident: Fan failure only causes the output of the thermal power unit to reduce, has not caused the thermal power unit to exit the operation, or send, the fan only a certain exit.
Class 3 Accident: Fan damage is not serious, do not need to send, induced draft fan to run out for maintenance.
Class 1 and 2 accidents directly affect the reliability of fan operation, and Category 3 is a potential influencing factor.
2.2 axial fan main failure
A) rotor failure. Such as rotor imbalance, rotor vibration, etc., the most serious even impeller accident occurred.
B) The blade is cracked or broken. In the delivery, induced draft fan are likely to occur in recent years in a number of large power plants have occurred in many cases.
C) blade wear. Mainly occurs in the induced draft fan. Due to improper timing of the electrostatic precipitator or electrostatic precipitator failure, causing the fan wear. This is the coal mine power station induced fan most prone to failure.
D) bearing damage.
E) motor failure. Such as over-current, etc., serious damage to the motor.
F) oil spill, adjust the oil pressure instability. Both affect the performance of the fan also threatens the safety of the fan.
2.3 Causes of the failure of the axial fan
2.3.1 Product design and manufacturing aspects
A) structural design is irrational, strength design is not fully considered dynamic load.
B) Pneumatic design is not perfect. Pneumatic characteristics, expansion is unknown.
C) leaf blade safety factor is not enough, poor blade material.
D) Poor blade casting quality.
E) welding, poor assembly quality. Such as leaf bolts fall off the leaves and so on.
F) Poor control of petrol stations.
G) monitoring, protection of accessories failure.
2.3.2 operation, maintenance aspects
A) axial flow fan long-term operation in the stall conditions, the pressure amplitude of airflow increased significantly, the blade resonance damage.
B) does not follow the fan characteristics required to start and the car, fan operating conditions and system characteristics do not match.
C) does not put the electric dust or dust removal efficiency is low, resulting in high dust inlet dust concentration.
D) When the two fans are running side by side, the working points of the two are quite different.
E) Axial fan surge protection failure.
F) No regular maintenance or poor maintenance.
2.3.3 installation aspects
A) shaft imbalance or poor connection, resulting in fan vibration, bearings, couplings easy to damage.
B) The actuator installation error is large, the local indication value and the control room feedback value is inconsistent, resulting in the operation is not accurate.
2.3.4 fan selection and system design aspects
Improper selection of the fan caused the actual operating point of the fan in the unstable air flow area or close to or even into the stall zone, and the fan pipe system characteristics of unreasonable, can cause the fan rotor parts of the fatigue and damage.
3 to improve the reliability of axial fans
Power plant boiler fan type generally centrifugal, static blade adjustable axial flow and adjustable axial fan, should be based on specific use of the situation, the technical economy to determine the type of fan. Comparison of the three kinds of fans in Table 1.
Table 1 Comparison of three kinds of fans
Item Centrifugal Static Shaft Flow Flow Axial Flow Structure Complexity Low Medium High Adaptability to Medium Dust Content Good Poor Poor Operating Efficiency Low Medium High Comparable Equipment Low Low High Reliability High High Low Low
When selecting an axial fan, the design point should fall on the highest efficiency, and on this basis, the angle of the re-opening will be 10 ° ~ 15 °, so that even if the unit is running below the rated operating conditions, Run in the highest efficiency area.
For coal-fired boilers, the axial speed of the adjustable axial fan is high, taking into account the wear problem, should be used in the speed, should not use too high speed.
3.2 parallel design and operation
In the selection of the parameters of the adjustable axial fan, in addition to the relevant provisions of the rules given margin, but also according to the actual situation of the power plant, not only to consider the maximum guarantee conditions, MCR conditions, 100% load conditions, but also To consider the ignition conditions and fan safety and car conditions. After the two conditions are often overlooked to the fan debugging and operation difficult. Therefore, we should pay attention to the design and operation of the parallel adjustable axial fan.
The two fans run in parallel at point C, but each fan runs at point A of the respective characteristic curve. When the first fan to maintain the same blade angle operation, the operating point will move to point B, the second fan to start and merge, close the exit door to start, the blade angle to a minimum. Open the isolation door, the second fan will run at the D point, and gradually open its large angle, and adjust the small fan angle, their operating point will be along the DE and BE line, respectively, to reach the E point when the two fans Parallel, and then adjust the two fans to the required parameters.
It can be seen that when the pressure of the first fan running point is higher than the pressure of the lowest point S of the second fan stall line, the second fan starts to surge, and the first fan is reduced, Point at point S and then start the second fan.
3.3 Other design measures
If you can reduce the fan load, can always be car, such as oil-fired boiler. However, for some coal-fired boilers, such as medium-speed direct-fired pulverizing system of cold primary fan, because of its milling system must have a minimum dry output requirements and powder pressure head, the fan output drop is limited , There are two ways to solve the parallel operation problem. First, select the fan when calculating a single fan according to the required operating conditions when the system resistance, so that the S point is higher than the resistance line, which means that the design point is located at the lower end of the characteristic curve, so that the higher pressure of the lower head pressure. Second, you can add a bypass in the axial fan duct and then turn the door, start the fan, the first turn off the door, open the cycle door. To be the second fan across the stall after opening the door, close the door, the shortcomings of doing so is to increase the initial investment, increasing the possibility of air back to the leak.
In the design of the fan inlet and outlet pipes, it is necessary to avoid the possibility of vortex generation, some of the corner should also be taken to install the deflector measures.
3.4 adjustment and maintenance
A) It is necessary to ensure that the actual angle of the rotor is consistent with the indication of the location and the feedback value of the control room. If the error is large, the operator will be difficult to determine the true angle of the moving leaves, thus affecting the operating conditions. Serious, the fan due to a long time in the stall edge or stall area running and lead to the occurrence of broken blade accident.
B) for coal-fired power plants, can not let the long-term exhaust fan in the excessive dust. The key to solving the problem of axial fan wear is to reduce the dust inlet and ash size of the fan inlet. To this end, should strengthen the cleaning and other work.
C) Strengthen the control of the electrostatic precipitator to ensure that the electrostatic precipitator is running normally and reduce the wear of the dust on the fan blades.
D) to ensure that the fan surge protection normal input.
4 concluding remarks
Axial fans are exceptionally adjustable blades Axial fans are now widely used in thermal power plants in the future, and their operational reliability is critical to power plants. China's power plant fan reliability and advanced national gap is narrowing. To improve the reliability of fan operation, in addition to improve the design of the fan itself, manufacturing quality, the design selection, operation and maintenance methods are also essential.