The large vibration of the induced draft bearing will cause damage to the installation foundation and damage to the blower. In Wuyang Thermal Power Plant, there was an accident of large induced draft fan vibration which caused damage to the fan and scrapped, resulting in boiler shutdown. The plant uses an advanced VT dynamic balancer to quickly and effectively perform high-speed dynamic balancing of the induced draft fan, which has achieved success, and has been continuously improved and innovated in practical applications.
The design plan of the online vibration monitoring and alarm system of the induced draft fan is to install CD-21-S (horizontal) and CD-21-C (vertical) vibration probes on the bearing housing of the induced draft fan, and the vibration signal output by the probe is connected to the LC-810 In the on-site dynamic balance instrument, the operator can continuously monitor the vibration status of the induced draft fan online, and then connect the alarm output contact signal of the monitor to the XXS-2A-32G microcomputer flash alarm and the electric bell circuit, and realize the The bell sounds an alarm function, and the system is installed and debugged and put into use. After the application of the system, the workload of the operating personnel is reduced, and the monitoring quality of the induced draft fan is improved. When the vibration of the induced draft fan exceeds the limit, the alarm function can remind the operating personnel to make a correct judgment and deal with the fault in a timely manner to ensure the normal and safe operation of the induced draft fan and the boiler.
When the vibration of the induced draft fan is out of operation, use the VT dynamic balancer to perform a dynamic balance test on the induced draft fan to find out its unbalanced point. After the calculation, the counterweight can be used to reduce the vibration value of the induced draft fan to the normal range. The problem of excessive vibration of the induced draft fan is solved, the hidden safety hazard is eliminated, and the operating cycle of the induced draft fan is extended. After this test was successful, it was extended to the boiler primary and secondary fans, and also achieved success.
1 Application of induced draft fan vibration online continuous monitoring and alarm system Use the LC-810 field dynamic balancer to monitor the radial vibration of the bearing in both horizontal (X direction) and vertical (Y direction) directions. Experience shows that the vibration amplitude of the bearing housing of the induced draft fan is the largest, and the CD-21 speed sensor is installed in the horizontal direction of the bearing housing on the fan impeller side and the vertical direction of the bearing housing on the motor side. , The output voltage enters the 85100XY vibration monitor, and the meter head is driven after being amplified to display the vibration speed value for the operator to monitor.
The LC-810 field dynamic balancer has alarm (alarm 1) and danger (alarm 2) output functions. When the induced fan vibration amplitude exceeds the set alarm or danger value, it is driven by an alarm comparator (or danger comparator) The alarm (or danger) relay works, connect a group of normally open contacts of the alarm relay to the XXS-2A-32G microcomputer flashing alarm light alarm circuit, and a group of normally open contacts of the danger relay to the electric bell alarm circuit. An audible and visual alarm of the induced fan vibration overrun is realized, reminding the operating personnel to make correct judgment and operation quickly when the induced fan vibration exceeds the limit.
After this system is put into operation, it has effectively realized the online monitoring and alarm of the induced fan bearing vibration, reduced the inspection workload of the workers, and improved the safety factor of the induced fan operation.
2 Use VT dynamic balancer for high-speed dynamic balancing on site to deal with the problem of excessive vibration of induced draft fan. Mass imbalance is the most common cause of high-speed rotating machinery bearing vibration. The coincidence of the inertial spindle of each section of the rotor and the rotation axis is the theoretical ideal balance State, but it is impossible in practice. In order to reduce the vibration caused by unbalanced mass, high-speed dynamic balancing on site is an effective conventional method.
The on-site high-speed dynamic balancing method is very mature, but in the actual operation process, a specific mechanical dynamic balancing weighting process and results are greatly affected by human factors. If the staff cannot properly grasp the methods and techniques for balancing, the residual vibration may still be too large after aggravating many times.
The dynamic balancing process usually includes the following steps
2.1 Acquisition and analysis of basic vibration data Basic vibration data refers to the test record of mechanical vibration before balance, including the amplitude / phase of the shaft vibration. The method of measuring vibration includes manual measurement records, computer automatic recording or the function of the vibration measuring instrument itself. The VT dynamic balancer combines vibration measurement and data analysis. It can measure the maximum amplitude and phase of the vibration of the unit, which determines the degree of unbalance and the position of the unbalance of the rotor. When this vibration occurs at the working speed, and the amplitude and phase of the vibration are basically stable, you can decide to do high-speed dynamic balancing.
The VT dynamic balancer has a photoelectric sensor, which uses low-power, high-brightness light-emitting diodes as the light source. It emits visible red light after being turned on. With the reflective mark, it can receive 60 ~ 3000r / min speed within a distance of 1 ~ 40mm. The signal is used to measure the speed of the fan. The VT dynamic balancer also has a magnetoelectric speed sensor, which is used to measure the absolute vibration of the device. When it is used, it is fixed on the point to be measured by a magnetic chuck. It can measure horizontal and vertical vibrations. The measured value is the bidirectional vibration value (peak-peak value) ).
Pay attention to the following points when using VT dynamic balance instrument to measure vibration.
(1) Measurement position: The measurement position should be selected at the point that best reflects the vibration of the rotor, generally on the bearing surface or on the housing of the machine closest to the bearing position.
(2) Measurement direction: The measurement should be carried out in both horizontal and vertical directions in the bearing, but at least in the direction capable of the maximum vibration amplitude. Under normal circumstances, it is often measured in the horizontal direction, and when the measurement result is in doubt, then measured in two directions.
(3) Reference mark: In order to provide the angle and frequency reference, the reference standard should be marked on the rotor where the angle is easy to see and the angle is easy to measure.
2.2 Obtaining the coefficient of influence by trial weighting When testing weighting, two values ​​must be determined, namely the angle and quality of the trial weighting. Experience has shown that the angle plays a major role in whether the vibration increases after weighting, and it must be ensured that the orientation of the test weighting is generally correct. Try to accentuate not close to the unbalanced position, and try to add it to the opposite position of the same plane (ie, the difference is 180 ≠). The mass of the test weight should be suitable. If it is too large, the vibration may increase too much, which may cause danger to the equipment. The following formula can be used as a reference:
Mt = Mr / [Rt * (n / 100)]
In the formula: Mt ——— weight of test weight, g; Mr ——— mass of rotor, g; Rt—weight of test weight, cm; n—speed, r / min
The most important part that affects the dynamic balance of the induced draft fan is the unbalanced configuration of the induced draft fan impeller, so the test weight should be added to the impeller.
Practice shows that adding test weight is the most critical step of induced draft fan dynamic balance. If the test weight is added properly, the induced fan vibration will have a significant change, and the obtained impact coefficient is accurate. Success rate.
2.3 After the formal weighting is carried out to obtain the coefficient of influence, the mass and phase of the first weighting can be calculated or calculated by using a VT dynamic balancer, and then the weighting is increased at the corresponding part. If the vibration result is not satisfactory after the weighting, the second time can be carried out Increase it until you are satisfied. If the influence coefficient is accurate, then this aggravating process can be completed in only 2 or 3 times, or even once.
The above-mentioned weighting process is dynamic balancing at high speed (working speed) of the induced draft fan. The signal analysis function of the VT dynamic balance instrument can record the vibration condition of the induced draft fan at low speed. If the rotor (shaft) has large vibration at low frequency. It may be caused by other reasons (such as loose installation foundation, loose mounting screws, or too large clearance between bearings). At this time, you can take corresponding measures to eliminate it, and then do high-speed dynamic balancing.
2.4 Application Example The # 1 induced draft fan of Wuyang Thermal Power Plant conducted a dynamic balance test on September 18, 2004. The photoelectric sensor was installed at a position 1 ~ 40mm away from the induced draft bearing, and then the photoelectric sensor, magnetoelectric speed sensor and VT were installed. Connect the dynamic balance instrument, connect the power supply of the VT dynamic balance instrument, turn on the induced draft fan, and use the magnetoelectric speed sensor to measure the maximum value and phase of the horizontal vibration of the induced draft fan on the induced draft bearing housing (taking the reflective mark as the phase) Zero position). According to experience, add a trial weight to the induced draft fan, turn on the induced draft fan for the second time, the maximum value and phase of the vibration can be measured, calculate the weight and phase point to be counterweighted according to the impact coefficient, and then weld on the corresponding position of the induced fan impeller The counterweight of the corresponding weight is then turned on to measure the vibration value and phase of the induced draft fan. Generally, the induced draft fan vibration value can be reduced to the normal value (below 50μm). If the vibration value is still too large, the counterweight can be continued until it is normal.
3 Conclusions Since the online monitoring of induced draft fan and on-site high-speed dynamic balancing technology have been applied in Wuyang Thermal Power Plant, it has been operating well. It has been monitored that the induced draft fan has exceeded the limit of operation 10 times, and the on-site high-speed dynamic balancing of the induced vibration fan over the limit has been achieved in time The induced fan accident happened again. Through this transformation, a good way was found for the online monitoring of induced draft fan vibration and the problem of handling vibration overrun.
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