1. Basic types and main uses of steam turbine bearings in power plants
In general, steam turbine bearings in power plants are mainly divided into thrust bearings and support bearings. The thrust bearing is mainly used to bear the axial thrust and axial positioning of some rotors. During normal operation, it will bear the reverse axial thrust generated during load shedding and some axial thrust in the direction of the airflow. If static friction occurs, the position of the rotor must be fixed. Support bearings are mainly used to support the mass of the rotor and bear the centrifugal force of the rotor under unbalanced conditions. In addition, the bearing also assumes the radial position of the rotor, so that the center of the rotor and the cylinder are kept consistent to ensure the normal operation of the steam turbine.
2. Common problems of steam turbine bearings in power plants
2.1 Common problems of thrust bearings
When the thrust bearing is damaged, the axial displacement data will increase, the Ugin temperature of the thrust pad will increase, which will cause the oil temperature to increase, and in severe cases, the thrust pad will emit smoke. The reasons are as follows:
(1) In the process of operation, momentary load shedding by the unit or incorrect closing of the medium pressure valve may cause the thrust bearing to burn out.
(2) The steam quality is not high, and the blades are fouled. This situation may also occur due to too little cleaning force when cleaning the steam blades.
(3) During the operation of the steam turbine, an excessive load or water hammer has occurred, and the incorrect method of handling the decrease in steam temperature will cause the thrust bearing to burn out.
(4) When using the oil system, due to inadequate management, the impurities in the oil system could not be cleaned in time, resulting in the damage of the oil film of the thrust pads.
(5) The gap of the baffle steam seal is too large, which increases the axial thrust.
(6) When the generator rotor is grounded incorrectly, the axis current will cause the electric corrosion of the thrust pads.
7 (7) During the transformation of the unit, the actual theoretical thrust value of the axial thrust has a large deviation from the theoretical value, causing the size of the return and inlet pipelines to expand to substandard standards, which has damaged the thrust bearings.
8 (8) Thrust pads, journal lift, and parallelism of thrust discs are not up to standard.
2.2 Air bearing vibration
In general, the vibration of air bearing mainly has the following characteristics:
(1) The steam density at the inlet of the supercritical steam turbine is too large and the steam pressure cooker is high. The energy provided by the disturbance capacity of the steam vortex is directly related to the density of the steam and the excitation point on the track. Therefore, the higher the steam density , The more prone to airflow vibration.
(2) The rotor of the unit is long and large, the rotor deflection is relatively large, the rigidity is reduced, and the rotor's natural vibration frequency is relatively low. When the excitation frequency is relatively close, vibration will occur.
(3) When the load of the unit increases to a certain value, the steam self-oscillation will occur. If it is not processed in time, the vibration will disappear after the load is reduced to a certain number.
(4) The airflow oscillations mostly appear on the rotor with a relatively large capacity, and the airflow vibration is most severe at the high-pressure cylinder airflow adjustment place.
2.3 Bearing vibration
Bearing vibration is a relatively common problem for steam turbines in power plants. If it is not handled in time, it will cause a trip accident of the steam turbine. In general, the main reasons for bearing vibration are as follows:
(1) The steam density at the inlet of the supercritical steam turbine is too high and the steam density is high. The density of the steam and the excitation point on the orbit directly affect the interference ability of the steam vortex. Therefore, the higher the density of the steam, the more severe the airflow vibration.
(2) The installation of the rotor is unqualified, and there is a deviation in the center of the dynamic and static parts. There is a large gap between the choke ring and the moving blade complex ring on the circumference. When the steam passes through these relatively small positions, the circumferential pressure will lose balance. , Increased the probability of steam-induced rotor vibration.
(3) Since the rotor of the unit is relatively long and the capacity is relatively large, the deflection of the rotor is relatively large, the rigidity will not be very good, and the natural frequency of the rotor will also be reduced accordingly. When approaching, vibration will occur.
(4) When the unit load increases to a certain value, steam-induced oscillations will occur. If it is not handled in time, the vibration will gradually disappear when the load decreases to cause this value.
3. Main measures to solve bearing problems
3.1 Management controls
In order to improve the service life of steam turbine bearings, it is necessary to improve management. Regular training of steam turbine operators is required to continuously improve the ability of emergency handling and anticipation of accidents. It is necessary to improve the supervision of tile temperature, pressure, vibration, oil return temperature, etc., and take prevention as the focus of control to further improve the safety of equipment. Finally, it is necessary to improve the control of the maintenance process and ensure the quality of the maintenance.
3.2 Management measures for air-induced vibration
(1) To perform the flow characteristics test of the high-adjustment valve of the steam turbine, optimize the adjustment quality of the valve, and adjust the sequence of the valve according to the specific characteristics of the valve and the bearing vibration.
(2) When the unit raises the load, the operating personnel should monitor the shaft system vibration. After the bearing vibration suddenly rises to the alarm value, immediately reduce the unit load or perform vacuum adjustment.
(3) Use the opportunity of the maintenance unit to upgrade the No. 1 bearing to improve the bearing's interference resistance.
(4) Adjust the rotor center and the cylinder to prevent the displacement of the cylinder center and the rotor during operation.
(5) Improving the direct axial clearance between the diaphragm and the rotor. With the increasing axial clearance between the stationary blades, the nozzles and the moving blades, the exciting force of the air flow vortex can be significantly reduced, and the internal efficiency of the turbine can be reduced.
3.3 Improvement measures in other areas
(1) Control of the fuel tank. First of all, the oil system and fuel tank control should be performed according to the specified requirements. The oil should always be controlled within the specified range, and the fuel tank should be inspected regularly. When the amount of oil is relatively small, timely replenishment and regular filtering of the fuel tank should be performed. Water, drain and filter operations. Secondly, the inlet door of the fuel tank exhaust fan should be adjusted to ensure that there is a certain negative pressure in the fuel tank and normal separation of oil and gas. Finally, do a good job of oil quality analysis and regularly deal with abnormal problems according to specific operating conditions. Avoid further deterioration.
(2) Control of auxiliary oil pump. In terms of auxiliary oil pumps, before the turbine is stopped and started, all auxiliary oil pumps should be tested for rotation, and the oil pump chain test before starting should be done well. In addition, check and test the oil pump regularly to ensure the stability of the auxiliary oil pump operation.
(3) Oil cooler. Before operating the oil cooler, it must be carried out in strict accordance with the relevant monitoring system. When switching or deactivating the oil cooler, control the oil pressure of the lubricating oil and ensure the stability of the oil temperature. No large fluctuations are allowed. . Finally, it is necessary to prevent cooling water from entering the oil side of the oil cooler, and the oil pressure may be slightly higher than the cooling water pressure. In addition, when the unit is stopped and started, it is necessary to prevent large fluctuations in the pressure of the cooling water, and regularly check the water leakage of the oil cooler.
(4) The bearing temperature of the steam turbine should be controlled within a reasonable range. When the temperature suddenly rises, stop the inspection. In addition, when unexpected events such as bearing oil breakage or water impact occur, the machine should be shut down and inspected in time to eliminate the hidden dangers before restarting the operation. In addition, the maintenance process must be improved to avoid inadequate maintenance and bearing damage.
(5) During the operation of the unit, the relevant personnel should do a good job of monitoring the bearing vibration. When the bearing vibration alarms or suddenly rises, immediately reduce the unit load to the load before the rise.
In summary, as the main component of a steam turbine, in order to ensure the normal operation of the turbine, it is necessary to continuously improve the level of maintenance, operation, and monitoring, and actively explore reasonable solutions to ensure the normal operation of the turbine.