The safety and reliability of nuclear power equipment guarantee the safety of nuclear power plant, so the reliability of nuclear power equipment is particularly important, and its centrifugal bearing system is an important part to ensure its safe operation. This paper mainly introduces the structure of the bearing system of the nuclear safety grade centrifugal pump, which is designed and researched to ensure the safety performance of nuclear power plant.
The production nature of the nuclear power plant determines its safety and reliability to meet high requirements. The main working equipment of nuclear power plants is nuclear power equipment, especially ad hoc safety equipment, their reliability is to maintain the safety of nuclear power plants. It is an important research topic to ensure the safe and reliable operation of nuclear power equipment and other equipment in nuclear power plants. Nuclear safety grade centrifugal pump is the special safety equipment in nuclear power plant, its reliable operation of bearing system is the guarantee of the reliability of the pump unit in nuclear power plant. Therefore, the structural design of the bearing system of the nuclear safety grade centrifugal pump is particularly important.
2 Nuclear safety grade centrifugal pump bearing system structure design
Nuclear safety-grade centrifugal pump bearing system structure design to the pump unit does not have a pre-lubricating start characteristics, so the bearing system is located at both ends of the radial bearing to select cylindrical roller bearings, to promote the thrust bearing to select the thrust plate or thrust tile structure, the lubrication between the bearings to select dilute oil, so that can be forced lubrication.
Through the shaft head oil pump, oil cooler, pressure regulator valve, filter, supply line, return tubing and temperature measurement components, such as the lubricating oil system of the bearing system, wherein the shaft oil pump can be linked with the pump shaft is through two a small gear to achieve. After the unit starts, the shaft topped pump will be sucked out of the bottom of the oil tank, the oil is sucked out of the lubricant through the regulator valve, oil cooler and filter later through the throttle respectively transported to the two ends of the rolling bearings and reasoning, and then after the return to the oil tank flow back, thus forming a circuit, The structure of the bearing system of the specific nuclear safety grade centrifugal pump can be referred to in Figure 1.
Bearing system of this structure to meet the requirements of nuclear safety-stage centrifugal pump bearing system, but taking into account the safety of nuclear power equipment and particularity of the time, if found in the lubricating oil system does not respond in a timely manner or oil system when a sudden occurrence of a component failure will lead to a decrease in reliability of the bearing system. That is, if the system response lag lubricating oil, lubricating oil system began its work after the entire unit has been launched for some time, there will be thrust pad scratch this state, since the thrust bearing has a certain dependence on oil system at work . Therefore, nuclear safety-stage centrifugal pump bearing system structure there is a certain security risk.
Reliability 3-stage centrifugal pump bearings nuclear safety system
in order to solve security risks of the bearing structure, improving the reliability of lubricating system and bearing system, the bearing system and lubricating system design and more in-depth research on nuclear safety structure-stage centrifugal pumps bearing system has been improved. Generally more common to use two methods is to increase the margin design and redundant design.
Margin increased 3.1 Design
gear transmission efficiency, resistance to oil cooler and oil pipelines and roads, the pressure regulating valve leakage, among other factors will affect the lubricating oil system, boot the system from the lubricating oil reaches the set pressure to take some time, during this time, the radial and thrust bearings at both ends can only rely on a small amount of oil remaining in the bearing cavity to work, so in order to avoid the wear of the thrust bearing to increase the reserve in the bearing cavity the amount of lubricating oil for the operation of the bearing system is advantageous.
Radial bearing system located at both ends of the cavity can be increased by increasing the amount of oil on the outside of the bearing small auxiliary tank.
3.2 redundancy method
for in terms of the "quality" of the bearing system reliability, an increase in the structural design of the bearing system of the auxiliary thrust bearing member, by the rear bearing support bidirectional thrust bearing, the bearing sleeve bearing jacket, anti-rotation pin and a spring plate and other parts.
Its inner bearing sleeve and the bearing outer bearing taking the form of an interference fit over the bearing bore and the outer bearing support bearing is a sliding fit, the bearing system after startup, rapidly produce an axial force component of the rotor shaft such that axial movement above , thrust plate and the thrust bearing in contact at this point to follow the action of the rotor while under tension, by controlling the axial clearance of the auxiliary bearing bearing outer cross section of the spring plate, the spring rigidity of the support plate after from its axial thrust, so that further increase the axial thrust, the spring plate is deformed, so that the thrust plate to move, and then close the thrust shoe.
In this process, the lubricating oil has been filled in the entire bearing cavity, the clearance between the thrust plate and thrust shoe after reaching a certain level, will form a lubricating oil film dynamic pressure, but this time the auxiliary bearing and the thrust plate work together to undertake since the remaining axial force.
3.3 bearing reliability in achieving the various stages of
(1) at the pump start-up phase centrifugal pump, centrifugal oil pressure has not been formally established, in which case you can use QJ secondary thrust bearing to bear a portion of the pump rotor residual axial force, while being able to achieve disengagement thrust plate.
(2) When the start-up time to achieve normal operation of the pump, QJ bear secondary thrust bearing and the thrust plate with an axial force, to ensure the normal operation of the pump bearing and normal use.
(3) after long-term use, pump the thrust pad will be varying degrees of wear and tear, in the case of serious wear and tear, thrust plate does not work, can not play the role of bear axial force, in which case the secondary thrust required QJ bearing bear all of the axial force. Since this design QJ secondary thrust bearing has a higher bearing capacity, generally it has more than 2-fold surplus affordability.
By analyzing the structural design of centrifugal pump bearing system used at this stage of nuclear power plants, we found that there are some problems in the structural design, likely to cause safety problems. Can effectively improve the structural design of the study to take concrete improvement measures to improve the reliability of the bearing system. After test trials found that by the improved design of the structure, the thrust bearing serious wear and tear will not be in use, and reliability of the entire bearing system can be effectively improved. In the latter part of the work bearing system designers to strengthen the study on the reliability of the bearing system, to further improve the reliability of the whole system to improve the operation, so as to effectively ensure the safe operation of nuclear power system, avoid system failures and accidents fundamentally.
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