Reasons for the lock of the pump core of the boiler water pump:
The boiler water pump needs to be turned on at a low speed before starting to warm up. Many domestic power plants have experienced multiple times when the small machine is warmed up at low speed or when the pump is stopped. The boiler water pump pump core locks up. Once it occurs, the pump must be removed for maintenance or returned. Plant processing, at least a week to more than one month to resume operation, especially in the initial stage of the newly commissioned unit, the performance is most obvious and outstanding, which has a serious impact on the commissioning of the power plant unit, directly jeopardizing the safe and stable operation of the unit, and processing and solving is also wasteful. A lot of financial and material resources. After searching for the reasons in many ways, it can be concluded that there are no more than the following situations:
(1) The cleanliness of the condensed water and deaeration water supply system is poor, and hard particles enter the pump at the beginning of operation, causing the pump core to lock up. In general, the condenser and condensate system of the new unit of the power plant are flushed and alkali washed before being put into operation. However, due to the large and complex equipment and piping system, there must be some dead angles and residues, so in the early stage of operation During hot operation, hard particles such as welding slag and rust often enter the pump body, which causes the static and dynamic parts of the pump body to grind and causes the pump core to jam. Especially when the pump unit is hot and the pump is stopped and turned into low-speed cranking, it is easy to cause the pump core to lock up. Once this happens, it is impossible to rotate easily. It can only be disassembled for maintenance or returned to the factory for treatment, but they are all found after disintegration. There are hard particles stuck between the static and dynamic gaps, which is the main reason why the pump core locks up.
(2) The small dynamic and static clearance of the upper water pump core package is also a non-negligible reason that causes the pump core to lock up. As mentioned earlier, hard particles and impurities are the main reason for the lock of the pump core. However, the size of the dynamic and static gap of the core package also plays a big role. It is worth studying and discussing how much the gap is right. Since the dynamic and static gap of the pump core package is relatively small (usually about 0.4mm), and the pump impeller is made of stainless steel, the hard particles enter the pump core and cause the dynamic and static parts to wear first, and finally evolve into the direct contact and friction of the dynamic and static parts of the pump core package. , Especially when turning at low speed, friction produces adhesion or particle extrusion causes the pump core to lock.
(3) The heating pump is poor when starting, causing the moving and static parts of the pump body to contact and lock up. Under normal circumstances, the feed water pump set must be warmed when the feed water temperature is greater than 110 °, but because the two ends of the pump use sealing water of about 36 °C, and the heat pump water temperature is about 160 °C, plus the heat pump pipe diameter is relatively large. If the sealing water is improperly adjusted, the sealing water will enter the pump, causing thermal stratification of the pump body, causing deformation of the cylinder and increasing the static deflection of the rotor. In addition, the heating time of the pump is not very long, and the surface seems to be warm, but the actual pump body is not sufficiently warm and even, often at this time, the jam phenomenon occurs after the car is turned at the start, and the more the card is, the more the disk is. The more the disk, the more it gets stuck so that the pump core is locked and cannot be started.
(4) Improper operation and lack of understanding of the characteristics of the pump at the initial stage of operation will also cause the failure of the pump core to lock up. In the early stage of operation, the feedwater pump trips in the thermal state, and it is often used when the rotation speed is zero. When the crank is not turned on, it is worried that the temperature difference between the upper and lower sides of the pump will cause the pump shaft to bend and increase the degree of jamming. Therefore, artificial strong disks are used. It turned out to be counterproductive, and the more the card got worse, the only option was to disassemble it for overhaul or return to the factory for processing.
(5) Unreasonable design and insufficient matching is also one of the reasons. Small steam turbines require low-speed cranking when starting and stopping, and it is best not to turn the feedwater pump when it is required to start and stop, and the cranking speed must be increased when the feedwater pump is required. That is to say, for the feedwater pump, either cancel the cranking or design it as High-speed cranking (greater than 100r/min). This kind of design divergence problem has not been fundamentally solved in most power plants. Therefore, some low-speed cranking will occur in the early stage of the new unit commissioning or the early stage after the overhaul, which will cause the pump core to lock up. The car seriously affects the normal operation of the unit.
Solutions to the lock-up of the pump core of the boiler water pump:
(1) The cleaning of the condensate and deaeration water supply system is a very important work content in the commissioning process of the unit. Strengthen the water flushing and alkaline cleaning of the system. The connecting pipeline between the front pump and the feed water pump is best to use a combined pickling pipeline, and then connect it with a flange. The small pipeline connected to the two major systems should be strengthened for cleaning. , No dead ends can be left, and finally ensure that the piping system and equipment before the water pump are free of impurities, so as to save the life of the water pump and avoid misfortune. In addition, pay attention to the quality of the manufacturing and installation process of the front pump and the inlet filter screen of the feedwater pump, and frequently check and flush and clean at the early stage of operation, so that the feedwater pump is safer and more reliable.
(2) The manufacturer of the boiler water pump should indicate in the contract that the dynamic and static gap should be appropriately increased, and the power plant and the manufacturer should negotiate together to do a good job of prevention. As to how large the gap is, it should be determined according to the filter design of the system and the performance design of the pump factory. In short, it is better to fully enlarge the dynamic and static clearance under the conditions allowed as far as possible (without affecting the pump output and efficiency).
(3) Before starting the boiler with the upper water pump, and when the pump is warmed up, the front pump should be started in advance and then the large flow heating pump treatment (public number: pump steward) should be used, and the temperature of the upper and lower shells of the pump body should be less than 15 °C and then start the feed water pump. In addition, increase the heating time of the pump according to the design requirements, and perform the heating without interruption when time permits, and control the sealing water pressure difference to ensure that the pump body is sufficiently warmed to avoid thermal stratification.
(4) For whatever reason, the pump core locks up in the end, which is mainly caused by the low-speed cranking. Therefore, the general power plant adopts the practice of not putting the cranking car in the initial stage of the new unit production (within half a year), and after the pump is warmed up Start directly, and do not turn on the crank after the pump is stopped. This is not conducive to the operating conditions of the small turbine, but it is also allowed in a short period of time. After the system is cleaned, the pump unit is operating reliably and then the crank is normally used as required. Device, this is also an effective method.
(5) When designing, it is necessary to consider adopting the method of combining the beauty of both worlds to deal with the requirements of the boiler water pump and the small steam turbine for the cranking. The small steam turbine and the feedwater pump supporting manufacturers are required to give consideration to the design and manufacturing to meet the high-speed cranking. Conditions to avoid the phenomenon of pump core lock due to high temperature shutdown of the pump. Nowadays, some domestic power plants adopt this method, and the effect is very good, which is a good start for the development of steam-driven feedwater pumps for large units in the future.
(6) Strengthen the operation management and supervision and restraint mechanism of the feedwater pump unit, strictly control the temperature difference of the feedwater pump casing and the temperature difference between the pump casing and the medium not to exceed the specified value. Once the pump unit is shut down, the pump core is locked, and the manual disc must not be forced. For the car, it is better to use steam impulse directly after cooling for a period of time.
