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Technical advantages of self-balancing boiler feed pump

Technical advantages of self-balancing boiler feed pump

(Summary description)When the traditional DG type segmented multistage centrifugal pump is in operation, most of the axial force is balanced by the balance disc device. The disadvantage of this method of balancing the axial force is that in the later stage of the pump, as the wear intensifies, the impeller and the guide vane sleeve, The gap between the seal rings gradually increases, and the amount of liquid leakage at the seal ring increases accordingly, which will increase the axial force greatly. The axial force that can be balanced by the balance plate cannot be balanced, and the wear of the balance plate and the balance ring is increased, which seriously affects the safe operation of the unit.

Technical advantages of self-balancing boiler feed pump

(Summary description)When the traditional DG type segmented multistage centrifugal pump is in operation, most of the axial force is balanced by the balance disc device. The disadvantage of this method of balancing the axial force is that in the later stage of the pump, as the wear intensifies, the impeller and the guide vane sleeve, The gap between the seal rings gradually increases, and the amount of liquid leakage at the seal ring increases accordingly, which will increase the axial force greatly. The axial force that can be balanced by the balance plate cannot be balanced, and the wear of the balance plate and the balance ring is increased, which seriously affects the safe operation of the unit.

Information

1. New structure

When the traditional DG type segmented multistage centrifugal pump is in operation, most of the axial force is balanced by the balance disc device. The disadvantage of this method of balancing the axial force is that in the later stage of the pump, as the wear intensifies, the impeller and the guide vane sleeve, The gap between the seal rings gradually increases, and the amount of liquid leakage at the seal ring increases accordingly, which will increase the axial force greatly. The axial force that can be balanced by the balance plate cannot be balanced, and the wear of the balance plate and the balance ring is increased, which seriously affects the safe operation of the unit.

 

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The typical feature of the self-balancing boiler feed water pump is that the balance disc system used to balance the axial force is completely eliminated in the structure. Instead, the impeller is arranged symmetrically and the inlet direction is opposite to balance the axial force. The front and rear parts of the pump are respectively In the water inlet section and the secondary water inlet section, the liquid is gradually boosted by the positive impeller and then introduced into the secondary water inlet section through the transition pipe. After being boosted by the reverse impeller again, the liquid is discharged from the water outlet section located in the middle of the pump body. The positive impeller and the reverse impeller are symmetrically arranged and the inlet direction is opposite, so two opposite axial forces are generated, and the magnitudes are approximately equal, so as to achieve the automatic balance of the pump itself, and the residual axial force is completely at the non-driving end of the pump Within the bearing capacity of the set angular contact ball bearing.

2, high reliability

In the process of automatic balancing of the traditional DG type feedwater pump, the rotor parts move from side to side, shuttle back and forth and gradually attenuate until the balance position and finally stop. When the feed water pump adopts a mechanical seal device, this balancing method is extremely harmful to the use of the mechanical seal. After a long time operation of the feedwater pump, the wear of the balance disc and the balance ring is intensified, the axial clearance increases, and the axial displacement of the mechanical seal gradually increases. Due to the axial force, the compression force of the sealing surface of the suction end increases, and the wear of the sealing surface increases, until the sealing surface is damaged and the sealing effect is lost. At the same time, the pressing force on the sealing surface of the extruder is reduced, which fails to meet the sealing requirements, and eventually the mechanical seals at both ends of the pump lose their sealing effect.

 

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The self-balancing boiler feedwater pump is equipped with angular contact ball bearings at the non-driving end, and is used in pairs and installed symmetrically. It can bear combined radial and axial loads at the same time to avoid axial movement of the feedwater pump during start and stop. There is no axial pulsation at all times, and there will be no momentary strong compression of the mechanical seal device due to changes in working conditions, which reduces the service life of the mechanical seal, which overcomes the problem of poor reliability of the mechanical seal that has been plagued by multi-stage pumps.

3, high efficiency and energy saving

The energy saving advantage of the self-balancing boiler feedwater pump is mainly reflected in the later period of operation. Because the balance plate device is eliminated, the automatic balance design concept is adopted. After a long period of operation, the feedwater pump will not move forward with the wear of the balance plate. The phenomenon of impeller and guide vane flow channel is good, and the equipment keeps running in the high efficiency zone for a long time. In addition, during the operation of the traditional DG pump, the motor current will gradually increase with the wear of the balance device, and the energy consumption will increase. The DG(P) pump can effectively eliminate such drawbacks.

 

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4. Pump expansion uniformity and symmetry are good

In view of the high water temperature of the feedwater pump, the thermal expansion of the pump body cannot be ignored. The self-balancing boiler feedwater pump adopts a six-point center support method to effectively prevent thermal expansion from harming the operation of the pump. That is, there are two longitudinal pins on the cat's paws at both sides of the center of the inlet section, which form a dead point with a longitudinal pin at the bottom of the inlet section, so that the pump body expands (contracts) uniformly and symmetrically in the circumferential direction and maintains The center of the pump remains unchanged. Since the inlet section is a dead point, the thermal expansion of the feedwater pump moves from the inlet section to the outlet section along the contact surface of the pump seat.

5. Good cavitation performance

In order to ensure good cavitation performance, the company has made the following two improvements in material selection and structural design of the self-balancing boiler feed water pump:

1. Material selection: Because the feedwater delivered by the feedwater pump has the characteristics of high temperature, high pressure, and high-speed flow, it will have a greater erosion effect on the impeller and guide vanes. Therefore, impellers, guide vanes, etc. generally made of phosphor bronze or ordinary steel materials are no longer suitable, but are made of high-chromium-containing stainless steel materials. This material has erosion resistance, corrosion resistance, low thermal expansion coefficient, good mechanical properties and easy repair The advantages of welding.

2. Structural design: The first-stage impeller adopts anti-cavitation material, and carries out the anti-cavitation blade structure design, so that the blade entrance edge is properly extended forward and the flow area is increased, so that the speed at the pump entrance is reduced and the pressure is increased. Improve its anti-cavitation performance.

 

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6. Odd-numbered balance device

Even-numbered pumps have the same number of positive and negative impellers. Theoretically, the axial force produced is the same, and because the direction of the axial force is opposite, an ideal balance can be achieved. For odd-numbered pumps, the reverse impeller is one more stage than the positive impeller, which results in an additional axial force of the impeller, pointing to the non-drive end. In order to balance the axial force, the inlet ring diameter of the first stage positive impeller is appropriately increased, so that the first impeller bears the axial force of more than one impeller, and the direction points to the driving end, so as to achieve a balance of counteracting the axial force of the reverse impeller. State, so that the axial force of the bearing is controlled within the allowable range.

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