Variation Design of Boiler Feedwater Pump Cheng Chongsheng Xin Helei

In the design and production of chestnuts, the boiler feed pumps used in each power plant are often encountered. The models are various, and the parameters are different. When designing these pumps, if we follow the hydraulic design steps of the new pump, first select the model pump, and then calculate and design according to the similar theory of the pump, then not only do we need to design a lot of drawings, it takes a lot of design time, and in production It also requires the production of a large number of molds. This will waste a lot of money and time and cause a great burden. At this time, if a variant design method of the pump is used which only changes the outlet width of the impeller, the guide vane, the diameter of the impeller vanes or the number of stages of the pump, the matter is relatively simple.

The modified design of boiler feed water chestnut need only change one or more of the four factors of the impeller, the guide vane outlet width, the diameter of the impeller guide vane or the pump stage, and the design workload is redesigned according to the similar theory of the pump. , greatly reducing the design workload, and even if the impeller, guide vane changes, the impeller, guide vane mold does not need to re-produce, inlet and outlet sections, middle section, water seal and other castings do not need to be changed at all, do not need to do Molds, production cycles and production costs can be significantly reduced. Therefore, we often use variant designs in our production. In fact, the design of more than 80% of boiler feed pumps in our factory is accomplished through the modified design of the pump.

2 Change the performance parameters of the pump by changing the impeller and guide vane runner width of the feed pump. If the head of the pump to be designed is close to the head of the pump that has already been produced, the speed is the same and the flow difference is large. At this time, the change is used. The method for designing the impeller and guide vane runners of the pump is a more suitable one.

Vw - velocity of the outlet shaft surface V, “volumetric efficiency When manufacturing the impeller wax model, by translating the impeller cover, only changing the outlet width of the impeller, the flow-related recognition, less 2, 7/ can all be considered unchanged. The flow rate is proportional to the impeller outlet width (as shown), ie: b2―Model pump impeller exit width b2′—Design pump impeller exit width H~~ Model pump lift W Design Chest lift can pass already produced vegetable performance test The report calculated the need to design the exit width of the pump impeller.

The impeller outlet width changes, the guide vane inlet width has to be changed accordingly, generally the guide vane inlet width change amount is equal to the impeller outlet width change amount. For example, if the impeller inlet width is increased by 5mm from 15mm to 20mm, then the guide vane inlet width should also be increased by 5mm, from 18mm to 23mm 111111 to 24mm, and the corresponding pump flow from 270t/h to 400t/h. The width of the blade inlet is changed from 19 mm to 26 mm. Several types of pumps are designed by varying the impeller outlet width and the guide vane inlet width.

It should be noted that when selecting the proper impeller outlet width and guide vane inlet width in the design, the conversion curve should be converted into the performance curve to be designed according to the test performance curve of the original pump to see if it is appropriate. The conversion method is: first select the appropriate 62′, can be in the mechanical drawing, the original performance curve of the pump (-77 curve were built blocks, the scale of the coordinates of the direction of the coordinates to the value of direct conversion According to our factory's many years of experience, the flow rate of the feed pump is not completely proportional to the impeller outlet width. The pump with a large outlet width of the impeller is converted to a pump with a small outlet width of the impeller, and the calculated flow rate is larger than the actual flow rate of the pump. A pump with a small outlet width is converted to a pump with a large outlet width of the impeller, and the calculated flow rate is smaller than the actual flow rate of the pump. This is because the impeller with a large outlet width of the impeller has a larger specific rotation speed and a higher pump efficiency. It should be noted that when a pump with a small impeller exit width is used as a model pump to design a pump with a small impeller exit width, the impeller exit width should be increased more than the calculated value, leaving an appropriate margin. At the same time, when selecting a model pump, select The pump closest to the flow rate of the pump is designed as a model pump.

3 Change the performance parameters of the pump by changing the diameter of the impeller of the boiler feed pump. If the head and flow of the feed pump required by the user are lower than the existing lift and flow of the existing pump, and there is not much low, the cutting design law H can be used for variant design. More suitable.

The impeller of the boiler feed pump in our factory is generally between 60 and 120. According to our factory's production experience, it is more suitable for the cutting of the general centrifugal pump impeller in the cutting law. That is, when the rotation speed is the same, the flow rate before and after cutting, the head ratio It is equal to the ratio of primary and secondary sides of the impeller diameter before and after cutting (as shown): when the rotation speed is different, the ratio of flow and head before and after cutting is converted into the performance curve of the pump to be designed according to the test performance curve of the original pump. Suitable. The conversion method is: first select the appropriate ZV, can be built in the mechanical drawing, the original 0-77 curve of the chestnut performance curve were built into blocks, the directional coordinates of the block scaling to 0V (f / n ) The value of the H coordinate scale is changed to the value of (ZV/U7n)2; the scale of the directional coordinate of the tile is changed to (iV/ is the value of (f/n), the 7-axis coordinate scaling is not Change, still 1, direct conversion curve.

In production, cutting the outer diameter of the impeller generally means cutting only the blades, leaving the front and rear covers intact.

If the head and flow rate of the feed pump required by the user are higher than the head and flow of the existing pump, and the height is not much, the cutting law may be reversed and the impeller of the existing pump may be regarded as the impeller after cutting. The pump was counted as an uncut impeller. This design method is often used in production. When the diameter of the impeller is increased, the size of the guide vanes to be fitted with the impeller should also be increased. After the guide vanes are enlarged, the gap between the impeller and the guide vane is maintained.

On the basis of existing pumps, there is no need to re-do molds by increasing the diameter of the impeller. The guide vane only needs to insert the guide van into the car during turning, and it can be completely processed with the original vane blank.

Increase the diameter of the impeller can not generally increase too much, because the increase in impeller diameter too much, not only wax mold production is difficult, and may be due to vane angle and impeller outlet angle change, resulting in decreased efficiency, increase the lift also no longer meet the cutting law. According to our factory's production experience, when the impeller diameter is cut or increased, it is generally not more than 5%. When the impeller diameter increases or decreases by 5%, it still can not meet the user's requirements, generally by adopting another variant design method one—increasing or reducing the impeller The number of levels to complete.

4 Change the performance parameters of the pump by increasing or decreasing the number of stages of the impeller. If the head and flow rate of the feed pump required by the user differ greatly from the head and flow rate of the existing pump, the diameter of the impeller increases or decreases by 5%, while the flow path is widened. When the user's requirement cannot be satisfied, the method of increasing or decreasing the number of stages of the pump is generally used. Due to considering the strength and stiffness of the pump shaft, increasing the number of stages of the pump generally only considers adding one stage.

Boiler feed pumps are mostly multistage segmented pumps, and the design of changing the pump stages is more convenient. If the progression of the chestnut is increased by one level, the lengths of the shaft, tension bolt and pump cover are correspondingly lengthened, and the number of parts related to the number of pump stages, such as the middle section and the guide vane, is increased by one, and the remaining parts of the pump need not be modified.

If the boiler feed water pump only increases or decreases the number of stages and the rotational speed remains the same, the flow parameter of the pump can be considered as the same flow rate. The lift algorithm is divided by the number of model pump stages to obtain a single-stage lift, and then the pump level is multiplied by the change. Number, that is: boiler water dish to increase or decrease the number of stages, when the speed is different, multi conversion points, draw the performance curve to design the pump, because the user's pump flow is not necessarily the same as the model pump, and the pump performance curve is Continuously, after drawing the performance curve of the chestnut design, as long as the flow rate required by the user is satisfied, the lift of the pump can meet the user's requirements, and the efficiency can be in the high efficiency zone. The new pump's rated operating point must not be compared with the model pump. correspond.

If the water pump is lengthened one level, the strength and stiffness of the pump shaft should be re-checked. If the strength and rigidity are not enough, the new pump cannot be designed by increasing the number of stages.

If the feed pump reduces the number of stages, it is not necessary to reduce the level by one. The balance force M of the balance plate should be recalculated to be sufficient; if it is not enough, the balance force of the balance plate and balance plate should be redesigned.

5 Change the performance parameters of the pump by changing the impeller, guide vane flow path width of the boiler feed water pump, impeller, guide vane diameter, and number of impeller stages. In the variable design of the pump, changes to individual factors often fail to meet the user's requirements. Modified new pumps can better meet the requirements of users, often need to change a number of factors to change the design.

Changing multiple factors for variant design can change any two of the three factors. Although the design is more complex, it can be seen as a single factor superposition. Such as a pump, in the same speed, not only change the impeller, guide vane flow path width, impeller, guide vane diameter, but also change the impeller stage, then: According to the test performance curve of the model chestnut, into the performance of the pump to be designed Curve to see if it is right. The conversion method is: first select the appropriate zv, 匕 can be in the mechanical drawing, if the speed of the original pump in the performance curve is different, then change the scale of the coordinates of the ugly direction of the map to this variant design, if If the pump is increased by one level, the strength and stiffness of the pump shaft must also be checked. If the feed pump is reduced in number, it can be reduced by more than one level. It is also necessary to recalculate whether the balancing force of the balance plate is sufficient.

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