Pump selection is an important issue in pumping station engineering design, the selection is reasonable or not, which is directly related to the investment of pumping station project, after the completion of the operation costs and water supply safety. . Domestic low-lift axial pump station deviated from the high-performance long-term operation, in addition to high-lift design, the pump lift is higher than the actual needs of one of the important reasons is 〔2 ~ 4〕, the paper analyzes the pump and pump characteristics of the device , Pointing out the shortcomings of the traditional method of pump selection and put forward a new selection method.1 The traditional pump selection method The traditional method of pump selection is to determine the required lift curve according to the net lift of the pump station and the installation form, Pump head loss, and then determine the total head, so that the selected pump in the design lift the highest efficiency can be seen that the traditional method is to choose the pump flow to increase the headache way to choose, did not consider whether the efficiency of the pump head design lift Highest. Assume the design point of the device is A (QZ, HZ). When the pump is selected by the traditional method, the pump head is calculated according to the following formula: HP = HZ + SQ2, (1) , Determine the selected pump design condition point as point B, as shown in Figure 1, and then select the pump according to point B, if the point B is the highest efficiency point of the pump, then that pump selection to achieve the best condition .However, the highest The efficiency of the pump in point B, which maximizes the efficiency of the pump unit at point C, shows that the highest efficiency point C deviates from the so-called design point A and that the pump unit actually operates in the low-lift, high-flow region. This is in contrast to the large number of model tests The measured data of the field are consistent with each other.The efficiency curve of axial flow pump device is on the high flow rate side, the efficiency drops sharply with the increase of flow rate, so it is easy to cause the pump station efficiency to be low and the cavitation performance to deteriorate.For the high lift pump station, The proportion of loss is small, little shift at point C and point A, coupled with high-lift centrifugal pump, wide area high efficiency mixed flow pump, therefore, the traditional equal flow to increase the pumping head pump does not show its drawbacks. Pumping station, due to a large proportion of pipeline loss, C and A large offset, the traditional pumping method will inevitably lead to low pumping station efficiency.For blade angle adjustable pump, the maximum efficiency point will also be from a large angle Move to a small angle, angle Of the offset reached 6 ~ 10 °, C and A point offset will be more serious.Figure 1 traditional pump method 2 pump and pump characteristics of the relationship between the definition of pump head lift HZ upstream and downstream water level difference, the pump head is HP, The relationship between pump flow and lift can be expressed as: HP (Q) = AQ2 + BQ + C, (2) The relationship between shaft power and flow rate for a particular plant can be expressed as: PQ = DQ2 + EQ + F , (3) For a given pump, A, B, C, D, E and F are constants, and the pump efficiency can be obtained: ηP = ÏgQHP (Q) / P (Q) The extremum can be calculated as the maximum efficiency point flow, the equation is: ADQ4 + 2AEQ3 + [3AF + BE-CD] Q2 +2 2BFQ + CF = 0, (5) For the pump device, assuming that the pump performance characteristics of the device unchanged, The hydraulic loss of the pipeline meets h = SQ2, (6) where S is the pipe resistance coefficient, then the head of the device can be expressed as: HZ = AQ2 + BQ + C-SQ2. (7) The device efficiency ηZ can be expressed as ηZ = ÏgQHZ Q) / P (Q). (8) The maximum efficiency point of the pump unit can be obtained from (8) as follows: ] Q2 + 2BFQ + CF. (9) It can be shown that the root QZ obtained from Eq. (9) near the design flow is better than that obtained from Eq. (5) In order to analyze the effect of different pump devices on efficient flow rate and head lift, three typical pump characteristic data are cited in this paper.The performance curve of model pump 1 (ns = 1129, blade angle 2 °) can be expressed as: (Q) = 22.2773 + 0.119194-0.345933Q.10-3Q2, (11) The basic performance parameters of the highest efficiency point are (QP = 396m3.s-1, HP = 4.229m, ηP = 0.86) .If the pipeline resistance coefficient of the device is assumed to be 0,1.348 × 10-6, 2.697 × 10-6, 4.045 × 10-6, 5.394 × 10- 6,6.742 × 10-6, can obtain a variety of pipeline hydraulic loss of the highest performance point of the performance parameters of the device, shown in Table 1. Can be seen from Table 1, low lift axial flow pump device with the pipe resistance coefficient (1000HLB-16) performance curve can be expressed as: HP (Q) = - 2.1754 × 10-5Q2 + 0.13163Q-179.4852, ( (13) The lift-flow relationship of the device is: HZ (Q) = HP (Q) -SQ2. (14) Assuming that the pipeline loss coefficients are respectively Is 0, 7.47 × 10 -8, 14.94 10-8,22.41 × 10-8,29.89 × 10-8,37.35 × 10-8, can find the device point changes in efficiency, shown in Table 2. Can be seen from Table 2, mixed flow pump device with the pipeline The resistance coefficient increases, the maximum efficiency of the device is reduced, the flow rate is reduced, but the head is fluctuated. When the drag coefficient is small, the effective lift point is increased, and when the drag coefficient is larger, the effective lift point is reduced. % And 20% respectively, within this range, the flow of this case can be reduced by 6% ~ 7% and the lift can be reduced by 1% ~ 5% .The performance curve of centrifugal pump (12sh-6) can be expressed as: HP (Q) = - 5.923 × 10 -4Q2 + 8.571 × 10-2Q + 99.95238, PQ = 6.694 × 10-4Q2 + 0.4035Q + 128.803, (16) HZQ = HPQ - SQ2. Resistance coefficient S were 0.3 × 10-5, 18.6 × 10-5,27.90.3 × 10-5, can be obtained from the device point changes in efficiency shown in Table 3. It can be seen from Table 3, centrifugal pump with the pipe resistance In this example, it is assumed that the pipe loss is 10% and 15% of the total head and the flow rate is reduced by 13.5% ~ 15%, the coefficient is increased, the highest efficiency of the device is reduced, the flow is reduced, the head is reduced, the flow reduction is larger, 17.86%, head reduced 2% ~ 3.4%. Table 1 Model Pump 1 device maximum efficiency point of change Pipeline resistance coefficient S (× 10-6) Q / m3.s-1 H / m P / kW ηmax 0.000 396 4.229 19.093 0.86 1.348 386 4.396 20.173 0.819 2.697 376 4.511 21.205 0.784 4.045 368 4.59 21.996 0.753 5.394 359 4.703 22.849 0.724 6.742 352 4.76 23.485 0.699 TABLE 2 Change of high efficiency point of mixed flow pump device S (× 10-8) QZ / m3.s- 1 HZ / m P / kW ηmax 0.000 3359.0 16.86 593.9 86.00 7.470 3214.6 17.73 616.0 83.56 14.94 3186.0 17.20 619 79.67 22.41 3160.0 16.65 621.9 75.90 29.89 3135.0 16.08 623.0 72.23 37.35 3111.5 15.50 624.0 68.00 TABLE 3 Change of High Efficiency Point of Centrifugal Pump Unit S ( × 10-5) QZ / m3.s-1 HZ / m P / kW ηmax 0.0 220.0 90.0 250.0 77.5 9.3 201.0 89.4 236.0 74.9 18.6 190.0 88.1 229.6 71.4 27.9 180.7 86.9 223.0 68.8 3 Increase the flow, The above analysis shows that the increase of the original flow pump head pumping method is only suitable for basic selection of centrifugal pumps for low-lift axial flow pump, should be appropriate to reduce the head, increasing the flow of the pump method for mixed flow Pump, pump head can be used to increase the flow of the pump method, for the centrifugal pump should be taken at the same time increase the flow and lift election pump method, the three pump devices on the efficient point flow, lift the situation in Table 4. Table 4 devices efficient point Flow and Lift Changes Item Axial Flow Pump Mixed Flow Pump Centrifugal Pump Q Reduced by 8% ~ 10% Compared to Design Flow Reduced by 5% ~ 10% Reduced by 10% ~ 15% H (Compared with Design Lift) Increased by 5% ~ 8% Reduce or increase 1% ~ 5% Reduce 2% ~ 4% 4 Conclusion Pumping point on the efficient flow rate and lift and pump characteristics and device type coefficient related to the need to pass a large number of experiments to reach the impact coefficient, Only by formula derivation and numerical analysis to illustrate the shortcomings of the traditional method of pump selection, increase the flow of variable lift method pump selection, you can make the device the highest efficiency.
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