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Centrifugal pump and piping system through the characteristic curve analysis of centrifugal pump flow adjustment of several major ways: the outlet valve adjustment, pump speed adjustment and pump series, parallel adjustment. Using the characteristic diagram to analyze the energy loss of the outlet valve and the pump speed regulation, it is pointed out that the variable speed flow control of the centrifugal pump can save energy consumption better than that of the outlet valve, and the energy efficiency and flow rate Change the size of the relevant. In the practical application should pay attention to the scope of variable speed adjustment, in order to better use centrifugal pump speed adjustment. Centrifugal pumps are a versatile fluid machinery widely used in chemical industrial systems. It has a wide range of performance to adapt to (including flow, pressure head and the nature of the transport medium adaptability), small size, simple structure, easy operation, low operating costs and many other advantages. Usually, the selected centrifugal pump flow, head pressure may be inconsistent with the requirements of the pipeline, or due to production tasks, process requirements change, this time require the pump flow control, in essence, to change the operating point of the centrifugal pump. Centrifugal pump operating point is determined by the pump characteristic curve and piping system characteristic curve, therefore, to change any of the characteristic curve can achieve the purpose of flow adjustment. At present, the centrifugal pump flow control methods are the main control valve, variable speed control and the pump and the series adjustment. Due to the different principles of various adjustment methods, in addition to their own advantages and disadvantages, the resulting energy loss is not the same, in order to find the best, minimum energy consumption, the most energy-efficient flow regulation, you must fully understand the centrifugal pump flow adjustment The relationship between mode and energy consumption. A main way to adjust the pump flow 1.1 to change the pipeline characteristic curve The most simple way to change the centrifugal pump flow is to use the pump outlet valve opening to control, its essence is to change the position of the pipeline characteristic curve to change the pump operating point . 1.2 Change the centrifugal pump characteristics curve According to the law of proportion and cutting law, change the pump speed, change the pump structure (such as cutting impeller diameter method, etc.) can change the centrifugal pump characteristics of the two curves, so as to adjust the flow (at the same time Change the pressure head) purposes. However, it is inconvenient to change the structure of the pump when it is already in operation, and the versatility of the pump is reduced by changing the structure of the pump, although it is economically convenient at some times to regulate the flow [1] Less used. Here only analyze the change of centrifugal pump speed regulation method. Analysis from Figure 1, when the pump speed to adjust the flow rate change from Q1 down to Q2, the pump speed (or motor speed) decreased from n1 to n2, the speed of n2 pump characteristics under the curve QH and the pipeline characteristic curve He = H0 + G1Qe2 (no change in line characteristic curve) to point A3 (Q2, H3), point A3 is the new operating point after adjusting the flow rate by speed regulation. The adjustment method has the advantages of obvious adjustment effect, quickness, safety and reliability, prolonging the service life of the pump and saving electric energy, and additionally reducing the running speed of the centrifugal pump can effectively reduce the NPSHr of the centrifugal pump and keep the pump away from the cavitation zone and reduce the centrifugal pump The possibility of cavitation occurs [2]. The disadvantage is the need to change the pump speed through the variable frequency technology to change the prime mover (usually the motor) speed, the principle of complex, large investment, and the flow adjustment range. 1.3 pump string, and even adjust the way When a single centrifugal pump can not meet the delivery tasks, you can use the centrifugal pump in parallel or series operation. In parallel with two centrifugal pumps of the same type, although the pressure head changes little, but increases the total delivery flow, the total efficiency of the parallel pump is the same with the efficiency of a single pump; when the centrifugal pump is connected in series, the total pressure head increases, Little change in flow, the total efficiency of tandem pumps with a single pump the same efficiency. 2 different regulation mode pump energy analysis In the different regulation mode of energy analysis, the article only for the current widely used valve regulation and pump variable speed regulation of two adjustment methods to be analyzed. As the centrifugal pump and the tandem operation aims to improve the pressure head or flow in the chemical industry is not much use of its energy consumption can be combined with Figure 2 analysis, the method is basically the same. 2.1 When the valve to adjust the flow of power consumption Centrifugal pump operation, the motor input shaft power N is: N = vQH / η Where N - shaft power, w; Q - pump effective pressure head, m; H - the actual pump flow, m3 / s; v - fluid specific gravity, N / m3; η - pump efficiency. When the valve is used to regulate the flow rate from Q1 to Q2, the shaft power consumed at the operating point A2 is: NA2 = vQ2H2 / ηvQ2H3 - Actual useful power, W; vQ2 (H2-H3) - Power loss on the valve, W; vQ2H2 (1 / η-1) - Centrifugal pump loss of power, W. 2.2 variable speed flow control power consumption in the analysis of variable speed centrifugal pump due to the need to use the law of proportion, according to its application conditions, the following analysis refers to the centrifugal pump speed range of ± 20%, and the centrifugal pump itself efficiency Little change [3]. When the motor is used to regulate the flow rate to the flow rate Q2, the shaft power consumed by the pump at the working point A3 is: NA3 = vQ2H3 / η The same can be obtained by transforming NA3 = vQ2H3 + vQ2H3 (1 / η- 1) Actual useful power, W; vQ2H3 (1 / η-1) - Centrifugal pump loss of power, W. 2.3 Comparison of Energy Consumption 3 Conclusion For the current centrifugal pump common outlet valve and pump speed regulation of two main flow control methods, pump variable speed control of energy saving than the regulation of the outlet valve is much larger, which can be from Both the power analysis and power consumption comparison analysis shows. Through the centrifugal pump flow and lift diagram, you can more intuitively reflect the energy consumption of the two adjustment mode. Reducing the flow through pump speed regulation also helps to reduce the possibility of cavitation in the centrifugal pump. When the flow rate decreases, the energy-saving efficiency of variable speed regulation is greater, that is, the greater the power loss of valve regulation, however, the pump efficiency is too large when the pump speed is too large, which is beyond the scope of the pump law of proportion. Therefore, Should consider from many aspects, in between the two out of the best flow control methods.