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Centrifugal Pump Regulating Way and Energy Consumption Analysis (1)
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. 1. The main method of pump flow regulation 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 characteristic curve According to the law of proportion and cutting law, changing the pump speed, changing 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 (while changing the pressure Head) of purpose. However, for already working pumps, the method of changing the pump structure is less convenient and the versatility of the pump is reduced by changing the pump structure, although it is economically convenient at some times to regulate the flow1 and is rarely used in production . Here only analyze the change of centrifugal pump speed regulation method. When the pump speed is changed to adjust the flow rate from Q1 to Q2, the pump speed (or motor speed) drops from n1 to n2, and the pump speed curve nH is equal to n2 and the pipeline characteristic curve He = H0 + G1Qe2 Curve does not change) to point A3 (Q2, H3), A3 is the new operating point after adjusting the flow through the speed. The adjustment method has the advantages of obvious regulation effect, quickness, safety and reliability, prolonging the service life of the pump and saving electric energy, and additionally reducing the rotational speed operation 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.