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yibocommunal
Oct 12, 2021
In General Discussions
Centrifugal pump is a general fluid machinery widely used in chemical industry system. It has the advantages of wide performance adaptability (including flow, pressure head and adaptability to the properties of conveying medium), small volume, simple structure, easy operation and low operation cost. Generally, the flow and pressure head of the selected centrifugal pump may be inconsistent with the requirements in the pipeline, or due to changes in production tasks and process requirements, it is required to adjust the flow of the pump, which is essentially to change the working point of the centrifugal pump. The working point of centrifugal pump is determined by the characteristic curve of pump and pipeline system. Therefore, changing any characteristic curve can achieve the purpose of flow regulation. At present, the flow regulation methods of centrifugal pump mainly include regulating valve control, variable speed control, parallel and series regulation of pump, etc. Due to the different principles of various regulation methods, in addition to their own advantages and disadvantages, the energy loss is also different. In order to find a flow regulation method with low energy consumption and energy saving, * * * better understand the relationship between the flow regulation mode of centrifugal pump and energy consumption. 1. Main modes of pump flow regulation 1.1 change pipeline characteristic curve The simple way to change the flow of centrifugal pump is to use the opening of pump outlet valve to control. Its essence is to change the position of pipeline characteristic curve to change the working point of pump. 1.2 change the characteristic curve of centrifugal pump According to the law of proportion and the law of cutting, changing the speed of the pump and changing the pump structure (such as cutting the outer diameter of the impeller) can change the characteristic curve of the centrifugal pump, so as to adjust the flow (and change the pressure head at the same time). However, for the working pump, the method of changing the pump structure is not convenient, and due to changing the pump structure, the universality of the pump is reduced. Although it is economical and convenient to adjust the flow at some times, it is rarely used in production. Here, only the method of changing the speed of centrifugal pump and regulating flow is analyzed. When the pump speed is changed to adjust the flow from Q1 to Q2, the pump speed (or motor speed) decreases from N1 to N2. When the speed is N2, the pump characteristic curve Q-H and pipeline characteristic curve he = H0 + g1qe2 (pipeline characteristic curve does not change) intersect at point A3 (Q2, H3). Point A3 is the new working point after adjusting the flow through speed regulation. This regulation method has obvious, fast and reliable regulation effect, which can prolong the service life of the pump and save electric energy. In addition, reducing the speed can effectively reduce the NPSHr of the centrifugal pump, keep the pump away from the cavitation area and reduce the possibility of cavitation of the centrifugal pump. The disadvantage is that changing the speed of the pump requires changing the speed of the prime mover (usually the motor) through frequency conversion technology. The principle is complex, the investment is large, and the flow regulation range is small. 1.3 series and parallel adjustment mode of pump When a single centrifugal pump cannot meet the conveying task, the parallel or series operation of centrifugal pumps can be adopted. Using two centrifugal pumps of the same model in parallel, although the pressure head changes little, the total conveying flow is increased, and the total efficiency of the parallel pump is the same as that of a single pump; When the centrifugal pump is connected in series, the total head increases and the flow changes little. The total efficiency of the series pump is the same as that of a single pump. 2. Energy consumption analysis of pump under different regulation modes When analyzing the energy consumption under different regulation modes, this paper only analyzes the two widely used regulation modes: valve regulation and pump variable speed regulation. Because the purpose of parallel and series operation of centrifugal pump is to improve the pressure head or flow, it is not widely used in the field of chemical industry. 3. Conclusion For the two main flow regulation modes of outlet valve regulation and pump variable speed regulation commonly used in centrifugal pumps, the energy consumption saved by pump variable speed regulation is much greater than that of outlet valve regulation, which can be seen from the power consumption analysis and comparative analysis of the two. The relationship between flow and head of centrifugal pump can more intuitively reflect the energy consumption relationship under the two regulation modes. Reducing the flow through variable speed regulation of the pump is also conducive to reducing the possibility of cavitation of the centrifugal pump. When the flow decreases, the greater the energy-saving efficiency of variable speed regulation, that is, the greater the power loss of valve regulation. However, when the pump speed changes too much, it will reduce the pump efficiency and exceed the range of pump proportional law. Therefore, in practical application, we should consider many aspects and synthesize a good flow regulation method between the two. Vacuum Pump Heat Treatment Guide,Heat Treatment Equipment Liquid Ring Vacuum Pump
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