Application of Frequency Control Technology in Pump Control System

Pump electricity consumption accounts for 30% - 50% of the cost of waterworks, how to reduce power consumption is to reduce the cost of each water plant is devoted to research, this paper through a specific example of how to rationalize the pump matching to achieve energy saving the goal of. I. INTRODUCTION Water pump is the most important energy-consuming equipment in urban water supply system. According to the investigation of running water pump in several water supply pump rooms, most of the actual pump lift is smaller than that of water pump Nameplate lift, and some even more than 30% difference. As a result, pump operation efficiency is reduced, energy is wasted and the motor is often overloaded. Reasons for this phenomenon include: In addition to the municipal infrastructure should have advanced, water forecast is too large, the pump selection method is not reasonable, the pump is not appropriate with the inappropriate one of the reasons. At present, most of the water supply pipe network is an anhydrous tower supply pipe network, according to the existing code of the highest daily maximum flow rate to calculate the pump lift election, and most of the cases outside the highest hours, the required lift is lower than the maximum Calculate head. When the highest working condition of the pump working point in the high-efficiency zone, the pump in most of the normal working hours will be moved outside the high efficiency zone, resulting in lower pump efficiency, resulting in energy waste. The improved method is to choose the pump, the lift should be based on the main average should be used to calculate the lift, the number of pumps should not be too small and should be different types of pumps with each other. This article will explore through examples how to properly select pumps to reduce energy consumption to meet the changing needs of urban water use. Second, an example: a water plant originally designed water supply capacity of 100,000 M3 / day, pump room selection of five single-stage double-suction in the open centrifugal pumps, respectively, RDL500-790AIS 3 pumps, pump head 57.5M, flow 3084M3 / h, with motor power 630KW; 2 sets of 14sh-9B pumps, pump head 55M, flow 1080M3 / h, the pump efficiency of 78%, equipped with motor power 250KW; the actual water demand in the city at 2.6 --- 36000 M3 / Day, the hour flow in the 1600M3 / h - 3000M3 / h between the pump outlet pressure of about 0.4MPa, the flow of 2000M3 / h around the year 8 months time. 1, the existing problems: due to the original design of the water is too large, usually usually open a small pump that is 14SH-9B to meet the demand, due to the original design of the pump head is high, the actual needs of the lower lift (factory pressure 0.40MPa) , When the pump outlet valve open all pipe pressure is low, the pump hourly flow can reach 1600M3 / h, resulting in cavitation phenomenon, the pump efficiency deviate from the high efficiency zone, and the motor overload, the motor heat, prone to burn motor phenomenon . When the water demand reaches 1700--2000M3 / h, it is necessary to open two small 14SH-9B pumps, then all the two pumps should close the small outlet valve to adjust the flow to meet the pressure demand of the pipe network. When two pumps very low efficiency, a lot of energy consumption in the valve, and the valve damage is serious. 2, the solution to the problem: First, we have to transform the 14SH-9B, without replacing the original motor under the premise of re-use a KQSN400-N13 head lift 45M, flow 1632M3 / h, the pump efficiency of 87%, so usually open 1 pump to meet the water demand, and the pump can run in the high-performance area; once again the original large RDL500-790AIS pump transformation (the pump is not equipped with matching motor), replace a KQSN600-M13 pump head 42M, flow 2980M3 / h, the pump efficiency of 85%, equipped with motor 450KW, and installed in the unit frequency control device to meet the needs of a variety of water changes through the above transformation, can adapt to the next 3-5 years of urban water changes The demand. 3, energy consumption calculation: According to the different water supply, under the conditions of head 40M, according to the pump performance curve, the motor efficiency of 92%, according to the formula W = QH / 102η (KWh) were calculated before and after the transformation of the pump unit consumption , The calculation results shown in the table, can be seen from the table before and after the transformation effect. Where Q - pumping station water (L / s); H - the actual pump lift (M); η - pump efficiency, η = η1 η2 η1 - pump operating efficiency; η2 - water pump Motor efficiency; Fourth, the conclusions based on the above calculation and analysis results, the following principles of rational selection of the pump: 1, at present most of the urban water supply pipe network in our country do not set up a water tower, the direct supply by the pumping station to meet user needs, in order to adapt to different water The demand, the number of pumps should not be too small, and the size of the pump should be reasonable with a ladder-type water supply to ensure that urban water demand. 2, with the size of the pump, small pump flow should be 40% to 60% of the pump flow, too small or too large will make the water pump in different combinations of uneven ladder of water, thus reducing the pump operating efficiency. 3, Where possible, the motor speed control device as far as possible, and the speed control device should be installed on a larger unit, speed control range should be controlled between 60% - 100%.

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