Energy saving analysis of the hottest water pump m

2022-08-16
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Energy saving analysis of water pump motor

energy saving analysis of water pump motor -- frequency conversion technology plays a leading role

energy saving analysis of water pump motor -- frequency conversion technology plays a leading role, which was collated and released by China mechanical and electrical products trading (hereinafter referred to as mechanical and electrical equipment) on November 14, 2016

1. The Huaneng Jinling gas turbine thermal power Co., Ltd. has two sets of S109FA gas steam combined cycle generator units, each of which is equipped with two feed pumps, one for operation and the other for standby. The two feed pumps are interlocked with each other. The rated power of the feed pump motor is 2240kw, the rated current is 245.4a, the rated voltage is 6000V, and the frequency is 50Hz; The pump set adopts multi-stage vertical centrifugal pump, with shaft power of 1772kw, rotating speed of 2985r/min, flow rate of 311m3/h at high pressure and 78m3/h at medium pressure. The motor power of the feed water pump is slightly larger than the shaft power of the water pump, so it can fully meet the operation requirements of the combined cycle unit

the feed pump adopts constant speed operation and high and medium pressure combined pump. The working medium extracted after the third stage of the feed water pump becomes medium pressure feed water and enters the medium pressure economizer. After the medium pressure feed water is heated to a temperature close to saturation in the medium pressure economizer, part of it goes to the natural gas performance heater and part of it enters the medium pressure steam drum. The water in the medium pressure steam drum enters the medium pressure evaporator from the downcomer, and then returns to the steam drum as steam water mixture after heating. Steam water separation is carried out in the separator in the steam drum. The separated water returns to the water space of the steam drum, and the saturated steam is sent to the medium pressure superheater through the saturated steam outlet pipe. It continues to be heated into superheated steam. After mixing with the exhaust steam of the high-pressure cylinder (cold reheat steam), it enters reheater 1 for heating. The outlet steam passes through the reheater desuperheater, and the desuperheating water from the medium pressure feedwater regulates the temperature and then enters reheater 2. After the temperature is further increased, it enters the medium pressure cylinder of the steam turbine to do work. The working medium at the outlet of the feed pump is high-pressure feed water, which enters the high-pressure steam drum through the 7-Stage high-pressure economizer in turn. The water in the high-pressure steam drum enters the high-pressure evaporator from the downcomer, becomes a steam water mixture after heating, and returns to the steam drum for steam water separation in the separator in the steam drum. The separated water returns to the water space of the steam drum. The saturated steam is sent to the high-pressure superheater 1 and 2 for heating through the saturated steam outlet pipe. The outlet steam passes through the high-pressure steam desuperheater. After the temperature is adjusted by the desuperheating water from the high-pressure feedwater, it is sent to the high-pressure superheater 3 and 4 for heating. After the temperature is further increased, it enters the high-pressure cylinder of the steam turbine to do work. In order to prevent cavitation of the feed pump during low load operation of the unit, a feed water recirculation pipeline is also designed

under normal operation, the feed water pump operates at power frequency, and the feed water control valves of the high and middle steam drums automatically level the water level according to the set value of the steam drum water level. The feed water pump adjusts and controls the water level by adjusting the opening of the feed water control valve. However, due to the large throttling loss of this control method and the mechanical adjustment structure of the control valve, the adjustment quality is poor. In actual operation, due to the limitation of the regulating characteristics of the water filling regulating valve of the high and medium pressure steam drum, various faults are prone to occur, which increases the amount of on-site maintenance, and there are problems such as high outlet pressure and easy pipeline damage. From the parameters of the supporting motor, it can be seen that the feed water pump uses a high-power motor to drive the small water pump to work. In the long-term operation, it is limited by the regulation and control mode. The system efficiency under this mode is low, which is very easy to cause motor aging and energy waste. In addition, the high-power motor is directly started, and the excessive starting current is easy to cause instantaneous damage to the equipment during startup (the plant has been put into operation for 9 times since the feed water pump was started), Under the guidance of modern energy conservation, emission reduction and cost reduction management concepts, this control method can no longer cover GB, ASTM, DIN, JIS, BS, etc. to meet the production needs of enterprises. Therefore, it is imperative to adopt frequency conversion control technology to carry out the technical transformation of feed pump, so as to realize the purpose of soft start of feed pump motor and energy saving and consumption reduction

2 analysis of energy-saving transformation of feed pump

the new frequency conversion control technology is to fully open the traditional control valve and use the frequency conversion technology to control the speed of the feed pump motor, so as to achieve the purpose of adjusting the outlet pressure and flow of the feed pump. Variable frequency control technology can reduce the impact of traditional regulation on the pipeline, and improve the operation reliability of feed pump by variable frequency speed regulation. Moreover, the adjustment of feed pump with frequency conversion control technology can also greatly improve the adjustment speed. Through frequency conversion technology, energy consumption is reduced to achieve the purpose of energy-saving transformation. As a high-tech power transmission technology integrating power electronics, motor drive and automatic control, frequency conversion and speed regulation technology has developed rapidly in the 1990s. With its superior speed regulation performance, remarkable energy-saving effect, perfect protection function and easy interface with DCS, it has become the preferred scheme for the transformation of feed pump speed regulation mode

2.1 working principle of variable frequency energy saving

according to the hydrodynamics knowledge of pumps and fans, the flow is proportional to the speed, the head is proportional to the square of the speed, and the output power is proportional to the cubic of the speed. The characteristic curve of the water pump can be changed by adjusting the motor speed, so as to obtain the desired flow and pressure. When the pump efficiency is certain, the speed of the feed pump decreases, and the output power of the motor decreases by the third power. The speed n of asynchronous motor has the following relationship with the power frequency f, slip ratio s and pole pair P: n=60f (China's high molecular material industry should also move towards intelligent manufacturing 1-s)/p. When the motor runs with load, the slip ratio changes slightly with the change of load. It can be approximated that the motor speed has a linear relationship with the power frequency, and changing the power frequency can change the motor speed. An important factor to be considered in the speed regulation of asynchronous motor is the magnetic flux M. If the magnetic flux is reduced, the motor core is not fully utilized, and the torque generated by the same current is small, which is a waste; If the magnetic flux is increased, the iron core will be saturated. On the one hand, the excitation current component in the stator current will increase, and in serious cases, the motor will be damaged due to overheating of the winding; On the other hand, the torque current component is reduced, and the motor power factor is reduced. Therefore, it is expected that the magnetic flux will remain unchanged at the rated value. The magnetic flux in three-phase asynchronous motor is generated by the synthesis of stator and rotor magnetic potential. The effective value of each phase of stator induced electromotive force is: e=4.44fnkn M. it can be seen from the above formula that as long as e and F are well controlled, the purpose of controlling magnetic flux can be achieved (here, only the case of fundamental frequency, that is, below the rated frequency, needs to be considered). To keep m constant, when the frequency is adjusted downward from the rated value FN, e must be reduced at the same time, so that e/f= constant, that is, the constant electromotive force frequency ratio control mode, but e is difficult to control directly. When e is high, the leakage impedance voltage drop of the stator winding can be ignored, and it is approximately considered that the stator phase voltage u= e, so as to obtain u/f= constant, that is, the constant voltage frequency ratio control mode. The frequency converter uses the on-off of power electronic devices to convert the power frequency power supply into another power supply with controllable frequency and voltage to supply the motor. The frequency is controllable, that is, the motor speed is controllable, so as to achieve the purpose of energy saving and speed regulation

2.2 frequency conversion transformation scheme and implementation

through the comprehensive research and analysis of the main technical parameters of the feed pump and supporting motor and the operation of the feed water system, it is decided to adopt the electrical control scheme of "one driven second-hand start/frequency conversion switching". The transformation uses the existing equipment, and adds a common frequency converter in the original 6kV switch room. During normal operation, the frequency converter drives one feed pump to operate, and the other feed pump is in the power frequency standby state. When the frequency converter trips, the standby pump immediately starts up at the power frequency and switches undisturbed, so as to ensure the stability of high and medium pressure steam drum water supply. This scheme can meet the requirements of regular rotation system of feed pump and improve the utilization rate of frequency converter. The control mode of "one driving two" can avoid that when the low voltage of the power supply system affects the normal operation of the frequency converter, the standby pump can be quickly switched to the power frequency state and put into operation, so as to ensure the normal and continuous operation of the unit equipment

the frequency conversion transformation scheme is that two feed pump motors are controlled and equipped with a special frequency converter for water pumps produced by Beijing harvest Electric Technology Co., Ltd. the special frequency converter is carefully designed and manufactured by introducing German Schneider advanced technology, which meets international electrical standards. After the frequency conversion transformation, the frequency conversion technology is used to receive 4~20ma control signals to adjust the speed of the feed pump motor, so as to change the outlet pressure and flow of the feed pump. The system eliminates the pressure flow loss caused by the change of pipe orifice, has good reliability, convenient adjustment, and saves energy. The control system can well meet the requirements of production process, and realize the soft start of feed pump motor at the same time. After the transformation, the power incoming line of #1 feed water pump is connected to the outgoing line of the original #1 feed water pump switchgear, and the power incoming line of #2 feed water pump is connected to the outgoing line of the original #2 feed water pump switchgear; The control power is supplied by 400vgt/st-mcc power supply of the unit

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