Foreword: In the operation and production process of oil depots, oil transfer pumps are the most frequently used equipment in the entire production system. Most oil transfer pumps in oil depots use star-delta start, because the star-delta start method affects the motor and oil pump. The increased impact has caused many weaknesses such as accelerated wear of the oil pump bearings and increased noise. The following is the field data obtained by the company during the transformation of China Coal’s Qinhuangdao Storage and Transportation Centralized Ao Oil Depot for oil delivery.
1. The current operating status
of the 37KW oil transfer pump of the Hua’ao Oil Depot The oil transfer pump of the Hua’ao Oil Depot consists of 4 37KW vertical oil pumps, which are mainly responsible for 8 oil filling points in 4 workbenches to carry out metering and filling of oil to the oil truck. The pipeline design output flow of each oil filling point is 60 cubic meters per hour, and the 37KW oil pump has a flow rate of 180 cubic meters per hour. One oil pump is responsible for the oil filling tasks of one workbench and two oil filling points (respectively No. 1 valve and No. 2 valve, the valve is opened to fill the tanker with oil); and in actual production and operation, only one oil delivery valve is opened most of the time. The two tankers are loaded with very little oil at the same time. The original design of the 37KW fuel pump was two The oil truck is designed to work at the same time, but when a valve is opened, it must work at full load. When working at full load, the output flow of the oil pump can reach 180 cubic meters per hour, and only one third of its flow is needed in actual use. To meet the production requirements, through the analysis of the working principle of the entire oil delivery system, the original oil delivery pump operation principle has the following problems:
1. The output flow of the 37KW oil delivery pump is too large, and only the oil delivery pump is needed when opening an oil delivery valve. One-third of the flow, the oil pump runs at full load of 180 cubic meters every time it is turned on, so that the oil pump and the pipeline produce a large pressure difference, forming eddy pressure. When the pipeline pressure difference increases, the motor load increases and the current rises, causing Electricity wasted.
2. Due to the large output volume of the oil pump and the small actual pipeline delivery volume, in such a working environment, a large amount of useless power consumption is generated during the operation of the oil pump, which greatly shortens the service life of the oil pump motor and increases equipment maintenance costs. Based on the above work background, it is necessary to upgrade the energy-saving operation of the oil pump motor system, use the frequency converter governor to run the oil pump to obtain adjustable flow and pressure, and automatically control the oil pump system according to the actual demand flow and pressure. .
2. The oil pump system adopts the energy-saving technology principle of variable frequency speed regulation operation. The
original working characteristic of the oil pump is that the motor starts running at 50Hz, the speed is 1420r/min, the output flow is 180 cubic meters, and the speed is proportional to the flow pressure, as shown in the figure.
We can see from the above figure that the flow rate decreases with the decrease of the speed of the oil pump motor through the change of the oil pump motor speed. Therefore, only by using the inverter can the speed of the oil pump motor become freely adjustable, and at the same time, the flow rate and pressure of the oil pump can be adjusted. Adjust, through frequency conversion adjustment to meet the existing production process requirements. We use the Linko LK600P series oil pump special inverter produced by Beijing Zhongda Linko Electric Co., Ltd. to improve the working characteristics of the oil pump, and make full use of the speed control function of the inverter to achieve adjustable flow and pressure, and adjust the motor at will The speed is used to achieve the goal, and it also saves electricity and the service life of the oil pump motor. Environmental protection and energy saving are the original intention of this project.
The energy-saving basis for the operation of the oil pump through the frequency conversion? — The working principle of the frequency conversion is not described in detail here. We can see through the comparison of the following chart that the motor speed changes during the frequency conversion operation, and the motor load current also changes. Of course, due to the reduction of the motor speed, the output voltage of the inverter is also reduced, and the load current of the oil pump is also reduced through the reduction of the voltage. The data described below is the actual data measured by our company on-site motor operation. Figure 2: The table shows the motor load current when the 37KW oil pump is operating at power frequency. Table 1: The speed of the oil pump motor, the motor operating current and the flow change at any speed when the 37KW oil pump is operating at a variable frequency. Table 1: Variation values of load current and flow at different speeds when the 37KW oil transfer pump is operating in frequency conversion. Oil pump motor model power frequency operation current (A) motor speed during variable frequency operation (Hz. r/min) oil pump actual load current (A) oil pump output flow (cubic) Y225M-4 37KW 74A 50Hz-1420r/min 74A 173 45Hz -1278r/min 61A 158 40Hz-1136r/min 51A 123 37Hz-1050r/min 49.5A 117 35Hz-994r/min 48A 110 33Hz-937r/min 47.5A 107 30Hz-852r/min 45A 90 25Hz-710r/min 43A 71 20Hz-568r/min 43A 40
Field data: One 37KW oil pump in Huaao Oil Depot supplies one workbench with two oil injection valves. One oil injection valve is designed to output 60 cubic meters. When the two are opened at the same time, the flow rate is 120 cubic meters, which can meet the production requirements. Requirement, how to realize an oil injection valve to open, the inverter only needs to output an accurate flow of 60 cubic meters? Explain in detail in the following solutions. When filling oil for an oil truck, the inverter runs at 25Hz, the motor current is 43A, and the current can be saved by 51A, and the power saving rate is below 60%. When the two oil filling valves are opened to fill the two oil trucks, the working frequency of the inverter is 35Hz, the motor current is 48A, the current saving is 26A, and the power saving rate is below 40%.
From the above list and on-site data to break down the working principle of the existing oil pump in the Qinhuangdao Storage and Transportation Centralized Ao Oil Depot, I can see the role of the frequency converter in the operation of the oil pump. The motor speed of the oil pump is controlled by the frequency conversion. The oil pump outputs a reasonable flow and pressure to meet the production requirements, while also greatly reducing the load current of the bottom motor, which is very energy-saving.
3. Inverter control mode
The function of the frequency converter is to provide a variable frequency power supply for the motor to realize the stepless speed regulation of the motor, so that the oil pressure of the pipe network can be continuously changed. The task of the pressure transmitter is to detect the flow and pressure of the pipe network. The setting unit of the flow and pressure provides the system with the expected value of the flow and pressure that meets the needs of users. The flow and pressure setting signals are input to the inverter through the 4-20mA current feedback signal, and then calculated by the inverter’s internal PID control program, and output to the inverter a speed control signal. The inverter starts to work when it receives the 4-20mA current signal. , First start the oil pump motor to make the pipe network flow and oil pressure reach the set value, and then when the output frequency of the frequency converter reaches the peak with the flow and pressure, the frequency of the frequency converter starts to decrease until the pipe network pressure and flow delivery are kept in line with the production Within the required predetermined value required. When the oil delivery volume increases or the pressure of the pipe network decreases when the two oil outlet valves are opened, the pressure transmitter will process this signal into a 4-20mA signal and send it to the inverter. (Note: The inverter is based on the 4-20mA current value. To determine the size of the output frequency, the size of the frequency is the high and low speed of the motor), the frequency of the inverter starts to rise, so that the output frequency of the inverter rises, the speed of the oil pump increases, and the flow and pressure rise accordingly. If the output flow of oil injection increases a lot, The output frequency of the inverter will reach the maximum value of 50Hz. Based on the above, the built-in PID control of the inverter can make the entire oil supply system more operability and greatly reduce the labor density. Because the electrical system of the entire Hua’ao oil depot uses a host computer for centralized control, the oil pump motor is started by soft start, and the start and stop of the oil pump are centralized control and machine-side control respectively. The console is two solenoid valves. The solenoid valve is switched on and off to fill the oil truck. The Mies solenoid valve has the functions of flow measurement and pressure transmission, which can provide a 4-20MA transmission signal output for the inverter, and the pressure transmission value can be set freely. , The set transmission value corresponds to 4-20MA output. When the 4-20mA signal input interface of Linko Inverter receives the current signal transmitted by the pressure transmitter, according to the size of the signal source and then through the built-in PID control calculation of the inverter, it can automatically and completely make the oil pump at the predetermined flow pressure In-house work to meet the production process requirements of this production line.
Fourth, the system plan
In the operation and production process of the oil depot, the oil transfer pump is a very important production equipment in the entire system. The inverter is required to operate continuously for a long time, and it must have extremely high reliability in addition to the required performance. Understand the characteristics of the on-site production process. Combined with this design plan, this system should be designed to adapt to on-site operation performance, and be fully compatible with the original electrical system, so as to keep the original control characteristics unchanged; this system is designed with the following functions:
1. Frequency conversion system The power frequency soft starter system with the original power cabinet can be switched freely manually. Once the frequency conversion system has a certain failure, you can manually switch to the power frequency soft start of the original power cabinet. During the maintenance of the frequency conversion system, the original soft starter system can normally guarantee the operation of the oil pump and meet the normal production of the oil depot.
2. The operating frequency of the variable frequency system is adjusted using PID closed-loop control loop mode. The output frequency of the inverter is determined according to the flow pressure and the 4-20mA signal. This ensures the safe operation of the oil delivery system and makes the entire system more convenient to operate. , Intelligent automation is stronger. 3. Considering the on-site working environment and the safety of the equipment, the panel of the frequency conversion control cabinet should not be equipped with too many Display devices. Only the soft starter and the frequency conversion switch, the running indicator light, the frequency conversion operation fault light, and the frequency conversion operation display panel should be configured. The operating parameters, motor current, and motor speed of the inverter are clear at a glance, which greatly facilitates the operation of the on-site operators and the monitoring of the operating status of the equipment.
4. The frequency conversion system is set with a 6-digit password, which can lock and protect the operating parameters of the frequency converter to ensure that the frequency conversion oil delivery system does not cause the oil delivery pump to stop due to human error operation, and realizes the continuous and stable operation of the system.
5. The inverter uses independent wiring for power supply to prevent electromagnetic interference to the equipment and ensure the safe operation of the equipment.
6. The frequency conversion system implements soft start and soft stop for the oil pump motor, which reduces the impact on the power grid during the startup process, improves the quality of power supply, and also extends the maintenance cycle of the oil pump motor. The motor speed is reduced compared with the original after using the frequency conversion. , Low-speed operation will reduce the wear of oil pump shafts and bearings, which will greatly extend the life of oil pump bearings, mechanical seals and other wearing parts.
5. Project cost
This project consists of 4 sets of 37KW oil pumps, and the frequency converter uses 4 sets of 37KW Linko LK600P series oil pump special frequency converters. The cost of the whole project is as follows: Serial number, product model, quantity, unit price RMB, total amount RMB, total project cost RMB 1 Linko LK600P- 037T4 37KW inverter 4 17800.00 71200.00 129900.00 2 Frequency conversion cabinet GPT 4 4300.00 17200.00 3 Air switch, contactor, display panel, transfer switch, indicator light, smart feedback card 4 5300.00 21200.00 4 Control wire and main motor cable 1 12000.00 12000.00 5 Field wiring Construction cost 1 8300.00 8300.00
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