The conventional screw pump lifting method has problems such as low transmission efficiency of the ground drive device, high repair costs for damaged reducers, and potential safety hazards in the transmission device. To solve this problem, DC motor direct-drive screw pump technology has been tested and applied. This article introduces the direct-drive type Principle, structure and characteristics of screw pumps. Analyze current energy-saving potential in screw pumps. Since the magnetic field of the motor rotor of the DC motor direct drag screw pump ground drive device is based on the permanent magnet principle, there is no need to absorb reactive power from the power grid, so the power factor is close to 1. Compared with ordinary ground drive devices, the average power saving rate is 26.5%. Direct drive The device operates smoothly, can achieve stepless speed regulation of the motor, is easy to operate and manage, reduces ground drive production and maintenance costs, and has obvious energy-saving effects.
In recent years, with the gradual improvement of screw pumps and related supporting technologies, they have been widely promoted and applied in oil fields. The currently commonly used screw pump lifting method has problems such as low transmission efficiency of the ground drive device, high repair costs for damaged reducers, and potential safety hazards in the transmission device. To address this situation, we have experimented with DC motor direct drag screw pump ground drive technology. This ground drive device has obvious effects in energy saving and is simple and convenient to operate on-site. The motor works under the control of the driver program and can automatically realize functions such as soft start, soft stop, and electromagnetic braking. At the same time, the safety performance is also greatly improved. The direct-drive screw pump drive device eliminates the mechanical reducer and belt of the ground drive device, reducing the number of transmission devices and reducing the ground failure rate.
The application of a direct-drive screw pump drive device further improves the reliability of the drive system and meets the drive system requirements of the screw pump under different working conditions. It improves the supporting process technology of the screw pump and is of great significance to the popularization and development of the screw pump.
1. Principle and characteristics of direct drive screw pump
Compared with the mechanical type, the direct-drive screw pump driving device eliminates the reduction mechanism of the original screw pump, reduces the transmission links, and has higher transmission efficiency. The polished rod is directly driven by the electric motor. The electric motor is a permanent magnet synchronous motor and is controlled by a variable frequency speed regulating device. Control, the motor operating power factor is 1, the entire drive system is efficient and energy-saving, and the average power saving rate reaches 25%.
The direct drag screw pump ground drive system is mainly composed of a polished rod square clamp, mechanical seal, drive motor, load-bearing bearing box and well sealing device. The polished rod passes through the hollow shaft of the motor and is connected to the hollow shaft of the motor through a square clip. The rotor of the motor is cast with magnetized permanent magnets. In order to detect the polarity of the motor rotor, a position sensor is installed in the motor. Its function is to accurately detect the position of the rotor and send the position signal to the intelligent computing and logic control part. , DC voltage is applied to each phase of the motor in sequence, and the magnetic field generated on the motor stator interacts with the rotor’s permanent magnetic field to cause the rotor to rotate.
2) Technical features and advantages
The permanent magnet brushless DC motor uses an electronic commutation device to replace the mechanical commutator of ordinary DC motors, which solves the problems of sparks caused by the commutation of ordinary DC motors. It has the advantages of simple structure, reliable operation and easy maintenance, and is very suitable for Load characteristics of screw pumps.
(1) The power factor is high.
The magnetic field of the motor rotor is a permanent magnet and does not need to absorb reactive power from the power grid, so the power factor is close to 1 and the energy-saving effect is significant.
(2) Good speed regulation performance.
It realizes step-less speed regulation of the motor, and the speed can be adjusted arbitrarily from 0min-1 to 200min-1, which is more convenient and stable than the frequency conversion speed regulation method.
(3) Good operating stability.
The centre of gravity of the direct drive device coincides with the polished rod, and the centring is good. Compared with the motor side-mounted device, the stability of high-speed operation is better.
(4) The motor has a large starting torque.
The starting torque can be 3 to 4 times the rated torque, ensuring the smooth start of the screw pump.
(5) Reliable anti-reversal system.
It consists of three stages: electromagnetic containment, overvoltage release and energy consumption braking. Braking is an energy-consuming braking method. When stopped, the elastic restoring force of the polished rod causes the polished rod to reverse, thereby driving the motor to reverse. The braking resistor is put in time to consume the motor’s reversal energy, thereby suppressing the motor’s reversal and making the system run more efficiently. Safe and reliable.
2. Energy saving effect analysis
The new direct-drive screw pump is more energy-efficient than the traditional mechanical screw pump.
1) The motor itself has low efficiency and consumes a lot of energy in a single well. When the output power is constant, the required input power is high and the energy consumption is high. The efficiency of induction motors with several kilowatts is generally around 0.7, while the efficiency of DC synchronous motors can reach 0.8-0.9.
2) Low power factor and large line loss are inherent shortcomings of AC motors. The magnetic field of the motor rotor of the DC motor direct drag screw pump ground drive device is a permanent magnet, so there is no need to absorb reactive power from the power grid. The power factor is close to 1, and the average comprehensive power saving rate reaches 26.5%.
3) There is a loss in the mechanical reducer part. The induction motor itself has a high speed. When the screw pump needs to be driven at low speed and high torque, only a mechanical or belt reducer can be installed. The efficiency of general mechanical reducers is 0.85-0.95. The DC motor direct drag screw pump ground drive system simplifies the driving part of the original mechanical screw pump on the ground. It does not require a reduction gearbox and a belt drive device. It can achieve step-less speed regulation of the motor, is easy to operate, and reduces ground drive production and maintenance costs.
The traditional mechanical screw pump motor efficiency is 75%, the belt efficiency is 92%, and the gear reduction is 92%. The drive system efficiency is only 63.5% (75% × 92% × 92%). Direct-drive screw pump drive system, the rotor is a permanent magnet type, and the cosΦ=1 control method alone has almost no excitation loss. The rated efficiency can reach 91%, and the efficiency can reach more than 88% at a 1/3 load rate. Compared with asynchronous motors, the motor efficiency is increased by about 10%. Calculated based on the permanent magnet motor efficiency of 88% and the brushless DC controller efficiency of 95%, the efficiency of the direct-drive screw pump drive system is 83.6% (88% × 95%), while the traditional mechanical type is only 63.5%, an increase of 20%.
3. Application and effect of direct drive screw pump
So far, the plant has replaced a total of 63 screw pump direct drive devices in 63 wells, of which 12 wells have changed from oil pumping units to screw pumps, and 51 wells have replaced ordinary screw pump drives with direct drive devices. The statistical test data shows that the power consumption dropped from 7.32 kW to 5.13 kW, a drop of 2.19 kW, the average power consumption per ton of liquid per 100 meters dropped from 1.02 kWh to 0.75 kWh, a drop of 0.27 kWh, and the average comprehensive power saving rate reached 26.5%. The energy-saving effect is obvious.
The two replacement methods were compared respectively. By comparing the energy consumption data of 12 wells before and after the replacement from pumping units to screw pumps, the power consumption dropped from 7.93 kW to 5.50 kW, a decrease of 2.43 kW, per ton of liquid. The power consumption per 100 meters dropped from 1.17 kWh to 0.72 kWh, a decrease of 0.45 kWh. The average comprehensive power saving rate reached 38.5%. The application of a screw pump direct drive device has a significant energy-saving effect compared with the pumping unit lifting method.
Comparing the energy consumption data of ordinary screw pumps before and after replacing the direct drive, the power consumption dropped from 6.39 kW to 4.03 kW, a decrease of 2.36 kW. The average power consumption per ton of liquid per 100 meters dropped from 0.97 kWh to 0.76 kWh, a decrease of 0.21 kWh. The average comprehensive energy-saving rate reaches 21.6%, and the screw pump direct drive device also has a very good energy-saving effect compared with ordinary drives. After replacing the ordinary screw pump driving device with a direct drive device, a detailed classification and comparative analysis were conducted on different levels of pump types. According to statistical data analysis, small pump types and low-yield liquid wells have better energy-saving effects than large pump types and high-yield liquid wells. The power saving rate is relatively high.
Production and energy consumption of G36-Pl well before and after replacement: production at 70 rpm before replacement, pump depth 898 meters, pump type 1200, daily liquid production volume 1177 cubic meters, water content 99%, current 67 amps, annual power consumption after testing 24.5 Thousands of kilowatt-hours. After the on-site operation test of the direct-drive screw pump, it has been shown that it has outstanding advantages. It perfectly combines the advanced step-less speed regulation drive system with the screw pump, making the oil well operation safer and more intelligent, and raising the screw pump oil production technology to a new level.