light industry

Abstract:
The electricity consumption accounts for 40% of the total electricity consumption of oil field, the operating efficiency is very low, the average running efficiency is only 25%, the power factor is low, and the power consumption is large. Therefore, the oil pumping unit energy saving potential is very huge, the oil industry is also promoting the "motor system energy saving" of the key industries. This paper introduces the use of frequency control technology, so that the movement of the pumping unit to adapt to the changing conditions of the oil well, to achieve the efficiency of the system, to achieve the purpose of energy saving.

 

一．survey
Oil pumping unit is the main equipment in the production of oil production, the number of which is more than 100 thousand units. Motor installed capacity of 35 million KW, the annual electricity consumption of more than ten billion degrees. Oil pumping unit power consumption accounts for about 40% of the total electricity consumption in oil field. The operating efficiency is very low, the average running efficiency is only 25%, the power factor is low, and the power consumption is large. Therefore, the oil pumping unit energy saving potential is very huge, the oil industry is also promoting the "motor system energy saving" of the key industries.

 

二．Several benefits of pumping unit frequency conversion
1, greatly improve the power factor, (0.25 ~ 0.5 increased by more than 0.9). The power supply current is reduced, thereby reducing the load of the power network and the transformer.
2, the dynamic adjustment of the extraction rate, on the one hand, energy saving, while increasing oil production.
3, to achieve truly "soft start" on the motor gearbox oil pumping machine, avoid excessive mechanical impact, to extend the life of equipment.

 

三．Oil pumping unit load analysis
1, the most widely used in the domestic application of beam pumping oil pumping unit, which has three parts:
1) the ground part: by motor, reducer and four link;
2) underground part: oil pump (suction valve, pump barrel, plunger and oil drain valve), it is hanging in the lower end of the casing;
3) sucker rod string: connecting the ground pumping unit and the middle part of the underground oil pump.
2, oil pumping unit motor load is according to the cycle of change, began to start, the load is very large, requires a lot of torque. The load rate of the normal operation is very low, generally around 20%, when the load rate is only 30%. The motor load curve has 2 peak, were dead pumping up and down stroke "".
Under the conditions of balance, the upper and lower stroke of the load is extremely uneven, in the last stroke, the need to mention the pumping rod and liquid column, the motor is required to pay a lot of energy. In the next stroke, the sucker rod string to the motor, so that the motor is in the power generation state. The balance block is usually added to the crank of the pumping unit, and the unbalance of the upper and the lower stroke load is eliminated. Balance block to adjust the good, the power state of time and energy on the small, due to the pumping load is every moment in change, balance weight, it is not possible to pumping load with exactly the same changes, most of the oil pumping machine counterweight imbalance leading to large impact current, impact current maximum but five times the current, even to 3 times of the rated current. Adjust the balance weight, can reduce the impact current is 1.5 times the normal operating current.
Load characteristics: constant speed operation, because of the balance weight is variable torque and power load power state two times in a cycle, starting torque, inertia. In domestic oil field, the use of pumping unit is a common problem: long running time, "big horse drawn cart", low efficiency, high energy consumption, stroke and stroke adjustment is not convenient, there is time and space pumping phenomenon.

 

四．Difficulties in the transformation of the traditional oil pumping unit frequency converter
Oil machine frequency conversion energy saving transformation has done a lot of attempts, but are not quite successful, the main problem is that:
1) pumping unit in a working cycle, two power state, especially when the counterweight imbalance, produced the "pump up voltage is very high, by increasing the electrolytic capacitor in the DC side of the converter and decreasing the value of the braking resistor, can not completely solve the problem, and with the change of reservoir," pump up voltage is also changing.
2) the starting torque of oil pumping unit is larger, such as the parameter of inverter is not set properly, which is easy to be built or can not be started.
3 in the past, the design scheme of frequency conversion and energy saving reconstruction has seldom considered the change of oil surface and oil concentration in oil well. In terms of increasing production, the effect is not good.

 

五．Solution
Oil pumping unit frequency conversion of the existing problems, I put forward the following solutions:
1) using variable frequency speed control technology, the motor speed and pump load matching. In the early stage due to the just exploitation, the amount of oil, so that the inverter to run to 65HZ, motor speed increased by 30%, the oil recovery rate of 20%, the work efficiency increased by 1.2 times. In the middle and late stage, the oil is reduced, the speed is reduced, the stroke is reduced, and the general frequency runs to between 35 and 40HZ, and the speed of the motor is reduced by 30%. Power saving rate is up to 25%, and the power factor is improved.
2) are dynamically regulated pumping oil machine stroke frequency, with the extraction of oil from the shallow to the deep, gradually decreases with the amount of oil, pump is insufficient, the drop of the pump efficiency, when the oil supply capacity is less than the pump displacement oil pump, causing pump evacuation and liquid hammer. Reduce the frequency, motor speed drop, improve the full degree, not only energy saving and increase the yield of crude oil.
3) are dynamically regulated oil machine speed in the down stroke of the pump, appropriate to reduce the down stroke speed, improve the pump fullness, an appropriate increase in the speed of travel, a decrease in ascension leakage coefficient, the pumping oil machine work in the best running state, effectively improve the oil yield per unit of time.
4) the starting torque is big, the load in operation is low, and the impulse current is large.
To fundamentally solve the problem, increase the number of motors or increase the number of gear box ratio, increase the output torque. Converter normal operation 80 ~ 90HZ. This is also conducive to reducing the power generation state energy, reduce the pump voltage".
5) the treatment of renewable energy
Increase the DC side filter capacitor capacity; reduce the value of the braking resistor, improve the power consumption of the braking system, or direct the use of regenerative braking, reduce energy loss; power generation, the frequency increases.
6) air defense pumping, increasing production. Dynamic adjustment of pumping unit stroke frequency and upper and lower travel speed. Set the motor output power standard value, real-time detection of motor output power, control motor speed, greater than the standard value, acceleration. On the contrary deceleration, to achieve closed-loop control.

 

六．Concluding remarks
Due to the different types of oil well and conditions vary widely, downhole of oil seepage and seepage water every time are changing. Pumping oil machine load change is no rules of, so the use of variable frequency speed control technology, the pumping oil machine movement adapt well condition changes, improve system efficiency, up to the purpose of increasing production and saving energy.