The application of Yaskawa inverter in the petroleum industry

1 Introduction

Over the years, Yaskawa has accumulated very rich experience in the petroleum industry, such as G7/P7/F7/G5/P5/G5HHP/VS and other different series of inverters have been widely used in OEMs, at present, the main fields are centrifugal separators, pumps, fans, conveying equipment, metering equipment, compressors, etc.

Yaskawa inverters used in the petrochemical industry have the following characteristics:

(1) Its NEMA 3R package is designed to withstand the harsh environments common in oilfields;

(2) Its dedicated customized driver software CASE can work very effectively on reciprocating loads such as kowtowers, so that there is no need to use energy-hungry dynamic braking resistors;

(3) Its excellent hardware design and PC board spraying process make the inverter work normally in harsh environments such as oil fields and occasions with high vibration rate.

This article mainly introduces several typical cases of Yaskawa in the oil industry.

2. Realize energy saving and consumption reduction of decanter centrifuge

In the petroleum industry, decanter centrifuges are often used to handle processes such as crude oil dewatering and sludge separation, and Yaskawa inverters have been successfully applied to DERRIC's DE-1000 series decanter centrifuges, and have achieved the effect of energy saving and consumption reduction.

The principle of the decanter centrifuge is shown in Figure 1, the material enters the centrifuge from the feed port, the cylinder and the spiral rotate at the same direction at low differential speed and high speed, so that the solid phase and liquid phase of the material are separated, the solid phase of the heavier particles is centrifuged to the cylinder wall and pushed out of the cylinder by the spiral, and the solid phase or liquid phase of the lighter particles is discharged from the other end of the pipe.

The application of Yaskawa inverter in the petroleum industry

　　In the left figure of Figure 1, the load that the main motor drags is the cylinder, and the load that the auxiliary motor drags is the spiral, because in the normal operation, the speed of the main motor is always higher than that of the auxiliary motor, the auxiliary motor works in the power generation state for a long time, and the traditional method adopts eddy current braking with serious energy consumption, and it is equivalent to the speed regulation difference of the braking system. Obviously, putting this part of the energy to good use is very impressive.

Yaskawa's scheme is based on the co-connection of the inverter bus, and the electric energy of the auxiliary motor is consumed into the electric state of the main motor through the bus bar between the two inverters, so that the energy is shared between the inverters through the busbar, which greatly improves the stability and reliability of the system, and at the same time can reduce energy consumption, saving 20%-40% compared with the traditional eddy current braking energy consumption. Yaskawa's GPD 515/G5 uses a vector operation method, and by installing an encoder, it is possible to accurately control the differential speed and provide sufficient torque in the event of material jamming.

The main features of the decanter control system with Yaskawa frequency conversion control are as follows:

(1) The human-machine interface HMI (generally using PC-BASED system) is used as the host for control, including DeviveNet communication between inverters, bus voltage monitoring, reading and writing of parameters of each inverter, and control of each point of feeding, etc.;

(2) The main motor adopts GPD 515G5 inverter to control the operation of the cylinder, because it works in the vector control mode, it can provide a large enough starting torque to overcome the inertia of the cylinder and start smoothly;

(3) The auxiliary motor also adopts GPD 515G5 to control the screw to run at a speed lower than the main motor, and the speed difference between the screw and the drum can be automatically adjusted according to the change of the feeding, and in the case of blockage, the screw can provide enough torque to push the material out, empty and run again;

(4) The regenerative energy is processed by the common bus mode, and the magnitude of the regenerative energy depends on the speed of the cylinder and the speed difference between the cylinder and the spiral;

(5) The coating design of the inverter circuit board and the explosion-proof motor can make the system work stably in the harsh environment of the oilfield, such as water vapor, corrosive gas, accidental vibration, etc.

Through applications in many oil fields around the world, decanters equipped with Yaskawa GPD series inverters have achieved remarkable results. The output of oilfield crude oil dehydration has been increased tenfold, because this type of centrifuge can run for a long time without failure, for the change of materials, the inverter can easily overcome and can be freely adjusted output; Due to the energy saving, environmental protection and convenient speed regulation of frequency conversion speed regulation, it can solve the problem of energy consumption and heating of eddy current braking and the leakage problem of hydraulic drive, and the transmission parts can be replaced by standard parts, so the decanter centrifuge can achieve maintenance-free operation; The application of the fieldbus DeviceNet makes it easy to set up and monitor the frequency converters, and the user only needs to get all the drive operation data and set the corresponding process data on the HMI. To realize the pressure PID control of the oil pumping station, the pipeline oil transportation is to pressurize and heat the crude oil (or oil products) through the oil pipeline from one place (generally oil field) to another place (generally refinery, wharf, etc.). The purpose of pressurization is to provide kinetic energy for crude oil to overcome the geographical difference along the route and the pressure loss along the pipeline; Heating is a measure taken for the "three high" crude oil with "high wax content, high freezing point and high viscosity", so that the temperature of the crude oil in the pipeline is always above the freezing point or higher to make the crude oil flow smoothly. To realize the long-distance transportation of crude oil, there must be two parts: oil stations and lines. The oil station includes oil pump units, heating equipment, metering and testing, communication equipment, oil storage tanks, etc.

Here's an example of how Yaskawa drives VS616P5 can be used at a Tulsa oil pumping station in Oklahoma (Figure 2). The main pump of the pumping station is a 110kW reciprocating pump, which pressurizes crude oil from nearby production points and sends it to a refinery several kilometers away.

　　In the original control scheme, the pressurized pumping station realizes simple pressure control through a programmable controller, that is, the pump is opened when the pressure is low and the pump is closed when the pressure is high. Frequent start-stop actions will have a strong impact on the power grid for large-load motors, and also have a certain damage effect on crude oil pipelines. Due to the simple on/off control, the pressure of transporting oil is unstable and the pressure fluctuates greatly, which causes certain difficulties in the process control of the gathering and transportation system of crude oil. At the same time, the amount of maintenance caused by frequent switching to valve parts and pipelines is increasing day by day, and in serious cases, large tank evacuation, pipeline blockage and crude oil tank accidents will occur, which will bring a lot of waste to production. In order to solve these contradictions, the introduction of frequency conversion speed regulation technology in the existing crude oil gathering and transportation network to automatically track and adjust the operating status has received good results.

In this pressurized pumping station, the original main pump is dragged by Yaskawa inverter, and the pressure can be easily controlled by using the PID function integrated in the inverter. As shown in Figure 2, the pressure sensor signal installed at the end of the user's pipeline goes directly to the FV or FI end of the inverter, and the inverter automatically calculates the difference from the set value before controlling the output of the inverter.

After using the frequency converter, the pumping station not only significantly reduces the mechanical loss and maintenance, but also greatly reduces the impact on the power grid, from the original direct start of the motor current 600%-800% to about 150%, and the power factor has also increased to about 98%. Due to the PID control, the operating speed of the motor is no longer idling at full speed, but the speed is reduced, and the average operating current is reduced from more than 160A to about 116A (about 30% reduction).

Due to the potential high pressure problems of oil transmission pipelines, users have to install pressure sensors that are 10 times higher than the conventional pressure standard, so the effective area of the actual sampled voltage value is very narrow, and only the high-precision pressure sensor can be controlled normally. At the same time, the inverter must effectively tune the dragged load to adjust the parameters so that the motor and the pump work in the best condition. In order to avoid pipeline resonance effects, it is also necessary to set mechanical resonance points.

3. Realize the flow and pressure control of the centrifugal pump of the water injection station

In the petroleum industry, water injection treatment is often carried out, which is mainly the use of water injection wells to inject water into the oil layer to supplement and maintain the pressure of the oil layer is called water injection. After the oilfield is put into development, with the growth of the production time, the energy of the oil layer itself will be continuously consumed, resulting in the continuous decline of the oil layer pressure, a large amount of underground crude oil degassing, viscosity increases, the production of oil wells is greatly reduced, and even the blowout will be stopped, resulting in a large amount of residual dead oil in the underground can not be recovered. Therefore, in order to make up for the underground deficit caused by crude oil recovery, maintain or increase the pressure of the oil layer, achieve high and stable production of the oilfield, and obtain a high recovery rate, it is necessary to inject water into the oilfield.

In the pump configuration of many oilfield water injection stations, the power is very large, usually using power frequency pressure reduction start, and most of them use centrifugal pumps, through the throttle valve to control the flow. We know that the use of frequency converters in centrifugal pumps has a very large potential for energy saving, so when the pump design margin is sufficient, it is the best way to adopt frequency conversion speed regulation. With Yaskawa F7, energy-saving operation and suppression of higher harmonics can be easily achieved. In the operating range of the F7's energy-saving control, it can exert excellent energy-saving effect on centrifugal pumps according to the maximum efficiency control.

There is a huge potential for energy saving in the transformation of frequency conversion speed regulation of centrifugal water pumps, and we have applied the F7 frequency converter to the water injection station pumps, and the practice has proved that its energy saving effect is 30-50%, sometimes as high as 70%. Why is there such an amazing energy saving in centrifugal pump equipment to adjust the flow rate through frequency conversion speed regulation? Here's how it works. As shown in the attached table, the flow rate of a centrifugal pump is proportional to the rotational speed (Equation 1), the pressure is proportional to the square of the rotational speed (Equation 2), and the power is proportional to the cubic of the rotational speed (Equation 3). Therefore, if the flow rate is reduced by 20%, the power consumption will be reduced by 50%. However, it must be noted that the speed is squared to the pressure, and when the speed drops by 20%, the pressure will drop to 64%, so it is necessary to pay attention to the process requirements.

Usually centrifugal pump equipment is controlled by traditional air volume and flow damper, and a large amount of energy is consumed on the resistance of the damper or shut-off valve, and the relationship between the power consumption and flow rate of the damper or shut-off valve control flow is shown in (Formula 4). Comparing the control of the shut-off valve and the frequency conversion speed regulation, it can be seen that in the range of flow changes, the method of frequency conversion speed regulation has great energy-saving potential, so the frequency conversion transformation on other water supply pumps in the oilfield will also achieve great energy-saving effects.

4 Concluding remarks

This article focuses on several typical applications of Yaskawa inverters in the petroleum industry, which can easily adjust the motor speed and save energy consumption to a certain extent, which is very suitable for use in the harsh environment of oil fields and chemical environments.

The application of Yaskawa inverter in the petroleum industry

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