Devices for automatic control of the quantity and quality of oil in tanks

Currently, the most widely used devices for measuring the level of liquids (float and non-float). Float gauges are generally more accurate than non-float gauges. However, the operating conditions of float level gauges are much more difficult due to the difficult operating conditions of floats in an aggressive environment with a large amount of mechanical impurities. Automation tools used to measure the weight of oil and oil products should provide output information in a form convenient for further processing, at the same time, these devices should be structurally simple and applicable to existing types of tanks. The amount of oil in tanks can be determined in two ways: by measuring the level of oil and its specific gravity; by direct measurement of the weight of a liquid. Each of these methods has its own advantages and disadvantages. Currently, the most widely used devices for measuring the level of liquids (float and non-float). Float gauges are generally more accurate than non-float gauges. However, the operating conditions of float level gauges are much more difficult due to the difficult operating conditions of floats in an aggressive environment with a large amount of mechanical impurities. The choice of this or that device is determined by the specific conditions of its operation, the required measurement accuracy, aggressiveness of the liquid, etc. Limit switches are installed on the level gauge, which, when the liquid level in the tank reaches the upper or lower limit mark, turn on the alarm circuit. The principle of operation of the level gauge is based on measuring the increase in the electrical capacitance of sensors when they are filled with a substance (oil product) that has a dielectric constant that is different from the dielectric constant of air. The measurement accuracy is achieved by the fact that the entire measured level is divided into separate equal sections and is determined, among other factors, by the length of each section.


Introduction
The amount of oil in tanks can be determined in two ways: by measuring the level of oil and its specific gravity; by direct measurement of the weight of a liquid.Each of these methods has its own advantages and disadvantages.
Currently, the most widely used devices for measuring the level of liquids (float and nonfloat).Float gauges are generally more accurate than non-float gauges.However, the operating conditions of float level gauges are much more difficult due to the difficult operating conditions of floats in an aggressive environment with a large amount of mechanical impurities [1].
The choice of this or that device is determined by the specific conditions of its operation, the required measurement accuracy, aggressiveness of the liquid, etc. Limit switches are installed on the level gauge, which, when the liquid level in the tank reaches the upper or lower limit mark, turn on the alarm circuit.The principle of operation of the level gauge is based on measuring the increase in the electrical capacitance of sensors when they are filled with a substance (oil product) that has a dielectric constant that is different from the dielectric constant of air [2,3].
Statement of the problem.The measurement accuracy is achieved by the fact that the entire measured level is divided into separate equal sections and is determined, among other factors, by the length of each section.The device consists of a receiver and a five-digit drum counter that counts the liquid level in the tank.The block diagram of the capacitive level gauge is shown in figure 1.It consists of a block of discrete sensors 1, a distribution block 2, a communication line 3, a measurement block 4, a control and registration block 5, and a power supply 6 [4].
The design of the sensors allows them to be attached to the fittings of the oil gauge glasses of the operated tanks.The sensors are pieces of two pipes of different diameters, located coaxially and isolated from each other by insulating washers.Sensors are grouped on a common pipe.
The pipe with sensors welded to it is inserted into the fittings of the oil gauge cocks.A threaded ledge emerges from the inner electrode of the sensor through an insulating sleeve, to which a filter is attached, consisting of an inductor, an isolation capacitor and a trimmer capacitor.The inductance of the filter, the capacitance of the sensor and the trimmer capacitor form a circuit tuned to the frequency of the generator of the measurement unit.

Results
The length of the section of each sensor is determined by the formula where l is the length of the section (sensor); k -coefficient; δ -permissible basic error.For k = 100, the basic error is acceptable δ = 0.5 cm, at l ≤ 50 cm.Considering that the length of each gauge glass (between the respective fittings) is 1 m, then the number of sensors installed in each section should be n 0 ≥ 2 [5,6].
When manufacturing a level gauge with capacitive sensors, it is assumed that n 0 = 3; thus, 30 sensors were installed on the entire tank.The sensors are connected by a coaxial cable to the stepping finder of the distribution unit, installed at a distance of 10-15 m from them.
The distribution block is a piece of pipe with a flange and a cover.The step finder, when pulses are received from the programming device, alternately connects the sensors to the measurement unit.
The step finder with the measurement unit is also connected with a coaxial cable.To stabilize the parameters of the communication line and reduce additional errors associated with changes in temperature and humidity of the environment, the line is laid in a pipe, and part of the measuring unit to the step finder (distribution unit) is laid in the ground, and from the step finder to the sensor is covered with special thermal insulation.
The device is powered by 220 V AC mains.The measurement unit consists of a 100 W power transformer, a rectifier, and a discriminator generator [7].
An inductive circuit is connected to the anode of the generator lamp through a capacitor, which consists of two high-frequency transformers, the primary windings (L1 and L2) of which are connected in series.Each of the secondary windings L3 and L4 forms a circuit tuned to the frequency Signals from the secondary windings go to the rectifier.The rectified currents are then fed for comparison to the input of an electronic potentiometer in the control unit.Parallel to the windings of the circuit L3 and L4, communication lines, additional inductances of low-pass filters, tuning capacitors and sensors are connected.
The variable load of the L4 winding is the capacitance of the main sensors, which are connected in turn to the winding by a stepper finder.Parallel to the winding L3, a control sensor located on the tank is permanently connected.Line connecting the control sensor with the winding L3, measuring block, has the same length as the line going to the main sensors and winding L4.Both lines are in the same conditions.
The above devices for automatic control of the amount of oil in tanks are based on the principle of measuring its level.Another method for determining the amount of oil in a reservoir is by weight.
The most convenient way to automate the measurement process is the so-called piezometric method (determining the weight of an oil product by its hydrostatic pressure).
Instruments designed for piezometric measurement of the weight of an oil product in a tank are compensatory pressure meters.
The operation of the device is based on the principle of force compensation, and discrete and continuous compensation is used to achieve the required high accuracy.Discrete compensation is carried out by weights, and continuous -by a lever with a movable weight.
As a sensitive element, which compares the measured and compensating parameters, a metal membrane with a rigid center, made of beryllium bronze, is used.The measurement error is mainly determined by the continuous compensation system, since discrete compensation is carried out with a high degree of accuracy.In this case, the total measurement error is the smaller, the more areas of discrete compensation for a given measurement range.
Indeed, if the entire range is divided into n parts, measured with a relative error δ q and continuous compensation is performed with a relative error δ continuous compensation , then the largest total relative measurement error will be Having for the instrument δ continuous compensation = 0.2% and n = 10 and neglecting δ q , because of its smallness compared to δ continuous compensation , we obtain the total compensation error up to δ = 0.02%.Then the accuracy of the device will be determined mainly by the stability of the characteristic and the sensitivity of the pressure element.The membrane used as a sensitive element has a linear dependence of the displacement force on the pressure within 0-1 kg/cm 2 and sensitivity 1-2 mm of water art., which provides the necessary measurement accuracy.The continuous compensation system is designed to create an accurate compensating force during the measurement process.During non-working hours, this system compensates for the weight of the plate, the elastic force of the rigid center, as well as the change in this force due to temperature and other external factors [8].
As noted above, during the measurement process, pulses are sent to dynamic errors from the system of discrete (coarse) and continuous (fine) compensation by the corresponding sensors.These pulses are fed to dynamic errors to the counting devices of the secondary device and the counting result is noted on the electroluminescent display.The block diagram of the secondary device is shown in the figure 2. The device consists of the following blocks: counting decades, decoder, indication, power supply and control.
The block of counting decades is a counter on non-contact triggers and carries out counting of impulses and storing results in the binary number system.
The decoder block, also made on non-contact semiconductor diode elements, decodes the results of the count in the decimal system.The decoded result of the count is transmitted to the display unit, consisting of four identical nodes with luminescent digital indicators (according to the number of decoder matrices), and is marked on it in the form of a four-digit number expressing the reading of the device.
The control unit sends pulses to start and end the measurement.When compensation is reached, the null-organ turns off the lever motor, the counting of pulses stops.
After the pressure is removed, the discrete and continuous compensation systems return to zero.
With the piezometric method, the weight of the oil product in the tank is determined by the formula G = pF av (H), where p is the hydrostatic pressure of the liquid column in the tank (determined by pulse counting), F av (H) -the average area of the tank at a given filling level H.The value of F av is found from the expression where F (h) dependence of the tank section on height h.Value F av (H) variable in height and determined by calibration tables.Thus, to find the weight G oil product with the piezometric method, it is necessary to know the filling height.For this purpose, the tanks must also be equipped with level gauges.However, in this case, the requirements for the accuracy of level gauges are low.Calculation of weight according to the reading of the weighing gauge with correction according to the data of the level gauge is simple and can be reduced to finding the weight according to pre-compiled tables [9].This counting can be performed automatically by adding a computing device to the display unit that performs the multiplication operation.
To improve operational properties, explosion and fire hazard, as well as to simplify the design, the device measures directly the hydrostatic pressure of the oil product, and to it the air pressure supplied by the hydrostatic pressure transducer.
Thus, the process of measuring moisture content with the device is divided into two stages: 1) obtaining dehydrated oil (standard); 2) comparison of the dielectric constants of dehydrated oil (reference) and oil containing water.
Upon receipt of the standard (dehydrated oil), the investigated oil in the amount of 1 liter is placed in an autoclave and heated to a temperature of 170-180 °C.
The pressure in the autoclave is 7-8 kg/cm 2 .Studies have established that this mode achieves the best separation of water and oil without changing its chemical properties.
To speed up the process of preparing the standard, forced cooling of oil in an autoclave is used.To do this, water is passed through a coil located inside the autoclave.Cooled to 38 °C, the oil enters the centrifuge, where the water is finally separated from the oil [10].

Conclusion
The article also deals with the design of sensor transducers for measuring various nonelectrical quantities, as well as methods and devices for obtaining and processing measurement information.
The use of devices allows you to automate the process of pumping oil and the most important technological parameter -the dynamic level, which is especially important for marginal wells.In the experience, electrical automatic control devices, a variety of designs and schemes of measuring instruments were developed and applied.
Depth parameters of the wells, received the technological parameters of the drilling process and the geometric parameters of the wells.I obtained the greatest possibilities for controlling deep parameters during electric drilling, since the power channel connecting the deep-seated electric motor with surface equipment is at the same time a reliable communication channel for telemetry of deep parameters.
In the technological parameters of the electric drilling process, we obtained: the pressure of the tool on the bottom hole, torque, voltage on the downhole electric motor, the temperature of the clay solution, the temperature of the bottom hole, etc.
In this regard, during electric drilling, it is possible to control a complex of technological and geometric parameters of the drilling process and at the same time perform geophysical surveys of wells.

Figure 1 .
Figure 1.Block diagram of a discrete capacitive level transmitter.

Figure 2 .
Figure 2. The block diagram of the secondary device.