RU2707124C1 - Method of measuring oil products mass flow in a pipeline - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement equipment, in particular, for measurement of mass flow rate of liquid petroleum products pumped via pipelines in a flow in a wide range of flow rates, as well as for determination of the type of oil product to be measured. Technical result is achieved by using for measurement of mass flow of oil products acoustic signals excited by piezoelectric elements in flow direction and back, not requiring direct contact with measured medium, installed with displacement in diametral plane on external surface of pipeline housing and providing higher frequency of measurements to increase accuracy of mass flow rate measurement in transient processes, as well as determination of material type and its density as to reference dependence. Use of this invention improves efficiency of oil refining and oil-filling works due to efficiency of the method, simplifies installation of equipment that realizes it, increases service life of equipment.

EFFECT: measurement of mass flow rate of oil products without disruption of the housing of the pipeline, high accuracy of measurements, high measurement frequency for more accurate measurement of mass flow in conditions of transient processes, determination of the type and density of pumped oil.

1 cl, 1 dwg

Description

The invention relates to measuring equipment, in particular, for measuring the mass flow rate of liquid petroleum products pumped through pipelines in a stream in a wide range of flow rates, as well as for determining the type of measured petroleum product.

Known flow meters, devices that use the Coriolis effect to measure the mass flow of liquids, gases. The principle of operation is based on phase changes in the mechanical vibrations of U-shaped tubes along which the medium is moving. The phase shift is proportional to the mass flow rate. The advantage of this method is the measurement of mass flow without the need for additional measurements of density and speed. The disadvantage is the need to use a special section of the pipe of complex shape and dependence on external vibrations.

Known flow meters based on the difference in pressure in the liquid depending on its flow rate, for example, patent RU 2222785.

The disadvantage of this solution is the need to install pressure sensors directly in the pipeline and a priori knowledge of the type of pumped liquid.

Known devices that weigh part of a pipe of known volume, and thus measuring the density of the material in the pipe, for example, “Method for measuring the mass flow rate of a gas-liquid mixture and a device for its implementation” - Patent No. 2279641 (07/10/2006)), as well as a flow meter measuring speed the movement of material in patent No. 2367912 (05/12/2008). "A method for determining the volumetric flow rate of a controlled medium in a pipeline." Knowing the mass of material in a pipe of known volume, the density is uniquely determined, and knowing the speed of the material and the cross section of the pipe, the mass flow rate of this material per unit time is uniquely determined. The advantage of this method is the measurement of density and speed by which the mass flow rate is calculated. Disadvantages - the complexity of the installation, the need for costly maintenance of the pipe elements: articulation, suspension system, the pipe itself in the process of wear and corrosion, dependence on the vibration of the pipe on which measurements are made.

The closest method of the same purpose to the claimed invention in terms of features is the "Method of measuring the mass flow of liquid material in the pipeline" Japanese patent JP 58-206926, G01F 1/80, 1983, the implementation of which is carried out by installing on a straight tube of a piezoelectric element deformed by application to it of alternating voltage, output piezoelectric elements and a unit for determining the phase difference of the output signals.

The disadvantage of the method adopted for the prototype is the need to replace part of the pipeline for pumping measured petroleum products with a special tube of known stiffness, on which three piezoelectric elements are fixed on the outside, one of which is the causative agent of vibration of the entire tube along with its contents, and the other two are receivers of output signals. The implementation of the method requires the insertion of a measuring tube with sensors into the pipeline, which violates the integrity of the pipeline and to a certain extent worsens the metrological characteristics of the method, since the accuracy and stability of the speed measurement result, mechanical parameters of the tube, protection from external vibrations, etc. are separately determined.

The technical result of the proposed method is the provision of measuring the mass flow rate of oil products without violating the integrity of the pipeline body, increasing the accuracy of measurements, increasing the frequency of measurements for more accurate measurement of mass flow rate under transient conditions, determining the type and density of the pumped oil product.

The technical result is achieved by using acoustic signals for measuring the mass flow of hydrocarbons that are excited by piezoelectric elements that do not require direct contact with the medium to be measured, which are installed on the outer surface of the pipeline body, and provide a quantitative increase in the measurement frequency, which is necessary for more accurate measurement of the mass flow in transients.

Quality control of products at oil refineries and petroleum products should be accurate enough to conduct technological processes and at the same time efficient and economical so as not to increase the cost of production.

Density is considered to be a generalized universal indicator of the quality of oil and oil products; its measurement is an indispensable element in most technological processes of processing and transportation of petroleum products [1].

The density of different types of petroleum products significantly (0.7 ... 0.97 g / cm ³ ) differs from each other [2.5]. It differs for different types of gasolines within the same group (0.71-0.76 g / cm ³ ).

Density measurement methods are divided into direct and indirect [2, 3]. Direct methods include those based on fluid mechanics, indirect methods based on the relationship between density and various physical properties of a fluid.

The most universal in measuring ranges, accuracy and ease of use are ultrasonic methods for measuring density, and the most accurate of them when using surface sensors to measure density through a pipe wall are high-speed measurement methods, that is, methods based on measuring the speed of sound in a medium.

The propagation velocity of ultrasound in petroleum products can be calculated based on their physico-chemical structure [4]:

1. An increase in density causes an increase in the speed of sound;

2. An increase in molecular weight causes a decrease in the speed of sound;

3. An increase in molecular volume leads to an increase in the speed of sound;

4. Of the two petroleum products with close molecular weights, the speed of sound is greater in a denser one;

5. In very viscous petroleum products, the speed of sound is greater than in less viscous;

6. When changing the chemical structure of a hydrocarbon mixture of an oil product, the primary is a change in compressibility. Since the compressibility of β depends on the molecular forces of attraction or repulsion, which are mainly electric forces, β will be the smaller, the greater the adhesion force, that is, the smaller the distance between the individual molecules;

- приводит к увеличению скорости звука;7. The increase in the ratio of specific heat

- leads to an increase in the speed of sound;

8. An increase in the number of OH groups in molecules causes a decrease in the speed of sound.

The speed of sound in various organic liquids, taking into account a number of factors characterizing the interaction of molecules, can be determined by the expression [5]:

where M is the molecular mass, ρ is the density of the liquid, b is the van der Waals constant.

Given that the density ρ is determined by the molecular weight M and the molar volume V, we can present the formula for the speed of sound in the form:

- отношение удельных емкостей.where b is the quadruple value of the volume occupied by the molecules in one mole;

- the ratio of specific capacities.

The molecular weight of oil and oil products as a mixture gives the concept of the relative molecular weight of the “average” molecule among the molecules that make up the mixture, since there is no “oil product molecule”. To determine the molecular weight of oil products, a number of empirical formulas are used, for example, the Voinov formula [4] for oil fractions of a paraffin base:

where t _cf is the average boiling point of the oil product.

Voinov's formula for motor fuels (gasoline, kerosene, etc.), taking into account the characteristic factor K:

Craig formula [4] for oil fractions:

where ρ is the density of the oil at 15 ° C.

Thus, it is possible to measure the density of the oil through a direct measurement of the speed of sound using acoustic signals.

The flow velocity in the pipe can be measured by the same acoustic sensors as the density, if you arrange them so that the signal propagates in the direction of flow and against it. The angle of entry of the signal into the medium is determined by the parameters of the pipe material and the measured liquid, and the smaller the angle between the direction of movement of the liquid and the direction of propagation of the signal, the better. But during the propagation of the signal from the electro-acoustic emitter through the pipe wall into the measured liquid, zones of total internal reflection may arise in which the propagation of the signal between the media becomes impossible. Therefore, for a steel pipe and oil products, the direction of the emitted acoustic signal is chosen at an angle equal to 22 ... 25 degrees from the normal to the pipe wall, since at large angles the amplitude of the signal emitted into the liquid decreases significantly.

The signal from the sensor in the direction of flow propagates faster than from the sensor sending the signal in the opposite direction, since the propagation velocity of the signal and the movement of the medium are summed in one case and subtracted in the other. When the flow moves at an angle to the signal propagation direction, the signal propagation velocity and the projection of the flow velocity on the signal propagation direction are summed. As a result, having obtained two measurements by two sensors in two directions, it becomes possible to separately measure the speed of sound in a stationary medium and the speed of the medium (two independent linear equations and two unknowns).

The proposed method is implemented, taking into account the foregoing, using the structure of the mass flowmeter shown in FIG. one.

The mass flowmeter consists of a probe pulse generator (1), two electro-acoustic transducers (2) and (3) mounted on the outer wall of the pipe (4) with oil products (5), an amplifier-limiter (6), an analog-to-digital converter (7 ), phase detector, temperature sensor and digital signal processing unit (8).

The digital signal processing unit 8 provides band-pass filtering, Hilbert transform, signal detection, calculation of the propagation time of the signal from the emitting transducer to the receiving one, calculation of the speed of sound at a known distance between transducers 2 and 3.

The implementation of the method using a mass flowmeter is as follows.

Signal generator 1 generates a signal (a packet of several pulses, a short tone signal or a complex signal), which is fed to the inputs of electro-acoustic transducers - piezoceramic sensors 2 and 3 mounted on the outer wall of the pipeline 4. Each sensor converts the electrical pulses into acoustic ones and emits them through the wall of the pipe into the oil flow 5 is directed to each other and receives a signal from the other side of the pipe. The sensors are placed on the outer wall in the longitudinal plane of the pipeline so that the flow rate of oil products significantly affects the propagation time of the signal between the sensors, that is, with an offset relative to the diametrical plane in the direction of flow. Received signals, each sensor 2 and 3 converts the acoustic signal into an electric signal, which then passes sequentially to the amplification 6, filtering, analog-to-digital converter 7 and digital signal processing units 8. At the output of the digital processing unit, the value is simultaneously generated using the reference dependence [5] density values, type of material, flow rate and mass flow rate of the product. The primary measurement is the propagation time of the signal between the sensors. The most accurate result allows to obtain the phase measurement method [6].

As already mentioned, the sound velocity in the direction of flow is calculated from the propagation time of the signal between the electro-acoustic transducers

where r is the distance between the sensors, Δt ₁ is the propagation time of the signal, s is the speed of sound in the oil product, V is the flow velocity, and is the angle of projection of the flow velocity on the direction of the signal. Against the movement of the stream

and average speed of sound (for relatively low speeds up to 20 ... 30 m / s)

The average speed of sound determines the type of material and its density, the difference in the speed of sound in the direction of flow and against the flow determines the speed of movement of the stream. By integrating over time the product of the velocity, density and cross-sectional area of the pipe, the mass of the pumped material is uniquely determined

Where ρ (t) is the current density at time t, V (t) is the current speed at time t, S is the cross-sectional area.

Thus, the proposed device implements the measurement through the wall of the pipe of the density of the oil product, identification of its type (from the list of preset), the speed of the mixture and mass flow rate, providing high sensitivity and, consequently, the measurement accuracy, as well as a wide range of measured densities and speeds .

The use of this invention improves the efficiency of oil producing, oil refining and operating organizations due to the use of a reliable, accurate and at the same time inexpensive way to measure the mass flow of oil products without breaking the body of the conveying pipeline, and as a result, reduces the cost of equipment for carrying out these measurements.

Literature:

1. Kogogin A.A. Accounting for oil and petroleum products. Metrological support / A.A. Kogogin, I.I. Fishman, A.G. Sladovsky // Product Quality Control. - 2010. - No. 1. - C 28-31

2. Fisherman B.M. Analysis of oil and oil products / B.M. Fisherman. - 5th ed., Ext. And perab. - M.: Gostoptekhizdat, 1962 .-- 888 p.

3. Belyakov V.L. Automatic control of parameters of oil emulsions: a reference guide. - M .: Nedra, 1992 .-- 202 p.

4. Shaevich A.B. Standard samples for analytical purposes / A.B. Shaevich. - M .: Chemistry, 1987 .-- 183 p.

5. P 50.2.076-2010. State system for ensuring uniformity of measurements. Density of oil and oil products. Calculation method. Program and cast tables.

6. Bazhenov V.G. Application of phasemetry methods for precision distance measurement / V.G. Bazhenov, E.K. Baturevich, S.M. Mayevsky, Yu.V. Kuts // K .: Vishcha school, publishing house at Kiev University, 1983. - 84 p.

Claims (6)

1. A method of measuring the mass flow rate of oil products in a pipeline, characterized by installing 2 transceiver electroacoustic transducers with offset relative to the cross section on the pipeline body, generating a signal by a generator, simultaneously sending a signal directed to each other by electroacoustic transducers through the pipeline wall, the first of which them in the direction of flow of the medium, the second - in the direction of the counterflow, signals that passed through the measured medium from each The browser enters the inputs of the signal preprocessing unit, then performs their analog-to-digital conversion, band-pass filtering and, using the phase method, determine the signal travel time in both directions, calculate the sound speeds in two directions, according to the arithmetic mean of the measured sound velocities and the reference velocity dependence sound density, calculate the density of the components of the medium, the mass flow rate of which is determined by the formula

, where ρ (t) is the density of the medium at time t, S is the cross section of the pipeline, V (t) is the flow velocity at time t. 2. The method according to p. 1, characterized in that the electro-acoustic transducers are installed with a displacement in the longitudinal plane on the pipeline body at an angle of 22-26 ° relative to each other.

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