RU2131600C1 - Process determining moisture content in oil product in dielectric pipeline - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: process determining moisture content in oil product in dielectric pipeline consists in excitation of electromagnetic oscillations in open resonator formed by two quarter-spherical reflectors installed in diametrical opposition on outer surface of dielectric pipeline, in measurement of inherent resonance frequency of open resonator and width of its resonance curve at half-power level and in determination of moisture content in oil product in correspondence with given relation. EFFECT: decreased measurement error. 1 dwg

Description

 The invention relates to the field of measuring equipment and can be used in process control systems.

 A known method for determining moisture content (AS USSR N 1015287, Bull. N 16, 1983), according to which the difference in the absorption of microwave radiation in a controlled oil and in a reference sample of fluoroplastic judge the value of moisture content in a continuous flow of crude oil.

 The disadvantage of this known method is the complexity of the procedure for determining moisture content associated with the introduction of a reference sample into the radiation propagation zone.

 The closest technical solution to the proposed one is the method adopted by the author for determining the moisture content of crude oil (V.A. Viktorov et al. "High-frequency method for measuring non-electric quantities", Moscow: Nauka, 1978, p. 254). A device that implements the specified method contains measuring and reference resonators connected through an amplifier to an oscilloscope, an attenuator, a detector, and a radiation source. In this development, the moisture content of the measured medium is determined from the frequency difference between the reference resonator filled with dehydrated oil and the measuring resonator, in the center of which a dielectric tube is mounted to pass the flow of the controlled medium branched from the main line.

 The disadvantage of this development should be considered the error due to changes in the dielectric constant of the measured oil.

 The objective of the proposed technical solution is to increase the accuracy of measuring moisture content.

где q - постоянное число, C - скорость распространения электромагнитных волн, α - относительная потеря энергии при единичном взаимодействии волны с отражателями, D - наружный диаметр трубопровода, ε_т - диэлектрическая проницаемость трубопровода.This object is achieved in that in a method for determining the moisture content of an oil product in a dielectric pipeline based on the use of the vibrational characteristics of a resonator excited by electromagnetic waves, electromagnetic waves are excited in an open resonator formed by two quarter-spherical reflectors installed diametrically on the outer surface of the dielectric pipeline, and the natural resonant frequency ω is measured open resonator and the width of its resonant cr willow Δω at half power and determine the moisture content W of the oil product according to the formula

where q is a constant number, C is the propagation velocity of electromagnetic waves, α is the relative energy loss during a single interaction of the wave with reflectors, D is the outer diameter of the pipeline, ε _t is the dielectric constant of the pipeline.

 The essence of the claimed invention, characterized by a combination of the above features, is that two informative parameters of the open resonator (natural resonance frequency and the width of the resonance curve) judge the moisture content of the oil in the dielectric pipeline.

 The presence in the claimed method of the totality of these essential features allows us to solve the problem of determining the moisture content of the oil product with the desired technical result, i.e. high accuracy of measurement.

 The drawing shows a functional diagram of a device that implements the proposed method.

 A device that implements this technical solution comprises a oscillating frequency generator 1, first and second quarter spherical reflectors 2 and 3 mounted diametrically on the outer surface of the dielectric pipe 4, an input coupling element 5, an output coupling element 6 connected to the input of the detector 7 and a unit for studies of amplitude-frequency characteristics 8.

 The proposed method is as follows.

где l - расстояние между отражателями, q - большое число (практически q>3) C - скорость распространения электромагнитной волны между отражателями. Здесь принимается, что величина дифракционных потерь P ≃ O.As is known, when electromagnetic waves are excited in an open resonator, for its resonant frequency ω, we can write

where l is the distance between the reflectors, q is a large number (practically q> 3) C is the propagation velocity of the electromagnetic wave between the reflectors. It is assumed here that the magnitude of diffraction loss is P ≃ O.

 In the case under consideration, if the reflectors are installed on the outer surface of the dielectric pipeline, then in the formula (I) instead of l, the outer diameter of the pipeline should be used, and instead of C, the value of the wave velocity when it propagates through the dielectric pipeline with the measured dielectric oil product.

где D - наружный диаметр трубопровода, K - параметр, учитывающий влияние диэлектрических свойств трубопровода и измеряемого водоэмульсионного потока на скорость распространения волны одновременно.By virtue of this, formula (I) takes the following form:

where D is the outer diameter of the pipeline, K is a parameter that takes into account the influence of the dielectric properties of the pipeline and the measured water-emulsion flow on the wave propagation velocity simultaneously.

In this case, the parameter K can be represented with a certain accuracy as the sum of the dielectric permittivities of the pipeline ε _t and the watered oil product ε _n . Since the value of ε _t depends on the material of which the pipeline is made, it can be considered constant during the measurement process.

Then, as follows from the last formula, at constant values of ε _t and D, the change in the resonant frequency ω will be determined by the change in the dielectric constant of the water emulsion flow.

 The above and the known dependence of the dielectric permittivity of the bypass stream (Wiener formula) on the moisture content allow us to obtain an expression that determines the relationship between the resonant frequency of the open resonator and the moisture content in the oil product stream.

Отсюда для влагосодержания W в потоке нефтепродукта имеем

Из последнего выражения видно, что при постоянных значениях диэлектрических проницаемостей нефтепродукта ε_н и диэлектрического трубопровода, а также его наружного диаметра по резонансной частоте открытого резонатора, образованного двумя отражателями, установленными на наружной поверхности диэлектрического трубопровода, можно оценить величину влагосодержания в обводненном нефтепотоке.

Hence, for the moisture content of W in the oil product stream, we have

It can be seen from the last expression that, at constant values of the dielectric constant of the oil product ε _n and the dielectric pipeline, as well as its outer diameter from the resonant frequency of the open resonator formed by two reflectors installed on the outer surface of the dielectric pipeline, it is possible to estimate the moisture content in the watered oil flow.

However, with a change in the dielectric constant of the oil product ε _n , an error in determining the moisture content may occur.

 According to the proposed technical solution, in order to exclude the indicated error, it is necessary to know one more parameter related to the moisture content of the oil product. In accordance with this, let us consider, for example, the Q factor of a given open resonator.

( λ - длина электромагнитных волн) может быть определена как

где α - относительная потеря энергии при единичном взаимодействии волны с отражателями.In the case under consideration, the Q factor of the measuring resonator taking into account

(λ is the electromagnetic wavelength) can be defined as

where α is the relative energy loss during a single interaction of the wave with reflectors.

Тогда с учетом этого и K = ε_т+ε_oн(ε_oн = ε_н(1+3W)) выражение (3) примет следующий вид:

Отсюда для искомой величины W получаем

Из последнего выражения получаем, что по величине ширины резонансной кривой на уровне половины мощности можно судить о влагосодержании в потоке нефтепродукта.It is known from electrodynamics that the Q factor of a resonator can be determined by the ratio of the resonance frequency ω to the frequency width Δω of the resonance curve at half power, i.e.

Then, with this in mind, and K = ε _t + ε _{OH (OH} e = ε _n (1 + 3W)) expression (3) takes the following form:

Hence, for the desired quantity W, we obtain

From the last expression we obtain that by the value of the width of the resonance curve at the level of half the power, one can judge the moisture content in the oil product stream.

Подставляя последнее соотношение в выражение (4) и выполняя преобразования, для W имеем:

Последнее выражение показывает, что путем изменения одновременно резонансной частоты открытого резонатора и ширины его резонансной кривой на уровне половины мощности можно исключить погрешность в измерении влагосодержания, обусловленную изменением диэлектрической проницаемости нефтепродукта.The analysis shows that, based on joint solutions of expressions (2) and (4), it is possible to provide a result of measuring the moisture content regardless of the change in the dielectric constant of the oil product. To do this, we determine the value of ε _n from the expression (2), equal to

Substituting the last relation into expression (4) and performing transformations, for W we have:

The last expression shows that by simultaneously changing the resonant frequency of the open resonator and the width of its resonance curve at half power, one can eliminate the error in measuring moisture content due to a change in the dielectric constant of the oil product.

 A device that implements the proposed method works as follows. The output signal of the oscillating frequency generator 1, passing through the input coupling element 5, excites electromagnetic waves in the measuring cavity formed by two quarter-spherical reflectors mounted diametrically on the outer surface of the dielectric conduit 4. In this case, for measuring the natural resonant frequency and the width of the resonance curve of the open measuring resonator the electromagnetic signal using the output element of the connection 6 is fed to the input of the detector 7. After that the detected signal is reproduced in the unit for studying the amplitude-frequency characteristics (AFC) 8.

In the device, at the top of the resonance curve (pulse) observed on the screen of the frequency response block, the natural resonance frequency ω of the measuring resonator is determined, and Δω is determined from the frequency difference corresponding to the lower and upper boundaries of the passband of the resonator at half the power of its resonance curve.
Thus, according to the proposed method, based on the simultaneous measurement of the resonant frequency of the open resonator and the frequency width at the level of half the power of the resonance curve of the specified resonator, it is possible to provide higher accuracy in measuring the moisture content of the oil product in the pipeline.

Claims (1)

A method for determining the moisture content of a petroleum product in a dielectric conduit, in which electromagnetic oscillations are excited in a resonator, and a controlled parameter is judged by its vibrational characteristics, characterized in that electromagnetic oscillations are excited in an open resonator formed by two quarter-spherical reflectors mounted diametrically on the outer surface of the dielectric conduit, natural resonant frequency ω of the open resonator and the width of its resonance curve oh Δω at half power and determine the moisture content W of the oil by the formula

where q is a constant number;
C is the propagation velocity of electromagnetic waves;
α is the relative energy loss during a single interaction of the wave with reflectors;
D is the outer diameter of the pipeline;
ε _t is the dielectric constant of the pipeline.