DEVELOPMENT OF AN OPTOELECTRONIC SYSTEM FOR MONITORING OIL CONTENT IN PURIFIED WATER BASED ON THE ELEMENT OF IMPAIRED TOTAL INTERNAL REFLECTION

ABSTRACT

At present, the basics of optical methods and the principles of constructing multifunctional optoelectronic systems for monitoring the physicochemical parameters of oil and petroleum products are given. Optical moisture meters using the ATR effect and an analysis of the main designs of ATR sensors are considered, practical diagrams of optoelectronic non-destructive testing systems are given. Basic block diagrams of optoelectronic monitoring devices.

АННОТАЦИЯ

В настоящее время даны основы оптических методов и принципы построения многофункциональных оптико-электронных систем контроля физико-химических параметров нефти и нефтепродуктов. Рассмотрены оптические влагомеры с использованием эффекта НПВО и проведен анализ основных конструкций датчиков НПВО, приведены практические схемы оптико-электронных систем неразрушающего контроля. Приведены основные структурные схемы оптико-электронных приборов контроля.

Keywords: PIP of automatic devices, composition and properties of oil and petroleum products, optical devices, (ATR) attenuated total internal reflection, photometric method.

Ключевые слова: PIP автоматических устройств, состав и свойства нефти и нефтепродуктов, оптические приборы, нарушенное полное внутреннее отражение (НПВО), фотометрический метод.

Introduction

Optoelectronic control of physical and chemical parameters of liquid media. Currently, throughout the world, the main sources of oil and petroleum product pollution are mining enterprises, pumping and transportation systems, oil terminals and oil depots, petroleum product storage facilities, railway transport, river and sea oil tankers, gas stations and filling stations. Sources of pollution include oil-containing drains that come out of oil-refining industries, causing global harm to our environment. When choosing a method and equipment for solving the analytical problem of monitoring oil content in purified water, ultra-sensitive express methods for analysis should mainly be used. Currently, in the oil industry, there are dozens of methods and hundreds of devices based on them for determining petroleum products in purified water, which are adopted in various standardization systems: ASTM, EN ISO, IP, GOST.

Analysis of literature on the topic (Literature review)

N.R. Rakhimov, A.N. Sereznov AFN films and their application. Monograph, Publishing house "SibNIA", Novosibirsk, 2004, 96 p. [7]. N.R. Rakhimov, O.K.Ushakov Optoelectronic sensors based on the APN effect. Novosibirsk, SSGA, 2010, p. 222 [8].  N.R. Rakhimov, A.M. Kasymokhunova, Sh. Usmanov Optoelectronic means of non-destructive testing of physical and chemical parameters of liquid media. Journal “Technical diagnostics and non-destructive testing”, No. 3, Kyiv, 2001, pp. 40-42. [9].

Research Methodology

For example, monitoring the sulfur content of oil and petroleum products is important for assessing the quality of these products [10]. Currently, in the domestic oil and oil refining industry there are no automatic flow analyzers for sulfur content, and the development of an optoelectronic device for determining the sulfur content in oil and oil products solves this problem [4].

A number of optoelectronic devices using the attenuated total internal reflection (ATR) element are used to solve problems of automatic analysis of structural and group composition.

It is also relevant to consider existing analytical methods for the determination of petroleum products in purified water in Russia, the results and conclusions of research work carried out in the USA and Europe, which were obtained by various existing analytical methods in interlaboratory tests [2]. However, at present, in the oil and oil refining industry, even during oil production, there are no express analyzers for determining petroleum products in purified water [5]. Optoelectronic control methods have received a new qualitative change thanks to the development of optoelectronics [1]. The main elements of instruments and devices operating on this principle are semiconductor emitters and receivers - LEDs, photoresistors, phototransistors, photodiodes, photodetectors - these elements have minimal dimensions, high sensitivity, low power consumption, which allows you to create reliable, sensitive optoelectronic devices for monitoring and measurements [3][6].

In no way inferior to other physical and chemical methods in the accuracy and convenience of determining oil content in purified water, the attenuated total internal reflection (ATR) method surpasses them in speed, while at the same time providing non-destructive testing.

  Sensors – ATR based

The ATR method (Fig. 1) is based on the phenomenon of penetration of a light wave into an optically less dense medium n₂, when the light flux propagates from an optically more dense medium n₁ to a less dense medium n₂ at an angle.

Figure 1. Physical basis of the ATR method

The physical meaning is as follows. Two light streams with different wavelengths are used, for example, l₁ = 1.93 μm (measuring) and l₂ = 1.7 μm (reference), corresponding to the maximum and minimum water absorption. The luminous flux Ф_0l propagates from an optically dense medium with refractive index n₁ to a less dense medium with n₂ at an angle Q exceeding the limiting (critical) angle of total internal reflection Q_к. The luminous flux Ф_0l1 partially penetrates into the medium n₂; to a depth of the order of the wavelength of the incident radiation:

                                                 (1)

where l₁ is the wavelength of radiation in an optically dense medium with refractive index n₁; n₂₁ = n₂/n₁ – relative refractive index. If the radiation angle is equal to or exceeds the critical Q_к = arcsin n₁/n₂, then total internal reflection is observed (TIR method). Since a less dense medium with a complex refractive index has absorption, the reflection will not be complete, i.e. the conditions for this are violated and the reflection coefficient (R = Ф_l1 / Ф_0l1) will become less than 1. The degree of attenuation R is proportional to the absorption index. Thus, the higher the absorption, the more the reflection is disrupted. This is called the ATR effect. In the IR region of the spectrum, to achieve the condition n₁ greater than n₂, ATR measuring elements made of highly refractive optical materials that are transparent in the corresponding range are used.

They are made mainly in the form of attachments (called “ATR attachments”) for various serial spectrometers and spectrophotometers, where the attachments are installed in the cuvette compartment between the illuminator and the monochromator. Set-top boxes are available in two versions: with single reflection or with multiple reflection (MNPVO set-top boxes). The first ones are designed to obtain single reflection spectra with the possibility of smoothly changing the angle of incidence and are used mainly for research purposes to determine optical constant media. MATTR attachments make it possible to obtain spectra with a large number of reflections and a limited number of fixed angles of incidence; they serve mainly to solve analytical problems. ATR attachments (Fig. 2) are produced according to two standard designs. Scheme a) is the simplest, since it uses only flat mirrors and a simple prismatic ATR element. The angle of incidence is changed by rotating the ATR element, as well as by rotating and linear movements of the mirrors (using a parallelogram mechanism). The ATR element in this attachment is illuminated by a converging (aperture »5°) beam of light, and therefore it is far from parallel; Accurate determination of the angle of incidence is also difficult due to the different refraction of the beam on the flat surfaces of the element when the angle of incidence changes.

а)                                                                    b)

Figure 2. NPVO attachments

a) – prismatic: 1-3 – flat mirrors; 4 – air defense element; b) – semi-cylindrical: 1, 5 – flat mirrors; 2, 4 – toroidal mirrors; 3 – air defense element.

Scheme b) with a semi-cylindrical ATR element is more advanced, since it provides a nearly parallel beam of light inside the element, but is somewhat more complex in design. In it, mirrors 1 and 2 are stationary, and the angle of incidence is changed by rotating the ATR element 3 around its axis and the corresponding rotation of mirror 4 by a double angle and rotation of mirror 5 by a small angle. The interaction of these rotations is carried out using special cams.

In the IR region of the spectrum, to achieve the condition n₁>n₂, ATR measuring elements made of highly refractive optical materials that are transparent in the corresponding range are used.

The optoelectronic system proposed by the authors for determining the content of emulsion water in oil and petroleum products (Fig. 3) includes a cylinder 1 with a cavity in the form of a prism 2 passing through its center, a master oscillator (pulse power source) 17, a trigger 18 with a counting input, light-emitting diodes (LED) 3–8 and compensation LED 15, measuring 9–14 and compensation 16 optical radiation receivers (ORR), adder 19, photoelectric signal processing unit 20 and recording device or computer 21.

The system works as follows. When the master oscillator 17 is turned on, the rectangular pulses it produces with a frequency of 8...10 kHz are fed to the input of the trigger 18. The divided pulses are supplied to LEDs 3–8 of the measuring channels and LED 15 of the reference channel. The radiation flux of light-emitting diodes is focused on the measuring surfaces and supplied to photodetectors 9–14. Next, the signals from the photodetectors are summed in the adder 19. The radiation of the compensating light-emitting diode passes through the light guide to the compensating photodetector 16. Then the signal from the compensating photodetector goes to the photoelectric signal processing unit 20, where the ratio of the compensation and measuring signals is measured. The ratio signal, proportional to the content of oil-containing media, is fed to a recording device or computer 21, according to the reading of which the oil content in purified water is judged.

Analysis and results

A block diagram of a system that carries out multifunctional monitoring with the simultaneous occurrence of all n primary signals YJ is shown in Fig. 1, in Fig. 2 is a view of the sensor along the section A-A.

Figure 3. Block diagram of an optoelectronic system for determining oil content in purified water

The disadvantage of the known sensors is the presence of errors caused by the uneven distribution of oil-containing media in the volume of purified water. The proposed device improves accuracy through multiple volumetric measurements, summation, and averaging of the photoelectric signal. In addition, it can be used to determine the content of petroleum products in emulsion water.

Conclusion

In conclusion, the main results of the research are presented in the form of brief conclusions:

The progress made in the development of optoelectronic sensors for the oil industry in recent years has been quite significant. Let us note, first of all, such areas as level measurements, phase boundaries, emergency level signaling and leaks from pipelines and storage facilities, pressure, temperature and density measurements, determination of the chemical composition of petroleum products.

The basic principles of the optoelectronic refractometric method of physicochemical analysis based on the ATR element are considered. It was revealed that the ATR method using open channel optocouplers is superior to other physicochemical methods in sensitivity, ease of determining optical parameters and speed, while at the same time providing non-destructive testing.

A method of an optoelectronic system for non-destructive testing of oil content in purified water based on the element of disrupted total internal reflection is proposed. For this purpose, the light transmission (k) of ATR elements and lens elements is calculated. It is shown that to calculate k it is necessary to specify a specific type of ATR element.

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