A method and system for detecting supercritical fluid phase equilibrium

Abstract

The application discloses a kind of supercritical fluid phase equilibrium detection method and device, through non-invasive active and passive acquisition sound wave signal generated in supercritical fluid system, and series processing is carried out to sound wave signal, so as to obtain series characteristic quantity to supercritical fluid phase equilibrium state is characterized.The sound wave detection used in the application is a kind of non-invasive detection method, detection device is simple, safe, environmental protection, suitable for the on-line detection of industrial production process, and fills the blank in relevant detection field.

Description

Technical Field

[0001] The present invention relates to the technical field of supercritical fluids, and in particular to a method and system for detecting supercritical fluid phase equilibrium. Background Art

[0002] In the chemical industry, many important chemical processes involve high-pressure operations (pressures even greater than 1000 bar), such as the preparation of low-density polyethylene, synthetic ammonia, synthetic methanol, and hydrogenation processes. In addition, processes such as oil / natural gas extraction, storage, and transportation also involve high-pressure processes. Considering that under high-pressure conditions, fluids may enter a supercritical state and their physicochemical properties differ significantly from those in the conventional state, it is extremely important to detect the physicochemical properties of supercritical fluids (phase equilibrium, diffusion coefficient, viscosity, etc.). However, since the supercritical state of a fluid is often near the phase transition point, the phase behavior in this region is extremely sensitive to operating conditions (such as temperature and pressure) and is more complex and variable than the phase behavior under general high-pressure conditions. Therefore, current research on supercritical fluids focuses more on simulation calculations (such as Chinese patent ZL201380056025.7) and less on experimental measurements.

[0003] Therefore, establishing a detection method and system for characterizing the phase equilibrium characteristics within supercritical fluid systems remains a major challenge in this field. The present invention aims to establish a non-invasive detection method and system for the phase equilibrium characteristics within supercritical fluid systems by employing non-invasive passive acoustic emission detection technology. By acquiring and analyzing the acoustic wave signals within the supercritical system using active and passive acoustic wave sensors, the present invention aims to establish a non-invasive detection method and system for the phase equilibrium characteristics within supercritical fluid systems. Summary of the Invention

[0004] The present invention aims to provide a method and apparatus for detecting phase equilibrium characteristics of supercritical fluids. By non-invasively collecting and analyzing acoustic signals within a supercritical fluid system, characteristic quantities of the acoustic signals are extracted to characterize the phase equilibrium characteristics of the supercritical fluid system (e.g., the position of the phase interface).

[0005] The present invention is achieved through the following technical solutions.

[0006] The present invention provides a method for detecting supercritical fluid phase equilibrium, which comprises the following steps:

[0007] (1) An acoustic source excitation is set at the bottom of the supercritical fluid system to be tested to generate a clear acoustic wave signal with adjustable amplitude and frequency;

[0008] (2) at least two acoustic wave sensors are arranged on the side wall of the supercritical fluid system to be measured, so as to capture the acoustic wave signals generated by the excitation of the sound source or the acoustic wave signals generated when the fluid state in the system to be measured changes;

[0009] (3) Preprocessing the collected acoustic wave signals to remove noise;

[0010] (4) performing data processing on the denoised acoustic wave signal to obtain a series of characteristic parameters representing the phase equilibrium characteristics of the supercritical fluid;

[0011] When the sound source at the bottom of the supercritical fluid system to be tested is excited to work and generate a sound wave signal, the sound wave sensor on the side wall is used to receive the sound wave signal generated by the sound source and flowing through the supercritical fluid, and processes it to obtain signal strength, signal frequency, and signal dispersion as characteristic parameters; at the same time, the received sound wave signal is compared with the sound source signal to obtain the sound wave velocity as a characteristic parameter;

[0012] When the acoustic source excitation at the bottom of the supercritical fluid system to be tested is not working, the acoustic wave sensor on the side wall is used to receive the acoustic wave signal generated when the supercritical system changes phase, and processes it to obtain the signal strength, signal frequency, and signal dispersion as characteristic parameters;

[0013] (5) Obtaining a determination factor AF based on the characteristic parameters of the acoustic signal;

[0014] The determination factor AF is defined as:

[0015] AF=2*abs(x n+1 -x n ) / (x n+1 +x n )

[0016] In the formula, abs means taking the absolute value, x n+1 is the acoustic signal characteristic parameter detected by the n+1th sensor in real time, x n is the acoustic signal characteristic parameter detected by the nth sensor in real time; the n+1th sensor and the nth sensor are two adjacent sensors in the height direction;

[0017] On the time scale, whether the phase equilibrium has changed is determined by whether there is a sudden change in AF; on the spatial scale, the position of the phase interface is determined by the sudden change in AF with the height of the system under test;

[0018] Among the characteristic parameters obtained in step (4), as long as there is a characteristic parameter whose AF is greater than 1, it is considered that the determination factor has undergone a mutation and the phase state has changed accordingly.

[0019] As a preferred embodiment of the present invention, the method for pre-processing and removing noise in step (3) is selected from one or more of smoothing, differentiation, multivariate scattering correction, orthogonal signal correction, Fourier transform, wavelet transform, and net analysis signal.

[0020] The collected acoustic wave signal includes a lot of noise. Therefore, a noise elimination method is very critical and necessary. Among the pre-processing methods in the detection method of the present invention, smoothing can improve the signal-to-noise ratio of the analysis signal. The most commonly used methods are moving average smoothing and Savizky-Golay polynomial smoothing. Differentiation can eliminate baseline drift, enhance spectral band characteristics, and overcome spectral band overlap. It is a commonly used spectral pre-processing method. The first-order differential can remove drifts that are independent of the wavelength, and the second-order differential can remove drifts that are linearly related to the wavelength. The Fourier transform can realize the conversion between spectral domain functions and time domain functions. Its essence is to decompose the original sound spectrum into the superposition of many sine waves of different frequencies. It can be used to smooth and denoise the sound spectrum, compress data, and extract information. The wavelet transform can decompose the signal into multiple scale components according to the frequency, and adopt corresponding coarse and fine sampling steps for scale components of different sizes, so that any part of the signal can be focused. The basic idea of ​​the net analysis signal algorithm is basically the same as that of the orthogonal signal correction. Both use orthogonal projection to remove information in the sound spectrum array that is irrelevant to the component to be measured.

[0021] As a preferred embodiment of the present invention, when it is necessary to actively determine the phase equilibrium state in the supercritical fluid system to be tested, the sound source at the bottom of the supercritical fluid system to be tested can be turned on to generate an acoustic wave signal, and the acoustic wave sensor on the side wall of the system to be tested receives the signal and analyzes and determines the phase equilibrium state and the phase interface position;

[0022] When it is only necessary to monitor the phase equilibrium state of the supercritical fluid system to be tested over a long period of time, there is no need to turn on the sound source excitation. Only the acoustic wave sensor on the side wall of the system to be tested needs to be turned on. When the phase equilibrium of the system to be tested changes, an acoustic wave signal will be generated and received by the acoustic wave sensor. After analyzing the signal, it can be determined whether the phase equilibrium state has clearly changed and the position of the phase interface can be determined.

[0023] The present invention also provides a supercritical fluid phase equilibrium detection device for implementing the above method, which includes at least one sound source excitation that can generate a sound wave signal with adjustable amplitude and frequency, at least two sound wave sensors, a signal amplification device, a signal acquisition device and a signal processing device; the sound wave sensors are evenly arranged on the side walls of the system to be measured and arranged along the height direction; the sound wave sensors are connected to the signal amplification device to convert the sound wave signal into an electrical signal and transmit it to the signal amplification device for amplification; the signal amplification device is connected to the signal acquisition device to transmit the amplified signal to the signal acquisition device for acquisition; the signal acquisition device is connected to the signal processing device to analyze the acquired signal to obtain characteristic parameters characterizing the phase equilibrium characteristics of the system to be measured.

[0024] As a preferred solution of the present invention, when the number of acoustic wave sensors increases, they are preferably arranged along the height direction of the side wall of the supercritical fluid system to be measured, so as to more accurately determine the position of the phase interface in the system to be measured.

[0025] As a preferred solution of the present invention, the acoustic wave sensor is selected from one or both of an acoustic emission sensor and an acceleration sensor, and the frequency response characteristics of the acoustic wave sensors are the same, and the frequency response range is 1 Hz to 10 MHz.

[0026] The present invention has the following advantages: the acoustic wave detection of the present invention is a non-invasive detection method, the detection device is simple, safe, and environmentally friendly, and is suitable for online detection of industrial production processes; the use of an acoustic wave sensor array and the fusion of multi-sensor data can effectively characterize the phase equilibrium characteristics in the supercritical fluid system, effectively filling the gap in detection methods in related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of the detection system of the present invention;

[0028] Figure 2 It is the sound wave signal in different states;

[0029] Figure 3 is a graph showing the change of signal energy with detection position;

[0030] Figure 4 It is a graph showing the determination factor changing with the detection position. DETAILED DESCRIPTION

[0031] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0032] like Figure 1 As shown, the detection system of this embodiment is applied to the supercritical system 2 to be tested, which includes an acoustic signal generator 1, an acoustic wave sensor 3, a signal amplifying device 4, a signal collecting device 5, and a signal processing device 6. The acoustic signal generator and the acoustic wave sensor are arranged on the outer wall of the supercritical system 2 to be tested. In this embodiment, the acoustic signal generator 1 is at the bottom of the supercritical fluid system to be tested, and is used to generate an acoustic wave signal with adjustable amplitude and frequency and a clear sound wave signal; the acoustic wave sensor is arranged on the side wall of the supercritical fluid system to be tested, and is used to capture the acoustic wave signal generated by the excitation of the sound source or the acoustic wave signal generated when the fluid state in the system to be tested changes; the acoustic wave sensor 3 is connected to the signal amplifying device 4 to convert the acoustic wave signal into an electrical signal and transmit it to the signal amplifying device 4 for amplification; the signal amplifying device 4 is connected to the signal collecting device 5 to transmit the amplified signal to the signal collecting device 5 for collection; the signal collecting device 5 is connected to the signal processing device 6 to analyze the collected signal.

[0033] When the sound source at the bottom of the supercritical fluid system to be measured is excited to work and generate a sound wave signal, the sound wave signal generated by the sound source and flowing through the supercritical fluid is received by the sound wave sensor on the side wall, and processed to obtain signal strength, signal frequency, and signal dispersion as characteristic parameters. At the same time, the received sound wave signal is compared with the sound source signal to obtain the sound wave velocity as a characteristic parameter;

[0034] When the sound source excitation at the bottom of the supercritical fluid system to be tested is not working, the acoustic wave sensor on the side wall is used to receive the acoustic wave signal generated when the supercritical system changes phase, and processes it to obtain signal strength, signal frequency, and signal discreteness as characteristic parameters.

[0035] The present invention describes the phase equilibrium characteristics of the supercritical fluid based on the obtained characteristic parameters; specifically, the determination factor AF is obtained based on the characteristic parameters of the acoustic signal.

[0036] AF=2*abs(x n+1 -x n ) / (x n+1 +x n )

[0037] In the formula, abs means taking the absolute value, x n+1 is the acoustic signal characteristic parameter detected by the n+1th sensor in real time, x n It is the characteristic parameter of the acoustic signal detected by the nth sensor in real time.

[0038] When AF>1, it is considered that the decision factor has mutated. In the time scale, the present invention determines whether the phase equilibrium has changed based on the mutation of AF; in the spatial scale, the position of the phase interface is determined based on the mutation of AF with the height change of the system to be tested.

[0039] The detection of the supercritical fluid phase equilibrium characteristics in this embodiment is as follows:

[0040] The system under test is a closed system. The fluid within the system is pressurized to a supercritical state. Once the system stabilizes, an acoustic signal generator at the bottom of the system generates an acoustic wave signal. Acoustic sensors on the side walls of the system receive the acoustic wave signal after it passes through the fluid. Figures 2 to 4 It is the acoustic wave signal, signal energy and determination factor detected at different positions of the system under test. Figure 2 It reflects the characteristics of the acoustic wave signals in different states at different positions of the system to be tested (from bottom to top). It can be seen that the amplitudes of the acoustic wave signals show significant differences in different states. Figure 3This reflects the acoustic signal energy at different locations in the system under test. It can be seen that as the detection position increases, the acoustic energy exhibits two distinct transition points, indicating two phase transitions. This characteristic is even more pronounced in the determination factors at different detection positions. At the phase transitions, the determination factors show significant changes, and their values ​​all exceed the critical value of 1, demonstrating the high accuracy of the detection method and system proposed in this invention.

[0041] Experimental results show that the detection method and detection device provided by the present invention can be used to detect the phase equilibrium characteristics of supercritical fluids with good accuracy.

Claims

1. A method for detecting supercritical fluid phase equilibrium, characterized in that: The following steps are involved: (1) An acoustic source excitation is set at the bottom of the supercritical fluid system to be tested to generate a clear acoustic wave signal with adjustable amplitude and frequency; (2) At least two acoustic wave sensors are installed on the side wall of the supercritical fluid system to be tested, so as to capture the acoustic wave signals generated by the excitation of the sound source or the acoustic wave signals generated when the fluid state in the system to be tested changes; (3) Preprocess the collected acoustic wave signals to remove noise; (4) Processing the denoised acoustic wave signal to obtain a series of characteristic parameters that characterize the phase equilibrium characteristics of the supercritical fluid; When the sound source at the bottom of the supercritical fluid system to be tested is excited to work and generate a sound wave signal, the sound wave sensor on the side wall is used to receive the sound wave signal generated by the sound source and flowing through the supercritical fluid, and processes it to obtain signal strength, signal frequency, and signal dispersion as characteristic parameters; at the same time, the received sound wave signal is compared with the sound source signal to obtain the sound wave velocity as a characteristic parameter; When the acoustic source excitation at the bottom of the supercritical fluid system to be tested is not working, the acoustic wave sensor on the side wall is used to receive the acoustic wave signal generated when the supercritical system changes phase, and processes it to obtain the signal strength, signal frequency, and signal dispersion as characteristic parameters; When it is necessary to actively determine the phase equilibrium state in the supercritical fluid system to be tested, the sound source at the bottom of the supercritical fluid system to be tested is turned on to generate an acoustic wave signal, and the acoustic wave sensor on the side wall of the system to be tested receives the signal and analyzes and determines the phase equilibrium state and the position of the phase interface; When only the phase equilibrium state of the supercritical fluid system to be tested needs to be monitored over a long period, there is no need to turn on the sound source excitation. Only the acoustic wave sensor on the side wall of the system to be tested needs to be turned on. When the phase equilibrium of the system to be tested changes, an acoustic wave signal will be generated and received by the acoustic wave sensor. After analyzing the signal, it is determined whether the phase equilibrium state has clearly changed and the position of the phase interface is determined. (5) Obtaining the decision factor AF based on the characteristic parameters of the acoustic signal; The determination factor AF is defined as: AF=2*abs( x n+1 - x n ) / ( x n+1 + x n ) In the formula, abs means taking the absolute value, x n+1 For the n +1 sensor detects the acoustic signal characteristic parameters in real time, x n For the n The characteristic parameters of the acoustic signal detected by a sensor in real time; On the time scale, whether the phase equilibrium has changed is determined by whether there is a sudden change in AF; on the spatial scale, the position of the phase interface is determined by the sudden change in AF with the height of the system under test; Among them, as long as there is a characteristic parameter with AF greater than 1 among the characteristic parameters obtained in step (4), it is considered that the determination factor has undergone a mutation and the phase state has changed accordingly.

2. The method for detecting supercritical fluid phase equilibrium according to claim 1, wherein: The method for pre-processing and removing noise in step (3) is selected from one or more of smoothing, differentiation, multivariate scattering correction, orthogonal signal correction, Fourier transform, wavelet transform, and net analysis signal.

3. A device for detecting supercritical fluid phase equilibrium for implementing the method according to any one of claims 1 to 2, characterized in that: The detection device includes at least one sound source excitation that can generate a sound wave signal with adjustable amplitude and frequency, at least two sound wave sensors, a signal amplifying device, a signal collecting device and a signal processing device; the sound wave sensors are evenly arranged on the side wall of the system to be measured, the sound wave sensors are connected to the signal amplifying device to convert the sound wave signal into an electrical signal and transmit it to the signal amplifying device for amplification, the signal amplifying device is connected to the signal collecting device to transmit the amplified signal to the signal collecting device for collection, and the signal collecting device is connected to the signal processing device to analyze the collected signal to obtain characteristic parameters that characterize the phase balance characteristics of the system to be measured.

4. The supercritical fluid phase equilibrium detection device according to claim 3, characterized in that: When the number of acoustic wave sensors increases, they are preferably arranged along the height direction of the side wall of the supercritical fluid system to be measured, so as to more accurately determine the position of the phase interface in the system to be measured.

5. The supercritical fluid phase equilibrium detection device according to claim 3, characterized in that: The acoustic wave sensor is selected from one or both of an acoustic emission sensor and an acceleration sensor, and the frequency response characteristics of the acoustic wave sensors are the same, and the frequency response range is 1 Hz to 10 MHz.

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