WO2019179293A1 - System for measuring gas-liquid two-phase flow - Google Patents

Abstract

A system for measuring a gas-liquid two-phase flow, comprising a differential pressure flow meter and a moisture content sensor that are fixed on a measurement pipeline, wherein the differential pressure flow meter and the moisture content sensor are installed in series, the differential pressure flow meter is used for measuring the total virtual high-mass flow of a two-phase flow, and the moisture content sensor is used for measuring liquid phase content in the two-phase flow to achieve the non-split metering of the two-phase flow; the moisture content sensor is a swirl split-phase capacitance moisture content sensor that comprises a swirl split-phase unit and a capacitance measuring unit, wherein the swirl split-phase unit comprises a spiral blade support rod, two or more spiral blades distributed at the outer circumference of the spiral blade support rod and an outer tube wall; the capacitance measuring unit comprises a metal inner core, an insulating layer that covers the outer circumference of the metal inner core and an outer metal tube wall. And a differential pressure and swirl split-phase capacitance moisture content sensor-based moisture measurement system.

Description

Gas-liquid two-phase flow measuring system Technical field

The invention belongs to the technical field of gas-liquid two-phase flow measurement, and relates to a novel gas-liquid two-phase flow measurement system based on a differential pressure method device and a device based on a swirling phase separation capacitance water content method.

Background technique

Gas-liquid two-phase flow is widely present in various fields of industrial production. With the advancement of technology, the measurement of gas-liquid two-phase flow using non-separation techniques is gradually accepted. At present, the relatively mature gas-liquid two-phase flow measurement technology that can be applied in industrial fields mainly includes "differential pressure + ray technology", "differential pressure + microwave technology", "double differential pressure technology" and the like. The invention is directed to the technical difficulties to be solved in the field: firstly, it is safe and radiation-free, and is convenient for on-site management; secondly, the measurement range is as wide as possible, and is applicable to changes of complex fluid flow patterns, for example, for layered wavy flow, annular flow, Complex flow patterns such as mixed flow and even slug flow; third, simple structure, light weight, and easy maintenance. The invention aims at starting from the above technical difficulties and proposes a novel gas-liquid two-phase flow measuring system.

The differential pressure type throttling device has a simple structure, high reliability, low cost, and good measurement accuracy within a certain range, and has become a measuring device capable of working stably under both flow patterns of two-phase flow. Commonly used throttling devices include standard throttling devices such as orifice plates, venturis, nozzles, venturi nozzles, and deformation structures of standard devices, such as shaped orifice plates, porous orifice plates, shaped venturis, shaped nozzles, cones, wedges, etc. Non-standard throttling device. In 1967, Chisholm D. used the phase separation method theory to derive the virtual height model of the gas-liquid two-phase flow in the orifice based on the flow of incompressible two-phase mixtures through sharp-edged orifices. In 1979, based on the results of experimental analysis of gas-liquid density ratio based on a large number of working conditions, it was proposed to apply to a pressure of 0.7-20.1 MPa, a dryness of 0.1-1, an orifice plate throttling ratio of 0.25-0.75, and a pipe inner diameter of 8 A virtual height model of -75 cm; in 1997, De Leeuw proposed a model for measuring the humidity of the venturi. The formula form borrows the aperture moisture measurement model proposed by Chisholm and corrects its parameters. In 2002, RNSteven used the experimental data of NEL to model the new venturi to measure the moisture model; in 2003, M .Van Werven and HREVan Maanen see moisture as a hazy flow and explore the flow model of a wet gas flow through a venturi. Since 2008, Xu Ying of Tianjin University has conducted in-depth research on conical, venturi and its heterogeneous venturi, and proposed a venturi gas-liquid two-phase flow based on the double throat differential pressure and the triple differential pressure double ratio method. Measuring device and measuring method.

Capacitance method is a traditional moisture content measurement technology with simple principle and convenient maintenance. At present, the technology based on capacitance method mainly adopts non-contact method. For example, in 1998, Jarle Tollefsen and Erling A. Hammer published a paper "Capacitance sensor design for reducing errors in phase concentration measurements", which studied the use of surface spiral electrodes to measure the aqueous and gas phase concentrations in crude oil; 2009 A. Jaworek, A. In the paper "Phase-shift detection for capacitance sensor measuring void fraction in two-phase flow", Krupa et al. used the phase shift information of the wall capacitive sensor to measure the phase content of the two-phase flow. Small pipe diameter (pipe inner diameter 1, 2, 4, 9.5 mm) and low flow rate two-phase flow; in 2015, Kathleen De Kerpel et al. used the opposite wall in "Two-phase flow regime assignment based on wavelet features of a capacitance signal" The capacitor is tested on a horizontal tube with an inner diameter of 8 mm. The flow pattern mainly includes slug flow, intermittent flow and annular flow. The wavelet characteristics of the capacitor signal are analyzed. It is considered that the flow pattern and dryness have a significant influence on the wavelet characteristics. In summary, according to the current situation analysis of measuring the phase fraction of multiphase flow according to the non-contact capacitance method, it is known that researchers at home and abroad have carried out a lot of work in the field of measuring the phase fraction of multiphase flow, optimizing the capacitor structure and Valuable experience has been accumulated in the incentive model. However, the measurement results are seriously affected by the two-phase flow pattern. The response of the sensor is still strongly dependent on the spatial distribution of each phase medium, which brings great difficulty to the measurement of phase content and is difficult to promote and apply in industry.

Summary of the invention

The object of the present invention is to provide a gas-liquid two-phase flow measuring system which is simple in structure, wide in range range and high in reliability, and can effectively overcome the influence of flow pattern and can be used for slug flow (ie, high volume content). The gas-liquid two-phase flow of the liquid rate is effectively predicted. The invention adopts the following technical solutions:

A moisture measuring system based on differential pressure and swirling split-phase capacitance water content sensor, comprising a differential pressure flow meter and a moisture content sensor fixed on a measuring pipe, a differential pressure flow meter and a moisture content sensor installed horizontally, to flow first The differential pressure flowmeter measures the total virtual high-quality flow of the two-phase flow, and then measures the liquid phase content in the two-phase flow through the moisture content sensor to realize the non-separation measurement of the two-phase flow; the moisture content sensor is a swirling flow The split-phase capacitance water content sensor comprises a cyclone phase splitting section and a capacitance measuring section, and the swirling phase-separating section comprises a spiral blade support rod, two or more spiral blades and an outer tube wall distributed around the outer circumference of the spiral blade support rod; capacitance measurement The segment includes a metal inner core covering the outer periphery of the inner core of the metal and the outer metal tube wall.

Preferably, the helix angle of the spiral blade is between 30° and 60°, and each of the spiral blades is evenly distributed along the circumference. The tail of the spiral blade support rod is matched with and connected to the size of the metal core, and the outer tube wall and the outer metal tube wall are matched and connected to each other. The inner diameter of the flow pipe is D, the inner diameter of the outer metal pipe wall is 1~3D, the pitch of the spiral blade is 0.5D~3D, the length of the capacitance measuring unit is 2D~6D, and the ratio of the diameter of the metal inner core to the diameter of the outer metal pipe wall is 1. : 2 to 1:8. The water-facing surface of the spiral blade support rod is streamlined.

The invention also provides a gas-liquid two-phase flow measuring system with wider application, including a differential pressure flowmeter and a moisture content sensor fixed on the measuring pipeline, a differential pressure flowmeter and a moisture content sensor installed in series, and a differential pressure flowmeter. For measuring the total virtual high-quality flow of the two-phase flow, the moisture content sensor is used to measure the liquid phase content in the two-phase flow, and realize the non-separating measurement of the two-phase flow; the moisture content sensor is a swirling split-phase capacitor containing water The rate sensor comprises a cyclone phase separation unit and a capacitance measuring unit, and the swirling phase separation unit comprises a spiral blade support rod, two or more spiral blades and an outer tube wall distributed around the outer circumference of the spiral blade support rod; the capacitance measuring unit comprises a metal inside The core covers the insulating layer on the outer circumference of the metal inner core and the outer metal tube wall.

Preferably, the helix angle of the spiral blade is between 30° and 60°, and each of the spiral blades is evenly distributed along the circumference. The tail of the spiral blade support rod is matched with and connected to the size of the metal core, and the outer tube wall and the outer metal tube wall are matched and connected to each other. The inner diameter of the flow pipe is D, the inner diameter of the outer metal pipe wall is 1~3D, the pitch of the spiral blade is 0.5D~3D, the length of the capacitance measuring unit is 2D~6D, and the ratio of the diameter of the metal inner core to the diameter of the outer metal pipe wall is 1. : 2 to 1:8. The water-facing surface of the spiral blade support rod is streamlined.

Compared with the prior art, the present invention has the following technical effects:

(1) The present invention combines a differential pressure method throttling device with a cyclone-phase-separating capacitance water content method to measure both moisture and high volume liquid content gas present in an industrial site. The liquid two-phase flow (such as the slug flow) is measured, and the liquid phase measurement range can be achieved from 0 to 100%.

(2) The upstream and downstream of the present invention only need to be flanged to the corresponding straight pipe section;

(3) After the gas-liquid two-phase flow flows into the cyclone phase separation unit, the flow guiding action of the spiral vane changes the flow direction and state of the fluid. Due to the large density of the liquid phase, the circular motion is performed under the action of centrifugal force, and the liquid phase is smashed through the gas phase to the wall of the tube to achieve gas-liquid separation. The gas phase is concentrated in the central region, the gas core rotates, and the liquid phase distributes along the tube wall to form a rotating liquid film. At this time, the capacitance measurement result of the capacitance measuring unit is independent of the distribution of the liquid phase in the space, that is, the flow is not affected. Type effect.

(4) The present invention will significantly enhance the gas-liquid two-phase spinning effect through a plurality of sets of flow-through spiral blades;

(5) No need to separate, do not rely on radioactive technology and tracer technology to measure the water content in the gas-liquid two-phase flow, the structure is simple, safe and reliable, and the maintenance cost is low.

DRAWINGS

Fig. 1 Schematic diagram of the installation method of the gas-liquid two-phase flow measurement system, a total of eight are given.

Wherein, 1-1 represents a differential pressure method throttling device; and 1-2 represents a cyclone phase separation capacitance water content method.

There are 8 different series installations, horizontal installation (1(a), 1(b)), vertical bottom-up installation (1(c), 1(d)), vertical top-down Installation (1(e), 1(f)), inverted U-type installation (1(g), 1(h));

The gas-liquid two-phase flow may first pass through the differential pressure throttling device (1(a), 1(d), 1(e), 1(g)), or may first pass through the swirling phase separation capacitor moisture content. Method (1(b), 1(c), 1(f), 1(h)).

Figure 2 is a block diagram of the measurement principle of the gas-liquid two-phase flow measurement system.

Fig. 3 Schematic diagram of the sensor of the cyclone phase separation capacitor moisture content method.

Figure 4 is a schematic view of a multi-spiral blade of a cyclone phase separation unit.

4(a1) is a left side view of the three-helix blade, FIG. 4(a2) is a front view of the three-spiral blade, and FIG. 4(a3) is an overall schematic view of the three-helix blade;

4(b1) is a left side view of the four-helix blade, FIG. 4(b2) is a front view of the four-spiral blade, and FIG. 4(b3) is an overall schematic view of the four-helix blade.

Figure 5 shows the relationship between the relative liquid film thickness and the volumetric liquid fraction LVF in a gas-liquid two-phase flow capacitor unit.

Figure 6 shows the relationship between the relative liquid film thickness and the relative capacitance value in a gas-liquid two-phase flow capacitor unit.

Figure 7 shows the relationship between the volumetric liquid fraction LVF and the capacitance value.

[Correct according to Rule 91 02.04.2019] wherein Figure 7(a) is 0.6Mpa, the apparent flow rate is 3m / s, 5m / s, 10m / s, 20m / s volume liquid rate LVF and capacitance value relationship Figure

[Correct according to Rule 91 02.04.2019] Figure 7(b) shows the volumetric liquid fraction LVF and capacitance value at three different pressures (0.6 MPa, 1.2 MPa, 1.6 MPa) at a gas phase apparent flow rate of 10 m/s. Change diagram.

Figure 8 shows the relationship between the virtual high OR of the differential pressure throttling device as a function of volumetric liquid fraction LVF.

detailed description

The invention will be further described in detail below with reference to the accompanying drawings.

In order to avoid the influence of the flow pattern when the cyclone phase-separated capacitor moisture content device is used, the present invention uses a multi-blade-flow type swirling split-phase capacitor water content method to rectify the gas-liquid two phases by the flow-through spiral blade. The liquid phase is forced to distribute on the wall of the tube to form a liquid film. Since the measuring system adopts multiple sets of spiral blades, the spinning effect is remarkable.

As shown in FIG. 1 , it is a schematic diagram of a method for measuring a gas-liquid two-phase flow rate system in combination with a differential pressure method throttling device and a cyclone phase-separating capacitance water content method. The measuring system is installed in series. There are 8 installation modes in the figure. The flow can be measured by the differential pressure method to measure the total virtual high-quality flow of the two-phase flow. It can also be measured by the cyclone-phase-capacitance water content method. The liquid phase content in the phase flow, the system can be installed horizontally, vertically upwards or vertically downwards, or can be installed in series through a U-shaped tube (not shown) or an inverted U-shaped tube, in addition, The schematic is either horizontal or vertical, and in practical applications it can also be mounted on a slanted measuring pipe.

2 is an embodiment of the present invention, which is a gas-liquid two-phase flow measuring system combined with a differential pressure method throttling device and a cyclone phase-separating capacitance water content method device, which adopts a horizontally mounted differential pressure flow meter + swirl The split-phase capacitance moisture content sensor constitutes a moisture two-phase flow measurement system to measure the two-phase flow of wet natural gas in the industrial site. The measurement method is as follows:

(1) Measuring the volumetric moisture content by using a capacitance measuring unit (capacitance measuring section)

The change in volumetric moisture content LVF in the gas-liquid two-phase flow causes a change in the thickness of the liquid film Δh/h ₀ , that is, the thickness of the liquid film divided by the thickness of the water layer h ₀ when the water is full, and further, the change in the thickness of the liquid film causes a capacitance value. The relative change ΔC/C ₀ , that is, the change in capacitance caused by the presence of the liquid phase of the two-phase flow divided by the capacitance value C ₀ of the single-phase gas, is: LVF → Δh / h ₀ → ΔC / C ₀ . According to the change law of volumetric water content and capacitance, the corresponding mathematical model is established.

LVF=Ψ(ΔC/C ₀ ) (1)

(2) measuring the gas-phase virtual high-quality flow W _tp by using a differential pressure throttling device,

Where: W _tp is the virtual high mass flow rate of the fluid; C _d is the outflow coefficient of the venturi; ε is the expansion coefficient of the measured fluid; β is the throttling ratio, ie the throat diameter and the inlet diameter The ratio d/D; ΔP _tp is the pressure difference before and after the two-phase flow passes through the throttle; ρ _g is the density of the gas.

(3) Virtual height definition

The ratio of the gas phase virtual high quality W _tp measured by the differential pressure method throttling device to the true gas phase mass W _g is false high,

(4) Establish a virtual height model

Using the dimensional analysis method, a virtual height measurement correction model is established in the form of

OR=Φ(LVF,ρ _l /ρ _g Fr _g ) (4)

Where LVF is the volumetric moisture content measured by the capacitance measuring unit, ρ _l /ρ _g is the liquid-gas density ratio, and Fr _g is the gas-phase Froude number, which is the ratio of the gas phase inertial force to the liquid gravity in the gas-liquid two-phase flow. Square root, for

Where U _sg is the gas phase apparent flow rate and D is the pipe diameter.

According to the formula (1), the volumetric liquid content can be obtained, and according to the formulas (2), (3), (4), and (5), an iterative calculation of the gas phase flow rate can be realized, thereby obtaining a gas phase and a phase separation flow rate.

The multi-blade cyclone phase-separating capacitor moisture content method of the present invention is shown in FIG. Can be combined with any single-phase differential pressure meter, such as orifice plate, venturi, V cone and so on. The present invention is different from the conventional moisture content measuring device in that the gas-liquid two phases are subjected to cyclone phase separation to measure the capacitance. As shown in Fig. 3, the gas-liquid two-phase flows into the cyclone phase separation unit (swirl phase separation section) through the differential pressure device, and simultaneously swirls with a plurality of sets of spiral blades, and the liquid phase can be completely separated from the gas phase to the pipe wall. Due to the large density of the liquid phase, the phase separation of the gas phase in the central region and the liquid phase along the tube wall is achieved under the action of centrifugal force, thereby overcoming the interference of the flow pattern on the phase content measurement. Simulation studies have found that the gas-liquid distribution is basically stable after the spiral blades. In the capacitance measuring unit, the metal inner core (Fig. 3, 2-1) serves as the inner electrode, and the outer metal tube wall (Fig. 3, 2-3) and the liquid film distributed on the tube wall together constitute the outer electrode, the gas phase and the insulating layer. (Fig. 3, 2-2) The insulating dielectric layer is formed to form a capacitor. To improve the sensitivity of the capacitor, it is necessary to ensure that the diameter of the outer metal tube wall is twice or more the diameter of the metal inner core.

As shown in FIG. 4, FIG. 4(a1) is a left-side view of the three-spiral blade, FIG. 4(a2) is a front view of the three-spiral blade, and FIG. 4(a3) is an overall schematic view of the three-spiral blade. The angle of each blade is 120°, the inner diameter of the pipe is D, and the pitch is 2.5D; Figure 4 (b1) is the left side view of the four-helix blade, and Figure 4 (b2) is the front view of the four-spiral blade, Figure 4 (b3) For the overall schematic diagram of the four spiral blades, each blade has an angle of 90°, and the inner diameter of the pipe is D, and the pitch is 1.5D.

The CFD numerical simulation method is used to simulate the variation of the air-water two-phase flow in the measurement system. The gas phase apparent flow rate is 3m/s-20m/s, the pressure is 0.6MPa, 0.8MPa, and the differential pressure throttling device is venturi. For example, the diameter of DN50, the throttle ratio of 0.55, the effect of volumetric liquid fraction on the thickness of the liquid film, the influence of the capacitance value and the effect of the false height are as follows:

Figure 5 shows the air-water two-phase flow relative to the liquid film thickness at a gas flow rate of 3 m/s, 5 m/s, 10 m/s, and 20 m/s at 0.6 MPa (the liquid film thickness value divided by the full pipe water) The relationship between the thickness of the water layer h ₀ ) and the volumetric liquid content LVF, namely LVF→Δh/h ₀ . It can be seen from Fig. 5 that at different gas phase flow rates, the relative thickness of the liquid film shows a monotonous upward trend with increasing liquid content; when the liquid content is the same, the higher the gas phase flow rate, the thinner the liquid film thickness.

Fig. 6 is a graph showing the relationship between the apparent flow velocity of the gas phase at 0.6 MPa and the relative change of the liquid film thickness of the 20 m/s air-water two-phase flow and its induced capacitance, that is, Δh/h ₀ → ΔC/C ₀ , indicating the same At the flow rate, the greater the rate of change of the relative thickness of the liquid film, the greater the rate of change of capacitance; the smaller the flow rate, the greater the relative change rate of the capacitance at the same rate of change of the liquid film, indicating that the capacitance change is more sensitive at a small flow rate, and the capacitance sensitivity is high. The lower the lower limit of the liquid phase range, the better the measurement of low liquid content.

[Correct according to Rule 91 02.04.2019]
Figure 7 is:
Fig. 7(a) is a graph showing the relationship between the apparent liquid flow rate of 3m/s, 5m/s, 10m/s, 20m/s volumetric liquid rate LVF and capacitance at 0.6MPa, ie LVF→ΔC/C ₀ . It can be seen from the figure that the higher the gas phase flow rate, the larger the capacitance value, and the capacitance value monotonously increases with the LVF.

Figure 7(b) shows the effect of the apparent gas flow rate of 10 m/s on the measured capacitance under three different pressures (0.6 MPa, 1.2 MPa, 1.6 MPa). The higher the pressure, the smaller the relative capacitance change. As the pressure increases, the gas phase density increases, the liquid flow rate increases under the same flow rate and liquid content rate, and the liquid film becomes thinner, resulting in a decrease in the capacitance change value. The relative change in capacitance under each pressure varies with volume. The trend of liquid rate LVF is consistent.

Figure 8 shows the apparent gas flow rates at 0.6 MPa of 3 m/s, 5 m/s, 10 m/s and 15 m/s (gas Froude numbers: 0.395, 0.645, 1.280 and 1.912, respectively). The relationship between the virtual height and the volumetric liquid fraction LVF produced by the standard venturi with a caliber DN50 and a throttle ratio of 0.55. In the figure, we can see that the imaginary virtual high value increases with the volumetric liquid content. Large, with good regularity.

According to the formula (1), the volume liquid content can be obtained. According to the iterative calculation of the formulas (2), (3), (4) and (5), the gas phase flow rate can be measured, and the total amount and the liquid phase content can be obtained. Liquid phase flow.

The invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and explain the embodiments of the invention. It will be apparent to those skilled in the art that various modifications can be made in the form of the invention without departing from the scope of the invention.

Claims (10)

1. A moisture measuring system based on differential pressure and swirling split-phase capacitance water content sensor, comprising a differential pressure flow meter and a moisture content sensor fixed on a measuring pipeline, wherein the differential pressure flow meter and the moisture content sensor are horizontally installed The flow firstly measures the total virtual high-quality flow of the two-phase flow through the differential pressure flow meter, and then measures the liquid phase content in the two-phase flow through the moisture content sensor to realize the non-separation measurement of the two-phase flow; the moisture content The sensor is a swirling split-phase capacitance moisture content sensor, including a swirling phase separation section and a capacitance measuring section, the swirling phase separation section includes a spiral blade support rod, and two or more spiral blades and an outer tube distributed on the outer circumference of the spiral blade support rod. The wall; the capacitance measuring section includes a metal inner core covering the outer insulating layer of the inner core of the metal and the outer metal tube wall.
2. The system of claim 1 wherein the helix angle of the helical vanes is between 30 and 60 and each spiral vane is evenly distributed circumferentially.
3. The system of claim 1 wherein the tail portions of the helical blade support rods are sized and interconnected with the metal core, and the outer tube wall and the outer metal tube wall are sized and interconnected.
4. The system according to claim 1, wherein the inner diameter of the flow pipe is D, the inner diameter of the outer metal pipe wall is 1 to 3D, the pitch of the spiral blade is 0.5D to 3D, and the length of the capacitance measuring unit is 2D to 6D. The metal core diameter to the outer metal tube wall diameter ratio is 1:2 to 1:8.
5. The system of claim 1 wherein the water-facing surface of the helical blade support rod is streamlined.
6. A gas-liquid two-phase flow measuring system comprises a differential pressure flow meter and a moisture content sensor fixed on a measuring pipe, wherein the differential pressure flow meter and the moisture content sensor are installed in series, and the differential pressure flow meter is used for measuring two phases The total virtual high-quality flow, the moisture content sensor is used to measure the liquid phase content in the two-phase flow, and realize the non-separating measurement of the two-phase flow; the moisture content sensor is a swirling split-phase capacitance moisture content sensor, including a cyclone phase separation unit and a capacitance measuring unit, the cyclone phase separation unit comprises a spiral blade support rod, two or more spiral blades and an outer tube wall distributed around the outer circumference of the spiral blade support rod; the capacitance measuring unit comprises a metal inner core, covered in The outer periphery of the metal core and the outer metal tube wall.
7. The system of claim 6 wherein the helix angle of the helical vanes is between 30 and 60 and each spiral vane is evenly distributed circumferentially.
8. The system of claim 6 wherein the tail portions of the helical blade support rods are sized and interconnected with the metal core, and the outer tube wall and the outer metal tube wall are sized and interconnected.
9. The system according to claim 6, wherein the inner diameter of the flow pipe is D, the inner diameter of the outer metal pipe wall is 1 to 3D, the pitch of the spiral blade is 0.5D to 3D, and the length of the capacitance measuring unit is 2D to 6D. The metal core diameter to the outer metal tube wall diameter ratio is 1:2 to 1:8.
10. The system of claim 6 wherein the water-facing surface of the helical blade support rod is streamlined.

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