JPH022521B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for measuring the flow rates of the gas and liquid phases, respectively, of a gas-liquid stream flowing in a conduit, and to a flow meter implementing the method. Two-phase flow refers to a flow containing gas and liquid phases of one or more components. Typical streams contain wet steam, oil and gas, and air and water. Generally, flow meters used to measure single-phase flow contain a device that measures the pressure drop of the flow, which pressure drop can be correlated to the flow rate of this flow through a theoretical mathematical model. can. However, in general for two-phase flow it is desirable to obtain individual gas and liquid flow rates, Wg and Wf, respectively. Generally, these flow rates are expressed in terms of total mass flow rate (W) and flow quality (x), where these terms are defined as: W=Wg+Wf; and x=Wg/Wg+Wf. A number of two-phase flowmeters have already been proposed. Two such instruments that correlate one of the aforementioned flow parameters with a differential pressure measurement are an orifice plate meter and a vent limeter. Orifice plate meters consist of an orifice mounted over a conduit carrying a two-phase flow.
An accelerating pressure drop is measured across this orifice plate. A mathematical model is then used to correlate the total mass flow rate of the stream with the measured acceleration pressure difference. A bench lily meter consists of a bench lily placed in a conduit carrying a two-phase flow. The accelerating pressure drop across the bench lily is measured and the Collins parameter (Collins parameter) which allows the mathematical model to modify the flow quality and total mass flow rate or the quality and dimensionless
Ep (detailed below). The two instruments both rely on a single pressure differential measurement to obtain the values of these parameters for two-phase flow. Other two-phase flow meters have been proposed that monitor two-phase flow with two or more measurements.
One such meter uses a gamma densitometer and eliminates a fraction measurement and a turbine meter or drag disc to obtain a second measurement. These two measurements are mathematically correlated to indicate the respective phase mass flow rates. This measurement method is limited to a very narrow quality range. Also, using delicate gamma densitometer equipment is expensive. For two-phase flows such as high pressure wet steam, such devices are impractical. Very recently, an orifice cut-pull flowmeter was proposed for two-phase flow, by K. Sekiguchi et.
“Two-Phase Flow Measurement Using Orifice Cut-Pull in Horizontal Pipelines” by Al.
Phase Flow Measurements with Orifice−
Couple in Horizontal Pipe Line,”Bulletin
of the ISME, Volume 21, No. 162, December 1978)
reference. This instrument contains two segmented orifices or baffles in a conduit that carries a two-phase flow. Three pressure drop measurements are obtained, two through the segmented orifice and a third through the two orifices. The two individual pressure drops and the total pressure drop are then correlated with the gas and liquid flow rates by a model specific to this device. This measuring device seems to give very good results. The disadvantage of this device is that the data is not represented in dimensionless form. Therefore,
The performance of different devices is difficult to predict. The present invention is designed to measure two-phase flow, i.e. four flow parameters: quality;
To determine the value of two of the parameters: total mass flow, gas mass flow, and liquid mass flow, the difference between two of these four parameters and two easily measured two-phase properties, such as pressure and temperature. Assume that two independent relationships are used.
In this method, two physical properties of two-phase flow, which follow independent laws, are used. A theoretical two-phase model is known that can be used to correlate acceleration pressure differential and flow rate and to correlate frictional pressure drop and flow rate. According to the invention, a method for measuring the flow rates of the gas and liquid phases, respectively, of a gas-liquid stream flowing in a conduit, comprises measuring a differential pressure in the conduit representative of said flow rate, the measuring method comprising: creating a frictional pressure drop in the conduit, measuring the frictional pressure drop, creating an accelerating pressure drop in the conduit, and measuring the accelerating pressure drop, and frictionally adjusting the flow rate of each phase of the gas-liquid flow. A method is obtained which is characterized in that the pressure drop and the accelerated pressure drop measurements are calculated using a predetermined relational expression. Further according to the invention, in an apparatus for carrying out the method, a frictional pressure in the conduit is provided by a longitudinally twisted tape arranged in the conduit and adapted to create a vortex in the flow. a first device for producing a drop, a device for measuring a frictional pressure drop, a second device consisting of a bench lily placed in the conduit for producing an accelerating pressure drop in the conduit, and a device for measuring an accelerating pressure drop. A flow meter is obtained, characterized in that the second device is advantageously arranged downstream of the first device. In an advantageous embodiment of the invention, a frictional pressure drop is measured across a twisted tape (hereinafter referred to as a helical tape) in a conduit carrying a two-phase flow, and an accelerated pressure drop is measured across a conduit carrying a two-phase flow. Measured via a bench lily placed downstream of the spiral tape. This advantageous measurement combination takes advantage of the known fact that the bench lily receives annular flow and provides excellent correlation between pressure drop measurements and total mass flow. Thus, the helical tape upstream of the bench lily increases the efficiency of the bench lily by promoting circular flow. Furthermore, it is a unique feature of the present invention that the spiral tape and bench lily measuring sections are independent. This is because the former measures the frictional pressure drop, and the latter measures the acceleration pressure drop. In another advantageous embodiment of the invention, a third parameter is measured to evaluate the physical properties of the two-phase flow. Most preferably this measurement is a measurement of the temperature or static pressure of the stream. like wet steam 2
For phase monocomponent flows, temperature or static pressure measurements can be used as a measure of flow density and viscosity. For two-phase, two-component flows, both temperature and static pressure measurements are required. These physical characteristic values are used in the mathematical model used to correlate pressure drop measurements and individual mass flow rates. In the following, the invention will be explained in detail with reference to drawing examples. FIG. 1 shows an embodiment of a helical tape vortex generator of a flow meter according to the invention, which generator is used to create a frictional pressure drop in a two-phase flow; FIG. FIG. 3 shows an embodiment of a flowmeter bench lily according to the invention, which is used to create an accelerated pressure drop in a two-phase flow; FIG. 4 shows the computer program used to correlate the flow rate of each of the phases; FIG. 4 shows the flow meter and the coordinates representing the accuracy of the correlation algorithm of FIG. Actual measurements are plotted against the gas flow rate obtained by correlating the pressure drop measurements from the flow meter with the gas flow rate; and FIG. These are coordinates representing the accuracy of the correlation algorithm for mass flow rate Wf. The flow meter 1 according to an advantageous embodiment of the invention has the function of generating and measuring a pressure drop during a two-phase flow, which pressure drop can be correlated to the respective flow rates of the two phases. As shown in FIGS. 1 and 2, the flow meter 1 contains a helical tape-shaped vortex generator 2 and a bench lily 3 mounted in a horizontal conduit 6 carrying a two-phase flow.
Pressure transducers 4 and 5 are provided to measure the differential pressure across the helical tape 2 and bench lily 3, respectively. A spiral tape-shaped vortex generator 2 is connected to a horizontal conduit 6.
providing a means for creating a frictional pressure drop in the
Furthermore, although a straight length of tubing could be used to create a frictional pressure drop, this would require a long length of tubing. Spiral tape-shaped vortex generators are known per se in heat exchangers, for example in E. Smithberg et al. et al.
“Friction and Forced Convection Heat−
Transfer Characteristics in Tubes with
Twisted Tape Swirl Generators, “Journal of Heat Transfer”
Heat Transfer), February 1964 issue, p. 39) and Narasimhaumaa Tei et al., ``Effect of turbulence promoters in two-phase gas-liquid flow in horizontal pipes'' (GS
R. Narasimhaumurty et al., “Effect of
Turbulence Promoters in Two−Phase Gas
Liquid Flow in Horizontal Pipes, “Chemical
Engineering Science, Vol. 24, 1969, p. 331)
reference. In short, the helical tape 2 contains a length of steel tape 7 having the same width as the diameter of the conduit 6. This tape 7 is screwed into the conduit 6 to the desired pitch and the end 8 is threaded into the conduit 6.
It is fixed to the notch 9 inside. Advantageously, the upstream end 10 of this tape is arranged vertically in order to evenly divide the incoming liquid phase. This spiral tape
Generates a vortex flow, also known as an annular flow. Annular flow is a two-phase flow pattern characterized by an annular film of liquid moving along the inner wall of the tube and an air stream moving at a greater velocity through the core of the tube.
A frictional pressure drop model for gas-liquid flow through a helical tape is disclosed in the paper by Narasim Hamarty. In order to measure the frictional pressure drop across the helical tape 2, two pressure taps 11 are provided communicating with the conduit 6, preferably at a slightly inward distance from the end 8 of the tape 7. This distance is
It allows the appearance of the annular flow pattern known to form in the helical tape 2 and avoids possible inlet and outlet pressure losses. Each pressure tap 11 consists of a piezoelectric ring 12 sealed around the conduit 6 surrounding an annular groove 13 between the ring 12 and the conduit 6. A plurality of holes 1 through the wall of the conduit 6
4 opens into the annular groove 13. A pressure pipe 16 is connected to the piezoelectric ring 12 via the connection hole 15 and leads to one side of the groove-membrane magnetoresistive transducer 17 . This transducer 17 includes itself and
The function of converting a pressure difference into an electrical signal is known. FIG. 2 shows the bench lily 3 in detail. This bench lily 3 provides a means for creating an accelerated pressure drop in the conduit 6. Optionally, a nozzle, orifice, segmented buffle or other device known to produce an accelerated pressure drop in a two-phase flow can be substituted for the bench lily. However, the bench lily 3 is advantageous because it easily accepts the annular two-phase flow from the helical tape 2 and also provides a good correlation between the accelerated pressure drop and the total mass flow rate (W) measured across this bench lily. be. The bench lily 3 is arranged downstream of the spiral tape 2 for the reasons mentioned above. This bench lily has a retractable throat portion 18 in which two
The velocity of the phase flow is increased and the pressure is reduced through the throat 18. In order to measure the acceleration pressure drop across the bench lily 3, two pressure taps 19 are provided which communicate with this bench lily. As shown in FIG. 2, these taps 19 are spaced inwardly from the terminal end of the bench lily 3. These pressure taps 19
is the same as pressure tap 11 and the same symbols and numerals have been used to represent the same parts. Pressure tubing 20 interconnects these pressure taps 19 to opposing faces of thin film magnetoresistive transducers 21. Since pressure fluctuations are generally large when measuring two-phase flows, pressure dampers 22 are advantageously included in the impulse lines 16, 20 between the respective pressure taps 11, 19 and transducers 17, 21. I am forced to do it. These pressure dampers 22 serve to dampen pressure fluctuations. The damper 22 consists of a variable force piston (not shown) inserted into a thin capillary tube (not shown). To further limit pressure fluctuations, the impulse lines 16, 20 are periodically cleaned using gas or liquid. Impulse tubes 16 and 2
The gas or liquid filling acts as a means of transmitting pressure from the pressure taps 11,19 to the transducers 17,21. Therefore, scavenging techniques are the norm for two-phase flow measurements. To protect the electronic transducers 17, 21, an isolation valve 25 protects the electronic transducers 17, 21.
are contained in impulse tubes 16, 20 to each side of the. A pressure equalization valve 26 is also included to further protect the transducer. Opposite ends 23,
24 is threaded. Advantageously, the diameter of the conduit 6 is the same as the diameter of the piping in order not to further block the two-phase flow. In most cases when measuring a two-phase flow, it is advantageous to measure a third parameter, such as the static pressure of this flow. As will be clear from the description below, this third parameter is generally required to correlate the two pressure drop measurements with the respective flow rates of the two phases. This correlation includes physical properties such as density and viscosity of each of the two phases. In the case of a one-component two-phase flow, such as wet steam, measurements of the static pressure or temperature of this flow allow the density and viscosity of each phase to be calculated. For example, for wet steam, a standard steam table can be used. For two-component two-phase flows, both temperature and static pressure measurements may be required. However, if the flow meter 1 is used with a two-phase flow with known physical characteristics, the third parameter is not required. In general, the third parameter can be measured at any location adjacent to the helical tape 2 and the bench lily 3. FIG. 2 shows an apparatus 30 for measuring static pressure in a two-phase flow downstream of a bench lily. This device 30 contains a pressure tap 27 identical to pressure tap 11 and is attached to conduit 6. A pressure line 28 leading from the tap 27 is connected to a pressure sensing device 29, such as an open-ended mercury manometer or an electronic pressure transducer. If it is desired to measure the temperature of the stream, a suitable temperature sensing device (not shown) can be attached to the flow meter. The invention will now be described in more detail with reference to an example showing the operating characteristics of an advantageous embodiment of a flow meter and illustrating examples of calculations carried out in correlating the flow meter measurements with the individual flow rates of the two phases. Example A diameter that forms a flow meter as shown in Figures 1 and 2 and carries a two-phase flow of air-water.
1" (approximately 25.4 mm). The spiral tape-shaped vortex generator is inserted into a 4-inch (approximately 102 mm) pipe in the counterclockwise direction (as viewed from the upstream end of the flow meter).
Consists of twisted stainless steel tape 1/16" x 1" x 12" long (approx. 1.6mm x 25.4mm x 305mm). The bench lily has an inlet and outlet diameter of 1" (approx. 25.4mm) and a throat diameter Consists of a 3 3/4" (approximately 95.3 mm) long bench lily with a 5/8" (approximately 15.9 mm) length. 2
The static pressure of the phase flow was measured downstream of this bench lily using an open ended mercury manometer. The DC signals from transducers 17 and 21 were fed into a digital reader, chart recorder and small computer (not shown).
The differential pressure signal recorded on the chart recorder is
Time averaged over 3 minutes. To first calibrate the flowmeter, an air-water flow was injected through the flowmeter with known air and water flow rates, Wg and Wf, respectively, and quality (x) ranging from 0.25 to 0.90. Finally, measurements from the bench lily, spiral tape, and static pressure sensor can be applied to any two of these parameters: total mass flow (W), liquid mass flow (Wf), gas mass flow (Wg), and quality (x). combined to determine. Also clearly the volumetric flow rate can be calculated. Theoretical models correlating these pressure drop measurements with the above parameters are known. In this example, the effect of the spiral tape is expressed by the Lockhart-Martinelli parameter (Lockhart-Martinelli parameter)
Martinelli parameters) ² and ² : (1) ² = [Re _gt /Re _ft ] ⁿ [ρ _g /ρ _f ] [W _f /W _g ] ² [However, Re _gt and Re _ft are respectively are the Reynolds numbers of the gas and liquid phases; ρ _g and ρ _f are the densities of the gas and liquid phases, respectively]; (2) ² = (ΔP/ΔL) _tpt D _H g _c ρ _g A ² /2fW _g ² [where (ΔP/ΔL) _tpt is the pressure drop across the helical tape, D _H is the equivalent diameter of the conduit,
g _c is the conversion factor = 32.17 lb.ft/lb _f s ² , A is the cross-sectional area of the conduit, and f is the Fanning coefficient of friction]. The effect of bench lily was modeled with the following modified Collins parameter F _p and quality (x): (3) F _p = D ² [g _c ρ _g ΔP _tpv /W ² ] ^1/2 [where D is and ΔP _tpv is the pressure drop across the bench lily]; and (4) X=W _g /W _g +W _f The flow meter was first calibrated with known flow rates Wf and Wg. Pressure transducers 17 and 21
was calibrated by a known method using a water column. The results of the transducer calibration were modeled by the following least squares linear equation: (5) (ΔP/ΔL) _tpt = 5.0509 × 10 ^-3 × (transducer reading) + 1.1301 × 10 ^-3 ; and (6) ΔP _tpv = 1.8756×10 ⁻² × (transducer reading) −2.1482×10 ⁻² ΔP _tpv at a large number of known flow rates Wf, Wg,
(ΔP/ΔL) From the measured values of _tpt and static pressure Ps, Fp,
Multiple values of x, ² and ² were calculated.
The values of Re _gt , Re _ft , ρ _g and ρ _f are calculated from the static pressure values Ps and these Using the results, the bench-lily effect was modeled by the following linear relationship: (7) x = mF _p + b and the spiral tape effect was modeled by the following relationship: (8) ² = B ₁ + B ₂ ⁺ _B32 . These parameters m, b, B ₁ , B ₂ and B ₃
was derived by least squares analysis of a large number of gas mass flow values Wg. For the purpose of specifying these values, Wg, B ₁ , B ₂ and B ₃ , m and b
The values are summarized in Table 1. Table 1 Least squares parameters for spiral tape and bench lily models Spiral tape model: _g ² = B ₁ + B ₂ + B ₃ ² Bench lily model: x = mFp + b

[Table] The computer program calculates the values of gas and liquid flow rates Wg and Wf for a given combination of pressure readings Ps, (ΔP/ΔL) _tpt and ΔP _tpv , using these relationships (7) and ( 8) was configured to be used in the interpolation method. Figure 3 summarizes the computer programs that can be used. Shown in Table 1
By using the Wg level dependence, the values of Wf were determined by the respective equations (7) and (8). Two sets of Wf and Wg values were subsequently obtained from equations (7) and (8) for the bench lily and spiral tapes. For each set of values, the slope of Wf with respect to Wg was completely different. Therefore, the intersection of the two sets of data consistently represented a simultaneous solution of the Bench-Lily and Spiral Tape equations (7) and (8). This intersection was evaluated by applying linear interpolation to each set of data points. The effectiveness of this measurement and correlation method is illustrated in FIGS. 4 and 5, in which predicted values of Wf and Wg are plotted against measured values of Wf and Wg. Generally the accuracy is about 3% for Wg and 6% for Wf.
It was within the range of %. The accuracy of these predicted values would be greater if more experimental data were used.
Improvements can be made to reduce the size of the interval that requires linear interpolation. Extrapolation beyond the original range used in calibrating the device is disadvantageous.

[Brief explanation of drawings]

1 and 2 are schematic longitudinal sectional views of an embodiment of a vortex generator and a bench lily, respectively, which partially constitute the device according to the invention;
3A to 3D are flowcharts of a computer program for carrying out the method according to the invention, and FIGS. 4 and 5 represent the measurement accuracy of the gas flow rate and the liquid flow rate, respectively, of the apparatus according to the invention. This is a diagram. 1... Flow meter, 2... Spiral tape type vortex generator, 3... Bench lily, 6... Horizontal conduit, 7...
Steel tape, 12...Piezoelectric ring, 17...
Thin film magnetoresistive transducer, 18... Throat portion, 21... Thin film magnetoresistive transducer, 22... Pressure buffer, 25... Separation valve, 26
... pressure equalization valve, 29 ... pressure detection device, 30 ... static pressure measurement device.

Claims (1)

[Scope of Claims] 1. A method comprising measuring a pressure difference in a conduit representative of said flow rate in order to measure the flow rates of the gas and liquid phases, respectively, of a gas-liquid flow flowing in a conduit, the measuring method comprising: , creating a frictional pressure drop in the conduit 6 and measuring this frictional pressure drop, creating an accelerating pressure drop in the conduit and measuring this accelerating pressure drop, and determining the flow rate of each phase of the gas-liquid flow. A method for measuring the flow rate of a gas phase and a liquid phase, respectively, of a gas-liquid flow flowing in a conduit, the method comprising: calculating the flow rates of a gas phase and a liquid phase, respectively, of a gas-liquid flow flowing in a conduit, the method comprising calculating the flow rate of a gas-liquid flow in a conduit using predetermined relational expressions from measured values of frictional pressure drop and acceleration pressure drop. 2 Gas mass flow rate Wg and liquid mass flow rate Wf are
The frictional pressure drop measurement value (ΔP/ΔL) _tpt and the acceleration pressure drop measurement value ΔP _tpt and Wg and Wf are expressed by the following relational expression: ² = [Re _gt /Re _ft ] ² [ρ _g /ρ _f ] [W _f /W _g ] ² [However, Re _gt and Re _ft are the Reynolds numbers of the gas phase and liquid phase, respectively, ρ _g and ρ _f are the densities of the gas phase and liquid phase, respectively, and these Re _gt ,
Re _ft , ρ _g and ρ _f are assumed to be known quantities of flow or determined from the static pressure Ps in the conduit]; ² = (ΔP/ΔL) _tpt D _H g _c ρ _g ^A2 /2fWg ² [However, D _H is the equivalent diameter of the conduit, and g _c is
32.17lb.ft./lb. conversion factor equal to _f s ² , where A is the cross-sectional area of the conduit and f is the Fanning coefficient of friction]; F _p = D ² [g _c ρ _g ΔP _tpv / A method according to claim 1, characterized in that it is determined by correlating using: W ² ] ^1/2 , where D is the inner diameter of the conduit; and x=Wg/Wg+Wf. 3. to measure the flow rates of the respective gas and liquid phases of the gas-liquid stream flowing in the conduit, comprising measuring the differential pressure in the conduit representative of said flow rates;
creating a frictional pressure drop in the conduit 6 and measuring the frictional pressure drop; creating an accelerating pressure drop in the conduit and measuring the accelerating pressure drop; and determining the flow rate of each phase of the gas-liquid flow. In an apparatus that implements a method of calculating from measured values of frictional pressure drop and acceleration pressure drop using a predetermined relational expression, the flowmeter 1
a first device 2 for creating a frictional pressure drop in the conduit 6, provided by a longitudinally twisted tape 7 arranged in the conduit 6 and adapted to create a vortex in the flow; Advantageously, it consists of a device 4 for measuring the frictional pressure drop, a second device 3 consisting of a bench lily arranged in a conduit 6 for producing an accelerating pressure drop in this conduit, and a device 5 for measuring the accelerating pressure drop. A flow meter for measuring the flow rate of the gas phase and the liquid phase, respectively, of a gas-liquid flow flowing in a conduit, characterized in that a second device 3 is arranged downstream of the first device 2. 4 The device 4 for measuring the friction pressure drop consists of a pressure transducer connected via at least one section of torsion tape 7 and the device 5 for measuring the acceleration pressure drop consists of at least one section of the bench lily 3.
4. A flowmeter according to claim 3, characterized in that it comprises a pressure transducer connected via a pressure transducer. 5. Claim 1, characterized in that a third device 29 is provided for measuring the static pressure in the conduit 6, said third device 29 advantageously consisting of a manometer connected to the conduit 6. Flowmeter according to any one of Item 3 and Item 4.