Device for measuring flow rate of wet gas based on an exempt radioactive source

Abstract

A device for measuring flow rate of wet gas based on an exempt radioactive source, includes a section of cylindrical pipe and a conical throttle located inside the cylindrical pipe and coaxially arranged therewith. The conical throttle includes a head cone section and a tail cone section arranged to have a common bottom surface. The head cone section faces a wet gas inlet of the cylindrical pipe. An annular gap is defined between the inner wall of the cylindrical pipe and the maximum diameter of the conical throttle for passage of wet gas. An exempt radioactive source block is arranged at the maximum diameter of the conical throttle in such a way that the gamma rays emitted from the radioactive source block can transmit radially through the annular gap to reach the gamma ray detector located outside the cylindrical pipe.

Claims

1. A method for measuring flow of a wet gas using a device for measuring a flow rate of the wet gas based on a Ba.sup.133 radioactive source, wherein the Ba.sup.133 radioactive source has an activity less than 1×10.sup.6 Bq, the device comprising: a section of a cylindrical pipe and a conical throttle located and coaxially arranged inside the cylindrical pipe; the conical throttle comprising a head cone section and a tail cone section arranged to have a common bottom surface, wherein the head cone section faces a wet gas inlet of the cylindrical pipe; an annular gap is provided between the inner wall of the cylindrical pipe and a maximum diameter of the conical throttle for passage of the wet gas; wherein, the Ba.sup.133 radioactive source includes a Ba.sup.133 radioactive source block, the Ba.sup.133 radioactive source block is arranged at the maximum diameter of the conical throttle, wherein, gamma rays emitted from the Ba.sup.133 radioactive source block transmit radially through the annular gap to reach a gamma ray detector located outside the cylindrical pipe; a differential pressure measuring device comprising a first pressure measuring port located at a side wall of the cylindrical pipe at an upstream of the head cone section, and a second pressure measuring port located at a tip of the tail cone section; the method comprising: flowing the wet gas through the inlet end of the cylindrical pipe, and measuring a temperature T and a pressure P of the wet gas during the flowing; thereafter, flowing the wet gas through the annular gap under a guidance of the conical throttle, to exert a throttling function; measuring a pressure differential ΔP caused by the throttling function by the pressure differential measuring device; measuring a mass phase fraction α.sub.gas of a gas phase, a mass phase fraction α.sub.oil of an oil phase, and a mass phase fraction α.sub.water of a water phase by the gamma ray detector; and then, using the following steps to calculate a mass flow rate of the gas, oil and water phases: 1) a mixed density of the wet gas is calculated according to the following equation:
ρ=ρ.sub.water×α.sub.water+ρ.sub.oil×α.sub.oil+ρ.sub.gas×α.sub.gas; 2) a total mass flow rate Q.sub.m of the wet gas is calculated according to the following equation:
Q.sub.m=K.sub.0.Math.√{square root over (ΔP.Math.ρ)} wherein: Q.sub.m - - - mass flow rate, kg/h; K.sub.0 - - - coefficient; ΔP - - - differential pressure, kPa; ρ - - - mixed density of the wet gas, kg/m.sup.3; wherein: $K_0=0.126447.Math.\frac{C.Math.\mathrm{.Math.}}{\sqrt{1-{\beta }^4}}.Math.\left(D^2-d^2\right)$ $\beta =\frac{\sqrt{D^2-d^2}}{D}$ wherein: β - - - equivalent diameter ratio, usually from 0.35 to 0.75; D - - - inner diameter of the cylindrical pipe 1, m; d - - - maximum diameter of the cone throttle, m; ε - - - compression coefficient, for liquids, ε=1, and as for gases, $\mathrm{.Math.}=\sqrt{\frac{k{\tau }^{2/k}}{k-1}\frac{1-{\beta }^4}{1-{\beta }^4{\tau }^{2/k}}\frac{1-{\tau }^{\frac{k-1}{k}}}{1-\tau }}$ wherein k is an isentropic coefficient, generally, for mono-atomic gases, k=1.67, for di-atomic gases, k=1.40, and for multi-atomic gases, k=1.10-1.29; wherein τ is the pressure ratio P.sub.2/P.sub.1, wherein P.sub.2 is the downstream pressure of the conical throttle, and P.sub.1 is the upstream pressure of the conical throttle; wherein the flowing coefficient C can be obtained in situ by flow rate calibration method, typically, in the numerical range from 0.75 to 0.85, or it can be calculated according to the following empirical equation: $C=1-\left(1-\frac{0.0254}{D+0.0254}\right)\beta +\left(2.5-\frac{0.1638}{D+0.1635}\right){\beta }^2-\left(2.15-\frac{0.2313}{D+0.1194}\right){\beta }^3$ 3) the mass flow rate of the oil, gas, and water phases are calculated according to the following equations:
Q.sub.gas=Q.sub.m×α.sub.gas
Q.sub.water=Q.sub.m×α.sub.water
Q.sub.oil=Q.sub.m×α.sub.oil; wherein the respective physical quantities in the above equation each are expressed by International System of Unit, and they should suit to each other.

2. The method of claim 1, wherein, the second pressure measuring port reaches fan exterior of the cylindrical pipe and connects the differential pressure measuring device via a pressure guiding pipe running through a central axis of the conical throttle.

3. The method of claim 1, wherein, a cone angle of the head cone section is from 30 to 45°, and an acute angle is formed between a cone surface of the head cone section and a cone surface of the tail cone section.

4. The method of claim 1, wherein, the Ba.sup.133 radioactive source includes a plurality of the Ba.sup.133 radioactive source blocks.

5. The method of claim 1, wherein, the device comprises a thermometer and a pressure meter.

6. The method of claim 1, wherein, the annular space is a gradually decreasing annular gap space provided between an inner wall of the cylindrical pipe and a cone surface of the head cone section for passage of the wet gas.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

(1) FIG. 1 is a schematic drawing of the structure of the device for measuring flow rate of wet gas based on an exempt radioactive source in the invention.

(2) FIG. 2 is a more broadly schematic drawing of the device for measuring flow rate of wet gas based on an exempt radioactive source in the invention.

(3) The reference numbers in these Figures have the following meanings:

(4) 1—cylindrical pipe; 2—conical throttle; 21—location at the maximum diameter of the conical throttle; 22—head cone section; 23—tail cone section; 3—annular gap; 4—exempt radioactive source block; 5—gamma ray detector; 6—differential pressure measuring device; 61—first pressure measuring port; 62—second pressure measuring port; 7—pressure meter; 8—thermometer; 9—gradually decreased annular gap space.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) The following examples are provided with the purpose for illustrating the contents in the invention, but not for further restricting the protection scope of the invention.

Example 1

(6) As shown in FIG. 1, the device for measuring flow rate of wet gas based on an exempt radioactive source according to the invention comprises a section of cylindrical pipe 1 and a conical throttle 2 located inside the cylindrical pipe and coaxially arranged therewith. The conical throttle 2 comprises a head cone section 22 and a tail cone section 23 which are arranged to have a common bottom surface and have the same bottom surface area, wherein the head cone section 22 faces a wet gas inlet of the cylindrical pipe 1. An annular gap 3 is defined between the inner wall of the cylindrical pipe 1 and the maximum diameter of the conical throttle 2 for passage of wet gas. A material block 4 of the exempt radioactive source Ba.sup.133 having an activity of lower than 25 μCi is arranged at the maximum diameter 21 of the conical throttle 2 in such a way that the gamma rays emitted from the radioactive source block can transmit radially through the annular gap 3 to reach the gamma ray detector 5 located outside the cylindrical pipe 1. A differential pressure measuring device 6 is arranged at the exterior of the cylindrical pipe 1, and it has two pressure measuring ports, wherein the first pressure measuring port 61 is located at the side wall of the cylindrical pipe 1 at the upstream of the head cone section 22, and the second pressure measuring port 62 is located at the tip of the tail cone section 23, and wherein the second pressure measuring port 62 reaches the exterior of the cylindrical pipe 1 and connects the differential pressure measuring device 6 via a pressure guiding pipe that runs through the central axis of the conical throttle 2. At the upstream of the first pressure measuring port, a thermometer 8 is arranged, and meanwhile, the first pressure measuring port is further connected to a pressure meter 7. The bending part of the above pressure guiding pipe should be apart from the first pressure measuring port in at least 2D distance, wherein the D represents the inner diameter of the cylindrical pipe. In this example, the cone angle of the head cone section 22 is 30°, and the angle between the cone surface of the head cone section 22 and the cone surface of the tail cone section 23 is 90°.

(7) The measurement is conducted as follows: the wet gas flows through the inlet end of the cylindrical pipe 1, and its temperature T and pressure P are measuring during the flowing; thereafter, the wet gas flows through the annular gap under the guidance of the conical throttle, thereby to exert the throttling function; hence, the pressure differential ΔP caused by the throttling function is measured by the above pressure differential measuring device. At the annular gap, the mass phase fraction α.sub.gas of the gas phase, the mass phase fraction α.sub.oil of the oil phase, and the mass phase fraction α.sub.water of the water phase are measured by the gamma ray detector, wherein α.sub.gas+α.sub.oil+α.sub.water=1, and then, the following steps are used to calculate the respective mass flow rate of the gas, oil and water phase:

(8) 1. the mixed density of the multiphase fluid is calculated according to the following equation:
ρ=ρ.sub.water×α.sub.water+ρ.sub.oil×α.sub.oil+ρ.sub.gas×α.sub.gas;

(9) 2. the total mass flow rate Q.sub.m of the multiphase fluid is calculated according to the following equation:
Q.sub.m=k.Math.√{square root over (ΔP.Math.ρ)}

(10) wherein:

(11) Q.sub.m - - - mass flow rate, kg/h; k - - - coefficient;

(12) ΔP - - - differential pressure, kPa;

(13) ρ - - - mixed density of the multiphase fluid, kg/m.sup.3;

(14) wherein:

(15) $k=0\mathrm{.126447}.Math.\frac{C.Math.\mathrm{.Math.}}{\sqrt{1-{\beta }^4}}.Math.\left(D^2-d^2\right)$$\beta =\frac{\sqrt{D^2-d^2}}{D}$

(16) wherein:

(17) β - - - equivalent diameter ratio, usually from 0.35 to 0.75;

(18) D - - - inner diameter of the cylindrical pipe 1, m;

(19) d - - - maximum diameter of the conical throttle, m;

(20) ϵ - - - compression coefficient, for liquids, ϵ=1, and as for gases,

(21) $\mathrm{.Math.}=\sqrt{\frac{k{\tau }^{2/k}}{k-1}\frac{1-{\beta }^4}{1-{\beta }^4{\tau }^{2/k}}\frac{1-{\tau }^{\frac{k-1}{k}}}{1-\tau }},$

(22) wherein k is the isentropic coefficient, generally, for mono-atomic gases, k=1.67, for di-atomic gases, k=1.40, and for multi-atomic gases, k=1.10-1.29; the k values of some common gases are listed as follows: argon gas k=1.67, helium gas k=1.67, hydrogen gas k=1.40, nitrogen gas k=1.40, oxygen gas 02 k=1.39, carbon monoxide k=1.40, air k=1.40, steam k=1.33, carbon dioxide k=1.29, sulfur dioxide k=1.25, methane k=1.30, and propane k=1.13;

(23) wherein τ is the pressure ratio P.sub.2/P.sub.1, wherein P.sub.2 is the downstream pressure of the conical throttle, and P.sub.1 is the upstream pressure of the conical throttle;

(24) wherein the flowing coefficient C can be obtained in situ by flow rate calibration method, typically, in the numerical range from 0.75 to 0.85, or it can be calculated according to the following empirical equation:

(25) $C=1-\left(1-\frac{0.0254}{D+0.0254}\right)\beta +\left(2.5-\frac{0.1638}{D+0.1635}\right){\beta }^2-\left(2.15-\frac{0.2313}{D+0.1194}\right){\beta }^3;$

(26) 3. respective mass flow rate of the oil, gas, and water phases are calculated according to the following equations:
Q.sub.gas=Q.sub.m×α.sub.gas
Q.sub.water=Q.sub.m×α.sub.water
Q.sub.oil=Q.sub.m×α.sub.oil.

(27) The respective physical quantities in the above equation each are expressed by International System of Unit, and they should suit to each other.

Example 2

(28) As shown in FIG. 2, the structure differs from the structure as shown in FIG. 1 in that the exempt radioactive source is located on the cone surface the head cone section 22 of the conical throttle 2, adjacent to the maximum diameter 21 of the conical throttle 2, and it is arranged in such a way that the gamma rays emitted from the radioactive source block can transmit radially through the gradually decreased annular gap space 9 to reach the gamma ray detector 5 located outside the cylindrical pipe 1, wherein the gradually decreased annular gap space 9 through which the gamma ray transmits has a radial width of less than 50 mm.

(29) The specific method for calculating the mass flow rates is completely identical to that in Example 1.