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

A method for measuring flow of a wet gas using a device for measuring a flow rate of the wet gas based on a Ba133 radioactive source, wherein the Ba133 radioactive source has an activity less than 1×106 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 Ba133 radioactive source includes a Ba133 radioactive source block, the Ba133 radioactive source block is arranged at the maximum diameter of the conical throttle, wherein, gamma rays emitted from the Ba133 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 αgas of a gas phase, a mass phase fraction αoil of an oil phase, and a mass phase fraction αwater 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=ρwater×αwater+ρoil×αoil+ρgas×αgas;
• 2) a total mass flow rate Qm of the wet gas is calculated according to the following equation:
• Qm=K0·√{square root over (ΔP·ρ)}
• wherein:
• Qm - - - mass flow rate, kg/h;
• K0 - - - coefficient;
• ΔP - - - differential pressure, kPa;
• ρ - - - mixed density of the wet gas, kg/m3;
• wherein:
• K
• 0
• =
• 0.126447
• ·
• C
• ·
• ɛ
• 1
• -
• β
• 4
• ·
• (
• D
• 2
• -
• d
• 2
• )
• β
• =
• 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,
• ɛ
• =
• k
• ⁢
• τ
• 2
• /
• k
• k
• -
• 1
• ⁢
• 1
• -
• β
• 4
• 1
• -
• β
• 4
• ⁢
• τ
• 2
• /
• k
• ⁢
• 1
• -
• τ
• k
• -
• 1
• k
• 1
• -
• τ
• 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 P2/P1, wherein P2 is the downstream pressure of the conical throttle, and P1 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
• -
• (
• 1
• -
• 0.0254
• D
• +
• 0.0254
• )
• ⁢
• β
• +
• (
• 2.5
• -
• 0.1638
• D
• +
• 0.1635
• )
• ⁢
• β
• 2
• -
• (
• 2.15
• -
• 0.2313
• D
• +
• 0.1194
• )
• ⁢
• β
• 3
• 3) the mass flow rate of the oil, gas, and water phases are calculated according to the following equations:
• Qgas=Qm×αgas
• Qwater=Qm×αwater
• Qoil=Qm×αoil;
• wherein the respective physical quantities in the above equation each are expressed by International System of Unit, and they should suit to each other.