RU2445581C1 - Method of fast determination of liquid phase volume content in gas-liquid flow and device to this end - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: proposed method consists in isokinetic sampling of gas pipeline, using filter to separate liquid phase and measuring said phase volume fraction at fixed volume flow rate of gas-liquid mix. Note here that a-priori known liquid density (ρ_l) is used. Then, measured is density of gas flow not containing liquid phase (ρ_g) while volume content of liquid phase in has-liquid flow (volume content of liquid η) is defined from relation:

Proposed device comprises isokinetic sampler, filter to separate liquid phase, volume flow rate meter and rotameter calibrated in units of density at constant flow rate. Aforesaid filter is made up of electric filter of elongated volume filled with thin-wall metal structure, cellular in crosswise direction and elongated in lengthwise directions. Filamentary electrode is located at the center of every cell whereto high voltage is fed.

EFFECT: continuous measurement and calculation of important parameter, actual density, ρ_c, possibility of use integrated with two-phase SHF-flow rate meters.

2 cl, 3 dwg

Description

The invention relates to measuring technique and can be used on metering units of gas producing enterprises, when conducting field studies of gas condensate formations, when calibrating flow meters of two-phase flows, and in other cases where knowledge of the volumetric content of the liquid phase in the gas-liquid stream is necessary.

One of the main characteristics of a working gas condensate well is its productivity - indicators of gas and condensate flow rates under various operating conditions. When studying new wells or periodically examining exploited wells to determine the component-wise consumption of production products, the latter are usually passed through a separator, where the liquid phase is separated from the gaseous one. Then each of the phases is passed through its own flow meter (liquid or gas flow meter) and is taken into account separately [1]. The disadvantage of this method is the high cost of the separator, due to its large weight and size characteristics. For the same reason, the separator technique is devoid of mobility - it is usually stationary and difficult to adapt to the study of new wells. In addition, due to the formation of hydrates, the separators do not work in the cold season.

Hence, to quickly determine the flow rates of gas condensate wells, a technique is developed for determining the component-by-phase flow rate without first separating them into liquid and gaseous. For this, at a minimum, it is necessary to measure the velocities of the gas and liquid phases (υ _g , υ _w ) and the density of the gas-liquid mixture ρ _s , which can be expressed [2] through the volumetric content of the liquid phase

where ρ _W , ρ _g - the density of the liquid and gas, respectively;

- объемное содержание жидкой фазы в потоке;

- volumetric content of the liquid phase in the stream;

V _m is the volume of liquid in the volume V of the gas-liquid mixture.

If a set of methods has been developed for determining the velocities υ _g and υ _g (on a narrowing device, correlation [2], by the Doppler effect [3], etc.), then a direct measurement of the density of the mixture ρ _s or the volumetric content of the liquid phase in the gas-condensate stream η encounters significant difficulties. The measurement of ρ _with a radioactive source is known [2], however, it is associated with the need to ensure radiation safety and is often unacceptable. There are also known methods and devices for determining the density ρ _with the shift of the natural frequency of the microwave cavity when filling it with a gas-liquid medium. Their disadvantage is the presence of empirical coefficients in the final calculation formulas. This necessitates the calibration of flowmeters at each field using a field separator, which is not always possible.

The closest in method and device to the present invention are a method and device for measuring droplet entrainment of liquid with gas used, for example, in the liquid abduction indicator IU-1 of the design of JSC TyumenNIIgiprogaz, the liquid ablation meter of the design of DAO TsKBN and the universal gas small-sized droplet separator of UGMK design LLC "Urengoygazprom" [4]. The latter will be taken as a prototype.

The main components of the UGKM droplet separator are: a sampling device providing isokinetic sampling; a filter element with a fluoroplastic filter separating the droplet-aerosol from the gas; gas meter RG-40 - volumetric flow meter; gas shutoff valves; temperature and pressure control devices. The principle of operation of the device in question is based on the fact that a certain amount of gas is passed through the filter, which leaves the liquid phase in the filter. The amount of liquid phase is determined by the amount of liquid retained by the filter and drained into a measured volume. Knowing the amount of gas passed through and the amount of liquid released, the volumetric content of the liquid phase in the initial gas-liquid stream is calculated.

The disadvantage of this method is the need for laboratory analysis, which does not allow for the organization of a constant, operational measurement of the volumetric content of the liquid phase.

The device for recording the entrainment of droplet liquid is designed to control the entrainment of diethylene glycol from gas glycol dehydration absorbers, due to which its measurement range of the volumetric content of the liquid phase lies significantly below the range of interest to us ~ 10 ÷ 100 cm ³ / nm ³ (liquid volume in cm ³ in one ^m3 gas normalized to normal conditions), and therefore in the present design the device in question can not be used to determine the volume content of the liquid phase in the gas-liquid stream at the condensate wells x. In addition, the filter used in the device needs periodic drying from accumulated moisture. These are the technical flaws of the device.

The technical result is the ability to organize continuous measurement of the volumetric content of the liquid phase in the stream and the calculation of the most important parameter of the gas-liquid stream - its real density ρ _s , and, as a result of this, the ability to use such a device to calibrate two-phase microwave flow meters based on the dielectric principle [3, 5 , 6], with the aim of expanding the scope of their application in fields that do not have operational field separators.

The technical result of the proposed method is achieved by the fact that in the method for quickly determining the volumetric content of the liquid phase in a gas-liquid stream, which consists in isokinetic sampling from the gas pipeline, the filter cuts off the liquid phase and then measures its volume fraction at a fixed volumetric flow rate of the gas-liquid mixture using a previously known density value liquid (ρ _g ), sequentially measure the density of the gas stream not containing the liquid phase (ρ _g ) and the real stream containing the liquid phase (ρ _s ), and the volumetric content of the liquid phase in the gas-liquid flow (volume fraction of liquid η) is found by the ratio

.

.

The technical result of the proposed device is achieved by the fact that in the device for the rapid determination of the volumetric content of the liquid phase in a gas-liquid stream containing a sampling device for isokinetic sampling, a filter that cuts off the liquid phase, a volumetric flow meter and a rotameter calibrated in density units at a constant flow rate, in as a filter that cuts off the liquid phase, an electrostatic precipitator is used, made in the form of an extended volume filled with a mesh in the transverse direction and extended In the longitudinal direction, there is a thin-walled metal structure in the center of each cell of which there is a filamentary electrode to which a high voltage is applied.

Figure 1 shows a diagram of a device operating according to the proposed method. It shows: 1 - gas pipeline; 2 - flow of gas-liquid mixture; 3 - tip of the intake device, 4 - flow regulator, 5 - pressure gauge, 6 - thermometer, 7 - intake device for isokinetic sampling; 8 - flow regulator intake device; 9, 10 - flow controllers; 11 - filter for cutting off the liquid phase; 12 - gas volumetric flow meter; 13 - pressure gauge; 14 - thermometer; 15 - rotameter used as a densitometer of gas or gas-liquid mixture; 16 is an adjustable valve in front of the flow tube 17. Points A and B mark connectors for replacing the filter 11 and adjustable valves 9 and 10 with the electrostatic precipitator shown in FIG. 2.

Figure 2 shows the electrostatic precipitator, where: 18 - the housing of the electrostatic precipitator; 19 - bushing high voltage insulator; 20 - electromagnet contactor supply high voltage; 21 - contactor; 22 - a source of high voltage; 23 - adjustable valve; 24 - valve condensate discharge into the measured volume; 25 - measured volume; 26 - valve for condensate removal; 27 - wire electrode; 28 - metal tube - the wall of the unit cell of the filter.

Figure 3 shows a cross-section of the electrostatic precipitator along the cross section CC ₁ with the unit cells of the filter in the form of cylindrical tubes (It is also possible to use other cross-sectional shapes of unit cells, for example, in the form of hexagons or squares).

Rotameter 15 has a scale in units of density. For this, it is pre-calibrated, passing through it gases of different densities at a constant volume flow. The gas flow equation through the rotameter can be written [7] in the form

where h is the height of the float; k (h) is a correction function that differs slightly from 1 and is determined during calibration; A is a constant coefficient; ρ is the gas density.

If the flow is kept constant, i.e. put Q≡Q ₀ = Const, then from (2) we find:

.ρ = B (h) · h ² , where

.

Thus, the rotameter turns into a densitometer. Function B (h) is determined by calibrating the rotameter while passing through it gases with different densities at a constant flow rate Q≡Q ₀ . The lower boundary of the rotameter density scale is determined by the density of pure methane ρ _c = ρ _cmin = 0.668 kg / m ³ ; the upper boundary ρ _cmax of η. If we take for the maximum value η = 200 cm ³ / nm ³ , and consider the liquid as hydrocarbon condensate with a density ρ _Ж = 800 kg / g ³ , then the value ρ _cmax will be 0.830 kg / m ³ . In order for the measurement error to be small (~ 10 ^-4 ), the rotameter should have a length of the measurement scale of about 1000 mm and the corresponding taper.

Particular attention should be paid to the gas volumetric flow meter 12: the flow rate Q ₀ must be reproduced and maintained constant with an error of no worse than 0.25% (turbine, tachometric and some other types of flow meters satisfy this requirement).

The method can be used both at operating pressures and at standard. Let us further describe its use at standard pressure.

A device diagram explaining the proposed measurement method is presented in figure 1. In the initial state, all valves are closed. We open the flow regulator 4 and the flow regulator 8 of the intake device. An intake device for isokinetic sampling 7 together with flow controllers 4 and 8 provides an unperturbed gas flow to the tip of the intake device 3. Such devices are described in the literature (see, for example, [4], [8]). We further open the flow regulator 9 and open the adjustable valve 16; we set the volumetric flow rate Q ₀ according to the gas volumetric meter 12 at a standard pressure at the inlet of the rotameter 15. In this case, gas with liquid aerosol passing through the filter for cutting off the liquid phase 11 is freed from the liquid and enters the gas volumetric flow meter 12 and then to the rotameter 15. We measure the temperature of the gas at the inlet to the rotameter 15 and fix the density on its scale (if necessary, make a correction for the temperature). After measuring the density ρ _g, close the flow regulator 9, open the flow regulator 10 and set again the previous value of the volume flow Q ₀ . On the scale of the rotameter 15, we determine the density of the gas-liquid flow ρ _s . By ratio

we calculate the volume fraction of the liquid, or, which is the same thing, the volume content of the liquid phase in the gas-liquid stream (we assume the density ρ _and known from preliminary measurements).

Figure 1 explains only the method for determining η. In practice, it can be inconvenient for two reasons. Firstly, if the filter is made of fabric, it will serve a relatively short time, after which it must be dried. Secondly, when gas passes through the filter, pressure drops on it by a certain ΔP value, which can change with time (due to the fact that the filter is saturated with liquid). This leads to an asymmetry of the arms along which the gas flows in the case of measuring ρ _g and ρ _s , which, in turn, requires additional adjustment of the flow by the flow regulator 10, and also affects the constancy of flow Q ₀ and leads to additional errors.

Hence, the device for implementing the method should be free from these shortcomings. This can be achieved by replacing the fabric or fluoroplastic filter 11 with a specially made electrostatic precipitator (Fig. 2), which replaces a part of the circuit in Fig. 1, namely: a filter 11 together with valves 9, 10 and connecting tubes (i.e., a part of the circuit between points A and B) is removed, and instead of it, a part of the circuit shown in FIG. 2 is inserted between points A and B.

An electrostatic precipitator is an extended vessel, inside of which there is a cellular structure, for example, thin-walled long metal tubes (figure 2, figure 3). In the center of each tube and in the center of the figure formed by the outer sides of the tubes, there are wire electrodes 27, to which a high voltage is supplied from the source 22. The metal tubes 28 are connected to the housing of the electrostatic precipitator 18 and are grounded. From the lower end of the electrostatic precipitator 18 a gas is supplied containing an aerosol in a drip-liquid form. When a high negative voltage is applied to the wire electrode 27, a strong electric field is created in the space between the electrodes 27 and 28, in which the aerosol is polarized or ionized and begins to drift to the negative electrode, and then is deposited on it. If the tubes are of sufficient length, then the entire aerosol manages to settle on the electrodes and then collect on the lower end of the filter, and the gas is cleaned from the droplet liquid. The liquid collected at the lower end can be removed by opening the condensate drain valve 24 and the condensate drain valve 26. At the same time, its volume can be measured (for additional control) using a volumetric volume 25.

The device operates as follows.

After setting the required volumetric flow rate Q ₀ as described above, the density of the gas-liquid mixture ρ _{s is} determined on the scale of the rotameter. After that, at the command voltage is applied to the electromagnet of the contactor 20, the high voltage circuit through the contactor 21 is closed and high negative voltage is applied to the electrodes 27. In this case, the gas is cleaned of aerosol and the rotameter marks the density of the "dry" gas ρ _g

Due to the low gas-dynamic resistance of the electrostatic precipitator, the pressure drop across it is extremely small. In addition, it is the same for the case when ρ _s or ρ _g are measured. These circumstances allow us to go from measuring ρ _c and ρ _g and back without adjusting the gas flow rate, which thus remains constant: Q ₀ = Const. Therefore, the measurement errors ρ _c and ρ _g associated with the unevenness of the costs are absent here.

, диаметром ⌀ 20 мм, толщиной стенки d=0,4 мм. По оси трубки была натянута молибденовая проволока диаметром ⌀~0,2 мм, на которую подавалось напряжение до 5000 В. В отсутствие напряжения визуально наблюдался аэрозольный туман, идущий из трубки; после подачи напряжения на центральный электрод туман исчезал, т.е. элементарная ячейка фильтра аэрозоля такой конструкции работает.The model of the electrostatic precipitator was tested in laboratory conditions on gas-liquid mixtures at atmospheric pressure. A medical aerosol generator for Boreal physiotherapy was used as a source of a gas-liquid mixture, giving an air stream with a known volumetric liquid content in the dispersed phase. A stainless steel tube was used as a filter unit cell.

, diameter ⌀ 20 mm, wall thickness d = 0.4 mm. A molybdenum wire with a diameter of ⌀ ~ 0.2 mm was pulled along the tube axis, to which a voltage of up to 5000 V was applied. In the absence of voltage, aerosol fog was visually observed coming from the tube; after applying voltage to the central electrode, the fog disappeared, i.e. an aerosol filter unit cell of this design works.

Literature

1. Shirkovsky A.N. Development and operation of gas and gas condensate fields. M .: Nedra, 1979, 304 p.

2. Kremlin P.P. Measurement of multiphase flow rates. L .: "Engineering", 1982, 214 p.

3. RF patent №2164340 dated 03.20.2001. A method for determining the component flow rate of a gas-liquid mixture of gas and oil products in a pipeline and a device for its implementation. Authors: Orekhov Yu.I., Moskalev I.N., Kostyukov V.E., Khokhrin L.P., Remizov V.V., Bityukov BC, Filonenko A.S., Rylov E.N., Embroidered I. G., Filippov A.G.

4. Lanchakov G.A., Kulkov A.N., Siebert G.K. Technological processes for the preparation of natural gas and methods for calculating equipment. M .: Nedra, 2000, 278 p.

5. RF patent No. 2289808 of 02.28.2005. Method and device for determining volume fractions of liquid hydrocarbon condensate and water in a stream of a gas-liquid mixture of natural gas. Authors: Vyshivanyi I.G., Kostyukov V.E., Moskalev I.N., Orekhov Yu.I., Tikhonov A.B., Belyaev V.B.

6. RF patent No. 2286546. Method and device for measuring the flow of gas-liquid flow. Authors: Embroidered I.G., Kostyukov V.E., Moskalev I.N., Orekhov Yu.I., Belyaev VB

7. Kremlin P.P. Flow meters and substance counters. Reference: book 2 / Pod. total ed. Shornikova E.A., 5th ed., Rev. and add. St. Petersburg: Polytechnic, 2004, 412 p.

8. Baibakov RB, Sharapov V.M. Control of impurities in compressed gases. M .: Chemistry, 1989, 158 S.

Claims (2)

1. A method for quickly determining the volumetric content of the liquid phase in a gas-liquid stream, which consists in isokinetic sampling from a gas pipeline, cutting off the liquid phase with a filter, and then measuring its volume fraction at a fixed volumetric flow rate of a gas-liquid mixture, characterized in that, using a previously known value of the liquid density ( ρ _w) successively produce measurement of the density of the gas stream containing no liquid phase (ρ _g), and the real stream comprising a liquid phase (ρ _s), and the volume content Yid second phase in the gas-liquid stream (liquid volume fraction η) is found by the relation

. 2. A device for the rapid determination of the volumetric content of the liquid phase in a gas-liquid stream, containing a sampling device for isokinetic sampling, a filter that cuts off the liquid phase, a volumetric flow meter and a rotameter calibrated in density units at a constant flow rate, characterized in that as a filter, cutting off the liquid phase, an electrostatic precipitator is used, made in the form of an extended volume filled with a mesh in the transverse direction and elongated in the longitudinal direction of a thin-walled metal llicheskoy structure in the center of each of cells which is filiform electrode to which high voltage is applied.

Images