FR2792071A1 - Mechanism for taking samples from liquid flowing in conduit, comprises Pitot tube in conduit, two cylinders with pistons which operate hydraulic switch and separating liquid link between cylinders - Google Patents

Abstract

Initially the high pressure side (4) of the Pitot tube (3) causes a first piston (7) to expel a separating liquid in a first buffer chamber (9). The expelled separating liquid enters a second buffer chamber (12) in a second cylinder (6b) causing a second piston (10) to operate a hydraulic switch (17). The static pressure (5) from the Pitot tube (3) reverses the second piston (10) movement causing a sample from the first cylinder (6a) to to pass to a reservoir (2)

Description

DESCRIPTION

TECHNICAL AREA

  The present invention relates to a device for taking samples of a liquid circulating in a pressure pipe. It is particularly suitable for taking samples of a liquid.

  which circulates in a pipe at a variable flow.

  It finds its application in particular in the petroleum industry and the petrochemical industry, to obtain a small quantity of a transported liquid whose physical and chemical characteristics are representative of the same average characteristics of the volume transported by a pipeline in a given time.

STATE OF THE PRIOR ART

  A device for withdrawing a fluid circulating in a pipe

  under pressure is described in document US 4,928,536 of May 29, 1990.

  This device essentially comprises a circuit for withdrawing the liquid or gas circulating in the pipe at a sampling rate which is a function of the flow of liquid or gas in the pipe, a sampling chamber of calibrated volume, a rod for ejecting the fluid contained in the sampling chamber controlled by a working piston and a circuit

  control of the engine piston comprising a valve controlled by a controller.

  During a first operating step of this device, part of the fluid withdrawn from the pipe by means of the sampling circuit is

  used to fill the sampling chamber.

  During a second step, the fluid which has filled the sampling chamber is expelled from this chamber by the ejection rod actuated by the driving piston and transferred to a storage tank through a non-return valve. . The driving piston is actuated by another part of the fluid taken from the line whose admission into the driving piston control circuit is

  ensured by the periodic opening of the valve controlled by the controller.

  Simultaneously with the action on the ejection rod the driving piston compresses a spring

reminder.

  During a third step, the ejection rod is extracted from the sampling chamber under the effect of the relaxation of the return spring which acts on the

engine piston.

  The sampling chamber thus emptied is ready to be refilled with part of the fluid withdrawn from the pipe by means of the sampling circuit. The course of the three stages is repeated as many times as necessary during the time of circulation of the fluid in the pressure line. The device described in document US Pat. No. 4,928,536 of May 29, 1990 therefore makes it possible to take, at a frequency given by the controller, a series of fluid samples of a calibrated volume equal to the volume of the sampling chamber. One of the drawbacks of this device is that the volume of fluid subsequently made up of the samples taken only depends on the volume of the sampling chamber and on the sampling frequency, it is therefore independent of the flow rate of fluid circulating in the pipe. Only the filling speed of the sampling chamber depends on this flow rate, which does not affect the volume of the

following the samples taken.

  This device also has the disadvantage of requiring a power supply to operate the controller and the valve of the control circuit of the engine piston, a device for measuring the flow rate of the fluid in the pipe and a servo-control of the opening frequency of the valve at this flow to control the sampled flow if it is to be proportional to the flow in the pipe. In addition, this device is sensitive to solid particles, has a very large number of static and moving parts, numerous seals which

gives poor reliability.

STATEMENT OF THE INVENTION

  The object of the present invention is precisely to remedy these drawbacks and to provide a device for taking a series of samples of a liquid circulating in a pressure pipe, the total volume of the series of samples taken during '' a given period of time being

  depending on the volume of liquid flowing during the same period in the pipeline.

  The device of the invention has the advantage of taking the energy necessary for its operation from the liquid circulating in the pipe to which it is connected, which makes it completely autonomous with respect to other

  sources of energy, especially electricity.

  To this end, the present invention provides a device for taking samples of a liquid in circulation in a pressure pipe comprising a sampling tank for collecting said samples, a pressure-reducing member inserted in the pressure pipe providing between a high outlet pressure and a low pressure outlet, a differential pressure depending on the volume flow rate of the circulating liquid, characterized in that it further comprises: - a primary cylinder inside which is mounted a primary piston which define a transfer chamber and a first buffer chamber filled with a separating liquid, - a secondary cylinder of the same dimensions as the primary cylinder inside which a secondary piston is mounted to define a downstream chamber and a second buffer chamber filled with separating liquid, - a pipe connecting the first buffer chamber to the second buffer chamber at through a restriction which determines a flow of separating liquid between the said buffer chambers for a given pressure difference between the said chambers, - a pipe connecting the downstream chamber to the low pressure outlet of the pressure-reducing member, - connecting means controlled, on the one hand by the primary piston to first connect the transfer chamber to the high pressure outlet of the pressure-reducing member, to move the primary piston and fill the transfer chamber with a sample of a predetermined volume of the liquid in circulation and on the other hand by the secondary piston to then connect the transfer chamber to the sampling tank, to transfer said sample in said tank by displacement of the primary piston under the effect of the pressure in the transmitted pipe by the low pressure connection, the secondary piston and the separating liquid to the first buffer chamber, According to another characteristic of the inv ention, the depressogenic organ

  inserted into the pressure line is a Pitot tube.

  According to another characteristic of the invention, the restriction of the connecting pipe from the first buffer chamber to the second buffer chamber is carried out

  by means of a needle valve.

  According to another characteristic of the invention, the restriction of the connecting pipe from the first buffer chamber to the second buffer chamber is carried out

  by means of a calibrated orifice plate.

  According to another characteristic of the invention, the connecting means controlled by the primary piston and the secondary piston comprise a

hydraulic switch.

  According to another characteristic, the device of the invention further comprises a first non-return valve mounted on the connecting pipe of the first buffer chamber so as to allow the passage of the separating liquid from the first buffer chamber to the second and a second pipe connecting the two buffer chambers through a second restriction and a second non-return valve mounted so as to allow the passage of the separating liquid

  from the second buffer chamber to the first.

  According to another characteristic of the invention, the second restriction is

  produced by means of a needle adjustment valve.

  According to another characteristic of the invention, the second restriction is

  produced by means of a calibrated orifice plate.

  According to another characteristic of the invention, the separating liquid has rheological characteristics whose values are close to those of the liquid circulating in the pipeline and preferably identical, so that the instantaneous flow rate of the separating liquid between the two buffer chambers is substantially proportional to the instantaneous flow rate of the liquid circulating in the pipeline.

BRIEF DESCRIPTION OF THE DRAWINGS

  The invention will be better understood using the following description given

  by way of example, with reference to the accompanying drawings in which: - Figure 1 shows schematically a first embodiment of the device for taking a sample of liquid according to the invention, Figure 2 shows schematically a second embodiment of

  device for taking a liquid sample according to the invention.

  - Figure 3 schematically shows a third embodiment of the

  device for taking a liquid sample according to the invention.

  - Figure 4 schematically shows a fourth embodiment

  of the device for taking a sample of liquid according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

  In general, the device of the invention is used to take a series of samples of constant volume of a liquid circulating in a pressure pipe for a given period of time whose total volume is a function of the volume of liquid which circulates in the pipeline during the same period and whose physicochemical characteristics are representative of the average physicochemical characteristics of the liquid which circulates in the

  pipeline during the same period.

  FIG. 1 schematically represents a first embodiment of the device of the invention which can be used to take a series of samples of a liquid in circulation in a pipe 1 under pressure. This device comprises a sampling tank 2 for collecting the samples collected at atmospheric pressure, a pressure-reducing member constituted by a Pitot tube 3 inserted in the pipe 2 which supplies a high pressure socket 4 and a low socket 5

  pressure differential pressure Dp.

  Dp is related to the speed of the liquid circulating in the pipeline by the following relation: Dp = (p v 2) / 2 in which p represents the density of the liquid

  and v its circulation speed in the pipeline.

  If the letter F represents the volume flow of the liquid circulating in the pipeline and the letter S the section of the pipeline 1, we have F = vS The relationship between Dp and the volume flow is given by the following formula: Dp = [p (F / S) 2] 1/2

Dp = a. F2 with a = p / 2S2.

  For a liquid circulating in the pipe 1 whose density p is constant, o is a constant and the differential pressure Dp is

  proportional to the square of the volume flow rate of the liquid in the pipe 1.

  According to this first embodiment, the device of the invention further comprises: - a primary cylinder 6a inside which is mounted a primary piston 7 which define a transfer chamber 8 and a first buffer chamber 9 filled with a liquid separator which has rheological characteristics similar to those of the liquid which circulates in line 1, obtained for example by filtration of a sample of this liquid in the case of crude oil coming from a production well, - a cylinder 6b secondary of the same dimensions as the primary cylinder 6a inside which is mounted a piston 10 which define a downstream chamber 11 and a second buffer chamber 12 filled with the same separating liquid as the primary chamber 9, - a pipe 13 for connecting the first buffer chamber 9 to the second buffer chamber 12, through a restriction constituted by a needle valve 14, - means for filling the buffer chambers 9 and 12 and of the pipe 13 with separating liquid, not shown in FIG. 1, - a pipe 15 for connecting the chamber 11 downstream to the low pressure outlet 5 of the Pitot tube 3, - connecting means comprising a hydraulic switch 17 in two positions, controlled alternately, on the one hand by a rod 19 secured to the primary piston 7 and on the other hand by a rod 20 secured to the secondary piston 10, which switch 17 in a first position connects the transfer chamber 8 with the high pressure outlet 4 of the Pitot tube, via the pipes 21 and 16 and which in a second position connects the transfer chamber 8 with the sampling tank 2 via the pipes 21 and 18. During a first operating phase of the device of the invention, the hydraulic switch 17 being in the position shown in FIG. 1, the transfer chamber 8 is subjected to the pressure delivered by the outlet 4 high e pressure of the Pitot tube. Under the effect of this pressure, the primary piston 7 moves from right to left and the transfer chamber 8 is filled with liquid withdrawn from the pipe 1. Simultaneously the first buffer chamber 9 empties of the separating liquid which it contains. and the second buffer chamber 12 is filled with the same liquid. The secondary piston 10 moves and empties the downstream chamber 1 by evacuating the liquid which it contains in the pipe 1 by the pipe 15

  and through the low pressure socket 5 of the Pitot tube.

  When the secondary piston 10 reaches the end of its travel, it acts by means of the rod 20 on the hydraulic switch 17 and causes it to tilt. The

  first phase of operation is completed.

  A second operating phase begins, during which the chamber 8 is then placed in communication with the sampling tank 2

  by the hydraulic switch 17 after tilting.

  The static pressure of the pipe 1 being higher than the pressure in the second buffer chamber 12, the secondary piston 10 moves so that the downstream chamber 11 is filled with liquid coming from the pipe 1. Simultaneously the chamber 12 is vacuum separator liquid and the first chamber 9 is filled. The primary piston 7 moves under the pressure of the separating liquid which fills the first chamber 9. The liquid withdrawn in the pipe 1 during the first operating phase contained in the transfer chamber 8 is poured into the withdrawal reservoir 2 by

  through the pipes 21 and 18 through the hydraulic switch 17.

  When the secondary piston 7 reaches the end of its travel, it acts via the rod 19 on the hydraulic switch 17 which swings back. The second operating phase is finished the switch 17 has returned to

  the position it had at the start of the first phase of operation.

  The device of the invention is then ready to execute a new cycle

of two operating phases.

  During the first operating phase, the flow rate of the liquid withdrawn in the pipe 1 to fill the sampling chamber 8 is equal to the flow rate of the separating liquid which circulates between the two buffer chambers. This flow rate is determined by the pressure difference applied to the needle valve 14 substantially equal to the pressure difference Dp delivered by the tube

  of Pitot and by opening the needle valve 14.

  For a given adjustment of the opening of the needle valve the flow rate of separating liquid is given by the following formula f = k (Dp.p) 112 f = k2.Dp.p in which f represents the flow rate of separating liquid in the pipe 13, Dp the differential pressure delivered by the Pitot tube, p the density of the separating liquid, k is a constant for a given opening of the needle valve, It has been shown previously that Dp = a. F2 We therefore deduce that: f2 = 2.F2 f = .F 1 being a constant equal to (k2.o.p) 1/2, the flow rate f of sampling during the first operating phase is proportional to the flow rate F of fluid

  circulating in the pipeline under the conditions indicated above.

  With the device of the invention, the duration of the first operating phase, that is to say the duration of the taking of a sample, is inversely

  proportional to the flow rate F of liquid circulating in the pipeline.

  It is possible to adjust the volume of the sample withdrawn by acting on the strokes of the two pistons 7 and 10, and to adjust the filling speed of the transfer chamber 8, that is to say the ratio between the flow rate of the liquid withdrawn and the flow of liquid circulating in the pipeline by acting on the opening of the

  needle valve which has the effect of modifying the value of the coefficient k.

  FIG. 2 schematically represents a second embodiment of the device of the invention which comprises the following elements: - a sampling tank 2, a Pitot tube 3 having a high pressure socket 4 and a low pressure socket 5, a cylinder 6a primary having a first buffer chamber 9, a cylinder 6b secondary having a second buffer chamber 12 and a downstream chamber 11, a pipe 15 for connecting the chamber 11 downstream to the low pressure outlet 5 of the Pitot tube 3 and connecting means controlled as described for the first embodiment and, - an orifice 30 calibrated as a restriction mounted on the pipe 13 connecting the

  first buffer chamber 9 to the second buffer chamber 12.

  These elements function in the same way as the elements of the

  device according to the first embodiment.

  FIG. 3 schematically represents a third embodiment of the device of the invention which comprises: - a sampling tank 2, a Pitot tube 3 having a high pressure socket 4 and a low pressure socket 5, a primary cylinder 6a having a first buffer chamber 9, a secondary cylinder 6b having a second buffer chamber 12 and a downstream chamber 11, a pipe 15 for connecting the downstream chamber 11 to the low pressure outlet 5 of the Pitot tube 3 and controlled connection means such as described for the first embodiment and operating under the same conditions, - a first pipe 13 connecting the first buffer chamber 9 to the second buffer chamber 12 through a first needle valve 14 and a valve 31 non-return allowing the flow of the separating liquid in the only direction of filling of the second buffer chamber 12, - a second pipe 34 connecting the second buffer chamber 12 to the first cham bre 9 buffer through a second needle valve 45 and a non-return valve 33 allowing the flow of the separating liquid

  in the only filling direction of the first buffer chamber 9.

  The first needle valve 14 makes it possible to fix the flow rate of separating liquid between the first buffer chamber 9 and the second buffer chamber 12 for a given differential pressure delivered by the pitot tube and consequently the flow rate for withdrawing liquid in the pipe 1 to which it is equal. The opening of the second needle valve 45 fixes the rate of emptying of the transfer chamber 8 into the tank 2 for a given static pressure of the

  liquid circulating in the pipeline 1.

  This opening will advantageously be adjusted so that the emptying time of the transfer chamber 8 is negligible compared to the time of

filling that same room.

  FIG. 4 schematically represents a fourth embodiment of the device of the invention which comprises: - a sampling tank 2, a Pitot tube 3 having a high pressure socket 4 and a low pressure socket 5, a primary cylinder 6a having a first buffer chamber 9, a secondary cylinder 6b having a second buffer chamber 12 and a downstream chamber 11, a pipe 15 for connecting the downstream chamber 11 to the low pressure outlet 5 of the Pitot tube 3 and controlled connection means such as described for the first embodiment and operating under the same conditions, a first pipe 13 for connecting the first buffer chamber 9 to the second buffer chamber 12 through a first calibrated orifice 30 and a non-return valve 31 return allowing the flow of the separating liquid in the only filling direction of the second buffer chamber 12, - a second pipe 34 connecting the second buffer chamber 12 to the first chamber 9 buffer through a second calibrated orifice 32 and a non-return valve 33 allowing the flow of the separating liquid

  in the only filling direction of the first buffer chamber 9.

  The first calibrated orifice 30 makes it possible to fix the flow of separating liquid between the first buffer chamber 9 and the second buffer chamber 12 for a given differential pressure delivered by the pitot tube and consequently the flow

  sampling liquid in line 1 to which it is equal.

  The second calibrated orifice 32 fixes the drain rate of the transfer chamber in the tank 2 for a given static pressure of the liquid in

circulation in the pipeline 1.

  The device of the invention therefore makes it possible to take, over a given period of time, a series of samples of constant volumes of a liquid circulating in a pipe, at a variable rate depending on the flow of liquid in circulation in the pipeline, the total volume of the series of samples taken being proportional to the total volume of liquid which circulated in the

  pipeline during the same period of time.

  The device of the invention has the advantage of eliminating a device for measuring the flow rate of liquid to be sampled and a controller

  electronic or pneumatic for controlling valves.

  The simplicity of embodiment of the device of the invention gives it a

  great robustness, good reliability and reduced cost.

  It is particularly suitable for isolated installations or to which access is

  dangerous in nature, such as nuclear or submarine installations.

Claims (6)

  1- Device for taking samples of a liquid circulating in a pipe (1) under pressure comprising a collecting tank (2) for collecting said samples, a pressure-reducing member (3) inserted in the pipe (1) under pressure supplying between a high pressure outlet (4) and a low pressure outlet (5), a differential pressure as a function of the volume flow rate of the liquid in circulation, characterized in that it additionally comprises: - a primary cylinder (6a) at the inside of which is mounted a primary piston (7) which define a transfer chamber (8) and a first buffer chamber (9) filled with a separating liquid, - a secondary cylinder (6b) of the same dimensions as the cylinder (6a) primary inside which is mounted a secondary piston (10) to define a downstream chamber (11) and a second buffer chamber (12) filled with separating liquid, - a pipe (13) connecting the first chamber (9 ) buffer the second buffer chamber (12) through a restriction (14) which determines a flow of separating liquid between the said buffer chambers for a given pressure difference between the said chambers, - a pipe (15) connecting the chamber (11) downstream of the low pressure outlet (5) of the pressure-reducing member (3), - means (16,17,18,21) of controlled connection, on the one hand by the primary piston (7) for d first connect the transfer chamber (8) to the high pressure outlet (4) of the pressure-reducing member (3), to move the primary piston (7) and fill the transfer chamber (8) with a sample of a predetermined volume of the liquid in circulation and on the other hand by the secondary piston (10) to then connect the transfer chamber (8) to the sampling tank (2), to transfer said sample in said tank (2) by displacement of the piston (7) primary under the effect of the pressure in the pipe (1) transmitted by the plug (5) low pres sion, the secondary piston (10) and the separating liquid to the first buffer chamber (9), 2- Device according to claim 1 characterized in that the member (3)   The pressure reducing agent inserted into the pressure line (1) is a Pitot tube.   3- Device according to claim 1 or 2 characterized in that the restriction of the pipe (13) connecting the first chamber (9) buffer to the second chamber (12) buffer is achieved by means of a tap (14) needle adjustment. 4- Device according to claim 1 or 2 characterized in that the restriction of the pipe (13) connecting the first chamber (9) buffer to the second   buffer chamber (12) is produced by means of a plate (44) with calibrated orifice.   - Device according to any one of claims 1 to 4, characterized in that   that the connecting means controlled by the primary piston (7) and the piston   (10) secondary include a hydraulic switch (17).   6- Device according to any one of claims 1 to 5, characterized in that   that it further comprises a first non-return valve (31) mounted on the pipe (13) connecting the first buffer chamber (9) so as to allow the passage of the separating liquid from the first buffer chamber (9) to the second buffer chamber (12) and a second pipe (34) connecting the two buffer chambers through a second restriction (32) and a second non-return valve (33) mounted so as to allow the passage of the liquid   separator of the second buffer chamber (12) towards the first.   7- Device according to claim 6 characterized in that the second restriction   is achieved by means of a needle adjustment valve (45).   8- Device according to claim 6 characterized in that the second restriction   is produced by means of a plate (32) with calibrated orifice.   9- Device according to any one of claims 1 to 8 characterized in that   the separating liquid has rheological characteristics whose values are close to those of the liquid circulating in the pipe (1) and preferably identical, so that the instantaneous flow of the separating liquid between the two buffer chambers (9,12) is substantially proportional at   instantaneous flow of the liquid circulating in the pipeline (1).