GB2106865A - Apparatus and method for sampling a liquid - Google Patents

Abstract

An apparatus for sampling liquids flowing in closed pipes includes a piston 3 and cylinder 4 combination linked to a manifold with an inlet valve 7 leading to the pipeline 15 and a delivery valve 10 leading to a collection bottle. With valve 7 open, reciprocation of the piston flushes the apparatus of old liquid. Cylinder 4 is then fully charged, valve 7 closed and the valve 10 opened so that, on the next stroke of piston 3, the contents of the cylinder 4 is discharged into collection vessel 11. Having taken the sample, valve 10 is closed. A controller 20 synchronizes the movements of the valves and piston. This apparatus is well situated for the application of pneumatic components to provide the control and working power. Variants on this apparatus include a return valve to enable liquid to be recirculated back to the pipeline and also an apparatus with a moving probe 14, syncronized to the movement of piston 3. <IMAGE>

Description

SPECIFICATION Apparatus and method for sampling a liquid BACKGROUND OF THE INVENTION The invention relates to apparatus and method for periodically sampling a liquid flowing in a pipe line.

The purpose of sampling a liquid is to obtain a representative portion of the liquid flowing through a pipeline from which the average composition of the flow can be determined. This is normally done by composing a set of individual sub samples taken with sufficient frequency to include all the effects of changing composition of the flow during the period of sampling. The more frequent the taking of these individual samples the more representative will be the composite sample.

The frequency of sampling may be at regular time intervals or at time intervals in inverse proportion to the rate of flow of the sampled liquid. The latter case being referred to as flow proportional sampling. When sampling crude liquids it is important to include any solids that are being carried by the liquid. In the particular case of crude oil the solids may be in the form of sand particulate matter or salt water or miscellaneous debris that have settled within the storage tanks. To obtain a representative sample of the solids or second phase liquids, the oil must be pumped at high velocity to prevent the settleable matter from being left behind and be transported through pipe work of sufficient bore to avoid the risk of internal blockage within the apparatus.

Hithertu pipeline samples have incorporated a line filter to remove any solids material from the apparatus prior to the sampling. This was necessary because the bore size of such apparatus was insufficient to accomodate normal solids found in crude oil and hence were liable to blockage. This has been the prime limitation on existing products and which prevented them from accurately assessing the quality of crude oil. It has therefore been virtually impossible to access the true value of a cargo of crude oil being discharged from a super tanker. In many cases the normal cargo value would be of the order of #5,000,000 but may contain up to 2 percent by volume of contaminants in particular, the brine used as ballast from previous cargoes.

OBJECT OF THE INVENTION It is an object of this invention to provide a means of obtaining liquid samples in small volumes from a liquid flowing at high pressure through a pipeline with apparatus that can easily be adapted to avoid obstruction by debris and second phase liquids flowing within the pipeline.

Other objects of this invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION According the present invention there is provided apparatus for and a method of sampling a liquid. The apparatus for sampling a liquid comprising: (a) a pump comprising a working piston and cylinder combination; (b) a drive means for reciprocating the working piston incorporating a means of signalling the two end of stroke positions of the working piston; (c) a manifold communicating with the outlet of the cylinder; (d) a feed valve communicating on one side with the manifold and on the other side with a sampling tube leading to a probe with inlet positioned in a pipeline; (e) a delivery valve communicating on one side with the manifold and on the other side with the delivery tube; (f) a container necessary for collecting sample from the delivery tube;; (g) a controller for regulating the operation of the working piston, the feed valve, and the sample valve; (h) means of signalling to the control that the open and closed positions of the return and delivery valves; The method of sampling a liquid comprising the steps of; (i) opening the feed valve to allow liquid in the pipeline to pressurise liquid within the manifold; (ii) causing the drive means to operate the working piston so that material within the cylinder is forced through the manifold and into the sampling tube; (iii) causing the drive means to operate the working piston so that material from the pipeline flows under pressure through the manifold into the cylinder; (iv) repeating the steps (ii) and (iii) to purge liquid originally in the cylinder from the cylinder and manifold and sampling tube; (v) closing the feed valve; (vi) opening the delivery valve;; (vii) causing the drive means to operate the working piston so that material from the cylinder is forced through the manifold and through the delivery tube into the collecting vessels; (viii) closing the delivery valve; (ix) opening the feed valve; (x) causing the drive means to operate the working piston so that material from the pipeline flows through the manifold and occupies the cylinder; (xi) closing the feed valve.

A further embodiment of the invention incorporates a displacer working in unison with the pump and working piston and cylinder combustion. The displacer communicates with liquid within the manifold. The apparatus works in a similar way to the above description except that in step (viii) only the displacer forces liquid from the manifold into the collection vessel. In step (x) only the displacer retracts to allow liquid to flow from the pipeline to the manifold.

A third embodiment of the invention includes a return valve communicating through a return tube to the pipeline. In this embodiment, instead of liquid returning into the pipeline via the feed valve and sampling tube, the return valve is opened to allow the liquid to pass return to the pipeline via the return tube. This embodiment is advantageous if the apparatus is positioned at a great distance from the pipeline in which case the purging action will not be adequate with a single tube with bi-directional flow.

A fourth embodiment of the invention incorporates a drive means for the working piston operated by double acting hydraulic cylinder, the hydraulic fluid being displaced at the two ends of the hydraulic cylinder by two sampling tubes leading to two secondary cylinders each with a piston separating the hydraulic fluid from a region of such cylinder that is fed with compressed air to move the hydraulic fluid and hence the working piston. One of the sampling tubes leads to a secondary hydraulic cylinder interposed between the double acting hydraulic cylinder and the secondary cylinder such that, the secondary cylinder moves in unison with the working piston.

This secondary cylinder actuates a sample probe so that as the working piston takes the sample, the probe traverses across the pipeline.

A BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of an apparatus made in accordance with the first embodiment of this invention.

Figure 2 is a schematic diagram of an apparatus made in accordance with the second and third embodiment of this invention.

Figure 3 is an elevationally view partly broken away and sectioned of an apparatus made in accordance with this invention in which the movement of the working piston is made by the displacement of hydraulic fluid which in turn is used to traverse the probe across the pipeline to give a more representative sample across the section of the pipeline.

DESCRIPTION OF THE EMBODIMENT The apparatus includes a sampler housing (22) mounted on supports (23) and supplied by energy through line (24). The controller (20) incorporates a sampling interval clock (21) and communicates through lines (18) with the drive means for the working piston (2), the feed valve (7), and the delivery valve (10). The drive means (2) is linked to the piston (3) by member (5) the working piston being guided within cylinder (4) the cylinder (4) communicates with the manifold (6) which also communicates with the feed valve (7) and the delivery valve (10) via tubes (8) and (9) respectively. Feed valve (2) is linked to a probe (14) in the pipeline (15) by a sampling tube (13). The delivery valve (10) leads to a delivery tube (11) which guides the liquid into the collecting vessel (12).Liquid from the pipeline (16) occupies manifold (6) and the working cylinder (4).

In operation the sample interval timer (21) is preset to required interval. Prior to sampling the working piston (3) is at the top of cylinder (4) with the cylinder contects fully charged with liquid (16). After the period of the sampling interval preset on clock (21) has lapsed the valve (7) opens and the drive means (2) forces the working piston (3) through the cylinder (4) displacing the liquid from the cylinder through the manifold and to return to the pipeline (14). With the valve (7) still open the working piston returns to its original position to allow liquid from the pipeline to pass through the manifold and recharge the cylinder. This cycle is repeated a sufficient number of times to refresh the liquid within the apparatus.The valve (7) is then closed and the valve (1 9) opened. The drive means then forces the working piston through the cylinder to expel the contents of the cylinder via the manifold and via delivery tube (11) into the collecting vessel (12) to form part of the sample (17). The delivery valve (10) is then closed and the feed valve (7) opened. The drive means then reverses the working piston to recharge the cylinder (4) with liquid from the pipeline. Valve (7) is then closed at the end of the sampling cycle.

DESCRIPTION OF THE SECOND AND THIRD EMBODIMENT Figure 2 shows an apparatus constructed in accordance with this invention and incorporating features of the second and third embodiments of the invention. For simplicity the housing is not shown on this diagram. The apparatus includes a controller supplied by energy through line (32) and incorporting a sample interval clock (31). The controller operates and receives signals from various parts of the apparatus through the control lines (28). These control lines are linked to the drive means for operating working piston (3), an auxilliary displacer drive unit (15) a feed valve (8) and a return valve (10) and two delivery valves (19) and (20).

Additional delivery valves could be linked to the manifold (6). All four valves, the chamber (17) for the displacer piston (16), and the main cylinder (4) all communicate with the manifold (6). The main cylinder (4) is swept by the working piston (3) linked via a connect ing rod with the displacer (2). The feed valve (8) communicates with a probe (12) in the pipeline (14) by way of the sampling tube (11). The returns valve (10) similarly communicates with the pipeline (14) via the return line (13). Delivery valves (19) and (20) communicate with delivery tubes (23) and (22) which guide the liquid into the collecting vessels (24) and (25). The drive means for the displacer (15) is linked to the displacer piston (16) by a connecting rod (18).

After the expiry of the intervals set by the sampler timer (31) a signal is sent to the return valve (10) to open this valve. The controller (30) then operates drive means (2) and drive means (15) to displace liquid from the cylinder (4) and the chamber (17) through the manifold, through return tube (13) into the pipeline (14). When displacer piston (16) and working piston (13) have reached the end of their strokes, valve (10) is closed and valve (8) is opened. The displacer (16) and the working piston (3) then return to their former positions drawing liquid in from the sample probe (12) through sampling tube (11) through the manifold (6) and into the cylinder (4) and chamber (17). This cycle is then repeated sufficiently to purge any former liquid from the apparatus. Delivery valve (19) is then opened.The displacer (15) then displaces a small volume from the chamber (17) through the manifold, through delivery tube (23) into the collecting chamber (24) to become part of the sample (26). Valve (19) is then closed and valve (8) opened. The displacer (16) is retracted to draw a quantity of liquid into the chamber (17). Valve (8) is then closed and valve (20) opened. The displacer (16) thc-n displaces liquid from chamber (17) through the manifold (6) into the second collecting sample vessel (25). Valve (20) is then closed and valve (8) opened. The displacer (16) then returns to its former position recharging the chamber (1 7) with sample via the pipeline through sampling tube (11).

Finally valve (8) is closed. This cycle is repeated at intervals preset by the sampling interval clock (31).

DESCRIPTION OF FOURTH EMBODIMENT Figure 4 shows an apparatus constructed in accordance with this invention and incorporating the features of the fourth embodiment.

For simplicity the housing is not shown on this diagram. The apparatus includes a controller (72) incorporating a sample interval clock (75) a purge timer (73) and an on/off switch (74). The controller operates and receives signals from various parts of the apparatus through the control lines (76), (77), (78), (80) and (81). These control lines are linked to a delivery valve (60), feed and return valves (40) and (50) and two displacement cylinders (18) and (19).

The valves (40) (50) and (60) are of similar construction. The actuator cases (41) (51) and (61) house working pistons (42) (52) and (62) with piston seals (43) (53) and (63). The pistons hold the cylindrical actuating rods (45) (55) and (65) in the extended position by the action of return springs (44) (54) and (64).

The movement of these actuating rods and pistons is governed by the controller (72) by air pressure fed through the control lines (76).

Rod seals (46) (56) and (66) prevent leakage of compressed air from the actuating cylinders. Spacers (47) (57) and (67) are located between the actuating cylinders (40) (50) and (60) and the body of the valves (49) (59) and (69). The inlet valve (40) is connected to the sample probe (3) by a sampling tube (5) with a flexible section (5a). The feed valve communicates with the pump body (36) via a tube (6) which continues through tube (8) to the return valve (50). The return valve is linked to the pipeline by the return tube (9). The tube (6) has a second brance (7) which links to the delivery valve (60). The outlet from the delivery valve (71) is sealed from the pressure of the pipeline in tube (7) by the 'o' ring seals (69). The outlet (71) leads to the collection bottle (70) which holds the sample (2).

The pump working piston (34) has a seal (35) and runs within the cylinder (36). The pump is actuated by the connecting rod (33) which leads to a hydraulic piston (31) within the hydraulic cylinder (30). Hydraulic fluid is sealed within the cylinder (30) by a seal (16).

Hydraulic fluid (22) is separated by the piston seals (32) from the lower and upper parts of the hydraulic cylinder (28) and (29) respectively.

The hydraulic fluid (22) is moved within the apparatus by the actions of the two pistons (20) within the duplex cylinders (18) and (19). Within these duplex cylinders the hydraulic fluid is separated from and propelled by the pistons (20) when the upper chambers (24) and (26) are subjected to compressed air through feed lines (80) and (81) from the controller (72). Hydraulic fluid passes to and from the duplex cylinder (18) to a double acting secondary hydraulic cylinder (11) through a hydraulic line (14). The hydraulic cylinder (11) contains a piston (12) fixed to the sampling proble (3) and carrying piston seals (12) within the cylinder.Another hydraulic line (1 3) from the secondary cylinder (11) transmits the hydraulic pressure of the fluid within the duplex cylinder (18) to the top of piston (31) in the pump actuating cylinder (30). A second duplex cylinder (19) feeds hydraulic fluid (22) through a hydraulic line (17) to the lower side of the pump piston (31).

Thus the hydraulic fluid (22) within the duplex cylinders (18) and (1 9) will transmit any air pressure in lines (80) and (81) to the hydraulic fluid (22) to displace that fluid through the double acting hydraulic cylinders that operate the pump working piston (34) and the probe (3).

Prior to sampling, the working cylinder (36) is fully charged with fluid from the pipeline, valves (40), (50) and (60) are closed, and the probe (3) is fully retracted. In this condition, the pistons of duplex cylinder (18) has minim ised the volume of chamber (24) and the piston of duplex cylinder (19) has maximised the volume of chamber (26). After expiry of the intervals set by sample timer (75), a signal is sent to the return valve (50) to open the valve. The controller (72) then supplies com pressed air through the feed line (80) to the duplex cylinder (18). This forces the piston (20) on the hydraulic fluid (22) to pressurise that fluid in the chamber (25). This hydraulic pressure is communicated to the secondary cylinder (11) forcing the piston (10) to move the probe (3) across the diameter of the pipeline (1).Simultaneously the fluid is dis placed from the bottom of the secondary cylinder (11) through the hydraulic line (13) to the top of the hydraulic cylinder (30). This actuates working piston (31) to move the pump working piston (34) down through cylinder (36) to displace pipeline fluid (2) from the cylinder and out through the return valve (50) through the return tube (9).

Simultaneously hydraulic fluid is displaced from the bottom of the hydraulic cylinder (30) through the hydraulic line (70) to the duplex cylinder (19) causing the piston in cylinder (19) to rise towards the top of duplex cylinder.

When the piston in Duplex cylinder (18) has reached the bottom of the chamber (25), the sample probe (3) will have reached the limit of its stroke across the pipeline (1) and the working piston (34) will have discharge the pipeline contents from its cylinder. At this stage the return valve (50) is closed and the inlet valve (40) is opened. The controller (72) then releases the pressure at the top of duplex cylinder (18) and pressurises the chamber (26) at the top of duplex cylinder (19). This reverses the process so that the piston (34) is drawn to the top of cylinder (36) thereby inducing pipeline liquid to enter the probe at inlet (4) and pass through the sampling tubes (5) and (6) to recharge the working cylinder with fluid.Simultaneously the inlet probe (3) is retracted across the diameter of the pipeline (1) by the movement of hydraulic fluid between the duplex cylinders via the working cylinder (30).

The controller (72) continues to operate the two Duplex cylinders and the inlet and return valves to cause liquid to be circulated from the inlet (4) on the pipeline probe through the apparatus be returned to the pipeline via the return tube (9). With each cycle, the inlet probe (3) is traversed across the diameter of the pipeline in such a way that its movement is sychronised with the movement of the working piston (34).

Having purged the apparatus of residual liquid from the previous sample, the controller (72), with the pump cylinder (36) fully charged with liquid from the pipeline (2), closes the inlet and return valves (40) and (50) and opens the delivery valve (60). The controller then operates the Duplex cylinder (1 8) so that the working piston (34) discharges the contents of the pump cylinder (36) through the sampling tube (7) and delivery tube (71) into the collective vessel (70).

The delivery valve (60) is then closed and the inlet valve (40) opened. The duplex cylinder (19) is then operated to drive the working piston (34) to the top of pump cylinder (36) thereby recharging the pump cylinder with fluid from the pipeline.

The apparatus has now returned to its start of cycle condition.

Claims (11)

1. Apparatus for sampling a liquid comprising: (a) a pump comprising a working piston and cylinder combination; (b) a drive means for reciprocating the working piston incorporating a means of signalling the two end of stroke positions of the working piston; (c) a manifold communicating with the outlet of the cylinder; (d) a feed valve communicating on one side with the manifold and on the other side with an inlet; (e) a delivery valve communicating on one side with the manifold and on the other side with a delivery tube; (f) a container necessary for collecting sample from the delivery tube; (g) a controller for regulating the operation of the working piston, the feed valve; and the sample valve; (h) means of signalling to the controller status of the return and delivery valves.

2. A sampler as claimed in claim 1. with a displacer having means of signalling its end of stroke positions to the controller, communicating with the manifold.

3. A sampler as claimed in claim 1. or claim 2. with two or more delivery valves, each with means of signalling their status to the controller, each valve communicating with the manifold.

4. A sampler as claimed in any of the preceeding claims, with a return valve having means of signalling its status to the controller, communicating on one side with the manifold and on the other with a return tube.

5. A sampler as claimed in any preceeding claim in which the means of reciprocating the working piston is a compressed air and double acting cylinder and piston combination.

6. A sampler as claimed in any preceeding claim wherein the valves are actuated by compressed air.

7. A sampler as claimed in any preceeding claim wherein the valve seals comprise a circular aperture with an elastic wall seal into which a circular rod is moved to effect closing of the valve.

8. A sampler as claimed any preceeding claim in which the means of ieciprocating the working piston is a hydraulic cylinder linked to the working piston by an actuating rod in which the hydraulic fluid is displaced by the movement of pistons within two auxilliary cylinders, the pistons being driven by force of compressed air.

9. A sampler as claimed in claim 8. in which the probe within the pipeline is driven by a second hydraulic cylinder connected in series with the pump hydraulic cylinder so that the inlet on the probe moves across the pipeline as the pump working piston moves within the pump cylinder.

10. A method of operating a sampler as claimed in claims 1 to 7, comprising the steps of; (i) opening the feed valve to allow liquid in the pipeline to pressurise liquid within the manifold; (ii) causing the drive means to operate the working piston so that material within the cylinder is forced through the manifold and into the sampling tube; (iii) causing the drive means to operate the working piston so that material from the pipeline flows under pressure through the manifold into the cylinder; (iv) repeating the steps (ii) and (iii) to purge liquid originally in the cylinder from the cylinder and manifold and sampling tube; (v) closir.g the feed valve; (vi) opening the delivery valve; ; (vii) causing the drive means to operate the working piston so that material from the cylinder is forced through the manifold and through the delivery tube into the collecting vessels; (viii) closing the delivery valve; (ix) opening the feed valve; (x) causing the drive means to operate the working piston so that material from the pipeline flows through the manifold and occupies the cylinder; (xi) closing the feed valve.

11. A method related to claims 8 and 9 as described in relation to the fourth embodiment.