GB2164021A

GB2164021A - Pipeline liquid sampling system

Info

Publication number: GB2164021A
Application number: GB08417724A
Authority: GB
Inventors: Joost Jakob Jiskoot
Original assignee: Jiskoot Autocontrol Ltd
Current assignee: Jiskoot Ltd
Priority date: 1984-07-12
Filing date: 1984-07-12
Publication date: 1986-03-12
Also published as: GB8417724D0

Abstract

A pipeline conditioning and sampling system for non-homogenous liquids in a pipeline, for example a crude oil pipeline, which collects a sample of fluid that is representative of a batch of fluid passing through the pipeline. The sampling system includes a jet mixing, pipeline contents conditioning system to thoroughly agitate the contents of the pipeline to produce a uniform mixture from which a sample is collected. The sample may be withdrawn, using a sampler probe, directly from the pipeline, downstream of the jet mixer. Alternatively, as shown, the sample may be collected, using a flow-through-cell sampler, from the return loop, through which a portion of the uniformly mixed fluid in the pipeline is pumped to the jet mixing nozzle(s), or from a bypass loop connected to the return loop. <IMAGE>

Description

SPECIFICATION Liquid sampling system This invention is concerned with a liquid sampling system, particularly for taking samples from crude oil pipelines.

The automatic collection of representative samples during liquid transfer operations has become increasingly important in recent years. The collected samples, which are used for laboratory analysis or retained for reference, are particularly important to determine crude oil properties for fiscal purposes. The samples will only be representative of the flow in the transfer line if the samples are taken from a homogeneous liquid flow. This is difficult with conventional sampling systems, in which a sampling probe is inserted into the transfer line; because of layering of the liquid in the transfer line. This layering of the liquid is particularly a feature of a crude oil pipeline flow.

According to one aspect of the present invention there is provided a method of obtaining a representative sample from a liquid transfer line. This comprises: removing liquid from the liquid transfer line and returning it to the transfer line through a return loop so that it re-enters the transfer line as a jet or jets of liquid which agitate the liquid in the transfer line to produce a substantially uniform mixture (see U.K. Patent 2030963); removing a sample from the uniform mixture.

The sample may be obtained conventionally, using a sampling probe, directly from the transfer line downstream of the outlet of the return loop at any point at which the liquid remains a uniform mixture (as shown in Fig. 1).

The sample may be removed from the return loop, using a flow-through-cell sampler or similar device, in which case the outlet of the return loop to the transfer line is upstream of the inlet to the return loop and the distance between the inlet and outlet and the flow velocity in the return loop are selected to ensure that the liquid in the transfer line is uniformly mixed at the inlet to the return loop (as shown in Fig. 2). The volume of the return loop and the upstream position of the mixing jet(s) gives partial liquid recirculation and provides an averaging effect on any quality transients or variations of the liquid flow in the transfer line.

Alternatively, if the diameter of the return loop is too large to accommodate a flow-through-cell sampler, the sample may be removed, using a flowthrough-cell sampler, from a pumped bypass loop connected to the return loop and of a smaller diameter than the return loop (as shown in Fig. 3).

Fig. 4 is in two parts and shows the flowthrough-cell sampler. The total flow of the return loop (for the arrangement shown in Fig.2) and the total flow of the bypass loop (for the arrangement shown in Fig. 3) passes through the sample chamber 18 of the sampler. The flow of liquid through the sampler is continuous irrespective of whether or not a sample grab is being taken. The bottom of the sampler chamber 18 is defined by a plug 19 mounted in the sampler body 17. The chamber 18 has an inlet 21 and an outlet 22. The sampler is connected into the return loop or bypass loop so that oil passes through the inlet 21 through the chamber 18 and out of the outlet 22. The upper surface of the chamber 18 is defined by the bottom edge 26 of a tubular sleeve 27 the bottom edge 28 of a tubular piston 29 and the bottom face 31 of a valve stem 32.The bottom face 31 is provided by a shaped resilient valve member 33. An annular passage 34 extends between the valve stem 32 and the tubular piston 29 and as is clear from the Fig. 4 the valve member 33 is shaped so as to sealingly engage with the bottom edge 28 of the tubular piston 29, to seal the annular passage 34 from the chamber 18. There is also provided an "0" ring seal 35 mounted in a slot in the outer surface of the tubular piston 29 to sealingly engage with the inner surface of the tubular sleeve 27.

The upper portion of the plug 19 includes an annular slot 36 of similar transverse dimensions to the tubular sleeve 27 and the inner surface of the annular slot 36 carries a continuous seal 37.

Figure 4 shows the sampler actuator assembly.

The actuator is described in a separate patent application (U.K. Patent Application Number 8415108). The actuator provides very rapid isolation of the sample.

It will be noted from Figure 4 that the annular passage 34 extends upwardly through the sampler and it will be seen that this annular passage 34 extends into the piston head 46 and connects with a side passage to an outlet port 48.

When it is desired to remove a sample from the return loop or bypass loop, the tubular sleeve 27 is moved downwards so that its bottom edge 26 passes into the annular slot 36 as shown in figure 4. As it does so it entraps the oil in the centre of the chamber 18. The seals 35, 37 seal with the sleeve 27 to prevent escape of the oil within the sleeve 27. The tubular piston 29 and the valve stem 32 are then moved downwards in unison. As the tubular piston 29 and valve member 33 move down together, the trapped oil sample exerts a back pressure on the valve stem 32 which overcomes a resistance of the spring 54 so that the valve stem 32 rises breaking the seal between the valve member 33 and the bottom edge 28 of the tubular piston 29. Sample oil thus flows into the annular passage 34. This causes oil already in the annular passage 34 to pass out of the outlet port 48 in the piston head 46.

Eventually the bottom edge 28 of the tubular piston 29 reaches the bottom face 24 of the chamber 18 and the motion ceases. The light spring 54 will then cause the valve stem 32 to be lowered into engagement with the bottom edge 28 of the tubular piston 29.

It will be understood, therefore, that by this means the oil sample trapped in the centre of the chamber 18 has been passed into the annular passage 34 which thereby provides an oil sample at the sample outlet and therefore out of the return loop or bypass loop.

The tubular sleeve 27, tubular piston 29 and valve stem 32 are then withdrawn upwards to al low flow through the centre of the chamber 18 whence the cycle may recommence.

The invention is not restricted to the details of the foregoing example.

Claims

1. A sampling system for a fluid pipeline comprising a jet mixing system, which withdraws a portion of the fluid and injects it, as high velocity jets, back into the pipeline, and a sampling device to withdraw the fluid sample from the uniform mixture produced by the high velocity jets.

2. A sampling system as claimed in claim 1 in which the sampling device is positioned either directly in the pipeline, in the return loop through which a portion of the uniformly mixed fluid in the pipeline is pumped to the jet mixing nozzle, or in a bypass loop connected to the return loop.

3. A sampling system as claimed in claim 1 or 2 in which the jet mix nozzles and the sampling device, if mounted directly in the pipeline, may be withdrawn for maintenance or when pigging the pipeline - all the other equipment being external to the pipeline.

4. A sampling system as claimed in any of claims 1 to 3 in which the sampling device has a chamber through which, in use, the fluid in the pipeline, return loop or bypass loop passes, said chamber having a fluid inlet and a fluid outlet for communicating with the pipeline, return loop, or bypass loop, and a fluid sample outlet through which the sampled fluid may be withdrawn from the chamber and out of the sampling device.

5. A sampling system as claimed in any of claims 1 to 4 in which the sampling device includes a sample outlet valve in the fluid sample outlet immediately adjacent to the chamber, and means may be provided to open the sample outlet valve from outside the sampling device.

6. A sampling system as claimed in any of claims 1 to 5 in which the sampling device has wall means provided to close said fluid inlet and fluid outlet and thereby further define said chamber, means defining a further wall of the chamber being movable into the chamber, said movable wall including a sample outlet valve openable as said wall moves into said chamber, so that fluid trapped within the chamber may pass through said sample outlet valve, and out of the sampling device.

7. A sampling system as claimed in claim 1 substantially as hereinbefore described with reference to the accompanying drawings.