US3408869A

US3408869A - Sampling device

Info

Publication number: US3408869A
Application number: US586482A
Authority: US
Inventors: Auger Frank Pawley
Original assignee: Distillers Co Yeast Ltd
Current assignee: Distillers Co Yeast Ltd; Distillers Co Ltd
Priority date: 1966-10-13
Filing date: 1966-10-13
Publication date: 1968-11-05
Anticipated expiration: 1985-11-05

Description

Nov. 5, 1968 F. P. AUGER 3,403,869

- SAMPLING DEVICE Filed Oct. 13, 1966 2 Sheets-Sheet 1 I I I I I '2 I z a FIG. I h

avdlLmluod,g

n'ronm' Nov. 5, 1968 F. P. AUGER 3,408,869

SAMPLING DEVICE Filed Oct. 13, 1966 2 Sheets-Sheet 2 I I o N ATTORNEY;

United States atent O ice 3,408,869 SAMPLING DEVICE Frank Pawley Auger, Surbiton, Surrey, England, assignor to The Distillers Company Limited, Edinburgh, Scotland, a British company Filed Oct. 13, 1966, Ser. No. 586,482 11 Claims. (Cl. 73-4215) This invention relates to sampling devices and in particular to devices for sampling a stream of fluid.

In order to monitor, for example, the vapour within the outlet pipe of a chemical reactor, where equilibrium conditions may be considered to obtain for all practical purposes, a part of the reactor output vapour can be diverted through valves to a receiver. If the receiver is an analysis instrument, such as a gas chromatograph, it is desirable that a reproducible sample be taken each time. For this purpose the valves are normally situated in a sampling pipe which is in parallel with the main reactor outlet pipe and through which reactor output vapour is continuously passed except momentarily during switching. This arrangement allows a reproducible sample to be taken as required by appropriate switching of the valves. This sample can be transferred from the sampling pipe to the receiver by a stream of a carrier gas, for example, helium.

A particularly useful type of valve for this purpose is a multi-position valve comprising a rotor face-to-face with a stator; the rotor having at least one channel cut in its face, and the stator having a plurality of ports cut in its face. Valves of this type have good sealing characteristics, thus providing reproducibility of sample size. However, when dealing with vapours above about 200 C., the lubrication and sealing of such a valve becomes difficult, since under such conditions lubricants are liable to carbonize and the elevated temperatures may lead to distortion of the valve faces and corrosion problems.

It is an object of the present invention to provide apparatus suitable for sampling a stream of fluid at high temperature which enables reproducible samples to be withdrawn from a reactor gas stream without relying on high precision mechanical valves to define the sample.

According to the present invention, there is provided apparatus which comprises an elongated vessel, provided with an inlet at one extremity and an outlet at the other extremity, flow restricting devices adjacent the said inlet and outlet, ports adjacent the said flow restricting devices and a third port situated between the aforesaid ports.

In a preferred embodiment the apparatus comprises two similar coiled tubes connected by a T-piece which thereby provides a central port at right angles to the flow direction of the vapour to be sampled. The apparatus is further provided with T-pieces at the free ends of the coiled tubes, thereby providing ports again at right angles to the sample flow. Flow restricting devices are also provided adjacent the inlet and outlet. They should be situated between the outlet, or inlet, and its nearest port.

In operation, the device is connected, for example, as a by-pass to a stream of reactor output vapour and carrier gas which is inert to the components of the reactant output vapour under the prevailing conditions is passed continuously into the apparatus through all three ports at very low fiow rate, so that no diffusion of reactor vapour occurs through the ports. Passage of reactor vapour is allowed continuously through the coiled tubes and the reactor vapour is diluted only with a small but constant amount of carrier gas. When a sample is required to be withdrawn, carrier gas at high pressure is introduced via the ports situated at the inlet and outlet ends, and simultaneously the slow feed at the central port is interrupted. On entering the sample device the high pressure Patented Nov. 5, 1968 carrier gas splits into two streams, one directed towards the centre of the device and the other directed away from it. Thus, at each end of the device the stream ofreactor vapour is interrupted by the flow of high pressure carrier gas, and swept either toward or away from the central port. The sample is therefore defined by the points of entry of high pressure gas. In order to obtain a definite break in the vapour stream it is important that the flow of high pressure carrier gas should take place in each direction from the ports and therefore the flow restricting devices must not at any time close the tubes entirely. The sample of reactor vapour is swept out via the central port and the slow bleed of carrier gas through the three ports is then resumed.

The restricting devices may, for example, be simple constrictions or other fixed mechanical contrivances designed to provide a back pressure. Alternatively they may be valves which need only be of a relatively crude type. It is particularly preferred however, to use a valve arranged to provide a higher degree of restriction than normal during the actual sampling operation. In one such embodiment a bellows valve is connected to the source of supply of high pressure gas. Adjacent the bellows valve is provided a small aperture in the wall of the sample ves sel. When high pressure gas is switched on, the bellows valve inflates and closes the tube, thereby creating a back pressure, while restricted flow of gas is permitted through the aperture.

The streams of carrier gas may suitably be introduced into the device by means of a multi-position valve of the type referred to above. The sample may be removed from the device by way of such a valve.

By means of the present invention the multi-position valve or valves need only receive hot reactor vapour during the actual sampling operation and therefore, bearing in mind their relatively large mass, the valves remain comparatively cool and are not maintained at the high reactor gas temperature.

The invention will now be described with reference to the accompanying diagrammatic drawings in which FIGURE 1 represents a fiow diagram of a vapour sampling device of the invention.

FIGURE 2 represents a flow diagram of a vapour sampling device of the invention, connected in an operative position.

The device shown in FIGURE 1 of the drawings is a simple embodiment of the invention which can be used, for example, in parallel with the output pipe of a chemical reactor. The device shown comprises a sample tube divided into two substantially equal portions V and V A T-piece X connects V and V and other T-pieces, Y, Z, are at the ends of V and V remote from X. Constrictions F, G are located in the arms of D, E of T-pieces Y, Z respectively.

In use, a stream of the vapour to be sampled flows through the device from D to E, through F, Y, V X, V Z and G in that order. Diffusion of the vapour up side-arms A, B, C of the T-pieces Y, X, Z is prevented by allowing a small amount of a suitable carrier gas, for example helium, to bleed into the vapour stream at a suitable rate through the side-arms A, B, C. Thus the vapour in the sample tube is admixed with a small amount of the carrier gas.

On taking a sample, side-arms A and C are connected to a high pressure source of carrier gas. Simultaneously, side-arm B is connected to a sample receiver (not shown), for example a gas chromatograph. The high pressure gas at Y and Z divides the vapour stream flowing through the device and pushes the vapour in V and V out through the side-arm B. The constrictions F, G restrict the flow of vapour and gas outwardly, thus providing the necessary pressure differential to drive the sample out through side-arm B. When all the samplehas been driven into the sample receiver, side-arms A, B and C are again connected to their sources of low pressure carrier gas and the carrier gas contained within the volumes V and V is swept out by the vapour stream through the device.

The device in FIG. 2 is represented as being within the outlet pipe of a chemical reactor, indicated by the broken lines, so that vapour flows through the device. The vapour flow through the device can be assisted by placing the device in parallel with a restrictor plate in order to augment a pressure difference between the inlet and outlet of the device. The device comprises two bellows 1, 2 connected by sample coils 3, 4. The ends of the coils 3, 4 adjacent the valves 1, 2 are connected by lines 5, 6 to a line 7 which is connected to a port 10 of a ten-port multiposition distributor valve 8. The junction of the sample coils 3, 4 is connected by line 9 to a port 17 of the tenport valve 8. The bellows of the bellows valves 1, 2 are connected by lines 20, 21 to a line 22 which, in turn, is connected to a port 13 of the ten-port valve. Between the valves 1, 2 and the lines 5, 6 there are apertures 23, 24 respectively, which permit restricted flow between the sample device and the outlet pipe of the chemical reactor. In a preferred alternative embodiment (not shown) the restricted flow apertures are built into the bellows valves. The remaining ports of the ten-port valve 8 are connected as follows:

Port 18 to a chromatograph column 25.

Ports 19, 11 and 16 to flow-

controllers

28, 27, 26 respectively.

Port is blanked off.

Port 12 is open to the atmosphere.

Port 14 is connected by line 29 to a pressure regulator 30, to which the

flow controllers

26, 27 and 28 are also connected.

A pre-column 31 is an optional feature which may be inserted in the line 9.

The pressure regulator is connected to a source of a suitable carrier gas which may be for sample, hydro gen, nitrogen, carbon dioxide or a noble gas, as required by the nature of the vapour to be sampled.

The connections between the ports of the ten-port valve 8 are made as indicated by the full lines in the steady state, and as indicated by the dotted lines when a sample is being taken.

In the steady state, the outlet vapour of the chemical reactor flows through the sample coils 3, 4. Carrier gas flows slowly, through controller 26, by way of port 16, port 17 and line 9, to the juncture of the sample coils 3, 4 at such a rate that there is no appreciable diffusion of vapour up line 9. Carrier gas also flows through controller 27 by way of port 11, port 10 and line 7 to lines 5 and 6. The rate of flow of carrier gas in lines 5 and 6 is such that there is no appreciable diffusion of vapour up lines 5 and 6. Carrier gas at a somewhat higher pressure flows through controller 28 by way of port 19 and port 18 to the column 25.

To take a sample of the vapour flowing through the coils 3, 4 the valve 8 is rotated so that the connections indicated by the dotted lines are made. In this position, carrier gas from controller 28 flows by way of port 19, port 10 and line 7 to lines 5 and 6. At the end of line 6 remote from line 7 the carrier gas stream divides into two parts, part pushing the vapour sample within coil 4 up line 9 and part pushing towards bellows valve 2. Bellows valve 2, having been connected to a source of carrier gas at high pressure, namely line 29, will then be in the closed position, as shown by the dotted lines, and the vapour between the valve 2 and the end of line 6 will slowly leak out into the reactor outlet pipe through the restricted flow aperture 24. A similar course of events occurs at the other end of the device, and a vapour sample flows up line 9 through the ports 17 and 18 onto the column 25.

When the sample is to be fed to a chromatographic column, it is desirable that condensation of vapour should not occur in the valve 8, as this would give rise to badly shaped peaks on a recorder. To avoid this a pre-column 31 may be inserted in the line 9 between the actual sampling device and the valve. The pre-column is packed with a material in which the vapour components of the sample are soluble so that the partial vapour pressures of the components are reduced before they reach the valve. This reduction in vapour pressure reduces the possibility of condensation occurring when hot vapours meet relatively cool valve parts.

When the whole of the vapour contained within the coils 3, 4 has passed through the port 18, the valve 8 is returned to the steady state position. The bellows valves 1, 2 open since they are vented to the atmosphere by the connection of the port 13 to port 12, and carrier gas within the coils 3, 4 is rapidly flushed out by the flow of vapour therethrough.

In order that the opening and shutting of the various valves shall occur in the correct sequence it may be advantageous to introduce pneumatic delays at various points in the control system described above.

I claim:

1. Apparatus suitable for sampling a streamof fluid, which comprises an elongated vessel having an inlet at one extremity, an outlet at the other extremity, flow restricting devices adjacent the inlet and outlet, ports adjacent the said flow restricting devices and a third port situated between the aforesaid ports.

2. Apparatus according to claim 1 wherein the three ports are provided by tubular T-pieces and the third port is separated from the other ports by two coiled tubes.

3. Apparatus according to claim 1 wherein the flow restricting devices are fixed constrictions.

4. Apparatus according to claim 1 wherein the flow restricting devices are valves which may be adjusted to provide an increased degree of constriction during the sampling operation.

5. Apparatus according to claim 1 wherein the flow restricting devices each comprise a bellows valve and an aperture in the wall of the elongated vessel adjacent the bellows valve, whereby during sampling operations the bellows may be inflated to close the inlet and outlet of the elongated vessel whilst restricted flow of fluid is permitted via the aperture.

6. A process for obtaining samples from a stream of fluid which comprises passing the fluid through an elongated vessel having a flow restricting device at each extremity, ports adjacent the said flow restricting devices and also a third port situated between the said two ports, passing carrier gas into the vessel via the ports at a velocity sufficient to prevent diffusion of the fluid to be sampled into the ports, and, when a sample is required, introducing carrier gas at high pressure via the ports adjacent the inlet and outlet while interrupting the flow of carrier gas at the third port, whereby the sample fluid between the ports adjacent the inlet and outlet is swept out through the third port, while the sample fluid not located between the said ports is swept out of the vessel past the flow restricting devices.

7. The process according to claim 6 wherein the flow restricting devices are provided as fixed constrictions.

8. The process according to claim 6 wherein the flow restricting devices are provided as adjustable valves.

9. The process according to claim 6 wheerin the flow restricting device comprises a bellows valve and an aperture in the wall of the elongated vessel adjacent the said bellows valve, wherein the bellows valve is so arranged that when high pressure carrier gas is supplied to the two ports for sampling purposes it is also supplied to the bel- 5 lows valve, thereby closing the said valve and thus allowing escape of carrier gas and fluid only by the Said aperture.

10. The process according to claim 6 wherein the carrier gas is hydrogen, nitrogen, carbon dioxide or a noble gas.

11. The process according to claim 6 in which the apparatus is situated in a sample pipe which is in parallel with the main outlet pipe of a chemical reactor.

References Cited UNITED STATES PATENTS Webber 73-421.5

Riordan 13781.5 Barrett 55--67 Roof 73-422 X S. CLEMENT SWISHER, Acting Primary Examiner.

Claims

1. APPARATUS SUITABLE FOR SAMPLING A STREAM OF FLUID, WHICH COMPRISES AN ELONGATED VESSEL HAVING AN INLET AT ONE EXTREMITY, AN OUTLET AT THE OTHER EXTREMITY, FLOW RESTRICTING DEVICES ADJACENT THE INLET AND OUTLET, PORTS ADJACENT THE SAID FLOW RESTRICTING DEVICES AND A THIRD PORT SITUATED BETWEEN THE AFORESAID PORTS.