GB2541053A

GB2541053A - Apparatus

Info

Publication number: GB2541053A
Application number: GB1606400.8A
Authority: GB
Inventors: Prickett Colin; John Heaton Christopher; Smidt Martin
Original assignee: Johnson Matthey Davy Technologies Ltd
Current assignee: Johnson Matthey Davy Technologies Ltd
Priority date: 2015-05-18
Filing date: 2016-04-13
Publication date: 2017-02-08
Anticipated expiration: 2036-04-13
Also published as: GB201508512D0; CN106168527A; GB2541053B

Abstract

Apparatus for identifying the presence of a process stream 2 in a heat exchange stream 5 of a heat exchange system said process stream being immiscible in the heat exchange stream said apparatus comprises: a reservoir 12b in fluid communication with a heat exchange system, said reservoir being configured such that the process stream and the heat exchange stream are allowed to separate such that there is an interface therebetween; and means for detecting the presence of an interface between the process stream and the heat exchange stream within the reservoir. The heat exchange system may be a closed circuit system, and the reservoir may be a pipe located in a substantially vertical orientation. The means for detecting the presence of an interface between the reaction stream and the heat exchange stream may be a sight-glass, a conductivity detector or a level detector such as a density float.

Description

Apparatus

The present invention relates to apparatus for identifying leakage of a process stream into a stream which is outside the process stream flowsheet. More particularly, the present invention relates to apparatus for detecting leakage of a process stream into a heat transfer stream which may be a closed heat transfer stream.

Many reactions are carried out in the presence of homogeneous catalysts. Since these catalysts are homogeneous they can be carried from the reaction £one with process streams. Generally these homogeneous catalysts are separated from the product and recovered. Reactions such as hydroformylation, hydrocyanation and carbonyiation typically use homogeneous precious metal catalysts, such as those formed from rhodium, platinum or palladium. Examples of hydroformylation catalyst systems are described in GB1387657, US4148830, US4247488, US4593127, US4789498, US5952530 and US7317128, the contents of which are incorporated herein by reference. Hydroformylation is used to produce aldehydes such as butyraldehyde, valeraldehyde and nonanai on a commercial scale. Typically around 7 million metric tonnes of butyraldehyde are produced each year. It will therefore be recognised that these reactions require significant amounts of catalyst.

As the catalysts for these reactions include precious metals, they are expensive. In addition, the catalysts may include ligands which may themselves be expensive. Given the expense of the catalysts, it is desirable to avoid catalyst losses within the system and ensure that the catalyst is recovered.

One means by which catalyst can be lost is through leakage of process stream from the equipment in which It is located. Any weakness in the equipment can lead to leakage occurring. This problem is exacerbated when the process is carried out under pressure.

For the purposes of the present invention, a process stream is any stream which is part of the process and includes feed streams, streams recovered from the reactors, product streams and by-product streams recovered from the reactor or from post-reactor separators, process streams recovered from post-reaction treatments and the like.

Generally, processes require the use of one or more heat exchangers to alter the temperature of process streams. These heat exchangers may add heat to, or remove heat from, process streams depending on the reaction being conducted and where in the flowsheet the heat exchangers are located. The heat exchange is affected by passing the process stream against a heat transfer stream. The heat transfer stream in any particular heat exchanger may be a process stream from elsewhere within the process system or may be a stream provided specifically to affect heat exchange, such as, for example, cooling water.

If a leak develops within the heat exchanger, process stream may pass into the heat transfer stream. Since the process stream comprises the expensive catalyst, such leakage results in loss of catalyst with its attendant economic consequences.

With a view to reducing catalyst losses, it has been suggested that a dosed heat transfer system be used to reduce the loss of valuable catalysts via the heat transfer system. Examples of closed cooling systems are described in CN203484572 and CN103520944, the contents of which are incorporated herein by reference. In these closed-circuit cooling systems, when a leak occurs, the process stream containing catalyst passes into the cooling system. Since the cooling system is a closed system, the catalyst is not lost and can therefore be recovered from the cooling system. However, since the system is a closed system, in order to recover the catalyst the process will have to be stopped, the heat transfer fluid removed, and the catalyst recovered therefrom.

Whilst the processes described in CN203464572 and CN103520944 describe the use of the closed cooling systems to collect any leaked product stream, there is no guidance as to how the operator knows when a leak has occurred and therefore when the coolant stream needs to be treated to recover leaked catalyst. Whilst a measurable effect such as a sudden increase in pressure in the heat transfer circuit would alert the operator of catastrophic failure, there is no mechanism for early stage detection which identifies that a leak has occurred before significant loss of process stream into the heat transfer circuit has taken place.

It is therefore desirable to provide a means which will allow simple detection of a leak at an early stage and before significant losses occur. Even when the catalyst does not include precious metals, it may still be desirable to know when a leak of a process stream occurs. It is also desirable that the leak detection mean is cost effective to install and operate.

It is therefore desirable to provide a cost effective means for identifying a leak of process stream into a heat transfer stream.

Thus, according to the present invention, there is provided apparatus for identifying the presence of process stream in a heat exchange stream of a heat exchange system said process stream being immisoibie in the heat exchange stream, said apparatus comprising: a reservoir in fluid communication with a heat exchange system, said reservoir being configured such that the process stream and the heat exchange stream are allowed to separate such that there is an interface therebetween; and means for detecting the presence of an interface between the process stream and the heat exchange stream within the reservoir. it wiii be understood that the heat exchange system is the system which enables the heat exchange to occur. It wiii include the heat exchangers, means for providing the heat exchange stream to the heat exchangers and removing it therefrom and the iike. in one arrangement the heat exchange system is a dosed heat exchange system.

Since the reservoir is in fluid communication with the heat transfer stream, heat transfer fluid together with any leaked process stream wiii flow into the reservoir where separation occurs and the presence of the interface between the two immiscible streams can be observed. This means that leaks can be detected at an early stage and long before they would be detected in prior art systems.

The reservoir may be of any suitable configuration. However, it may be advantageous for the reservoir to be a pipe located in a vertical or substantialiy vertical orientation. By substantially vertical, it is meant any orientation which is within 10 degrees of a vertical orientation.

The reservoir may be of any suitable size. Generally the size selected wil! depend on the volume of heat exchange stream being used in the heat exchange system. In one arrangement, the reservoir may be from about 0.5m to about 30m in height, although a size of about 1m may be used. The reservoir may be of any suitable cross-section. For ease of manufacture, a circular cross-section may be used such that the reservoir is a cylinder. In this arrangement, the cylinder may have a diameter of from about 3mm to the diameter of the pipe on which it is mounted. Where the cross-section of the reservoir is not circular, it will have a cross-sectional area similar to that described for a circular cross-section.

The reservoir may be placed at any suitable position in the heat exchange system. It will be understood that in order for a point to be suitable it must allow for the reservoir to be flooded with fluid from the heat exchange system. Generally, the reservoir wifi be configured and located within the heat exchange system such that if there is reaction stream present in the heat transfer stream, at least a portion will enter and remain In the reservoir, even if the reaction stream has a lower density than the heat transfer stream. This may be achieved by positioning the reservoir in an elevated position and ensuring that the pressure at the entry to the reservoir is greater than or equal to the pressure at the opposite end of the reservoir.

The reservoir may be located at any suitable position within the heat exchange system. Particular advantages may be noted where the reservoir is in fluid communication with a quiescent region of the heat exchange system, it wifi be understood that a quiescent zone is one where the flow of heat transfer stream is not agitated. Whilst there may be flow, the liquid is not agitated. Without wishing to be bound by any theory, it is expected that process stream which have leaked into the heat exchange stream will collect in quiescent zones which makes such areas particularly suitable for the positioning of the apparatus of the present invention. Further as the region is quiescent, there is minima! agitation such that the separation and the formation of the interface are not hampered.

The reservoir may be in fluid communication with a fine in the heat transfer system. An area where the line is substantially horizontal will offer some advantages. In one arrangement, the reservoir may be placed in fluid communication with a line which is substantially horizontal. The line which with the reservoir is in fluid communication may be modified, at least in part, in order to make it more suitable for receiving the apparatus. Suitable modifications may include increasing the diameter of the line at, and optionally around, the region of the line with which the reservoir is in fluid communication. The line may also optionally comprise one or more baffles In this region. The baffles, where present assist the collection of organic fluids.

In an alternative arrangement, the reservoir may be in fluid communication with a heat exchanger. A primary heat exchanger which facilitates heat exchange from the reaction stream to the heat exchange stream may be particularly suitable. Preferably the heat exchanger will comprise a quiescent zone. The quiescent zone will typically be found at or near the top of the heat exchanger. The apparatus may be used with any form of heat exchanger, for example tube and shell, plate and frame and the like. These types of heat exchangers will generally be external of the reactor.

Alternatively, the heat exchanger may be incorporated within the reactor, in this case, the heat exchanger may be integral with the reactor. Thus in one example, it may be formed of coils. A combination of internal heat exchangers incorporated within the reactor and external heat exchangers may also be used.

The heat exchanger with which the reservoir is in fluid communication may be a condenser. Examples of suitable condensers include those used in connection with a reactor, a knockout pot, or a vapouhser vent.

Whilst the apparatus of the present invention may be used with a conventional heat transfer system, it may also be used with a closed heat transfer system. Any suitable closed heat exchange system may be used. Suitable systems include those described in CN203464572 and CN103520944. Such systems contain a fixed amount of heat exchange stream. Where a closed heat exchange system is used, the amount of heat transfer stream required is generally relatively small in comparison with the amount of process stream present.

Where a closed heat transfer system is used, the reservoir may be in fluid communication with a surge tank. When the apparatus is positioned in connection with the surge tank, it will be understood that for effective functioning of the apparatus the fluid ievei in the surge tank should be higher than the top of the reservoir. One or more baffles may be used to direct the fluids into the reservoir to prevent it from remaining in the surge tank where it will be undetectable due to the volume of heat exchange stream present.

In a still further aspect, the heat exchange system may comprise a single shell comprising two bundles of tubes where process stream passes through one bundle and the heat exchange stream passes through the second bundle. The shell will include a second heat exchange stream, in this arrangement, leakage of process stream from the tube bundle will place process stream into the second heat exchange stream in the she!!. In this arrangement, the reservoir will be in fluid communication with the second heat exchange stream in the shell.

Any suitable heat exchange stream may be used provided that it is Immiscible with the process stream. The heat transfer stream is typically aqueous when the process stream is organic. The heat transfer stream will generally by in the liquid phase.

When process stream ieaks into the heat exchange system, it may be in the liquid phase. Generally, the heat exchange stream is only able to solubilise a smali amount of the process stream and so the heat exchange stream rapidly becomes saturated. Once the heat exchange stream is saturated, further process stream that enters the heat exchange circuit will form a separate phase. Since there is generally poor miscibility between the heat transfer stream and the process stream, the additional reaction liquid will form a separate layer. The process stream typically has a lower density than the heat exchange stream and so will be the upper stream when separation occurs.

In an alternative arrangement, the leaked process stream may be in the gaseous phase when it enters the heat exchange stream. This can occur when the operating pressure within the heat exchange stream is lower than the vapour pressure of the process stream. As the process stream leaks into the heat exchange stream it vaporises. Under these conditions, it may be advantageous for the heat exchange stream to be in the liquid phase.

The bubbles of the gaseous process stream will rise within the reservoir, and coalesce. This iii be facilitated by the low flow rate within the quiescent region. In this arrangement, the presence of an interface between the gaseous process stream and the liquid heat exchange stream will be a change, i.e. a lowering, of the liquid level since the gas accumulating at the top of the reservoir will force the level of the heat exchange level downwardly. Thus when this lowering is noted, the existence of the leak is detected.

The formation of the interface between the process stream whether as a liquid or as the accumulation of gas in the reservoir will occur relatively quickly after the leak has begun thereby giving an eariy warning of a leak.

Where the heat exchange system Is a closed system, if will be understood that periodic addition of heat exchange stream may be needed as a result of routine maintenance and removal of sediment from, for example, a surge tank. This will not prevent the effective functioning of the apparatus of the present invention.

The reservoir may additionally comprise a vent which will allow air to be removed. This can be particularly important at start-up. The presence of the vent may assist in the formation of the interface. Any suitable location of the vent may be used although it will generally be advantageous to position the vent towards the top of the reservoir. Where the reservoir comprises a pipe dosed at one end, the vent will generally be positioned at or near to the closed end.

It wii! be understood than any suitable means for revealing an interface between the reaction stream and the heat exchange stream may be used. Suitable means include a sight-glass, a conductivity detector, a level detector or other similar device. The selection of detector means may depend on whether the interface will be formed between two immiscible liquids or between a liquid and a gas.

An alternative means for revealing the presence of the interface may be the use of a density float. Where a density fioat is to be used, it will generally be calibrated such that it will sit at the interface.

Where the heat transfer stream is under pressure, particularly if it is at high pressure, if a sight-glass is to be used, the materials used to construct the sight-glass should be selected such that it can withstand the pressure of the system. However, it may be preferable In some arrangements, to select an alternative means for revealing the interface.

The apparatus of the present invention may additionally comprise an alert system. The function of the alert system is to notify users when an interface is detected in the reservoir. Any suitable alert system may be used. For example, the alert system may comprise an audible aiarm which sounds when reaction fluid is detected in the reservoir. The alert system may obviate the need for regular manual observations of the means for revealing the interface.

The apparatus of the present invention may be used in any process where it is desirable to know if there is a leak from the process stream into the heat exchange stream, such as when expensive catalysts made from precious metals are being used.

The present invention will now be described, by way of example, by reference to the accompanying drawings in which:

Figure 1 is a schematic representation of a system including the apparatus of the present invention;

Figure 2 is a schematic representation of one arrangement for the apparatus of the present invention; and

Figure 3 is a schematic representation of an alternative arrangement for the apparatus of the present invention.

Two possible locations for the reservoir are illustrated in Figure 1. It would be unlikely that more than one reservoir may be used; two have been illustrated in Figure 1 to assist in understanding. Although in the illustrated system, a closed heat exchange system is used, it will be understood that the teaching is equally relevant to conventional heat exchange system. A reaction is carried out in reactor 1. It will be understood that there be inlets ant the like associated with the reactor but for clarity these are omitted from Figure 1. The process stream will leave the reactor in line 2 and be passed to heat exchanger 4. In this example, the process stream is cooled but it will be understood that in other embodiments, the process stream may be heated. The cooled process stream is then returned to reactor 1 in line 3.

The process stream is cooled in heat exchanger 4 against heat transfer stream passed to the heat exchanger in fine 5 and removed from the heat exchanger in line 6. Line 8 has a region of larger diameter 7. Since this will be a quiescent region, it acts as a settling zone. A reservoir 12a is in fluid communication with the region of larger diameter 7. Since the reservoir 12a is in fluid communication with line 7, the heat exchange fluid will flow into reservoir 12a. If any immiscible process stream is located within the heat exchange fluid it will separate within the reservoir and the interface between the layers can be detected.

The heat exchange stream will be passed in line 11 to a surge tank 8 which may include a baffle 13. A reservoir 12b may be In fluid communication with the surge tank. If any immiscible process stream is located within the heat exchange fluid it will separate within the reservoir and the interface between the layers can be detected.

Heat exchange fluid will then be passed in line 9 to a second heat exchanger 10 where it is cooled against cooiing water passed to the heat exchanger 10 in line 14 and removed in line 15.

The cooled heat exchange stream is then passed to line 5 to the heat exchanger 4.

One example of a reservoir is illustrated in Figure 2. Here the reservoir 20 is in fluid communication with a line 23 in which the heat transfer liquid flows. This will generally be located at a quiescent point in the line. The reservoir comprises an essentially vertical tube 20 having a dosed end and an integral sight-glass 21. A vent 22 is positioned at the top of the reservoir on the dosed end. Routine monitoring of the sight-glass 21 will allow even small leaks to be detected quickly.

One alternate arrangement for the reservoir 12b for the surge tank 8 is illustrated in Figure 3. In this arrangement, this arrangement is similar to that illustrated in Figure 1 except that the area in which the interface is detected is located within the surge tank 8. In this arrangement, the baffle wifi be constructed to form the reservoir. A sight-glass may be located at an appropriate place in the wall of the surge tank or, as illustrated here, a level detector L may be used. This may be of any suitable configuration.

Claims

1. Apparatus for identifying the presence of process stream in a heat exchange stream of a heat exchange system said process stream being immiscible in the heat exchange stream, said apparatus comprising: a reservoir in fluid communication with a heat exchange system, said reservoir being configured such that the process stream and the heat exchange stream are allowed to separate such that there is an interface therebetween: and means for detecting the presence of an interface between the process stream and the heat exchange stream within the reservoir,

2. Apparatus according to Claim 1 wherein the heat exchange system is a closed circuit system.

3. Apparatus according to Claim 1 or 2 wherein the reservoir is a pipe located in a vertical or substantially vertical orientation.

4. Apparatus according to any one of Claims 1 to 3 wherein the reservoir is from about 0.5m to about 30m in height.

5. Apparatus according to any one of Claims 1 to 4 wherein the reservoir is a cylinder having a diameter of from about 3mm to about the width of the pipe on which it is mounted.

6. Apparatus according to any one of Claims 1 to 5 wherein the reservoir is located in a quiescent zone

7. Apparatus according to any one of Claims 1 to 8 wherein the reservoir is in fluid communication with a substantially horizontal line in the heat transfer system.

8. Apparatus according to Claim 7 wherein the substantially horizontal line in the heat transfer system may have an increased diameter at and around the region of the line with which the reservoir is in fluid communication.

9. Apparatus according to any one of Claims 1 to 8 wherein the reservoir is in fluid communication with a heat exchanger. 1Q. Apparatus according to Claim

10 wherein the heat exchanger is a condenser.

11. Apparatus according to any one of Claims 1 to 8 wherein the reservoir is in fluid communication with a surge tank.

12. Apparatus according to any one of Claims 1 to 11 wherein the apparatus means for revealing an interface between the reaction stream and the heat exchange stream includes a sight-glass, a conductivity detector, or a levei detector.

13. Apparatus according to Claim 12 wherein the level detector is a density float.

14. Apparatus according to any one of Claims 1 to 13 wherein the apparatus additionally comprises an alert system.

14. Apparatus according to any one of Claims 1 to 13 wherein the apparatus additionally comprises an alert system. Amendments to the claims have been filed as follows: Claims

1. Apparatus for identifying the presence of process stream in a heat exchange stream of a heat exchange system said process stream being immiscible in the heat exchange stream, said apparatus comprising: a reservoir in fluid communication with a heat exchange system, said reservoir being configured such that the process stream and the heat exchange stream are allowed to separate such that there is an interface therebetween; and means for detecting the presence of an interface between the process stream and the heat exchange stream within the reservoir.

2. Apparatus according to Claim 1 wherein the heat exchange system is a ciosed circuit system.

4. Apparatus according to any one of Claims 1 to 3 wherein the reservoir is from 0.5m to 30m in height.

5. Apparatus according to any one of Claims 1 to 4 wherein the reservoir is a cylinder having a diameter of from 3mm to the width of the pipe on which it is mounted.

7. Apparatus according to any one of Claims 1 to 6 wherein the reservoir is in fluid communication with a substantially horizontal line in the heat transfer system.

9. Apparatus according to any one of Claims 1 to 8 wherein the reservoir is in fluid communication with a heat exchanger.

10. Apparatus according to Claim 10 wherein the heat exchanger is a condenser.

11. Apparatus according to any one of Claims 1 to 6 wherein the reservoir is in fluid communication with a surge tank.