AU784230B2 - Induced circuit evacuation - Google Patents

Description

P/001011 2815191 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Induced Circuit Evacuation The following statement is a full description of this invention, including the best method of performing it known to :-us INDUCED CIRCUIT EVACUATION FIELD OF THE INVENTION The present invention relates to a method and plant for conveying liquid through continuous pipelines and equipment which are used for delivering liquids from one point to another in a liquid processing plant.

BACKGROUND OF THE INVENTION The present invention has been developed in light of perceived shortcomings of known plants and methods for conveying liquids through delivery pipeworks, in particular in order to minimise wastage of valuable liquid product or 10 material at the end of the conveying operation, after the bulk of the liquid has been delivered.

A necessary feature of liquid food processing plants are lengths of fixed (and temporary) pipework which serve to transport liquid products such as milk, juice etc. between stations of such platns, e.g. between a product intake to S 15 storage vessels, between storage vessel and processing elements, between product intake station to final packaging, etc. Such pipework normally includes horizontal line sections as well as vertical, or angled, inclines and declines to :accommodate access ways around the plant.

In particular raw materials and products, but also cleaning chemicals, have a significant value for the manufacturer, either for their intrinsic value, or for the costs that may be incurred from water treatment authorities if these liquids are allowed to enter the drainage system. Therefore, it is an important consideration when laying out the pipework and the plant to minimise the amount of liquid product that will remain in the pipework, after the bulk of it has passed therethrough, and requires flushing out in a subsequent cleaning operation.

In the food processing industry, the current trend is for the size of manufacturing plants to increase, in order to take advantage of economies of scale. This leads to a concomitant increase in the length of delivery pipework which are required to transport liquid products throughout these plants.

Increased pipework lengths and an increased number of intermediate pipeline rises would dictate the use of multiple valves and pumps along the pipework.

These conventional measures are aimed at avoiding increased plant complexity and maintenance, but make it difficult to use the large amounts of liquid remaining in the pipework after the bulk of it has been transported therethrough.

In addition to this, the trend of the processing industry is towards greater numbers of different types of products to be manufactured at the same plant, therefore requiring that the same pipelines be used for different materials. This has driven a need for efficient methods of removing residual liquids from pipework in order to prevent cross contamination of liquids, wastage of materials, and lengthy production delays while pipelines are being cleared and cleaned.

The three main techniques that would usually be considered when seeking 10 to minimise the amount of product liquid that is likely to remain in the pipework after a conveying system are water purge, air purge or "pigging".

Water purging involves the pumping of water through the pipeline :I immediately after the bulk of the product has passed therethrough. Water is introduced at the feed end and forces residual liquid product remaining in the S 15 pipeline to its outlet. Accordingly, liquid product can be recovered in this manner and may be diverted to a specified product destination, or to the drain. A typical result of this type of "water residual product purging" is that a proportion of the liquid product that is purged from the pipeline tends to become diluted with the purged water.

Typically, water flushing results in a mixed water-product phase, the volume of which is proportional to the length of the line being purged and is typically about 20% of the volume of the line. This can cause a considerable loss of value for the manufacturer. Sometimes this diluted product is captured in a dedicated product recovery system. However, such systems tend to increase the capital cost of the plant and introduce further problems, such as the need for recovering product from the diluted phase (or disposal of this diluted phase), and the need to build several different recovery systems if several different products are to be run through the same pipeline. Also, with some liquid products there are miscibility problems which make water purging inapplicable.

In order to overcome some of the difficulties posed by water purging, some operators have attempted to use air purging. The advantages of air purging over water purging are that the residual liquid in the pipeline does not mix permanently with the air and thereby does not become diluted or contaminated. This obviates the need for a separate, diluted product recovery system and eliminates the possibility of contamination of the products with water. Air purging is typically effected by attaching a compressed air source to the feed end of the pipeline, thereby introducing compressed air into the pipeline in such a manner as to force the remaining liquid through the pipeline into the receiving vessel.

There are often a number of disadvantages associated with this procedure.

These include the requirement for a large volume of compressed air in order to force the liquid upward through any net or intermediate rises in the level of the pipeline, and the likelihood that rises or bends in the pipeline will cause an uneven distribution of pressure on the air liquid interface which will in turn cause the compressed air to "blow a hole" through the liquid column in the pipeline.

Once such a "hole" has been created through the liquid column there no longer exists a unitary trailing face that can push the liquid column forward through the pipeline. Once the liquid column has been broken, thereby establishing two separate phases of gas and liquid through the length of the pipeline, the compressed air, or other driving medium, will preferentially travel through the gas phase and will no longer be able to force the remaining liquid through the pipeline to the destination point.

~Therefore, for long and convoluted pipelines, great difficulties exist in setting up the air purge in such as way as to overcome the above outlined "hole blowing" problems.

'Pigging' systems are somewhat akin to air and water purge systems.

However, to prevent the above outlined problem of the air "blowing a hole" through the liquid product column, a physical barrier is inserted between the product and the compressed air to maintain the "integrity of separation" between the two phases. This process is known as "pigging" and the physical barrier is known as the "pig".

This process is usually carried out by inserting a cylindrical shape pig, e.g.

made from a foam rubber-type material, into the feed end of the pipeline via a pig launching station. The liquid product source and its conveying pump are then isolated from the pig via a valve and compressed air is introduced into the line immediately upstream of the pig. The compressed air forces the pig through the line while the pig forces the residual liquid ahead of it to the destination point.

The pig is then captured in a specially designed pig recovery station. These type of systems are typically very successful at recovering a high proportion of the residual liquid in the pipeline.

However, there are a number of disadvantages associated with these systems. These include the expense of the specialised equipment required for carrying out the process, a lack of hygiene when associated with liquid food conveying, the requirement for very high pressure air when attempting to overcome significant net or intermediate rises in pipe height or to overcoming significant static head at the discharge of the liquid into the storage vessel, and the inability of the pig to pass through many items of equipment, such as heat i.:"exchangers or valves, which are ordinarily incorporated into many liquid product .":delivery pipelines used in the food processing industry. In general, pigging systems also tend to be "messy", as they involve opening up of the pipeline to insert and recover the pig.

S 15 A "reverse" pigging system that operates from the delivery end to a source location of a pipeline is disclosed in Japanese Patent Publication No. 03284388.

The system is used for returning concrete, which remains in a delivery pipeline, S. after completion of delivery of concrete from a hopper to an outlet. The process involves placing a "pig" into the delivery end of the pipeline, then engaging a suction pump to pull the concrete in the pipeline back to the feed hopper located e near what was originally the supply end of the pipeline. The pig prevents air from infiltrating the pipeline and thus destroying the suction effect. Once the remaining concrete has been sucked back into the hopper, the pipeline exiting the hopper is isolated from the cleared delivery line and connected to the disposal (e.g.

concrete mixing truck), and the direction of the suction pump is reversed in order to push the concrete from the hopper back into the disposal vehicle.

SUMMARY OF THE INVENTION In light of the above described background, it is a first object of the present invention to provide a method of operating a plant for conveying liquid product through pipework that allows extraction from the pipelines of a substantial portion of otherwise residual liquid product after the bulk of the product has been delivered to a delivery point, e.g. a storage vessel. In a preferred form, the extracted portion would be delivered directly to the delivery point which receives the bulk portion, without additional treatment steps and/or intermediate reservoirs.

In a first aspect of the invention there is provided a method of conveying liquid product through a pipeline of a liquid product processing plant after a bulk portion of the liquid product has been delivered through a delivery outlet of the pipeline network, including the steps of: determining an activation moment at which the bulk portion of the liquid product has been discharged through the delivery outlet, the liquid product being fed into the pipeline by means of a positive feed pump located at or near a source inlet of the pipeline network; activating, as a function of the activation moment, a suction pump located at or near the delivery outlet thereby to generate a suction head within the :pipeline to maintain liquid discharge through the delivery outlet; deactivating or otherwise isolating the positive feed pump from the source inlet within a predetermined first time interval of the activation moment; and venting to atmosphere of the pipeline network near or at the source inlet within a predetermined second time interval of the activation moment.

S" In accordance with the inventive method described above, the first and second time intervals are chosen such as to ensure that the momentum and integrity of the liquid column travelling through the pipeline is maintained by the suction pump, upon deactivation (or isolation) of the primary feed pump. The trailing face of the liquid column is then subjected to atmospheric pressure (and no longer to the positive pressure otherwise provided by the feed pump) whilst the column is being "pulled" through the pipeline towards the discharge outlet.

This measure minimises air blow-through effects experienced with conventional air-purging and obviates the need for a separate, physical interface, i.e. the pig, to push the product through the line..

The timed, push-pull conveying and the arrangement of the pumps near the inlet and outlet of the pipeline network, respectively, permits to extract and deliver a greater portion of liquid product to the discharge outlet than would be delivered by using conventional air purging at the end of the conveying operation.

Similarly, a vastly smaller amount of residual liquid will be left in the pipeline once 6 the suction pump near the outlet cavitates at the end of the conveying operation.

Water purging may subsequently be effected for cleaning the pipeline network.

Preferably, the suction pump is activated (or brought in-line) before the feed pump is deactivated (or brought off-line) such that the liquid column is subject to pumping action by both pumps.

The first and second time intervals employed in switching the pumps and venting the pipe to atmosphere will depended on, amongst other factors, the overall pipeline/network length, net level raise between source inlet and delivery outlet, and others, and can be determined experimentally to suit requirements.

In applying the inventive concept to the layout of a liquid product conveying plant, the following physical configuration is preferred: a feed inlet arranged for connection to a source reservoir of liquid product; S a delivery outlet arranged for connection to a storage facility or 15 processing facility for the liquid; a pipe line network linking the feed inlet with the delivery outlet; a feed pump operatively connected to the source reservoir and the .:pipeline network, and located proximate to the feed inlet; a suction pump operatively connected to the delivery outlet and the 20 pipeline network, and located proximate to the delivery outlet; an air inlet valve, operative on the pipeline network near to the feed pump, preferably immediately downstream the feed pump; a liquid isolation valve, operative on the pipeline network between the feed pump and the air inlet valve; and a controller to switch the feed pump, suction pump, air inlet valve and liquid isolation valve such as to enable operation of the plant in accordance with the method stated above.

A number of liquid product processing apparatus may be incorporated in series or in parallel in the pipeline network, such as heat exchangers, mixing stations etc. Where a processing apparatus is unsympathetic, from a product flow point of view, to liquid extraction using the suction pump, such as is the case with certain types of multi-chamber cascade heat exchangers, it is preferred to have a valved by-pass line that enables short-circuiting the respective processing apparatus during circuit evacuation. In such case, by-pass valve operation can be coupled to that of the main liquid isolation valve for adequate controller response.

Choice of pump type at the feed and suction end of the pipeline, and rating thereof, will depend on the pipeline layout (including length, net pressure head difference between inlet and outlet, intermediate rises, product viscosity and other factors) and is within the normal skill-set of a person skilled in the engineering art pertaining to liquid transport.

A preferred embodiment of the invention exists where the length of the pipeline network is in excess of 100 metres.

A further preferred embodiment of the invention exists where the circuit itself features elevations or pressure difference which is unsympathetic to the :direction of liquid flow.

The method of the invention is intended to work with the liquids having a viscosity in the range 1cP to 50cP, as this range represents the typical viscosity S 15 of liquids that are used in liquid food processing plants, and represents the range of liquid viscosities for which this invention will be particularly useful.

The liquid may be a food product for human consumption, for example milk or fruit juice, etc., as these are the types of liquids for which the invention is envisaged to be most useful.

Other aspects of the invention will be better understood from the following description of a preferred embodiment and example thereof, provided with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a schematic and simplified layout of a liquid product conveying plant embodying the invention; Figure 2 depicts a pipeline configuration of a typical liquid liquid processing plant, the lengths of individual sections of pipeline being indicated in millimeters, used for carrying out experimental testing of the invention; Figure 3 depicts an alternative arrangement of the pipeline network depicted in figure 2, including a plate heat exchanger (PHE) incorporated into the pipeline network, used for carrying out experimental testing of the invention; Figure 4 depicts another typical liquid food processing plant pipeline, used for carrying out experimental testing of the invention.

8 DESCRIPTION OF PREFERRED EMBODIMENT Turning first to figure 1, there is shown a sketch of a simplified liquid product conveying plant inventively arranged for removal of liquid from a pipeline network 1, after a bulk portion thereof has been pumped from source reservoir to storage reservoir 3. The identity of the source reservoir 5 and the storage reservoir 3 are defined by the direction of fluid delivery, and recovery, chosen for the given practical application. Pipeline network 1 includes pipe sections la-ld that provide for level rises and falls between the source tank 5 of the liquid and the storage reservoir 3 located distantly from one another. The pipeline network 1 overall has elevations that may or may not be unsympathetic to the direction of liquid flow. That is, the pipeline may contain an overall increase in height between inlet and outlet, or various intermediate increases between inlet and outlet. An :isolation valve 9 is situated close to the storage reservoir 3 on a short branch line 8. A suction pump 2 is located between the isolation valve 9 and the storage reservoir 3 on the branch line 8. A feed pump 4 is situated close to the source S"reservoir 5. An air inlet valve 6 is attached to the pipe network 1, located immediately downstream of the feed pump 4. A liquid isolation valve 7 is located between the feed pump 4 and the source reservoir 5. A liquid level sensor 10 is located on the source reservoir Under normal operation, the liquid will be delivered from the source reservoir 5 to the storage reservoir 3, via the pipeline network 1, by the action of the feed pump 4. After the greater part of the liquid in the source reservoir 5 has been delivered by the feed pump 4, via the pipeline network 1, the circuit evacuation phase is initiated.

When the level probe 10 detects a pre-determined low level of liquid in the source reservoir 5, isolation valve 11 is closed, isolation valve 9 is opened and the suction pump 2 is activated. As the last of the liquid passes through the feed pump 4 (this can be detected by a flow meter or a cavitation sensor, not shown, or simply computed as a function of the liquid remaining in source reservoir 5 and pumping rate), the liquid isolation valve 7 is closed and the air inlet valve 6 is opened. This allows the liquid flow to be isolated from the feed pump 4 and allows air to flow into the pipeline 1, following the trailing end of the liquid.

9 Due primarily to the momentum of the liquid in the pipeline 1, and to the replacement of the liquid by the air, which is drawn in to the line through the inlet valve 6, the surface tension at the trailing end of the liquid remains undisturbed and thus forms what may be termed as a "liquid plug" or "pig".

The liquid continues to be drawn through the pipeline network 1 by suction pump 2 until the greater part of the liquid has been delivered to the storage reservoir 3. The liquid discharge to the storage reservoir 3 may be a discharge to the bottom of a large storage tank, in which case the suction pump 2 needs to be rated for delivering the liquid against a considerable static head. Once most of the liquid remaining in the pipeline 1 has reached the storage reservoir 3 the suction pump 2 is shut down. The shut down moment can be determined using a separate pressure sensor within the pipeline near the discharge, or be chosen to coincide with cavitation being experienced a the suction pump. Any liquid then still remaining in the pipeline 1 may be removed via conventional means such as flushing with water.

EXAMPLE: INDUCED CIRCUIT EVACUATION TRIAL IN A LIQUID FOOD PROCESSING PLANT A trial was conducted to illustrate the use of the invention in maximising the collection of residual liquid in the pipelines of a large commercial liquid food processing plant. The objectives of the trial were to: a) confirm the effectiveness of a product recovery system utilising the invention's induced circuit evacuation; b) determine limitations in the utilisation of a product recovery system featuring induced circuit evacuation; c) determine the system configuration best suited to utilising an induced circuit evacuation system in accordance with the invention.

An additional objective of the test was to recover as much liquid product from the pipeline as possible with down stream processors in or off-line.

Test 1 Figure 2 depicts the pipeline configuration which was trialled in this experiment, which forms part of a typical liquid food processing plant. In essence, the line trialled in this test corresponds to the basic configuration depicted in Figure 1. It will be noted that in this particular trial, the 'test circuit' features numerous vertical and horizontal pipeline sections 20 24, as well as valves 25 26 and a section of flexible hose 27. It will also be noted that the flow of recovered liquid occurs from left to right in the drawing. The specific details of the pipeline system are: Line volume between test points 425 Litres Line diameter generally 101 mm Maximum lift in pipeline 3880 mm Volume recovered 368 Litres Recovery efficiency (as of line volume) 87% Recovery pump MR300 The pipeline was flooded using a water purge system, with ambient water at 17°C being used to simulate liquid food product. The plate heat exchanger (PHE) 28 was isolated using the manual valve 29. The route to the pump (PU190) was opened, and the pump was started. When suction was apparent at the outlet of the PHE 28, the air inlet valve 31 was partly opened. The discharge of pump 30 (PU190) was throttled to simulate the effect of back pressure on the pump. The pump 30 was run until no flow was detected through the pump.

Product was captured at the manual drain valve 32 at the outlet of the PHE 28 and the drain valve 26 (AV131) on the manifold at the pump 30 (PU190).

The resulting observations from this test are as follows: Much of the elevated horizontal piping was sloped against the direction of flow during product recovery.

At a back pressure of 300kPa, pump PU190 effectively stopped pumping.

0 The maximum back pressure on PU190 enabling effective pumping was 250kPa, and lower pressures did not significantly improve product recovery effectiveness.

0 The vacuum at the outlet of the PHE ranged between -20kPa and OkPa.

9 The air inlet valve was adjusted manually to ensure a negative pressure at all times. Most of the time the manual 101 mm valve only needed to be opened slightly.

11 When the pump lost suction, liquid started to irregularly flow out of the air inlet valve.

The irregular flow from the air inlet valve suggested that the bulk of this liquid was that which was running back from the horizontal sections of pipeline, rather than simply the liquid dropping from the vertical lift of 3880 mm.

S Much more product was remnant in the section of pipeline which was closer to the suction pump, rather than in the sections of pipeline furthest away from the suction pump (39 Litres vs 19 Litres), even though the latter section features the greatest vertical lift.

An air bleed was introduced directly into the suction of the liquid ring pump (PU190), in an attempt to improve suction performance. The slight air bleed had minimal beneficial effect.

It is concluded from this test that it is possible to use induced circuit S 15 evacuation to recover a significant portion of liquid remaining in a pipeline, where the pipeline is of a significant volume, and features numerous bends, and an overall increase in height.

.i Test 2 In this test, a slightly different configuration of pipeline was used. In S 20 particular, an attempt was made to use induced circuit evacuation to clear liquid from a line which included a plate heat exchanger (PHE). Figure 3 depicts the pipeline configuration that was trialled in this experiment, which is almost identical to that used in Test 1, shown in Figure 2. It will be noted that in this particular trial, the 'test circuit' includes the PHE 28, the CIP return pump (PU081) 40 and the section of pipeline 42 and flexible hose 41. It will also be noted that the flow of recovered liquid occurs from right to left, opposite to that in Test 1. The specific details of the pipeline system are: Line volume between test points 500 Litres Line diameter generally 101 mm Maximum lift in pipeline 2400 mm Volume recovered 400 Litres Recovery efficiency (as of line volume) Recovery pump MR200 Details of the test procedure are as follows. The pipeline was flooded with water at 170C. The CIP return pump 40 (PU081) was started, with the route open 5 to drain. When vacuum was apparent at the PHE 28, the pipeline route to the pump 40 was opened. The manual valve 43 was opened to enable air flow into the end of the circuit. The pump 40 was allowed to run until cavitation was apparent. Product was captured the open union 44 at the outlet of the PHE 28, at the drain on the strainer 45 and the drain valve 26 (AV132) on the reception 10 manifold.

The results and observations from this test were: S-o Product appeared to pull through the PHE without great difficulty.

It is possible to recover liquid from a pipeline in either direction of product flow, via induced circuit evacuation.

15 Most of the remnant product was again caught at the AVI31 (40 Litres), with minimal amounts caught at the hoses, strainer drain valves and at the entry to the PHE (20 Litres total).

It was impractical to open the PHE to determine remnant product levels, however, the little product caught at the drain points implied that the PHE was sufficiently emptied to catch some product. This was detected because when suction was lost at the suction pump, product appeared to dribble out of the PHE connection drain point when the valve was opened.

As no product was accumulated in the pipe when the valve was closed, this implies that flow must have gone into the PHE. For the efficiency calculation, it was assumed that only 10% of the volume of the PHE was recovered.

S

13 From this test it was concluded that induced circuit evacuation may also be effective in recovering product from pipelines which also include irregularly shaped items, such as plate heat exchangers. However, it was noticed that such items to have a deleterious effect on product recovery efficiency, although in this case the reduction was relatively small, being from 87% to Test 3 In this test a different pipeline system was trialled; see figure 4 for the actual pipeline configuration. Again, this pipeline configuration conforms to the basic configuration shown in Figure 1. The overall summary of the trial is as 10 follows: Line volume between test points 640 Litres Line diameter generally 101 mm Maximum lift in pipeline 3500 mm Volume recovered 600 Litres Recovery efficiency (as of line volume) 94% Recovery pump MR200 The trial procedure was as follows. The pipeline was flooded with water at 17 0 C. The route to the CIP retum pump 50 (PU590) was opened, and the pump was started. The CIP return pump 50 route was opened to drain at the CIP set 52. When suction was apparent at the outlet of the PHE 51, the flexible union 53 was cracked to provide air inlet. The CIP pump 50 was run until no flow was detected. Product was captured at the open coupling point 53 at the outlet of the PHE 51, and at the drain valve 52 on the CIP return pump manifold.

The results and observations from this test were as follows: In this test the elevated horizontal piping sloped with the direction of flow during product recovery.

S A product sump was formed at a low point between the 101 mm piping and the 63 mm piping. The section was fully welded so it was not possible to check for remnant product. For the efficiency calculation it was therefore assumed that only half the volume was recovered in this piece of pipework.

14 Overall Conclusions S It is possible to use induced circuit evacuation to recover the bulk of liquid remaining in pipelines that feature overall rises in liquid height, numerous vertical and horizontal pipeline sections, large volumes and PHEs integrated in the line, regardless of the direction of fluid flow through the lines.

S Product recovery efficiencies ranged between 80% and 94% of the pipeline volume.

S For best recovery results the slope of reticulation should be sympathetic to 10 the direction of product recovery.

Once a liquid plug is broken, and air is allowed to pass over or through the °liquid, the product recovery effect is minimal.

ooo Product was effectively recovered from a reticulation when a PHE was connected into the circuit.

S• 15 As the product recovery effect is much reduced when air is allowed to pass over or through the product, it is believed that product recovery from parallel path heat exchangers will be limited.

The product recovery system tested was capable of lifting product more than 3500 mm.

20 e The product recovery system tested was capable of discharging to a down stream head of 25 m.

9 As the pumping effectiveness is reduced when the liquid plug is broken, it would be preferred to have vertical lifts distant from the recovery pump so that there is adequate liquid to ensure good suction and flow at the point of lift during recovery.

0 Reticulation should be configured to encourage liquid plug formation in the direction of flow.

Claims (14)

1. A method of conveying liquid product through a pipeline of a liquid product processing plant after a bulk portion of the liquid product has been delivered through a delivery outlet of the pipeline network, including the steps of: determining an activation moment at which the bulk portion of the liquid product has been discharged through the delivery outlet, the liquid products being fed by means of a positive feed pump located at or near a source inlet of the pipeline network activating, as a function of the activation moment, a suction pump located at or near the delivery outlet thereby to generate a suction head within the pipeline to maintain liquid discharge through the delivery outlet; deactivating or otherwise isolating the positive feed pump from the source inlet within a predetermined first time interval of the activation moment; and venting to atmosphere of the pipeline network near or at the source inlet within a predetermined second time interval after the activation moment.

2. The method of claim 1, in which the first and second time intervals are chosen such as to ensure that the momentum and integrity of the liquid column travelling through the pipeline, is maintained by the suction pump upon deactivation (or isolation) of the feed pump, the trailing face of the liquid column being subjected to atmospheric pressure whilst the column is being pulled through the pipeline towards the discharge outlet.

3. The method of claim 1 or claim 2, wherein the activation moment is determined as a function of the level of liquid product contained in a reservoir connected to the source inlet.

4. The method of claim 1 or claim 2, where the activation moment is determined as a function of flow of liquid product through the positive feed pump.

The method of any one of claims 1 to 4, wherein the suction pump is activated before the positive feed pump is deactivated or otherwise isolated. 16

6. The method of any one of claims 1 to 5, wherein venting takes place concurrently with or after the feed pump is deactivated.

7. A liquid product conveying plant arranged for removal of liquid product remaining in pipework of the plant after the bulk of the liquid product has passed through the pipework, including; a feed inlet arranged for connection to a source reservoir of liquid product; a delivery outlet arranged for connection to a storage facility or processing facility for the liquid; 000 0a pipe line network linking the feed inlet with the delivery outlet; a feed pump operatively connected to the source reservoir and the pipeline network, and located proximate to the feed inlet; a suction pump operatively connected to the delivery outlet and the pipeline network, and located proximate to the delivery outlet; an air inlet valve, operative on the pipeline network near to the feed pump, •"preferably immediately downstream the feed pump; a liquid isolation valve, operative on the pipeline network between the feed pump and the air inlet valve; and S* a controller to switch the feed pump, suction pump, air inlet valve and liquid isolation valve, the controller being arranged to detect when a bulk part of the liquid has been discharged past said delivery outlet by means of said feed pump to deactivate or isolate said feed pump, to activate said suction pump preferably before the deactivation of said feed pump, and switch the air inlet valve and liquid isolation valve such as to allow atmospheric air into the pipeline behind, a trailing face of liquid being conveyed through the pipeline network after isolation of said feed pump from said pipeline and closing of said liquid isolation valve.

8. The plant of claim 7, wherein the controller includes a gauge arranged to provide a signal indicative of remaining liquid level within the source reservoir.

9. The plant of claim 1 or 8, wherein the controller includes a cavitation detector associated with the feed pump.

The plant of any one of claims 7 to 9, wherein the pipeline network has an elevation or pressure differential that is wholly or partly unsympathetic to the direction of liquid flow.

11. The plant of any one of claims 7 to 10, further including liquid product processing equipment arranged in-line the pipeline network.

12. The plant of claim 11, further including valved bypass lines arranged to permit liquid product flow bypassing of selected ones of said processing equipment.

13. The plant of any one of claims 7 to 12, wherein it is a human food processing plant. S..

14. The plant of claim 13, wherein the plant is a fruit juice, wine or dairy processing plant. eS A system for removing residual liquid from a pipeline substantially as herein described with reference to any of the accompanying figures or examples. DATED this 1 1lth day of February 2002 TETRA LAVAL HOLDINGS FINANCE S.A. 000000 WATERMARK PATENT TRADE MARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA CJS:ALH:ES