GB2046361A - Pumping assembly for discharging oil from tankers - Google Patents

Abstract

The assembly comprises a pump 1 drawing in fluid via a suction branch conduit 8 and a gas separator 2 and delivering it to a delivery branch conduit 15, said gas separator including a first chamber 4 connected in conduit 8, a further chamber 5 connected at a lower end thereof with said first chamber via a first stop valve 6, and connected at an upper end thereof with the delivery branch conduit 15 or with some other system which conducts the fluid, via a second stop valve 14, a gas bleeding duct 11 extending from an upper end of the chamber 4 via a non-return valve to a position in chamber 5 adjacent the upper end thereof, and a control unit 18 which operates said stop valves so as to cause alternation between a state in which valve 6 is open and the valve 14 is closed, to allow liquid within chamber 5 to pass to the first chamber 4, while gas passes to said further chamber 5 via duct 11 and a state in which valve 14 is open and valve 6 is closed, to allow gas to pass from chamber 5 to the delivery branch conduit 15 or said other system to be replaced by liquid from conduit 15. <IMAGE>

Description

SPECIFICATION Pumping assembly This invention relates to a pumping assembly, for example a pumping assembly incorporating a centrifugal oil charging pump for use as a bilge pump in a tanker vessel and also incorporating a gas separator which is disposed in suction branch conduit of the pump.

In tanker vessels it is desirable to minimise the time required for discharging the vessels and therefore to reduce the time spent in port. This is made possible if the oil charging pumps which are provided on the ship can be used throughout the entire discharge operation i.e. throughout each stage of the discharge operation. However, this means also that these oil charging pumps are used for bilge operation and separate bilge pumps are omitted. Since the pump medium always contains a certan amount of gas and since an increased proportion of gas must be expected in bilge operation, it is necessary for the pumps to be preceded by associated gas separators and bleeding systems which substantially ensure continuous discharge operation.

Two systems are known for discharging gas yielded in the gas separator. In one of the systems the gas is extracted from the gas separator by a separate plant and the extracted gas is blown to atmosphere on the deck of the tanker vessel. This so-called external gas discharge represents a substantial risk to the vessel because a spark would be sufficient to explode the gas cloud thus produced.

The counterpart of this system, the so-called internal gas discharge, provides for feeding the gas removed from the gas separator into the liquid which is already being pumped by the oil charging pump, downstream of the pump. The best known embodiment of this kind is the so-called Prima-Vac system by Hudson Engineering Co. In this system, the suction branch conduit of the pump is preceded by and extends from, a gas separator. The top part of the gas separator in which gas normally accumulates communicates with the delivery branch of the pump via a bleed line and a non-return valve disposed therein. The so-called Prima-Vac-Automat, comprising a venturi nozzle and a non-return valve controlled thereby, is then disposed downstream in the delivery branch of the pump.In normal operation the non-return valve closes the connecting line between the delivery branch and the gas separator by virtue of the pressure difference supplied by the venturi nozzle. In normal operation the pump draws from the gas separator and delivers via the delivery duct. Separated gas from the pumped medium is accumulated in the gas separator. If the amount of gas in the gas separator becomes excessive the pump will draw gas. Delivery of the pump is then interrupted and the delivery rate within the venturi nozzle becomes zero. Accordingly, there will be no further pressure difference between the venturi nozzle and the delivery branch, thus leading to opening of the non-return valve which is driven by the venturi nozzle.Owing to its dead weight any liquid disposed in the delivery branch downstream of the non-return valve flows back into the gas separator via the pipe-lines disposed between the Prima-Vac-Automat and the gas separator. At the same time, the gas in the gas separator can escape via the bleed line and the non-return valve, which again opens, into the space made available in the delivery branch of the pump. When the liquid level in the gas separator has risen sufficiently the pump will again draw liquid and resume pumping. Owing to the pressure differences which will then be established across the venturi nozzle, the non-return valve of the Prima-Vac-Automat will close and pumping will change to normal operation. The gas fed into the delivery branch is discharged by the pumped medium.The important disadvantage of this system is due to the fact that the accumulated amount of gas can be exchanged only if pump delivery is interrupted. Such constant interruption of pumping and "snapping on" - i.e. commencement of pumping - of the centrifugal pump during the bleeding operation imposes an enormous stress on the centrifugal pump and the pipeline system connected thereto.

Bleeding operations results in continuous interruption and snapping on of the centrifugal pump since a gas yield higher than that of normal operation must be expected in or during the last part of bilge operation. In addition to the sudden and alternating stress imposed on the entire system such intolerable continuous states also result in a reduction of the entire pumping capacity. This is because pumping collapses with each bleeding operation and must be re-established each time after a specific time interval during which gas and liquid exchange takes place.

It is therefore an object of the invention to provide a pumping assembly, particularly, but not exclusive lysuitablefora bilge pumping operation and wherein it is possible in a tanker vessel to ensure safe and complete bleeding of the suction side of the oil charging pump without any detrimental impairment of pump operation.

According to the invention there is provided a pumping assembly comprising a pump arranged to draw in fluid via a suction branch conduit and to deliver fluid to a delivery branch conduit, and a gas separator disposed in said suction branch conduit, said gas separator including a first chamber connected in series with portions of said suction branch conduit upstream and downstream of the gas separator, a further chamber connected at a lower end thereof with said first chamber via a first stop valve, and connected, at an upper end thereof, with said delivery branch conduit, or with some other system which conducts the fluid, via a second stop valve, and a gas bleeding duct extending from an upper end of the first chamber via a non-return valve, to a position in said further chamber adjacent the upper end thereof, and a control unit operable to operate said stop valves so as to cause the apparatus to alternate between a state in which said first stop valve is open and said second stop valve closed to allow liquid within said further chamber to pass to said first chamber while gas passes to said further chamber, and a state in which said second stop valve is open and said first valve is closed to allow gas to pass from said further chamber to said delivery branch conduit orto said other system conducting the fluid, to be replaced by liquid from said delivery branch conduit.

In a pumping assembly embodying the invention it is possible to bleed gas into the delivery branch during pump operation, without the pump interrupting delivery. In one embodiment of the invention the gas separator or the suction side of the centrifugal pump communicates with the delivery branch via a rising two-chamber or multi-chamber lock system, each chamber having associated therewith alternately operable stop valve fittings.

Another embodiment is arranged so that the gas separator is connected to the trap system via a bleeding duct and a controlled stop valve fitting or automatic non-return valve fitting disposed therein and the bleeding duct enters the trap system beneath the top stop valve fitting. This bleeding duct results in a further acceleration of the exchange of gas and pumped liquid in the system.

In another embodiment the lock system can also communicate with a storage vessel or system containing pumped liquid. In this embodiment it is possible, for example, for different centrifugal pumps constructed in accordance with the invention to be bied together into a separate tank.

Another embodiment of the invention in which the delivery branch of the centrifugal pump communicates, via at least one pipeline and a controlled stop valve fitting disposed therein, with the bottom region of the chamber associated with the gas lock system is intended to further accelerate the gas/ liquid exchange process. In this embodiment a bypass of the delivering centrifugal pump would drive out the gas into the delivery branch and therefore substantially accelerate the entire exchange procedure during the process of exchanging the accumulated gas.

In preferred embodiments of the invention the control means for controlling the changeover process includes a level switch, attached to the trap system and/or to the gas separator to operate the stop valves. It is also possible for a float switch installed in the trap system and actuated by the level to alternately operate the stop valves.

In another embodiment of the invention the level switch may comprise a plurality of switching stages and be arranged to regulate the delivery rate of the centrifugal pump by means of a fitting disposed in the delivery branch in dependence on the level in the gas separator or in the trap system so that interruption of pumping is reliably prevented in the event of a sudden or increased gas yield in the separator part.

Further protection for the pump is provided in other embodiments of the invention in which the gas separator or the suction branch of the centrifugal pump communicates with the delivery branch of the centrifugal pump via a pipeline and a regulating fitting, disposed in the pipeline, is connected to the level switch. Alternatively, a level switch, attached to the gas separator or to the trap system, may regulate the rotational speed of the centrifugal pump.

Since space on board ship is usually very confined and on the other hand there is a general demand for good accessibility of parts of the system, another embodiment of the invention provides that the gas separator comprises, separable from one another, a top and a bottom container part, that the two container parts communicate with each other via a controlled stop valve fitting, that the top container part communicates with the pump delivery branch via a controlled stop valve fitting and that the stop valve fittings are alternately driven by the control unit. The extension of this embodiment is characterised in that both the top and the bottom container part and the gas separator are embodied as individual components and communicate with each other via the interposition of a controlled stop valve fitting.Accordingly, the pump system could be distributed in the form of containers over several decks and would thus be readily accessible for maintenance and inspection. To accelerate the bleeding operation the top and bottom container part of the gas separator may also communicate via a bleed line and an automatic or controlled fitting ensuring gas exchange in only one direction may be provided in the bleed line.

Various embodiments of the invention are described below by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic diagram showing a first form of pumping assembly embodying the invention, Figure2 is a schematic diagram which shows a modified form of the embodiment of Figure 1 in which the gas/liquid exchange rate is increased by a bypass line, Figure 3 is a schematic view which shows a pumping assembly embodying the invention and incorporating a two-chamber gas-lock system, and Figure4shows schematicaily another embodiment of the invention which includes a singlechamber gas-lock system and in which the gas-liquid exchange rate is increased via a bypass line.

The system illustrated in Figure 1 comprises a centrifugal charging oil pump 1 with a suction conduit branch 8, (i.e. an intake conduit) and a delivery branch conduit 15 extending therefrom. A gas separator 2 is connected in conduit 8 upstream of the pump, the separator including a vessel or container. A bulkhead 3 disposed in the vessel or container divides the latter into a bottom container part 4, forming a first chamber and a top container part 5 forming a major part of a further chamber. The bottom container part 4functions as a separator part and is connected in the conduit 8 so that the liquid passes through said first chamber on its way to the pump. The top container part 5 functions as a gas trap part. Both container parts communicate via a stop-valve 6 which in this case is disposed in a short pipe member 7 connecting the parts 4 and 5.

The connections 9 and 10 of the first chamber of the gas separator with the parts of conduit 8 respectively upstream and downstream of the gas separator are disposed in vertically offset configuration with respect to each other. This step produces a vortex effect within said first chamber and therefore produces good phase separation of the gas which is mixed with the pumped liquid medium. The sepa rated gas is collected in the top region of the bottom container part 4 which communicates via a bleed line 11 and a non-return valve 12, selected as an example in this case, with the top region of the top container part 5. Furthermore, a pipeline 13 with a stop valve 14 disposed therein connects the top region of the top container part 5 to the delivery branch 15 of the oil charging pump. A regulating fitting 16 is disposed downstream of the oil charging pump in the delivery branch 15.The valves 6 and 14 and the regulating fitting 16 are controlled by control means which is constructed in two parts and comprises a liquid level sensor 17 mounted in the bottom container part 4 and a control unit 18 which can be installed as desired. The control unit 18 and the level sensor 17 are interconnected and are connected to the fittings 6, 14 and 16. The most convenient method of connection can be selected, i.e. electrical, pneumatic or hydraulic. The sensor 17 and unit 18 can also be combined in one unit. The sensor 17 may, for example comprise one or more switches operable by a float disposed in chamber 4.

Operation is as follows: It is assumed that the system is in equilibrium and the full pump delivery rate is supplied without malfunctioning. In one operational state, normally assumed when the liquid level in container part 4 is between desired limits, the stop valve 14 is open and the stop valve 6 is closed. During the pumping operation gas is accumulated in the top region of the bottom container part 4 so that the liquid level in the bottom container part is necessarily lowered. When a specific lower level 19 is reached the level sensor 17 transmits a corresponding signal to the control unit 18. The oil charging pump 1 however continues to provide trouble-free operation without impairing the delivery rate. The control unit 18, on receipt of said signal then changes the states of the stop valves 6 and 14 to place the assembly in another operational state, i.e.

the stop valve 6 is opened and the stop valve fitting 14 is closed.

After the stop valve fitting 6 is opened pumping liquid flows from the top container part 5 into the bottom container part 4 and at the same time the gas stored in the bottom container part 4 escapes via the pipeline 11 andthroughthe non-return valve 12 inserted therein into the top container part 5. The liquid level in the bottom container part 4 therefore rises. The unit 18 subsequently, after a predetermined period returns the assembly to said first operational state. The arrangement may be such that by the time the assembly thus returns to said first operational state thereof, the liquid level in container part 4 will normally have risen substantially above said lower level 19, and such that, in this event, the assembly will remain in this state until the lower level 19 is again reached causing a further cycle to take place.Alternatively the control unit 18 may be arranged, once said lower level is reached, to cause said operational states of the assembly to alternate until an upper threshold level is reached whereupon such alternation is terminated, with the assembly in said first state, by a signal passed by the sensor 17 to the unit 18, until the lower threshold level is again reached, and soon. The period of the operational cycle of unit 18, and thus the frequency of such alternation, may be variable to achieve the desired mode of operation. The stop valve 6 is closed and the stop valve 14 is open, gas and liquid exchange takes place via the pipeline 13 between the top container part 5 and the delivery branch 15 of the oil charging pump disposed above.Thus liquid flows into the top container part 5 from delivery branch 15 and fills part 5 while gas rises from part 5 through the pipeline 13 into the delivery branch 15 and is correspondingly discharged. In the event that, over a period, the rate at which gas is accumulated in the bottom container part 4 is greater than the rate at which the gas can be discharged by the trap system, the level sensor 17 will transmit a corresponding signal to the regulating fitting 16 which will then reduce the delivery rate of the oil charging pump 1 and therefore the amount of gas yielded in the gas separator 2. This reliably ensures that the pump does not draw any gas from the gas separator and delivery cannot therefore be interrupted.

A variant embodiment shown in Figure 2 differs from that shown in Figure 1 in that a separate duct 20 extends from the delivery branch 15, upstream of the connection of the delivery branch with the pipeline 13, to the chamber 5 and a stop valve 21, also controlled by unit 18 is disposed in duct 20. In this case the valves 14 and 21 are operated jointly by the control switch 18 and are simultaneously opened or closed. When the fittings 14 and 21 are opened a bypass flows from the pump through the duct 20, the top container part 5 and the pipe line 13 and as a result more rapid filling of chamber 5 with oil, and flushing of gas from chamber 5, is obtained. The time required for flushing the gas from chamber 5 can thus be substantially shortened.

In Figure 3 parts having the same reference numerals as parts in Figures 1 and 2 correspond substantially with the latter parts.

Figure 3 shows a two-chamber trap system comprising two pipelines 22, 23, rising from a gas separator 2 forming a first chamber. The gas separator 2 in this case has no bulkhead and has therefore not been designed as a trap part. The top region of the gas separator 2 is connected to the lower ends of pipelines 22, 23 which are connected, at their upper ends with the delivery branch 15. The pipelines 22, 23 could as readily communicate at their upper ends with a storage container or system containing the corresponding pumped liquid. Adjacent their upper ends the pipelines 22, 23 are provided with stop valve fittings 25 and 27 respectively and adjacent their lower ends are provided with stop valve fittings 24 and 26 respectively. A bleed line 28 extends upwardly from the separator 2 and via the interposition of a valve unit 29, is connected with the interiors of pipelines 22, 23, adjacent and below the upper stop valve fittings 25, 27. The valve unit 29 comprises, or acts as, two non return valves or check valves, one disposed between line 28 and pipeline 22, to allow flow only in the direction from line 28 to pipeline 24, and the other disposed between line 28 and pipeline 23, to allow flow only in the direction from line 28 to pipeline 23. The stop valve fittings 24, 25 and the stop valve fittings 26,27 are operated by the control unit 18, controlled in turn by level sensor 17.The part of each pipeline 22, 23 between the upper and lower stop valve fittings therein forms a respective further chamber corresponding in function to the chamber 5 of Figures 1 and 2.

The description of the method of operation again proceeds from normal operation. In a first operation al state of the assembly, the stop valve fittings 24 and 25 are open and the stop valve fittings 26, 27 are closed. The pipeline 22 is therefore filled with the liquid being pumped, from the delivery line 15 while any gas in pipeline 22 passes to the delivery line 15, and at the same time the pipeline 23 is filled with gas from chamber 2 while any liquid in pipeline 23 drains into chamber 2. As gas accumulates in the gas separator 2 while the appropriate oil tanks are being discharged, the liquid level in separator 2 falls.As soon as the liquid level in the gas separator 2 reaches a specific lower level 19 the level sensor 17 will transmit a signal to the control unit 18 which will then close the stop valve fittings 24 and 25 and open the stop valve fittings 26 and 27, and thus place the assembly in another operational state thereof. The liquid column in the pipeline 22 will then drop into the gas separator 2 and the gas disposed therein will flow via the bleed line 28 and the non-return valve 29, into the pipeline 22. The gas in the pipeline 23 on the other hand is displaced into the delivery branch by the pumped medium which flows from the delivery branch 15 into pipeline 23. The gas flowing into the delivery branch 15 is discharged by the pumped medium while the pipeline 23 is filled with liquid as far as the stop valve fitting 24.The assembly may remain in the last noted operational state until the liquid level in chamber 2 again drops to lower level 19, to cause the control unit 18 to change the apparatus once more to its first operational state, or alternatively the operational states of the assembly may be alternated repeatedly by the unit 18 at a rate determined thereby, until a predeter mined upper-liquid level is reached in gas separator 2, whereupon such alternation will be terminated by a signal transmitted by the level sensor 17 to the control unit 18. The delivery rate of the pump can be restricted by means of the regulating fitting 16 controlled via the level sensor 17 if the level 19 continues to fall in the event of the amount of gas yielded in the gas separator 2 being greater than the exchange capacity of the trap system.As an alterna tive, or in addition, in this and the other embodi ments disclosed herein, the delivery of pump 1 can also be reduced by reducing the rotational speed of the pump under the control of the level sensor 17.

There may be provision for operating control unit 18 manually when necessary in order to obtain constant continuous bleeding which persists over the entire duration of the discharging operation.

Figure 4 shows a pumping assembly which differs from the assembly of Figure 3 mainly in having only one pipeline, referenced 32, in place of the two pipelines 22,23.

The pipeline 32 may be regarded as correspond ing, for example, to the pipeline 22, with the pipeline 23 being omitted and stop valve fittings 30 and 31 corresponding to fittings 26 and 25 respectively in Figure 4. A pipeline 33 which branches from the pump delivery branch 15 and can be closed by a stop valve fitting 34, is connected with the lower part of the trap chamber defined within pipeline 32, between valves 30 and 31. A bleed line 35 with a non-return valve 36 disposed therein also extends from the gas separator 2 to the upper region of the trap chamber defined within pipeline 32 and is connected with pipeline 32 below the stop valve fitting 31. The bleed line 35 and valve 36 thus correspond to line 28 and valve 29 in Figure 3. Other parts in Figure 4 which correspond with parts in Figure 3 have corresponding references.

In a first operational state of the assembly of Figure 4, normally occupied when the liquid level in vessel 2 is between desired limits, stop valve fittings 31 and 34 are closed and the stop valve fitting 30 is open. The gas yielded in the gas separator 2 is collected, in this operational state, within the trap chamber 32 and when required is discharged therefrom as a result of a control instruction from the control unit 18 causing the assembly to be changed to a second state in which the stop valve fittings 31, 34 are opened and the stop valve fitting 30 is closed.

A bypass route 37 is thus established for liquid to pass from the delivery branch 15 along pipe 33 and up pipeline 32 in to the downstream part of delivery branch 15. Thus the liquid passed along this bypass route flushes out the gas in the top chamber 32 and flushes it into the delivery branch 15. On completion of the flushing operation the stop valve fittings 31,34 are again closed and the stop valve fitting 30 is opened so that the assembly is returned to its first state and the pumped liquid remaining in the trap chamber 32 drops back into the gas separator 2 through the opened stop valve fitting 30.

As in the embodiments of Figures 1 and 2 the control unit 18 may be arranged, each time a lower liquid level is reached in separator 2, as detected by sensor 17, to cause the assembly to change once from its first to its second state, then back to its first state until lower level 12 is again reached, or may be arranged to cause said states to alternate until a predetermined upper level is reached, the assembly then remaining in its said first state until the lower level is again reached. The period of the operating cycle of unit 18 may again be adjustable.

The control unit 18 in any of the embodiments described can also be constructed as a continuously operating automatic device which provides for a constant alternating bleeding operation.

Claims (19)

1. A pumping assembly comprising a pump arranged to draw in fluid via a suction branch conduit and to deliver fluid to a delivery branch conduit, and a gas separator disposed in said suction branch conduit, said gas separator including a first chamber connected in series with portions of said suction branch conduit upstream and downstream of the gas separator, a further chamber connected at a lower end thereof with said first chamber via a first stop valve, and connected at an upper end thereof with said delivery branch conduit, or with some other system which conducts the fluid, via a second stop valve, and a gas bleeding duct extending from an upper end of the first chamber via a non-return valve, to a position in said further chamber adjacent the upper end thereof, and a control unit operable to operate said stop valves so as to cause the apparatus to alternate between a state in which said first stop valve is open and said second stop valve closed to allow liquid within said further chamber to pass to said first chamber while gas passes to said further chamber, and a state in which said second stop valve is open and said first valve is closed to allow gas to pass from said further chamber to said delivery branch conduit or to said other system conducting the fluid, to be replaced by liquid from said delivery branch conduit.

2. A pumping assembly according to claim 1 comprising a plurality of such further chambers, each connected at a lower end thereof with said first chamber via a respective first stop valve and each connected, at a lower end thereof, with said delivery branch conduit or with said other system, via a respective second stop valve, said control unit being operable to cause each said further chamber and the associated stop valves to alternate between a first state in which the respective first stop valve is open and the respective second stop valve is closed and a second state in which the respective second stop valve is open and the respective first stop valve is closed, the control means being so arranged that the operating cycle of each said further chamber and the associated stop valves is displaced in phase relative to the corresponding cycles for the other said further chamber.

3. A pumping system according to claim 2 wherein there are two said further chambers and wherein said control means is arranged to operate said stop valves so that one said further chamber, with its associated stop valves, is in said first state while the other said further chamber, with its associated stop valve is in said second state, and vice versa.

4. A pumping system according to any preceding claim wherein the or each said further chamber is connected with said first chamber via a gas bleeding duct having a non-return valve or a controlled stop valve therein.

5. A pumping system according to any of claims 1 to 4, in which the gas separator communicates with a storage tank or system containing the pumped fluid.

6. A pumping assembly according to claims 1 to 5, in which the or a said further chamber is further connected, via a pipeline and a further stop valve controlled by said control means, with the delivery branch of the centrifugal pump, said further pipeline communicating with said further chamber adjacent the lower end thereof, above said first valve associated with the further chamber.

7. A pumping assembly according to any of claims 1 to 6, wherein said control means includes a level sensor disposed in said first chamber of the gas separator.

8. A pumping assembly according to claim 7 wherein said level sensor comprises at least on switch operable by a float disposed in said first chamber.

9. A pumping assembly according to claim 8 wherein said level sensor comprises a plurality of switching stages operable by said float, and wherein means is provided for regulating the delivery rate of the centrifugal pump, said means being controlled by said switching stages so that said delivery rate is controlled in dependence on the liquid level in said first chamber.

10. A pumping assembly according to claim 9 wherein said means for regulating the delivery rate of the pump comprises a regulating fitting disposed in the delivery branch conduit.

11. A pumping assembly according to claim 9 in which said means for regulating the delivery rate of the pump includes a pipeline connecting the delivery side of the centrifugal pump with said suction branch conduit or said first chamber of the gas separator, and a regulating fitting disposed in the pipeline.

12. A pumping assembly according to claim 9 wherein said means for regulating the delivery rate of the centrifugal pump is arranged to regulate the rotational speed of the centrifugal pump.

13. A pumping assembly according to claim 1 or any of claims 4 to 12 when dependent on claim 1 in which said gas separator includes a vessel having an internal partition defining, below the partition, said first chamber, and above said partition, said second chamber.

14. A pumping assembly according to claim 13 in which the chambers defined within said container above and below the partition communicate with one another via a bleed line in which is disposed an automatic or controlled fitting, ensuring gas exchange in only one direction.

15. A pumping assembly substantially as hereinbefore described with reference to, and as shown in, Figure 1 of the accompanying drawings.

16. A pumping assembly substantially as hereinbefore described with reference to, and as shown in, Figure 2 of the accompanying drawings,.

17. A pumping assembly substantially as hereinbefore described with reference to, and as shown in, Figure 3 of the accompanying drawings.

18. A pumping assembly substantially as hereinbefore described with reference to, and as shown in, Figure 4 of the accompanying drawings.

19. Any novel feature or combination of features disclosed herein.