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1. WO1997027403 - IMPROVEMENTS IN AN UNLOADING PUMP WHICH IS SUBMERSIBLE IN THE CARGO OF A SHIP'S CARGO TANK

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[ EN ]

Improvements in an unloading pump which is
submersible in the cargo of a ship's cargo tank

The present invention relates to an unloading pump arrangement, which is submersible in the cargo of a ship's cargo tank and which has a pump inlet arranged in or by a well at the bottom of the tank, where the pump arrangement comprises a main pump and an auxiliary pump which is drive connected to the impeller of the main pump and which has a lower inlet end arranged at a level between the bottom of the well and the under side of the inlet of the main pump and an upper outlet end at a level above the under side of the blades of the main pump, and where the unloading pump has a discharge pipe to a delivery location via the deck of the ship.
By means of an unloading pump submerged in the cargo it is possible to unload cargo in a controlled manner by stepless capacity control in all manner of types of cargo (fluid) . It is possible, especially in relatively small ships, to employ pump arrangements where the pump is connected to the drive motor via a relatively long shaft, so that the drive motor for example can be placed on deck, while remaining parts of the pump arrangement can be submerged in the cargo. In other instances, and especially in relatively large ships, there is employed for practical reasons an unloading pump in the form of an elongate, rigid pump arrangement, which is readily dismountable, that is to say inter alia easily immersible or hoistable relative to the well at the bottom of the cargo tank. Then there is employed a pump impeller which is driven by a motor via a short drive shaft, the pump impeller and the pump motor being adapted to be located just by the bottom of the ship's cargo tank, submerged in the cargo. In such a case the pump motor is preferably enclosed in a
protective housing.
In a practical embodiment the inlet for the unloading pump is defined between the bottom of a well in the tank and the impeller of the unloading pump. The distance between the impeller of the unloading pump and the bottom of the well of the cargo tank is inter alia adapted according to the cross-sectional flow through the pump. Normally the unloading pump can empty cargo to a level substantially flush with the under side of the unloading pump. Consequently there remains behind a first residue of cargo in the well at the level below the impeller of the main pump. In addition there remains behind a second residue of cargo within the pump itself. The second cargo residue is emptied most often back to the well by a stopping of the unloading operation or the stripping operation. The portions of the cargo, which pass the unloading pump, can be removed in a known manner via the associated discharge pipe in the stripping operation.
In practice special problems are presented in getting emptied out the last residues of the cargo, which are collected in the well of the tank, that is to say in the region between the under side of the unloading pump and the bottom of the tank well, in the concluded unloading operation. As is shown for example in NO Patent
Application 920380, separate suction arrangements have hitherto been employed for collecting up such residues of cargo, that is to say special suction arrangements, which operate independently of the unloading pump itself.
Consequently it is possible to suck up the residues by means of separate suction arrangements having separate drive means, but this requires extra piping, extra drive medium and extra cleaning of the associated additional equipment, something which creates extra complications. In practice such suction arrangements are placed on the outer side of the pump arrangement, as a separate unit, but can also be arranged, as in NO Patent Application 953132, internally in the pump arrangement.
Alternatively there have been employed in practice so-called stripping arrangements for collecting such residues of cargo, that is to say stripping arrangements, which operate together with and partially independently of the unloading pump. With such stripping arrangements it has been possible, with an emptied loading tank, to undertake cleaning in a controlled accurate and effective manner, together with cleaning of the unloading pump itself. By means of such stripping arrangements it has been usual - while the impeller of the unloading pump is kept in operation with a certain pump pressure against the residual cargo in the pump - with an extra supplied counterpressure, produced by compressed air or compressed gas, to blow the residues of the cargo from the pump pipe via a connected stripping conduit to a suitable delivery location via the deck of the ship.
In NO Patent Application 933729 it is proposed to suck inwardly into the pump the largest possible quantity of the cargo residue which otherwise is retained in the tank well, by arranging an extra pump (auxiliary pump) in drive connection with the impeller of the main pump, but then placed a considerable distance forwards, that is to say upstream of the impeller of the main pump. With such a solution one has indeed been able to fetch up portions of the cargo residue from the tank well, but a considerable problem is however that the stripping equipment has produced at the same time an undesired reduced capacity of the unloading pump during remaining working conditions, that is to say during normal unloading operations. It can be a question of a reduction of a couple of per cent of the usual unloading capacity. In order to avoid this problem the distance between the bottom of the tank well and the inlet of the unloading pump has had to be
increased and the effect of the solution has therefore not been satisfactory for all purposes.
Furthermore various proposals are known for feeding extra pump medium via an extra pump to the impeller of the main pump. More specifically it is proposed to locate a feeding pump upstream of the impeller of the main pump, which induces an extra flow of pump medium to the impeller of the main pump. Such known proposals are evident from DE 1 045 237, DE 2 037 785, DE 2 545 736, US 3 304 877 and US 3 588 280. In all the said publications the flow of pump medium first passes the feeding pump and immediately thereafter the impeller of the main pump in a continuous course in a coherent flow path. The placement and the design of the said feeding pumps cause however an
interruption in the passage of the pump with a significant reduction of the unloading capacity of the pump as the end result.
The aim of the present invention is to ensure the largest possible removal of the residues of cargo from the bottom of the tank including feeding of such residues in the impeller of the main pump. This is sought to be solved by a favourable design of the auxiliary pump.
According to NO 178 244 an auxiliary pump is known which is formed of a substantially cylindrical casing portion, which is supported via a middle anchor pin which is fastened to the under side of the impeller of the main pump. The casing portion is carried on the anchor pin via one or more supporting ribs, which maintain the casing portion on the anchor pin and which can form lifting blades of the auxiliary pump.
Substantially the same flow through cross-section is employed at the upper end of the main pump as at its lower end.

According to US 3 904 306 an auxiliary pump is known which is formed of a double-conical bell portion, that is to say with a lower skirt portion, which extends conically upwards converging from its lower portion towards the middle of the bell portion, and an upper portion, which extends conically upwards diverging from the middle of the bell portion obliquely upwards and outwards in the flow through passage in the impeller of the main pump. In this instance the bell portion is carried via sideways directed support ribs in a common hub fastened to the under side of the main impeller. In this case also the support ribs can form blades of the auxiliary pump.
With the present invention the aim inter alia is to be to design the auxiliary pump in a constructionally and operatively simpler, and more effective manner. More specifically the aim is to adjust the conditions, so that the largest possible quantity of the cargo residues can be removed, which had to be retained in the pump arrangement after the concluded usual unloading operation, in a flow favourable manner.
This is solved according to the invention in that the auxiliary pump, which has the form of a part conical sleeve portion or bell portion, has the largest radial internal and external dimensions at the upper outlet end of the auxiliary pump and the least radial internal and external dimensions at the lower inlet end of the
auxiliary pump, and that the internal flow passage of the auxiliary impeller comprises an upper discharge chamber and a number of outlet openings, which empty directly out into the flow through passage of the main impeller from the periphery of the discharge chamber.
With the afore-mentioned solution an extra pumping effect can be obtained with the auxiliary pump without reducing the pumping effect of the main pump. A first significant result is that the auxiliary pump can be active in the whole pumping phase, that is to say both in the unloading phase and in the concluding stripping phase, without damaging effects on the normal unloading
operation. More specifically, by means of the part conical sleeve portion of the auxiliary pump and the upper
discharge chamber defined thereby, there can be ensured in a controlled manner an effective flow of pump medium to the upper portion of the discharge chamber with the possibility of uniform emptying from the discharge chamber to the flow-through passage in the impeller of the main pump. In this connection it is important that an active guide face is obtained for the pump medium both on the upwardly diverging, conical inner side of the sleeve portion and on the upwardly diverging, conical outer side of the sleeve portion. It is correspondingly important to arrange the sleeve portion with a restricted inlet in the centre of the rotation zone of the pump medium and with equivalent outlet passages to the flow-through passages of the main pump, at the same time as the conically upwardly diverging discharge chamber gives the possibility for effective outflow of pump medium via outlet passages arranged at the radially outermost peripheral portion of the auxiliary pump. By means of the portion of the pump medium, which flows on the outer side of the sleeve portion, a hand can be lent during the normal unloading operation with bringing the pump medium in the intended rotating flow path now in front of the inlet to the main pump. In addition by said rotating flow path an equivalent rotating flow path can be ensured branched off inwardly into and further upwardly through the sleeve portion along its inner side.
It will also be possible to continue the course of the said part-flows in a coinciding manner in a common flow path through the main pump. In this connection one or more outlets from the auxiliary pump can empty out into a region, which is defined by the pump space of the main pump and a region just downstream of said pump space.
It is aimed to be able to conduct the flow of pressure medium from outlet (s) of the auxiliary pump directly into the flow path of the flow of medium through the pump space of the main pump.
In practice the outlets from the auxiliary pump empty out into the pump space of the main pump just downstream of the inlets to the impeller of the main pump, that is to say at the level of or above the radially inner portion of the impeller blades of the main pump in a lower portion of the impeller of the main pump.
Practical trials have shown that a surprisingly good result is achieved with the pump arrangement according to the invention, having an especially simple design of the auxiliary pump, by means equivalent inner and outer outwardly and upwardly converging guide faces in the sleeve portion of the auxiliary pump.
This good result is obtained by relatively smooth and uniform guide faces in the sleeve portion itself without special projections. Particularly favourable conditions are obtained by designing the sleeve portion with
uniformly deflected guide faces, which extend curved from below from an essentially vertical path to a more or less radially outwardly directed path above.
Without significantly influencing the course of the flow via the main impeller of the pump and without
reducing the capacity and efficiency of the unloading pump, there is achieved according to the invention an increased suction effect via the auxiliary pump towards the cargo residue in the tank well and in addition it is made possible to ensure an effective sucking up and removal of the cargo residue which necessarily finds itself in the unloading pump and its cargo discharge pipe. According to the invention it is preferred that the auxiliary pump is formed from a sleeve of relatively thin- walled material converging from below obliquely upwards and outwards, and that the sleeve is secured via its upper peripheral edge portion at a guide portion in the impeller of the main pump, the outlet openings being designed just by, that is to say immediately below the fastening of the sleeve to the impeller of the main pump.
By means of a constructionally simple, separately produced sleeve of thin-walled material, the sleeve can be fastened according to the invention by simple means, such as a welding operation, to the impeller of the main pump in a ready manner.
Further features will be evident from the following description having regard to the accompanying drawings, in which:
Fig. 1 shows a schematic cross-section of a tanker equipped with the pump arrangement according to the invention.
Fig. 2 shows schematically the pump arrangement according to Fig. 1 illustrated in side view and in segment .
Fig. 3 shows, in a segment of Fig. 2, a vertical section of a lower portion of the pump arrangement according to a first embodiment.
Fig. 4 shows a plan view of the impeller of the main pump of the pump arrangement together with in part the discharges from the auxiliary pump to the main pump.
Fig. 5 shows in segment the auxiliary pump
illustrated as a separate unit segregated from the main pump according to a second embodiment.
Fig. 6 shows in segment a vertical section of the impeller of the main pump and an associated auxiliary pump according to a third embodiment .
By way of introduction there will be described with reference to Figures 1,2 and 3, plus parts of Fig. 4, known components which for a part of a pump arrangement according to the invention.
In Fig. 1 an unloading tank 10a in a tanker 10 is shown, where bottom 11 of the tanker 10 is illustrated, which is provided with a locally defined tank well 12. In the tank well 12 a lower end of an unloading pump is submerged, that is to say an inlet end 13 to a pump arrangement 14. The pump arrangement 14 is adapted to operate submerged in the cargo in the tank 10a in a relatively free downwardly hanging condition, with local, centering side support not shown further arranged at suitable height levels in the cargo tank, for example along the one tank wall .
The tank well 12 is, as clearly shown in fig. 2, given an optimal design with respect to the collection and flow of cargo to the unloading pump and is in this
connection given a concavely rounded form.
The pump arrangement 14 according to the present invention is of a corresponding submersible type and has corresponding sealing and a corresponding mode of
operation to that which is shown and described in NO 123 115.
In Fig. 2 there is shown a pump structure comprising a pump impeller 15, which is received in a snail houselike pump housing 16. During mounting and dismounting the pump housing 16 is freely axially moveable relative to the well 12 and is centered relative to this by means of a combined support/control ring and spurt screen 16a, which is fastened with paws 16b to the bottom 11 of the tank 10a in or by the tank well 12. At 16c (Fig. 3) there is shown an inverted funnel-shaped guide shield fastened to the pump housing 16 just below the lower edge 15a of the impeller 15. The impeller 15 is driven via a short drive shaft 17 by a drive motor, for example such as shown in NO 123 115, submerged in the cargo.
From two diametrically opposite sides of the pump housing 16 a respective branch pipe 25a converges, of which only the one is shown herein, upwardly towards a transition portion 26a to a common cargo discharge pipe 26. The discharge pipe 26 and protective pipe 23 of the hydraulic supply and discharge conduits extend in parallel upwards and pass individually through a cover 10b on a hatchway 10c on the deck of the ship. The discharge pipe 26 extends further to a suitable discharge location, as shown by an arrow C just above deck lOd of the ship.
Stripping operation known per se
After terminating the normal unloading operation the residue of cargo, which remains behind in the discharge pipe 26 and the branch pipes 25a and in the pump housing 16, and the residue of cargo, which remains behind in the tank well 12, are removed by means of a stripping
operation, in which the pump impeller 15 continues to be kept working. One can continue hereby without a break from the normal unloading operation to the subsequent stripping operation, without delay.
According to the invention importance is attached on being able to conduct normal unloading operations under optimum conditions and having to adapt the remaining, sub-sequent functions according to existing unloading
equipment. The stripping operation is consequently
undertaken in a manner which is adapted according to the equipment and the arrangement, which is used in the preceding unloading operation.
In Fig. 1 and 2 a stripping pipe 28 is shown, which has an intake opening 29 connected to a discharge pipe 26 at the transition portion 26a. In he illustrated
embodiment the opening 29 is connected to the transition portion 26a, that is to say connected downstream of the adjacent discharge branch conduits 25a. By means of the stripping pipe 28 the cargo residue in the discharge pipe 26 and at least parts of the discharge branch conduits 25a can be emptied.
In a typical cargo tank of a ship the pump
arrangement has a height from the bottom 11 of the tank 10a to just above the hatch cover on the deck lOd of the tank 10a, of 25 - 30 metres, while the remaining unloading equipment at the unloading location requires an additional lifting height of the order of magnitude of 10 metres. With submersible pump arrangements of known construction it is usual, that at pump pressures of said order of magnitude a significant out flow (leakage) of pump medium takes place via upper and lower fissures in the pump housing 16 of the pump arrangement between the impeller 15 and certain sealing arrangements in the pump housing 16.
The afore-mentioned stripping operation removes in practice the major portion of the cargo, which has reached into the discharge pipe, but hitherto it has been
difficult to get rid of the last residues of cargo in the well 12 and that portion, which is still to be found in the lower branch pipe 25a of the discharge system and in the pump housing 16, as a result of static pressure from such cargo residues.
In the following there will be described the solution according to the present invention, at the same time as consideration is given to the desire for optimal working conditions in the normal unloading operation.
The embodiment, which is shown herein, is based on the principle known per se that an auxiliary pump is utilised in addition to the main pump.
The solution according to the invention
According to the present invention the known impeller 15 forms a part of the main pump 14a, while in the
illustrated embodiment an auxiliary pump 30 forms one piece with the impeller 15, that is to say the main pump 14a and the auxiliary pump 30 constitute an integral member.
In Fig. 5 an auxiliary pump 30' is shown in the form of a separate member, comprising an impeller member 31' and a cover member 32'. The auxiliary pump 30' is adapted to be able to be fastened to the impeller 15 of the main pump via fastening screws received in bores 33'
correspondingly as shown to the left in Fig. 5.
Alternatively the auxiliary pump 30' can constitute an integral part of the impeller of the main pump.
The cover 32' is adapted to be clamped in place between impeller member 31' of the auxiliary pump 30' and impeller 15 of the main pump adapted for this.
Alternatively the cover member 32' can be screwed in place or secured in another suitable manner to impeller member 31' of the auxiliary pump 30'.
For the sake of simplicity certain details are shown on a larger scale in the impeller member 31' according to Fig. 5, which correspond to the details in the impeller member 31 according to Fig. 3. In the following
description therefore reference is made alternately to Fig. 3 and Fig. 5 for the sake of simplicity. Details which are corresponding in the two solutions are
represented by the same reference numerals.
The auxiliary pump 30 (see Fig. 3 and 4) is
especially effective in connection with the stripping phase according to the present invention, that is to say on stripping via the auxiliary pump 30, but is necessarily also active during the unloading operation itself.
In the embodiment illustrated in Fig. 3 the auxiliary pump 30 consists of an upwardly and outwardly diverging, sleeve-shaped or bell-shaped impeller member 31. The impeller member 31 projects, as shown in Fig. 2, with a lower inlet 35 a considerable length below lower edge 15a of the impeller 15 and an additional length below lower edge 16c' of the guide shield 16c, downwards towards the bottom of the tank well 12. If desired the inlet 35 can be localised so tightly above the bottom of the tank well 12 that the free inflow of the pump medium to the interior of the impeller 31 can be accurately ensured (such
alternative localising is not shown further herein) .
The impeller member 31' (see Fig. 5) has externally an upwardly and outwardly diverging guide face 36, which at a lower portion 36a extends approximately rectilinearly upwards at an oblique angle u and continues thereafter obliquely upwards and outwards with an upper curved portion 36b, which in turn continues in impeller 15 of the main pump 14a further radially outwards via a curved portion 15b (see Fig. 3) and a subsequent rectilinear portion 15c.

The impeller member 31' (see fig. 5) has internally an equivalent upwardly and outwardly diverging guide face 37, which at a lower portion 37a extends approximately rectilinearly upwards at an oblique angle v and continues thereafter obliquely upwards and outwards with an upper curved portion 37b, which empties out into an upper circular outlet chamber 38.
The outlet chamber 38 is defined above by the cover 32' (see Fig. 5) or a terminating face 32 (see Fig. 3) , while below it communicates with a relatively smooth-walled flow-through chamber 39, which has an increasing cross-section from the inlet 35 towards the chamber 38. The inlet 35 is shown with a minimum diameter Dl (see Fig. 5) , while the outlet chamber 38 is shown with a maximum diameter D2 , where the maximum diameter D2 is at least one and a half times greater than the minimum diameter Dl and preferably, such as is shown in Fig. 3 and 5, twice as large as the minimum diameter Dl .
In Fig. 4 seven outlet ducts 40 are shown, which empty radially outwards from the outlet chamber 38 to an adjacent equivalent seven mutually separated flow through ducts 41 of the impeller 15. In practice the number of outlet ducts 40 and the number of ducts 41 can be greater or smaller than seven, all according to need.
In Fig. 4 there is shown in section flow through ducts/openings 41, central axis 41a of which extends curved in a radial plane along the centre axis 40a of the outlet ducts/openings 40.
In the embodiment illustrated in Fig. 5 the outlet ducts 40 extend radially outwards in a vertical plane through coinciding central axis of chambers 38 and 39, that is to say at right angles to the peripheral wall of the chamber 38, and thereby at a considerable angle to guide blades 42 of the impeller 15 (see Fig. 5) .
Alternatively the central axis 40a of the outlet ducts/openings 40 can extend in a vertical plane parallel to the centre line 39a of the chamber 39, that is to say at a significant oblique angle to the peripheral wall of the chamber 38 and thereby at a smaller oblique angle to -or more or less in a direction along - respective guide blades 42 (see Fig. 5) of the impeller 15. According to Fig. 3 axis 40a of the outlet ducts/openings 40 forms a vertical angle u with central line 41a of the ducts 41 and a vertical angle v with upper defining face 36c of the duct 41.
During consideration of Fig. 3 it is evident that by means of auxiliary pump 30 two separate flows A and B are obtained for the supply of cargo medium to the main pump in a conventional unloading sequence, namely a main flow A arranged radially outside the auxiliary pump 30 and an extra flow B arranged internally in the auxiliary pump 30. It is evident from Figs. 3 and 4 that the combined flow through the seven ducts/openings 40 constitutes a small fraction of the main stream A through the ducts 41. When the unloading operation, which is based on the main flow A, goes towards conclusion, the flow B can continue fully in that the inlet 35 of the auxiliary pump 30 is submerged in the cargo to a level below the lower edge 16c' of the screen 16c.
By means of the internal guide faces 37 diverging conically upwards several practical advantages are obtained.
As a consequence of the relatively uniform and smooth external and internal guide faces 36,37 of the auxiliary pump 30 diverging conically upwards, there can be created controlled, relatively calm movements of the cargo externally on the auxiliary pump and internally in the passage 39 and particularly in and by the lower inlet 35 of the auxiliary pump 30.
As a consequence of the cross-section increasing upwardly relatively uniformly in combination with the upper, radially directed outlet ducts/openings 40, there is achieved firstly a generally favourable suction effect or pumping effect internally in the duct 39. In combination with the above-mentioned suction effect there is obtained an additional suction effect, namely that which is exerted towards the chamber 38 via the
ducts/openings 40 from the flow through passages 41 by means of the impeller 15 of the main pump 14a. The design of the duct/the chamber 39, such as shown in Fig. 3, having a gradually increasing cross-section in the flow direction B gives in itself a pumping effect internally in the impeller 30. In addition said cross-sectional increase provides a tendency for an accumulation of pump medium in the chamber 38 just in front of the outlet ducts 40, so that the external suction effect from the ducts 41 towards the ducts 40 can be utilised in an effective manner internally in the impeller 30. It is considered as an advantage that the portions of the pump medium which are introduced into the duct/chamber 39 can be kept in place relatively stable within the impeller independently of possible variations in the flow of pump medium to the inlet 35 of the impeller 30.
In practice it has been found that even small changes of the flow path of the cargo through the impeller 15 can act negatively on the wish for an optimally adjusted unloading operation.
Further it has been found in practical trials that the application of an extra pump arrangement, can provide an effective collecting up of residues of the cargo from the tank well 12 especially when these cargo residues are picked up by the usual guide blades 42 of the main
impeller 15.
Alternatively to the construction according to Fig. 5 the ducts 40 can, if desired, be milled ("utfrese") or remoulded ("utstĪ†pe") partly in the impeller 30' and partly in a cover which covers the auxiliary pump 30' at a level above the chamber 38. In such a case the cover member and the impeller member are fastened effectively together in a mutually non-rotatable manner, for example by means of fastening bolts and/or guide pins.

Without examples of it being shown herein the use can also be considered of a separate insert member, which is arranged axially displaceable internally in the auxiliary pump 30 and which is movable a limited axial length internally in the auxiliary pump 30. The insert member can initially project radially below the inlet 35 and for example by means of a spring force be pressed downwards to a level just above the bottom of the tank well. By
arranging sideways directed intake openings in the insert member the insert member can if necessary be arranged rather tightly up to the bottom of the tank well.
In a third embodiment, as illustrated in Fig. 6, an auxiliary pump 30' ' is shown of corresponding external contour to that which is shown in Figs . 3 and 5 , but with a somewhat differing wall thickness and somewhat differing internal contour. The auxiliary pump 30'' is made of a plane steel plate, which is pressed to the part-conical contour illustrated, so that a part-conical sleeve is formed of essentially uniform wall thickness. In the finally fashioned sleeve, such as shown in Fig. 6, a number (for example six or seven) flow-through openings 40'' (of which only two are shown in Fig. 6) are drilled in an obliquely upwardly and outwardly directed direction. Provision is made for the upper edge portion 40a' ' of the bores to be flush with an internal guide face 36a' ' on impeller 15 of the main pump. More specifically the upper peripheral edge portion 30a' ' of the sleeve, that is to say the peripheral edge portion just above the openings 40'', is fixed inserted into and fast welded to an annular cavity 36'' in an external guide face 36b'' on impeller 15 of the main pump.
The auxiliary pump 30'', which is in the form of said sleeve, is shown in Fig. 6 in a permanently integrated condition in impeller 15 of the main pump. A cup-shaped portion 15'' known per se on the impeller 15 projects a distance downwardly into the sleeve or the auxiliary pump 30'' and forms internal guide means in the upper half of the passage 39 and defines an upper chamber 38, which has a decreasing cross-section heightwise in the same.