US3824364A

US3824364A - Apparatus for heating a viscous liquid

Info

Publication number: US3824364A
Application number: US00367867A
Authority: US
Inventors: J Cachat
Original assignee: Park Ohio Industries Inc
Current assignee: Park Ohio Holdings Inc
Priority date: 1973-06-07
Filing date: 1973-06-07
Publication date: 1974-07-16
Anticipated expiration: 1991-07-16
Also published as: CA977833A

Abstract

An open ended tubular heating unit is provided which is comprised of a stainless steel tube surrounded by an induction heating coil which is disposed in magnetically coupled relationship with the tube. The tube and coil are encapsulated in insulating material, and the unit is submersible in a viscous liquid such as oil which is disposed in a vessel and the temperature of which liquid inhibits pumping thereof from the vessel. The unit is adapted to be supported in suspension and the coil energized to inductively heat the stainless steel tube, whereby the liquid inside and surrounding the unit is heated to elevate the temperature thereof and reduce the viscosity thereof. A driven impeller may be provided within the tubular unit to impel liquid flow therethrough, and a driven pump may be provided within the unit to pump the heated liquid from the vessel.

Description

[11] 3,824,364 [451 July v16, 1974 2,881,301 4/1959 Bowman....................,.,.. 3,031,106

[54] APPARATUS FOR HEATING A VISCOUS 4/1962 H0oker...........

LIQUID 3,053,959 9/1962 Christmann.........fff..........219/1o.49

[75] Inventor: John F. Cacliat, Cleveland, Oliio Assignee: Park-Ohio Industries, Inc., I

Primary Examiner-A. Bartis Cleveland, Ohio Attorney, Agent, 0r Firm-Meyer, Tilberry & Body a w mm APPARATUS FOR HEATING A VISCOUSLIQUID The present invention relates to the art of induction heating and, more particularly, to a device for elevating the temperature of a viscous liquid to facilitate pumping thereof.

Viscous liquids such as oil are often stored in tanks and other vessels which are exposed to temperature conditions which lower'the temperature of the oil to the extent that free pumping of the oil is most difficult, if at all possible. For example, a vessel such as an oil tanker is adapted to store thousands of gallons of oil for transportation from one location to another across a waterway. Water and/or air temperature conditions can cause the oil temperature to drop during the transportation period to a level which inhibits freepumping of the oil from the vessel when it reaches its destination. Temperature conditions in cold climates and during winter months can similarly affect oil contained in storage tanks and the like. Further, in the event that a vessel such as an oil tanker sinks before reaching its destination, it becomes desirable to salvage the oil carried therein. While the air and/or water temperatures on the surface vmay not have an undesirable affect on the viscosity of the oil, the temperature of the water at the depth of the sunken vessel is likely to be sufficiently low to adversely effect the viscosity.

To achieve free pumping of the oil under such conditions it is necessary to elevate the temperature of the oil in order to lower the viscosity thereof. lt has been the practice heretofore to use steam to raise the temperature of the oil so that it can be freely pumped. The use of steam together with the necessary devices and arrangements for transmitting the steam to the vessel entails considerable expense both in time and cost of equipment. Further, once the temperature of the oil has been sufficiently elevated to enable pumping thereof, such pumping must be achieved by apparatus separate from that employed to generate and direct the steam to the oil vessel. It will be appreciated, therefore, that the pumping of oil from a vessel or the salvaging of oil from a sunken vessel in accordance withprior practices is at best a cumbersome operation.

ln accordance with the present invention, a device is provided which enables a moreexpeditious and economical heatingof viscous liquids in a vessel to elevate the temperature thereof to a level at which the liquid effort and in a minimum amount of time. More particuv larly, the device is adapted to be lowered such as by a support cable into the vessel and submerged in the liquid, and once so disposed the device is ready for operation.

Basically, the device of the present invention is tubular and comprised of an inductively heatable metal tube submersible in the liquid and open at its upper and lower ends to provide for liquid flow therethrough. In accordance with one aspect of the present invention, the liquid within and immediately surrounding the tube is heated to elevate the temperature of the liquid. Convection current flow causes the heated liquid in the tube to rise and flow out the upper end thereof and colder liquid to enter the lower end of the tube.

In accordance with another aspect of the present invention, a motor driven impeller is disposed within the tube to facilitate circulation of liquid through the tube from one end thereof to the other. Such forced circulation of heated liquid from one end of the tube and cold 'liquid into the other endof the tube enables the pro- Inaccordance with a preferred embodiment, the tube is cylindrical and is stainless steel. The tube is surrounded by an induction heating coil which is disposed invmagnetically coupled spaced relationship with respect to the tube. The tube .and coil are encapsulated in insulating material and the resulting tubular unit is adapted to be suspended in the liquid with its axis extending generally vertically. A support cable arrangement or the like is provided at one end of the tubular unit to facilitate raising,v and lowering the unit into the vessel. The support cable extends to a working location remote from the vessel and at which location the power supply for the coil and other operating equipment for the unit is disposed. It will be' seen, therefore, that the heating device .can readily be elevated and lowered with respect to a liquid vessel and that nothing more is required to place the device in readiness for operation beyond locating the device in the liquid vessel.

An outstanding object of the present invention is the provision of an induction heating device submersible in a viscous liquid and operable to elevate the temperatureof the liquid to a level which enhances pumping of the liquid from the vessel.

Another object is the provision of an induction heating device of the foregoing character which is adapted to be lowered into and raised from a liquid vessel from a location remote from the vessel and controlled from the remote location to facilitate the heating and circulating of liquidin the vesselv relative thereto.

A further object is theprovision of a device of the foregoing character which is of tubular construction yto facilitate the flow of liquid therethrough and which is provided .with a driven impeller to impel liquid flow therethrough.

Still another object is the provision of a device of the foregoing character which is provided with a pump for pumping the heated liquid'from the vessel to the remote location. y

Yet another object is the provision of a device of the foregoing character which enables the heating and removal of viscous liquid from a vessel in a more expeditious and economical manner than heretofore possible.

The foregoing objects, and others, will in part be obvious and in lpart more fully pointed out hereinafter in conjunction with the description of the accompanying drawing wherein preferred embodiments of the invention are depicted, and in which:

FIG. 1 is a sectional elevation view of a heating device made in accordance with the present invention;

FIG. 2 is a cross-sectional-view of a preferred conductor 4arrangement for transmitting power to the induction heating coiliof the device, the vsection being .along line 2 2 in FIG. 1;

. cable can be elevated and lowered from such location wherein the showings are for the purpose of illustrating preferred embodiments of the invention only and not for the purpose of limiting the invention, a heating device is illustrated in FIGS. 1-3 which is comprised of a metal tube 12 surrounded by an induction heating coil 14. Preferably, tube 12 is cylindrical and is a stainless steel tube having an outer diameter of approximately ten inches and a wall thickness of approximately l inch. Coil 14 is insulated from tube l2 by suitable refractory insulating material 16 which is non-flamable and capable of withstandingy a temperature of atleast 1,000F.' Any suitable refractory Y insulating material y can be used, one suitable material being glass impregnated mica. Preferably, both coil 14 and tube 12 are embedded in insulating material 16 in a manner l whereby the inner and outer surfaces of the heating device and the opposite ends thereof are vdefined by such insulating material.

Heating device 10 is adapted to be lowered and raised relative to a vessel in which viscous liquid to be heated is disposed. Such a vessel is not illustrated, but it will be appreciated that the vessel will have or will be provided with an .opening of sufficient size for the heat'- ing device to be introduced and removed from the vessel. Heating device 10 is adapted to be displaced relative to such a vessel by a support cable arrangement interconnected with the heating device in any suitable manner. In the embodiment illustrated in FIG. l, one end of the device is provided with a metal support plate 18 including a central portion 20 and legs 22 extending radially therefrom and having outer ends extending through insulating material 16 and suitably interconnected with tube 12. Suchin'terconnection can, for example, be defined by riveting the outer ends of legs 22 to tube 12 and, preferably, insulating plates 23 are disposed between the legs and tube to thermally insulate support plate 18 from tube 12. Legs 22 are each provided with lan eyelet component 24 adapted to be interconnected with a suitable support cable arrangement such as that provided by cables 26 in the embodiment illustrated in FIG. l. Cables 26 can be connected together at a point axially spaced from the end of the such as by hand, or by a winch or the like provided at the remote location. The remote location may be defined, for example, by a platform adjacent a liquid storage tank, or by a recovery ship in the event that the liquid to be heated is disposed in a submerged vessel such as an oil tanker'. Further, such remote location might be defined by a dock or the like at which a vessel such as an oil tanker is docked for unloading. In any event, it will be appreciated that the heating device when disposed inthe vessel containing the viscous liquid will be spaced a considerable distance from the remote location from which the device is manipulated.

The power'supply 42 for energizing the coil will also be located at the remote location and thus will be considerably spaced from the heating device. Anysuitable alternating current power supply may be provided at the remote location for the purpose of energizing the coil. In order to reduce line losses in delivering power to coil 14, the coil and power source preferably are interconnected by a lplurality of flexible conductors connected transversely with respect to one another. In the embodiment illustrated, end 30 of coil 14 is connected by coupling device34 to a pair of conductors 38 and, similarly, end 32 of coil 14 is connected by coupling device 36 with a pair of flexible conductors 40. The pairs of

conductors

38 and 40 extend from heating device l0 to a common juncture such as the point at which cable 28 is connected to cables 26. At this

point conductors

38 and 40 extend parallel to one another along cable 28 and are arranged as illustrated in FIG. 2. More particularly, conductors 38 are of one polarity and conductors 40 are of the opposite polarity. The specific arrangement illustrated in FIG. 2 provides forreducing line losses in transmitting current from power source 42 at the remote location to coil 14. It will be appreciated that pairs of

conductors

38 and 40 will be separated at the remote location for connection of correspending ones of the pairs of conductors to opposite sides of power supply 42. y

Heating device 10 as thus far described is adapted to be lowered into a vessel containing viscous liquid such as oil which is ata temperature below that at which the oil can be readily pumped. The device is supported in the vessel with its axis in a generally vertical disposition. Once the heating device is submerged in the liqheating device by a single cable 28 extending to the remote location from which the heating device is raised and lowered relative to the vessel in which it is to be employed. u

Coil 14 preferably is a continuous conductor of solid cross section having convolutions l5 axially vspaced apart along the length of tube l2. The coil includes

end portions

30 and 32 provided with

coupling device

34 and 36, respectively, for connecting the coil with a suitable source of alternating current, as set forth more fully hereinafter. Coil ends 30 and 32 extend through corresponding openings in tube 12, which openings are lined with sleeves 33 of insulating material.

Support cable28 extends from heating device l0y to a remote location and it will be appreciated that the uid, coil 14 is energized from power supply 42 and the current flowing through the coil causes steel tube 12 to be inductively heated. Theheat from tube 12 is conducted to the viscous liquid within and surrounding de vice l0, whereby the temperature of the liquid is elevated. As the temperature of the liquid increases, the

liquid will circulate in a well known manner by convection, whereby the warm liquid will move upwardly through the tubular unit and colder liquid will enter the lower end of the unit, as indicated by the arrows in FIG. 1. In this manner, the temperature of the liquid in the vessel is 'gradually increased in that the warmer liquid rises in the vessel and the colderliquid descends therein.

The extent to which the entire volume of liquid in a given vessel can be heated to elevate the temperature thereof to the desired level depends, of course, on the size of the vessel, the surrounding temperature conditions and the extent to which circulation of the liquid relative to the heating device is achieved. Accordingly,

.it may be ,desirable in certain instances to provide v means within the. heating device to positively circulate liquid therethrough so as to increase the amount of liquid that can be heated'during a given period of time. Such positive circulation of the liquid is also advantageous in assisting the transfer of heat from the metal tube to the liquid. Any suitable liquid circulating arrangement may be provided for this purpose and, in the embodiment illustrated in FIG. 1, such circulation of the liquid is achieved by a motor driven impeller disposed within heating device 10.

As illustrated in FIG. 1, the motor driven impeller bodiment illustrated, the pump is a centrifugal pump in which impeller 62 receives fluid centrally thereof and displaces the fluid in a radial direction. The pump has an inlet opening 66 for fluid within the heating device and an outlet 68 extending through a suitable opening therefor in support plate 18. The pump is mounted on unit includes a rotatable blade 44 mounted on the drive shaft of electric motor 46. It will be appreciated that motor 46 is potted or otherwise made fluid tight and impervious to the liquid to be heated. Motor 46 is supported by support plate 18 and, for this purpose, the housing of the motor may be suitably interconnected with center portion 20 of plate 18 such as by a plurality of studs 48 extending through corresponding apertures in center portion 20 and into threaded engagement with apertures in the motor housing. Preferably, the motor housing is insulated from support plate 18 such as by interposing a plate S of insulating material between the motor housing and support plate. Motor 46 is adapted to be energized through a conductor 52 extending from the motor to the remote location for interconnection with a suitable power supply therefor. Motor 46 may be operated intermittently or continuously to rotate impeller 44 to impel liquid through the heating device from one end of tube 16 toward the other. Moreover, the rate at which the liquid is impelled through the heating device by impeller 44 can be controlled such as by intermittent operation of the motor or, for example, by providing for motor 46 to'be a variable speed electric motor. If theheating device is suspended in the liquid so that 4the axis-of the metal tube l2 is substantially vertical, it is preferred to provide for the impeller to move the liquid through the heating device from the lower end thereof toward the upper end thereof so as to supplement the aforementioned flow of liquid by convection through the heating device.

When heating device l0 is employed either alone or in conjunction with a fluid circulating impeller, the liquid in the vessel is heated to elevate the temperature thereof to a level which provides for the liquid to be readily pumped from the vessel. Such pumping can be achieved by a suitable pump unit introduced into the vessel independently of the heating device. Heating device 10, however, advantageously provides for pumping to be achieved by a pump unit physically associated with the heating device, thus to eliminate the necessity of introducing two separate units into the vessel to achieve heating and removal of the liquid from the vessel. Such a heating and pumping arrangement is illustrated in the embodiment of FIG. 4, wherein a heating unit is depicted which corresponds in structure to the heating unit illustrated in FIG. l. Accordingly, like numberals are used in FIG. 4 to designate components of the heating device corresponding with the 'components of the device in FIG. 1.

In the embodiment illustrated in FIG. 4, a pump 60 is mounted on support plate 18 in place of the motor driven impeller. Pump 60 includes an impeller 62 disposed within the pump housing and adapted to be driven by a motor 64 disposed within the housing. Any suitable pump device may be employed and in the ernuid from the vessel to any desired destination point `such as the remote location.

o As in the embodiment illustrated in FIG. l, the energization of induction heating coil 14 inductively heats steel tube 12 to heat the viscous liquid in the vessel and cause circulation thereof by convection through the heating device in the direction of the arrows in FIG. 4.

' When pump motor 64 is energized, impeller 62 is rotated to draw heated liquid within the heating device into the pump and through outlet 68 to conduit 72 leading to the delivery location.l Accordingly, the embodiment illustrated in FIG. 4 provides a unitary heating and pumping device which enables the temperature of the viscous liquid to be elevated sufficiently for the liquid to be freely pumped and for the heated liquid to be pumped from the vessel. In order to coordinate the pumping rate with the heating rate of the heating device, motor 64 may be operated intermittently or may be a variable speed electric motor.

In the embodiment illustrated in FIG. 4, operation of pump 60 will to some extent induce liquid flow through the heating device from the lower end thereof toward the upper end thereof by the suction created at the pump inlet. This induced flow supplements the circulation of liquid resulting'from flow thereof by convection. While circulation of the liquid by convection and induced flow may be adequate, it'may be desirable in certain instances'to supplement the liquid flow by a positive circulating device in order to increase the rate at which the liquid is heated and accordingly the rate at which it can be pumped from'the vessel.

An arrangement suitable for the foregoing purpose is illustrated in the embodiment of FIG. 5 of the drawing. In FIG. S, heating device 10 corresponds in structure to the heating devices illustrated in FIGS. 1 andv 4, whereby like numerals are employed in FIG. 5 to designate corresponding components of the heating device. In the embodiment illustrated in FIG. 5, heating device 10 is provided with both a liquid pump and a liquid impeller unit. More particularly, a motor-pump unit is mounted on support plate 18 in a manner similar to that described hereinabove in connection with the motor and pump units in FIGS. l and 4. Motor-pump assembly 80 includes a pump 82 and a drive motor 84- interconnected as a unit in a well known manner so that the motor, when energized, operates the pump. Motor 84 includes a drive shaft 86 extending from the lower end'thereof, and an impeller 88 is mounted on drive shaft 86 for rotation therewith. Pump 82 has an inlet 90 for heated liquid within the heating device and an outlet 92 to which a flexible conduit 94 is attached. Con- :duit-19,4, ofcourse, .leads ipoi'nt forthe liquid, such as the remote location;y

lustrative of the present tion..

Energizati'on of: motor 84 causes liquidg'within .the

I heating device {to be purnpedfrom` the vessel tothe destination point and causes "liquid ftov bev circulated to av delivery Ior y.destination i being submersible in `sir-aid liquid, .m eal1` 5. t0 Support lsaid device in` saidfliquid froma location remote from said vessel,andmeansf to connect said coil means acrossa throughthe heating device by impeller'88.j Whilefthe f .pump `'and impeller are illustratedas `4beingdriven by a be-appreciated thatl'where'a ysingle driveniotorfis employed suitable gear box arrangements'can ybe usedto provide for the'pumpl and impeller' to be operatedlat different rotationalspeeds.

.t -ln the embodiments described hereinabove, the heating'device is suspended by the support cable within the liquid containing vessel with. the axisiof the heating de- ,vice in a generally vertical disposition. Moreover, the device as llustrated would be suspended abovetlie botjltornfwall-'or the like of the-vesselingorder ,tofacilitate "circulation of the viscous liquid through't'h'e lheating de'- f .source of alternating :current 'at saidlocation: for said 'coil meanswhen @energized to inductively heat s aid :tubular, lmerriber to `raise the temperature of the-liquid.

' 12'.' The .device according 'toclainr l, andfurther in cluding a1 motor driven impel-lersupported by said tuspacedfromtheinner surface 'of said passageway to impart movement 'to' Said :liquid from' one endthereof l, toward the' other, andisupportrnensinterconnecting vice. lt will'be appreciated'however, that in these arrangements the bottom' endof the heating devicecould arrangement'which would venable the vdevice to rest on v be provided with suitable axially extending support leg saidmoto'r drivenrimpellerfarid said' tubular member. 3; The device according to claim l,"and furtherincludihg motor driven'pump means 'supported by said tubularmernber -withinj saidpas's'ageway, said pumpmeans being radially spaced inwardly from'the inner surface of'saidlpassageway, 'and support means interconnecting lsaid pump. meansand saidtubular'member.

. pump rneansfhas an inleffr'liquidwithin said passageway` and an "outlet, and 'conduit means connected to said outlet for delivering pumpedl liquid from said vessel. l, 5. The :devicel accordingto-claimA, and a motor driven impeller supported-within said -passagewaygby' the bottom surface of ,a fvesselwithout hindering free heating' device. Further, while considerable emphasisy has been placed hereinonthe `fact that'theheatingdecirculationof the liquidy into the bottom'endof `,they

said ,tubular vmernber to impel liquidlilow through said device, said `rnotort d r'iven impeller being radially spaced inwardly `.from the inner surface `o f said-,passagevice" is supportedwithits axisfin ajgenerally vertical dist position to facilitatenatural circulation; of liquid therethrough. by convection,l it will beap'preciatedthati in those'embodiments'in which a pu'mp'rand/or' impelleris employed that the heating device could b e4 disposed within theliquidgwith'its axisy ina` generally horizontal disposition. `ln this respect, rthe pumpand/or impeller providefor circulation of theliquid .through the heating device `to Aachieve l`progressive vheating ofthe liquid in the vessel. It w ill be appreciated to` thatv many suitable 'arrangementsv can be p rovidedfto `achieve support of vthe unit infafhorizontaldisposition, and that-'many arrangements otherthan the specific support plate `and cable arrangement described herein'fcan' be devisedfor suppo'rtinglthe unitin a vertical disposition.

f j-oJn-indiiction device'i'o'r usein recovering a-'viscous' liquid froma vessel in which the liquid is -at a temperature Which inhibits-pumping of [the liquid from-thevessel comprising, a single cylindrical steel tube ,having axially.,oppo sed open upper and lower ends-,ian induction'heat'ing coilsurrounding the exterior of said tube and-disposed in magnetically coupled relationship therewith, insulating 'material enclosing .said coil and tube and'fllling 'the space between said coil and tube, the portion of saidinsulating material withinv said tube defining anaxialtpa'ss'ageway through said .device,

Asmany possiblelernbodiments of the present invention may be made and as manypossible changes maybe made in the embodiments herein illustratedandde- I scribed, it is to be distinctly understood'tha't the foregoing descriptive matter is to be interpreted merely as ilinvention and not as a limital-laving thus described myl'invention, I claim:

l. A tubular induction heating device foruse inrecovering a v iscousliquid from a vessel `in which theliquid is at a temperature which inhibits pumping of the said device'being'Submersible in said liquid, means for supporting said device in' said liquid from a location remot'e from said vessel and in agenerally vertical disposition, said support means including axially open support arrnmeans extending across said passageway and connected tofsaid steel tube adjacent said upper end` thereof,l andmea'nsfor connecting said coil across-a source of alternating current at said locationfor said coil when energized toinductively heat said steel tube liquid from the vessel comprising, alsingle tubular metal member-having axially opposed-open ends, induction heating coil means surrounding the exterior of v said member between said opposite ends and disposed in magnetically coupled spaced relationship therewith, insulating material enclosing saidcoilfmeans and tubular metal member and tillingthe space between said coil means and tubular member, the portion of said insulating material within said'tubular member defining `an axial passagewaythrough said device, saidldevice l65v f `opening and a liquid outlet, and condult means connected to said outlet fordelivering pumped liquid from -to raise the temperature of liquid within said passageway and promote circulation of liquid in the direction from said lower end of the tube toward'said upper end.

.7 The device according to claim 6, and motor driven impeller means connected to said support arm'means and -supported in said passageway adjacent said upper end of said tube to impel liquid'through said passageway in said direction.`

t 8. The device according to claim 6, and motor driven I pump means connected to said support arm means and supported in said passageway adjacent said upper end of vsaid tube,l said pumpmeans having a'liquid inlet said vessel. i

passageway in said direction, said pump having an inlet port for liquid and an outlet port, and conduit means connected to said outlet port for delivering pumped liquid from said vessel.

* =l =l= ik

Claims

1. A tubular induction heating device for use in recovering a viscous liquid from a vessel in which the liquid is at a temperature which inhibits pumping of the liquid from the vessel comprising, a single tubular metal member having axially opposed open ends, induction heating coil means surrounding the exterior of said member between said opposite ends and disposed in magnetically coupled spaced relationship therewith, insulating material enclosing said coil means and tubular metal member and filling the space between said coil means and tubular member, the portion of said insulating material within said tubular member defining an axial passageway through said device, said device being submersible in said liquid, means to support said device in said liquid from a location remote from said vessel, and means to connect said coil means across a source of alternating current at said location for said coil means when energized to inductively heat said tubular member to raise the temperature of the liquid.

2. The device according to claim 1, and further including a motor driven impeller supported by said tubular member within said passageway and radially spaced from the inner surface of said passageway to impart movement to said liquid from one end thereof toward the other, and support means interconnecting said motor driven impeller and said tubular member.

3. The device according to claim 1, and further including motor driven pump means supported by said tubular member within said passageway, said pump means being radially spaced inwardly from the inner surface of said passageway, and support means interconnecting said pump means and said tubular member.

4. The device according to claim 3, wherein said pump means has an inlet for liquid within said passageway and an outlet, and conduit means connected to said outlet for delivering pumped liquid from said vessel.

5. The device according to claim 4, and a motor driven impeller supported within said passageway by said tubular member to impel liquid flow through said device, said motor driven impeller being radially spaced inwardly from the inner surface of said passageway.

6. An induction heating device for use in recovering a viscous liquid from a vessel in which the liquid is at a temperature which inhibits pumping of the liquid from the vessel comprising, a single cylindrical steel tube having axially opposed open upper and lower ends, an induction heating coil surrounding the exterior of said tube and disposed in magneticaLly coupled relationship therewith, insulating material enclosing said coil and tube and filling the space between said coil and tube, the portion of said insulating material within said tube defining an axial passageway through said device, said device being submersible in said liquid, means for supporting said device in said liquid from a location remote from said vessel and in a generally vertical disposition, said support means including axially open support arm means extending across said passageway and connected to said steel tube adjacent said upper end thereof, and means for connecting said coil across a source of alternating current at said location for said coil when energized to inductively heat said steel tube to raise the temperature of liquid within said passageway and promote circulation of liquid in the direction from said lower end of the tube toward said upper end.

7. The device according to claim 6, and motor driven impeller means connected to said support arm means and supported in said passageway adjacent said upper end of said tube to impel liquid through said passageway in said direction.

8. The device according to claim 6, and motor driven pump means connected to said support arm means and supported in said passageway adjacent said upper end of said tube, said pump means having a liquid inlet opening and a liquid outlet, and conduit means connected to said outlet for delivering pumped liquid from said vessel.

9. The device according to claim 6, including a pump, an impeller and drive means therefor in said passageway and radially spaced from the inner surface thereof, said support arm means supporting said pump, impeller and drive means within said passageway, said impeller being operable to circulate liquid through said passageway in said direction, said pump having an inlet port for liquid and an outlet port, and conduit means connected to said outlet port for delivering pumped liquid from said vessel.