US2892416A - Conveyance of liquids through pipelines - Google Patents

Description

, June 30, 1959 Filed Dec. 2, 1955 I R. ALEXANDER CONVEYANCE OF LIQUIDS THROUGH PIPELINES Sheets-Sheet 1 June 30, 1959 R E A R 2,892,416

CONVEYANCE OF LIQUIDS THROUGH FIPELINES June 30, 1959 R. ALEXANDER CONVEYANCE OF (LIQUIDS THROUGH PIPELINES 4 Sheets-Sheet 3 Filed Dec. 2, 1955 I W a!!! lllllll Ilfllr June 30, 1959 R ALEXANDER 2,892,416

CONVEYANCE OF LIQUIDS THROUGH PIPELINES Filed Dec. 2, 1955 4 Sheets-Sheet 4 having anontletcomml nicatin with ,a.lower pa U it S e te 2,892,416 .CONVEXANGE or LIQUIDS 'THLRQUGH Rolf Alexander -Montreah Quebec, Canada A i'sa ian- Breann {Seria1 Na 55- =73 Claims priority, application CanadaDeeemQber 13,-154 melamoar -.23

Th s i vention relates to metho o onvey ng a q h o gh- .p p l n ,ran zt taepara rfo car y vout this method.

gasoline, and-for this reasonwthe,invention, will fly exemplified: below, with reference tosuch -produotsgwhieh will be referred. to hereinjafter,generally as .oil, 311-. .zthough,,as will he more fully explained later, theinvention in its broadest aspect his applic b t .the sq v an of any liquid .suitable -ro passag sth pug ap pelins- The term p peline is s mi y. nt nded: denot iany conduit however long or short it may be.

In the Past meeonv yanceo .Q nhIQu n Wl Qs-JA quired h ping mach nery t upply th tneqe s rv Pre .sure. .irThepresen't invention. entirely avoids any need for pumps ,and relies Lsolely ,on pressure generated on "the formation. otv p "pr -used. e e by. eatin th oil itself or some other liquid augh; as. water.

:In one preferred method-pf operation -expressed in broad terms, the inventioneonsists of amethcrdpfponveying a liquid through a pipeline, eomp ising-eoniiningp uantity. of therl qui t b conv ye interior of ,said ,vessel, and ;wit h .lthe p ipelipe, pro

the surface of said liquid whereby a to; fierce, sushthrough such outlet and through the pipeline, supplying ..a: further quantity. ofsaid lignidtqa secgnirfilp i arranged at; least inpar above theleveI oflsaidputlet, establishing afirst connection be iweenzthein fi i 0 t first vessel andflthe interior of the; secondvessel, (advantageously between upperpartsofsuch'ginteiiors) whereby to communicate the vapour pressure .to said second vessel,

establishing a second connection between theainterior .of

said second vesseLand the-interior .ofthe first tvessel;(ad-

vantageously between lowerparts .of such interiors) whereby to allow-the liquid in saidseoondlvessel :toxfiow under gravity-into theqfirst vessehsuch connectionsnbeing established before the levelwin 's'aid first.vessel falls below the level of said outlet, .interrupting.said connections to isolate said secondvessel.from the.pressure.inithe first vessel and. continuing. .toprovide a further quantity of vapour under pressure-in the; first vessel above-{the surface of the liquid therein.

It is preferred that thevapourremployedahe a vapour of the liquid or .oil being conveyed. For thislpurposeqlit is preferred to generate the vapour in the firstyessel by heating such. vessel sufiicient ly. to cause aportion oft-the liquid therein. to evaporate-and form abody ofva'pour under pressure above the surface .ofsuch liquid this .application of: heat to :the-afirst. vessel being maintained ,to

ensure continuation of. thisevaporatiqn.process each time rate boiler. Afteritspassage intothe second vessel on establishment of the connections referred to above,.the

steam will rcondense and flowback into the first vessel --duringthenext operation there to be reheated and .re- 5 .ev-aporated. This method of operationwill be more (fully explainedbelow.

Theinvention alsorelates toapparatus for carrying out these, methods, and .one convenient form of such .ap-

paratus is illustrated diagrammatically and by way 'of lexamp'le. in the accompanying drawings, in whieh:

:Figure 1 shows diagrammatically the layout of the apparatus;

' Figure 2 is a-fragrnent. of the apparatus shown in Figure' 1., demonstrating the condition at a later stage in .the process; and

Figure 3 is ,a similar fragment tothat of Figure 2, showing the conditions at afurther stage in the process.

1 1 Figure :4 is a similar fragment to that of Figure 52,

showing a modifiedversion of theapparatus; Figure Sis another fragment of the apparatus, illustra tingastill:further.modification;

Figure 6.is an enlarged fragmentary view of a float valvejtor use in the apparatus of Figures 1 to .5; vand "Figure 7 is a diagram illustratinga typical control circuit.

The apparatus illnstratedconsists of alcylindricaldischarge e'ssel..1-.having an outlet pipe Zextending from .a point near thebottom thereof, this. pipe 2 beingiconnected to apiplinetnot shown). The dischargevessel 1;is

otherwise closedexcept for a. pair ofpassages =3 and ,4 which establish connections between such vessel 1 .and

each of one or several supply vessels 5. In :Figure 1 two such supply vessels .5, identical in character, are

shown. Inlpracticeany required number of such supply I vessels 5 may be employed, this depending upon the rate at whichsuch vessels can convenientlybe recharged.

Only one such .supply vessel .5 need be v,employedifit .can:be recharged as quickly as thedischargevessell is emptied, as will become more clearly apparent fromthe subsequent description of the operation of the apparatus.

Each passage 3 extends between .an upper part of the :d-ischargevessel land an upper. .part of a supply vessela5, avalve 6 whereby communication between the two: vessels maybe established or interrupted as required being arranged at a convenientflpoint along such passage; while each passage 4 extends between a lower part. of. thedischarge vessel 1 and-a lower part of a supply vessel :5, a valve 7 whereby this communication between the two vessels may be established or interrupted as required being arranged at a suitable point in such passage 4. Each supply vessel 5 is otherwise closed except for ,anJinlet passage 8 extending to and fed from a mainreservoir Itank 9, a valvelllbeing arranged in such passage 8;for con'troLof the flow of liquid therethrough.

The discharge vessel 1 is arranged to beheated by a number of burners 11 which may conveniently be fired withoil when oil is. the liquid being conveyed. .For this purpose a branch pipe .12 is shown. extendingfrom the 'pipe- 2 to a. tank 13 from-which a controlled quantity of oilpasses to the burners 11. A non-return valve shown as a simple flap-typevalve 14 is provided in the pipe 2.

To consider the operation of this system letv it-be assumed that initially there is a quantity of oil in'the;dis- 'chargevessel 1 extending up to the level v15 shownin Figure 1 and that the left hand supply vessel 5 contains a further quantity of such oil. The burners 11 .are started and they beat the oilxin the discharge vessel "1 ausing some of the more volatile fractions of such oil to evaporate and form a body of vapour at the ,topof such vessel 1. The valves 6 and 7 are closed at this time, ;.so :that. such pressure is contained in the vessel, 1. .;pressure, which may in practiC finally reach ayalue of the order of ten atmospheres, acts downwardly on the surface of the oil in the vessel 1 thus causing a quantity of such oil to be discharged along the pipe 2, as indicated by the arrows 16 shown in Figure 2, until an oil level shown at 17 in Figure 2 is reached.

It is possible to detect when this level has been reached visually, but it is preferred to achieve automatic operation by providing some form of level-sensitive means, such as a float. A typical such float-type device 18 is shown in Figure 6 and consists of a tube 32 secured to the side of the discharge vessel 1 and having openings 33 top and bottom so that the level of the liquid inside the tube 32 will be the same as in the body of the vessel 1. A float 34 travels up and down the tube 32 in accordance with the level of the liquid and in its lower position bears on a stop 36 mounted in the centre of a flexible diaphragm 35. On the other side of the stop 36 in a fluidtight chamber 38 the flexible diaphragm 35 carries an electric contact 37 positioned for c'o-operation with a spaced stationary electric contact 37'. It will be obvious that when the level of the liquid falls sufiiciently for the weight of the float to bear against the stop 36, the diaphragm 35 will be deflected downwardly to cause the contacts 37 and 37' to engage. These contacts are connected to electrical leads 39. This form of float device is conventional. The level sensitive means 18 is connected to a control device 19 (see Figure l) which isoperated to open the valves 6 and 7 of the passages 3 and 4extending to the left-hand supply vessel when the oil falls to the level 17. Opening these valves causes the vapour under pressure in the discharge vessel 1 to pass into the top of the supply vessel 5. Substantially the same pressure is, of course, also transmitted through the oil into the lower part of the supply vessel 5, so that the pressure throughout the two vessels becomes equalized. Since the vessel 5 is arranged at a level above the discharge vessel 1, the oil in the vessel 5 is now free to flow under gravity into the discharge vessel 1, until the situation illustrated in Figure 3 is achieved with the level of oil in the discharge vessel 1 again near the top of such vessel as shown at 20, the supply vessel 5 having been drained.

In the apparatus illustrated the bottoms of the supply vessels 5 are shown approximately on a level with the top of the discharge vessel 1. If preferred, the supply vessels 5 may be positioned well above the discharge vessel 1 to promote more rapid flow, or on the other hand there may even be rather more overlap between these' levels than shown in the drawings. In the latter case, the supply vessels 5 will not be fully emptied until the level of oil in the discharge vessel 1 has fallen somewhat. The essential relationship between these levels is that they should be such that transfer by gravity of at least the bulk of the liquid in the supply vessel 5 into the discharge vessel 1 will take place reasonably quickly and that there will be adequate time available for refilling the supply vessel 5, having regard to the number of such vessels employed.

As soon as the supply vessel 5 is emptied, i.e. the Figure 3 condition has been achieved, the valves 6 and 7 may be reclosed and for this purpose further level-sensitive means 21 structurally similar to the level-sensitive means 18 may be provided in each such supply vessel 5. Alternatively, since it is really the level in the discharge vessel 1 that requires precise control, the valves 6 and 7 may be closed in accordance with the operation of level-sensitive means 22 in the vessel 1. Figure 7 shows diagrammatically a typical arrangement of control device 19 operated by the level sensitive means 18 and 22. In this case the control device 19 consists of a valve opening relay 40 and a valve closing relay 41. Electric power is supplied through terminals 42 and 43. Through electric leads 39 the energizing coil of the relay 40 is connected across the supply terminals 42 and 43 in series with the contacts in the level-sensitive means 18. In a similar manner the valve closing relay 41 is connected in series with the contacts in the level-sensitive means 22, across these same supply terminals 42 and 43. Thus, when the level falls to the position shown in Figure 2 and the contacts in the level-sensitive means 18 are closed, the relay 40 will be energized thus closing its normally open contacts and connecting the lead 44 to the terminal 43. Each of the valves 6 and 7 which are conventional motor-driven valves have three electric power leads. The central lead 45 is at all times connected to the power supply terminal 42 and the two outside leads 44 and 46 are connected intermittently as required. When the lead 44 is energized the motors in the valves 6 and 7 are operated to open the valves; when the lead 46 is energized by connection to the terminal 43 the motors in the valves 6 and 7 are driven in the reverse direction to close the valves 6 and 7. It will thus be seen that, when the level-sensitive means 18 operates the relay 40, the lead 44 is energized and the valves 6 and 7 are opened. When the level in the discharge vessel 1 has risen to submerge the level-sensitive means 22, the contacts 37 and 37' in such means 22 will deenergize the relay 41 which is shown in Figure 7 in the energized position. This release of the relay 41 closes its contacts to connect the lead 46 to the terminal 43, thus driving the motors in the valves 6 and 7 to close such valves. This is a conventional manner of operating valves in accordance with liquid level changes. If it is preferred to operate the valves 6 and 7 in accordance with the level in a supply vessel 5, then the valve opening and closing relays 40 and 41 can be similarly connected to the levelsensitive means 21 and 23. As soon as the valves 6 and 7 have been closed by one of such control methods, the emptied supply vessel can be recharged by opening the valve 10, the actuation of all these valves 6, 7 and 10 being achieved automatically through the control device 19 in a manner generally similar to that already 'described in connection with Figure 7. The vapour 'the burners 11 and the pressure of the vapour formed thereby in the top of such vessel causing the oil to continue to flow out through the pipe 2. Since the rate at which the discharge vessel 1 is emptied will often be greater than the rate at which a single vessel 5 can be recharged with a further quantity of oil from the reservoir 9, the second supply vessel 5 is provided, the control device 19 being arranged to operate these vessels alternately. Similarly, if more than two supply vessels are found necessary, they will be operated in sequence.

It is found in practice that there is only a momentary lull in the flow of oil into the pipe 2 on refilling of the discharge vessel 1, the level-sensitive means 18 being adjusted to ensure that an appreciable quantity of oil is left in such vessel to communicate heat to the cold incoming oil. If found necessary, the oil may be subjected to a degree of pre-heating in the supply vessels 5. Moreover, if an especially steady flow of oil in the pipeline is desired, the assembly shown in the drawings may be duplicated, two discharge vessels 1 being provided and arranged to operate out of phase with one another so that one is forcing oil into the pipeline while the other is refilling.

In the apparatus so far described and illustrated it will be observed that the capacity of each supply vessel 5 has been shown as rather less than the capacity of the discharge vessel 1, so that each charge of liquid dis- :Qflsedfroiii? a supplyivssel wiltserve tobring the disehatge vesselifrom the. not quite-empty condition (Fig. *2) to-the notquite full condition (Fig. lor 3) bear ing in dnind that there isa constant outflow of liquid. through itheqpipe .2. Clearly, if the supply 'vessels -.were:.made much smaller than the. discharge vessel, more frequent :filling of the supply vessels would be required in order to r keep the discharge vessel supplied withliquid, al-

though-it may in certain casesbe found. desirable to-add .small quantities of-liquid to the discharge-vessel at comparatively frequent intervals. This would prevent the =leve'l .of liquid. in the discharge vessel from rising or Dialling to theiextreme ends of the vessel, .but would cause it to oscillate instead between agpair of relatively closely spaced intermediate levels. .Such a-method of operatiorr. reduces the extent of fluctuations of temperature and pressure and, therefore, results in a steadier flow from 'theout-let pipe. 'Onthe other hand, it-somewhat icomplicates the apparatus in that it=would be'necessary to use a fairly large number=of small supply vesselsland to providethe means for connecting them in-sequence to the discharge vessel.

mentioned above, .wthe primary application. of, the invention industrially will be to the conveyance, of oil and -.oil products. It is also anticipated that otherindustrial productsusuchmas molasses may be conveyed by such means. Asphaltisalso .a'product -which is sometimes conveyed through pipelines, although it is necessary to mix the asphalt with steamto render it sulficiently fluid -to' travel through a pipeline. 1f the liquid being. transported does not includea sufiiciently volatile constituent to produce the necessary vapour. in the'discharge vessel .1, then a separate supply of a vapour may be used. For example, if akheavyoil from which insufiicient vapour can be obtained isrbeing conveyed', aseparate. supply of steam may he fed to =the'discharge vessel llfrom an auxiliary boiler 30 heated by-burn'ers'31, say through a connection such as shown at 24 in Figure 4. This steam will-then act similarly "to the vapour formed inzsitu .in the method previously described, toforce the oil.through the pipe 2. When thevalves 6 and 7 open, thesteam will pass into the supply vessel 5, and the .fresh supply of oil will run :doWn intothe discharge vessel 1 as before. 'When the v'alveshave been re closed, further steam will be supplied.

"-t-hrou'gh the connection 24; indeed such supply of steam may not have been interrupted. In the meantime the steam that has passed into the supply vessel will condense and will findits way tothe bottomof .such

vessel to pass eventually b ack to-the discharge vessel 1 with the next charge of oil travelling along the pipe 4. This 'water will not mix with the oil and will be evaporated again by the heatapplied to the discharge vessel 1. Thus, a large quantity of the steainwill continue to cycle around the apparatus, although some fresh steam will be needed to compensate for the small quantity of --water that will be carried over with theoil :into the pipe 2. "This trapping of the water-in the oil may necessitate the provision-of means for separating the water from the oil at the receiving end of the pipeline.

is much preferred in most circumstances, because of its conservation of the heat energy imparted to the vapour within the system. Clearly, however, it is not basic .to

the operation of the system that thevapour'allowed to.

charge vessel. could. then be used, such supply vessel constituting, in effect; the reservoir (the vessel. .9. shown in Figure 5). If steam, is the vapour concerned and .it is vented :to atmosphere,..this.less eflicient but somewhat -sirnplifiedmethod .of. operation, in accordance .withthe .invention can .be applied either. when water .is the .liquid .being conveyed along :the pipeline, or. alternatively .when the steamds being 'used toforcealong such pipelinea liquid from which insufiicient vapourcan be obtained byheating, i.e. the system for pumping heavy oil discussed above.

Thus, .in accordancewith [a further method ofoperation expressed in .broad terms, :the invention consists of. a method .of conveying .a. liquid. through a pipeline, comprising confiningasql antity ofthe .liquid to be conveyed -in a closed vessel jhavingan outlet communicating with a lower partof theinterior of said vesseland with the pipeline, providing a quantity of vapourunder pres- ..surein said. vessel above the surface ofsaidliquid where- .by. toforce-.suchliquid through such outlet andthrough the,.pipeline,..supplying a further quantity of said liquid in a secondvesseharranged at least in part above the .level ofs-aid outlet, establishinga passage from the-interior oftheifirst vessel whereby to, allow the vaporpre'ssure in. saidfirst vesselto escape therefrom, establishing a connection between the .interiorof said second vessel and theinterior ofthe ,first, vessel whereby to allowthe liquid ,in said .second. vessel to flow under gravityinto .thefirst vessel, .such passage and connection being established .before .the .level of. the liquid in said first vessel falls .belowthe level of .said o.utlet,,interrupting said passage. and connection to isolate said first vessel and con- :tinuing to provide afurther quantity of vapour under pressure. in the first vessel 'abovethe surface of the liquid there- 111.

It will be observed that by virture .ofthe invention a very simple form of apparatus has been provided for forcing oil .or other liquids .through a pipeline. In particular; the. apparatus has the merit of avoiding pumping machinery, .1and, except for the simple valves and levelsensitive control means, it is entirely devoid of moving parts. This simplicityleads to reduced cost of installation ,andrmaintenancexand, greatly reduces-the need for skilled supervision. The apparatus .does not call for any special features in, the construction of, the pipeline itself, so that it can .be readily fitted to existing in- .60 The closed circuittype of operation describ'ed above stallations.

Furthermore, the apparatus is especially convenient when itis desired .to clean the pipeline. The most satisfactorymethod .ofcleaning a pipeline is to pass steam therealong, and the provision of the heated discharge ves- .se1-in the present apparatus renders the generation of -such steam a relatively simplematter with the existing installation. A suitable connection 25 (Fig. 1) having a normally .closed valve 26 and extending between the upper part of, the heateddischarge vessel and the pipeline may be provided-to facilitate such a cleaning operation.

The heat absorbed by theoil inthe discharge vesselis notwasted, since it serves tolower the viscosity of the .oil and .thus to increase the efi'iciency ,of the pipeline. ,This feature isnot. in itself new, as it has already; been proposed to .heat oil prior to its being pumped along a pipeline. Such heathas, however, been provided ressentially for the purpose ofloweringthe viscosity of the .oil, and noprior methodhas employedthe-pressure of a vapour formed either. .by heating the oil or other liquid to ,beconveyed, or by heatingan auxiliary liquid, to

. force .the mainliquid. along .thepipeline.

:As :in conventional pipelines, booster stations maybe positioned-along along pipe. .Suchybooster .stationsmay be similar to the basicunit alreadydescribed or..may functionmerelytoadd further heat to the oil .to maintain its low viscosity. Once the system has been in opera- 1 vtion for some time all the .parts will havebecome well heated andless heat willrequiretobe added to maintain 7 a fast flow of oil. The economics obtained by use of the invention are so extensive that it may even be found practical to bury or lag the pipeline in cold climates in order to conserve the heat imparted to the oil.

It has previously been considered economically necessary to deparafiinate oils rich in paraffin before conveyance through a pipeline to avoid the parafiin deposits that form in the pipe and gradually reduce its diameter.

The temperature of operation in accordance with the present invention will normally be sufiiciently high, e.g. at least 40 C., to retain the parafiin in liquid state and thus entirely avoid or at least very considerably reduce deposition of parafiin. Even if a certain degree of paraffin deposition is experienced, the simplification in the cleaning of the pipeline afforded by apparatus according to the present invention is expected to avoid the need for such deparaffination of the oil before transportation.

I claim:

1. A method of conveying a liquid through a pipeline, comprising confining a quantity of the liquid to be conveyed in a closed vessel having an outlet communicating with a lower part of the interior of said vessel and with the pipeline, providing a quantity of vapour under pressure in said vessel above the surface of said liquid whereby to force such liquid through such outlet and through the pipeline, supplying a further quantity of said liquid to a second closed vessel arranged at least in part above the level of said outlet, establishing a first connection between the interior of the first vessel and the interior of the second vessel whereby to communicate the vapour pressure to said second vessel, establishing a second connection between the interior of said second vessel and the interior of the first vessel whereby to allow the liquid in said second vessel to fiow under gravity into the first vessel, such connections being established before the level of the liquid in said first vessel falls below the level of said outlet, interrupting said connections to isolate said second vessel from the pressure in the first vessel and continuing to provide a further quantity of vapour under pressure in the first vessel above the surface of the liquid therein.

2. A method of conveying a liquid through a pipeline, comprising confining a quantity of the liquid to be conveyed in a closed vessel having an outlet communicating with a lower part of the interior of said vessel, applying heat to said vessel sutficient to cause a portion of the liquid therein to evaporate and form a body of vapour under pressure above the surface of said liquid whereby to force such liquid through such outlet and through the pipeline, supplying a further quantity of said liquid to a second closed vessel arranged at least in part above the level of said outlet, establishing a first connection between the interior of the first vessel and the interior of the second vessel whereby to communicate the vapour pressure to said second vessel, establishing a second connection between the interior of the second vessel and the interior of the first vessel whereby to allow the liquid in said second vessel to How under gravity into the first vessel, such connections being established before the level of the liquid in the first vessel falls below the level of said outlet, interrupting such connections to isolate the second vessel from the pressure in the first vessel and continuing to apply such heat of the first vessel.

3. A method of conveying a liquid through a pipeline, comprising confining a quantity of the liquid to be conveyed in a closed vessel having an outlet communicating with a lower part of the interior of the said vessel and with the pipeline, heating a second liquid in a boiler sufiiciently to cause a portion of such second liquid to evaporate and form a body of vapour pressure, feeding a quantity of such vapour of the second liquid into said vessel above the surface of the first liquid therein whereby to force said first liquid through such outlet and through the pipeline, supplying a further quantity of said first liquid to a second closed vessel arranged at least in part above the level of said outlet, establishing a first connection between the interior of the first vessel and the interior of the second vessel whereby to communicate the vapour pressure to said second vessel, establishing a second connection between the interior of the second vessel and the interior of the first vessel whereby to allow the liquid in said second vessel to flow under gravity into said first vessel, such connections being established before the level of the liquid in the first vessel falls below the level of said outlet, interrupting said connections to isolate said second vessel from the pressure in the first vessel and continuing to provide a further quantity of said vapour under pressure to the first vessel above the surface of the liquid therein.

4. A method as claimed in claim 1, including the step of recharging said second vessel with a further quantity of said liquid.

5. A method as claimed in claim 1, wherein said first connection extends to the interior of the second vessel from an upper part of the interior of the first vessel.

6. A method according to claim 1, wherein said first connection extends, from an upper part of the interior of the first vessel to an upper part of the interior of the second vessel.

7. A method according to claim 1', wherein said second connection extends between the interior of the first vessel and a lower part of the interior of the second vessel.

8. A method according to claim 1, wherein said second connection extends from 'a lower part of the interior of the second vessel to a lower part of the interior of the first vessel.

9. A method according to claim 3 wherein said second liquid is water.

10. A method of conveying a liquid through a pipeline, comprising confining a quantity of the liquid to be conveyed in a closed vessel having an outlet communicating with a lower part of the interior of said vessel and with the pipeline, providing a quantity of vapour under pressure in said vessel above the surface of said liquid whereby to force such liquid through such outlet and through the pipeline, supplying a further quantity of said liquid to a second closed vessel arranged at least in part above the level of said outlet, establishing a first connection between the interior of the first vessel and the interior of the second vessel whereby to communicate the vapour pressure to said second vessel, establishing a second connection between the interior of the second vessel and the interior of said first vessel whereby to allow the liquid in said second vessel to fiow under gravity into the first vessel, such connections being established before the level of the liquid in said first vessel falls below the level of said outlet, interrupting said connections to isolate said second vessel from the pressure in the first vessel, continuing to provide a further quantity of vapour under pressure in the first vessel above the surface of the liquid therein whereby to continue to force it through such outlet and through the pipeline, supplying a still further quantity of said liquid to a third closed vessel arranged at least in part above the level of said outlet, establishing a first connection between the interior of the first vessel and the interior of the third vessel whereby to communicate the vapour pressure to said third vessel, establishing a second connection between the interior of said third vessel and the interior of the first vessel whereby to allow the liquid in said third vessel to fiow under gravity into the first vessel, such connections being established before the level of the liquid in the first vessel falls below the level of said outlet, interrupting said connections, to isolate said third vessel from the pressure in the first vessel and continuing to provide a further quantity of vapour under pressure in the first vessel above the surface of the liquid therein.

11. The combination of a pipeline and apparatus for conveying a liquid therethrough, said apparatus comprising a first closed vessel having at a lower part thereof an outlet communicating with the pipeline, means operatively associated with said vessel for providing vapour in said vessel, a second closed vessel arranged at least in part above the level of said outlet, a first connecting passage extending between an upper part of the interior of the first vessel and the interior of the second vessel, a second connecting passage extending between the lower part of the interior of the second vessel and the interior of the first vessel, flow controlling valves one in each of said passages, and means for determining the level of liquid in the first vessel, such liquid level determining means being operatively connected to said valves to open said valves when said level attains a predetermined minimum level higher than that of said outlet and to close said valves when said level attains a predetermined maximum level.

12. The combination of claim 11, including an inlet passage connecting the second vessel with a reservoir, a third valve controlling flow along said inlet passage, and means sensitive to the level of liquid in said second vessel effective to open said third valve when the level in said second vessel attains a predetermined low level and effective to close said valve whenever said level attains a predetermined higher level.

13. The combination of a pipeline and apparatus for conveying a liquid therethrough, said apparatus comprising a first closed vessel having at a lower part thereof an outlet communicating With the pipeline, means for heating said vessel, a second closed vessel arranged at least in part above the level of :said outlet, a first connecting passage extending between an upper part of the interior of the first vessel and the interior of the second vessel, a second connecting passage extending between the lower part of the interior of the second vessel and the interior of the first vessel, a flow controlling valve in each of said passages, and means for determining the level of liquid in said first vessel, such liquid level determining means being operatively connected to said valves to open said valves when said level attains a predetermined minimum level higher than that of said outlet and to close said valves when said level attains a predetermined maximum level.

14. The combination of a pipeline and apparatus for conveying a liquid therethrough, said apparatus comprising a closed vessel having at a lower part thereof an outlet communicating with the pipeline, a boiler for heating a second liquid, means for supplying a quantity of vapour of said second liquid formed in said boiler to said vessel, a second closed vessel arranged at least in part above the level of said outlet, a first connecting passage extending between an upper part of the interior of the first vessel and the interior of the second vessel, a second connecting passage extending between a lower part of the interior of the second vessel and the interior of the first vessel, a flow controlling valve in each of said passages, and means for determining the level of liquid in the first vessel, such 10 liquid level determining means being so arranged as to be operative to open said valves when said level attains a predetermined minimum level higher than that of said outlet and being so arranged as to be operative to close said valves when said level attains a predetermined maximum level.

15. A method of conveying a liquid through a pipeline, comprising confining a quantity of the liquid to be conveyed in a closed vessel having an outlet communicating with a lower part of the interior of said vessel and with the pipeline, applying heat to said vessel suflicient to cause a portion of the liquid therein to evaporate and form a body of vapour under pressure above the surface of said liquid whereby to force such liquid through such outlet and through the pipeline, supplying a further quantity of said liquid in a second vessel arranged at least in part above the level of said outlet, establishing a passage from the interior of the first vessel whereby to allow the vapour pressure in said second vessel to escape therefrom, establishing a connection between the interior of said second vessel and the interior of the first vessel whereby to allow the liquid in said second vessel to flow under gravity into the first vessel, such passage and connection being established before the level of the liquid in said first vessel falls below the level of said outlet, interrupting said passage and connection to isolate said first vessel and continuing to provide a further quantity of vapour under pressure in the first vessel above the surface of the liquid therein.

16. The combination of a pipeline and apparatus for conveying a liquid therethrough, said apparatus comprising a first closed vessel having at a lower part thereof an outlet communicating with the pipeline, means for heating said vessel, a second vessel arranged at least in part above the level of said outlet, a first passage extending to atmosphere from an upper part of the interior of the first vessel, a connecting second passage extending between a lower part of the interior of the second vessel and the interior of the first vessel, flow controlling valves one in each of said passages, and means for determining the level of liquid in the first vessel, such liquid level determining means being operatively connected to said valves to open said valves when said level attains a predetermined minirnum level higher than that of said outlet and to close said valves when said level attains a predetermined maximum level.

References Cited in the file of this patent UNITED STATES PATENTS 135,765 Brock Feb. 11, 1873 504,849 Peck Sept. 12, 1893 728,084 Colson May 12, 1903 1,900,656 Munters Mar. 7, 1933 2,300,039 Yeomans et al Oct. 27, 1942 2,412,723 Elliott Dec. 17, 1946 2,669,941 Stafiord Feb. 23, 1954

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