US3021809A

US3021809A - Marine tankers

Info

Publication number: US3021809A
Application number: US725709A
Authority: US
Inventors: Brown Robert Henry
Original assignee: WM Cory and Son Ltd
Current assignee: WM Cory and Son Ltd
Priority date: 1957-04-05
Filing date: 1958-04-01
Publication date: 1962-02-20
Anticipated expiration: 1979-02-20
Also published as: GB892041A; DE1092338B; FR1205334A; FR1205329A; BE566496A

Description

R. H. BROWN MARINE TANKERS F eb. 20, 1962 3 Sheets-Sheet 1 Filed April l, 1958 lhllFLlllr Attorneys' R. H. BROWN MARINE TANKERS F eb. 20, 1962 5 Sheets-She 2 Filed April l, 1958 F/GLS.

By a? Attorney;

Feb. 20,V 1962 R. H. BROWN 3,021,809

MARINE TANKERS Filed April l, 1958 5 Sheets-Sheet 3 nventor @oww um ttorneyg United States Patent O 3,021,839 MARINE TANKERS Robert Henry Brown, Worting, near Basingstoke, England, assigner to Wm. Cory & Son Limited, London,

Engiand Filed Apr. 1, 1958, Ser. No. 725,709

Claims priority, application Great Britain Apr. 5, 1957 7 Claims. (Cl. 114-74) This invention relates to water-borne tankers, particularly ocean-going tankers, for the transport in liquid form at low temperature and approximately atmospheric pressure of substances which are normally in a gaseous state. The gas which comes mainly into question is methane, but the references herein to methane are, wherever the context allows, to be read as references also to like gases which it may be desirable to transport in the liquid state.

Methane liqueties at about minus 260 Fahrenheit (minus 162 centigrade). If, therefore, liquid methane is brought into contact with metal which is at ordinary atmospheric temperature (say 60 Fahrenheit), very rapid evaporation will take place, depending on the amount of heat given up by the metal to the methane and the rate of heat transfer.

This gives rise to a problem in connection with the loading of liquid methane into a marine tanker, and it is an object of the invention to overcome this problem.

According to the present invention, in a marine tanker for the bulk transport in the liquid state at low temperature of methane (or like ordinarily-gaseous substance),

provision is made for introducing into the empty cargo tank or tanks during the period between discharge of one cargo and loading of the next a sufcient small quantity of the liquid methane from a reserve supply to keep the tank or tanks at a low temperature and maintain therein an atmosphere of methane to the exclusion of air.

Thus, the tanker may comprise a plurality of cargo tanks to contain the liquid methane, additional storage means for a relatively small reserve supply of liquid methane which does not form part of the cargo discharged, one or more spray units in each cargotank, and connections between the spray units and the reserve storage means arranged for effecting, throughout the period in which the cargo tanks are empty between the discharge of one cargo and the loading of the next, the spraying of liquid methane from the reserve supply into the tanks in quantity suliicient to keep the tanks at a low temperature and maintain therein an atmosphere of methane.

Preferably, the sprays are located at or near the tops of the tanks and arranged to direct their discharge reasonably uniformly over substantial areas of the internal surfaces at or toward the bottoms of the tanks.

For reasons of economy and other important considerations, an ocean-going methane tanker is preferably provided with large methane tanks each of which may extend across practically the full width of the ship. These tanks will normally be made of a metal such as aluminium alloy. Thus, each tank, because of its size and construction, will have a very large internal surface area, will be made of a good heat conductor, and will have a `large heat-storage capacity.

If a methane tanker having a number of such tanks were to arrive for loading with its methane tanks empty and at an ordinary atmospheric temperature of about 60 F., and the liquid methane were then to be pumped into the tanks in the same way, for example, as oil'is pumped into an oil tanker, the heat diiierential between the tanks and the liquid methane would be so great as to give rise to the evaporation of'a very substantial quantity of methane as it came into contact with each tank.

3,621,809 Patented res. ao, rss2 ice This gaseous methane would therefore be wasted, and could easily lead to the formation of a highly explosive mixture with the air in the tanks. Another important consideration is that the sudden contact between the cold liquid methane and the part of the tank on to which it was directed would set up considerable thermal stresses in the tank which could easily result in fracture of the tank.

ln the arrangement according to the invention, the cargo tanks are not allowed to go up to atmospheric temperature when the cargo is discharged but are kept down at a temperature only slightly above the usual loaded temperature all the while until the next cargo is loaded. in this way excessive methane evaporation when the new cargo is loaded is avoided, and stresses on the material of the tanks are minimised. The risk of gaseous methane in the tanks forming an explosive mixture with air is entirely removed, because air is not allowed into the tanks.

The above and other features of the invention will be apparent in the following description, given by way of example, of one embodiment in accordance'with the invention, reference being had to the accompanying drawings in which: Y

FEGURE l shows in elevation a marine tanker for the transport of methane,

FIGURE 2 is a plan showing the arrangement of the methane tanks in the holds, and

FiGURES 3 and 3A together constitutev a diagram showing the pipework and other plant associated with the tanks, and

FIGURE 4 is a diagram to show the proper relative disposition of FIGURES 3 and 3A.

Referring rstly to FIGURES 1 and 2, the cargo-carrying section of the tanker hull 11 is divided into six sepalong the oreand-aft centre line of the vessel4 are six i.

main cargo tanks 18 to 23 bearing external insulation -80. These main tanks are, for the most part, substantially cylindrical in form with their principal axes vertical, and in general they extend at their widest parts for substantially the whole width of the vessel although tanks 19 and 23 are somewhat less in diameter than

tanks

20, 21 and 22, and the most forward tank 18 is a good deal less in diameter.

The vessel is of turret construction, that is to say it has a main deck at the level 24 and a narrower turret deck above at the level 25. Each of the main tanks 18 to 23 extends up through the main deck at level 24, and, with the exception of the tank 20, the portions of the tanks that protrude above the main deck are as large in diameter as can be conveniently accommodated within the turret structure 26. To this end,

tanks

19, 21, 22 and 23 have stepped-in upper portions 28, 29, 30 and 31, but the forward tank 18, being already relatively narrow, does not need to be stepped-in. Each of the six tanks terminates at its upper end in a narrow neck 27 surmounted by a pump motor housing 32. In the case of the five

tanks

18, 19, 2l, 22 and 23 the narrow tank neck 27 reaches up through the turret deck at level 25 and the housing 32 is situated on said deck, but the tank 20, for reasons which need not be discussed here, is not as high as the other five, having its neck 27 terminating only just above the main deck level 24 and its pump motor housing 32 disposed on the main deck within the turret structure.

Owing to the circular plan form of the main tanks 18 to 23, there is an appreciable space below decks between one tank and the next at opposite sides of the vessel, and in the case of tanks 19 to 23 these spaces be- 3 A. tween are utilised by disposing in them eight additional wing tanks 33 of much smaller capacity bearing external insulation 81. The wing tanks 33 are all cylindrical with their principal axes upright, and are located wholly below the main deck level 24. As will be seen in FIGURE 2, the arrangement of bulkheads between the main tanks 19 to 2,3 is such that each wing tank 33 has its own individual water-tight hold compartment 34, each of the bulkheads i7 branching, as it were,V into two diverging bulkheads 35 to' embrace a Wing tank as it approaches each side of the hull. l

Referring now to FIGURES 3 and 3A, these together show the layout of piping and ancillary equipment associated with the cargo tanks. The proper relative dispositions of FIGURES 3 and 3A are indicated in FGURE 4. It will be seen that the piping affords two methane loading and discharging stations 36 for the Vessel, connecting into a circulating ring main 37 by way of handoperated -valves 38. From the ring main 37 there extend six branches 39 to each of the main cargo tanks 18 to 23, and a further eight branches 40 to each of the wing tanks 33, each of the

branches

39 and 40 incorporating ahand-operated valve 41. Each of the tanks has its own individual discharging pump together with a standby pump of similar capacity 42, and spray unit 43 for filling it, the pumps drawing from the tanks and discharging into the

branch lines

39, 40 by way of hand-operated non-returnv valves 44 while the spray units 43 are used to load liquid methane from shore through the branch lines into the tanks byway of further hand-operated non-return valves 4S.

In addition to the filling and discharging connections, each tank has a quantity-control valve 46 for -determin ing the level to which the tank is filled. In the case of the main cargo tanks 18 to 23 the quantity control is effected through separate branch lines 47 connecting with the ring main 37, but in the case of the small wing tanks 33 the quantity-control valves 46 are connected into the lines feeding the spray units 43. Provision is made for isolating the main cargo tanks in tworgroups of three by hand-operated valves 48 in the ring main37, one between 1 the connections for the branch lines 39 to tanks Ztl and 21, and. another two beyond the connections for the branch lines 39 of the end tanks 18 and 23. There are also hand-operated valves 49 in the quantity-control lines 47 of the main tanks.

Gas lines are provided for removing gaseous methane from the top of every cargo tank and feeding it to a liquefaction plant,v whence it is returned after re-liquefying to the liquid side of the system. Thus there is a gas line S for each ofthe main tanks 18 to 23 and a gas line 51 for eachy ofk thewing tanks 33, with all the gas lines feeding into a common gas main 52, and each of the gas lines S0, 51 incorporates an automatic non-return valve 53. The. main liquefaction plant 54, shown in block form in FIGURE 3A and also shown as to the position it occupies in the ship in broken lines in FIGURES 1 and 2, supplied by the gas main 52, comprises duplicated installations 55 each consisting of a refrigerating unit and a circulating pump. The main liquefaction plant 54 feeds into a liquid line 56 returning to the ring main 37, and the respective iiows through the duplicate installations are controlled by four hand-operated non-return valves 57.

In addition to the main liquefaction plant 54 there is a secondary installation 58, comprising a `further refrigeration unit andy circulating pump, this installation being located toward the aft end of the vessel adjacent the crew accommodation. The installation S has gas main and liquid line connections by way of non-return valves 59 and 6D respectively.

For venting methane gas forming in the liquid lines, connections 61 between the liquid and gas lines are provided, each incorporating a non-returnvalve 62 which opens.y automatically when there is gas present to be vented. Invr theA event of an emergency arising during donnees which more methane gas is being generated that can safely be handled by the liquefaction plant, venting to atmosphere can be carried out through six pairs of mast vents 69, one pair opposite each of the main cargo tanks 18 to 23. Twelve branch lines 7G, two opposite each of the main cargo tanks, extend from the gas main 52 individually to the twelve mast vents 69, and each incorporates an automatic non-return valve '71. When the vessel is in port or under other similar circumstances any excess methane gas may be burnt olf at two flares 63, one at the top or" the foremast 64 and the other on the mainmast 65. Connectionsto the iiares 63 from the gas main 52 are afforded by branch lines 66, 67 incorporating handoperated non-return valves 68.

ln addition to the piping installation described above, the individual hold compartments 11 to 16 and 34 are provided with gas-freeing connections 72, which communicate through lines 73, and by way of automatic non-return valves 74, with the mast vents 69.

As indicated above, loading of a cargo into the main cargo tanks t8 to 23 and wing tanks 33, is carried out through the spray units 43 which each direct their discharge reasonably uniformly over a. substantial area of the door of the empty tank. In addition, these sprays are caused to operate at all times when the tanks are empty between cargoes. In other words, spraying is cornmenced as the discharge of the cargo is completed and is continued throughout the return voyage of the vessel right up until the loading of a new cargo. The rate of spray during the period when the tanks are empty is, however,'considerably less than during loading.

The continuous spray of liquid methane into the tanks when they are empty keeps them at a temperature not v appreciably above the normal loaded temperature and also ensures that no air at all need enter the tanks. Thus, when the tanks are loaded they contain a large amount of liquid methane and a very small amount of gaseous methane above the liquid level, and when the tanks are empty they actually contain cold gaseous methane and a small amount of liquid methane which has been sprayed into them and which is in the process of evaporating. During discharge of the methane cargo, the liquefaction plant is stopped, or almost stopped, so as to allow cold gaseous methane to fill the space in each tank above a gradually-falling liquid level'.

When a cargo is discharged, a relatively small reserve supply of liquid methane is kept in the vessel to enable the spraying of the empty tanks to be carried out, and this reserve supply can be accommodated in one or more of the small wing tanks 33. The gaseous methane generated in excess in the empty tanks is drawn ott' for reliquefaction at the liquefaction plant and the liquid methane returned to the reserve supply. It will be appreciated that, besides the reserve liquid in the wing tank or tanks, the gaseous methane in the empty cargo tanks also forms part of the methane retained on board for cooling purposes.

I claim:

i. In a marine tanker for the bulk transport of liquid methane at low temperature and substantially atmospheric pressure, the combination of a plurality of transverse liquid-tight bulkheads dividing up the cargospace into a plurality of separate main hold compartments, a plurality of externally-insulated main tanks for liquid methane cargo each having a configuration that is mainly of upright cylindrical form and occupying at its Widest part substantially the whole available width of the vessel, said tanks being disposed in a closely-spaced row one in each of the hold compartments with their upright axes intersecting the fore-and-aft centre line of the vessel, at least Aone additional insulated storage tank for a relatively small reserve supply of liquid methanev which does not form part of the cargo discharged, a liquid methane line, a methane gas line, fillingY connections between each tank and the liquid line, liquid methane sprays terminating i i Y the filling connections inside the main tanks, a methane boil-off connection from the top of each main tank to the gas line, refrigerating plant to reliquefy the methane boiling-ofi from the main tanks and having an input and an output, a gas line connection from the gas line to the input of the refrigerating plant, a liquid line connection from the output of the refrigerating plant to the liquid line, and connections between the sprays and the reserve storage tank whereby throughout the period in which the main tanks are empty between the discharge of one cargo and the loading of the next liquid methane can be sprayed into the main tanks from the reserve tank in quantity sufficient to keep the main tanks at a low temperature and maintain therein an atmosphere of methane.

2. In a marine tanker for the bulk transport of liquefied gas at low temperature and substantially atmospheric pressure, the combination of a plurality of externally insulated main tanks for liquefied gas cargo each having a configuration that is mainly of upright cylindrical form and occupying at its widest part substantially the Whole available width of the vessel, said tanks being disposed in a closely-spaced row with their upright axes intersecting the fore-and-art centre line of the vessel and each tank being stepped in at at least one level near the top thereof so as to give the tank a centrally-placed narrow neck portion, a plurality of smaller externally-insulated wing tanks also for the liquefied gas each having a substantially upright cylindrical configuration, said wing tanks being disposed in wing spaces between the main tanks toward the sides of the ship, at least one of said wing tanks constituting storage for a relatively small reserve supply of liquefied gas which does not form part of the cargo discharged, a liquefied gas circulating line, a boilof gas line, filling connections between each tank and the liquefied gas line, liquefied gas sprays terminating the filling connections inside the cargo tanks, a boil-off connection from the top of each cargo tank to the boilotf gas line, refrigerating plant to reliquefy the gas boiling-ofi from the tanks and having an input and output, a gas line connection from the boil-ofi gas line to the input of the refrigerating plant, a liquid line connection from the output of the refrigerating plant to the liquefied gas line, and connections between the sprays and the reserve storage tank whereby throughout the period in which the cargo tanks are empty between the discharge of one cargo and the loading of the next liquefied gas can be sprayed into the cargo tanks from the reserve tank in quantity sufiicient to keep the cargo tanks at a low temperature and maintain therein an atmosphere of the liquefied gas.

3. in a marine tanker for the bulk transport of liquid methane at low temperature and substantially atmospheric pressure, the combination of a main deck, a narrower turret deck above the main deck, a plurality of externally-insulated main tanks for liquid methane cargo each having a configuration that is mainly of upright cylindrical form and occupying at its widest part substantially the whole available width of-the vessel, said tanks being disposed in a closely-spaced row with their upright axes intersecting the fore-and-aft centre line of the vessel and each tank being stepped in at least one level near the top thereof so as to give the tank a centrally-placed narrow neck portion with the full-diameter portion of the tank disposed wholly below the main deck and the central neck portion projecting above the main deck and lying within the confines of the portion of the deck width defined by the turret deck, a plurality of smaller externally insulated wing tanks for liquid methane cargo each having a substantially upright cylindrical configuration, said wing tanks being disposed wholly below the main deck in wing spaces between the main tanks toward the sides of the ship, at least one of said wing tanks constifilling connections between each tank and the liquid line, liquid methane sprays terminating the filling connections inside the cargo tanks, a methane boil-off connection from the top ofeach tank to the gas line, refrigerating plant to reliquefy the methane boiling-olif from the tanks and having an input and an output, a gas line Connection from the gas line to the input of the refrigerating plant, a liquid line connection from the output of the refrigerating plant to the liquid line, and connections between the sprays and the reserve storage tank whereby throughout the period in which the cargo tanks are empty between the discharge of one cargo and the loading of the next liquid methane can be sprayed into the cargo tanks from the reserve tank in quantity suflicient to keep the cargo tanks at alow temperature and maintain therein an atmosphere of methane.

4. in a marine tanker for the bulk transport of liquid methane at low temperature and substantially atmospheric pressure, the combination of a plurality of externally-insulated liquid methane cargo tanks designed for substantially atmospheric internal pressure, at least one additional storage tank for a relatively small reserve supply of liquid methane which does not form part of the cargo discharged, a liquid methane line, a methane gas line, a filling connection between the reserve storage tank and the liquid line, a boil-ofi connection from the top of each cargo tank to the gas line, refrigerating plant to reliquefy tuting storage for a relatively small reserve supply of liquid methane which does not form part of the cargo discharged, a liquid methane line, a methane gas line,

the methane boiling-ofi from the tanks and having an'input and an output, a gas line connection from the gas line to the input of the refrigerating plant, a liquid line connection from the output of the refrigerating plant to the liquid line, a spray unit in each cargo tank for spraying liquid methane into the tank, and connections between the spray units and the reserve storage tank whereby throughout the period in which the cargo tanks are empty between the discharge of one cargo and the loading of the next liquid methane can be sprayed into the cargo tanks from the reserve tank in quantity sufcient to keep the cargo tanks at a low temperature and maintain therein an atmosphere of methane.

5. In a marine tanker for the bulk transport of liquid methane, the combination of a main deck, a plurality of externally-insulated cargo tanks for liquid methane disposed principally below the main deck, additional belowdeck storage means for a reserve supply of liquid methane which does not form part of the cargo discharged, a liquid methane ring main, a methane gas line, filling connections between each tank and the ring main, liquid methane sprays terminating the filling connections inside the tanks, a methane boil-ott connection from the top of each tank to the gas line, refrigerating plant toreliquefy the methane boiling-off from the tanks and having an inpnt and an output, a gas line connection from the gas line to the input of the refrigerating plant, a liquid line connection from the output of the refrigerating plant to the ring main and to the reserve storage means, and connections between the sprays and the reserve storage means whereby liquid methane from the reserve storage means can be sprayed into the cargo tanks when they are empty after a cargo has been discharged.

6. A marine tanker for the bulk transport in the liquid state at low temperature of methane, comprising a plurality of cargo tanks to contain the liquid methane, additional storage means for a relatively small reserve supply of liquid methane which does not form part of the cargo discharged, at least one spray unit in each cargo tank, connections between the spray units and the reserve storage means arranged for effecting, throughout the period in which the cargo tanks are empty between the discharge of one cargo and the loading of the next, the spraying of liquid methane from the reserve supply into the tanks in quantity sufficient to keep the tanks at a low temperature and maintain therein an atmosphere of methane, the spray units being located near the tops of the tanks and arranged to direct their discharge reasonably uniformly over substantial areas of the internal surfaces toward the bottoms of the tanks, and connections and spray-rate controls whereby the same spray units can be employed for lling the tanks with their liquid cargo.

7. A marine tanker for the bulk transport in the liquid state at low temperature of ordinarily-gaseous substance, comprising cargo tanks to contain the liquid which cargo tanks include a plurality of main tanks disposed in a closely-spaced row along the fore-and-aft centre line of the ship and a plurality of smaller wing tanks, the main tending at their widest parts for substantially the full width of the ship and the smaller wing tanks being situated inthe spaces between the main tanks toward the sides of the ship, at least one of the Wing tanks constituting reserve storage means for a relatively small reserve supply of the liquid which does not form part of the cargo discharged, at least one spray unit in each cargo tank, connections between the spray units and said reserve storage means arranged for effecting, throughout the period in which the cargo tanks with the exception of the reserve storage means are empty between the discharge of one cargo and the loading of the next, the spraying of liquid from the reserve supply into the empty tanks in quantity sufficient to keep the tanks at a low temperature and maintain therein an atmosphere of the gaseed liquid.

References Cited in the file of this patent UNTED STATES PATENTS 10 f tanks being each of circular cross-section in plan and ex- 1,085,086 Jack Ian. 20, 1914 2,480,472 Jackson Aug. 30, 1949 2,550,886 Thompson May 1, 1951 2,689,461 Brandon Sept. 2l, 1954 2,896,416 Henry July 28, 1959 2,897,657 Rupp Aug. 4, 1959 OTHER REFERENCES The Oil and Gas Journal, published March 22, 1954, (pages 104 and 105 relied on).