GB2528461A

GB2528461A - Tanker gas displacement apparatus and method

Info

Publication number: GB2528461A
Application number: GB1412946.4A
Authority: GB
Inventors: John Macdonald
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-07-22
Filing date: 2014-07-22
Publication date: 2016-01-27
Anticipated expiration: 2034-07-22
Also published as: GB201412946D0; GB2528461B

Abstract

Tanker gas displacement apparatus includes a plurality of tanks 1 which are connected in parallel and a serially connected further tank 30. In one aspect, the plural tanks are discharged through said further tank. Various isolating valves 7, 8, 9, 10, 33-37 and 41 may be actuated to admit an inert gas via inlet 6 into a lower end of the plural tanks 1 to displace the hydrocarbon gas into the further tank 30. The hydrocarbon gas from the further tank 30 may be passed through isolation valve 41 for utilisation. The inert gas may be applied until the plural tanks 1 are filled, whereupon the isolation valves are actuated to admit air into a top end of the tanks 1 to displace the inert gas out of the lower end of the tanks 1 into a lower end of the further tank 30. Air may be admitted to the tanks 1 until they are substantially filled with air, and the air from the tanks 1 may be admitted into a top of the further tank 30 to displace the inert gas from a lower end thereof to be diverted via an isolation valve 9 to a vent mast 11.

Description

TANKER GAS DISPLACEMENT APPARATUS AND METHOD

This invention i-elates to tanker gas displacement apparatus and a method theiefor arid, iii particular, although not exclusively, to displacement of hydrocarbon gas such as liquid natural gas (LNG) or liquid petroleum gas (LPG). The invention has particular. although not exclusive, use in a ship borne tanker environment.

In the operation of LNG/LPG ship borne tankers, it is known to have a plurality of tanks connected in parallel and for the tanks to be routinely emptied of LNG/LPG by replacing said LNG/LPG gas with an inert gas and then subsequently i-emoving the inert gas with air. A current problem is that the inerting of a gas tanker requires a large amount of tüel to displace another fuel to atmosphere where the gas displaced is unused and is a pollutant. Safety is paramount in displacing the LNG/LPG and so as not to have a potentially flammable atmosphere, the LNG/LPG is first replaced with a ship borne generated inert gas having a very low oxygen content.

The gas displaced is burnt in a highly controlled manner u sing a mixture of aft.

At present, the provision of inert gas is derived from an oil fired inert gas generator venting the hydrocarbon gas, for example LNG/LPG, to atmosphere. As well as using a considerable amount of oil for the inert gas generator, the gas that is vented is a greenhouse gas that is unwelcome and problematic.

A known tanker gas displacement apparatus is shown in the accompanying Figures 1 and 2 in which use is made of different gases. i.e. hydrocarbon gas. inert gas, and air such that one medium is used to push out the other as an increasing layer" in the tanks.

Referring to Figures 1 and 2, five hydrocarbon gas, for example LNG/LPG, tanks I are shown, the number of tanks being exemplary and not restrictive. The tanks are connected in parallel by a first pipe 2 having first spurs 3 to a lower end of each tank and a second pipe 4 having second spurs 5 extending from an upper end of each tank. The right hand end tank 1 (as shown in the Figures) is denoted as being upstream and the left hand end tank 1 is denoted as being downstream herein. Inert gas from an inert gas generator (not shown) is applied to an inlet 6. The inlet 6 is connected to a hifuicated branch, one limb of which is connected to an isolation valve 7 preceding the fit-st of the spurs 3 and another limb being connected to an isolation valve 8 preceding the first of the spurs 5. A further isolation valve 9 is connected between the last (downsft-eam) spur 3 and the second pipe 4 which also has a vapour head isolation valve 10 interposed between the last (downstream) spur S and a downstream side of the isolation valve 9, the second pipe 4 terminating in a vent mast 11.

In operation. with the tanks 1 initially substantially filled with hydrocarbon gas 12, inert gas is input via inlet 6 and isolation valve 7 to the lower end of the tanks 1 to produce a layer of inert gas 13 that displaces the hydrocarbon gas 12, It will be realised that in this mode isolation valves 7 and 10 are open, whereas isolation valves 8 and 9 are closed so that the hydrocarbon gas is driven out of spurs 5 to the second pipe 4 to be vented via mast 11. Subsequently. as shown in Figure 2. dry air is applied at inlet 6, usually from the inert gas generator, and isolation valves 7 and 10 are closed, whereas isolation valves 8 and 9 are open so that the air 14 enters each tank 1 from the top of each tank via spurs 5 and the inert gas 13 is driven out from the bottom of each tank via spurs 3 to travel via the isolation valve 9 to the vent mast 11.

In order to develop and maintain an interface layer between the different gases. low velocities are required. However, if the hydrocarbon gas is to be used as a fuel for the inert gas plant, it is neeessaiy to dynamically suck the hydrocarbon gas out of the tanks I which sets up a differential flow in the tanks causing a breakdown of the interface layer. It will be realised that if such a breakdown of the interface layer should occur, then the hydrocarbon gas and inert gas would mix and the methodology would change to one called "dilution", whereby the inert gas is fed in and the tanks arc vented to atmosphere until the hydrocarbon gas content falls to a required amount. Such a procedure takes approximately 2.5 dines as much inert gas with consequential increased fuel costs. Furthermore, the contents of the tanks I can no longer he used as fuel due to the increasing amount of inert gas in the tanks.

The present invention seeks to at least partially mitigate the foregoing problems.

According to a first aspect of this invention, tanker gas displacement apparatus includes plural tanks each for containing a hydrocarbon gas, said plural tanks being connected in parallel. and a further tank connected in series with said plural tanks, whereby in operation said plural tanks are discharged through said further tank.

Advantageously, isolating valves are provided to facilitate said discharge through said further tank.

Preferably, one end of said plural tanks is connected to a first pipe and another end of each said plural tanks is connected to a second pipe, said first and second pipes each being connected to an inlet defining an upstream end and to an outlet defining a downstream end, a first and second isolating valve which are each serially connected toward a downstream end of said first pipe between the plural tank which is adjacent said downstream end and said further tank, a third, fourth and fifth isolating valve which are each serially connected to a downstream end of said second pipe between the plural tank which is adjacent the downstream end and said further tank, and a sixth isolating valve connected between a junction of said first and second isolating valves and a junction of said third and fourth isolating valves.

Conveniently, a downstream end of said fifth isolating valve is connected to a vent mast and to a sixth isolating valve, an output side of sixth isolating valve being connected to utilisation means.

Advantageously, a seventh isolating valve is provided between a downstream side of the second isolating valve and a downstream side of the fifth isolating valve to conmiunicate with the vent mast and an upstream side of the sixth isolating valve.

Preferably, an eighth isolating valve is connected in said first pipe between the inlet and said one end of the plural tank adjacent said upstream end and a ninth isolating valve is connected in said second pipe between the inlet and said another end of said plural tank which is adjacent said upstream end.

According to a second aspect of this invention there is provided a method of displacing gas from plural tanks connected in parallel through a serially connected further tank.

Preferably, said plural tanks contain a hydrocarbon gas and, in a first step, valve means are actuated to introduce an inert gas into said plural tanks to displace said hydrocarbon gas therefrom into the further tank.

Conveniently, the hydrocarbon gas is rnmoved from the further tank for utilisation.

Advantageously, the utilisation is to supply one of compressors for auxiliary plant, to power an inert gas generator and for application to a vapour manifold shore connection.

Advantageously, in a second step, said valve means are actuated to introduce air into said plural tanks to displace the inert gas therefrom into the further tank so that the inert gas in the further tank is displaced therefrom.

Preferably, said second step is continued until said plural tanks are emptied of inert gas.

The invention will 110W he described, by way of example, with reference to the accompanying drawings in which: Figures 1 and 2 show, in schematic form, steps in a prior art tanker gas displacement apparatus hereinbefom described, Figure 3 shows, in schematic form, a tank configuration and fhst step of tanker gas displacement in accordance with this invention in which hydrocarbon gas, e.g. LNG/LPG. is starting to be displaced by incrt gas.

Figui-e 4 shows, in schematic form, completion of displacement of hydrocarbon gas in parallel connected tanks by inert gas.

Figure 5 shows, in schematic form, the displacement of the inert gas with air from the parallel connected tanks, and Figure 6 shows the completion of aeration of the parallel connected tanks.

In the Figures like reference numerals denote like parts.

Referring to Figure 3. a further tank 30. or in the example shown herein the remotest downstream tank, is arranged to be connected in series with the plural parallel connected tanks 1, the tank 30 having a first spur 31 connecting with the first pipe 2 and a second spur 32 connecting with the second pipe 4. On the downstream side of the first pipe 3 from the last, i.e. downstream, spur 3 is a serial connection of an inert gas header isolation valve 33 and serial inerting isolating valve 34. an output side of the isolation valve 34 being connected to the first spur 31 and the isolation valve 9. A downstream side of the isolation valve 10 is connected to serially connected isoladon valves 35 and 36, the second spur 32 being connected to a junction intermediate between the isolation valves 35 and 36. An isolation valve 37 is connected in parallel with the tanks I having a first connection 38 coniniunicating intermediate the isolation valves 10 and 35 and a second connection 39 communicating intermediate the isolation valves 33 and 34. A fuel gas pipe 40 is connected intermediate isolation valve 36 and the vent mast 11 and the fuel gas pipe is connected to a fuel gas supply isolation valve 41, an output (upstream) side 42 of which is connected for utilisation. for example to a vacuum pump which supplies suction for supplying compressors for auxiliary plant and/or the inert gas generator, or for application to a vapour manifold shore connection.

The Figure 3 shows inert gas 13 from an inert gas generator (not shown) being applied to the inlet 6, and hydrocarbon, for example LNG/LPG 12, being displaced by the inert gas 13 entering a lower end of each of the parallel connected tanks 1. Thus, isolation valves 8. 33. 35 and 9 are closed whilst isolation valves 7, 10, 37. 34. 36 and 41 are open. Therefore, hydrocarbon gas is displaced from an upper end of the tanks 1 into tank 30 and, thence, via second spur 32 and isolation valve 36 to vent mast 11 and isolation valve 41 to the output side 42.

Figure 4 shows a further step where the inert gas 13 has filled tanks 1 and is starting to enter the tank 30. Thus, it will he understood that the inert gas 13 enters the lower end of each tank 1 and the hydrocarbon gas leaves the tanks 1 from the upper end, as in the prior art. However, instead of the hydrocarbon gas going directly to the vent mast 11, it is directed to the lower end of tank 30 via isolation valves 10, 37 and 34. The hydrocarbon gas exits the tank 30 via second spur 32 and via isolation valve 36 fuel gas pipe 40 and isolation valve 41 to suction supply equipment for use as fuel for both the inert gas generator and any auxiliaries that may use gas. Because output Ibm the tanks 1 now liows through tank 30, the pipes 31 and 32 are of larger diameter to accommodate the flow and fuel pipe 40 may be in communication with the outlet of tank 30 without disturbing the interface with the tanks 1. By using the configuration of this invention, hydrocarbon gas can he used both to fuel the inert gas generator and may also be discharged via the vent mast 11. but it will be understood that the amount of hydrocarbon gas discharged to the atmosphere will be substantially reduced by the use of this invention.

The inerting operation continues until the inert gas 13 enters the tank 30.

There is then no need to continue making inert gas because the next step of displacing the inert gas with air can commence which will displace the inert gas from tanks 1 to the tank 30 -this step being shown in Figure 5. As shown in Figure 4 because tank 30 initially (at this stage) still has hydrocarbon gas in the upper portion thereof, so this gas is transferred via isolation valves 36 and 41 for utilisation.

RefelTing to Figure 5, isolation valves 7, 10, 35 and 9 are closed, and isolation valves 8.33.34,36 and 41 are opened. Dry air from the inert gas generator is applied to the inlet 6 so that air 14 enters the upper end of each of the tanks 1 to displace the inert gas 13 out of the lower end of the tanks 1, the inert gas travelling via isolation valves 33 and 34 into the lower end of the tank 30.

Because the tanks 1, in combination, contain a greater volume than the tank 30, so the tank 30 will he completely inerted before the tanks 1 are aerated. As shown in Figure 6. to ensure an inert gas/air interface in the tank 30. the valves are now configured such that the air enters the tank 30 at the top to discharge the remaining inert gas from the lower end of the tank 30 (as shown in Figure 6). Thus, isolation valves 7. 10, 34, 36 and 41 are closed and isolation valves 8, 33, 37, 35 and 9 are opened. By such a configuration. air travels via valve 8 into the top of tanks 1 and out of the lower end of tanks I along first pipe 2 via isolation valves 33. 37 and 35 into the top of tank 30 and the inert gas is displaced from the lower end of tank 30 via isolation valve 9 to the vent mast 11. This operation continues until the tanks I are substantially filled with air.

The present invention has the following advantageous features.

1. An existing tank may be used as a plenum chamber to permit the use of hyclroc arbon gas as a fuel for utilisation. for example for the inert gas generator.

2. Larger capacity pipes 31 and 32 allow full flow through the tank 30 acting as a plenum chamber.

3. The use of isolation valves and pipe allow the tank 30 to he in series with the other tanks I which remain coiinected in parallel, thereby not requiring change of connection of the existing apparatus.

4. A ship may be inerted using only hydrocarbon as fuel which would otherwise be vented to atmosphere.

5, No oil is used to inert the tanks, thereby saving substantial expense.

6. It is estimated that the emission of hydrocarbon gas to the atmosphere is i-educed by approximately 1 5%.

7. Auxiliaries, such as generators and boilers, may continue to run on hydrocarbon gas up until inerting of the tank acting as a plenum chamber commences.

8. Auxiliaries, such as boilers, may continue to use gas on free flow during the inerting of 90% of the tank acting as a plenum chamber.

9. The use of a hydrocarbon powered hiert gas generator allows for shore supply gas to be used dur ng subsequent inerting and gassing up.

10. If the inert gas plant is used in fuel/oil niodc, the ship may be inerted using 20% less fuel.

11. The ship maybe inerted conventionally, if required.

RefelTing. again, to Figure 3, instead of output side 42 being connected to the auxiliary plant and the inert gas generator. it may be connected to go ashore or to a vapour mani old shore connection and discharge ashore may continue unuil a safe level of inert gas in the tank 30 is reached, at which point the isolation valve 41 is closed and the inert gas is redirected to the vent mast 11.

Claims

CLAIMSL Tanker gas displacement apparatus includes plural tanks each for containing a hydrocarbon gas, said plural tanks being connected in parallel, and a further tank connected in series with said plural tanks, whereby in operation said plural tanks are discharged through said ftrther tank.
2. An apparatus as claimed in claim 1, wherein isolafing valves are provided to facilitate said discharge thi-ough said further tank.
3. An apparatus as claimed in claim 1 or 2, wherein one end of said plural tanks is connected to a first pipe and another end of each said plural tanks is connected to a second pipe, said first and second pipes each being connected to an inlet defining an upstream end and to an outlet defining a downstream end, a first and second isolating valve which are each serially connected toward a downstream end of said first pipe between the p1w-al tank which is adjacent said downstream end and said further tank, a third, fourth and fifth isolating valve which are each serially connected to a downstream end of said second pipe between the plural tank which is adjacent the downstream end and said further tank, and a sixth isolating valve connected between a junction of said first and second isolating valves and ajunedon of said third and fourth isolating valves.
4. An apparatus as claimed in claim 3, wherein a downstream end of said 111th isolating valve is connected to a vent mast and to a sixth isolating valve, an output side of sixth isolating valve being connected to utilisation means.
5. An apparatus as claimed in claim 4, wherein a seventh isolating valve is provided between a downstream side of the second isolating valve and a downstream side of the fifth isolating valve to communicate with the vent mast and an upstream side of the sixth isolating valve.S
6. An apparatus as claimed in claim 5, whercin an cighth isolating valve is connected in said first pipe between the inlet and said one end of the plural tank adjacent said upstream end and a ninth isolating valve is connected in said second pipe between the inlet and said another end of said plural tank which is adjacent said upstream end.
7. A method of displacing gas from plural tanks connected in parallel through a serially connected further tank.
8. A method as claimed in claim 7, wherein said plural tanks contain a hydrocarbon gas and, in a first step. valve means ate actuated to introduce an inert gas into said plural tanks to displace said hydrocarbon gas therefrom into the further tank.
9. A method as claimed in claim 8, wherein the hydrocarbon gas is removed from the further tank for utilisation.
10. A method as claimed in claim 9, wherein the utilisation is to supply one of compressors for auxiliary plant, to power an inert gas generator and for application to a vapour manifold shore connection.
11. A method as claimed in claim 10, wherein in a second step. said valve means are actuated to introduce air into said plural tanks to displace the inert gas therefrom into the further tank so that the inert gas in the further tank is displaced therefrom.
12. A method as claimed in claim 11, wherein said second step is continued until said plural tanks are emptied of inert gas.
13. An apparatus substantially as herein described with reference to and as shown in Figures 3 to 6 inclusive of the accompanying drawings.
14. A method substantially as herein described with reference to and as shown in Figures 3 to 6 inclusive of the accompanying drawings.