GB2535425A

GB2535425A - LNG bunker vessel

Info

Publication number: GB2535425A
Application number: GB1413486.0A
Authority: GB
Inventors: Scott Andrew; Alfred Eltringham John
Original assignee: Bernhard Schulte Shipmanagement (uk) Ltd; Liquid Gas Equipment Ltd
Current assignee: Bernhard Schulte Shipmanagement (uk) Ltd; Liquid Gas Equipment Ltd
Priority date: 2014-07-30
Filing date: 2014-07-30
Publication date: 2016-08-24
Also published as: KR20170069999A; WO2016016647A1; EP3175165A1; JP2017523084A; GB201413486D0; CN107076364A

Abstract

An LNG bunker vessel 2 having: one or more LNG tanks 4, a first pipeline 10 able to transfer liquefied natural gas (LNG) 12 from a LNG tank on the LNG bunker vessel to an off-vessel LNG receiver tank 8, one or more natural gas compressors 12 on the LNG bunker vessel able to compress natural gas and provide compressed natural gas (CNG), a second pipeline 14 able to transfer natural gas from the off-vessel LNG receiver tank to the one or more natural gas compressors on the LNG bunker vessel; and a CNG storage tank 16 on the LNG bunker vessel to store CNG provided by the one or more natural gas compressors as a fuel source. The apparatus and operation for transforming natural gas from the off-vessel LNG receiver tank into a suitable fuel source as CNG is provided on the LNG bunker vessel, and does not require ancillary equipment and operation at the location or site of every off-vessel LNG receiver tank. Also claimed is a process and a system using such a vessel.

Description

LNG Bunker Vessel The present invention relates to an LNG bunker vessel including a CNG storage tank, and a process for providing CNG as a fuel source on an LNG bunker vessel.

Liquefied natural gas (LNG) is natural gas, predominately methane, that has been converted to liquid form for ease of storage and/or transport. Natural gas is being used increasingly as a fuel source, especially commercially, and the most efficient form of transporting it from its source to a major supply hub for users is in the form of LNG, frequently by LNG cargo vessels.

An increasing use of LNG as a fuel source is in small and medium vessels such as ferries. LNG can be supplied to such vessels using LNG bunker vessels, which are generally smaller than LNG cargo vessels, and include one or more LNG tanks. LNG bunker vessels are able to provide the LNG directly as a fuel source to LNG 'receivers', generally being the fuel tanks of such vessels or on-shore fuel tanks used by such vessels.

LNG bunker vessels are known in the art, and may become an increasingly important means of transporting LNG from major hubs to smaller fuel tanks as stricter environmental regulations are introduced. However, as LNG is transferred from a tank of an LNG bunker vessel to the fuel tank of another vessel or to an onshore fuel tank, boil-off gas (BOG) and/or flash gas are typically created. Boil-off gas is simply that portion of the LNG which naturally evaporates as part of the transfer.

Flash gas is particularly created where conditions in the receiving fuel tank are not optimal (usually too warm), creating instant evaporation of some LNG. Both BOG and flash gas are still 'natural gas'.

Some of the natural gas created in this way can be returned into the LNG tank to help balance or re-equalise the pressure change in the LNG tank as the LNG is transferred from the tank to the receiver fuel tank. However, there are many occasions where there is an excess amount of natural gas created during the transfer. Currently, such excess natural gas is either simply vented to atmosphere, or combusted.

It is an object of the present invention to recover excess natural gas during such an LNG transfer for use or reuse as a fuel source.

Thus, according to one aspect of the present invention, there is provided an LNG bunker vessel having: one or more LNG tanks, a first pipeline able to transfer liquefied natural gas (LNG) from a LNG tank on the LNG bunker vessel to an off-vessel LNG receiver tank, one or more natural gas compressors on the LNG bunker vessel able to compress natural gas and provide compressed natural gas (CNG), a second pipeline able to transfer natural gas from the off-vessel LNG receiver tank to the one or more natural gas compressors on the LNG bunker vessel; and a CNG storage tank on the LNG bunker vessel to store CNG provided by the one or more natural gas compressors as a fuel source.

In this way, the apparatus and operation for transforming natural gas from the off-vessel LNG receiver tank into a suitable fuel source as CNG is provided on the LNG bunker vessel, and does not require ancillary equipment and operation at the location or site of every off-vessel LNG receiver tank.

The nature, size, shape and design of LNG bunker vessels are known in the art.

Generally, an LNG bunker vessel comprises one or more LNG tanks, typically two or three tanks, and can be designed to carry hundreds or thousands of litres or cubic metres (e.g. 6000 m-3) of LNG, generally to supply LNG as a fuel source to more than one off-vessel LNG receiver tanks. The storage requirements, process and conditions of the LNG on an LNG bunker vessel is known to those skilled in the art The LNG bunker vessel comprises a first pipeline able to transfer LNG from an LNG tank on the LNG bunker vessel to an off-vessel LNG receiver tank.

The term "off-vessel LNG receiver tank" as used herein includes any tank intended to store and provide LNG as a fuel source to a vessel or other means of transport or industrial factory or premises etc... Thus, the off-vessel LNG receiver tank may be on-shore or off-shore. A typical example is the fuel tank of a vessel such as a ferry, such as a passenger ferry or a commercial ferry. Other examples include other seagoing vessels such as cruise liners, barges, and commercial transport vessels. On-shore users include factories, etc. The off-vessel LNG receiver tank may also be a fuel depot or hub for other, usually smaller, users of LNG.

The size, design and use of the off-vessel LNG receiver tank is not limiting to the present invention, subject only to such a receiver tank not being on the LNG bunker vessel, and hence 'off-vessel'.

Optionally, the off-vessel LNG receiver tank is the fuel tank of a vessel.

The nature of the first pipeline, which is able to transfer LNG from an LNG tank on the LNG bunker vessel to an off-vessel LNG receiver tank, is also known in the art and is not further described herein.

In use, the LNG bunker vessel is connected via at least the first and second pipelines to the off-vessel LNG receiver tank. Optionally, the LNG bunker vessel is secured to the support or base for the off-vessel LNG receiver tank.

As LNG is passed into the off-vessel LNG receiver tank, BOG, or flash gas, or both, are usually created. Thus, optionally, the natural gas from the off-vessel LNG receiver tank comprises boil-off gas, flash gas or both.

In the present invention, the second pipeline is provided to transfer such natural gas from the off-vessel LNG receiver tank to one or more natural gas compressors on the LNG bunker vessel. The nature, design and shape of the second pipeline is not limiting, and is generally able to transfer natural gas in a manner known in the art.

Optionally, the second pipeline is wholly or substantially located alongside the first pipeline between the LNG bunker vessel and the off-vessel LNG receiver tank.

Natural gas compressors are known in the art, and are generally intended to compress natural gas to a higher pressure. Typically this can be from ambient pressure. or a low pressure of a few bars, to a pressure greater than 100 bar, optionally greater than 200 bar, and frequently in the range 240-260 bar, such as 250 bar.

Compressed natural gas (CNG) is generally methane stored at a high pressure, and it is being increasingly used for transport in place of gasoline. Typically, CNG combustion produces fewer undesirable gases than gasoline and similar fuels, and CNG is typically safer than other fuels in the event of a spill (especially because natural gas is lighter than air and disperses quickly when released). An increasing number of cars and public transport vehicles such as buses are now being fuelled with CNG.

The CNG storage tank on the LNG bunker vessel is able to receive the CNG created by the natural gas compressor(s), and store it as a fuel source. The CNG storage tank may comprise one or more tanks or bunkers or compartments or storage areas or combination of same, optionally with the inclusion of internal materials able to store CNG at a greater density.

In one embodiment of the present invention, the CNG is a fuel source for the LNG bunker vessel. Thus, there can be provided a third pipeline between the CNG storage tank and either to the engine(s) or a part thereof of the LNG bunker vessel, or to the fuel tank(s) of the LNG bunker vessel, or to both, optionally with the required intermediate apparatus or provisions for providing the CNG as the correct fuel, generally in the form of lower pressure gas, to the or each relevant engine.

In particular, where the LNG bunker vessel itself uses the CNG from the CNG storage tank, there is an increased meeting of zero emissions targets now being presented to users of LNG bunker vessels.

Further, and BOG created during the journeying of the LNG bunker vessel when loaded with LNG in its LNG tank(s) can also be compressed to CNG using the same apparatus, and then used as a fuel source, in particular in the engine(s) of the LNG bunker vessel.

According to an alternative embodiment of the present invention, the CNG in the CNG storage tank can be transferred to another off-vessel tank, either through a transfer pipeline or by relocation of the CNG storage tank (to be replaced by another or empty CNG storage tank), and for use as a fuel source for one or more other motors or engines separate from the LNG bunker vessel.

The present invention is not limited by the ultimate use or user of the CNG created by the one or more natural gas compressors on the LNG bunker vessel.

According to a second aspect of the present invention, there is provided a process for providing CNG as a fuel source on an LNG bunker vessel, comprising at least the steps of: (i) providing an LNG bunker vessel having one or more LNG tanks, one or more natural gas compressors, and a CNG storage tank; (ii) transferring liquefied natural gas (LNG) from a LNG tank on the LNG bunker vessel to an off-vessel LNG receiver tank; (iii) transferring natural gas from the off-vessel LNG receiver tank to the LNG bunker vessel; (iv) compressing the natural gas in the one or more natural gas compressors to provide compressed natural gas (CNG); (v) storing the CNG in the CNG storage tank on the LNG bunker vessel for use as a fuel source.

According to one embodiment of the present invention, the process of the present invention further comprises: (vi) transferring the CNG in the CNG storage tank to the engine of the LNG bunker vessel.

According to an alternative embodiment of the present invention, the process of the present invention further comprises: (vi) transferring the CNG in the CNG storage tank to an off-vessel tank for use as a fuel source.

According to a third aspect of the present invention, there is provided a system for providing CNG as a fuel source on an LNG bunker vessel, the system comprising an LNG bunker vessel having one or more LNG tanks, a first pipeline between an LNG tank and an off-vessel LNG receiver tank, the transfer of LNG from the LNG bunker vessel to the off-vessel receiver tank via the first pipeline, the creation of natural gas in the off-vessel receiver tank due to the LNG transfer, the transfer of the so-formed natural gas from the off-vessel receiver tank via a second pipeline to one or more natural gas compressors on the LNG bunker vessel, the creation of compressed natural gas (CNG) by the one or more natural gas compressors, and the passing of the so-formed CNG into a CNG storage tank on the LNG bunker vessel for use as a fuel source.

Optionally, the off-vessel receiver tank is on a separate vessel. Preferably, the off-vessel receiver tank is the fuel tank of the separate vessel.

Optionally, the system further comprises passing the CNG in the CNG storage tank to the engine(s) and/or fuel tank(s) of the LNG bunker vessel as a fuel source for the engine(s) of the LNG bunker vessel.

As used herein, the term "system" is the assembly or arrangement of the LNG bunker vessel and a connected off-vessel LNG receiver tank.

Embodiments and an example of the present invention will now be described by way of example only and with reference to the accompanying schematic drawings, data and graphs in which: Figure 1 is a side schematic view of an LNG bunker vessel according to one embodiment of the present invention; Figure 2 is a side schematic view of a second embodiment of the present invention; Figure 3 comprises example data; and Figure 4 comprises CNG tank pressure and CNG feed to engine graphs.

Referring to the drawings, Figure 1 shows an LNG bunker vessel 2 having two LNG tanks 4. As mentioned hereinbefore, LNG bunker vessels are known in the art, and may comprise one or more LNG tanks in order to provide, generally within a supply chain, LNG as a fuel to one or more on-shore or off-shore tanks of vessels, means of transport, factories etc., or fuel hubs therefor.

By way of example only, an LNG bunker vessel could be loaded with LNG at or near a major LNG hub in a harbour or storage area such as the Port of Rotterdam, and then travel to one or more, usually at least two or three, destinations, to supply the LNG as a fuel source, usually a marine fuel source, to one or more other vessels of fuel sources or hubs.

Figure 1 shows a second vessel 6 having a fuel tank 8 (usually located within the vessel) for an engine 9 of the second vessel 6. Thus, the fuel tank 8 of the second vessel 6 can be designated as an "off-vessel LNG receiver tank 8".

Figure 1 shows a first pipeline 10 able to transfer liquefied natural gas (LNG) 12 from an LNG tank 4 on the LNG bunker vessel 2 to the off-vessel LNG receiver tank 8. This is generally carried out in a manner known in the art, and the process, and process conditions and parameters, will be known to the person skilled in the art.

As the LNG reaches the off-vessel LNG receiver tank 8, either boil-off gas (BOG), or flash gas, or both will be created in a manner known in the art, and hereinafter generally termed 'natural gas'.

Conventionally, whilst some of this natural gas is used to help balance or equalise the pressure in the LNG tank 4 during the LNG transfer, any excess natural gas is currently typically either vented straight to atmosphere, or sent to a gas combustion unit. Environmentally, this is increasingly not preferred or desired.

Figure 1 shows the LNG bunker vessel 2 having one or more natural gas compressors 12 located on the LNG bunker vessel 2, and a second pipeline 14 able to transfer natural gas from the off-vessel LNG receiver tank 8 to the one or more natural gas compressors 12. The process and process parameters and conditions for the transfer of natural gas along the second pipeline are not further described, and will be known to those skilled in the art.

Natural gas compressors are also known in the art, and generally increase the pressure of natural gas by a significant multiple, generally into a form known as compressed natural gas (CNG) having a pressure (at ambient temperature) of several bar, or tens of MPa, typically greater than 100 bar, greater than 200 bar, and optionally at or approximately 250 bar.

Figure 1 shows a CNG storage tank 16 on the LNG bunker vessel 2 to store the so-formed CNG from the one or more natural gas compressors 12 as a fuel source.

Figure 1 shows a third pipeline 18 able to pass the CNG from the CNG storage tank 16 directly to an engine or engine control unit, apparatus, etc. 20 of the LNG bunker vessel 2, generally via one or more required apparatus such as a let-down valve 22.

Figure 1 shows the ability of the present invention to provide a means of recovery of natural gas from the off-vessel LNG receiver tank into a useful CNG fuel source, and in particular as a fuel source for the LNG bunker vessel itself. In this way, the LNG bunker vessel is able to increasingly meet a zero emissions target by its reuse of the natural gas created by the transfer of its LNG to the off-vessel LNG receiver tank.

Figure 1 also shows a fourth pipeline 24 between the LNG tank 4 and the second pipeline 14 useable for two purposes. Firstly, it can transfer BOG created in the LNG tank 4 into the second pipeline 14, to also be compressed by the one or more natural gas compressors 12 into CNG as a fuel source in the CNG storage tank 16. Secondly, it can be used to transfer any portion of the natural gas provided by the off-vessel LNG receiver tank 8 during the LNG transfer to help balance or equalise the pressure in the LNG tank 4 during the transfer of LNG 12 out of the same tank 4.

Figure 2 shows a second embodiment of the present invention. In the second embodiment the LNG bunker vessel 2 comprises LNG tanks 4, and a first pipeline 10 able to transfer liquefied natural gas 12 from an LNG tank 4 to an on-shore tank 30, which tank 30 is also an off-vessel LNG receiver tank. The on-shore tank 30 may be the same type of tank as the fuel tank 8 of the second vessel 6 shown in Figure 1. It may also be a fuel depot or fuel hub for other (typically on-shore or land based) users such as commercial vehicles.

The on-shore tank 30 will create boil-off gas, flash gas or both in the same way as Figure 1 during an LNG transfer thereinto. This so-formed natural gas that can be transferred via the second pipeline 14 extending from the on-shore tank 30 to one or more natural gas compressors 12 on the LNG bunker vessel 2. The CNG created thereby can be stored in a downstream CNG storage tank 16.

Figure 2 also shows a fifth pipeline 32 able to transfer CNG in the CNG storage tank 16 for use as a fuel source in another location. This transfer could be directly or indirectly to an off-vessel fuel source (not shown). The provision of CNG via the fifth pipeline 32 may be in addition to or as an alternative to the supply of CNG to the engine 20 of the LNG bunker vessel 2.

Figures 3 and 4 are data and graphs for an example voyage of an LNG bunker vessel according to the present invention having a natural gas compressor(s) and CNG storage tank thereon..

The LNG bunker vessel has a total LNG capacity of 6803 m3 in two LNG tanks to store LNG at -161CP.

Starting at "0.0" hours, there is a 10 hour 'loading' period during which the LNG bunker vessel is loaded with 5900 m3 of LNG at a suitable hub, terminal or port. At this time, the CNG storage tank is effectively 'empty', and thus there is a minimum CNG tank pressure, and a 'zero' CNG feed therefrom to the engine of the LNG bunker vessel.

After a 2 hour period of 'outboard loaded pilotage' from the hub, the loaded LNG bunker vessel then has a 'loaded transit journey of 386 nautical miles over a time of 32.17 hours. During the loaded transit journey, BOG from the LNG tanks is compressed to provide CNG: hence filling the CNG storage tank and thereby increasing the CNG tank pressure. This CNG is used as a fuel source, for example half way along the transit loaded period, to feed the engine of the LNG bunker vessel.

After an Inbound loaded pilotage' of 2 hours, and a co& down period of 1 hour, the LNG in the LNG tanks is discharged over a period of 19.67 hours to one or more off-vessel LNG receiver tanks having a total volume of 6400m3 at an average cargo transfer rate of 300m3/h. In this example, the cargo transferred is 5900m3. During the transfer, BOG and possibly flash gas is created, which is wholly or substantially provided to the one or more natural gas compressors on the LNG bunker vessel.

This creates CNG to be stored in the CNG storage tank, which therefore increases the CNG tank pressure in the CNG storage tank over the discharge period, until the end of the discharge.

The LNG vessel is then ready to return to its loading hub facility, starting with a 2 hour 'outbound ballast pilotage', followed by a ballast transit journey or period of 32.17 hours before a final 2 hour inbound ballast pilotage.

During the ballast transit journey, the CNG in the CNG storage tank is provided to the engine of the LNG bunker vessel, optionally at a constant flow rate as shown in Figure 4 lower, such that the pressure in the CNG storage tank correspondingly decreases during the ballast transit period back down to its minimum, prior to the next loading and transit cycle.

Thus, in the loading, outward transit, discharge, and the return transit, the LNG bunker vessel has used the CNG created as a fuel source, and the present invention provides a system on or with the LNG bunker vessel to better meet zero emissions targets for the LNG bunker vessel by recovery of the natural gas created over the whole voyage.

Claims

Claims 1. An LNG bunker vessel having: one or more LNG tanks, a first pipeline able to transfer liquefied natural gas (LNG) from a LNG tank on the LNG bunker vessel to an off-vessel LNG receiver tank, one or more natural gas compressors on the LNG bunker vessel able to compress natural gas and provide compressed natural gas (CNG), a second pipeline able to transfer natural gas from the off-vessel LNG receiver tank to the one or more natural gas compressors on the LNG bunker vessel; and a CNG storage tank on the LNG bunker vessel to store CNG provided by the one or more natural gas compressors as a fuel source.
2. An LNG bunker vessel as claimed in Claim 1 wherein the off-vessel LNG receiver tank is on-shore.
3. An LNG bunker vessel as claimed in Claim 1 wherein the off-vessel LNG receiver tank is off-shore.
4. An LNG bunker vessel as claimed in Claim 2 wherein the off-vessel LNG receiver tank is the fuel tank of a vessel.
5. An LNG bunker vessel as claimed in any one of the preceding claims wherein the natural gas from the off-vessel LNG receiver tank comprises boil-off gas, flash gas or both.
6. An LNG bunker vessel as claimed in any one of the preceding claims wherein the CNG is a fuel source for the LNG bunker vessel.
7. An LNG bunker vessel as claimed in any one of claims 1 to 5 wherein the CNG is transferred to another off-vessel tank.
8. A process for providing CNG as a fuel source on an LNG bunker vessel, comprising at least the steps of: (i) providing an LNG bunker vessel having one or more LNG tanks, one or more natural gas compressors, and a CNG storage tank; (ii) transferring liquefied natural gas (LNG) from a LNG tank on the LNG bunker vessel to an off-vessel LNG receiver tank; (Hi) transferring natural gas from the off-vessel LNG receiver tank to the LNG bunker vessel; (iv) compressing the natural gas in the one or more natural gas compressors to provide compressed natural gas (CNG); and (v) storing the CNG in the CNG storage tank on the LNG bunker vessel for use as a fuel source.
9. A process as claimed in claim 8 further comprising: (vi) transferring the CNG in the CNG storage tank to an engine of the LNG bunker vessel.
10. A process as claimed in claim 8 further comprising: (vi) transferring the CNG in the CNG storage tank to an off-vessel tank for use as a fuel source.
11. A system for providing compressed natural gas (CNG) as a fuel source on an LNG bunker vessel, the system comprising an LNG bunker vessel having one or more LNG tanks, a first pipeline between an LNG tank and an off-vessel LNG receiver tank, the transfer of liquefied natural gas (LNG) from the LNG tank to the off-vessel receiver tank via the first pipeline, the creation of natural gas in the off-vessel receiver tank due to the LNG transfer, the transfer of the so-formed natural gas from the off-vessel receiver tank via a second pipeline to one or more natural gas compressors on the LNG bunker vessel, the creation of CNG by the one or more natural gas compressors, and the passing of the so-formed CNG into a CNG storage tank on the LNG bunker vessel for use as a fuel source.
12. A system as claimed in claim 11 wherein the off-vessel receiver tank is on a separate vessel.
13. A system as claimed in claim 11 or claim 12 wherein the off-vessel receiver tank is the fuel tank of the separate vessel.

14 A system as claimed in any one of claims 11 to 13 wherein the CNG is a fuel source for the LNG bunker vessel.