WO2011032556A1

WO2011032556A1 - Cooled bunkering pipe system

Info

Publication number: WO2011032556A1
Application number: PCT/DK2009/000209
Authority: WO
Inventors: Jørgen BERTH; Heine Visnes Husted; John Koldbrovej 9 NIELSEN John NIELSEN; Ole Nygaard
Original assignee: Lr Marine A/S
Priority date: 2009-09-18
Filing date: 2009-09-18
Publication date: 2011-03-24

Abstract

The invention relates to an insulated bunkering pipe (100) used for bunkering LNG from at least one LNG storage tank to another. The bunkering pipe comprises an inner pipe (102) in which the LNG is transported. The inner pipe is enclosed by an outer pipe (104), forming a cavity (103) between the two pipes. Before, during and optionally after bunkering, a cooled refrigerant is circulated through the cavity so as to ensure that the LNG is kept at its temperature.

Description

COOLED BUNKERING PIPE SYSTEM

The present invention relates to a cooled bunkering pipe for both onshore and offshore installations. FIELD OF THE INVENTION

Natural gas is increasingly used to fuel e.g. ships, marine vessels, ferries, etc. The increased use of natural gas is motivated by present and especially future demands on limiting the emission of for example carbon dioxide (CO₂), nitrogen oxide (ΝΟχ), and sulfur dioxide (SOx). Hence, compared to the traditional fuels, natural gas provides a better alternative, as the combustion of natural gas produces far lower amounts of sulfur dioxide and nitrous oxides than any other fossil fuel. Therefore, e.g. ships, marine vessels and ferries are built or rebuilt with power means fuelled with natural gas. To ease the transportation of natural gas, it is cooled down to a temperature of about -162°C (-260°F) where it becomes liquefied natural gas, which is also commercially known as LNG. LNG takes up about 1/600th the volume of natural gas in the gaseous state. The LNG is normally stored in highly insulated tanks from where it is typically led into a heating unit where LNG again is brought into the gaseous state and ready for use.

Once stored in an insulated tank, LNG is easy to transport. However, when LNG has to be transferred from one tank to the other, a number of challenges arise. Such transfer could be between an LNG carrier and a land based storage tank or from storage tank to a marine vessel. In marine and naval settings such transfer is known as bunkering and the pipeline or fuel line between the storage tanks is also known as the bunkering line. The primary challenge during bunkering is to deal with the temperature difference between the LNG at -162°C and the bunkering pipeline, which could be at an ambient temperature of for example 20°C. If the LNG is transferred through such a relatively warm pipe this causes the LNG to boil, leading to a two- phase flow of gas and liquid. Such a flow is difficult to control, whereas the flow initially has to be kept very low. Later on, when the bunkering line has been cooled down by the LNG, the flowrate can be increased. Despite this, the bunkering time would be too long for e.g. a ferry, as the port time would be greater than allowed by the timetable. To eliminate this problem the bunkering line is often kept at cryogenic temperature by re-circulating LNG through the bunkering line continuously. This is common practice in most LNG terminals. But for a marine vessel it is not desirable to have the bunkering line filled with LNG when the vessel is not bunkering.

The document WO 2009/063127 provides a system and method for operating a LNG fuelled marine vessel. The marine vessel comprises a LNG storage tank and a LNG fuelled power plant. LNG is stored in the LNG storage tank, and in connection with a bunkering operation the marine vessel is supplied with LNG by connecting a source of LNG to a bunkering line of the marine vessel and subsequently supplying the marine vessel with LNG through the bunkering line. In order to achieve a faster bunkering operation, the bunkering line is cooled down prior to the bunkering operation. This is done by circulating LNG from the storage tank of the marine vessel through the bunkering line, which then cools it down. However, circulating LNG through the bunkering line is associated with great risk on e.g. a passenger ship, and often it is required that the bunkering line is purged by an inert gas when it is not in operation. SUMMARY OF THE INVENTION

The present invention provides a bunkering pipe comprising an inner pipe in which a fuel such as a gas or oil can flow. The bunkering pipe further comprises an outer pipe enclosing the inner pipe, thereby forming a cavity between the inner pipe and the outer pipe, such that a refrigerant can flow through the cavity. The cavity is sealed in each end of the bunkering pipe. The refrigerant which is to flow through the cavity can enter the cavity through at least one refrigerant inlet and exit through at least one refrigerant outlet. The advantage of the present invention is that the bunkering pipe will only contain e.g. LNG during bunkering. The need for circulating e.g. LNG through the inner pipe prior to the bunkering process is therefore eliminated. Thus, by circulating a harmless refrigerant through a cavity, the security measures that would have to be taken on for example a marine vessel or passenger ship are reduced heavily.

In another embodiment the bunkering pipe comprises a return pipe of which one end is connected to the cavity and where the other end of the return pipe is connected to the refrigerant outlet. The refrigerant inlet and the refrigerant outlet can be placed proximate to each other at one end of the bunkering pipe, by connecting the return pipe to the cavity in one end of the bunkering pipe and connecting the return pipe to the refrigerant outlet at the opposite end of the bunkering pipe. The return pipe serves to place the refrigerant outlet where needed along the course of the bunkering pipe. By having the refrigerant inlet and outlet proximate to each other the connection to a refrigerant system is easier. A pipe similar to the return pipe could also be used to connect the refrigerant inlet to the cavity.

In yet another embodiment the bunkering pipe comprises at least one distance piece, positioning the inner pipe relative to the outer pipe. The distance pieces serve to position the inner pipe relative to the outer pipe in such a way that they form a uniform cavity, enabling an approximately uniform flow through the cavity and thereby a uniform cooling of the inner pipe.

In one embodiment the bunkering pipe comprises at least one layer of insulation directly or indirectly bonded to the outer surface of the outer pipe. In a further embodiment the bunkering pipe comprises at least one layer of casing directly or indirectly bonded to the outermost surface of the insulation material. By insulating the outer pipe, the convection and radiation of cold or heat is brought to a minimum. Further, when cooled it is avoided that water condensates on the outer pipe and on the connection plug. Hence, the energy needed to circulate the refrigerant is reduced by isolating the bunkering pipe. The casing can also be covered with metal cladding.

In another embodiment the bunkering pipe comprises a connection plug in each end of the bunkering pipe, through which connection plug the bunkering pipe can be connected directly or indirectly to at least one storage tank. The connection plug can be embodied as known in the art.

The present invention further relates to a method for bunkering a fuel such as a gas or oil and comprises the steps of

- connecting at least two storage tanks using at least one bunkering pipe of the present invention,

- circulating a refrigerant in the cavity, whereby the bunkering pipe is cooled down,

- leading the fuel between the at least two storage tanks via the inner pipe of the bunkering pipe (100).

The advantage of this method is that the inner pipe will only contain a fuel, such as LNG during bunkering. The refrigerant, however, (e.g. cooled nitrogen) circulates continuously at least during and before bunkering.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described referring to the figures, where figure 1 illustrates a cross section A-A of figure 2 of a cooled bunkering pipe and figure 2 illustrates a longitudinal cross section of a cooled bunkering pipe.

DESCRIPTION OF EMBODIMENTS

Figure 1 illustrates a cross section of a bunkering pipe 100 comprising an inner pipe 102, an outer pipe 104, insulation material 108, and a casing 110. The bunkering pipe 100 further comprises a plurality of distance pieces 106 between the inner pipe 102 and the outer pipe 104, thereby forming a cavity 103. The cavity 103 is sealed 121 ,123 in both ends 120,122 of the bunkering pipe 100 (see figure 2). The sealing 121 ,123 of the cavity 103 is referenced 121 ,123, (see figure 2), which is also used to reference the connection plug 121 , 123. The sealing of the cavity 103 could also be embodied as an end piece, such as a metal plate cut to size and welded to the ends of the inner pipe 102 and the outer pipe 104. Apart from ensuring the forming of the cavity 103, the plurality of spacers 106 also serve to center the inner pipe 102 and the outer pipe 104 relative to each other. Centering of the inner pipe 102 relative to the outer pipe serves two purposes. One is to ensure that the inner pipe 102 is centered relative to the entire bunkering pipe 100, and a second purpose is to ensure that the formed cavity 103 is uniform along the longitudinal axis of the bunkering pipe 100. The cavity 103 primarily serves as a cooling channel in which a refrigerant (not shown) can be circulated. The refrigerant enters through the refrigerant inlet 112 and returns to the refrigerant outlet 114 via a return pipe 105. The return pipe 105 can be placed on or in proximity of the outer pipe 104, and thus also be covered by the insulation material 108 of the bunkering pipe 100. The outer pipe 104, the insulation 108 and the casing constitute a fully bonded construction, meaning that all forces leading to compressive, shear, tensile stresses can be transferred. In another embodiment all elements of the bunkering pipe 100 can constitute a fully bonded construction. Figure 2 illustrates a longitudinal cross section of a cooled bunkering pipe 100. Typically one of the ends 120, 122 of the bunkering pipe 100 will, via the connection plug 121 , 123, be connected directly or indirectly to a storage tank (not shown) and the opposite end would be free to be connected directly or indirectly to another storage tank. The refrigerant (not shown) for cooling the inner pipe 102 enters the cavity 103 through the refrigerant inlet 112 placed at or in the proximity of the first end of the bunkering pipe 120. The refrigerant then flows from the first end of the bunkering pipe 120 to the second end of the bunkering pipe 122 through the cavity 103. At or in the proximity of the second end of the bunkering pipe 122, the cavity 103 is connected to the return pipe 105, which runs from the second end of the bunkering pipe 122 and back to the first end of the bunkering pipe 120, where the refrigerant can exit through the refrigerant outlet 114. Hereby the refrigerant inlet 112 and refrigerant outlet 114 are placed in proximity of each other.

The bunkering pipe 100 can be operated and used as follows:

Before the bunkering process commences, a refrigerant is circulated in the cavity 103 so as to cool the inner pipe 102, and the bunkering pipe as such. The refrigerant can be a fluid, such as a liquid or a gas. In order to obtain the best possible conditions for bunkering LNG from one storage tank to the other, the refrigerant can advantageously be at a temperature that is lower than the LNG, for example below -162°C. The refrigerant could for example be an inert gas, such as nitrogen (N2). When the bunkering pipe 100 has reached the desired temperature, the end of the bunkering pipe 100 is connected directly or indirectly to a storage tank. The connection could also have been established prior to circulating the refrigerant in the cavity 103. Hereafter the bunkering process can begin, leading LNG from one storage tank to the other. During the bunkering process, the refrigerant is continuously circulated through the cavity 103. Since the bunkering pipe 100 is continuously cooled, the LNG will not experience any temperature increase when passing through the bunkering pipe 100, and so it can pass at a high flow rate. After the bunkering process, the bunkering pipe 100 is disconnected from at least one of the storage tanks. The refrigerant can still be circulated through the cavity 103.

After a bunkering operation, the inner pipe 102 of the bunkering pipe 100 can be purged and/or emptied so as to ensure that LNG does not vaporize in to the atmosphere and to reduce the potential danger of being close to the bunkering pipe 100. The bunkering pipe 100 could be emptied for example by leading an inert gas through the inner pipe 102. In addition, the end of the bunkering pipe 100 that is not connected to a storage tank (not shown) can be plugged after the bunkering process and preferably also during or after the emptying or purging process. By plugging the bunkering pipe 100 the ingress of atmospheric air and humidity in the inner pipe 102 is hindered. Hereby it is avoided that water condensates on the inner side of the inner pipe 102 or at the external surface of the connection plug 121 ,123, which would make it difficult to connect the bunkering pipe to a LNG receiver or LNG source. In order to save time and reduce the stress on the bunkering pipe 100 caused by the continuous cooling and heating of the bunkering pipe 100, the refrigerant can be circulated continuously both when the bunkering pipe 100 is in operation and when not in operation. The plug (not shown) for the bunkering pipe 100 could be insulated so as to ensure that water does not condensate on the outer surfaces of the plug and to ease the connection of the bunkering pipe 100. The bunkering pipe 100 could also comprise an LNG leakage detector or sensor (not shown), which could be placed where the refrigerant flows, e.g. in the cavity or in the outlet. If a leakage from the inner pipe 102 is detected during bunkering, the operation can be stopped. The leakage detector will thus contribute to the safety of the bunkering process. To ensure continuous leakage detection, the refrigerant could be continuously circulated, however not necessarily at low temperature.

The inner pipe 102, the outer pipe 104 and the return pipe 105 can for example be manufactured in stainless steel. The insulation material 108 can for example be made of any closed-cell and/or solid thermal insulation material. The casing can be made of a polymer-based material such as HDPE. If required, the casing 108 can comprise a metal covering, such as a metal sheet to improve surface flammability

In another embodiment the cavity 103 of the bunkering pipe 100 of the present invention could also be used for heating the inner pipe 102. In yet another embodiment the bunkering pipe 100 does not comprise a return pipe 105, whereas the refrigerant inlet 112 and refrigerant outlet 114 would be placed in opposite ends 120, 122.

In another embodiment the cavity 103 is unsealed, whereby the connection plug could be embodied such that the fuel, e.g. LNG, could flow in the inner pipe 102 and a refrigerant could flow in the cavity 103. This embodiment requires that the part, typically a pipe, to which the bunkering pipe is connected, would have to be embodied in a similar way. Further, this embodiment would make it possible to circulate the same refrigerant in the entire bunkering line connecting the two storage tanks. In yet another embodiment the bunkering pipe could comprise at least one valve. REFERENCES

100 bunkering pipe

102 inner pipe

103 cavity

104 outer pipe

105 return pipe

106 distance piece or spacer

108 insulation material

1 0 casing

1 12 refrigerant inlet

114 refrigerant outlet

120 first end of the bunkering pipe

121 connection plug of the first end of the bunkering pipe 122 second end of the bunkering pipe

123 connection plug of the second end of the bunkering pipe

Claims

1. A bunkering pipe (100) comprising an inner pipe (102) in which a fuel such as a gas or oil can flow, characterized in that said bunkering pipe (100) further comprises an outer pipe (104) enclosing said inner pipe 102, thereby forming a cavity (103) between said inner pipe (102) and said outer pipe

(104) , such that a refrigerant can flow through said cavity (103).

2. A bunkering pipe (100) according to claim 1 , characterized in that said cavity (103) is sealed (121 , 123) in each end (120, 122) of said bunkering pipe (100).

3. A bunkering pipe (100) according to any of the preceding claims, characterized in that said cavity (103) can be accessed through at least one refrigerant inlet (112) and at least one refrigerant outlet (114).

4. A bunkering pipe (100) according to any of the preceding claims, characterized in that said bunkering pipe (100) comprises a return pipe

(105) of which one end is connected to said cavity (103) and where the other end of said return pipe (105) is connected to said refrigerant outlet (114).

5. A bunkering pipe (100) according to any of the preceding claims, characterized in that said refrigerant inlet (112) and said refrigerant outlet (114) are placed proximate to each other at one end (120, 122) of said bunkering pipe (100).

6. A bunkering pipe (100) according to claim 5, characterized in that said return pipe (105) is connected to said cavity (103) in one end (120, 122) of said bunkering pipe (100) and where said return pipe (105) is connected to said refrigerant outlet (114) at the opposite end (120, 122) of said bunkering pipe (100).

7. A bunkering pipe (100) according to any of the preceding claims, characterized in that said bunkering pipe (100) comprises at least one distance piece (106), positioning said inner pipe (102) relative to said outer pipe (104).

8. A bunkering pipe (100) according to any of the preceding claims, characterized in that said bunkering pipe (100) further comprises at least one layer of insulation (108) directly or indirectly bonded to the outer surface of said outer pipe (104).

9. A bunkering pipe (100) according to any of the preceding claims, characterized in that said bunkering pipe (100) further comprises at least one layer of casing (110) directly or indirectly bonded to the outermost surface of said insulation material (108).

10. A bunkering pipe (100) according to any of the preceding claims, characterized in that said bunkering pipe (100) comprises a connection plug (121 , 123) in each end (120, 122) of said bunkering pipe (100), through which connection plug (121 , 123) said bunkering pipe (100) can be connected directly or indirectly to at least one storage tank.

11. A method for bunkering a fuel such as a gas or oil characterized in that said method comprises the steps of

- connecting at least two storage tanks using at least one bunkering pipe (100) according to claims 1-10,

- circulating a refrigerant in said cavity (103), whereby said bunkering pipe 100 is cooled down,

- leading said fuel between said at least two storage tanks via said inner pipe (102) of said bunkering pipe (100).