Patent Publication Number: US-2016231050-A1

Title: Expandable lng processing plant

Description:
FIELD OF THE INVENTION 
     The present invention relates to an expandable liquefied natural gas (LNG) processing plant. More particularly, some embodiments of the invention are related to LNG production plants. Other embodiments of the invention are related to natural gas regasification plants. 
     BACKGROUND TO THE INVENTION 
     Large volumes of natural gas (i.e., primarily methane) are located in remote areas of the world. This gas has significant value if it can be economically transported to market. Natural gas (“NG”) is routinely transported from an onshore LNG production plant to another location in its liquid state as liquefied natural gas (“LNG”) by way of loading the LNG in the cryogenic storage tanks of purpose built large ocean going vessels known as “LNG Carriers”. Liquefaction of the natural gas makes it more economical to transport as LNG occupies only about 1/600th of the volume than the same amount of natural gas does in its gaseous state. Prior to liquefaction, raw natural gas that has been sourced from a wellhead is subjected to a series of gas pre-treatment processes including acid gas removal and dehydration to remove contaminants. After liquefaction, LNG is typically stored in cryogenic storage tanks at the LNG production plant either at or slightly above atmospheric pressure at a temperature of around −160 degrees Celsius. 
     Gas pre-treatment, liquefaction and storage are typically undertaken at a fixed onshore LNG production plant associated with a jetty that is built in sufficiently deepwater to allow berthing of the LNG Carriers. A typical LNG Carrier can be 300 m long with a draft of 15 to 20 meters. The docking of such LNG Carriers requires special conditions of water depth and sea state. In some countries, it is necessary to construct a pipeline and jetty several kilometers offshore to locate water that is deep enough to allow the approach of an LNG Carrier. The costs associated with the construction and installation of a jetty to allow berthing of an LNG Carrier is a major cost. To ship liquefied natural gas (LNG) by sea, a way to transfer LNG between the cryogenic storage tanks of the onshore LNG production plant and the cryogenic storage tanks of the LNG Carrier is required. Traditionally, the transfer means has taken the form of an insulated pipe that is laid on an elevated supporting trestle structure between the onshore LNG production plant and the jetty so that the insulated pipe remains at all times above the water line. These prior art transfer facilities include a vapour return line to return boil-off gas to the onshore LNG production plant. After LNG have been loaded into the cryogenic storage tanks of the LNG Carrier vessel for marine transport LNG is regasified before distribution to end users through a pipeline or other distribution network at a temperature and pressure that meets the delivery requirements of the end users. 
     The cost of traditional onshore LNG storage and offloading facilities has continued to increase through the years and is now a very significant component of the total installed cost for an LNG project. Efforts to reduce this cost have largely been focused on storage tank size optimization and seeking to leverage the economics of scale via increased LNG train capacity size and improvement in LNG berth utilization. To avoid the costs associated with the construction of a port to service an onshore LNG production facility, it has been proposed to produce LNG at sea. In this context, the entire LNG production is performed on a floating LNG production vessel. Alternatively, it has been proposed to conduct gas pre-treatment onshore with liquefaction conducted offshore on a floating vessel with equipment optimized in terms of size and layout to keep deck size to a minimum. Such gas pre-treatment includes the removal of water, sour gas species (CO 2  and H 2 S) and heavy hydrocarbons. The pre-treated gas is then sent by pipeline to the floating liquefaction facility. Given their size and complexity, the costs associated with the implementation of a complete LNG liquefaction plant at sea are extremely high. 
     Onshore plants used to liquefy natural gas are typically built in stages as the supply of feed gas, i.e. natural gas, and the quantity of gas contracted for sale, increase. Each stage normally consists of a separate, stand-alone unit, commonly called an ‘LNG train’. An LNG train comprises all of the individual components necessary to liquefy a stream of feed gas into LNG and send it on to a cryogenic storage tank. As the supply of feed gas to the plant exceeds the capacity of one stand-alone LNG train, additional stand-alone LNG trains are installed at the onshore plant, as needed, to handle increasing LNG production. In contrast, the processing feed rate of an LNG plant onboard a floating LNG production vessel, once constructed, cannot be altered, as all available deck space is utilised and optimised to keep the overall size of the floating LNG production vessel to a minimum. 
     The cost of LNG storage and offloading facilities has continued to increase through the years and is now a very significant component of the total installed cost for an LNG project. Efforts to reduce this cost have largely been focused on storage tank size optimization and seeking to leverage the economics of scale via increased LNG train capacity size and improvement in LNG berth utilization. 
     There remains a need for an alternative LNG processing plant that may address one or more of the above-described disadvantages of conventional LNG processing plants. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided an LNG processing plant positioned at a processing location adjacent to a body of water, the LNG processing plant comprising:
         A) a first phase LNG processing plant for processing an initial plant capacity of LNG, the first phase LNG processing plant comprising a plurality of first phase facilities, each first phase facility provided with plant equipment related to a pre-determined function associated with the processing of LNG, wherein one or more of the plurality of first phase facilities is arranged on a deck of a structure wherein the deck is arranged above the level of the water at a selected offshore or near-shore location; and,   B) one or more second phase facilities provided on the deck of the structure to provide a second phase LNG processing plant, said second phase LNG processing plant having a maximum plant capacity that is higher than the initial plant capacity, wherein the one or more second phase facilities are provided to expand the plant capacity of the first phase LNG processing plant in one or more incremental stages, and, the deck of the structure is sized to provide a pre-allocated space for the installation of the one or more second phase facilities on the deck of the structure.       

     In one form, the one or more of the plurality of first phase facilities is arranged towards a first end of the deck with the pre-allocated space being arranged towards a second opposite end of the deck. In one form, the one or more of the plurality of first phase facilities is arranged towards a first side of the deck with the pre-allocated space being arranged towards a second opposite side of the deck. 
     In one form, the structure is a fixed structure or a floating structure or a gravity based structure having a base that rests on the seabed at the selected location. 
     In one form, the structure includes a first cryogenic storage tank for receiving and storing LNG. In one form, the first cryogenic storage tank is prismatic storage tank or a membrane storage tank. In one form, the first cryogenic storage tank is one of a plurality of first cryogenic storage tanks. In one form, the first cryogenic storage tank has an LNG storage capacity of at least 160,000 m 3 . In one form, the first cryogenic storage tank has an LNG storage capacity in the range of 160,000 m 3  to 520,000 m 3 . 
     In one form, the structure has a length of up to 500 meters and a width of up to 150 meters. In one form, the structure has a depth of up to 50 metres. 
     In one form, the initial plant capacity of the first phase LNG processing plant is in the range of 0.5 to 7 million tons per annum of LNG. In one form, the maximum plant capacity after expansion to provide the second phase LNG processing plant is in the range of 2 million to 50 million tons per annum of LNG. In one form, one or more of the plurality of first phase facilities is sized for processing both the initial plant capacity and the maximum plant capacity. 
     In one form, one or more of second phase facilities is located on a fixed platform, a semi-submersible or a jacket structure. 
     In one form, the one of more second phase facilities are modules having a weight of greater than 7,000 tons. In one form, the modules have a weight of greater than 8,000 tons and up 100,000 tons. 
     In one form, the gravity structure includes one or both of a condensate storage tank and an LPG storage tank. 
     In one form, the structure includes an LNG transfer facility for loading LNG between from the first cryogenic storage tank of the structure to a second cryogenic storage tank onboard an LNG Carrier, or for unloading of LNG from the second cryogenic storage tank of an LNG Carrier to the first cryogenic storage tank of the structure. 
     In one form, the structure is constructed at a construction location and floated in to the first processing location before being positioned at the selected location. In one form, the structure is arranged to provide a breakwater for an LNG Carrier at the selected location. 
     In one form, the structure is transportable from a first processing location to a second processing location. In one form, the structure is a gravity based structure and the gravity based structure includes a ballast storage compartment arranged around the periphery of the gravity based structure or arranged toward the base of the gravity based structure, for ballasting. In one form, the ballast storage compartment is one of a plurality of ballast storage compartments. 
     In one form, the LNG processing plant is an LNG production plant arranged to receive a feed stream of natural gas and liquefy the natural gas to produce a product stream of LNG. 
     In one form, the first phase LNG processing plant includes a first phase gas receiving facility for receiving a hydrocarbon stream comprising hydrocarbon gas and liquids and separating the liquids, including one or both of condensate and free water, from the hydrocarbon stream to produce a hydrocarbon feed gas stream for a gas pre-treatment facility. In one form, the first phase gas receiving facility is arranged on the deck of the structure. In one form, the first phase gas receiving facility is arranged offshore or subsea. In one form, the first phase gas receiving facility is arranged onshore. 
     In one form, the first phase LNG processing plant includes a first phase gas pre-treatment facility for receiving a hydrocarbon feed gas stream from a gas receiving facility and removing contaminants from the hydrocarbon feed gas stream to produce a stream of pre-treated gas. In one form, the first phase gas pre-treatment facility is arranged on the deck of the structure. In one form, the first phase gas pre-treatment facility is arranged onshore. In one form, the first phase gas pre-treatment facility is arranged offshore. In one form, the first phase LNG processing plant includes a first phase LNG liquefaction facility for receiving the stream of pre-treated gas from a gas pre-treatment facility and liquefying the natural gas to produce a product stream of LNG. 
     In one form, the first phase LNG liquefaction facility is arranged on the deck of the structure. In one form, the first phase LNG liquefaction facility is arranged onshore. In one form, the first phase LNG liquefaction facility is arranged offshore. In one form, the structure includes a boil-off gas reliquefaction facility for liquefying at least a portion of the boil off gas that is generated in first cryogenic storage tank. 
     In one form, the LNG processing plant is an LNG regasification plant arranged to receive a feed stream of LNG and vaporise the LNG to produce a product stream of natural gas. In one form, the first phase LNG regasification plant includes a first phase power generation facility for generating a supply of power using a first phase product stream of natural gas as a source of fuel to generate electricity. In one form, the first phase power generation facility is arranged on the deck of the structure. In one form, the first phase power generation facility is arranged offshore. In one form, the first phase power generation facility is arranged onshore. In one form, the first phase power generation facility is a pre-existing onshore power plant. 
     In one form, the first phase LNG regasification plant includes a first phase vaporised gas receiving facility arranged to receive a stream of vaporised natural gas from a first phase regasification facility and send out a first phase product stream of vaporised natural gas. In one form, the first phase vaporised gas receiving facility is arranged on the deck of the structure. In one form, the first phase vaporised gas receiving facility is arranged offshore. In one form, first phase vaporised gas receiving facility is arranged onshore. In one form, the first phase LNG regasification plant includes a first phase regasification facility arranged to vaporise a first phase feed stream of LNG to produce a first phase stream of vaporised natural gas which is transferred to a first phase vaporised gas receiving facility. In one form, the first phase regasification facility is arranged on the deck of the structure. In one form, the first phase regasification facility is arranged offshore. In one form, the first phase regasification facility is arranged onshore. 
     In one form, the initial plant capacity is at least 0.5 million tons per year and the maximum feed processing capacity is at least 2 million tons per year. In one form, the first initial plant capacity is at least 0.5 million tons per year and the maximum feed processing capacity is not greater than 50 million tons per year. In one form, the first initial plant capacity is at least 0.5 million tons per year and the maximum feed processing capacity is not greater than 70 million tons per year. 
     According to a second aspect of the present invention there is provided a method of processing LNG in an LNG processing plant is positioned at a processing location adjacent to a body of water, the method comprising:
         A) providing a first phase LNG processing plant for processing an initial plant capacity of LNG, the first phase LNG processing plant comprising a plurality of first phase facilities, each first phase facility having plant equipment related to a pre-determined function associated with the processing of LNG, wherein one or more of the plurality of first phase facilities is arranged on a deck of a structure, wherein the deck is arranged above the level of the water at a selected offshore or near-shore location; and,   B) expanding the plant capacity of the first phase LNG processing plant in one or more incremental stages by providing one or more second phase facilities on the deck of the structure to provide a second phase LNG processing plant, said second phase LNG processing plant having a maximum plant capacity that is higher than the initial plant capacity, wherein the deck of the structure is sized to provide a pre-allocated space for the installation of the one or more second phase facilities on the deck of the structure.       

     In one form, the step of processing LNG from the first phase LNG processing plant during step B). In one form, the step of arranging the one or more of the plurality of first phase facilities towards a first end of the deck with the pre-allocated space being arranged towards a second opposite end of the deck. In one form, the step of arranging the one or more of the plurality of first phase facilities towards a first side of the deck with the pre-allocated space being arranged towards a second opposite side of deck. 
     In one form, the initial plant capacity of the first phase LNG processing plant is in the range of 0.5 to 7 million tons per annum of LNG. In one form, the maximum plant capacity after the step of expanding to the second phase LNG processing plant is in the range of 2 million to 70 million tons per annum of LNG. In one form, the step of sizing the one or more of the plurality of first phase facilities for processing both the initial plant capacity and the maximum plant capacity. 
     In one form, the step of locating one or more of second phase facilities is on a fixed platform, a semi-submersible or a jacket structure. In one form, the method comprising providing the one or more second phase facilities as modules having a weight of greater than 7,000 tons. In one form, the modules have a weight of greater than 8,000 tons and up 100,000 tons. 
     In one form, the method comprises the step of constructing the structure at a construction location and floating the structure into the first processing location for positioning of the structure at the selected location. In one form, the method comprises the step of arranging the structure to provide a breakwater for an LNG Carrier at the selected location. In one form, the method comprises the step of moving the structure from a first processing location to a second processing location. In one form, the LNG processing plant is an LNG production plant arranged to receive a feed stream of natural gas and liquefy the natural gas to produce a product stream of LNG. In one form, the LNG processing plant is an LNG regasification plant arranged to receive a feed stream of LNG and vaporise the LNG to produce a product stream of natural gas. 
     In one form, the initial plant capacity is at least 0.5 million tons per year and the maximum feed processing capacity is not greater than 50 million tons per year. In one form, the initial plant capacity is at least 2 million tons per year and the maximum feed processing capacity is not greater than 50 million tons per year. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to facilitate a more detailed understanding of the nature of the invention several embodiments of the present invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic plan view of a first embodiment illustrating one incremental stage of expansion of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines; 
         FIG. 2  is a schematic plan view of the first embodiment of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in solid lines; 
         FIG. 3  is a schematic side view of the first embodiment of an LNG processing plant illustrating a subsea pipeline extending from onshore to a gravity based structure; 
         FIG. 4  is a schematic side view of the first embodiment of an LNG processing plant illustrating a trestle extending from onshore to a gravity based structure; 
         FIG. 5  is a schematic representation of the structure being floated or towed from a construction location or an assembly location to a first processing location or being de-ballasted at a first processing location and floated or towed to a second processing location for re-ballasting; 
         FIG. 6  is a schematic plan view of a second embodiment illustrating one incremental stage of expansion of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines, with all facilities being arranged on the deck of the structure; 
         FIG. 7  is a schematic plan view of the second embodiment of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in solid lines, with all facilities being arranged on the deck of the structure; 
         FIG. 8  is a schematic plan view of a third embodiment illustrating one incremental stage of expansion of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines, with all of the facilities located on the deck of the structure; 
         FIG. 9  is a schematic plan view of a third embodiment illustrating one incremental stage of expansion of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines, with one of the facilities located off the deck of the structure; 
         FIG. 10  is a schematic plan view of a third embodiment illustrating one incremental stage of expansion of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines, with one of the facilities located onshore; 
         FIG. 11  is a schematic plan view of a fourth embodiment illustrating one incremental stage of expansion of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines, with all of the facilities located on the deck of the structure; 
         FIG. 12  is a schematic plan view of a fourth embodiment illustrating one incremental stage of expansion of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines, with one of the facilities located off the deck of the structure; 
         FIG. 13  is a schematic plan view of a fourth embodiment illustrating one incremental stage of expansion of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines, with one of the facilities located onshore; 
         FIG. 14  is a schematic plan view of a fifth embodiment illustrating three incremental stages of expansion of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines; 
         FIG. 15  is a schematic plan view of the fifth embodiment of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in solid lines, after the addition of the first incremental stage; 
         FIG. 16  is a schematic plan view of the fifth embodiment of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in solid lines, after the addition of the first and second incremental stages; 
         FIG. 17  is a schematic plan view of the fifth embodiment of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in solid lines, after the addition of the first, second, and third and final incremental stages; 
         FIG. 18  is a schematic plan view of a sixth embodiment illustrating three incremental stages of expansion of an LNG processing plant by adding units or facilities installed on a fixed structure, with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in dotted lines; 
         FIG. 19  is a schematic plan view of the sixth embodiment of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in solid lines, after the addition of the first incremental stage; 
         FIG. 20  is a schematic plan view of the sixth embodiment of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in solid lines, after the addition of the first and second incremental stages; 
         FIG. 21  is a schematic plan view of the sixth embodiment of an LNG processing plant with the first phase LNG processing plant shown in solid lines and the second phase LNG processing plant shown in solid lines, after the addition of the first, second, and third and final incremental stages; 
         FIG. 22  is a schematic side view of the sixth embodiment of an LNG processing plant illustrating a trestle extending from onshore to a floating structure; and, 
         FIG. 23  is a schematic side view of the sixth embodiment of an LNG processing plant illustrating a subsea pipeline extending from onshore to a fixed structure. 
     
    
    
     It is to be noted that the drawings illustrate only preferred embodiments of the invention and are therefore not to be considered limiting of the invention&#39;s scope as it may admit to other equally effective embodiments. Like reference numerals refer to like parts. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, all drawings are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely. 
     DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 
     Particular embodiments of the present invention are now described. The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. 
     The acronym ‘LNG’ refers to liquefied natural gas. The acronym ‘LPG’ refers to liquefied petroleum gas. The term ‘LNG Carrier’ refers to a marine transport vessel that is capable of carrying a cargo of liquefied natural gas over water. 
     The term ‘onshore facility’ as used in this specification and in the claims refers to a facility that is arranged entirely on land, preferably near a coastline. 
     The term ‘offshore facility’ as used in this specification and in the claims refers to a facility that is arranged entirely in or over water, whereby the facility is surrounded by seawater in all directions. The term ‘near-shore facility’ as used in this specification and in the claims refers to an offshore facility that is located in shallow water. The term ‘shallow water’ as used in this specification and in the claims refers to water that has a water depth of less than 50 m or less than 15 m or less than 10 m or less than 5 m deep. 
     The distance between the onshore facility and the offshore facility where there is a connecting pipeline may vary. This distance is preferably greater than or equal to 5 km or greater than or equal to 10 km, or greater than or equal to 15 km, or greater than or equal to 20 km, or greater than or equal to 30 km or greater than or equal to 200 km. 
     As used herein and in the claims the phrase ‘LNG processing plant’ means any processing plant that produces a product that is changed in some way from the feed, with the feed or the product being LNG. One example of a LNG processing plant is a LNG production plant for producing LNG. Another example of a LNG processing plant is a LNG vaporisation or regasification plant where the feed is LNG. 
     As used herein and in the claims the phrase ‘liquefaction facility’ means a facility that processes a feed stream that includes gaseous methane into a product stream that includes liquid methane. An LNG liquefaction plant includes at least one cryogenic heat exchanger and at least one refrigerant compression system. 
     As used herein and in the claims, the phrase ‘gas pre-treatment facility’ means a facility that receives a feed stream which includes at least methane, ethane, carbon dioxide, and hydrogen sulfide and produces a pre-treated gas stream which contains methane and reduced amounts of the other non-methane species as compared to the feed stream. The gas pre-treatment plant may include equipment for the removal of hydrogen sulphide, carbon dioxide and water. The gas pre-treatment plant may optionally include equipment for the removal of mercury. The gas pre-treatment plant may include equipment for the removal of heavy hydrocarbons. The term ‘heavy hydrocarbon’ refers to a hydrocarbon compound with more than three carbon atoms in the chain. 
     Using the method and system of the present invention LNG is processed in an LNG processing plant is positioned at a processing location adjacent to a body of water, the method comprising:
         A) providing a first phase LNG processing plant for processing an initial plant capacity of LNG, the first phase LNG processing plant comprising a plurality of first phase facilities, each first phase facility having plant equipment related to a pre-determined function associated with the processing of LNG, wherein one or more of the plurality of first phase facilities is arranged on a deck of a structure, wherein the deck is arranged above the level of the water at a selected offshore or near-shore location; and,   B) expanding the plant capacity of the first phase LNG processing plant in one or more incremental stages by providing one or more second phase facilities on the deck of the structure to provide a second phase LNG processing plant, said second phase LNG processing plant having a maximum plant capacity that is higher than the initial plant capacity, wherein the deck of the structure is sized to provide a pre-allocated space for the installation of the one or more second phase facilities on the deck of the structure.       

     In order to facilitate expansion, the deck of the structure is designed and sized to provide a pre-allocated space on the deck for the installation of the one or more second phase facilities on the deck. Advantageously, processing of LNG from the first phase LNG processing plant is able to continue during the step of expansion. The first phase LNG processing plant is arranged on the deck of the structure in such a way as to provide easy access to the pre-allocated space. 
     The LNG processing plant may be an LNG production plant arranged to receive a feed stream of natural gas and liquefy the natural gas to produce a product stream of LNG with reference to the first to the sixth embodiments of the present invention as described in detail below. Alternatively, the LNG processing plant may be a LNG regasification plant arranged to receive a feed stream of LNG and produce and product stream of natural gas as described in detail below with reference to a seventh embodiment. 
     A first embodiment of the present invention is now described with reference to  FIGS. 1 to 4  in the context of the LNG processing plant being an LNG production plant. More specifically, there is provided a first phase LNG production plant for producing an initial plant capacity of LNG, the first phase LNG production plant comprising a plurality of spaced-apart facilities, each facility provided with plant equipment related to a pre-determined function associated with the liquefaction of LNG. The first phase LNG production plant includes at least the following facilities:
         a) a gas receiving facility for receiving a hydrocarbon stream comprising hydrocarbon gas and liquids and separating the liquids, including one or both of condensate and free water, from the hydrocarbon stream to produce a hydrocarbon feed gas stream for a gas pre-treatment facility;   b) a gas pre-treatment facility for receiving a hydrocarbon feed gas stream from the gas receiving facility and removing contaminants from the hydrocarbon feed gas stream to produce a stream of pre-treated gas;   c) a liquefaction facility for receiving the stream of pre-treated gas from a gas pre-treatment facility and liquefying the natural gas to produce a product stream of LNG;   d) a storage facility operatively associated with a transfer means for receiving the product stream of LNG from the liquefaction facility for receiving and storing LNG in a first cryogenic storage tank; and,   e) an offloading facility including LNG transfer facilities to transfer the LNG from the first cryogenic storage tank of the storage facility to a second cryogenic storage tank onboard an LNG Carrier on an as-needs basis.       

     Referring to  FIGS. 1 to 4 , an LNG processing plant  10 , in the form of an LNG production plant, is positioned at a first processing location  12  adjacent to a body of water  14 . The LNG production plant  10  includes a first phase LNG production plant  16  for producing an initial plant capacity of LNG illustrated in solid lines in both  FIG. 1  and  FIG. 2 , with a pre-allocated space provided on the deck of the structure for the later expansion of the LNG processing plant  10  in one or more incremental stages to provide a second phase LNG production plant  18 , said second phase LNG production plant having a maximum plant capacity that is higher than the initial plant capacity. The second phase LNG production plant  18  is illustrated in dotted lines in  FIG. 1  and solid lines in  FIG. 2 . In the first embodiment illustrated in  FIGS. 1 and 2 , the plant capacity of the first phase LNG production plant  16  is increased in one incremental stage by installing one or more second phase facilities to provide the second phase production plant. This expansion is able to be conducted without interruption to the processing of LNG by the first phase LNG production plant. 
     In the first embodiment now described with reference to  FIGS. 1 to 4 , the first phase LNG production plant  16  includes a first phase gas receiving facility  20  (hereinafter referred to as a ‘slugcatcher’) for receiving a hydrocarbon stream  21  comprising hydrocarbon gas and liquids and separating the liquids, including one or both of condensate and free water, from the hydrocarbon stream to produce a first phase hydrocarbon feed gas stream  23 . The LNG production plant  10  includes a first phase offshore gas pre-treatment facility  22  for producing a first phase stream of pre-treated gas  25 . In this embodiment, the first phase LNG production plant  16  includes a first phase liquefaction facility  24  for receiving the first phase stream of pre-treated gas  25  from the gas pre-treatment facility  22  and liquefying the first phase pre-treated gas stream  25  to produce a first phase product stream of LNG  26 . The first phase product stream of LNG is produced at a rate that is determined by the initial plant capacity of LNG of the first phase LNG production plant  16 . 
     By way of example only, the initial plant capacity of the first phase LNG production plant is in the range of 0.5 to 7 million tons per annum of LNG. The maximum plant capacity after expansion to provide the second phase LNG production plant is in the range of 2 million to 50 million tons per annum of LNG. 
     The first phase gas pre-treatment facility  22  includes equipment for acid gas removal, dehydration and, optionally, mercury removal and heavy hydrocarbon removal of the kind that is known in the art. Liquefaction is achieved in the first phase liquefaction facility  24  using any liquefaction process well established in the art which typically involve compression, expansion and cooling. Such prior art liquefaction processes include processes based on a nitrogen cycle, the APCI C3/MR™ or Split MR™ or AP-X™ processes, the Phillips Optimized Cascade Process, the Linde Mixed Fluid Cascade process, the Shell Double Mixed Refrigerant or Parallel Mixed Refrigerant process, or the Axens LIQUEFIN™ process. 
     In the embodiment illustrated in  FIGS. 1 to 4 , the LNG production plant  10  includes a structure  28  in the form of a gravity based structure having a base  30  that rests on the seabed  32  at a selected location  34  within the body of water  14 , the gravity-based structure having a deck  38  arranged above the level  40  of the water at the selected location  34 . The selected location is offshore or near-shore. The shoreline is designated with the reference numeral  29 . 
     By way of example, when the structure is in the form of a gravity based structure, the gravity based structure may be constructed using lightweight or semi-lightweight concrete (having a density of less than about 2000 kg/m 3 ). Alternatively or additionally, the gravity based structure may be constructed of steel or a hybrid comprising a combination of steel and concrete or a composite material. Advantageously, the gravity based structure is able to be constructed and commissioned at a construction location, such as a shipyard, where a trained and cost-efficient labour force is available and then floated in to the first processing location  12  before being positioned at the selected location  34 . Alternatively, the structure may be constructed in the form of one or modules constructed on floated in barges or substructures with a topsides weight of up to 100,000 tons. 
     The structure  28  has a first cryogenic storage tank  42  operatively associated with the first phase liquefaction facility  24  for receiving LNG from the first phase liquefaction facility  24  and storing the first phase product stream of LNG in the first cryogenic storage tank  42 . Preferably, the first cryogenic storage tank  42  is one of a plurality of first cryogenic storage tanks with two storage tanks shown in  FIG. 3  by way of example only. The first cryogenic storage tank  42  may be a double containment, full containment, prismatic or membrane systems with a primary tank constructed from, by way of example, stainless steel, aluminum, and/or 9%-nickel steel. The first cryogenic storage tank may include pre-tensioned concrete to provide structural resistance to the stored LNG, boil off gas pressure loads and to external hazards. The structure  28  further includes an LNG transfer facility  44  for transferring LNG from the first cryogenic storage tank  42  to a second cryogenic storage tank  46  onboard an LNG Carrier  48 . Advantageously, the structure  28  acts as a breakwater for the LNG Carrier  48  to reduce environmental loads on the LNG Carrier. 
     Referring to  FIG. 5 , the structure  28  is transportable from a construction location  50  to the first processing location  12  or from an assembly location  52  to the first processing location  12  by towing or on floating barges. The construction location  50  may be one of a plurality of constructions locations with three shown in  FIG. 5  by way of example only. Advantageously, testing or pre-commissioning of the structure  28  can be conducted before transportation of the structure  28  to the processing location  14 . This feature not only allows the structure to be deployed where required but is also advantageous when maintenance or upgrading is required. The structure may be re-deployed at a different location at a later time to suit LNG supply and demand, for example, due to changes in the capacity of the LNG production plant or towards the end of a gas field life. Thus with reference to  FIG. 5 , the structure can be moved from the first processing location  12  to a second processing location  13 . 
     Referring to  FIG. 3 , the first phase feed gas stream from the slugcatcher  20  is delivered to the gravity based structure  28  via a subsea pipeline  33 . Referring to  FIG. 4 , the first phase feed gas stream from the slugcatcher  20  is delivered to the gravity based structure  28  via a pipeline  35  arranged on a trestle  37 . To allow sufficient water depth for an LNG Carrier  48  to berth alongside the gravity based structure  28 , the selected location  34  has a water depth as measured from the waterline  40  to the seabed  32  of between 15 and 50 meters. 
     When the structure  28  is in the form of a gravity based structure, the gravity based structure includes a ballast storage compartment  56 , preferably arranged around the periphery of the gravity based structure or arranged toward the base of the gravity based structure, for ballasting. For flexibility to adjust the level of ballasting to suit the seabed conditions at a given selected location  34 , the ballast storage compartment  56  may be one of a plurality of ballast storage compartments with four ballast storage compartments shown in  FIGS. 1 and 2 , by way of example only. The gravity based structure  28  is towed from the construction or assembly location ( 50  or  52 , respectively) to the first processing location  12  and then arranged at the selected location  34  where settling is achieved by the addition of a ballasting material to the ballast storage compartment  56  until the base  30  of the gravity based structure  28  rests on the seabed  32  to secure the position of the gravity based structure  28 . This provides the gravity based structure with greater stability than a floating structure. The amount of ballasting material required to secure the gravity based structure to the seabed at the selected location depends on a number of relevant factors including but not limited to the shear strength of the underlying clay or silt material found at the bottom of the body of water at the selected location. If required, the gravity based structure  28  may include a piling system  58  to anchor the gravity based structure  28  into the seabed  32 . The ballasting material may be a solid ballasting material or a liquid ballasting material. By way of example, one or both of iron ore and sand may be used as the solid ballast material. In one embodiment of the present invention, the liquid ballasting material is water, condensate, monoethylene glycol (MEG), methanol, diesel, demineralised water, LPG or combinations thereof. The liquid ballasting material may be stored in a non-cryogenic storage tank. 
     In this first embodiment of the present invention, the first phase LNG production plant  16  is provided for producing an initial plant capacity of LNG. The first phase LNG production plant  16  is provided with all of the equipment needed to produce the initial plant capacity of LNG with the LNG so produced being stored in the first cryogenic storage tank onboard the structure  28 . In use, an LNG Carrier  48  comes in to berth at the structure  28  to receive a cargo of LNG. When the LNG Carrier is docked at the structure  28  the first phase product stream of LNG  26  can be directed into the second cryogenic storage tank  46  onboard the LNG Carrier. When there is no LNG Carrier docked at the gravity based structure  28 , the first phase product stream of LNG  26  is directed to the first cryogenic storage tank for storage onboard the gravity based structure  28 . 
     The structure  28  is designed so that the LNG Carrier  48  may approach the structure from either direction depending on the prevailing weather conditions. A side of the structure that is sheltered from the prevailing weather conditions is referred to as the “lee side”. Preferably, the structure  28  has a lee side  60 , whereby, in use, the LNG Carrier  48  approaches the structure  28  from the lee side  60 . The structure  28  is designed and sized to have at least one lateral side  68  which has a length of a sufficient size to allow an LNG carrier  48  to be docked along alongside the structure  28  without overhang of any portion of the LNG Carrier  48  beyond an end  61  of the gravity based structure. The structure  28  can be fitted with fendering equipment (not shown) to absorb a substantial portion of a load generated by any impact of the LNG Carrier  48  with the structure during transfer of LNG from the first cryogenic tank  32  to the second cryogenic tank  46 . 
     The first cryogenic storage tank  42  which is arranged below the deck of the structure  28  is operatively associated with the first phase liquefaction facility  24  and receives a first phase product stream of LNG  26  from the first phase liquefaction facility  24 . The integrated LNG transfer facility  44  located on the structure  28  includes a fixed or swivel joint loading arm or flexible hose above the water surface  40 , preferably fitted with an emergency release system at one end of the loading arm or hose. Between transfer operations, the LNG transfer facility  44  may be kept cold by re-circulation of a small quantity of LNG. The LNG transfer facility  44  may include an emergency safety system to allow loading to be stopped if required in a quick, safe, and controlled manner by closing an isolation valve on the LNG transfer lines or shutting down the cargo pumps associated with the second cryogenic storage tank  46  onboard the LNG carrier  48 . The emergency safety system is designed to allow LNG transfer to be restarted with minimum delay after corrective action has been taken. 
     In a preferred embodiment, the structure  28  includes a boil-off gas reliquefaction facility  63  for liquefying at least a portion of the boil off gas that is generated in first cryogenic storage tank  42  of the structure  28  or during the transfer of the LNG from the first cryogenic storage tank  42  to the second cryogenic storage tank  46  of the LNG Carrier  48 . The reliquefied boil-off gas may be returned for storage in the first cryogenic storage tank. Boil off gas is generated due to one or more of the following: a) cooling down of the interior surfaces of the second cryogenic storage tank onboard the LNG Carrier; b) heat leaking in from the environment through the exterior surfaces of the second cryogenic storage tank onboard the LNG Carrier; c) heat from the cryogenic pumps used to transfer the LNG from the first cryogenic storage tank to the second cryogenic storage tank; and d) heat ingress from the LNG transfer facility transfer hoses or loading arms; e) flashing off due to a temperature increase during the transfer operation, and, f) flashing due to pressure drop during LNG transfer from liquefaction to storage. Alternatively or additionally, a portion of the boil off gas may be used as a source of fuel for a first phase power generation system  62  arranged on the deck  38  of the structure  28 . The first phase generation system  62  may be configured to provide power to the first phase LNG liquefaction facility  24  as well as providing power to other services and utilities of the structure  28 , including the electrical utility systems, the crew and cargo systems and associated pumps, fans or other equipment associated with the liquefaction and gas pre-treatment facilities, the lighting systems, the accommodation unit, communications systems, inert gas and nitrogen generation systems, air supply systems, water systems, and waste treatment. 
     The first phase LNG production plant  16  described above and illustrated in solid lines in  FIG. 1  is provided, commissioned, and operated at an initial plant capacity. Using the method and system of the present invention, the plant capacity of the first phase LNG production plant  16  is expanded in one or more incremental stages by installing one or more second phase facilities to provide a second phase LNG production plant, said second phase LNG production plant having a maximum plant capacity that is higher than the initial plant capacity. As can be seen from the arrangement of solid and dotted lines in  FIG. 1 , the first phase gas pre-treatment facility  22  and the first phase liquefaction facility  24  are arranged towards a first end  70  of the structure  28  with a pre-allocated space  71  being provided on the deck  32  of the structure  28  in anticipation of the subsequent addition of one or more process units to provide a second phase gas pre-treatment facility  122  and a second phase liquefaction facility  124 . When installed, the second phase gas pre-treatment facility  122  and the second phase liquefaction facility  124  are arranged towards a second opposite end  72  of the structure  28 . In this way, it is possible to continue to process LNG in the first phase LNG production plant  16  whilst undertaking the step of installing and commissioning the second phase LNG production plant  18  for expanding the overall plant capacity from the initial plant capacity to a maximum plant capacity. 
     Referring to  FIG. 2 , after expansion, the second phase LNG production plant  18  is arranged to receive a second phase hydrocarbon feed gas stream  123  from a second phase gas receiving facility  120  positioned onshore. In this embodiment, the second phase gas receiving facility  120  is arranged to receive a second phase hydrocarbon stream  121  comprising hydrocarbon gas and liquids and separating the liquids, including one or both of condensate and free water, from the hydrocarbon stream to produce the second phase hydrocarbon feed gas stream  123 . In this embodiment, after expansion, the LNG production plant  10  includes a second phase offshore gas pre-treatment facility  122  for producing a second phase stream of pre-treated gas  125 , and a second phase offshore liquefaction facility  124  for receiving the second phase stream of pre-treated gas  125  from the second phase gas pre-treatment facility  122  and liquefying the second phase pre-treated gas stream  125  to produce a second phase product stream of LNG  126 . Using the first embodiment of the present invention illustrated in  FIGS. 1 and 2 , when the second phase product stream of LNG is combined with the first phase product stream of LNG, the overall plant capacity of the LNG production plant  10  has been expanded from the initial plant capacity to a maximum plant capacity in one incremental stage. 
     In the embodiment illustrated in  FIGS. 1 to 4 , the first cryogenic storage tank  42  is operatively associated with both the first phase LNG production plant  16  and the second phase LNG production plant  18  and both the first phase LNG product stream and the second phase LNG product stream are stored in the first cryogenic storage tank  42  or in one of a plurality of first cryogenic storage tanks. By way of example, the second cryogenic storage tank may have an LNG storage capacity in the range of 125,000 m 3  to 260,000 m 3 . The first cryogenic storage tank  32  has an LNG capacity of at least 160,000 m 3 . The upper limit of the LNG capacity of the one or more first cryogenic storage tanks aboard the gravity based structure is around 400,000 m 3  to 520,000 m 3 . The LNG transfer facility  44  continues to perform the function of transferring LNG from the first cryogenic storage tank  42  to a second cryogenic storage tank  46  onboard an LNG Carrier  48  when an LNG Carrier is docked at the structure  28 . 
     In use, after expansion, an LNG Carrier  48  comes in to berth at the structure  28  to receive a cargo of LNG. When the LNG Carrier  48  is docked at the structure  28  one or both of the first phase product stream of LNG  26  and the second phase product stream of LNG  126  may be directed into one or more of the first cryogenic storage tank  42  of the gravity based structure  28  or directed into the second cryogenic storage tank  46  onboard the LNG Carrier  48  using the integrated transfer facilities  44 . When there is no LNG Carrier docked at the structure  28 , the first phase product stream of LNG  26  and the second phase product stream of LNG  126  are directed to the first cryogenic storage tank  42  for storage onboard the structure  28 . 
     In the first embodiment of the present invention illustrated with reference to  FIGS. 1 to 4 , the first cryogenic storage tank  42  or the plurality of first cryogenic storage tanks  42  is/are sized from the outset to accommodate storage of LNG based on the maximum plant capacity of the LNG processing plant. In addition, the second phase LNG production plant  16  is provided with all of the equipment needed to produce the second phase product stream of LNG  126  with the LNG so produced being stored in the first cryogenic storage tank  42  onboard the gravity based structure  28 . In order to accommodate expansion, the structure is designed and sized to have a sufficient space on its deck  38  to allow for installation of the one or more second phase facilities to provide the second phase LNG production plant  18 . By way of example, the deck  38  of the structure may have a length of up to 370 meters and a width of up to 150 meters. The depth of the structure may be up to 50 metres. 
     A second embodiment of the present invention is now described with reference to  FIGS. 6 and 7  for which like reference numerals refer to like parts. As for  FIGS. 1 and 2 , the first phase LNG production plant  16  is shown in solid lines in  FIG. 6  and  FIG. 7  whilst the second phase LNG production plant  18  is shown in dotted lines in  FIG. 6  with solid lines indicating that expansion has been completed in  FIG. 7 . The dotted lines in  FIG. 6  represent the pre-allocated space  71  provided on the deck  38  of the structure  28  for subsequent expansion. In this embodiment the first phase gas receiving facility  20  is arranged on the deck  38  of the structure  28  with a pre-allocated space  71  being provided on the deck  38  of the structure  28  in anticipation of the subsequent addition of the second phase gas receiving facility  120  to be installed at a later time when expansion of the plant capacity is desired. The pre-allocated space  71  is arranged towards a first side  81  of the structure  28  with the pre-allocated space being arranged towards a second opposite side  83  of the structure. 
     A third embodiment of the present invention is now described with reference to  FIGS. 8 to 10  for which like reference numerals refer to like parts. As for  FIGS. 1 and 2 , the first phase LNG production plant  16  is shown in solid lines in  FIGS. 8 to 10  whilst the second phase LNG production plant  18  is shown in dotted lines. The dotted lines in  FIGS. 8 to 10  represent the pre-allocated space  71  provided on the deck  38  of the structure  28  for subsequent expansion. In this embodiment, the first phase gas receiving facility  20  is designed and sized of sufficient capacity to produce both the first phase hydrocarbon feed gas stream  23  and the second phase hydrocarbon feed gas stream  123 . In other words, the first phase gas receiving facility  20  is capable not only of operating at the initial plant capacity prior to expansion, but is also capable of operating at the maximum plant capacity after one or more additional units are added to provide the second phase production plant  18 . In  FIG. 8 , the first phase gas receiving facility  20  is arranged on the deck  38  of the structure  28 . In  FIG. 9 , the first phase gas receiving facility  20  is arranged offshore or near-shore at a subsea location  78 . In  FIG. 10 , the first phase gas receiving facility  20  is arranged onshore. In each of the embodiments illustrated in  FIGS. 8 to 10 , the first phase gas facility  20  is designed and sized to perform the function of both the first phase gas facility  20  and the second phase gas facility  120 . 
     A fourth embodiment of the present invention is now described with reference to  FIGS. 11 to 13  for which like reference numerals refer to like parts. As for  FIGS. 1 and 2 , the first phase LNG production plant  16  is shown in solid lines in  FIGS. 11 to 13  whilst the second phase LNG production plant  18  is shown in dotted lines. The dotted lines in  FIGS. 11 to 13  represent the pre-allocated space  71  provided on the deck  38  of the  28  for subsequent expansion. In this embodiment, the first gas pre-treatment facility  22  is designed and sized of sufficient capacity to produce both the first phase pre-treated gas stream  25  and the second phase pre-treated gas stream  125 . In other words, the first phase gas pre-treatment facility  22  is capable not only of operating at the initial plant capacity prior to expansion, but is also capable of operating at the maximum plant capacity after one or more additional units are added to provide the second phase production plant  18 . In  FIG. 11 , the first phase gas receiving facility  20  and the first phase pre-treatment facility  22  are arranged on the deck  38  of the structure  28 . Both are designed and sized to handle the maximum plant capacity but operate at the initial plant capacity prior to expansion. In  FIG. 12 , the first phase gas receiving facility  20  and the first phase pre-treatment facility  22  are arranged onshore. As for  FIG. 11 , both are designed and sized to handle the maximum plant capacity but operate at the initial plant capacity prior to expansion. In  FIG. 13 , the first phase gas pre-treatment facility  22  is arranged on the structure  28  with the first phase gas receiving facility  20  being arranged at a subsea location  78 . As for  FIG. 11 , both are designed and sized to handle the maximum plant capacity but operate at the initial plant capacity prior to expansion. 
     In each of the embodiments illustrated in  FIGS. 1 to 4 and 6 to 13 , the plant capacity of the first phase LNG processing plant is expanded in one incremental stage from the initial plant capacity to the maximum plant capacity. However, the plant capacity of the first phase LNG processing plant could equally be expanded in more incremental stages from the initial plant capacity to the maximum plant capacity with three such incremental stages illustrated in the fifth embodiment now described with reference to  FIGS. 14 to 17  for like reference numerals refer to like parts. As for  FIGS. 1 and 2 , the first phase LNG production plant  16  is shown in solid lines in  FIG. 14  whilst each of the three incremental stages of the second phase LNG production plant  18  are shown in dotted lines. It is to be understood that any number of incremental stages may be added to the expandable LNG processing plant of the present invention to achieve the desired maximum plant capacity, with one and three incremental stages being shown in the figures and described herein by way of example only. In the interests of clarity, the LNG Carrier is not shown in  FIGS. 14 to 17 . In  FIG. 15 , a first incremental stage  80  has been added to the plant to increase the plant capacity from the initial plant capacity of the first phase LNG processing plant to a first selected increased plant capacity. In  FIG. 16 , a second incremental stage  82  has been added to the plant to increase the plant capacity from the first selected increased plant capacity to a second increased plant capacity. In  FIG. 17 , a third and final incremental stage  84  has been added to the plant to increase the plant capacity from the second selected increased plant capacity to the maximum plant capacity. As can be seen from the arrangement of solid and dotted lines in  FIGS. 14 to 17 , the first phase facilities  16  are arranged towards a first end  70  of the structure  28  with space  71  on the deck  38  of the structure  28  pre-allocated for the installation of additional units for the first incremental stage  80 , the second incremental stage  82 , and, the third and final incremental stage  84 . 
     In a sixth embodiment, now described with reference to  FIGS. 18 to 24 , for which like reference numerals refer to like parts, three incremental stages of expansion are illustrated as for  FIGS. 14 to 17 , by way of example only. The dotted lines in  FIGS. 18 to 21  represent the pre-allocated space  71  provided on the deck  38  of the structure  28  for subsequent expansion. In this embodiment, the first phase gas receiving facility  20  is designed and sized to handle the initial plant capacity and each incremental increase in capacity up to the maximum plant capacity. In the interests of clarity, the LNG Carrier is not shown in  FIGS. 18 to 21 . The first phase gas receiving facility  20  may be located onshore, subsea or on the deck of the structure. In this embodiment, the plant capacity of the first phase LNG production plant  16  is expanded in three incremental stages by installing one or more second phase facilities on the deck of the structure. In this embodiment, the one or more second phase facilities take the form of one or more additional gas pre-treatment facilities  122 ,  222  and  322  in incremental stages to provide a second phase LNG production plant, said second phase LNG production plant having a maximum plant capacity that is higher than the initial plant capacity. It is apparent from  FIGS. 18 to 21  that the deck of the structure is sized to provide sufficient room for installing the one or more additional gas pre-treatment facilities  122 ,  222  and  322  in the pre-allocated space  71 . 
     Depending on the demand for LNG, the final incremental stage may not be required to be installed at the first processing location but may be required to be installed at the second processing location or vice versa. In any event, sufficient pre-allocated space on the deck of the structure is provided to allow expansion to occur with the first phase LNG production plant arranged on the deck of the gravity based structure in a configuration that allows optimum access for later installation of additional units. 
     In the sixth embodiment illustrated in  FIGS. 18 to 21 , one or more additional LNG liquefaction facilities  124 ,  224  and  324  are also added in incremental stages in sequence with the one or more additional gas pre-treatment facilities  122 ,  222  and  322  to provide the second phase LNG production plant  18 . As best seen in  FIGS. 22 and 23 , the one or more additional LNG liquefaction facilities  124 ,  224  and  324  are located on a fixed platform, a semi-submersible platform (such as a tension-leg platform or a “SPAR”) or a “jacket” structure. This embodiment has a number of advantages. Firstly, it allows for the liquefaction facilities to be installed as modules of up to 100,000 tons in weight which is higher than the maximum size of module that can be installed onshore because these modules can be floated in and installed on the fixed structure, avoiding the limitations to size associated with heavy lifting for installation at an onshore facility. Onshore module installations are limited in size by the available crane capacity, limiting the highest possible size of an onshore module to around 7,000 tons. Secondly, it allows for the liquefaction facilities to be located at a safe working distance away from the gravity based structure which is particularly advantageous if the liquefaction facilities rely on propane for cooling as part of the liquefaction process. Power is supplied to the liquefaction modules from the first phase power generation facility  62  onboard the structure  28  via a subsea power cable with the compressors and liquefaction equipment being driven by electric motors. As each of the one or more additional LNG liquefaction facilities  124 ,  224  and  324  are added during expansion, one or more additional second phase power generation facilities (not shown) can be installed on the deck of the gravity based structure. This allows for a more compact design of the one or more additional LNG liquefaction facilities  124 ,  224  and  324 . Alternatively, as illustrated in  FIGS. 18 to 21 , the first phase power generation facilities  62  can be designed and sized to meet the anticipated power demands of the expandable LNG processing plant when it is operating at both the initial plant capacity and the maximum plant capacity. 
     Using any of the embodiments described above, structure  28  may include one or both of a condensate storage tank and an LPG storage tank. By way of example, the condensate storage tank may be up to 130,000 m 3  in size with the LPG storage tank being up to 90,000 m 3  in size. Suitable marine vessels can berth at the gravity based structure for offloading of one or both of the condensate or LPG as desired. 
     The embodiments described above were all in the context of the LNG processing plant being used for LNG liquefaction. When the LNG processing plant is used for LNG regasification, the present invention provides a system and method of vaporising LNG in an LNG regasification plant positioned at a processing location adjacent to a body of water. The method comprises:
         A) providing a first phase LNG regasification plant for vaporising an initial plant capacity of LNG, the first phase LNG regasification plant comprising a plurality of spaced-apart first phase facilities, each first phase facility provided with plant equipment related to a pre-determined function associated with the regasification of LNG, wherein one or more of the plurality of spaced-apart first phase facilities is arranged on a gravity based structure having a base that rests on the seabed at a selected location within the body of water, the gravity based structure having a deck arranged above the level of the water at an offshore or near-shore selected location; and,   B) expanding the plant capacity of the first phase LNG regasification plant in one or more incremental stages by providing one or more second phase facilities on the deck of the gravity based structure to provide a second phase LNG regasification plant, said second phase LNG regasification plant having a maximum plant capacity that is higher than the initial plant capacity.       

     In order to facilitate expansion, the deck of the structure is designed and sized to provide a pre-allocated space on the deck for the installation of the one or more second phase facilities on the deck in an analogous manner to the embodiments described above for an LNG liquefaction plant. Advantageously, regasification of LNG from the first phase LNG regasification plant is able to continue during the step of expansion. The first phase LNG regasification plant is arranged on the deck of the gravity based structure in such a way as to provide easy access to the pre-allocated space. 
     Any of the embodiments illustrated in  FIGS. 1 to 23  and described above in the context of the LNG processing plant being an LNG liquefaction plant could equally be modified for use an as LNG regasification plant by way of the following substitutions:
         a) the first phase gas receiving facility is replaced with a first phase power generation facility  20  for generating a supply of power  21  using a first phase product stream of natural gas  23  as a source of fuel to generate electricity;   b) the second phase gas receiving facility is replaced with a second phase power generation facility  120  for generating electricity using a second phase stream of natural gas as a source of fuel (designed by reference numeral  123 );   c) the first phase gas pre-treatment facility is replaced by a first phase vaporised gas receiving facility  22  arranged to receive a stream of vaporised natural gas  25  from a first phase regasification facility  24  and send out a first phase product stream of vaporised natural gas  25 ;   d) the second phase gas pre-treatment facility is replaced by a second phase vaporised gas receiving facility  122  arranged to receive a stream of vaporised natural gas from the second phase regasification facility  124  and send out a second phase product stream of vaporised natural gas  125 ;   e) the first phase liquefaction facility is replaced by the first phase regasification facility  24  arranged to vaporise a first phase feed stream of LNG  26  to produce the first phase stream of vaporised natural gas  25  which is transferred to the first phase vaporised gas receiving facility  22 ; and,   f) the second phase liquefaction facility is replaced by a second phase regasification facility  124  arranged to vaporise a second phase feed stream of LNG  126  to produce the second phase stream of vaporised natural gas  125  delivered to the second phase vaporised gas receiving facility  122 .       

     The first cryogenic storage tank  42  of the structure  28  is used to store LNG for the LNG regasification plant in the same manner as it was used to store LNG for the LNG liquefaction plant. When used for regasification, the LNG transfer facilities  44  are used to transfer LNG from a second cryogenic storage tank  46  onboard an LNG Carrier  48  to the first storage tank  42  of the structure  28 . 
     A seventh embodiment of the present invention is now described in detail with reference to the embodiment illustrated in  FIGS. 1 and 2  in the context of the LNG processing plant being an LNG regasification plant, with like reference numerals referring to like parts or the substitutions set out above. Referring to  FIGS. 1 to 4 , an LNG processing plant  10 , in the form of an LNG regasification plant, is positioned at a first processing location  12  adjacent to a body of water  14 . The LNG regasification plant  10  includes a first phase LNG regasification plant  16  for producing an initial plant capacity of LNG illustrated in solid lines in both  FIG. 1  and  FIG. 2 , with a pre-allocated space  71  provided on the deck  38  of the structure  28  for the later expansion of the LNG processing plant  10  in one or more incremental stages to provide a second phase LNG regasification plant  18 , said second phase LNG regasification plant having a maximum plant capacity that is higher than the initial plant capacity. The second phase LNG regasification plant  18  is illustrated in dotted lines in  FIG. 1  and solid lines in  FIG. 2 . In the first embodiment illustrated in  FIGS. 1 and 2 , the plant capacity of the first phase LNG regasification plant  16  is increased in one incremental stage by installing one or more second phase facilities to provide the second phase LNG regasification plant. This expansion is able to be conducted without interruption to the processing of LNG by the first phase LNG regasification plant. 
     In the first embodiment now described with reference to  FIGS. 1 to 4 , the first phase LNG regasification plant  16  includes first phase power generation facility  20  for generating electricity using natural gas as a source of fuel. The LNG production plant  10  includes a first phase vaporised gas receiving facility  22  arranged to receive a stream of vaporised natural gas  25  from a first phase regasification facility  24 . In this embodiment, the first phase LNG regasification plant  16  includes a first phase regasification facility  24  arranged to vaporise a first phase feed stream of LNG  26  to produce the first phase stream of vaporised natural gas  25  which is transferred to the first phase vaporised gas receiving facility  22 . The first phase feed stream of LNG is vaporised at a rate that is determined by the initial plant capacity of LNG of the first phase LNG regasification plant  16 . The initial plant capacity of the first phase LNG regasification plant  16  is in the range of 0.5 to 7 million tons per annum of LNG. The maximum plant capacity after expansion to provide the second phase LNG regasification plant  18  is in the range of 2 million to 20 million tons per annum of LNG. 
     Vaporisation of the LNG is achieved in the first phase regasification facility  24  using any regasification process well established in the art. Such prior art regasification processes include use a variety of sources of heat for vaporization of LNG. However, the use of forced or natural draft ambient air as a primary source of heat for vaporization of LNG is preferred to keep emissions to a minimum compared with other regasification technologies that rely on the use of seawater or the burning of liquid fuels as the primary heat source for vaporization. 
     In the embodiment illustrated in  FIGS. 1 to 4 , the LNG regasification plant  10  includes a gravity based structure having a base  30  that rests on the seabed  32  at a selected location  34  within the body of water  36 , the gravity based structure having a deck  38  arranged above the level  40  of the water at the selected location. The selected location is offshore or near-shore. The gravity based structure  28  has a first cryogenic storage tank  42  for storage of LNG. The first cryogenic storage tank  42  is preferably one of a plurality of first cryogenic storage tanks with only one shown in the figures in the interests of clarity. The gravity based structure  28  further includes an LNG transfer facility  44  for transferring LNG from a second cryogenic storage tank  46  onboard an LNG Carrier  48  to the first cryogenic storage tank  42 . LNG from the first cryogenic storage tank is delivered as a first phase feed stream to the first phase regasification facility  24  for vaporisation. 
     Referring to  FIG. 3 , the first phase product stream of natural gas  23  is delivered from the gravity based structure  28  to the first phase power plant  20  via a subsea pipeline  33 . Referring to  FIG. 4 , the first phase product stream of natural gas  23  is delivered from the gravity based structure  28  to the first phase power plant  20  via a pipeline  35  arranged on a trestle  37 . 
     In this first embodiment of the present invention, the first phase LNG regasification plant  16  is provided for vaporising an initial plant capacity of LNG. The first phase LNG regasification plant  16  is provided with all of the equipment needed to vaporise the initial plant capacity of LNG with the LNG being stored in the first cryogenic storage tank onboard the gravity based structure. In use, an LNG Carrier  48  comes in to berth at the gravity based structure  28  to deliver a cargo of LNG. When the LNG Carrier is docked at the gravity based structure  28  the first phase feed stream of LNG  26  is offloaded from the second cryogenic storage tank  46  onboard the LNG Carrier  48  into one or more of the first cryogenic storage tanks  42  of the gravity based structure. When there is no LNG Carrier docked at the gravity based structure  28 , the first phase feed stream of LNG  26  is sourced from the LNG stored in a first cryogenic storage tank  42  of the gravity based structure  28 . Given the large capacity of the first cryogenic storage tank  42 , this allows for the first phase power plant  20  to be provided with a continuous source of natural gas a fuel to generate electricity in between cargo deliveries from an LNG Carrier. 
     The first phase LNG regasification plant  16  described above and illustrated in solid lines in  FIG. 1  is provided, commissioned, and operated at an initial plant capacity. Using the method and system of the present invention, the plant capacity of the first phase LNG regasification plant  16  is expanded in one or more incremental stages by installing one or more second phase facilities to provide a second phase LNG regasification plant  18 , said second phase LNG regasification plant having a maximum plant capacity that is higher than the initial plant capacity. As can be seen from the arrangement of solid and dotted lines in  FIG. 1 , the first phase vaporised gas receiving facility  22  and the first phase regasification facility  24  are arranged towards a first end  70  of the structure  28  with a pre-allocated space  71  being provided on the deck  32  of the structure  28  in anticipation of the subsequent addition of one or more process units to provide the second phase gas vaporised gas receiving facility  122  and the second phase regasification facility  124 . When installed, the second phase vaporised gas receiving facility  122  and the second phase regasification facility  124  are arranged towards a second opposite end  72  of the structure  28 . In this way, it is possible to continue to vaporise LNG in the first phase LNG regasification plant  16  whilst undertaking the step of installing and commissioning the second phase LNG regasification plant  18  for expanding the overall plant capacity from the plant capacity to a maximum plant capacity. 
     Referring to  FIG. 2 , after expansion, the second phase LNG regasification plant  18  is arranged to produce a second phase natural gas product stream  123  to act as a source of fuel to a second phase power generation facility  120  positioned onshore. Using the first embodiment of the present invention illustrated in  FIGS. 1 and 2 , when the second phase feed stream of LNG  126  is combined with the first phase feed stream of LNG  26 , the overall plant capacity of the LNG regasification plant  10  has been expanded from the initial plant capacity to a maximum plant capacity in one incremental stage. The number and arrangement of gas turbines used in the first power generation facility  20  and the second phase power generation facility  120  depends on the capacity of LNG regasification facility. Using this embodiment of the present invention, the first phase power generation facility  20  operates on the basis of the initial capacity of the first phase LNG regasification plant and is subsequently expanded to the maximum capacity of the second phase LNG regasification plant. 
     In an analogous manner, the second to sixth embodiments described in detail above can be applied to the vaporisation of LNG using the substitutions described above to change the LNG processing plant from a liquefaction plant to a regasification plant. 
     Using any of the LNG regasification embodiments illustrated in  FIGS. 1 to 23 , the first phase power generation facility  20  and the second phase power generation facility  120  use a product stream of natural gas ( 23  and  123 , respectively) as a source of fuel for generating electricity. By way of example, the power generation facility  20  includes one or more gas-fired power generation units, in this example a gas turbine arranged to use unodorized natural gas that has been vaporized from LNG stored in the first cryogenic storage tank as a source of fuel gas. Natural gas which is generated during vaporization of LNG is “unodorized” in that sulfur compounds are removed from well head gas prior to liquefaction. In contrast, pipeline natural gas sourced from an onshore gas distribution facility includes a sulfur containing odorant which is deliberately added to gas intended for use by consumers prior to distribution for the purpose of facilitating detection of leaks. The use of “unodorized” vaporized LNG leads to a reduction in the level of sulfur dioxide produced in the exhaust gas from the gas turbine of the present invention. LNG also does not contain heavy hydrocarbons (which have been removed during gas conditioning prior to liquefaction) and this leads to reduction in the particulates present in the exhaust gas produced by the gas turbine of the present invention compared with a gas turbine operated using odorized natural gas from an onshore gas distribution facility. The unodorized natural gas is used as one of the sources of fuel for the gas turbines of the power generation facility is derived from one or more of the following sources: a) natural boil off gas from the first cryogenic storage tank; b) forced boil off gas from the first cryogenic storage tank; and, c) LNG vaporized to natural gas using the first or second phase regasification facilities. 
     Each gas turbine produces energy by combustion of a source of fuel gas mixed with intake air from an air compressor. The hot combustion gases are directed to flow across the blades (not shown) of the gas turbine, causing the turbine to spin providing rotation to a mechanical shaft to drive a first generator. Additional thrust can be provided by acceleration of the combustion gases through a nozzle. During combustion of any fuel gas, pollutants are produced which report to the exhaust gas. The quantity and type of pollutant produced in the exhaust gas depends on such relevant factors as the efficiency of combustion, the degree of air compression, the air-to-fuel ratio, the inlet temperature of the compressed air and the fuel gas, the humidity of the inlet air, ignition timing, efficiency of combustion and the type of fuel gas supplied to the gas turbine. Advantageously, the power generation facility of the present invention uses unodorized natural gas that has been vaporized from LNG as the source of fuel gas, which produces a lower level of emissions and pollutants than would be produced by burning oil or coal to fire the burners of a traditional prior art steam turbine. 
     A fuel gas conditioning unit can be provided with temperature regulator for measuring and adjusting the temperature of the vaporized gas, as required, to improve the combustion efficiency of the gas turbine. Heat is supplied to the temperature regulator using electrical heating, steam heating, or by circulating a warm intermediate fluid. 
     It is readily apparent from the embodiments illustrated in  FIGS. 1 to 23  that the first power generation facility  20  may be located onshore, offshore on the deck of the gravity based structure or near shore as a separate facility. The first phase power generation facility  20  may be an existing onshore power generation facility or purpose-built as one of the plurality of facilities of the first phase LNG regasification plant  16 . 
     Whilst the various embodiments have been described above in the context of the structure  28  being a gravity based structure, the structure  28  may be in the form of a floating structure as illustrated by way of example only in  FIG. 22 , provided only that the deck of the structure is sized to provide a pre-allocated space for the installation of the one or more second phase facilities on the deck of the structure to facilitate expansion of the plant capacity of the first phase LNG processing plant in one or more incremental stages to form the second phase LNG processing plant. Alternatively, the structure may be a fixed platform, a semi-submersible platform (such as a tension-leg platform or a “SPAR”) or a “jacket” structure as illustrated, by way of example only, in  FIG. 23 , provided that the deck of the structure is sized to provide a pre-allocated space for the installation of the one or more second phase facilities on the deck of the structure to facilitate expansion of the plant capacity of the first phase LNG processing plant in one or more incremental stages to form the second phase LNG processing plant. 
     Various embodiments of the present invention provide at least the following advantages over the prior art:
         a) expansion of the capacity of the first phase processing plant the second phase processing plant is made possible using larger process units than those able to be accommodated during the expansion of an onshore processing plant. When conducting expansion operations onshore, the size of the modules that can be mobilized using cranes and land-based transport vehicles are limited to around 2500 to 7000 tons. In contrast, using the present invention, process units and modules of 30,000 to 40,000 tons and up to 100,000 tons can be floated in without ever needing to be lifted or transported on land.   b) sizing the first cryogenic storage tank onboard the structure to accommodate the initial plant capacity and the maximum plant capacity allows for the addition of second phase liquefaction facilities which do not require any LNG storage of their own. The result of this is that the size of the second phase liquefaction facilities can be larger than possible to achieve onshore.   c) the present invention provides an offshore LNG production option that is expandable in terms of capacity which is not possible using prior art ‘floating LNG’ options which rely on the deck space being fully occupied with processing equipment.   d) the costs associated with the dredging and construction of port facilities to provide a jetty for berthing of LNG Carriers is avoided as the fixed or floating structure of the present invention provides berthing facilities and serves as a breakwater for LNG Carriers.   e) the structure can be manufactured in a shipyard and then floated in to the first processing location, which greatly reduces costs compared to in situ construction of a long jetty and breakwater reducing the cost of construction and installation.   f) In addition when the structure is a gravity based structure, the gravity based structure can be de-ballasted, transported from the first processing location to a second processing location, and re-ballasted at the second processing location, avoiding the costs associated with in situ construction of a jetty and breakwater at both the first processing location and the second processing location.   g) The structure can be used as a liquefaction plant, a regasification plant, or an offshore or near shore power station, whereby the capital costs are lower than the costs of a separate land based liquefaction plant, regasification plant or power station.   h) The structure can be provided with a first cryogenic storage tank with an extremely large storage capability which enables continuous operation of the LNG processing plants even though deliveries to or from LNG Carriers are made intermittently and, even more importantly, can be sized to accommodate the largest supertankers.   i) Using the present invention results in substantial savings in the overall operation of the process at maximum capacity and provides for great ease in expanding the process incrementally.       

     Now that several embodiments of the invention have been described in detail, it will be apparent to persons skilled in the relevant art that numerous variations and modifications can be made without departing from the basic inventive concepts. All such modifications and variations are considered to be within the scope of the present invention, the nature of which is to be determined from the foregoing description and the appended claims. 
     It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art, in Australia or in any other country. In the summary of the invention, the description and claims which follow, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.