Patent Application
20120324910
1. Field of the Invention
The present invention relates generally to an articulated tug and barge arrangement, and more particularly, to the transportation, storage and regasification of liquefied natural gas (LNG) aboard a barge unit and to the ballasting of the barge unit.
2. Description of Related Art
Large volumes of natural gas are produced in many remote areas of the world. Natural gas in stranded gas reserves has significant value if it can be economically transported to a market with commercial demand. When the terrain and distance permit, natural gas is often transported by submerged and/or land-based pipeline. However, it is well appreciated that where the natural gas is produced in distant locations where a pipeline is infeasible or economically prohibitive, other techniques must be developed and used to transport this gas to market.
Liquefaction of natural gas facilitates storage and transportation of the natural gas because liquefied natural gas or “LNG” takes up only about 1/600 of the volume that the same amount of natural gas does in the gaseous state. The most commonly used technique for transportation of such distant natural gas resources involves liquefying the natural gas at or near the production site and then transporting the liquefied natural gas or “LNG” to market in massive, specially designed tanker ships called LNG carriers. LNG carriers have cryogenic compartments for carrying LNG to a destination port, where the LNG is offloaded to the storage tanks of a land-based regasification facility, where it may be stored in a liquid state or regasified. It is well understood that this requires the building and maintaining of onshore storage and gasification facilities at a major financial and time-consuming expense.
For safety and ecological reasons, it has also been proposed to offload LNG in its liquid state into floating storage and regasification units (FSRUs), acting as LNG import terminals, which are typically between 350 to 400 meters long by up to 70 meters wide. LNG carriers are typically berthed and unloaded alongside the FSRU, and the LNG is stored in the FSRU's storage tanks. It is equally understood that building and maintaining FSRUs is an expensive and time consuming process and that relocation of FSRUs is slow, expensive and not common due to their physical limitations.
U.S. Pat. No. 7,047,899, issued to Laurilehto et al., discloses a pusher-barge system in which a tug unit is supplied power by a barge unit by energy generated by LNG boil off gas on the barge unit. U.S. Pat. No. 6,089,022, issued to Zednik et al., discloses a method for regasification onboard an LNG carrier before transferring the gas to an onshore facility. U.S. Pat. No. 7,293,600, issued to Nierenberg, discloses an LNG carrier with a heat exchanger partially submerged in surrounding seawater. Thus while it has been proposed that regasification take place onboard an LNG carrier, financial and accessibility limitations remain major disadvantages.
It has also been proposed that when the regasification facility is located onboard an LNG carrier, the source of heat used to regasify the LNG may be through the intake and discharge of seawater in the vicinity of the LNG carrier. However, discharging of the chilled seawater into the vicinity of the LNG carrier can have an undesirable impact on the environment and certain regulations now preclude the use of such an open loop system.
It is thus a principal object of the present invention to provide a new system and method for storing, transporting and regasifying LNG, which is more economically feasible, environmentally friendly and in accord with regulations.
Methods and systems of the present invention achieve aforementioned objects and goals by effectively replacing the storage tanks of the loading and discharging ports, thereby eliminating or minimizing the cost of otherwise necessary infrastructure.
Methods and systems of the present invention achieve aforementioned objects and goals by providing an efficient, closed loop means for regasifying LNG using the inherent heat in seawater in conjunction with ballasting operations.
To overcome the limitations of the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, embodiments of the present invention provide a cost effective method and simplified means for transportation and regasification of LNG as well as an economically and environmentally acceptable way of regasifying LNG and performing ballasting operations.
In addition, floating power production facilities, otherwise known as power generation barges or floating power plants (“FPPs”), are considered highly suitable and economically effective means for providing transportable power in the form of electricity to hard-to-reach regions of the world. FPPs were initially conceived as a means of monetizing stranded offshore natural gas, while simultaneously permitting offshore oil production in the deep waters of the world. Interest is now being shown to generate electrical power offshore in order to reduce the need for lengthy permitting applications needed for land based power plants.
Moreover, FPPs may often be the only suitable means for power generation due to geographic and topographic restrictions precluding land-based power systems. In the operation of FPPs, greater consideration is being given to emissions and different fuels, particularly as the cost of oil increases to higher levels. Natural gas is considered a highly efficient and clean fuel for the operation of FPPs, yet the cost of supplying natural gas to FPPs such as through the construction and operation of new natural gas pipelines may prove uneconomical, and thus a needs exists for a system for transporting, storing and regasifying LNG for supply to FPPs.
Since FPPs are typically not designed to sit in waters that are aggravated by waves but rather are normally designed for services in protected inland waters such as rivers, lagoons or small ports, FPPs are often not accessible by conventional large LNG carriers. Accordingly a need therefore exists for an efficient and economically sound system for transporting, storing and regasifying LNG for supply to floating power production facilities. Embodiments of the present invention are particularly suited to transport, store and supply fuel to floating power production facilities and thus satisfy these and other objects.
The following present a simplified summary of the present disclosure in a simplified form as a prelude to the more detailed description that is presented herein.
The present invention is directed to an articulated tug and barge arrangement, to a method for transporting and regasifying LNG (liquefied natural gas) aboard a barge unit, to a method for storing LNG, and to a method for regasification aboard and ballasting of a barge unit.
In one aspect, the present invention relates to an articulated tug and barge arrangement for transporting and regasifying LNG. The articulated tug and barge arrangement comprises a tug unit and a barge unit for conveying and regasifying a load of LNG, the barge unit comprising at least one type C tank for conveying the load of LNG under pressure, a gas combustion unit operatively coupled to the type C tank for the management of over pressurized gas within the type C tank, and at least one regasification unit fluidly coupled to receive LNG from said type C tank for regassifying LNG aboard the barge unit. The tug unit is operatively coupled to the barge unit and has a propulsion system capable of propelling the barge unit such that the tug unit may propel the barge unit and thus the load of LNG from a supply terminal to a desired location such as a natural gas pipeline or an offshore floating power production facility. In preferred embodiments, the present invention relates to an articulated tug and barge arrangement and method for transporting and storing LNG aboard a barge unit and to regasifying LNG aboard the barge unit.
In one embodiment of the present invention, the barge unit comprises at least one ballast tank having ballast water and the regasification unit is fluidly coupled to the at least one ballast tank such that the ballast water may be circulated from the ballast tank through a heat exchanger disposed within said regasification unit to warm and regasify the LNG.
In another embodiment of the present invention, the barge unit further comprises at least one ballast tank for the containment of ballast water, and the regasification unit is fluidly coupled to a water inlet disposed along the exterior surface of said barge unit such that water may be withdrawn from the body of water surrounding said barge unit and circulated through a heat exchanger disposed within the regasification unit to warm and regasify the LNG; and the regasification unit is also fluidly coupled to the at least one ballast tank such that water may be flowed from the regasification unit into said ballast tank for ballasting operations of the barge unit.
Preferably, the barge unit further comprises a means for heating the ballast water. For instance, a second heat exchanger and a third heat exchanger fluidly coupled to a boiler may be provided aboard the barge unit for heating the ballast water. The second heat exchanger may be configured such that water from the water inlet is heated by steam from a boiler prior to circulation of the water through the regasification unit. The third heat exchanger may be configured such that chilled water flowing from the regasification unit would be heated prior to circulation into the ballast tanks.
In another embodiment, the propulsion system of the tug unit is powered by LNG.
In yet another embodiment, the barge unit further comprises a nitrogen injection system fluidly coupled to the send-out piping that is fluidly coupled to the regasification unit aboard the barge unit for adjustment of the calorific value of the natural gas being transferred to off board facilities such as a natural gas pipeline or an offshore floating power production facility.
In another aspect, the present invention relates to a method for transporting and regasifying liquefied natural gas (LNG) aboard an articulated tug and barge arrangement wherein said tug and barge arrangement comprises a tug unit operatively coupled to a barge unit having at least one type C tank, and the method comprises loading LNG directly from a liquefaction plant into the or each type C tank disposed within the barge unit, employing the tug unit to propel the barge unit from the liquefaction plant to an off board facility, regasifying the LNG aboard the barge unit, and transferring the natural gas to the off board facility. In embodiments of the present invention, the off board facility may be an offshore floating power production facility, a natural pipeline, and/or an onshore power production facility.
In yet another aspect, the present invention relates to a method for transporting and regasifying liquefied natural gas (LNG) aboard an articulated tug and barge arrangement and fueling an offshore power production facility, wherein said tug and barge arrangement comprises at least one barge unit having at least one type C tank and a tug unit operatively coupled to the at least one barge unit, and the method comprises loading LNG directly from a liquefaction plant into the or each type C tank disposed within the barge unit, employing the tug unit to propel the barge unit from the liquefaction plant to a floating power production facility, regasifying the LNG aboard the barge unit, and supplying fuel to said floating power production facility for power generation.
In another aspect, the present invention relates to a method of regasifying liquefied natural gas (LNG) aboard a barge unit and ballasting said barge unit, where the method comprises withdrawing seawater from the body of water surrounding said barge unit and flowing said seawater through a regasification unit which is positioned aboard said barge unit for the heating and regasification of LNG, flowing said seawater from the regasification unit into ballast tanks disposed within the barge unit for the ballasting down of the barge unit, flowing LNG from type C tanks disposed within the barge unit for storing LNG during transport through said regasification unit to heat and transform said LNG into natural gas within said regasification unit, and transferring natural gas from the regasification unit to off board facilities. Preferably, the method further comprises heating the seawater.
In another aspect, the present invention relates to a method for regasifying liquefied natural gas (LNG) aboard a barge unit and ballasting said barge unit, said barge unit having at least one ballast tank for the containment of water and at least one type C tank for the containment of LNG, and wherein the barge unit has at least one regasification unit fluidly coupled to the at least one ballast tank and to the at least one type C tank, and the method comprises the steps of introducing water into the at least one ballast tank of the barge unit, directing said water from the ballast tank through at least one heat exchanger disposed within said regasification unit for the regasification of LNG to a gaseous state, unloading said natural gas from the barge unit, directing said water from the heat exchanger to at least one ballast tank, and allowing the barge unit to ballast while unloading natural gas from the barge unit. Preferably, the method comprises heating the ballast water.
By regasifying LNG aboard the barge unit before it is off-loaded from the barge unit to desired facilities such as a natural gas pipeline or an offshore floating power production facility, the need for onshore LNG storage tanks is eliminated thereby allowing transportation and deployment of LNG to markets that would not otherwise be available due to restrictions such as size preventing the use of conventional LNG carriers. Moreover, by using ballast water as a primary heat exchange medium for the onboard regasification units, embodiments of the present invention provide an environmentally-friendly method and system, by safely and efficiently enabling regasification and unloading operations without discharge to surrounding seawater while providing necessary ballast water to the barge unit offsetting respective displacements.
Illustrative embodiments of the present invention are described herein with reference to the accompanying drawings, in which:
Persons of ordinary skill in the art will realize that the following disclosure is illustrative only and not in any way limiting. Other embodiments of the disclosure will readily suggest themselves to such skilled persons having the benefit of this disclosure.
The present disclosure is directed to embodiments of an articulated tug and barge arrangement and methods for transporting, storing and regasifying LNG (liquefied natural gas) aboard a barge unit and a method for regasifying aboard and ballasting down a barge unit.
For natural gas to be transported by sea, natural gas is typically liquefied into liquid form. This is known as liquefied natural gas or LNG. LNG is typically stored at a liquefaction facility in storage tanks, at which point it may be transferred to an LNG carrier for transport. Upon arrival at a destination, the LNG cargo is typically transferred to storage tanks at a terminal facility. Thereafter, the LNG is regasified back into natural gas and is transferred to a natural gas pipeline for distribution to a gas network and to consumers.
Referring initially to
In
While the articulated tug and barge arrangement 100 in
The barge unit 102 comprises at least one type C tank 112 for conveying a load of LNG under pressure, a gas combustion unit 114 operatively coupled to the type C tank 112 for the management of over pressurized boil-off gas within the type C tank 112, and at least one regasification unit 116 fluidly coupled to receive LNG from said type C tank 112 for regassifying LNG aboard the barge unit 102. In one embodiment, the barge unit 102 comprises a dome 170 disposed atop a type C tank 112 for the collection of boil-off gas, and the dome 170 has a small boil-off gas vapor header fluidly coupled to a gas compressor, for allowing for pressure reduction within the type C tank 112. This is an economic and effective means of controlling the cargo tank pressure while the barge is at a discharging location.
As will be understood by those skilled in the art, it is common practice to transport LNG in LNG receptacles aboard an LNG carrier, typically ranging in capacity from 100,000 m3 to 160,000 m3, and when the LNG carrier reaches its destination, the LNG is offloaded (at typical rates of 10,000-12,000 cubic meters per hour (m3/hr)) in its liquid state onto shore where it is stored and thereafter revaporized before sending it on to end users as a gas. It is well understood that this requires the building and maintaining of onshore storage and gasification facilities at a major financial and time-consuming expense. It has also been proposed to offload LNG in its liquid state into floating storage and regasification units (FSRUs), acting as LNG import terminals, which are typically between 350 to 400 meters long by up to 70 meters wide. LNG carriers are typically berthed and unloaded alongside the FRSU, and the LNG is stored in the FSRU's storage tanks. Due to the large size of the LNG carriers, the resulting change in draft as a result of unloading cargo is typically very small and negligible. It is equally understood that building and maintaining FSRUs is an expensive, and time consuming process and that relocation of FSRUs is slow, expensive and not common due to their physical limitations.
In accordance with the present invention, the articulated tug and barge arrangement 100 is relatively inexpensive to build and operate compared to the LNG carrier and FSRU. The preferred size of the barge unit 102 is up to approximately 30,000 m3. The most preferred length of the barge unit is approximately 177 meters. A type C tank 112 is a pressure vessel having a design pressure of at least 2 bar. Referring to
Preferably, the type C tanks 112 are of bi-lobe design (
Referring to
In a preferred embodiment, the liquid header 124 is fluidly connected to an upper manifold 126a and to a lower manifold 126b of each loading manifold 126 (
The heat exchanger 134 of the regasification unit 116 of the present invention may be a shell and tube heat exchanger, a printed circuit heat exchanger, a bent-tube fixed-tube-sheet exchanger, plate-type exchanger, spiral wound exchanger, falling-film exchanger, or other heat exchangers commonly known by those skilled in the art that meet the temperature, volume and heat absorption requirements for the LNG to be regasified.
Considering space limitations onboard the barge unit 102 and cost comparison, the regasification unit 116 preferably uses saturated steam as the direct heating medium. The regasification unit 116 allows the LNG to be pressurized and regasified to the discharge pressure of approximately 30 to 120 bar.
Preferably, one or more dual fuel generators 136 are disposed upon the aft deck of the barge unit 102 and are used to power the barge unit 102 operations, including providing power to the conventional pressure pumps 150 used for water/fluid pumping and circulation as described herein. For instance, suction pumps or single stage centrifugal pumps are frequently used for water/fluid pumping in maritime and industrial applications, and are well known to those skilled in the art. In a preferred embodiment, two cargo pumps of centrifugal design submergible type are disposed within each type C tank 112, one within each lobe, for discharging LNG when necessary. In a preferred embodiment, two suction pumps of centrifugal design are disposed within each type C tank 112, one within each lobe, for transferring LNG to the regasification unit 116.
A nitrogen injection system comprising a nitrogen generator 138 is preferably provided aboard the barge unit 102 to supply nitrogen gas for drying out and inerting the type C tanks 112 before LNG cargo loading or grade changing operations and after discharging cargo. A nitrogen generator is, in effect, an air compressor which pushes air through a permeable membrane and separates nitrogen from air, as would be known to one skilled in the art. The nitrogen generator 138 is fluidly coupled to the type C tanks 112 by an inert gas header 140. Preferably, a deck storage tank 142 for LNG is provided aboard the barge unit 102 and is fluidly coupled to the type C tanks 112 for gassing-up operations, to remove nitrogen from the type C tanks 112 or to remove cargo vapors of the previous cargo. A vapor return line 144 provides a fluid connection between the type C cargo tanks 112 and the loading manifold 126 to maintain tank pressure during loading and discharge operations. As vapor is generated during cool down operations, the vapor return line 144 allows the vapor to be sent from the type C tanks 112 through the manifold 126 to the supply facility 130. While it is preferable to employ a nitrogen generator 138 aboard the barge unit 102, it can be appreciated that an alternative is to employ a nitrogen storage tank aboard the barge unit 102.
A vapor header 146 provides a fluid connection to the regasification unit 116 for send-out or unloading of the natural gas directly from the barge unit 102 at the high pressure vapor discharge manifold 148 to the desired off board facility 152, obviating the need for LNG storage tanks at the destined off board facility 152. The off board facility 152 may be a natural gas pipeline 154 supplying natural gas to consumers, as illustrated in
Alternatively, referring to
Referring to
In embodiments of the present invention, as examples, the off board facility 152 may be an offshore floating power production facility, a natural pipeline, and/or an onshore power production facility.
In yet another embodiment of the present invention, a method is provided for transporting and storing LNG. Referring to
While it has been proposed to use seawater as a heat source for the regasification of LNG aboard an LNG carrier, conventional discharging of the chilled seawater to the surrounding water body can have undesirable impact on the environment.
Referring to
It may be appreciated that the water inlet 158 may be disposed along an external surface of the barge unit 102 or within a sea chest disposed within the barge unit 102.
Preferably, the barge unit 102 further comprises a strainer 160 configured such that seawater may be flowed through the strainer 160 prior to entering the heat exchanger 134 of the regasification unit 116, as schematically depicted in
In one preferred embodiment, the barge unit 102 comprises at least one set of upper ballast tanks 120a, 120b disposed within the barge unit 102 vertically above the draft water line of the barge unit 102, wherein the regasification unit 116 is fluidly coupled to the set of upper ballast tanks 120a, 120b. Providing ballast tanks 120a, 120b above the draft water line of the barge unit 102 mitigates the heat transfer between the chilled ballast water in ballast tanks 120a, 120b and the surrounding water body, thereby further preventing or mitigating the impact on the environment. Moreover, providing chilled water to the ballast tanks 118, 12a, 120b in effect cools down the outer containment system of the barge unit 102 and thereby mitigates boil-off within the type C tanks 112 within the barge unit 102.
In a preferred embodiment, the barge unit 102 receives ballast water at a water inlet 158 and via circulation through the heat exchanger 134 and into the ballast tanks 118, 120a, 120b at a typical rate (e.g., 2000 m3/hour) during the offloading of the regasified cargo (i.e., natural gas) such that positive displacement of the barge unit 102 achieved from ballasting down is offset by negative displacement of the barge unit 102 achieved from offloading the cargo. In a most preferred embodiment, the barge unit 102 receives ballast water via circulation through the heat exchanger 134 and into the ballast tanks 118, 120a, 120b at substantially the same rate as the offloading of the regasified cargo (i.e., natural gas) such that the positive displacement of the barge unit 102 achieved from ballasting down is substantially offset by the negative displacement of the barge unit 102 achieved from offloading the cargo.
Moreover, since ballast tanks 118, 120a, 120b are fluidly coupled to the regasification unit 116, ballast water may also be pumped from the ballast tanks 118, 120a, 120b and circulated through the heat exchanger 134 disposed within the regasification unit 116 to warm and liquefy the LNG and thereafter circulated back to the ballast tanks 118, 120a, 120b, as schematically depicted in
Referring to
Referring to
By using ballast water as a primary heat exchange medium for the onboard regasification units 116, embodiments of the present invention safely and efficiently enable regasification, unloading and ballasting operations without discharge to surrounding seawater while providing necessary ballast water to the barge unit 102 thereby offsetting respective displacements.
It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made without departing from the spirit and scope of the invention. While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should only be defined in accordance with the following claims and their equivalents. All patents and publications discussed herein are incorporated in their entirety by reference thereto.
