AND LIQUEFIED CARBON DIOXIDE

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The invention and its various embodiments relate to methods for carrying liquefied natural gas (LNG) and liquefied carbon dioxide (L-CO2). In particular, the invention and its various embodiments relate to the use of vehicles or conveyances that transport LNG to also transport L-CO2.

Description of Related Art

[0002] Natural gas (NG) is a fossil fuel often found in underground rock formations or other planetary reservoirs of hydrocarbon sources. NG consists primarily of methane (CH4) and is used as a fuel source, both industrially and commercially. In addition to being used as a fuel, NG is also used as a raw material for certain products, such as paints, fertilizer, plastics, and the like.

[0003] To enable easier storage and transport, NG is often converted to a liquid form or liquefied natural gas (LNG). The volume of LNG is roughly 600 times smaller than NG in its gaseous form, which enables the shipping of LNG in carriers or tanker ships. Therefore, LNG can be transported long distances from NG sources to power plants and pipelines and ultimately to consumers. Once LNG reaches its destination, it is re-gasified, i.e., returned to its gaseous form, and distributed in pipelines as NG.

[0004] LNG carriers or transport vehicles, often specially outfitted tanker ships, are used to ferry LNG from a loading terminal to an unloading terminal. The LNG transport vehicle is filled with LNG at a loading terminal and then unloads its LNG cargo at an unloading terminal. Thus, during the vehicle's return trip to a loading terminal, its cargo hold is empty. This poses potential issues for ships that act as LNG transport vehicles. After discharging LNG cargo, a ship must lower its center of gravity to be adequately stable and seaworthy. Most ships that carry LNG, therefore, use one or more water ballasts for this purpose. Such water ballasts, which are well known in shipping, are filled, often with seawater, to add weight to a ship after that ship's cargo has been discharged. Water ballasts, therefore, improve a ship's stability by weighing it down and lowering its center of gravity. Cargo vessels, including LNG carriers, are required by various international agreements to be capable of withstanding specific kinds of damage. As an example, the International Convention for the Safety of Life at Sea (SOLAS) mandates that ships flagged by signatory nations obey certain minimum safety standards in construction and operation. However, the use of water ballasts is economically inefficient since a ship is not carrying any cargo during its return voyage from an LNG unloading terminal to an LNG loading terminal. Thus, there exists a need to modify the use of LNG transport vehicles, especially ships, so that such vehicles can ferry cargo relevant and useful to LNG processing and/or storage during their return trips, thereby enabling more efficient LNG transport.

BRIEF DESCRIPTION OF THE INVENTION

[0005] In general, the present invention is directed towards methods and apparatuses for transporting LNG and liquefied carbon dioxide (L-CO2). In some embodiments, the method utilizes an LNG transport vehicle to carry LNG and L-CO2. In certain other embodiments, the LNG transport vehicle comprises a specially outfitted ship capable of carrying liquid gases, including, without limitation, LNG and L-CO2.

[0006] In one particular embodiment of the invention, the method for transporting

LNG and L-CO2 comprises loading LNG onto a LNG transport vehicle at an LNG loading terminal; transporting the LNG on the LNG transport vehicle from the loading terminal to an LNG unloading terminal; unloading the LNG from the LNG transport vehicle; filling the LNG transport vehicle with L-CO2; carrying the L-CO2 on the LNG transport vehicle from the unloading terminal back to the loading terminal; and removing the L-CO2 from the LNG transport vehicle. In one aspect of this embodiment, the LNG transport vehicle comprises a ship that is specially outfitted to transport liquid forms of gases, including LNG and L-CO2. , such as an LNG carrier. In another embodiment of the invention, L-CO2 can be removed from the LNG transport vehicle and stored in specially outfitted L-CO2 storage tanks. The L- CO2 can then be harnessed for further use.

[0007] The economic benefits of this invention may be realized in many ways. The cold energy that will be carried with the L-CO2 and LNG will provide a significant reduction of power use by any natural gas liquefaction plant at the LNG exporting terminal, will allow carrying back L-CO2 for injection into a supercritical CO2 pipeline after recovering the cold energy. The carried L-CO2 and subsequent supercritical CO2 may be utilized for enhanced oil recovery, therefore a significant portion of the carried L-CO2 will be classified as zero- carbon-footprint if the L-CO2 is a by-product of the a power generation plant in which 100% of CO2 is captured while generating power from natural gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is process diagram illustrating one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0009] Various embodiments of the present invention are more fully described below with reference to the accompanying drawing. While the invention will be described in conjunction with particular embodiments, it should be understood that such is exemplary of various embodiments that fall within the scope of the present invention, including alternatives, modifications, and equivalents that are within the scope of the invention. Moreover, the invention can be applied to a wide variety of applications. Accordingly, the following description should not be viewed as limiting or as setting forth the only embodiments of the invention, as the invention encompasses other embodiments not specifically recited in this description. Further, the terms "invention," "preferably," and "for example," are used broadly and are not intended to mean that any particular portion of the description is the only manner in which the invention may be made or used. In fact, various embodiments with common and differing features are described herein.

[0010] In general, the present invention is directed towards methods and apparatuses for transporting LNG and L-CO2. In some embodiments, an LNG transport vehicle is used to transport LNG and L-CO2. In further embodiments, the LNG transport vehicle comprises a specially outfitted ship capable of transporting liquid gases, including, without limitation, LNG and L-CO2. In one specific embodiment, the method for transporting LNG and L-CO2 comprises loading LNG on to a LNG transport vehicle at an LNG loading terminal;

transporting the LNG on the LNG transport vehicle from the loading terminal to an LNG unloading terminal; unloading the LNG from the LNG transport vehicle; filling the LNG transport vehicle with L-CO2; carrying the L-CO2 on the LNG transport vehicle from the unloading terminal back to the loading terminal; and removing the L-CO2 from the LNG transport vehicle.

[0011] LNG transport vehicles are often specially outfitted ships, often referred to as

LNG carriers. Often, LNG carriers contain one or more tanks capable of holding LNG at a suitable temperature to maintain the liquefied state of LNG. There are typically multiple pumps inside each storage tank, both for cooling the tank and for discharging the cargo, such as, for example, LNG, at the carrier' s final destination, such as, for example, an LNG unloading terminal. [0012] Before loading LNG onto an LNG carrier, storage tanks are often "inerted" to eliminate the risk of an explosion. Inert gas, usually predominantly nitrogen, is blown into each storage tank to reduce the amount of oxygen inside each tank. Then, LNG is taken on board the carrier and a certain amount of LNG is heated, for example, to 20°C, and blown into each storage tank to displace the mostly inert gas currently residing in each tank. Once the mostly inert gas is removed, spray heads located in each storage tank begin spraying LNG. The sprayed LNG vaporizes and thus begins to cool down the storage tank. LNG in its liquid form thus accumulates in each storage tank and is ready to be transported.

[0013] The temperature to which storage tanks on LNG carriers are cooled in order to transport LNG depends on the pressurization of each storage tank. Generally, increasing the pressure of a storage tank results in a higher temperature at which LNG can be stored and effectively transported. For example, if a storage tank on an LNG carrier is operating at near- atmospheric pressure (1.013 bars), the temperature of LNG in the tank will be roughly - 161°C. However, if the pressure is at least 5.2 bars, the LNG temperature will be roughly - 137.1°C. If the pressure is even higher, around 8.013 bars, the LNG temperature will be warmer, around -128.7°C. Tanks capable of operating at still higher pressure, around 12.013 bars, will carry LNG at a temperature of roughly -1 19.8°C. The pressurization of storage tanks on any given LNG carrier depends on the carrier' s construction and the amount of pressure its storage tanks can adequately handle.

[0014] Once the LNG carrier arrives at its final destination, such as, for example, an

LNG unloading terminal, pumps inside each storage tank remove the LNG, pumping it ashore. The empty storage tanks can then be filled with atmospheric gas. However, during the return trip from an LNG unloading terminal back to an LNG loading terminal, LNG carriers have to utilize water ballasts in order to remain safe and stable. Because the use of water ballasts is economically inefficient since a ship is not carrying any cargo, in one embodiment of the present invention, water ballasts are unnecessary when an LNG transport vehicle, such as an LNG carrier, returns from an unloading terminal to a loading terminal. Instead of being empty of cargo, the LNG transport vehicle will load L-CO2, thus weighing it down and rendering water ballasts unnecessary. In this embodiment, L-CO2 will be loaded on to the LNG transport vehicle at an LNG unloading terminal. After the LNG transport vehicle completes its journey to the LNG loading terminal, it will discharge its L-CO2 cargo, rendering it capable of loading LNG again.

[0015] Accordingly, the following description of the use of LNG transport vehicles is presented in the context of transporting LNG and L-CO2. It should be appreciated that any vehicle capable of transporting liquid gases, including, but not limited to, LNG and L-CO2, can be utilized. As a non-limiting example, one such type of LNG transport vehicle is a ship specially outfitted to transport LNG, commonly known as an LNG carrier.

[0016] Figure 1 is a process diagram illustrating one embodiment of the invention. The process 100 represents one embodiment for transporting LNG and L-CO2. At a loading terminal, or LNG export and CO2 receiving terminal, an LNG liquefaction and export terminal 102 is used to load LNG 104 onto an LNG carrier 106. It should be appreciated that the LNG 104 loaded onto the LNG carrier 106 may come from a natural gas pipeline that provides natural gas that is cooled to produce LNG in a liquefaction process or plant.

[0017] The LNG carrier 106, now carrying LNG cargo, transports the LNG to an unloading terminal, or LNG import and CO2 export terminal, where the LNG 110 is offloaded or pumped to a plant 108 that vaporizes or re-gasifies the LNG and passes it, in a gaseous state, to a natural gas pipeline for use. It should be appreciated that the plant 108 may be a power plant.

[0018] The plant 108 also provides L-CO2 112 that is loaded onto the LNG carrier

114, which may be the same LNG carrier 106 that transported the LNG from the original loading terminal to the unloading terminal. In some embodiments, the LNG carrier 114 will be purged of the LNG and any vaporous natural gas through the loading of the L-CO2. The LNG carrier 114 is now carrying L-CO2 and returns to the original loading terminal. It should be appreciated that in some embodiments, a portion of the L-CO2 may be removed to comply with any tank weight restrictions, given that L-CO2 has a higher density than LNG. The LNG carrier 1 14 then transports the L-CO2 back to the LNG export and CO2 receiving terminal, thus completing a round trip.

[0019] At the LNG export and CO2 receiving terminal, the LNG carrier 114 unloads or pumps the L-CO2 1 16 to a L-CO2 preheating facility where the L-CO2 is heated to produce, in some embodiments, supercritical CO2 that can be passed to a supercritical CO2 pipeline, such as pipeline 118, for use in, for example, enhanced recovery of oil. Such usages of L- CO2 and/or S-CO2 would further reduce economic costs of L-CO2 transportation, as well as ensuring that a significant portion of the transported L-CO2 has a zero carbon footprint.

[0020] It should be appreciated that in some embodiments, the preheating of the L-

CO2 is accomplished with heat supplied by cooling of the natural gas provided by a natural gas pipeline that will be converted to LNG for transportation by the LNG carrier. In other words, the L-CO2 "cold energy" is used to cool the natural gas, thus lowering the amount of energy required by the natural gas liquefaction process. Thus, the present invention can provide substantial economic benefits. In other embodiments, the L-CO2 can be pumped from the LNG carrier 1 14 to L-CO2 storage tanks. Such heat exchange may be accomplished by any method known in the art.

[0021] The LNG carrier 1 14 is now empty and capable of loading LNG 104 once again and repeating the cycle. In other words, in some embodiments, one LNG carrier 1 14 can be used to transport LNG from one starting point to one destination and transport L-CO2 from that destination to the original starting point in a single round trip. Therefore, the LNG carrier would be used during both legs of the round trip, as opposed to returning to the original starting point empty or without carrying any cargo. It should also be appreciated that any residual carbon dioxide can be purged from the LNG carrier 1 14 using vaporous natural gas.

[0022] The LNG carrier 1 14 that is carrying L-CO2 will have storage tanks that operate at a specific pressure that enables the LNG carrier 114 to safely transport the L-CO2 in a liquid form. As a non-limiting example, an LNG carrier 1 14 could transport L-CO2 at a pressure of at least 5.2 bars. At this pressure, the temperature of L-CO2 is roughly -56.6°C. An LNG carrier 114 could also transport L-CO2 at a pressure higher than 5.2 bars, such as, for example, 8.013 bars. At such a pressure level, the L-CO2 temperature will be roughly - 45.9°C. L-CO2 can be transported at an even higher pressure level, such as, for example, 12.013 bars. At a pressure level of 12.013 bars, the L-CO2 temperature will be roughly - 35.0°C. Thus, as is the case with LNG, an increase in the pressurization of L-CO2 will result in a concomitant increase in the temperature of the liquid gas.

[0023] In the embodiment of the invention represented by the process 100 shown in

Figure 1, one of skill in the art will appreciate that transport vehicles other than ships can be used. The process 100 shown in Figure 1 can be executed by any transport vehicle capable of carrying liquid gases, including, but not limited to, LNG and L-CO2. As purely non-limiting examples, the vehicles transporting LNG and L-CO2 in process 100 could be land

conveyances such as trucks, trailers, or rail cars.

[0024] It should also be appreciated that "cold energy" from the re-gasification process of LNG to NG at the unloading terminal, or the LNG export and CO2 receiving terminal, can be further utilized in additional ways. As an example, the cold energy from

LNG re-gasification in the plant 108 can be used for liquefaction of CO2 or supercritical CO2, which can either be generated directly or provided via a supercritical CO2 pipeline. For example, the plant 108 may be a thermodynamic cycle that uses supercritical CO2 as a working fluid and that generates supercritical CO2 that can be liquefied for transport, while at the same time generating power that can be passed to a power grid. One example of such a thermodynamic cycle is described in International Patent Application No.

PCT/US2016/61582, entitled "Open Thermodynamic Cycle Utilizing Supercritical Carbon Dioxide Without Compressors," which is incorporated herein in its entirety by reference. Reusing cold energy from LNG re-gasification also reduces general operating costs and expenses of unloading terminals.

[0025] In some embodiments, the following conditions may be used:

[0026] It should be appreciated that the LNG carriers may be provided by constructing new carriers or modifying the existing pressurized carriers. The modification of the existing low pressure gas (LPG) tankers, for instance, would involve applying low- temperature insulation, new pump equipment, and on-board liquefaction allowing for maintaining the cargo pressure without releasing any content. In case of carrying LNG the vapor may be used for propulsion or could be, in part, liquefied while the balance may be used for propulsion. In case of carrying L-CO2, the vapor will be liquefied to the extent require for maintaining the cargo pressure without the necessity of releasing any cargo. [0027] Various embodiments of the invention have been described above. However, it should be appreciated that alternative embodiments are possible and that the invention is not limited to the specific embodiments described above.