This invention relates to an apparatus and a method for the regasification of liquefied natural gas (LNG). More particularly, this invention relates to a single-compact LNG regasification apparatus that utilizes indirect heating means to build up pressure in a storage tank, vaporize LNG and superheat natural gas.
When natural gas is to be used as an energy source for powering combustion engines in vessels or vehicles, the natural gas may be safely stored in its liquefied state in cryogenic tanks on the vessel or vehicle. The LNG may then be regasified as required, before the natural gas is used to power the combustion engine of the vessel or vehicle.
There are numerous methods and systems known in the art for the regasification of LNG. Vaporizers that are typically utilized in the regasification process are Open Rack Vaporizers, Submerged Combustion Vaporizers, Intermediate Fluid Vaporizers, Shell and Tube Vaporizers or Ambient Air Vaporizers. Each of these systems uses a vaporization process whereby LNG are passed through pipes that are in contact with a heating medium. As the LNG passes through these heated pipes, the LNG absorbs heat from the pipes thereby vaporizing into a gaseous form.
However, the vaporizing systems mentioned above have various drawbacks. For example, these systems require large amounts of space, limiting these systems to land based operations whereby space is of lesser constraint. Some of these systems also typically utilize large volumes of seawater or ambient air as the heating medium for the vaporization of the LNG. The utilization of seawater has adverse environmental drawbacks to marine life, as the seawater discharged back into the ocean is at a temperature lower than the surrounding water. Further, systems that utilize ambient air or forced air drafts as heating mediums are only operable in environments with warm climates. Amongst the systems mentioned above, a closed loop Shell and Tube Vaporizer would be the most suited for use on vessels or vehicles as this system takes up the least amount of space.
Such vaporizers are disclosed in US Patent Publication No. 20130269633, published on 17 Oct. 2013, in the name of Wartsila Finland OY. This publication discloses a fuel feeding system for storing liquefied gas and feeding gaseous fuel to a piston engine. In this publication, it is disclosed that at least two pressurized cryogenic fuel tank arrangements are connected to each other and that gaseous fuel lines connect the two pressurized tanks to the engines whereby the first pressurized tank is connected to an external pressure build up system to build up the pressure within the pressurized tanks. It is further disclosed that two independent heat exchangers are utilized to vaporize the liquefied gas before the vaporized gas is directed to the piston engine.
Existing LNG regasification systems are disadvantageous because such systems are overly complex and are inherently unsafe due to the use of pressurized tanks. Hence, those skilled in the art are constantly looking for ways to devise a LNG regasification apparatus or a method that utilizes a LNG regasification apparatus that is compact in size, inherently safe to use and addresses the problems faced by existing systems.
The above and other problems in the art are solved and an advance in the art is made in accordance with this invention. A first advantage of an apparatus and a method for the regasification of liquefied natural gas (LNG) in accordance with this invention is that the regasification apparatus is compact and does not require an additional heat exchanger with pressurized shell and tubes. A second advantage of an apparatus and a method in accordance with this invention is that a single external heat source may be utilized to simultaneously build up pressure within an LNG storage tank, to vaporize LNG and to superheat natural gas. A third advantage of an apparatus and a method in accordance with this invention is that the invention being a closed loop system does not have any adverse impact on the environment.
In accordance with embodiments of the invention, the LNG regasification apparatus comprises a non-pressurized tank filled with a heat thermal fluid. An auxiliary vaporizer, a main vaporizer and a heat source unit are all provided within the non-pressurized tank and the auxiliary vaporizer, the main vaporizer and the heat source unit are all in fluid contact with the heat thermal fluid in the non-pressurized tank. The auxiliary vaporizer and the main vaporizer are configured to vaporize LNG into natural gas, and the heat source unit is configured to connect to an external heat source. The auxiliary vaporizer has an inlet configured to connect to a storage tank, for receiving LNG from the storage tank, and an outlet configured to connect to the storage tank, for providing natural gas to the storage tank. Similarly, the main vaporizer has an inlet configured to connect to the storage tank, for receiving LNG from the storage tank, and an outlet configured to provide superheated natural gas.
In accordance with embodiments of the invention, the non-pressurized tank of the LNG regasification apparatus is provided with an expansion tank that has an exposed opening.
In accordance with embodiments of the invention, the auxiliary vaporizer has a first surface area and the main vaporizer has a second surface area wherein the first surface area of the auxiliary vaporizer is smaller than the second surface area of the main vaporizer.
In accordance with embodiments of the invention, the LNG regasification apparatus further includes a pump that has an inlet configured to connect to a first end of the non-pressurized tank and an outlet configured to connect to a second end of the non-pressurized tank. In this embodiment, the first end of the non-pressurized tank is located distal from the second end of the non-pressurized tank. The pump is configured to propel the heat thermal fluid in a circulating motion within the non-pressurized tank.
In accordance with embodiments of the invention, the heat thermal fluid used in the LNG regasification apparatus comprises an anti-freeze solution.
The above advantages and features of a method and apparatus in accordance with this invention are described in the following detailed description and are shown in the drawings:
This invention relates to an apparatus and a method for the regasification of liquefied natural gas (LNG). More particularly, this invention relates to a single-compact LNG regasification apparatus that utilizes indirect heating means to simultaneously build up pressure in a storage tank, vaporize LNG and superheat natural gas. From hereinafter, one skilled in the art will recognize that any reference made in the description to LNG refers to liquefied natural gas and any reference made in the description to natural gas refers to LNG that has been vaporized into a gaseous form.
As illustrated in
In an embodiment of the invention, heat thermal fluid 105 comprises an anti-freeze mixture comprising water mixed with ethylene and/or propylene glycol. Such a mixture is advantageous because it is a good heat transfer medium for efficiently transferring heat from heat source unit 103 to auxiliary vaporizer 101 and main vaporizer 102 while preventing heat thermal fluid 105 from freezing when cryogenic LNG is passed through the auxiliary and/or the main vaporizer. In embodiments of the invention, the anti-freeze mixture comprises a solution that has 30% ethylene glycol and 70% water. One skilled in the art will recognize that other types of anti-freeze solutions or mixtures may be used as the heat thermal fluid without departing from this invention provided that these other types of anti-freeze solutions or mixtures have high thermal conductivity and anti-freeze properties.
As illustrated in
In an embodiment of the invention, external heat source 125 may be an engine or any other source of heat on a vessel or a vehicle. As the engine is being operated, the engine will produce waste heat. This waste heat may be transferred to steam, oil, hot water or any other type of heating medium that is able to convey heat from the engine to the heat source unit from which the heat is dissipated. The heating medium heated by the waste heat will then be directed to heat source unit 103 via inlet 141. As the heating medium passes through heat source unit 103, the heating medium imparts heat to heat source unit 103 thereby increasing the temperature of heat source unit 103. As the heating medium would have lost a substantial amount of heat to heat source unit 103, the heating medium exiting outlet 142 would be at a much cooler temperature than the heating medium entering heat source unit 103 at inlet 141. This cooled heating medium may then be returned to the engine to cool down the temperature of the engine. One skilled in the art will recognize that external heat source 125 is not limited to just an engine. For example, a boiler tank, may be used as the external heat source that generates heat. In other words, other types of external heat sources may be used as external heat source 125 without departing from this invention provided that the other types of external heat sources are able to provide heat. This heat may then in turn be transferred to a heating medium that is deliverable to heat source unit 103 via inlet 141 and exits heat source unit 103 via outlet 142.
In a LNG regasification operation, inlets 131 and 136 are in fluid connection with storage tank 115 to receive LNG from tank 115 while outlet 132 is connected to storage tank 115 to provide natural gas to tank 115. Inlet 141 is connected to external heat source 125 to receive the heating medium from the heat source while outlet 142 is connected to external heat source 125 to return the cooled heating medium to external heat source 125. The regasification process begins once the heating medium is provided from external heat source 125 to heat source unit 103 via inlet 141. As heat source unit 103 increases in temperature, heat source unit 103 also increases the temperature of surrounding heat thermal fluid 105 that is in fluid contact with heat source unit 103. Through natural convection, the heated thermal fluid subsequently heats auxiliary vaporizer 101 and main vaporizer 102 simultaneously. The flow of the heating medium from external heat source 125 to heat source unit 103 and back to external heat source unit 125 may be controlled using a series of control valves that may be in turn controlled by a heat control system (not shown). In embodiments of the invention, the heat control system controls the operation of the control valves to ensure that the temperature of heat thermal fluid 105 is maintained between 40° C. and 70° C.
The flow of LNG from storage tank 115 to auxiliary vaporizer 101 via inlet 131 may be controlled using a series of pressure valves that may be in turn controlled by a pressure control system (not shown). In embodiments of the invention, the pressure control system controls the operation of the pressure valves to ensure that the pressure within storage tank 115 is between 450 and 650 KPa. When LNG is introduced to auxiliary vaporizer 101 from storage tank 115 via inlet 131, the LNG absorbs heat from auxiliary vaporizer 101. The LNG then vaporizes, becoming natural gas. The natural gas is then directed back into storage tank 115 via outlet 132. As the volume of natural gas within storage tank 115 increases, this causes the pressure within storage tank 115 to gradually build up. Once the built up pressure within storage tank 115 achieves a particular pressure range, the built up pressure will cause LNG to flow from storage tank 115 to main vaporizer 102 via inlet 136. As the LNG passes through main vaporizer 102, the LNG absorbs heat from main vaporizer 102. The LNG then vaporizes, becoming natural gas.
In this embodiment of the invention, main vaporizer 102 is configured to have a larger surface area than the surface area of auxiliary vaporizer 101. Due to the increased surface area of main vaporizer 102, as compared to auxiliary vaporizer 101, main vaporizer 102 imparts additional heat to the natural gas within, as the natural gas passes through. The superheated natural gas then exits main vaporizer 102 through outlet 137. In embodiments of the invention, the surface area of main vaporizer 102 may be increased by increasing the number of coils, the length or the area of the main vaporizer that is in fluid contact with heat thermal fluid 105.
In accordance with other embodiments of the invention, LNG regasification apparatus 100 may further comprise expansion tank 120. Expansion tank 120 may be mounted on non-pressurized tank 110 as illustrated in
Another embodiment of the invention is illustrated in
In the embodiment illustrated in
A LNG regasification process that utilizes indirect heating means to build up pressure in a storage tank, and to vaporize LNG and superheat natural gas according to embodiments of the this invention is described in the following description and in
The above is a description of a LNG regasification apparatus and process that utilizes indirect heating means to simultaneously build up pressure in a storage tank and to vaporize LNG and superheat natural gas. It is foreseen that those skilled in the art can and will design alternative embodiments of this invention as set forth in the following claims.
Filing Document | Filing Date | Country | Kind |
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PCT/SG2014/000332 | 7/16/2014 | WO | 00 |