Abstract:
Regasification systems and processes for converting liquid natural gas (LNG) from a liquid into a gaseous state are described. The process includes a closed-loop system that uses geothermal wells as a heat source. A warming fluid circulates through the closed-loop system coupled with a geothermal well and a LNG heat exchanger. The warming fluid is heated as it passes through the geothermal well and cooled as it passes through the LNG heat exchanger, thus heating and gasifying the LNG. The cooled warming fluid then returns to the geothermal well. The closed-loop system minimizing environmental impact by eliminating the need to discharge the warming fluid.

Description:
This application claims the benefit of priority of U.S. provisional application Ser. No. 61/752,885 filed on Jan. 15, 2013. 
    
    
     FIELD OF THE INVENTION 
     The field of the invention is regasification of liquid natural gas (LNG). 
     BACKGROUND 
     The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art. 
     Natural gas is a common fuel source that has many important applications. Natural gas is often transported in its liquid form, referred to herein as liquid natural gas (LNG), since it takes up much less volume. Upon arriving at its destination near a source of use (e.g., power plant) the LNG can be converted back into a gaseous state via a regasification process. 
     Numerous regasification devices, systems, and processes are known. For example, Conversion Gas Imports, L.P. (“CGI”) is the owner of the following U.S. Patents related to regasification: U.S. Pat. Nos. 5,511,905; 6,739,140; 6,813,893; 6,880,348; 6,848,502, 6,945,055, 7,036,325. These and all other referenced extrinsic materials are incorporated herein by reference in their entirety. Where a definition or use of a term in a reference that is incorporated by reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein is deemed to be controlling. 
     Some of the patents listed above describe designs for a LNG receiving terminal using salt cavern storage. The LNG may come directly from a ship or from a conventional storage tank. The LNG receiving terminal may be located onshore or offshore. 
     Some of these patents also describe methods for warming LNG and storage in compensated or uncompensated salt caverns, which is referred to as the Bishop Process™. 
     Some of the patents listed above also describe pipe-in-pipe heat exchanger designs. One embodiment of the LNG receiving terminal uses multiple salt caverns for blending of gas from different sources to achieve a pipeline standard BTU (i.e., British Thermal Units) content. 
     Unfortunately, current regasification technology suffers from numerous drawbacks. For example, some of the patents listed above describe systems in which a warming fluid (e.g., seawater) is discharged into the sea after use. The discharged fluid can have a negative impact on the environment (e.g., the discharged seawater is often too cold and can kill fish eggs, thus reducing the population of sea life). 
     The company GTherm has recently conceived of a new approach for power generation that relies on geothermal wells (see  FIG. 1 ). The GTherm approach utilizes a closed-loop system and a circulating fluid. The circulating fluid is heated as it passes through a geothermal well and cools as it passes through an evaporator. GTherm has also conceived of applying similar principles to enhanced oil recovery systems. However, to the best of applicant&#39;s knowledge, those of ordinary skill in the art have failed to provide a closed-loop system with a circulating fluid that utilizes heat from geothermal wells for LNG regasification systems. 
     US20070079617 describes methods and systems for geothermal vaporization of liquefied natural gas. However, the system described in US20070079617 does not appear to provide a pipe-in-pipe heat exchanger to efficiently utilize heat from geothermal wells. 
     Thus, there remains a need for improved systems and methods for LNG regasification. 
     SUMMARY OF THE INVENTION 
     The inventive subject matter provides apparatus, systems, and methods for the warming of cold fluids, such as liquefied natural gas (LNG), using the heat from a geothermal energy heat source (e.g., geothermal well). In one aspect of some embodiments, a warming fluid (e.g., water, oil, brine, etc.) is circulated in a closed-loop system that passes through or near a geothermal energy heat source and then passes through a heat exchanger. As the warming fluid passes near the geothermal energy heat source, heat is transferred to the warming fluid. The warming fluid then passes through a heat exchanger where the warming fluid transfers heat to a liquid natural gas stream. The heat transferred from the warming fluid to the LNG stream helps to convert the LNG stream from a liquid state to a gaseous state as the LNG stream passes through the heat exchanger. The warming fluid is then circulated back to the geothermal energy heat source to repeat the process. 
     In one aspect of some embodiments, the heat exchanger comprises a pipe-in-pipe configuration, in which the LNG stream passes through an inner pipe and the warming fluid passes through an annular space around the exterior of the inner pipe. A portion of the length of the inner pipe has a bulkhead for stress and thermal expansion containment between cold LNG (upstream) and warm gas (downstream). The warming fluid crosses over the bulkhead section of the inner pipe via a bypass conduit (e.g., cross over piping). 
     Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic of a power generation process that utilizes geothermal energy. 
         FIG. 2  is a schematic of a pipe-in-pipe LNG regasification system that utilizes geothermal energy. 
         FIG. 3  is a perspective cross-sectional view of the pipe-in-pipe heat exchanger shown in  FIG. 2 . 
         FIG. 4  is a side cross-sectional view of the pipe-in-pipe heat exchanger shown in  FIG. 2 . 
         FIG. 5  is an exploded view of the pipe-in-pipe bulkhead configuration shown in  FIG. 2 . 
         FIGS. 6 a  and 6 b    are perspective and cross-sectional views, respectively, of one embodiment of a geothermal well for use in a regasification system. 
         FIG. 7  is a perspective view of the geothermal well of  FIG. 6 a    with an optional vacuum insulated tubing. 
         FIGS. 8 a  and 8 b    are perspective and cross-sectional views, respectively, of a geothermal well with a grout tube for installing thermal grout. 
         FIGS. 9 a  and 9 b    are perspective and cross-sectional views, respectively, of another embodiment of a geothermal well for use in a regasification system. 
         FIGS. 10 a -10 e    are various views of another embodiment of a geothermal well for use in a regasification system. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed. 
     The inventive subject matter provides apparatus, systems, and methods for the regasification of liquid natural gas (LNG) using geothermal energy. 
       FIG. 2  shows a general configuration and piping diagram for a LNG closed-loop regasification system  100 . System  100  has a closed-loop conduit (e.g., fluid pathway) with a warming fluid  105  circulating therein. A pump  130  creates a negative pressure in the closed-loop conduit, causing the circulating fluid  105  to circulate through the geothermal well  110  and the heat exchanger  120 , and through distribution piping  132 . (Shut off and control valves, leak detection and controls instrumentation are not shown for clarity.) When passing through the geothermal well  110 , the circulating fluid  105  is heated. The heat  111  is transferred to the LNG  140  flowing through the pipe-in-pipe heat exchanger  120 , causing the LNG  140  to change from a liquid state to a gaseous state (e.g., natural gas  150 ). Distance  122  is the distance to turn LNG into natural gas and is dependent upon the heat transfer required. 
     The warming fluid  105  (also referred to as the circulating fluid) can be water, oil, brine, or any other fluid suitable for transferring heat under the required specifications. In some embodiments, the circulating fluid has a high heat capacity so that it retains heat over long distances and/or time. 
     Pipe  170  carriers LNG  140  from a LNG source to heat exchanger  120 .  FIG. 3  shows a cross-sectional view of a pipe  170 . Pipe  170  comprises a cryogenic rated inner pipe  171  surrounded by an insulation material  172  (e.g., aerogel insulation, a suitable commercially-available example of which includes NANOGEL® EXPANSION PACK™, available from CABOT). Surrounding insulation material  172  is an external carbon steel casing pipe  173 , however, another cryogenic rated pipe could be used if so required. Around pipe  173  is a concrete weight coating  174 , if required. Various pipe configurations for transporting LNG are known and may be used with the inventive principles presented herein unless stated otherwise in the claims. 
       FIG. 4  shows a side cross-sectional view of the pipe-in-pipe heat exchanger  120 . Warming fluid  105  enters exchanger  120  at point  401  at a high temperature. Fluid  105  transfers heat to LNG  140  as it flows along distance  122  (fluid  105  flows in the inner pipe and warming fluid  105  flows in the annular space between the outer and inner pipe). Fluid  105  exits exchanger  120  at point  402  at a lower temperature than it was at point  401 . Heat exchanger  120  has a bulkhead  125 , which provides stress and thermal expansion containment as LNG  140  converts to natural gas  150 . Fluid  105  crosses over bulkhead  125  via cross over piping  126 . 
       FIG. 5  shows an exploded view of pipe bulkhead  125 . Bulkhead  125  helps provide integrity to handle stress and thermal expansion containment between the cold LNG entering heat exchanger  120  and the warm natural gas (i.e., gaseous state) exiting heat exchanger  120 . In some embodiments, the configuration of bulkhead  125  can be similar in principle to the pipe-in-pipe bulkhead described in WO2005119150, which is incorporated herein by reference. As illustrated in  FIGS. 2, 4 and 5 , the bulkhead  125  may be characterized as a tube having two longitudinal ends and a body portion between the first end and the second end that form two conical portions, the two conical portions converging at the smallest diameter of the respective conical portion, the body portion thereby having a longitudinal v-shaped cross sectional area. 
       FIGS. 6 a  and 6 b    are perspective and cross-sectional views, respectively, of one embodiment of a geothermal well heat exchanger  600 . The heat exchanger  600  comprises a pipe  616  that has an open hole  620  partially filled with thermal grout  640 . Heat exchanger  600  is disposed within a geothermal region  670 . The heat exchanger  600  also includes a u-shaped conduit (e.g., pipe) disposed within pipe  616  for circulating a fluid  610  into and out of the well (via inlet piping  612  and outlet piping  614 ). The u-shaped pipe is part of a closed-loop system  605  such as is shown in  FIG. 2 , and has at least one welded connection  650  at the elbow and at least one joint/weld  630  (e.g., screwed drill collar). Thermal grout  640  facilitates the transfer of heat  660  from geothermal region  670  to the warming fluid  610 . The exact configuration (e.g., size, dimension, shape, materials, temperatures) of the conduit will vary depending on the application.  FIG. 6 b    provides examples of diameters, weights, materials, and specifications, which are not intended to limit the application of the inventive concepts described herein. In this particular embodiment, pipe  616  is casing pipe that has a 30 inch outer diameter (OD) and 1 inch width, and inlet  612  and outlet  614  have a 4 inch inner diameter and 2 inch width. 
       FIG. 7  shows a perspective view of an alternative embodiment  700  of the geothermal well  600  of  FIG. 6 a   , with an optional vacuum insulated tubing  780  near the top end of the well. 
       FIGS. 8 a  and 8 b    are perspective and cross-sectional views, respectively, of the geothermal well  600  of  FIG. 6  with a removable grout tube  885  in the center of the well and a spacer  890  for installing thermal grout in the bottom end of the well. 
       FIGS. 9 a  and 9 b    are perspective and cross-sectional views, respectively, of another embodiment of a heat exchanger  900  in a geothermal well for use in a regasification system. The well comprises a cased hole  916  grouted in place and a vacuum insulated tubing  980  in the center. The circulating fluid  910  flows into the geothermal well through the cased hole  912  (e.g., annular space) and out of the center vacuum tubing  980  (via the open bottom of return line/pipe  914 ). Spacers and centralizers  990  keep return line/pipe  914  centered. 
       FIGS. 10 a -10 b    show various views of an alternative embodiment  1000  of heat exchanger  900  in a geothermal well for use in a regasification system. The well comprises a center vacuum insulated tube  1012  with an open end near the bottom of the well. The well also includes an outer casing  1016  surrounded by thermal grout  1040 . The circulating fluid  1010  flows into the well via the center tube  1012  and out of the well via the casing  1016  (e.g., annular space  1014 ). 
       FIG. 10 c    shows a heat exchanger  1110  what has a manifold  1115  at the top end of the well. The manifold  1115  brings the casing  1116  outer diameter space into one smaller diameter tubing  1114 . A granular insulation can be used around the exterior surface of the manifold and within the casing. Heat exchanger  1110  has a center pipe  1112  that provides an inlet. 
       FIGS. 10 d  and 10 e    show cross sectional views near the top end and bottom end, respectively, of the geothermal well. 
     Grout  111 , developed by Brookhaven National Laboratories specifically for geothermal applications, is one example of a grout that can be used with geothermal wells. Unlike other grouting materials, Grout  111  is virtually water impermeable, is shrink resistant, is crack resistant, and boasts the highest known heat conductivity of any other known grout in existence. 
     A newer grout, called Mix  111 , can also be used. Mix  111  is composed of cement, water, silica sand and small amounts of super plasticizer and bentonite. The formula for Mix  111  has been publically provided by Brookhaven National Laboratories. 
     By utilizing this material, and grouting from the bottom up, a total seal around the well is provided. This both protects the tubing and provides a safe sealant to prevent the cross-contamination of underground aquifers at varying depths. 
     The systems and methods described herein are useful for a LNG import situation where there is a need for a regasification system from a LNG tanker at a berth, where the LNG can be converted in the pipeline running from the shop to shore and an onshore natural gas grid. The systems and methods described herein can also be used for heat-upon-demand applications. 
     In addition, the systems and methods described herein can also be used for a re-gas system for a LNG plant where LNG is stored over time and natural gas is needed to enter a pipeline grid (e.g., a peak shaving plant). The systems and methods could be used in a LPG (liquefied petroleum gas) system as well, although the temperatures are lower. 
     Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims. 
     As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
     As used herein, and unless the context dictates otherwise, the term “coupled to” is intended to include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms “coupled to” and “coupled with” are used synonymously. 
     Unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints, and open-ended ranges should be interpreted to include commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary. 
     It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the scope of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.