The present invention relates to an apparatus and a method for supplying a liquid fuel gas, using a liquefied natural gas (which may be hereafter referred to as "LNG") as a source material and utilizing the coldness thereof, and is useful particularly as an apparatus and a method for supplying a liquid fuel gas containing methane, which is used as a fuel for power generation or the like, as a major component.

A natural gas (NG) is stored as a liquefied natural gas (LNG) for facility in transportation and storage and is used mainly for thermal power generation or for a city gas after vaporization thereof. Also, after 'Shale Gas Revolution', an inexpensive LNG has come to be available in an LNG spot market and, for this reason, there are an increasing number of cases in which LNGs obtained from various countries of origin are utilized.

Also, for example, in the case in which the NG is used as a fuel for power generation, it is convenient when the content of methane is 100% in view of increasing the amount of power generation by increasing the combustion energy. On the other hand, a component having a large carbon number such as ethane (which may be hereafter referred to as "component of ethane or the like") is not only valuable as a source material in chemical plants but also is advantageous in that the amount of use of an LPG can be reduced by using the component as an LNG made to have a higher calorie. In view of such circumstances, it is demanded in an LNG consumption place (LNG receiving base) that a process having a high energy efficiency of separating the LNG into a methane-rich gas and a component of ethane or the like is provided.

For example, referring to Fig. 10, there is known an apparatus for separating a high-pressure natural gas which uses a high-pressure natural gas or a city gas in a gas pipeline as a source material and which is provided with a rectifying tower 110 by cryogenic separation that stores a high-boiling-point component in the source material gas on the lower side thereof in a liquid state and stores a methane-rich gas on the upper side thereof, a heat exchanger 102 that cools the source material gas, a reboiler 101 that cools the source material gas that has passed through the heat exchanger 102, a source material gas expansion means (source material gas expansion valve 103) that causes adiabatic expansion of the source material gas that has passed through the reboiler 101 , a first product gas flow passageway M that guides the methane-rich gas existing in the upper portion of the rectifying tower through the heat exchanger 102 to the outside as a first product gas, and a second product gas flow passageway E that guides the high-boiling-point component existing in the lower portion of the rectifying tower through the heat exchanger 102 to the outside as a second product gas (See, for example, Document 1 : J P-A-2013-064077). Here, the reference numeral 110a represents a top portion of the rectifying tower 110; the reference numeral 110b represents a bottom portion of the rectifying tower 110; and the symbol S represents a source material gas flow passageway.

However, an apparatus for separating a high-pressure natural gas such as described above may raise various problems such as the following.

(i) In the above separation apparatus, a construction example is shown in which an LNG or the like of an ordinary temperature to about -50°C from a pipeline is supplied as a source material and is guided into a rectifying tower after being cooled to about -80 to -120°C. The product gas guided out from the rectifying tower is used as coldness for cooling. In this process, the demanded amount (supplied amount) of the supplied LNG or the like or the product gas may generally fluctuate due to the fluctuation in the demand of thermal power generation or city gas, and also the amount of the available coldness may fluctuate. In conventional apparatus using a high-pressure natural gas as a source material including such a construction, there are cases in which the coldness for cooling that is available by self-supply within the apparatus cannot be sufficiently ensured when only the tower top gas or the tower bottom liquid guided out from the rectifying tower is used. Introduction of the coldness from the outside invites a great loss in the energy efficiency in addition to cumbersomeness of the equipment.

(ii) Because the components of the LNG fluctuate depending on the place of origin, the LNG is often pressurized and stored in a high-pressure tank in a supercooled state (for example, about -160°C, 8.5 MPa). In the conventional apparatus using a high-pressure natural gas as a source material, a method for skillfully using the coldness thereof could not be found and, as in the above separation apparatus, the LNG once processed into a heated state is cooled again by using a separate coldness so as to satisfy the optimum conditions of the rectifying tower and guided into the rectifying tower as an adjusted source material. An apparatus and a method for efficiently using the coldness of the LNG are demanded.

(iii) Also, in a production process of making the separated methane-rich gas into a compressed gas, a large energy must be added in order to pressurize the gas having an ordinary temperature and an ordinary pressure, and also coldness for suppressing the gas temperature rise accompanying the compression is needed. Under conditions in which the amount of consumption and the amount of supply fluctuate, there is a big problem for overall reduction of energy, efficient use of the coldness and comprehensive reduction of energy.

An object of the present invention is to provide an apparatus and a method for supplying a liquid fuel gas having a high energy efficiency, which is efficiently using the coldness of the LNG and being capable of ensuring a supply amount of the liquid fuel gas according to the fluctuation in the composition or the demanded amount of the LNG serving as a source material with little need of the external energy by effectively using the coldness, the compression energy, and the expansion energy that are needed in preparing the liquid fuel gas. Also, another object of the present invention is to provide an apparatus and a method for supplying a liquid fuel gas having a high energy efficiency and being capable of efficiently taking out various liquid fuel gases such as a methane-rich NG, a natural gas liquid (which may be hereafter referred to as "NGL"), an ethane-rich NG, and a liquefied petroleum gas by using LNG as a source material.

As a result of eager researches repeated in order to solve the aforementioned problems, the present inventors have found out that the aforementioned objects can be achieved by an apparatus and a method for supplying a liquid fuel gas shown below, thereby completing the present invention.

The present invention is characterized to an apparatus for supplying a liquid fuel gas in which a liquefied natural gas is guided as a source material into a distillation tower, whereafter a methane-rich natural gas is prepared from a gas component guided out from a tower top portion of the distillation tower, and a natural gas liquid is prepared from a liquid component guided out from a tower bottom portion of the distillation tower, having:

a source material supplying flow passageway in which the pressurized liquefied natural gas in a supercooled state is guided as the source material into the distillation tower via a source material supplying portion, a first heat exchanger, a second heat exchanger, a third heat exchanger, a vaporizer, an expander, the second heat exchanger again, and a gas-liquid separator;

a natural gas supplying flow passageway in which one gas component A derived from branching of the gas component is supplied out as the natural gas via a compressor linked to the expander and a natural gas supplying portion;

- a reflux flow passageway in which the other gas component B derived from branching of the gas component is guided as a reflux liquid into an upper portion of the distillation tower via the first heat exchanger; and

a natural gas liquid supplying flow passageway in which the liquid component is supplied out as the natural gas liquid via the third heat exchanger and a natural gas liquid supplying portion, wherein

• in the first heat exchanger, the gas component B is subjected to condensation by coldness of the liquefied natural gas supplied from the source material supplying portion, thereby to prepare the reflux liquid,

• in the second heat exchanger, the liquefied natural gas guided out from the expander is subjected to low-temperature condensation by coldness of the liquefied natural gas guided out from the first heat exchanger, thereby to prepare the source material, and

• in the third heat exchanger, the liquid component guided out from the tower bottom portion is subjected to lowering of temperature by coldness of the liquefied natural gas guided out from the second heat exchanger, thereby to prepare the natural gas liquid.

The present invention is also characterized to a method for supplying a liquid fuel gas in which a liquefied natural gas is guided as a source material into a distillation tower, whereafter a methane-rich natural gas is prepared from a gas component guided out from a tower top portion of the distillation tower, and a natural gas liquid is prepared from a liquid component guided out from a tower bottom portion of the distillation tower, wherein

a whole amount of the pressurized liquefied natural gas in a supercooled state is guided as the source material into the distillation tower via a source material supplying portion, a first heat exchanger, a second heat exchanger, a third heat exchanger, a vaporizer, an expander, the second heat exchanger again, and a gas-liquid separator;

(1 ) the liquefied natural gas supplied from the source material supplying portion is guided into the first heat exchanger and is heated by releasing coldness thereof through heat exchange with the gas component; (2) the liquefied natural gas guided out from the first heat exchanger is guided into the second heat exchanger and is heated by releasing the coldness thereof through heat exchange with the liquefied natural gas guided out from the expander;

(3) the liquefied natural gas guided out from the second heat exchanger is guided into the third heat exchanger and is heated by releasing the coldness thereof through heat exchange with the liquid component;

(4) the liquefied natural gas guided out from the third heat exchanger is guided into the vaporizer and is vaporized by being heated;

(5) the liquefied natural gas guided out from the vaporizer is guided into the expander and is subjected to lowering of pressure and temperature by adiabatic expansion;

(6) the liquefied natural gas guided out from the expander is guided into the second heat exchanger again and is condensed by being subjected to lowering of temperature by the heat exchange in the step (2);

(7) the liquefied natural gas containing a condensate guided out from the second heat exchanger is guided into the gas-liquid separator to be subjected to gas-liquid separation;

(8) a gas separated in the gas-liquid separator is guided as the source material into an upper portion of a middle tower of the distillation tower, and a liquid separated in the gas-liquid separator is guided as the source material into a lower portion of the middle tower of the distillation tower;

one gas component A derived from branching of the gas component is subjected to adiabatic compression in a compressor linked to the expander and is supplied out as the heated and pressurized natural gas;

- the other gas component B derived from branching of the gas component is condensed through being subjected to lowering of temperature by the coldness of the liquefied natural gas in the step (1 ) and is refluxed as a reflux liquid into an upper portion of the distillation tower; and

the liquid component is supplied out as the natural gas liquid subjected to lowering of temperature by the coldness of the liquefied natural gas in the step (3).

A construction such as described above makes it possible to provide an apparatus and a method for supplying a liquid fuel gas having a high energy efficiency, which is efficiently using the coldness of the LNG and being capable of ensuring a supply amount of the liquid fuel gas according to the fluctuation in the composition or the demanded amount of the LNG serving as a source material with little need of the external energy by effectively using the coldness, the compression energy, and the expansion energy that are needed in preparing the liquid fuel gas.

Specifically, the coldness of the LNG can be completely used by sequentially releasing the whole amount of the coldness of the pressurized LNG in a supercooled state via the first to third heat exchangers and using the coldness in preparing the reflux liquid, the source material in a gas-liquid mixed state after adiabatic expansion, and the NGL.

Also, by using the coldness of the LNG in the releasing process thereof for lowering of temperature and condensation of the LNG itself once vaporized, an intersection of giving and receiving the coldness in a countercurrent manner is formed in the flow of the LNG in the process of preparing the source material that is guided into the distillation tower, whereby the coldness of the LNG can be further more effectively used.

The present invention is also characterized to the apparatus for supplying the liquid fuel gas described above, further having:

a fourth heat exchanger and a fifth heat exchanger provided downstream of the third heat exchanger in the source material supplying flow passageway;

a second distillation flow passageway in which a part or a whole amount of the liquid component guided out from the tower bottom portion is guided into a second distillation tower;

a second natural gas supplying flow passageway in which one gas component C derived from branching of a second gas component guided out from a second tower top portion of the second distillation tower is supplied out as a second natural gas via a second compressor, a second vaporizer, and a second natural gas supplying portion;

a second reflux flow passageway in which the other gas component D derived from branching of the second gas component guided out from the second tower top portion of the second distillation tower is guided as a second reflux liquid into an upper portion of the second distillation tower via the fourth heat exchanger; and

a liquefied petroleum gas supplying flow passageway in which a second liquid component guided out from a second tower bottom portion of the second distillation tower is supplied out as a liquefied petroleum gas via the fifth heat exchanger and a liquefied petroleum gas supplying portion, wherein

• the gas component D is condensed in the fourth heat exchanger by the coldness of the liquefied natural gas guided out from the third heat exchanger, thereby to prepare the second reflux liquid, and

• the second liquid component guided out from the second tower bottom portion is subjected to lowering of temperature in the fifth heat exchanger by the coldness of the liquefied natural gas guided out from the fourth heat exchanger, thereby to prepare the liquefied natural gas.

The present invention is also characterized to the method for supplying the liquid fuel gas described above, wherein

a part or a whole amount of the liquid component guided out from the tower bottom portion is guided into a second distillation tower;

an ethane-rich second natural gas is prepared from a second gas component guided out from a second tower top portion of the second distillation tower;

a liquefied petroleum gas is prepared from a second liquid component guided out from a second tower bottom portion of the second distillation tower;

in place of the step (4),

(4a) the liquefied natural gas guided out from the third heat exchanger after passing through the steps (1 ) to (3) is further guided into the fourth heat exchanger and is heated by releasing the coldness thereof by heat exchange with the second gas component;

(4b) the liquefied natural gas guided out from the fourth heat exchanger is guided into the fifth heat exchanger and is heated by releasing the coldness thereof by heat exchange with the second liquid component;

(4c) the liquefied natural gas guided out from the fifth heat exchanger is guided into the vaporizer and is vaporized by being heated;

thereafter, the resultant is guided as the source material into the distillation tower after passing through the steps (5) to (8);

one gas component C derived from branching of the second gas component is subjected to adiabatic compression by a second compressor and is supplied out as the heated and pressurized second natural gas; the other gas component D derived from branching of the second gas component is condensed through being subjected to lowering of temperature by the coldness of the liquefied natural gas in the step (4a) and is refluxed as a second reflux liquid into an upper portion of the second distillation tower; and

- the second liquid component is supplied out as the liquefied petroleum gas by being subjected to lowering of temperature by the coldness of the liquefied natural gas in the step (4b).

A construction such as described above makes it possible to provide an apparatus and a method for supplying a liquid fuel gas having a high energy efficiency and being capable of efficiently taking out not only a methane-rich NG and an NGL but also various liquid fuel gases such as an ethane-rich NG and a liquefied petroleum gas by using LNG as a source material. In particular, by disposing the two distillation towers in series with respect to the LNG serving as the source material, each of the liquid fuel gases can be individually supplied out in an arbitrary amount, and also a liquid fuel gas obtained by blending these in an arbitrary ratio can be supplied out in accordance with a demanded specification.

Also, the pressurized LNG in a supercooled state still has an effective coldness after releasing a predetermined amount of the coldness via the first to third heat exchangers. By using this residual coldness in preparing the ethane-rich gas, propane, and the like via the fourth heat exchanger and the fifth heat exchanger, the present invention makes it possible to prepare various liquid fuel gases such as LPG effectively with little need of the external energy.

The present invention is also characterized to the apparatus for supplying the liquid fuel gas described above, wherein a whole amount of the liquefied natural gas supplied from the source material supplying portion is processed into an ordinary-temperature pressurized state via the first to third heat exchangers and the vaporizer, thereafter subjected to lowering of temperature and lowering of pressure through adiabatic expansion by the expander, further subjected to low-temperature condensation by being guided into the second heat exchanger again, and subjected to separation by being guided into the gas-liquid separator, whereafter a gas separated in the gas-liquid separator is guided as the source material into an upper portion of a middle tower of the distillation tower, and a liquid separated in the gas-liquid separator is guided as the source material into a lower portion of the middle tower of the distillation tower.

The above-described apparatus for supplying the liquid fuel gas can achieve effective use of the coldness that could not have been made in the past in giving and receiving heat energy in that the whole amount of the coldness of the LNG, particularly the coldness of the pressurized LNG in a supercooled state, can be used. During this process, the supplied LNG is in a high-pressure state, and the LNG serving as the source material that is guided into the distillation tower is preferably set to have a pressure that attains the optimum conditions of distillation.

The present invention realizes such a function by vaporizing the whole amount of the supplied LNG to release the coldness thereof and thereafter subjecting this to adiabatic expansion and cooling to prepare the material. This makes it possible to ensure the optimum temperature and pressure conditions in the distillation tower even when fluctuation occurs in the supply amount, the composition, the temperature, or the pressure of the LNG, and to reduce the energy loss accompanying the transmission of the coldness to a great extent.

The present invention is also characterized to the apparatus for supplying the liquid fuel gas described above, wherein the expander is made of a plurality of expansion turbines arranged in series; the liquefied natural gas guided out from the vaporizer is branched to be guided into each of the expansion turbines; one or a plurality of the expansion turbines are linked to the same number of the compressors; the other expansion turbines are linked to the same number of power generators; and the gas component A is guided into the compressors.

In the apparatus for supplying the liquid fuel gas, a fluctuation may occur in the supply amount or the supply temperature and pressure of the prepared methane-rich natural gas (which may be hereafter referred to as "NG") or natural gas liquid (which may be hereafter referred to as "NGL") in addition to the fluctuation in the supply amount, the composition, or the delivery temperature and pressure of the LNG. Also, in order to improve the total energy efficiency in the apparatus for supplying the liquid fuel gas, it is preferable to ensure electric energy as a driving power source within the apparatus.

The present invention makes it possible to ensure the function of the optimum conditions according to the above fluctuation by using the expander having a plurality of expansion turbines and adjusting the amount of operation of each of the turbines and the compressors linked to a part thereof, and also makes it possible to ensure a power generation amount according to the operation of only the expansion turbines by linking the power generators to a part of the expansion turbines.

The present invention is also characterized to the apparatus for supplying the liquid fuel gas described above, further having a flow passageway that connects between the source material supplying portion and the upper portion of the distillation tower, whereby a part of the liquefied natural gas supplied from the source material supplying portion is guided as the source material into the distillation tower through the upper portion of the distillation tower when the apparatus is started.

When the distillation tower is started, a predetermined period of time is needed until an optimum gas-liquid equilibrium is formed in the inside of the tower. In particular, part of the reflux liquid is one of the rate-limiting conditions for forming a stable gas-liquid equilibrium. The present invention allows that, by introducing the low-temperature LNG supplied as the source material through the upper portion of the distillation tower, such formation of the reflux liquid is complemented, whereby a stable gas-liquid equilibrium can be formed quickly.

Fig. 1 is a schematic view illustrating a basic construction example of an apparatus for supplying a liquid fuel gas according to the present invention;

Fig. 2 is a verification result as exemplified in a basic construction example of an apparatus for supplying a liquid fuel gas according to the present invention;

Fig. 3 is a schematic view illustrating the second exemplary structure of an apparatus for supplying a liquefied gas according to the present invention;

Fig. 4 is a verification result as exemplified in the second exemplary structure of an apparatus for supplying a liquefied gas according to the present invention;

Fig. 5 is a schematic view illustrating the third exemplary structure of an apparatus for supplying a liquefied gas according to the present invention;

Fig. 6 is a schematic view illustrating the fourth exemplary structure of an apparatus for producing a liquefied gas according to the present invention;

Fig. 7 is a verification result as exemplified in the fourth exemplary structure of an apparatus for producing a liquefied gas according to the present invention;

Fig. 8 is a schematic view illustrating the fifth exemplary structure of an apparatus for producing a liquefied gas according to the present invention;

Fig. 9 is a verification result as exemplified in the fifth exemplary structure of an apparatus for producing a liquefied gas according to the present invention; and

Fig. 10 is a schematic view illustrating an apparatus for separating a high-pressure natural gas according to a conventional art.

In an apparatus for supplying a liquid fuel gas according to the present invention (hereafter referred to as "present apparatus"), a liquefied natural gas (LNG) is guided as a source material into a distillation tower, whereafter a methane-rich natural gas (NG) is prepared from a gas component guided out from a tower top portion of the distillation tower, and a natural gas liquid (NGL) is prepared from a liquid component guided out from a tower bottom portion of the distillation tower. The apparatus comprises a source material supplying flow passageway in which the pressurized LNG in a supercooled state is guided as the source material into the distillation tower via a source material supplying portion, a first heat exchanger, a second heat exchanger, a third heat exchanger, a vaporizer, an expander, the second heat exchanger again, and a gas-liquid separator; a natural gas supplying flow passageway in which one gas component A derived from branching of the gas component is supplied out as the NG via a compressor linked to the expander and a natural gas supplying portion; a reflux flow passageway in which the other gas component B derived from branching of the gas component is guided as a reflux liquid into an upper portion of the distillation tower via the first heat exchanger; and a natural gas liquid supplying flow passageway in which the liquid component is supplied out as the NGL via the third heat exchanger and a natural gas liquid supplying portion.

The gas component B is subjected to condensation in the first heat exchanger by coldness of the LNG supplied from the source material supplying portion, thereby to prepare the reflux liquid. The LNG guided out from the expander is subjected to low-temperature condensation in the second heat exchanger by coldness of the LNG guided out from the first heat exchanger, thereby to prepare the source material. The liquid component guided out from the tower bottom portion is subjected to lowering of temperature in the third heat exchanger by coldness of the LNG guided out from the second heat exchanger, thereby to prepare the NGL. Hereafter, embodiments of the present invention will be described with reference to the attached drawings. Here, in the present embodiments, conditions such as the temperature, the pressure, and the flow rate of each portion can be suitably changed in accordance with other conditions such as the kind and the flow rate of the gases.

A summary of a basic construction example (first construction example) of the present apparatus will be exemplified in Fig. 1. In the present apparatus, a pressurized LNG in a supercooled state is guided as a source material into a distillation tower 10; a methane-rich NG is prepared from a gas component (tower top gas) guided out from a tower top portion 11 ; and an NGL is prepared from a liquid component (tower bottom liquid) guided out from a tower bottom portion 12. Here, the LNG supplied from a source material supplying portion 1 is vaporized via coldness releasing process through a first heat exchanger 21 , a second heat exchanger 22, a third heat exchanger 23, a vaporizer 30, and an expander 41 , and the vaporized LNG is passed through the second heat exchanger 22 and a gas-liquid separator 50 to form a gas-liquid mixture to be guided as the source material into the distillation tower 10. In view of the passage of the LNG, an intersection of the LNG with itself is formed at which the returning LNG gives and receives the coldness in a countercurrent manner. At the intersection, the coldness of the LNG in a releasing process is used for lowering of temperature and condensation of the LNG itself once vaporized. In other words, in the flow of the LNG in a process of preparing the source material that is guided into the distillation tower, the coldness of the LNG is not only released but also received, that is, a part of the released coldness is received, whereby the coldness can be further more effectively used.

Specifically, there is provided a source material supplying flow passageway in which the pressurized LNG in a supercooled state is guided as the source material into the distillation tower 10 via the source material supplying portion 1 , the first heat exchanger 21 , the second heat exchanger 22, the third heat exchanger 23, the vaporizer 30, the expander 41 , the second heat exchanger 22 again, and the gas-liquid separator 50. A low-temperature high-pressure LNG (for example, about -150°C, about 6 MPa) is supplied in a liquid form from the source material supplying portion 1 and vaporized by the vaporizer 30 after sequentially releasing the coldness via the first to third heat exchangers 21 to 23.

The coldness of the LNG can be used to the maximum extent. The vaporized LNG is subjected to adiabatic expansion by the expander 41 to be subjected to lowering of temperature and also to lowering of pressure down to a predetermined pressure (for example about 2.3 MPa) that is optimal as the source material, so as to form a gaseous low-temperature and low-pressure LNG.

The gaseous LNG is further subjected to lowering of temperature to a predetermined temperature that is optimal as the source material by the second heat exchanger 22 again. The predetermined temperature at this time refers to a temperature at which an LNG having a predetermined composition is condensed under an optimum pressure to form a gas-liquid coexistence state. For example, in the case of an LNG having a composition exemplified in the following Table 1 , about -80°C is suitable under about 2.3 MPa. The condensed LNG is separated into a gas and a liquid by the gas-liquid separator 50 and guided into the distillation tower 10.

At this time, it is preferable that the gas separated by being guided into the gas-liquid separator 50 is guided as the source material into an upper portion of a middle tower portion 13 (upper portion of a middle tower) of the distillation tower 10, and the liquid separated by being guided into the gas-liquid separator 50 is guided as the source material into a lower portion of the middle tower portion 13 (lower portion of the middle tower) of the distillation tower 10. By guiding the low-temperature liquid LNG into the lower portion of the middle tower together with a later-described reflux liquid and guiding the low-temperature gaseous LNG into the upper portion of the middle tower, the gas-liquid separator 50 can be made to function as a pre-positioned distillation tower, whereby the efficiency of separation into a methane component and components other than methane can be further increased.

At this time, it is preferable that a whole amount of the LNG supplied from the source material supplying portion 1 is processed into an ordinary-temperature pressurized state via the first to third heat exchangers 21 to 23 and the vaporizer 30, thereafter subjected to lowering of temperature and lowering of pressure through adiabatic expansion by the expander 41 , further subjected to low-temperature condensation by being guided into the second heat exchanger 22 again, and subjected to separation by being guided into the gas-liquid separator 50, whereafter the gas separated by being guided into the gas-liquid separator 50 is guided as the source material into the upper portion of the middle tower portion 13 (upper portion of the middle tower) of the distillation tower 10, and the liquid separated by being guided into the gas-liquid separator 50 is guided as the source material into the lower portion of the middle tower portion 13 (lower portion of the middle tower) of the distillation tower 10. Even when fluctuation occurs in the supply amount, the composition, the temperature, or the pressure of the LNG, the optimum temperature and pressure conditions in the distillation tower 10 can be ensured, and the energy loss accompanying the transmission of the coldness can be reduced to a great extent. However, when the amount of the supplied coldness exceeds an amount sufficient for preparation of desired NG and NGL, the coldness can be drawn out for other purposes in the middle of the source material supplying flow passageway.

This applies, for example, to a case in which the LNG containing a large amount of methane is supplied; the coldness of the usable LNG is large in amount; a large amount of the NG can be prepared from the distillation tower 10; and the NGL can be prepared with a smaller amount of the coldness.

In the present apparatus, a branching portion is disposed in a flow passageway for guiding out the gas component (tower top gas) from the tower top portion 11 of the distillation tower 10. The present apparatus is provided, in the one of the branching portion, with a natural gas supplying flow passageway in which the gas component A derived from branching at the branching portion is made into a methane-rich NG via a compressor 42 linked to the expander 41 and is supplied out via a natural gas supplying portion 2. The tower top gas is a methane-rich NG having a low temperature and a low pressure (for example, about -100°C and about 2.3 MPa), so that a temperature-raising and pressure-raising process must be carried out in order to take out as a product NG having a predetermined temperature and pressure (for example, about -30°C and about 6 MPa).

In the present apparatus, a desired product NG can be supplied out without introduction of additional energy by subjecting the one gas component A derived from branching to adiabatic compression by the compressor 42 that is linked to the expander 41 used for preparation of the source material.

However, when the tower top gas is guided out in a low-temperature low-pressure state equivalent to that of the product NG, the tower top gas is supplied out directly from the tower top portion 11 without performing such a process.

Also, the compressor 42 is meant to include not only a single-body construction but also a construction in which a plurality of compressors are arranged in series in a case such as having a large compression ratio or a construction in which a plurality of compressors are arranged in parallel in a case of such as performing adjustment of the compression ratio independent from the expander 41.

The present apparatus is provided, in the other of the branching portion, with a reflux flow passageway in which the gas component B derived from branching at the branching portion is guided as a reflux liquid into an upper portion 14 of the distillation tower via the first heat exchanger 21. The branched gas component B is guided into the first heat exchanger 21 to be efficiently condensed by ensuring sufficient condensation heat together with temperature-lowering energy through heat exchange with the LNG having the maximum amount of coldness and thereafter used as the reflux liquid to the distillation tower 10, thereby achieving effective use of the coldness of the LNG and also performing a buffering function for ensuring stable performance of the distillation tower 10 when fluctuation occurs in the supply amount of the product gas prepared from the gas component A.

Specifically, for example, when the product NG is decreased in amount, the distillation tower 10 can be operated without fluctuation in the guided-out flow rate of the tower top gas by decreasing the supply flow rate of the gas component A (for example, from about 500,000 to 400,000 kg/h) and increasing the flow rate of the gas component B (for example, from about 500,000 to 600,000 kg/h).

By increase of the reflux liquid in a state in which the distillation efficiency of the distillation tower 10 is maintained, the yield of the NG can be lowered, and rise in the yield of the NGL can be obtained. Conversely, when the product NG is increased in amount, the yield of the NG can be raised, and the yield of the NGL can be lowered by decreasing the flow rate of the gas component B and decreasing the amount of the reflux liquid.

The present apparatus is provided with a natural gas liquid supplying flow passageway in which the liquid component (tower bottom liquid) guided out from the tower bottom portion 12 of the distillation tower 10 is made into an NGL via the third heat exchanger 23 and supplied out via a natural gas liquid supplying portion 3. The tower bottom liquid is an NGL having an ordinary temperature and a low pressure (for example, about 25°C and about 2.3 MPa), so that a temperature-lowering process (and further a pressure-lowering process depending on the cases) must be carried out in order to take out as a product NGL having a predetermined temperature and pressure (for example, about -10°C and about 2.3 MPa). In the present apparatus, a desired product NGL can be supplied out without introduction of additional energy by subjecting the tower bottom liquid to lowering of temperature efficiently by heat exchange with the LNG having coldness.

Here, when the component having a carbon number of 3 or more such as propane is large in amount in the LNG serving as the source material, the tower bottom liquid can be, as it is, supplied out as the product NGL without lowering the temperature. Also, in the present apparatus, although not illustrated in the drawings, the tower bottom liquid may be branched to supply the product NGL out on one hand, and the tower bottom liquid may be heated via a reboiler (not illustrated in the drawings) on the other hand to be guided into a lower portion 15 of the distillation tower, whereby a high distillation function can be obtained.

As described above, in the present apparatus, the LNG supplied from the source material supplying portion 1 sequentially releases a part of the coldness in the first heat exchanger 21 to condense the tower top gas (gas component B) to prepare the reflux liquid, further releases a part of the coldness in the second heat exchanger 22 to subject the LNG guided out from the expander 41 to low-temperature condensation to prepare the source material, and releases the residual amount of the coldness in the third heat exchanger 23 to subject the tower bottom liquid to lowering of temperature to prepare the NGL. The LNG supplied from the source material supplying portion 1 refers, for example, to a pressurized LNG in a supercooled state that has been stored in a high-pressure tank. By completely using this coldness, an apparatus for supplying a liquid fuel gas having a high energy efficiency can be constructed.

The LNG supplied in the present apparatus has, for example, a composition such as exemplified in the following Table 1 , with the components fluctuating according to the place of origin and with differing temperature and pressure conditions under which the LNG is stored in a high-pressure tank. Specifically, the LNG is stored under temperature conditions of about -120 to -160°C and under pressure conditions of about 5 to 10 MPa.

Here, the LNGs according to the present invention are meant to include a shale gas such as already described in addition to the LNG conventionally referred to, or are meant to include not only a refined LNG but also a non-refined LNG. Table 1

The first to third heat exchangers 21 to 23 are not particularly limited; however, a plate fin type heat exchanger, a shell tube type heat exchanger, or the like can be used, for example. In particular, in the first heat exchanger 21 in which heat exchange is carried out between the low-temperature liquid LNG and the low-temperature gaseous NG and in the second heat exchanger 22 in which heat exchange is carried out between the low-temperature liquid LNG and the low-temperature gaseous LNG, the coldness can be given and received more efficiently by using a plate fin type heat exchanger having a larger heat transmission area. Also, in the third heat exchanger 23 in which heat exchange is carried out between the low-temperature liquid LNG and the ordinary-temperature liquid NGL, the coldness can be given and received more efficiently by using a shell tube type heat exchanger having a smaller passage resistance and having a larger heat transmission area.

With use of the present apparatus, an LNG having a composition exemplified in the above Table 1 was supplied as a source material, so as to verify the temperature (°C), the pressure (MPa), the flow rate (kg/h), and the composition (G/L: gas/liquid) in each portion, (i) Verification result

When an LNG (-150°C, 6.00 MPa) was supplied at 427,000 kg/h, the temperature, the pressure, the flow rate, and the composition in each of the portions a to r in Fig. 2 resulted as exemplified in the following Table 2. Table 2

(ii) Next, the income and the outcome of energy in the present apparatus were verified in comparison with a conventional "separation apparatus". In the conventional "separation apparatus" in which the pressure of a source material LNG is reduced to a predetermined pressure using a separate expander, and a separated NG is separately pressurized using a compressor to prepare a reflux liquid using an external coldness, a supply amount of energy from outside that was needed in the conventional "separation apparatus" was estimated in the case in which the LNG was supplied to a distillation tower under the same conditions as in the present apparatus and the NG and the NGL under the same conditions were supplied out, and the result was compared with the supply amount of energy from outside that was needed in the present apparatus. As will be understood from the following Table 3, a result has been obtained in which the supply amount of energy from outside in the present apparatus was smaller by a sum amount of 9,393 kW (as converted in terms of electric power) when compared with that of the conventional "separation apparatus". Table 3

A summary of the second construction example of the present apparatus will be shown in Fig. 3. Hereafter, constituent elements common to those of the basic construction will be denoted with common appellations and reference symbols, and the description thereof may be omitted. The present apparatus has a construction in which, in the source material supplying flow passageway of the basic construction example, the expander 41 is comprised of expansion turbines 41a, 41 b that are arranged in parallel; the LPG guided out from the vaporizer 30 is branched to be guided into each of the expansion turbines 41a, 41 b; the expansion turbine 41a is linked to the compressor 42; and the expansion turbine 41 b is linked to a power generator 60. The functions under the optimum conditions of the present apparatus comprising the distillation tower 10 can be ensured by adjusting the operation amount of the expansion turbines 41a, 41 b and the operation amount of the compressor 42 in accordance with the fluctuation in the supply amount, the composition, the supply temperature, the pressure, and the like of the LNG or the fluctuation in the supply amount, the supply temperature, the pressure, and the like of the NG and the NGL that are supplied out.

Also, by linking the power generator 60 to the expansion turbine 41 b, a power generation amount corresponding to the operation amount of the expansion turbine 41 b can be ensured. Here, a construction example is shown in which the expander 41 is made of two expansion turbines 41a, 41 b that are arranged in parallel; however, the number of the expansion turbines is not limited thereto.

The present apparatus is meant to comprise a construction in which the expander is made of two or more expansion turbines 41a, 41 b ... 41 n (not illustrated in the drawings). By linking one or more expansion turbines to the same number of compressors, the operation amount of the expander (amount, temperature, and pressure of adiabatic expansion of LNG) can be adjusted, and the operation amount (compression ratio) of the compressor can be adjusted in accordance with the fluctuation in the supply amount, the supply temperature, the pressure, and the like of the NG that is supplied out.

For example, the compression ratio of the compressor can be varied by linking two expansion turbines having different expansion functions to two compressors having different compression ratios and varying the operation amount of the compressors by changing the ratio of the operation amount thereof while maintaining the total expansion function to be constant.

At this time, a high compression ratio can be obtained when the gas component A is branched and guided into each of the compressors in series, and a high adjustment precision of the compression ratio can be obtained when the gas component A is branched and guided into each of the compressors in parallel. Also, by linking one or more expansion turbines to the same number of power generators, the operation amount of the expander can be adjusted, and the operation amount of the power generator can be adjusted in accordance with the needed amount of power generation.

For example, the power generation amount can be varied by linking two expansion turbines having different expansion functions to two power generators having different power generation capabilities and varying the operation amount of the power generators by changing the ratio of the operation amount thereof while maintaining the total expansion function to be constant.

With use of the second construction example of the present apparatus, an LNG having a composition exemplified in the above Table 1 was supplied as a source material, so as to verify the temperature (°C), the pressure (MPa), the flow rate (kg/h), and the composition (G/L: gas/liquid) in each portion. When an LNG (-150°C, 6.00 MPa) was supplied at 427,000 kg/h, the temperature, the pressure, the flow rate, and the composition in each of the portions s to v in Fig. 4 in addition to each of the portions a to r in Fig. 2 were obtained as exemplified in the following Table 4. Also, a power generation amount of about 500 kW/h could be obtained from the power generator 60 linked to the expansion turbine 42. Table 4

A summary of the third construction example of the present apparatus will be shown in Fig. 5. The present apparatus according to the third construction example has a construction in which a flow passageway Ld that connects between the source material supplying portion 1 and the upper portion 14 of the distillation tower is provided, whereby a part of the LNG supplied from the source material supplying portion 1 is guided as the source material into the distillation tower 10 through the upper portion 14 of the distillation tower 10 when the apparatus is started. By guiding the LNG in a supercooled state into the tower at the time of the start of the distillation tower 10, a formation of the reflux in the tower, which is one of the rate-limiting conditions for forming a stable gas-liquid equilibrium, can be complemented, whereby the distillation tower 10 can be started quickly.

Specifically, a quick formation of the gas-liquid equilibrium in the tower can be achieved by providing a valve Lv in the flow passageway Ld and introducing, for example, an LNG having a low-temperature and a high-pressure (for example, about -150°C and about 6 MPa) and having a composition exemplified in the above Table 1 through the upper portion 14 of the distillation tower 10 while limiting to the low-temperature low-pressure conditions (for example, about -150°C and about 2.3 MPa) in the same manner as in the basic construction example.

A method for supplying a liquid fuel gas according to the present invention is such that, by using the present apparatus described above, an LNG is guided as a source material into a distillation tower, whereafter a methane-rich NG is prepared from a gas component guided out from a tower top portion of the distillation tower, and an NGL is prepared from a liquid component guided out from a tower bottom portion of the distillation tower.

Here, the whole amount of the pressurized LNG in a supercooled state is guided as the source material into the distillation tower via a source material supplying portion, a first heat exchanger, a second heat exchanger, a third heat exchanger, a vaporizer, an expander, the second heat exchanger again, and a gas-liquid separator. The coldness of the LNG can be used to the maximum extent by sequentially releasing the whole amount of the coldness of the pressurized LNG in a supercooled state via the first to third heat exchangers to vaporize the whole amount of the LNG.

The vaporized LNG is subjected to adiabatic expansion and further to lowering of temperature and condensation in the second heat exchanger by the coldness of the LNG itself, whereby the LNG can be adjusted to become a source material optimal for distillation processing and, in addition, effective use of the coldness of the LNG can be made. Specifically, a construction example comprising the following steps can be raised as an example. Here, in the following description, each of the portions in the present apparatus is denoted with the reference symbol exemplified in Fig. 1 , and the conditions exemplified in the above Table 2 may be applied as the conditions of each gas or liquid; however, it goes without saying that the present invention is not limited thereto.

The pressurized LNG stored in a supercooled state is prepared into a gaseous LNG by the following steps.

(1 ) The LNG supplied from the source material supplying portion 1 is guided into the first heat exchanger 21 and is heated by releasing the coldness thereof through heat exchange with the gas component B guided out from the tower top portion 11. For example, the LNG having a temperature of about -150°C and a pressure of about 6 MPa is heated to about -124°C by releasing the coldness thereof in the first heat exchanger 21. Simultaneously, the gas component B having a temperature of about -104°C and a pressure of about 2.3 MPa is cooled to prepare a condensate of about -104°C. The prepared condensate is guided as a reflux liquid into an upper portion 14 of the distillation tower.

(2) The LNG guided out from the first heat exchanger 21 is guided into the second heat exchanger 22 and is heated by releasing the coldness thereof through heat exchange with the LNG guided out from the expander 41. For example, the LNG having a temperature of about -124°C and a pressure of about 6 MPa is heated to about -65°C by releasing the coldness thereof in the second heat exchanger 22. Simultaneously, the LNG having a temperature of about -36°C and a pressure of about 2.3 MPa is cooled to prepare a condensate (gas-liquid mixture) of about -94°C. The prepared condensate is guided as a reflux liquid into the upper portion 14 of the distillation tower.

(3) The LNG guided out from the second heat exchanger 22 is guided into the third heat exchanger 23 and is heated by releasing the coldness thereof through heat exchange with the liquid component guided out from the tower bottom portion 12. For example, the LNG having a temperature of about -65°C and a pressure of about 6 MPa is heated to about -64°C by releasing the coldness thereof in the third heat exchanger 23. Simultaneously, a tower bottom liquid having a temperature of about 21 °C and a pressure of about 2.3 MPa is cooled to prepare an NGL of about 10°C. (4) The LNG guided out from the third heat exchanger 23 is guided into the vaporizer 30 and is vaporized by being heated. For example, the LNG having a temperature of about -64°C and a pressure of about 6 MPa is vaporized by releasing the coldness thereof in the vaporizer 30 and being heated to about 15°C.

(5) The gaseous LNG guided out from the vaporizer is guided as the source material into the distillation tower by passing through the following steps.

(6) The LNG guided out from the vaporizer 30 is guided into the expander 41 and is subjected to lowering of pressure and lowering of temperature by adiabatic expansion. For example, the gaseous LNG having a temperature of about 15°C and a pressure of about 6 MPa is subjected to adiabatic expansion by the expander 41 and is subjected to lowering of temperature to about -36°C and to lowering of pressure to about 2.3 MPa. A part of the gaseous LNG may be liquefied (gas-liquid mixture state). The lowering pressure is set to be under the optimum conditions of distillation based on the composition of the LNG and the characteristics of the distillation tower 10.

(7) The LNG guided out from the expander 41 is guided into the second heat exchanger 22 again and is condensed by being subjected to lowering of temperature through heat exchange in the step (2). For example, the LNG cooled to about -36°C is liquefied (gas-liquid mixture state) in the second heat exchanger 22 by receiving the coldness of the LNG having a temperature of about -124°C and a pressure of about 6 MPa and being subjected to lowering of temperature to about -94°C. The cooling temperature is set to be under the optimum conditions of distillation based on the composition of the LNG and the characteristics of the distillation tower 10. Simultaneously, the LNG having released the coldness is heated to about -65°C.

(8) The LNG containing a condensate guided out from the second heat exchanger 22 is guided into the gas-liquid separator 50 to be subjected to gas-liquid separation. For example, the LNG cooled to about -94°C is separated into a gas having a volume ratio of about 3/5 and a liquid having a volume ratio of about 2/5 in the gas-liquid separator 50.

(9) The gas separated in the gas-liquid separator 50 is guided as the source material into an upper portion of a middle tower of the distillation tower 10, and the liquid separated in the gas-liquid separator 50 is guided as the source material into a lower portion of the middle tower of the distillation tower 10. At this time, the separated gas has a higher concentration of methane than the LNG of the source material, and the separated liquid has a higher concentration of components such as ethane than the LNG of the source material (which can be said to be a pre-treatment of distillation).

From the LNG guided into the distillation tower 10, a methane-rich NG is supplied out from the tower top gas coming from the tower top portion 11 of the distillation tower 10, and an NGL is supplied out from the tower bottom liquid coming from the tower bottom portion 12 of the distillation tower 10, by passing through the following steps.

(8a) The LNG guided into the distillation tower is separated into a methane-rich tower top gas and a tower bottom liquid containing a component such as ethane as a major component.

Specifically, for example, in the distillation tower 10 having a pressure of about 2.3 MPa, a tower top temperature of about -104°C, and a tower bottom temperature of about 21 °C, the gaseous LNG guided into the upper portion of the middle tower forms an ascending flow and is brought into gas-liquid contact with a descending flow, which is mainly made of the methane-rich reflux liquid, to increase the purity of methane (tower top gas). On the other hand, the liquid LNG guided into the lower portion of the middle tower forms the descending flow and is brought into gas-liquid contact with the ascending flow, which contains a component such as ethane and is heated at the tower bottom portion, to increase the purity of the component such as ethane (tower bottom liquid).

(8b) A methane-rich NG is prepared from the tower top gas guided out from the tower top portion of the distillation tower.

From the tower top portion 11 , a tower top gas having a temperature of about -104°C and a pressure of about 2.3 MPa and containing methane at 99.9% or more is guided out, and about 90% thereof is subjected to adiabatic compression, for example, to about -43°C and about 6 MPa as the gas component A by the compressor 42 to be made into a methane-rich NG, which is supplied out via the natural gas supplying portion 2.

By using the compressor 42 linked to the expander 41 , a desired product NG can be supplied out without introduction of additional energy. In this process, about 20% of the tower top gas is guided as the gas component B into the first heat exchanger 21 , where a condensate of about -104°C is prepared, and the prepared condensate is guided as a reflux liquid into the upper portion 14 of the distillation tower. (8c) An NGL is prepared from the tower bottom liquid guided out from the tower bottom portion of the distillation tower.

From the tower bottom portion 12, a tower bottom liquid having a temperature of about 21 °C and a pressure of about 2.3 MPa and containing a component such as ethane at 99.9% or more is guided out and cooled to about 10°C via the third heat exchanger 23 to be made into an NGL, which is supplied out via the natural gas liquid supplying portion 3. A desired product NGL can be supplied out by effectively using the coldness of the LNG

Also, in the present apparatus, although not illustrated in the drawings, the tower bottom liquid may be branched to supply the product NGL out on one hand, and the tower bottom liquid may be heated via a reboiler (not illustrated in the drawings) on the other hand to be guided into the lower portion 15 of the distillation tower, whereby a high distillation function can be obtained.

As shown in the above Table 1 , the LNG serving as the source material contains not only methane constituting a major component but also substances having different boiling points such as ethane, propane, and butane. These are not only individually used as fuels but also used as various chemical materials that are extremely useful, so that the demand for each of these is high.

In the present apparatus, not only an NG and an NGL but also an ethane-rich natural gas (sNG) and a liquid fuel gas (LPG) having a carbon number of 3 or more can be individually supplied out in an arbitrary amount by disposing a plurality of distillation towers in series instead of a single distillation tower as in the above construction example and sequentially taking out substances containing a low-boiling-point substance as a major component.

Hereafter, description will be given on the fourth construction example in which two distillation towers are disposed on the basis of the first construction example described above and on the fifth construction example in which two distillation towers are disposed on the basis of the second construction example described above.

Here, description of a construction example corresponding to the third construction example described above and a construction example in which three or more distillation towers are disposed will be omitted; however, application can be made by adding a construction equivalent to those added to the fourth construction example and the fifth construction example. A summary of the fourth construction example of the present apparatus will be shown in Fig. 6. Hereafter, constituent elements common to those of the basic construction will be denoted with common appellations and reference symbols, and the description thereof may be omitted. The fourth construction example has a construction further comprising a fourth heat exchanger 24 and a fifth heat exchanger 25 provided downstream of the third heat exchanger 23 in the source material supplying flow passageway of the basic construction example (first construction example); a second distillation flow passageway in which at least a part of the liquid component guided out from the tower bottom portion 12 of the distillation tower (which may be hereafter referred to as "first distillation tower") 10 is guided into a second distillation tower 70; a second natural gas supplying flow passageway in which one gas component C derived from branching of a second gas component guided out from a second tower top portion 71 of the second distillation tower 70 is supplied out as a second natural gas via a second compressor 43, a second vaporizer 31 , and a second natural gas supplying portion 4; a second reflux flow passageway in which the other gas component D derived from branching of the second gas component guided out from the second tower top portion 71 of the second distillation tower 70 is guided as a second reflux liquid into an upper portion 74 of the second distillation tower 70 via the fourth heat exchanger 24; and a liquefied petroleum gas supplying flow passageway in which a second liquid component guided out from a second tower bottom portion 72 of the second distillation tower 70 is supplied out as a liquefied petroleum gas via the fifth heat exchanger 25 and a liquefied petroleum gas supplying portion 5.

By disposing the two distillation towers 10, 70 in series with respect to the LNG serving as the source material in addition to the functions of the basic construction example, not only the NG and the NGL but also the sNG and the LPG can be supplied out individually in an arbitrary amount. Further, the LNG still having a residual effective coldness after releasing a predetermined amount of coldness via the first heat exchanger 21 to the third heat exchanger 23 may be guided into the fourth heat exchanger 24 and the fifth heat exchanger 25 so as to perform heat exchange with the tower top gas or the tower bottom liquid of the second distillation tower 70 via these heat exchangers, whereby the sNG and the LPG can be prepared effectively with little need of the external energy. Specifically, a part or a whole amount of the liquid component having an ordinary temperature and a low pressure (for example, about 22°C and about 2.3 MPa) that has been guided out from the tower bottom portion 12 of the first distillation tower 10 is guided into a middle tower portion 73 of the second distillation tower 70 by the second distillation flow passageway.

This liquid component obtained by removal of the methane component from the LNG (including a case in which a slight amount of the methane component remains) is separated in the second distillation tower 70 into a second gas component containing ethane as a major component and a second liquid component (having a carbon number of 3 or more) such as propane.

The second gas component having a low temperature and a low pressure (for example, about -63°C and about 2.3 MPa) that has been guided out from the tower top portion 71 is branched, and one gas component C derived from the branching is pressurized (about 6 MPa) in the second natural gas supplying flow passageway via the second compressor 43 and is further heated (for example, -41 °C) via the second vaporizer to be made into an ethane-rich sNG, which is supplied out via the second natural gas supplying portion 4.

The other gas component D derived from the branching is guided into the fourth heat exchanger 24 in the second reflux flow passageway to be subjected to a low-temperature condensation process (for example, about -63°C) by the coldness of the LNG guided out from the third heat exchanger 23, and thereafter guided as a reflux liquid into the upper portion 74 of the second distillation tower. T

he second liquid component having a high temperature and a low pressure (for example, about 84°C and about 2.3 MPa) that has been guided out from the tower bottom portion 72 is guided into the fifth heat exchanger 25 in the liquefied petroleum gas supplying flow passageway to be subjected to a low-temperature process (for example, about 20°C) by the coldness of the LNG guided out from the fourth heat exchanger 24, and thereafter supplied out as the LPG via the liquefied petroleum gas supplying portion 5.

Also, in the present construction example, various kinds of liquid fuel gases such as "methane- and ethane-rich gas" (NG + sNG) and an LPG containing an NGL can be prepared and supplied out effectively with little need of the external energy by blending the NG, the NGL, the sNG, and the LPG supplied out from each flow passageway in an arbitrary manner in accordance with a demanded specification.

Specifically, as exemplified in a broken line of Fig. 6, a branching passageway may be provided in the second natural gas supplying flow passageway in which the second natural gas is transferred from the second vaporizer 31 to the second natural gas supplying portion 4, and may be connected to the natural gas supplying flow passageway in which the natural gas is transferred from the compressor 42 to the natural gas supplying portion 2, whereby a mixture of the methane-rich NG and the ethane-rich sNG, that is, "gas having a carbon number of 1 and 2 as major components" (NG + sNG), can be supplied out from the natural gas supplying portion 2 or the second natural gas supplying portion 4.

In Fig. 6, a case is exemplified in which the second natural gas is supplied out from the second natural gas supplying flow passageway to the natural gas supplying flow passageway as shown by an arrow symbol; however, the present invention is not limited thereto, and it goes without saying that the present invention comprises a case of an opposite flow and a case in which the two flow passageways each supply out a part to prepare a mixture gas. Also, in addition to mixing the prepared liquid fuel gases with each other, various kinds of liquid fuel gases can be prepared and supplied out by mixing the LNG serving as the source material or mixing, for example, a butane gas or the like from outside of the system to these.

With use of the fourth construction example of the present apparatus, an LNG having a composition exemplified in the above Table 1 was supplied as a source material, so as to verify the temperature (°C), the pressure (MPa), the flow rate (kg/h), and the composition (G/L: gas/liquid) in each portion,

(i) Verification result

When an LNG (-150°C, 6.00 MPa) was supplied at 427,000 kg/h, the temperature, the pressure, the flow rate, and the composition in each of the portions a to r2 in Fig. 7 were obtained as exemplified in the following Table 5.

Here, a case is shown in which the whole amount of the liquid component guided out from the tower bottom portion 12 of the distillation tower 10 is guided into the second distillation tower 70 (q1 = g2 and r1 = 0 in Fig. 7); however, a part of the liquid component may be supplied to the third heat exchanger 23 (r1 = q1 - g2 > 0 in Fig. 7) to be supplied out as an NGL. Table 5

(ii) Next, the income and the outcome of energy in the present apparatus were verified in comparison with the first construction example described above. As will be understood from the following Table 6, a result has been obtained in which the supply amount of energy from outside in the present apparatus was smaller by a sum amount of 858 kW (as converted in terms of electric power) when compared with that of the first construction example. Table 6

A method for supplying a liquid fuel gas according to the fourth construction example is such that, in the steps (1 ) to (8) of supplying the liquid fuel gas according to the first construction example described above, at least a part of the liquid component guided out from the tower bottom portion is guided into a second distillation tower; an ethane-rich second natural gas is prepared from a second gas component guided out from a second tower top portion of the second distillation tower; and a liquefied petroleum gas is prepared from a second liquid component guided out from a second tower bottom portion of the second distillation tower. At this time, in place of the step (4) in this process,

(4a) the LNG guided out from the third heat exchanger after passing through the steps (1 ) to (3) is further guided into the fourth heat exchanger and is heated by releasing the coldness thereof by heat exchange with the second gas component;

(4b) the LNG guided out from the fourth heat exchanger is guided into the fifth heat exchanger and is heated by releasing the coldness thereof by heat exchange with the second liquid component;

(4c) the LNG guided out from the fifth heat exchanger is guided into the vaporizer and is vaporized by being heated; and

thereafter, the resultant is guided as the source material into the distillation tower after passing through the steps (5) to (8).

Also, one gas component C derived from branching of the second gas component is subjected to adiabatic compression by a second compressor and is supplied out as the heated and pressurized second natural gas; the other gas component D derived from branching of the second gas component is condensed through being subjected to lowering of temperature by the coldness of the LNG in the step (4a) and is refluxed as a second reflux liquid into an upper portion of the second distillation tower; and the second liquid component is supplied out as the liquefied petroleum gas subjected to lowering of temperature by the coldness of the LNG in the step (4b).

Specifically, a supplying method comprising the following steps can be mentioned as an example. Here, in the following description, description of the constituent elements overlapping with those of the steps (1 ) to (8c) described above may be omitted, and each of the portions in the present apparatus is denoted with the reference symbol exemplified in Fig. 1 or Fig. 6. Also the conditions exemplified in the above Table 2 may be applied as the conditions of each gas or liquid; however, it goes without saying that the present invention is not limited thereto. The pressurized LNG stored in a supercooled state and serving as the source material is guided out from the third heat exchanger 23 after passing through the above steps (1 ) to (3), and

(4a) the LNG supplied from the third heat exchanger 23 is guided into the fourth heat exchanger 24 and is heated by releasing the coldness thereof through heat exchange with the gas component D guided out from the tower top portion 71. For example, the LNG having a temperature of about -71 °C and a pressure of about 6 MPa is heated to about -51 °C by releasing the coldness thereof in the heat exchanger 24. Simultaneously, the gas component D having a temperature of about -63°C and a pressure of about 2.3 MPa is cooled to prepare a condensate of about -63°C. The prepared condensate is guided as a second reflux liquid into an upper portion 74 of the second distillation tower.

(4b) The LNG guided out from the fourth heat exchanger 24 is guided into the fifth heat exchanger 25 and is heated by releasing the coldness thereof through heat exchange with the second liquid component guided out from the tower bottom portion 72 of the second distillation tower 70. For example, the LNG having a temperature of about -71 °C and a pressure of about 6 MPa is heated to about -47°C by releasing the coldness thereof in the fifth heat exchanger 25. Simultaneously, the second liquid component having a temperature of about 84°C and a pressure of about 2.3 MPa is cooled, whereby a liquefied petroleum gas of about 20°C is prepared and supplied out.

(4c) The LNG guided out from the fifth heat exchanger 25 is guided into the vaporizer 30 and is vaporized by being heated. For example, the LNG having a temperature of about -47°C and a pressure of about 6 MPa is vaporized by releasing the coldness thereof in the vaporizer 30 and being heated to about 15°C.

In this process, the gaseous LNG guided out from the vaporizer 30 is guided as the source material into the distillation tower 10 by passing through the above steps (5) to (8). From the LNG guided into the distillation tower 10, a methane-rich NG is supplied out from the tower top gas coming from the tower top portion 11 of the distillation tower 10, and an NGL is supplied out from the tower bottom liquid coming from the tower bottom portion 12 of the distillation tower 10, by passing through the above steps (8a) to (8c). Also, a part or a whole amount of the tower bottom liquid coming from the tower bottom portion 12 is guided into the second distillation tower 70, whereafter an ethane-rich sNG is prepared from a second tower top gas (second gas component) guided out from a second tower top portion 71 of the second distillation tower 70, and an LPG is prepared from a second tower bottom liquid (second liquid component) guided out from a second tower bottom portion 72 of the second distillation tower 70, by passing through the following steps (9a) to (9c).

(9a) The LNG guided into the second distillation tower 70 is separated into an ethane-rich second tower top gas and a second tower bottom liquid containing a component having a carbon number larger than that of ethane (which may be hereafter referred to as "component such as propane") as a major component. Specifically, for example, in the second distillation tower 70 having a pressure of about 2.3 MPa, a tower top temperature of about -63°C, and a tower bottom temperature of about 84°C, the liquid LNG guided into the middle tower portion 73 forms a descending flow and is brought into gas-liquid contact with an ascending flow, which contains ethane and the component such as propane heated and vaporized in the second tower bottom portion 75, to increase the purity of the component such as propane (second tower bottom liquid). The ascending flow formed within the tower is brought into gas-liquid contact with the descending flow mainly made of the ethane-containing LNG and the ethane-rich reflux liquid, to increase the purity of ethane (second tower top gas).

(9b) The ethane-rich sNG is prepared from the second tower top gas guided out from the second tower top portion 71. From the second tower top portion 71 , the second tower top gas having a temperature of about -63°C and a pressure of about 2.3 MPa and containing ethane at 99.9% or more, for example, is guided out, and about 20% thereof is compressed, for example, to about -61 °C and about 6 MPa as the gas component C by the second compressor 43 and is further heated by the second vaporizer 31 to be made into the ethane-rich sNG of, for example, about 35°C and about 6 MPa, which is supplied out via the second natural gas supplying portion 4. In this process, about 80% of the second tower top gas is guided as the gas component D into the fourth heat exchanger 24, where a second condensate of about -63°C is prepared, and the prepared second condensate is guided as a second reflux liquid into the upper portion 74 of the distillation tower.

(9c) The LPG is prepared from the second tower bottom liquid guided out from the second tower bottom portion 72. From the second tower bottom portion 72, the second tower bottom liquid having a temperature of about 84°C and a pressure of about 2.3 MPa and containing a component such as ethane at 99.9% or more, for example, is guided out and cooled to about 20°C via the fifth heat exchanger 25 to be made into the LPG, which is supplied out via the liquefied petroleum gas liquid supplying portion 5. A desired product LPG can be supplied out by effectively using the coldness of the LNG Also, in the present apparatus, although not illustrated in the drawings, not only the tower bottom liquid coming from the distillation tower 10 but also the second tower bottom liquid coming from the second distillation tower 70 may be branched to supply the product (LPG) out on one hand, and the second tower bottom liquid may be heated via a reboiler (not illustrated in the drawings) on the other hand to be guided into the lower portion 75 of the second distillation tower, whereby a high distillation function can be obtained.

A summary of the fifth construction example of the present apparatus will be shown in Fig. 8. The present apparatus has a construction in which, in the source material supplying flow passageway of the fourth construction example, the expander 41 is made of expansion turbines 41a, 41 b that are arranged in parallel; the LPG guided out from the vaporizer 30 is branched to be guided into each of the expansion turbines 41a, 41 b; the expansion turbine 41a is linked to the compressor 42; and the expansion turbine 41 b is linked to a power generator 60. Hereafter, constituent elements common to those of the first, second, and fourth construction examples will be denoted with common appellations and reference symbols, and the description thereof may be omitted.

The functions under the optimum conditions of the present apparatus comprising the distillation tower 10 and the second distillation tower 70 can be ensured by adjusting the operation amount of the expansion turbines 41 a, 41 b and the operation amount of the compressor 42 in accordance with the fluctuation in the supply amount, the composition, the supply temperature, the pressure, and the like of the LNG or the fluctuation in the supply amount, the supply temperature, the pressure, and the like of the NG and the NGL that are supplied out. Also, the linkage of the expansion turbine 41 b to the power generator 60, the number of the expansion turbines, and the linkage of the plurality of expansion turbines to the compressors and the power generators are the same as those in the second construction example.

With use of the fifth construction example of the present apparatus, an LNG having a composition exemplified in the above Table 1 was supplied as a source material, so as to verify the temperature (°C), the pressure (MPa), the flow rate (kg/h), and the composition (G/L: gas/liquid) in each portion. When an LNG (-150°C, 6.00 MPa) was supplied at 427,000 kg/h, the temperature, the pressure, the flow rate, and the composition in each of the portions s to v in Fig. 9 in addition to each of the portions a to r2 in Fig. 7 were obtained as exemplified in the following Table 7. Also, a power generation amount of about 500 kW/h could be obtained from the power generator 60 linked to the expansion turbine 42.

Table 7

As shown above, each construction example has been described with reference to each explanatory view; however, the present apparatus is not limited to these and is constructed in a wide concept comprising a combination of the constituent elements thereof or a combination with related known constituent elements.