EP1853846B1 - Plant for regasification of liquefied natural gas - Google Patents

Abstract

The invention relates to a plant for regasification of liquefied natural gas (GNL), comprising a liquefied gas storage reservoir (10) and a regasification device (12) for the GNL through which the natural gas and a heat transfer medium flow. According to the invention, the plant comprises a loop circuit (16) in which the heat transfer medium circulates in the form of a low-viscosity organic liquid with a low crystallisation point and the regasification device (12) comprises at least two exchangers (60, 62).

Description

The present invention relates to a regasification plant for liquefied natural gas and a method used in such an installation.

Generally, when natural gas is to be transported between a production site and an operating site that are close to each other, this transportation is done through onshore or submerged pipelines. In this case, the natural gas is transported in its gaseous form and can be used as such at its place of destination.

However, when the two sites are too far apart or the configuration of the land does not allow the laying of pipelines, the gas is transported in liquefied form by land vehicles or boats (usually LNG tankers) between the site production and the operating site. For this, the natural gas is liquefied near the production site during compression and cooling operations to a temperature of -160 ° C. The liquefied natural gas (LNG) is then stored in appropriate tanks and then transferred in liquid form into tanks for land or sea transport to the operating site. Once arrived at this site, this liquefied gas is discharged into LNG storage tanks from which this gas can be regasified on demand and used, either directly on the site of operation or transported in gaseous form via pipelines. to other places of exploitation.

Usually, in the case of maritime transport of LNG, the liquefied gas is stored and transported to the vicinity of the coastal terminal in isothermal tanks of the LNG carrier. This liquefied gas is either regasified from the tanks of the LNG tanker and then transported in gaseous form via pipelines to the operating sites, or sent in liquid form to tanks of the coastal terminal for storage and regasification on demand.

Currently, in order to perform the regasification operation, the gas in liquid form is pumped from the tank or tank and then passes through a set of heat exchangers that act as a vaporizer or vaporizer. regasification. In order to ensure a heat exchange, this set of heat exchangers is traversed by sea water, possibly heated, so that the calories present in this water are transmitted to the gas. Thanks to the transmission of these calories, the gas is warmed along its path in the heat exchanger assembly and gradually changes state to emerge from this set of exchangers in gaseous form.

He is also known by the patent application US 4,331,129 an installation comprising a first loop circuit in which circulates water heated by a solar heater, and a second circuit also in a loop in which circulates water heated by a conventional heating means. Each of these circuits has a heat exchanger in which the natural gas circulates to be vaporized.

Such provisions have significant disadvantages both in terms of nature preservation and the integrity of the exchangers.

Indeed, the seawater that has passed through the heat exchangers is discharged into the sea with a very low temperature, resulting in a degradation of the flora and fauna underwater. In addition, seawater is a corrosive agent for all the metal parts of the exchangers and therefore leads to greater maintenance of these exchangers. In addition, given the fact that LNG circulates in the exchangers with a very low temperature, the seawater must travel these exchangers with a large flow rate so as to avoid forming crystals, which necessitates pumping installations. large size with a high cost.

The present invention proposes to overcome the disadvantages mentioned above through a regasification installation that uses a heat-transfer agent that is environmentally friendly and that can be used far from any coastal terminal.

Thus, the present invention relates to a regasification plant of liquefied natural gas as defined by claim 1.

The installation may comprise a heating unit of the heat transfer agent.

Advantageously, the reheating unit can be traversed by air.

The heat transfer agent may have a crystallization temperature of between -90 ° C. and -150 ° C.

Preferably, the heat transfer agent may be an alcohol such as methanol, ethanol or propanol.

One of the exchangers can be co-current between the LNG and the heat transfer agent and the other exchangers can be against the current.

The countercurrent exchanger may be in two parts between which is interposed a phase separator.

At least the countercurrent exchanger may be of the type with brazed plates and fins.

The circulation circuit of the heat transfer agent may comprise an additional heat exchanger.

The installation may comprise means for liquefying a hydrocarbon by heat exchange with the heat transfer medium.

The hydrocarbon can be in gaseous form after its application to driving a turbine.

Advantageously, the hydrocarbon may be propane.

The installation may also include means for trapping CO ₂ by the heat transfer medium.

Preferably, the heat transfer agent may be used as a CO ₂ solvent.

• la figure 1 est une vue schématique de l'installation de regazéification du GNL selon l'invention ;
• la figure 2 est une vue en coupe partielle du réchauffeur utilisé dans l'installation selon l'invention ;
• la figure 3 est une vue en coupe schématique du regazéificateur utilisé dans cette installation ;
• la figure 4 est une première variante de l'installation de regazéification selon l'invention ;
• la figure 5 est une autre variante de l'installation de regazéification selon l'invention ;
• la figure 6 montre un exemple sur une utilisation particulière de l'installation selon l'invention et
• la figure 7 montre un autre exemple d'une utilisation de l'installation selon l'invention.

The other characteristics and advantages of the invention will appear better on reading the description which follows, given solely by way of illustration and in no way limiting, with reference to the appended drawings in which:

• the figure 1 is a schematic view of the regasification plant of LNG according to the invention;
• the figure 2 is a partial sectional view of the heater used in the installation according to the invention;
• the figure 3 is a schematic sectional view of the regasifier used in this installation;
• the figure 4 is a first variant of the regasification plant according to the invention;
• the figure 5 is another variant of the regasification plant according to the invention;
• the figure 6 shows an example of a particular use of the installation according to the invention and
• the figure 7 shows another example of a use of the installation according to the invention.

The figure 1 schematically shows a regasification plant of a liquefied natural gas (LNG) which comprises a storage tank 10 LNG at atmospheric pressure and at a temperature of -160 ° C, a regasification device with a unit of heat exchangers or regasifier 12, traversed by a heat transfer agent and by the LNG from the tank, and a heating unit 14 of the heat transfer medium.

The coolant is an organic fluid whose crystallization point is close to that of LNG and has a viscosity sufficiently low to be able to be easily circulated in pipes even at very low temperatures. In addition, this agent remains in the liquid state under conditions of use at atmospheric pressure and at room temperature. Preferably, this heat transfer agent may be an alcohol or a hydrocarbon or a compound thereof. In the following description, the organic fluid considered by way of example is methanol whose crystallization point is around -98 ° C but it can also be used other alcohols such as ethanol (point of crystallization: - 114 ° C) or propanol (crystallization point: -126 ° C).

This installation comprises a circulation loop 16 of the heat transfer medium which, in the example shown, is a closed loop with a hot part and a cold part. This loop comprises a circulation pump 18, a circulation line 20 of this agent between the pump and the regasifier 12, a circulation line 22 between the regasifier and the reheating unit 14, a return line 24 between this unit of reheating and the circulation pump, a tank 26 of coolant being interposed on this return line. The installation also comprises an LNG suction pump 28 generally immersed in the tank 10, a circulation pipe 30 of the LNG between this pump and a circulation pump 32, a pipe 34 bringing the LNG of this circulation pump to the regasifier. 12, and an outlet conduit 36 for conveying gas in gaseous form exiting the regasifier to any suitable means. The heating unit is also traversed by a heating fluid 38 which is, in the example shown, outside air at room temperature and comprises a discharge 40 of the condensates from this air. Of course, this reheating air can also come from any devices present at the place of operation, such as fumes discharged by a gas turbine.

To perform the regasification, the LNG is pumped from the tank 10 by the pumps 28 and 32, circulates in the lines 30 and 34 to be sent into the regasifier 12. This gas circulates in the regasifier which is also traversed by the methanol as heat transfer agent. To do this, the methanol present in the reservoir 26 is pumped by the pump 18 and is sent via line 20 into the regasifier 12. In this regasifier, the calories present in the methanol are transmitted to the LNG and heat it up so that that the liquid phase of the LNG is changed into a gas phase by vaporization and then, if necessary, superheated to reach a temperature close to that of the ambient temperature.

The temperature of the methanol at the inlet of the regasifier 12 is about 20 ° C. and about -160 ° C. for the LNG flowing in the pipe 34. At the exit of this regasifier, the natural gas is at a temperature close to of 5 ° C while the methanol reaches a temperature of about -70 ° C at the exit of this regasifier in line 22.

During the exchange in the regasifier, the methanol is cooled to a temperature above its crystallization point, in this case -70 ° C. for the example under consideration. The cold methanol is sent via the pipe 22 to the reheating unit 14 so that the air circulating in this unit, and whose temperature is higher than that of the cold methanol, exchanges its calories with this methanol to obtain a methanol heated in the pipe 24 and consequently in the reservoir 26.

The temperature of the methanol at the inlet of the heating unit is of the order of -70 ° C. whereas the air is introduced into this heater at a temperature of about 30 ° C. After heat exchange in this unit, the methanol is discharged at the outlet of the unit at a temperature of 0 ° C while the air leaves at a temperature of 5 ° C.

Thus, the hot part of the loop 16 is formed by the pipe 24, the reservoir 26, the pump 18 and the pipe 20, while the cold part of this loop comprises the pipe 22.

To achieve reheating of methanol at the exit of the regasifier, and as illustrated on the figure 2 , the heating unit 14 comprises a heat exchanger comprising a vertical calender 42 with an air inlet 44 and an air outlet 46 disposed at each end of this calender. Inside this shell is housed a set of vertical tubes 48 connected at one of their ends by an intake manifold 50 with an inlet 52 for cold methanol from the regasifier and at the other their ends by an exhaust manifold 54 with an outlet 56 connected to the pipe 24 leading to the methanol tank 26. In this heat exchanger, the methanol arrives through the inlet 52, enters the intake manifold 50, circulates in all vertical tubes 48, to open into the exhaust manifold 54 and be discharged through the outlet 56. Simultaneously, air, either at room temperature, or heated by any known means, is introduced into the calender 42 through the inlet 44, then scans all the tubes as well as the collectors. During this sweep, the calories contained in this air are transmitted to methanol so as to heat it up and obtain a hot methanol at the outlet 56. During this exchange, the water droplets contained in the air are condensed and then fall by gravity to the bottom of the calender 42 to be then discharged in the form of condensates through the pipe 40. The tubes 48 may be coated with a film of hydrophobic material ("water shedding film") of polymethylsiloxane type to facilitate the separation of water droplets .

Now referring to the figure 3 the regasifier comprises a vertical envelope 58 which contains at least two exchangers in which the gas and the methanol circulate, an upper exchanger 60 placed in the upper part of the envelope and a lower exchanger 62 placed in the lower part of this envelope. Preferably, these exchangers are in the form of heat exchangers. plates and fin brazed, preferably aluminum. The upper exchanger is said against the current because the natural gas and methanol flow in opposite directions while the lower exchanger is said to co-current, the fluids flowing in the same direction. Thus for the lower exchanger, it comprises, on one of its sides and in the lower part of this exchanger, an inlet 64 of the methanol connected to the pipe 20 and an outlet 66 on one side of the exchanger. This lower heat exchanger also comprises an inlet 68, connected to the LNG pipe 34, which is located at the bottom and on the side opposite to that of the methanol inlet, and an outlet 70 placed in the upper part of the exchanger. Thus, in the lower exchanger 62, the flows of methanol and LNG flow in the same direction, that is to say from the bottom to the top of this exchanger. Thanks to this, the skin temperature inside this exchanger remains above -100 ° C and the exchange surfaces can be minimized. The outlet 66 of methanol is connected via a line 72 to an inlet 74 of the upper exchanger which is located at the top and on one side of this exchanger. Similarly, the outlet 70 of natural gas is connected by a pipe 76 to a gas inlet 78 located on the lower part of this exchanger. The vapor form gas is discharged through an outlet 80 which is located on the upper part of this exchanger while the outlet 82 of the methanol is located in the lower part of this exchanger to be connected to the pipe 22 leading to the reheating unit . This exchanger is therefore called a countercurrent heat exchanger because the flow of gas and methanol flow in opposite directions, for the gas from the bottom to the top of the exchanger and for methanol from the top to the bottom of this exchanger .

In the variant represented by way of example on the figure 4 the regasifier 12 is separated into two distinct parts. Thus, the co-current exchanger 62 is in the form of a tube and shell heat exchanger and comprises the inlets 64, 68 and the outlets 66, 70 of methanol and LNG. The outlets 66 and 70 are connected by the lines 72, 76 to the countercurrent exchanger 60 which is a brazed plate and fin exchanger, advantageously aluminum, and which has the inputs 74, 78 and outputs 82, and 80 of methanol and natural gas.

Preferably, the tube and shell heat exchanger comprises a mechanical expansion joint 83 which absorbs all the dimensional variations of this exchanger during the passage of LNG and methanol.

In this variant, the operation of the installation is identical to that described in connection with the Figures 1 to 3 .

We are now going back to figure 5 which shows a variant of the regasification facility illustrated in figure 4 and which, for that, includes the same references for the common parts.

This variant is distinguished by the fact that regasification is carried out in several stages. In addition, the countercurrent exchanger 60 is in two parts 60A, 60B and a phase separator 84 is provided between these two exchanger parts.

The natural gas exiting the co-current heat exchanger 62 with tubes and calender through the outlet 70 is preheated to its boiling point corresponding to the pressure in the separator 84. This heated natural gas passes through the lower part 60A of the countercurrent exchanger 60 for performing a vapor phase transformation. This converted natural gas is sent via line 86 into the separator 84 where separation of the natural gas in gaseous form in the upper part 88 of this separator takes place with a composition, a molecular weight and a lower heating value and in liquid form in part. bass 90 of this separator. The natural gas in vapor form present in the separator is then directed, via a pipe 92, from this separator to the inlet of the part 60B of the exchanger 60 where it undergoes, by exchange with the methanol circulating therein, an elevation The liquid phase, which has a molecular weight and a heating value greater than that of the steam, is extracted by a pump 94 connected to this separator by a pipe 96. The liquid phase leaving the pump 94 is directed by a pipe 98 to all storage means to be subsequently treated. Advantageously, it is possible to control the composition and the power heat of natural gas in gaseous form in the pipe 92 before it enters the exchanger 60 by injecting a predetermined quantity of liquid from the separator through a pipe 98A originating after the pump 94 on the pipe 98 and ending on the driving 92.

In this configuration, the temperature at the exit of the natural gas regasifier is of the order of 0 ° C. and that of the methanol is approximately -70 ° C.

Additionally, it is conceivable to heat the methanol at the outlet of the pump 18 by placing on the pipe 20 a heat exchanger 100 between the methanol and a hot fluid which is usually used on or near this regasification plant, such as hot water from trickling towers.

As previously described, the methanol at the exit of the regasifier is at a low temperature of the order of -70 ° C. and must be reheated in order to be able to ensure the transformation of the LNG into the regasifier in the gas phase. For this, it can be taken advantage of the presence on the site of a power plant with a combined cycle gas turbine as shown on the figure 6 . In this case, the central 102 is supplied with air through a path 104 and natural gas via a path 106, this path being able to be a bypass of the pipe 36 described previously. The combustion of the air-natural gas mixture within the turbine generates, after recovery of the generated calories (abbreviated to HRSG), at the outlet 108 of the fumes with temperatures of the order of 130 ° C. As shown on the figure 6 these fumes are introduced through an inlet 110 in a heat exchanger assembly 112, separated into at least three parts 112A, 112B, 112C, to emerge by an evacuation 114 and then be directed by a conduit 116 to any suitable means, such as a fireplace. The heat exchanger assembly is also traversed by a phase-change fluid, such as propane, circulating in a closed loop 118. This loop comprises a liquid propane tank 120, a circulation pump 122 connected to the tank via a pipe 124 and a propane phase separator 126 connected to the pump via a line 128E which brings the liquid propane into the portion 112A of the assembly. heat exchanger and a 128S pipe which directs the propane, preheated to its boiling point, in this separator. From this separator, leave two pipes, a pipe 130, called liquid pipe, wherein the liquid contained in the separator is fed to the portion 112B of the heat exchanger assembly to cross and return in gaseous form in the separator 126, and a pipe 132, called gas line, which brings the gas phase of the propane contained in the separator to the portion 112C of the heat exchanger assembly so as to superheat the propane gas. A line 134 brings the propane in gaseous form pressurized to an expansion turbine 136 rotatably connected to all energy producing means, such as an alternator 138. At the outlet of the expansion turbine, the propane gas is supplied by a pipe 140 to a heat exchanger 142, said condenser, for cooling the propane gas and thus change phase to obtain a liquid phase before it returns through a pipe 144 to the tank 120. To cool the propane, the condenser 142 is traversed by the methanol flowing in the pipe 22, as described above, and, at the outlet of this condenser, the methanol is at a temperature higher than that of its introduction because it has captured the calories contained in propane gas phase.

In operation, the propane in liquid form is pumped from the tank 120 to cross the portion 112A of the exchanger assembly 112. After this crossing, the preheated propane in liquid form is sent into the separator 126. The liquid phase extracted from this separator passes through the portion 112B of the assembly 112 to return in gaseous form in the separator to achieve the separation between the liquid phase and the gas phase of the propane. The gaseous phase contained in this separator is also extracted to cross the portion 112C of the exchanger assembly 112 to be completely converted into the gas phase and superheated if necessary. The propane in gaseous form passes through the turbine 136 which it drives in rotation, which turbine rotates the alternator 138. At the outlet of the turbine, the gas-form propane passes through the condenser 142 where it changes phase and goes into liquid phase through the exchange of its calories with cold methanol that also circulates in this condenser. At the outlet of this condenser, the liquid propane is stored in the tank 120.

The treatment group as schematically illustrated on the figure 7 shows a potential use of the LNG regasification facility with a methanol loop to capture and liquefy the CO ₂ contained in releases, such as fumes from gas turbine fumes.

In this configuration, there is provided an LNG regasification unit 146, a CO ₂ capture / separation unit 148, a methanol heating unit 149 and a CO ₂ liquefying unit 150.

The regasification unit 146, as already described in connection with the preceding figures, comprises a regasifier 12 traversed by hot methanol circulating in a loop 152 and by LNG coming from the pipe 34.

CO ₂ capture / separation unit. 148 comprises an absorption column 154 containing transfer elements 156 with an entry 158 of methanol from the regasifier, an entry of a gaseous fluid 160 containing CO ₂ , an evacuation 162 of gaseous fluid stripped of CO ₂ and an exit 164 a mixture of methanol and CO ₂ . This CO ₂ capture / separation unit also comprises a flash drum 166 with an inlet of the mixture of methanol and CO ₂ , an outlet 168 of CO ₂ in gaseous form and a 170 output of methanol removed from a very large portion of CO ₂ .

The heating unit 149 comprises elements identical to those already described in relation to the figures 1 and 2 , that is to say a heater traversed by the methanol coming from, in the illustrated example of the figure 7 from the outlet 170 of the flask 166 by a reheating fluid 38 which may be outside air at room temperature. This exchanger also comprises an evacuation 40 of the condensates coming from this outside air. This unit finally comprises a heat exchanger 174 for heating the methanol after passing through the heater by an outlet 172 and a flash tank 175 for separating methanol in liquid form, which is then directed by a line 176 to the methanol loop, and CO ₂ in gaseous form which joins via a line 178, a line 180 also connecting the CO _{2 line} 168 of the flash tank 166.

The liquefaction unit 150 comprises a condenser 181 which has the particularity of using an intermediate fluid, such as ethane, to participate in the liquefaction of CO ₂ and the heating of the natural gas in vapor form.

This condenser comprises an enclosure 182 which contains at least two parts of condensers 184 and 186, each against the current and preferably in the form of brazed aluminum plates and fins, in which the CO ₂ in vapor form circulates and the ethane for one and LNG and ethane for the other. The lower condenser 184 is placed in the lower part of the enclosure and comprises, on one of its sides and in the upper part of this condenser, an inlet 188 of the CO ₂ connected to the pipe 180 and a liquid CO ₂ outlet 190 on the lower part of the condenser. The upper condenser 186 comprises an LNG inlet 192, connected to the LNG pipe 34, which is located in the lower part of this condenser and an outlet 194 placed in the upper part of the exchanger. A closed loop of ethane 196 allows the ethane to circulate between the two exchangers. More specifically, the ethane vapor is introduced into the upper ethane condenser 186 through an inlet 198 located on the upper part of the condenser, through this condenser to result in a liquid ethane outlet 200 located in the lower part of this condenser, is fed via a pipe 202 to a liquid ethane inlet 204 located in the lower part of the lower CO ₂ condenser, passes through the lower condenser to reach an outlet 206 located in the upper part of this condenser and then leads to the inlet 198 by a conduct 208.

During operation of the treatment group described above, the LNG substantially follows the same regime as that described in relation to the figure 1 with the only difference that a bypass of the LNG line 34 leads to the inlet 192 of the CO ₂ liquefaction unit 150 to pass through the upper condenser 186 and exit through the outlet 194 to join the line 36.

At the outlet of the regasifier, the methanol is sent via the inlet 158 to the column 156 which also receives a fluid containing a significant part of CO ₂ , of the order of 12%, through the inlet 160. After treatment in this column, the CO ₂ is captured by methanol and a mixture of methanol and dissolved CO ₂ is discharged through the outlet 164. The CO ₂ -freeed fluid is discharged through the outlet 162 to any appropriate means. The mixture of CO ₂ and methanol is separated in the expansion flask 166 from which the CO ₂ in the vapor phase is discharged through the outlet 168 to the pipe 180 and from which the methanol in the liquid phase from the outlet 170 is heated in the heating unit by successive crossing of the heater and the exchanger 174. At the outlet of the exchanger 174, the residual CO ₂ contained in the methanol is separated once more from this methanol in the expansion tank 175. During this separation, the CO ₂ is evacuated through the outlet 178 to join the pipe 180 connected to the outlet 168 and the CO _2- freed methanol joined, through the outlet 176, the pump 18 of the methanol loop. The CO ₂ in the vapor phase is liquefied in the lower condenser 184 in which it exchanges its calories with the ethane which circulates in a loop between the two condensers. After this exchange, the CO ₂ is in liquid form at the outlet 190 and can be sent to a storage tank where it can be removed for possible sequestration in underground tanks.

Claims (11)

1. A liquefied natural gas (LNG) regasification plant comprising a tank (10) for storing the gas in liquefied form and an LNG regasification device (12) through which a heat carrier and the natural gas flow, a loop circuit (16) in which the heat carrier that circulates is methanol, ethanol or propanol, the regasification device (12) comprising at least two exchangers (60, 62), characterized in that one (62) of the exchangers is co-current between the LNG and the heat carrier, and in that the other (60) exchanger is counter-current, exchanger (60) being in two parts (60A, 60B) between which a phase separator (84) is interposed.
2. A regasification plant as claimed in claim 1, characterized in that it comprises a heat carrier heating unit (14).
3. A regasification plant as claimed in claim 2, characterized in that air flows through heating unit (14).
4. A regasification plant as claimed in any one of the previous claims, characterized in that the heat carrier has a crystallization temperature ranging between -90°C and -150°C.
5. A regasifcation plant as claimed in any one of the previous claims, characterized in that at least counter-current exchanger (60) is of brazed plate-fin exchanger type.
6. A regasification plant as claimed in any one of the previous claims, characterized in that heat carrier circulation circuit (16) comprises an additional heating exchanger (100).
7. A regasification plant as claimed in any one of the previous claims, characterized in that it comprises means for liquefying a hydrocarbon by calorific exchange with the heat carrier.
8. A regasification plant as claimed in claim 7, characterized in that the hydrocarbon is in gaseous form after being used for driving a turbine (136).
9. A regasification plant as claimed in claim 7 or 8, characterized in that the hydrocarbon is propane.
10. A regasification plant as claimed in any one of claims I to 6, characterized in that it comprises means for CO₂ trapping by the heat carrier.
11. A regasification plant as claimed in claim 10, characterized in that the heat carrier is used as solvent of the CO₂.

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