PT1853846E - 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

DESCRIPTION

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

Normally, when natural gas has to be transported between a production facility and an operating facility close to one another, the transport takes place via overland or underwater piping. In this case, the natural gas is transported in gaseous form and is usable as such in its place of destination.

However, when these two facilities are too far apart, or when the ground configuration does not allow the piping to be placed, the gas is transported in liquefied form by land vehicles or boats (usually metaneiros) between the production facility and the operating facility. For this, the natural gas is liquefied in the vicinity of the production facility during the compression and refrigeration operations up to a temperature of -160 ° C. The liquefied natural gas (LNG) is then stored in suitable tanks and then transported in liquid form to tanks for land or sea transportation to the operating facility. Once there, this liquefied gas is discharged into LNG storage tanks, from which this gas can be regasified on request and used, either directly at the place of operation or transported in gaseous form through the piping to other locations of exploitation. 1

Usually, in the case of LNG maritime transport, the liquefied gas is conserved and then transported to the proximity of the coastal terminal in isothermal tanks of the metanean. This liquefied gas is either regasified from the tanks of the vessel and then transported in the gaseous form through the piping to the exploration sites or sent in liquid form to the reservoirs of the coastal terminal to be stored and regasified upon request.

At present, to carry out the regasification operation, the gas in the liquid form is pumped from the tank or the reservoir and then passes through a set of heat exchangers acting as vaporizer or regassifier. In order to ensure a heat exchange, this set of heat exchangers is traversed by seawater, possibly reheated, so that the calories present in that water are transmitted to the gas. Thanks to the transmission of these calories, the gas is reheated along its path in the set of exchangers and progressively changes state to leave that set of exchangers in the gaseous form. It is also known from patent application US 4 331 129 an installation comprising a first ring circuit in which water reheated by a solar heater circulates, and a second loop, also ringed, in which the water reheated by a medium conventional heating. Each of these circuits comprises a heat exchanger in which circulates the natural gas to be vaporized.

These provisions present not insignificant drawbacks, both in terms of the preservation of nature and the integrity of the heat exchanger.

Indeed, the sea water that has passed through the heat exchangers is rejected at sea having a very low temperature, 2 which causes a degradation of the underwater flora and fauna. On the other hand, sea water is a corrosive agent for all metal parts of the heat exchanger, thus requiring a more important maintenance of these heat exchangers. In addition, since LNG circulates in the heat exchanger at a very low temperature, seawater must travel through these exchangers at a high flow rate to avoid the formation of crystals, which requires large and costly pumping installations high. The present invention proposes to overcome the aforementioned drawbacks by means of a regasification plant which utilizes an environmentally friendly heat transfer agent and which can be used away from all coastal terminals.

Thus, the present invention relates to a regasification plant for liquefied natural gas as defined by claim 1. The plant may comprise a reheating unit of the heat transfer agent.

Advantageously, the reheating unit can be traversed by air. The heat carrier may have a crystallization temperature of from -90 ° C to -150 ° C.

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

One of the exchanger may be of the type of parallel chains between the LNG and the heat transfer agent, the other of the exchangers may be countercurrent. The counter-current exchanger can be divided into two parts, between which a phase separator is interleaved. 3

At least the counter current exchanger may be of the type of plates and brazed blades. The circulation circuit of the heat transfer agent may comprise a further heat exchanger. The plant may comprise means for liquefying a hydrocarbon by heat exchange with the heat carrier. The hydrocarbon may be in gaseous form after its application in the drive of a turbine.

Advantageously, the hydrocarbon may be propane. The plant may also comprise CO2 capture means by the heat carrier.

Preferably, the heat carrier may be used as the CO2 solvent.

The other features and advantages of the invention will become more apparent upon reading the following description, given solely by way of illustration and without limitation, with reference to the accompanying drawings in which: Figure 1 is a schematic view of the LNG regasification plant according to the invention; Figure 2 is a partial cross-sectional view of the heater used in the installation according to the invention; Figure 3 is a schematic cross-sectional view of the regassifier used in this installation; Figure 4 is a first variant of the regasification plant according to the invention; figure 5 is another variant of the regasification plant according to the invention; figure 6 shows an example of a specific use of the installation according to the invention, and figure 7 shows another example of a use of the installation according to the invention. Figure 1 schematically shows a regasification plant for a liquefied natural gas (LNG) comprising a LNG storage tank 10 at atmospheric pressure and at a temperature in the region of -160øC, a regasification device with a heat exchanger unit heat, or regasifier 12 run by a heat transfer agent as well as by the LNG from the reservoir and a heat exchanger unit 14 of the heat carrier. The heat transfer agent is an organic fluid whose crystallization point approaches that of LNG and has a viscosity low enough to be able to be easily circulated in the ducts even at very low temperatures. In addition, this agent remains in the liquid state in use condition at atmospheric pressure and at room temperature. Preferably, this heat carrier may be an alcohol, or a hydrocarbon, or a compound thereof. Following the description, the organic fluid considered by way of example is methanol whose crystallization point is in the vicinity of -98 ° C, but other alcohols, such as ethanol (crystallization point: -114 ° C) or propanol (crystallization point: -126 ° C). The circulation comprises a circulating ring 16 of the heat-carrying agent which, in the example shown, is a closed ring with a hot part and a cold part. This ring comprises a circulation pump 18, a circulation conduit 20 of this agent between the pump and the regassifier 12, a circulation conduit 22 between the regassifier and the reheat unit 14, a return conduit 24 between this reheat unit and the circulation pump, a reservoir 26 of the heat transfer agent being interposed in this return conduit. The plant also comprises a LNG suction pump 28, generally immersed in the reservoir 10, a LNG circulation conduit 30 between this pump and a circulation pump 32, a conduit 34 conveying the LNG of this circulation pump to the regasifier 12, and an outlet conduit 36 for conveying gas in the gaseous form exiting the regassifier to all suitable means. The heating unit is also traversed by a heating fluid 28 which is, in the illustrated example, the outside air at room temperature, and comprises an exhaust 40 of the condensates coming from this air. Of course, this reheating air can thus come from all the apparatus present in the operating facility, such as the flue gas rejected by a gas turbine.

To effect regasification, the LNG is pumped from the reservoir 10 by the pumps 28 and 32, circulates in the conduits 30 and 34 to be sent to the regasifier 12. This gas circulates in the regasifier which is also traversed by methanol as a heat carrier. To this end, the methanol present in the reservoir 26 is pumped by the pump 18 and is sent by the conduit 20 to the regasifier 12. In this regasifier, the calories present in the methanol are transmitted to the LNG and reheat it so that the liquid phase of the LNG is transformed into a gaseous phase by vaporization and then, if necessary, superheated to reach a temperature close to room temperature. The temperature of the methanol at the inlet of the regasifier 12 is about 20Â ° C and about -160Â ° C for the LNG circulating in the conduit 34. At the outlet of this regasifier, the natural gas is at a temperature close to 5Â ° C, while the methanol reaches a temperature of about -70 ° C at the outlet of this regassifier in the conduit 22.

During the regase exchange the methanol is cooled to a temperature higher than its crystallization point in the case -70 ° C for the example under consideration. The cold methanol is sent through the conduit 22 to the reheat unit 14 so that the air circulating in that unit, and whose temperature is higher than that of the cold methanol, change its heat with this methanol to obtain the reheated methanol in the conduit 24 and, consequently, in the reservoir 26. The temperature of the methanol at the inlet of the reheating unit is of the order of -70 ° C, while the air is introduced into this reheater at a temperature in the vicinity of 30 ° C. After heat exchange in this unit, the methanol is evacuated from the unit at a temperature in the vicinity of 0 ° C, while the air exits at a temperature in the vicinity of 5 ° C.

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

In order to reheat the methanol at the outlet of the regassifier, and as shown in 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 in each end of this calender. Within this calender is housed a set of upright tubes 48 connected at one of its ends by an inlet manifold 50 with an inlet 52 for the cold methanol 7 from the regassifier and at the other of its ends by an evacuation manifold 54 with an outlet 56 connected to the conduit 24 leading to the methanol reservoir 26. In this heat exchanger, methanol arrives at the inlet manifold 52, enters the inlet manifold 50, circulates in all of the upright tubes 48, to drain into the exhaust manifold 54 and is evacuated through the outlet 56. Simultaneously, the air, whether at ambient temperature, is heated by all known means, is introduced into the calender 42 by the inlet 44, then sweeps all the tubes as well as the manifolds. During this scan, the calories contained in this air are transmitted to the methanol to reheat and a hot methanol is obtained at the outlet 56. During this exchange the water droplets contained in the air are condensed and fall by gravity into the bottom of the calender 42 to be subsequently evacuated in the form of condensates through the conduit 40. The tubes 48 may be coated with a water-shedding film of the polymethylsiloxane type to facilitate separation of the water droplets.

Referring now to Figure 3, the regassifier comprises a vertical carton 58 containing at least two exchangers in which gas and methanol circulate, an upper exchanger 60 placed in the upper part of the carton and a lower exchanger 62 placed in the lower part of this carton . Preferably, these exchangers are in the form of plate exchangers and brazed blades, advantageously in aluminum. The upper exchanger is countercurrent, because natural gas and methanol circulate in opposite directions, while the heat exchanger is in parallel currents, the fluids flowing in the same direction. Thus, for the lower exchanger, it comprises on one side and at the bottom of this exchanger an inlet 64 of the methanol connected to the conduit 20 and an outlet 66 on one side of the exchanger. This lower exchanger also comprises an inlet 68, connected to the LNG conduit 34, which is located on the lower side and opposite the methanol inlet, and an outlet 70 placed in the upper part of the exchanger. Thus, in the lower exchanger 62, the methanol and LNG streams circulate in the same direction, that is, from the bottom up in this exchanger. Thanks to this, the surface temperature inside this exchanger remains above -100 ° C, and the exchange surfaces may be smaller. The methanol outlet 66 is connected by a conduit 72 to an inlet 74 of the upper exchanger which is located at the top and one side of this exchanger. Likewise, the natural gas outlet 70 is connected by a conduit 76 to a gas inlet 78 located at the bottom of this exchanger. The gas in the form of vapor is evacuated through an outlet 80 which is situated at the top of this exchanger, while the outlet 82 of the methanol is situated at the bottom of this exchanger to be connected to the conduit 22 leading to the reheat unit. This exchanger is therefore designated as countercurrent heat exchanger because the gas and methanol flow circulate in opposite directions to the gas upstream of the exchanger and to the methanol from above downstream of this exchanger.

In the variant shown by way of example in figure 4, the regifier 12 is divided into two distinct parts. Thus, the parallel chain exchanger 82 is in the form of a tube and calender exchanger and comprises the inlets 64, 68 as well as the methanol and LNG outlets 60, 70. The outlets 66 and 70 are connected by the conduits 72, 76 to the countercurrent exchanger which is a plate exchanger and brazed blades, advantageously in aluminum, and which comprises the inlets 74, 78 and the outlets 82 and 80 of methanol and natural gas.

Preferably, the tube and calender exchanger comprises a mechanical expansion joint 83 which absorbs all dimensional variations of these exchangers upon passage of LNG and methanol.

In this variant, the operation of the plant is identical to that described with respect to Figures 1 to 3. Reference is now made to Figure 5, which shows a variant of the regasification plant shown in Figure 4 and which for this comprises the same references for the common parts.

This variant is distinguished by the fact that regasification takes place in several stages. Further, the countercurrent exchanger 60 is divided into two portions 60A, 60B, a phase separator 84 being provided between these two parts of the exchanger. The natural gas exiting the countercurrent tube and calendering exchanger 62 through the outlet 70 is preheated to its boiling point corresponding to the pressure in the separator 84.

This heated liquid natural gas flows through the lower portion 60A of the countercurrent exchanger 60 to effect a phase transformation by vaporization. This transformed natural gas is sent through a conduit 86 to the separator 84 where the natural gas is separated into the gaseous form in the upper part 88 of this separator having a lower composition, molecular weight and calorific value and in the liquid form in the lower part 90 of this tab. The natural gas in the form of vapor present in the separator is then directed by a conduit 92 from this separator into the inlet of the part 60B of the exchanger 60 where it is subjected, in exchange with the methanol circulating therein, to a temperature rise up to to the outlet 80. The liquid phase, which has a molecular weight and a heat value higher than that of the steam, is drawn by a pump 94 connected to this separator by a conduit 96. The liquid phase exiting the pump 94 is directed by a conduit 98 for all storage media to be subsequently treated therein. Advantageously, it is possible to control the composition and calorific value of the gaseous natural gas in the conduit 92 prior to its entry into the exchanger 60 by injecting therein a predetermined quantity of liquid from the separator through a conduit 98A which is born after the pump 94 in conduit 98 and terminating in conduit 92.

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

In addition, heating of the methanol can be envisaged at the outlet of the pump 18, by placing in conduit 20 a heat exchanger 100 between methanol and a hot fluid which is commonly used in or in the vicinity of this regasification plant, such as water from the sprinkler tower.

As already described, the methanol at the outlet of the regassifier is at a low temperature of the order of -70 ° C and must be reheated to ensure the gas phase transformation of the LNG into the regasifier. To this end, there may be an advantage in utilizing the presence of a power plant with a combined cycle gas turbine in the installation, as shown in figure 6. In this case, the central unit 102 is supplied with air through a channel 104 and with natural gas through a channel 106, this channel may be a bypass of the conduit 36 described above. The combustion of the air-natural gas mixture in the turbine generates, after recovery of the generated calories 11 (briefly HRSG) to the outlet 108 of the fumes with temperatures in the order of 130 ° C. As shown in Figure 6, these fumes are introduced by an inlet 110 into a heat exchanger assembly 112, separated at least in three portions 112A, 122B, 112C, to re-exit through an outlet 114 and are subsequently directed by a conduit 116 for all suitable means, such as a chimney. The heat exchanger assembly is also traversed by a phase-exchange fluid, such as propane, circulating in a closed loop 118. This ring comprises a liquid propane reservoir 120, a circulation pump 122 connected to the reservoir by a conduit 124 and a separator 126 connected by a conduit 128E which carries the liquid propane to the portion 112a of the heat exchanger assembly and a conduit 128S which routes the propane, preheated to its boiling point, to this separator. From this separator two conduits, a conduit 130, said liquid conduit, in which the liquid contained in the separator is brought to the heat exchanger portion 112B to cross it and return in the gaseous form to the separator 126, and a conduit 132, said conduit which carries the propane gas phase contained in the separator to the heat exchanger assembly portion 112c in order to overheat this propane gas. A conduit 134 brings the propane in pressurized gas form to an expansion turbine 136 rotatably connected to all power producing means, such as an alternator 138. At the outlet of the expansion turbine, the propane gas is led by a conduit 140 to a heat exchanger 142, said condenser, to cool this propane gas and thereby cause it to change phase to obtain a liquid phase before it returns through a conduit 144 to the reservoir 120. To cool the propane, the condenser 142 is driven by the methanol circulating in conduit 22, as previously described, and, at the outlet of this condenser, the methanol is at a higher temperature than its introduction by having captured the heats contained in the gas phase propane .

In operation, the propane in liquid form is pumped from the reservoir 120 to traverse the portion 122 of the heat exchanger 112. After this passage, the preheated propane in the liquid form is sent to the separator 126. The liquid phase withdrawn from this separator passes through the portion 112B of the assembly 112 to return the quasi-gaseous form to the separator to effect the separation between the liquid phase and the gas phase of the propane. The gas phase contained in this separator is also withdrawn to traverse the portion 112 of the exchanger assembly 112 to be therein completely transformed into the gaseous phase and superheated, if necessary. The propane in the gas phase passes through the turbine 136 which it traverses in rotation, the turbine of which causes the alternator to rotate 138. At the outlet of the turbine, the propane in the gaseous form passes through the condenser 142 where it changes phase and passes into the liquid phase thanks to exchange of these calories with the cold methanol also circulating in the condenser. At the outlet of this condenser, the liquid propane is stored in the reservoir 120. The treatment group, as schematically illustrated in Figure 7, shows a potential use of the LNG regasification facility with a methanol ring to capture and liquefy the contained CO2 as well as fumes from gas turbine fumes.

In this configuration, there is provided a LNG regasification unit 146, a C02 pickup / separation unit 148, a methanol reheat unit 149 and a CO2 liquefaction unit 150. The regasification unit 146, as already described with respect to the preceding figures, comprises a regasifier 142 driven by the methanol which circulates in the ring 152, and by the LNG from the conduit 34. The CO2 capture / separation unit 148 comprises a absorption column 154 containing transfer elements 156 with a methanol inlet 158 issued by the regassifier, an inlet of a C02-containing gaseous fluid 160, a non-CO2 gas exhaust 162 and an outlet 164 of a mixture of methanol and CO2. This C02 pickup / separation unit also comprises an expansion tang 166 with an inlet of the methanol and CO 2 mixture, a CO 2 outlet 168 in the gaseous form and a methanol outlet 170 without a large portion of CO 2. The reengineering unit 149 comprises elements similar to those already described in connection with Figures 1 and 2, i.e., a methanol driven reactant coming from, in the illustrated example of Figure 7, the outlet 170 of the expansion tang 166, by a fluid of which may be the outside air at room temperature. This heat exchanger also comprises an exhaust 40 of condensates from this outside air. This unit finally comprises a heat exchanger 174 allowing to heat the methanol upon passage into the reheater through an outlet 172 and an expansion tank 175 allowing to separate the methanol in liquid form, which is then directed by a conduit 176 to the methanol ring, and the C02 in gaseous form which is joined by a conduit 178, a conduit 180 also connecting the conduit 168 of CO2 of the expansion tank 166. The liquefaction unit 150 comprises a capacitor 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 the form of steam.

This capacitor comprises a housing 182 which contains at least two portions of capacitors 184 and 186, each countercurrent and preferably with aluminum plate and paddles, in which the CO2 in the form of steam and ethane are circulated by one, and LNG and ethane by another. The lower condenser 184 is disposed in the lower part of the carton and comprises on one side and at the top of this condenser a CO2 inlet 188 connected to the conduit 180 and a liquid CO2 outlet 190 in the lower part of the condenser. The upper condenser 186 comprises an LNG port 192 connected to the LNG conduit 34 which is situated at the bottom of this condenser and an outlet 194 located at the top of the exchanger. A closed ring of ethane 196 allows the ethane to circulate between the two exchangers. More precisely, the ethane in vapor is introduced into the upper ethane condenser 186 through an inlet 198 located in the upper part of the condenser, passes through this condenser to drain into a liquid ethane outlet 200 located in the lower part of this condenser, is carried by a conduit 202 to a liquid ethane inlet 204 located in the lower portion of the lower CO2 condenser, passes through the lower condenser to exit an outlet 206 located at the top of this condenser and then arrives at the port 198 via a conduit 208.

During the operation of the treatment group described above, LNG follows substantially the same regime as that described with respect to Figure 1, with the only difference that a bypass of the LNG conduit 34 ends at the inlet 192 of the CO2 liquefying unit 150 for crosses the upper condenser 186 and exits the outlet 194 to resume the conduit 36. At the outlet of the regassifier, the methanol is sent through the inlet 158 in the column 156 which also receives a fluid containing a non-insignificant portion of CO2, in the order of 12% through the inlet 160. After treatment in this column, the CO2 is captured by methanol and a mixture of methanol and dissolved CO2 is evacuated through the outlet 164. The non-CO2 fluid is evacuated through the outlet 162 to all suitable means. The mixture of CO2 and methanol is subjected to a separation in the expansion tank 166 from where the CO2 in the vapor phase is evacuated through the outlet 168 into the conduit 180 and from which the methanol in the liquid phase from the outlet 170 is heated in the unit of reheating by successive passages in the reheater and the exchanger 174. At the outlet of the exchanger 174, the residual CO2 contained in the methanol is again separated from this methanol in the expansion tank 175. At this separation, the CO2 is evacuated through the outlet 178 to resume the conduit 180 connected to the outlet 168 and the CO2-free methanol resumes, through the outlet 178, the methanol ring pump 18. The CO2 in the vapor phase is liquefied in the lower condenser 184 in which it exchanges its calories with the ring-boring ethane between the two capacitors. After this exchange, the CO2 is in liquid form at the outlet 190, and may be sent to a storage tank from which it may be withdrawn to eventually be stored in an underground tank.

Lisbon, July 6, 2012. 16

Claims (11)

A liquefied natural gas (LNG) regasification plant comprising a liquefied gas storage tank (10), a regasification device (12) for LNG traversed by a natural gas and heat transfer agent, a liquefied natural gas (16) in which the circulating heat transfer agent is methanol, ethanol or propanol, the regasification device (12) comprising at least two exchangers (60, 62), characterized in that one (62) of the exchangers are in chains the counter-current exchanger 60 being in two parts 60A, 60B between which a phase separator 84 is interleaved, and the counter-current exchanger 60 is in countercurrent, . A regasification plant according to claim 1, characterized in that it comprises a reheating unit (14) of the heat transfer agent. A regasification plant according to claim 2, characterized in that the reheat unit (14) is run through the air. A regasification plant according to any one of the preceding claims, characterized in that the heat transfer agent has a crystallization temperature of from -90 ° C to -150 ° C. A regasification plant according to any one of the preceding claims, characterized in that the at least one counter-current exchanger (60) is plate-like and brazed blade type. A regasification plant according to any one of the preceding claims, characterized in that the circulation circuit (16) of the heat transfer agent comprises an additional heat exchanger (100). A degassing plant according to any one of the preceding claims, characterized in that it comprises means for liquefying a hydrocarbon by heat exchange with the heat transfer agent. A regasification plant according to claim 7, characterized in that the hydrocarbon is in the gaseous form after its application to the drive of a turbine (136). A regasification plant according to claim 7 or 8, characterized in that the hydrocarbon is propane. A regasification plant according to any one of claims 1 to 6, characterized in that it comprises carbon capture means for the heat transfer agent. A regasification plant according to claim 10, characterized in that the heat transfer agent is used as the CO2 solvent. Lisbon, July 6, 2012. 2