EP3824164A1

EP3824164A1 - Cryogenic thermodynamic cycle with heat recovery

Info

Publication number: EP3824164A1
Application number: EP19773927.9A
Authority: EP
Inventors: Salvatore DE RINALDIS; Anton Marco FANTOLINI; Luca Davide INGLESE
Original assignee: Saipem SpA
Current assignee: Saipem SpA
Priority date: 2018-08-22
Filing date: 2019-08-22
Publication date: 2021-05-26
Also published as: IT201800008157A1; WO2020039380A1

Abstract

The present invention relates to a process for the regasification of a flow of liquefied natural gas (LNG1), contained in a tank together with a quantity of Boil Off Gas (BOG), and for the production of electricity comprising: a step al) in which a flow of the LNG (LNG1) is subjected to a low-pressure pumping step, thus obtaining a flow LNG2; a step b) in which a portion of said flow (LNG1') is heated in a recondenser, thus obtaining a flow LNG1'' then combined with the flow LNG2; a step c) in which said flow LNG2 is heated in a condenser (COND); a step d) in which said flow LNG2 is subjected to a step of superheating in a superheater (SUR), thus obtaining regasified LNG; a step I) in which a flow (B0G1) of the Boil Off Gas (BOG) contained in the tank is compressed in a first step la), thus obtaining a flow of Boil Off Gas (BOGa), and in a second step lb), thus obtaining a flow of Boil Off Gas (BOGb); a step II) in which said flow of Boil Off Gas (BOGb) is cooled in a step of heat recovery in a recuperator (REG, REC1, REC2); a step III) in which said flow of Boil Off Gas (BOGb) is recondensed in the recondenser of step b); in which the step II) of heat recovery and the step c) of condensation are carried out respectively in a step 1) and 3) of a cycle which employs a flow of an organic fluid (F0A1), which, after step 1) and before step 3), is subjected to a step 2) of expansion in a turbine (TURB) for the production of electricity.

Description

DESCRIPTION

"CRYOGENIC THERMODYNAMIC CYCLE WITH HEAT RECOVERY"

Technical field of the invention

The present invention relates to the energy industry, in particular for improving the energy efficiency of liquefied gas regasification plants.

Background art

Technologies for the regasification of liquefied gases, such as Liquefied Natural Gas (LNG) , are known.

Liquefied Natural Gas is a mixture of natural gas mainly consisting of methane, and in lesser measure, of other light hydrocarbons, such as, for example, ethane, propane, iso-butane, n-butane, pentane, and nitrogen, which is converted from the gaseous state, in which it is at room temperature, to about -160°C, to allow its transportation .

The liquefaction systems are located near the natural gas production sites, while the regasification systems (or "regasification terminals") are situated near the users .

Most systems (about 85%) are situated onshore, while the remaining part (about 15%) are offshore on platforms or ships . More commonly, each regasification terminal comprises multiple regasification lines to satisfy the liquefied natural gas load or the demands, and for reasons for flexibility or technical needs (e.g. for line maintenance) .

Regasification technologies normally concern liquefied natural gas stored in tanks at atmospheric pressure at a temperature of -160°C, and comprise the steps of compressing the fluid to about 70-80 bar and of vaporizing and superheating to about 3°C.

The thermal power required for the regasification of 139 t/h is about 27 MWt for regasification line, while the electrical power is about 2.25 MWe (4.85 MWe if the other auxiliary loads of the plant are taken into account; 20 MWe maximum electrical load of the plant on 4 working regasification lines) .

Among these, the most used, either singularly or in mutual combination, are regasification technologies comprising the Open Rack Vaporizer (ORV) technology, used in about 70% of regasification terminals (worldwide), and Submerged Combustion Vaporizer (SCV) technology.

Other technologies use Intermediate Fluid Vaporizer (IFV) or Ambient Air Vaporizer (AAV) .

Open Rack Vaporizer (ORV)

In this technology, the natural gas in liquid state (about 70-80 bar and at a temperature of -160°C) is made flowing from the bottom upwards inside aluminum pipes arranged side-by-side to form panels; vaporization occurs gradually as the fluid flows.

The heat carrier is the seawater which, by flowing from the top downwards on the outer surface of the pipes, provides the heat needed for vaporization by difference of temperature.

In particular, heat exchange is optimized by the pattern of the profile and by the surface roughness of the pipes, which achieve a uniform distribution of the thin film of seawater on the panel.

Submerged Combustion Vaporizer (SCV)

Such technology exploits a demineralized water bath heated by a submerged flame burner as heat carrier; in particular, Fuel Gas (FG) is burnt in the combustion section and the produced fumes pass through a serpentine of perforated pipes from which the burnt gas bubbles exit, which heat the water bath also transferring the condensation heat.

The liquefied natural gas (LNG) vaporizes in another serpentine in pipes made of stainless steel and submerged in the same bath of demineralized and heated water.

The same water of the bath is maintained in circulation in order to guarantee a uniform temperature distribution .

The exhaust fumes are discharged from the discharge stack of the SCV, instead.

Organic Rankine Cycle

Organic Rankine Cycles (ORC) are widely used in geothermal and biomass applications or for waste heat recovery from industrial processes.

Such cycles include the possibility of selecting the working fluid from a wide variety of candidate fluids and allow efficient thermodynamic cycles to be carried out, even at heat source of low temperatures and for small amounts of available thermal energy.

Furthermore, the choice of a low-boiling fluid allows to carry out a condensing cycle at cryogenic temperatures, without incurring in problems of freezing or excessive vacuum levels.

Submerged Combustion Vaporizer (SCV) and Open Rack Vaporizer (ORV)

Such a technology implies a consumption of fuel gas equal to about 1.5% of the processed gas, produces carbon dioxide, which lowers the pH of the water bath, thus requiring treatments with caustic soda and determining a production of about 50,000 t/year of CO2 for regasifying 139 t/h of LNG .

Open Rack Vaporizer (ORV) technology, instead, may cause in part the freezing of the seawater in the outer part of the pipes, especially in the sections in which the LNG is coldest; furthermore: i) it may be exploited in geographic regions and/or in seasons in which the seawater temperature is at least 5-9°C, which are prevalently represented by subtropical zones; ii) the seawater must be preventively treated to either eliminate or reduce the heavy metal content which would damage the zinc coating of the pipes; iii) it implies a consumption of electricity for operating the seawater pumps which must overcome a geodesic difference of level equal to the extension in height of the ORV, with additional consumptions of about 1 MWe per regasification line with respect to SCV technology (requiring a total power of about 20 MWe for a plant with four regasification lines of 139 t/h each) ; iv) it implies an environmental impact in returning the colder and treated seawater; v) finally, the technology is rather complex and available from a limited number of suppliers and limited in size.

Furthermore, in general, the conventional technologies do not allow the production of the electricity needed for the system and cause the loss of a large amount of energy in form of frigories.

Despite the insulation of the tank (TANK) in which the Liquefied Natural Gas is stored, it is not possible to prevent the dispersion of frigories or the acquisition of heat from the environment, whereby generating Boil Off Gas (BOG) in balance with the liquid phase.

Such BOG is normally managed, after having been recompressed, by reintroducing it into the network, either by means of reliquefaction in a device called a Recondenser, from where it is successively pumped to the regasification pressure, or by subjecting it to combustion, e.g. in SCV (Submerged Combustion Vaporizer) systems .

As shown in Figure 1, the LNG is pumped from the tank by a low-pressure cryogenic pump (PCBP) and then by a high-pressure cryogenic pump (PCAP) to a regasification section, e.g. operating with SCV or ORV technology, and then introduced into the NG distribution network and exploited in a power cycle, e.g. by a turbine (GTG) or internal combustion engine (ICGE) .

From the LNG tank, the developed Boil Off Gas (BOG) is sent to a recompression section and then to an air- cooling section.

A portion of the BOG exiting the cooling section is sent to a recondenser, in which it is liquefied by virtue of the LNG.

The flow exiting the recondenser is then sent to the regasification section after high-pressure pumping. US Patent Application 2013/0160486 (Ormat

Technologies Inc.) describes single- or dual-pressure level cycles which operate with a single fluid, with and without heat exchanges (regenerations) within the cycle on both levels; in an embodiment, two cycles are operated in cascade with two different fluids, in which the heat of a first cycle is used exclusively to evaporate the second fluid and the liquefied natural gas is vaporized by the heat released by the second fluid cycle only.

The described technology does not allow the production of electricity necessary for the operation of the plant, leaving a large amount of energy available in the form of frigories to be degraded.

Summary of the invention

The authors of the present invention have surprisingly found that it is possible to exploit the heat of the recompression of the BOG (Boil Off Gas) in an ORC cycle, which uses the LNG to be regasified as a cold source, together with the heat obtained from the environment, with production of electricity, thus increasing the overall energy efficiency of the regasification line and of the plant which comprises it.

Object of the invention

According to a first object, a liquefied gas regasification process is described, which allows the production of electricity.

According to a second object, a liquefied gas regasification line which allows the production of electricity and a plant comprising such as line are described .

Brief description of the drawings

Figure 1 shows an LNG regasification line with BOG management according to the prior art;

Figure 2 shows a new regasification line of low- or medium-capacity according to the present invention, i.e. with BOG heat recovery, using an Organic Rankine Cycle (ORC) with a single pressure level;

Figure 3 shows an embodiment of the present invention applied to an existing regasification line (retrofit) of low or medium-capacity;

Figure 4 shows a high-capacity regasification line according to the present invention using an organic fluid cycle (ORC) with a single pressure level;

Figure 5 shows an embodiment of the present invention applied to an existing high-capacity regasification line (retrofit) ;

Figure 6 shows a regasification line according to the present invention using a single organic fluid cycle (ORC) with two pressure levels;

Figure 7 shows a regasification line according to the present invention using two organic fluid cycles (ORC) in cascade ;

Figure 8 shows a regasification line according to the present invention using two organic fluid cycles (ORC) in cascade with a heat recovery section from the BOG coolers to the economizers mediated by a carrier fluid;

Figure 9 shows a further embodiment of the regasification line according to the present invention in which a heat recovery from the BOG Cooler to the recuperator is implemented mediated by a carrier fluid and exploiting heat recoveries from high-temperature energy sources and low-temperature heat recoveries;

Figure 10 shows an embodiment of the invention in which a carrier fluid is used for the heat recovery from each of the compression stages of the BOG to the economizer;

Figure 11 shows an embodiment of the invention in which a gas turbine is included, the exhaust fumes of which are used in a superheater of the organic fluid circuit, which is also used to cool the air entering the turbine, recovering heat at low temperature.

Detailed description of the invention

The present invention is described in particular with regard to the regasification of liquefied natural gas (LNG) , but equally applies to the regasification or the vaporization of other liquefied fluids stocked at low temperatures (lower than approximately 0°C) or at cryogenic temperatures (lower than -45°C) .

For example, the present invention is equally applied to the regasification of a liquefied gas chosen from the group which comprises, for example: air, nitrogen, commercially available hydrocarbon compounds, e.g. alkanes, such as, for example, propane and butane, or alkenes, such as, for example, ethylene and propylene.

Hereinafter in the description, the terms "evaporation" and "vaporization", applicable to the LNG under sub-critical conditions, are to be understood as synonyms; the term "regasification" is more properly applied with reference to LNG under sub-critical or super critical conditions.

For the purposes of the present invention, in the description that follows from figure 2 to figure 7, reference is made to an "economizer", meaning with this term a heat exchanger made by means of a pressure vessel in which a heat exchange is carried out with a mixture (i.e. with direct contact) between an organic vapor current (either saturated or superheated) at the inlet and an organic fluid current in subcooled liquid state, also at the inlet, thus obtaining a saturated organic liquid current at the outlet. For the purposes of the present invention, in the description that follows from figure 8 to figure 11, reference is made to an "economizer", meaning with such term a heat exchanger made by means of a pressure vessel in which a heat exchange is carried out between an inlet current of organic vapor in subcooled liquid state and a heat carrier fluid current, thus obtaining a saturated organic liquid current at the outlet; in general, such an exchange allows heat recovery at low temperature.

The term "recondenser" means a column in which an exchange of heat and a transfer of mass occurs between the vapor phase and the liquid phase.

In particular, the recondenser is made by means of a pressure vessel, into one part of which filling material is placed (e.g. metal or plastic fillings), which has the purpose of increasing the contact surface, and consequently the heat exchange, between the fluids to be mixed; the mixture accumulates to the bottom of the vessel after the heat exchange.

The system is controlled, in terms of level, temperature and other process parameters, by means of control valves.

Furthermore, in the present description, "liquefied natural gas", hereinafter also named "liquefied gas", means a liquid obtained from natural gas after appropriate purification and dehydration treatments and subsequent steps of cooling and condensing.

More generally, in the present description, "liquefied gas" means a fluid with a predominantly liquid component .

Furthermore, in the present description, the term "low-temperature heat source" means, for example: ambient air, seawater, low-temperature thermal solar, waste heat from a low-temperature thermodynamic cycle, process thermal recoveries and/or from low-temperature machinery.

A low-temperature source generally operates at temperatures below 180°C, preferably below 120°C.

The term "high-temperature heat source", on the other hand, means e.g.: high-temperature thermal solar, exhaust heat from a high-temperature thermodynamic cycle, exhaust gas from a gas turbine or internal combustion engine, process heat recovery and/or from high- temperature machinery.

A high-temperature source generally operates at temperatures above 180°C, preferably above 300°C and even more preferably above 400°C and above.

Hereinafter, in the description, the term "seawater" means not only pumped seawater, appropriately treated to remove sediments, but more in general environmental water obtained from rivers, canals, wells, natural basins, such as lakes, etc., and artificial basins .

For the purposes of the present invention, a carrier fluid is represented by a fluid capable of transferring heat from one heat source to another.

In particular, a carrier fluid is chosen from the group which comprises: water, superheated water, saturated steam, superheated steam, appropriate water- glycol solutions, diathermic oil.

The term "organic fluid" or "working fluid" means a fluid which circulates in an ORC (Organic Rankine Cycle) circuit and which carries out heat exchanges between a heat source and another heat source at a lower temperature (cold well ) .

For the present purposes, a "first organic fluid" (hereinafter FOA) is chosen in the group which comprises: commercially available hydrocarbon compounds selected from the group which comprises: alkanes, e.g. ethane, propane and butane; alkenes for instance ethylene, propylene; mixtures thereof; refrigerants, for instance represented by R41, R143a, R125.

In a preferred aspect of the present invention, the first organic fluid is propane.

In another preferred aspect of the present invention, the first organic fluid is ethane. For the present purposes, a "second organic fluid" (hereinafter FOB) is chosen in the group which comprises: commercially available hydrocarbon compounds selected from the group which comprises: alkanes, for instance ethane, propane and butane; alkenes for instance ethylene, propylene; mixtures thereof; refrigerants, for instance represented by R41, R143a, R125.

In preferred aspect of the present invention, the second organic fluid is ethane.

In the scope of the present invention, the Boil Off Gas is generated by the evaporation of the process fluid in the respective storage tanks; e.g. in an LNG storage tank, the steam created by the incoming heat from the environment is called Boil Off Gas (BOG) , vapor which at storage pressure is in equilibrium with the liquid phase (this is a volume corresponding to about 2b per day of the tank, i.e. 160000 m³ of storage tank volume correspond to about 8 t/h) . For ease of reading, in the following description and in the figures reference is always made to a turbine (TURB) with a single shaft, wherein there could be two generators and two separate shafts, or a reducer could be placed between the two turbines, or between the turbines and generators, or different combinations, such as an Integral Gear solution (i.e. a mechanical system consisting of gears and multiple machine axes coupled together in a single configuration, as the solutions provided by Atlas Copco) ; alternatively, an operating machine may be actuated directly, e.g. such as

According to a first object of the present invention, a regasification line for liquefied natural gas (LNG) is described, which allows the production of electricity also by exploiting the compression heat of the BOG.

The term "regasification line" means the independent and replicable portion of the plant which comprises the regasification structures, the apparatuses, the machinery and the systems of a given flow of liquefied natural gas (LNG) .

Such structures, equipment, machinery and systems originate, in particular, from the tank in which the LNG is stored, comprising cryogenic pumps, possibly at low and high pressure and a recondenser, which can be in common to several regasification lines, and a regasification section, and end with the point of entry of the regasified LNG into the gas distribution network itself .

More specifically, the regasification line of the present invention implements the process described below.

According to a first object of the present invention, a process for the regasification of Liquefied Natural Gas (LNG) is described, contained in a tank together with a quantity of BOG, and for the production of electricity comprising:

a step al) in which a flow (LNG1) of the LNG is subjected to a step of pumping with a low-pressure pump (PCBP) , thus obtaining a flow (LNG2);

a step b) in which a portion of said flow (LNG1') is heated in a step of recondensation of a flow of said quantity of Boil Off Gas (BOGb) in a recondenser, thus obtaining a flow LNGl^{, f} then combined with the flow LNG2 ; a step c) in which said flow LNG2 is heated in a condenser (COND) of the organic fluid in an organic fluid cycle ;

a step d) in which said flow LNG2 is subjected to a step of superheating in a superheater (SUR) , thus obtaining regasified LNG;

a step I) in which a flow of Boil Off Gas (BOG1) contained in the tank is compressed in a first step la) , thus obtaining a flow of Boil Off Gas (BOGa) , and in a second step lb) , thus obtaining a flow of Boil Off Gas (BOGb) ;

a step II) in which said flow of Boil Off Gas (BOGb) is cooled in a step of heat recovery in a recuperator

(REC, REC1 , REC2 ) ;

a step III) in which said flow of Boil Off Gas (BOGb) is recondensed in the recondenser of step b) .

For the purposes of the present invention, step II) of heat recovery from the flow of Boil Off Gas (BOGb) and step c) of heating of the flow LNG2 are carried out respectively in a step 1) and 3) of an organic fluid cycle using a flow of a first organic fluid (FOA1), which after step 1) and before step 3) is subjected to a step 2) of expansion in a turbine (TURB) , thus producing electricity.

In an aspect of the invention, step I) may comprise several sub-steps of compression, e.g. from 2 to 4 or 5 compression steps; this depends on the delivery pressure of the Boil Off Gas, which can be from 7 to about 15 bara and up to about 60-80 bar.

In a preferred aspect, after step b) the flow LNG2 is subjected to a step a2) of pumping with a high-pressure pump (PCAP) .

In particular, after the step 3) of condensation, the flow of organic fluid (FOA1) is subject to a step 4) of heating in an economizer (ECO) and to a step 5) of evaporation in an evaporator (EVA) .

In a first aspect of the invention, after the step 5) of evaporation, a portion of the organic fluid FOA2, separated according to a mass split is recirculated in the economizer (ECO), while the rest of the flow (FOA1) is sent to the recuperator (REC, REC1) for recovering the heat from the BOG obtained from the step I) of compression .

More in particular, this is the heat exchange with the flow of Boil Off Gas (BOGb) obtained from the step lb) of compression.

In another aspect of the invention, the entire flow of the organic fluid (FOA1) can be sent to the recuperator (REC, REC1 ) .

After the step 3) of condensation, the flow of organic fluid (FOA1) is sent to the economizer (ECO), possibly after a step of pumping by means of a pump (PFOA) , whereby closing the cycle of the organic fluid (FOA) .

In a particularly preferred embodiment, after step 2) of expansion, a portion of the flow of organic fluid (FOA3) is separated according to a mass split and subject to the further steps:

1' ' ) of heat recovery with a flow of Boil Off Gas (BOGa) obtained after the step la) of compression in a second recuperator (REC2);

2') of expansion in a second turbine (TURB2) for the production of electricity;

3') of condensation in a second condenser (COND2) with the flow of LNG (LNG2) obtained after step a2) of pumping.

In a further aspect of the present invention, the portion of the flow of the organic fluid (FOA3) not separated after step 2), is used in a step of evaporation in an evaporator (EVA2) with the flow (FOB1) of a second organic fluid used by the cycle of a second organic fluid.

For the purposes of the present invention, such a second organic fluid may be either equal to or different from the first organic fluid (generally, a cycle with two pressure levels is indicated when the same organic fluid operates two cycles - after a mass split; the term "cascade cycles" is used when two cycles are operated using different organic fluids) .

In particular, said flow of the second organic fluid (FOB1) exiting the evaporator (EVA2) is subject to the steps :

1' ' ) of heat recovery in a second recuperator (REC2) with the flow of Boil Off Gas (BOGa) obtained after the step la) of compression;

2'') of expansion in a second turbine (TURB2) for the production of electricity;

3'') of condensation in a second condenser (COND2) with the flow LNG2.

Furthermore, after step 3' ' ) , the flow of the second organic fluid FOB1 may be subject to a step 4' ' ) of heating in an economizer (EC02), possibly after a step of pumping by means of a pump (PFOB) .

Furthermore, after step 4' ' ) , the flow of the second organic fluid FOB1 may be sent to the evaporator (EVA2) for the heat exchange with the portion of the first organic fluid (FOA3) .

In a particular aspect of the invention, a portion of the flow of the second organic fluid (FOB2) exiting the evaporator (EVA2) separated after a mass split is recirculated in the economizer of the cycle of the second organic fluid (EC02) .

More in particular, the heat exchange takes place in the economizer (EC02) with the flow of organic fluid obtained after the step 3'') of condensation.

The flow of the first organic fluid coming from step 4'') (FOA3) is combined with the flow FOA1 exiting the condenser and sent to the economizer for step 4), possibly after a step of pumping by means of a pump (PFOA) .

According to an embodiment of the present invention, the step II) of heat recovery may be replaced by a step X) in which the flow of Boil Off Gas (BOGb) carries out an indirect heat exchange with the flow of first organic fluid (FOA1) in the economizer (ECOl) by means of a first carrier fluid (FV1) .

In a particularly preferred aspect, in such circumstances, a portion of the first and/or second organic fluid exiting the evaporator is not recirculated.

More in detail, said step X) comprises the steps:

X' ) in which said flow of Boil Off Gas (BOGb) carries out a heat exchange with a first carrier fluid (FV1) in a first cooler (BOGC1), and

X' ' ) in which said first carrier fluid (FV1) obtained from step X' ) carries out a heat exchange with the flow of organic fluid (FOA) in the economizer of the cycle which uses the first organic fluid (ECOl) .

In an alternative aspect of the present invention, either alternatively or in addition to the substitution of step II) with step X), step II') may be replaced by step Y) in which the flow of Boil Off Gas (BOGa) carries out an indirect heat exchange with the flow of the second organic fluid (FOB1) in the cycle economizer which uses the second organic fluid (EC02) by means of a second carrier fluid (FV2) .

More in detail, said step Y) comprises the steps:

Y' ) in which said carrier fluid (FV2) carries out a heat exchange with the flow of Boil Off Gas (BOGa) in a second cooler (BOGC2 ) ,

Y' ' ) in which said carrier fluid (FV2) obtained in step U' ) carries out a heat exchange with the flow of the second organic fluid (FOB1) in the economizer (EC02) of the cycle which uses the second organic fluid.

For the purposes of the present invention, the first and second carrier fluids may be mutually equal or different .

In a particularly preferred aspect, if steps II) or II') are replaced by steps X) and/or Y) , a portion of the first and/or second organic fluid, EVA1 and EVA2 respectively, exiting the evaporator is not recirculated to the economizer.

In a further embodiment of the invention, step II) can be replaced by a step Z) in which the Boil Off Gas (BOGb) flow obtained after the step lb) of compression carries out an indirect heat exchange with the flow of organic fluid (FOA1) in the recuperator of the cycle which uses the first organic fluid (REC) .

More in detail, said step Z) comprises the steps:

Z' ) in which said flow BOGb carries out a heat exchange with a carrier fluid (FV) in a cooler (BOGC) , and

Z' ' ) in which said carrier fluid (FV) obtained from step Z’ ) carries out a heat exchange with the flow of the first organic fluid (FOA) in the recuperator (REC) of the cycle which uses the first organic fluid.

Before step Z’ ' ) , said carrier fluid (PV) may be further subject to a step of heat recovery with a high- temperature heat source in a carrier fluid recuperator (RECFV) .

In a particularly preferred aspect, if step II) is replaced by step Z) described above, a portion of the first organic fluid exiting the evaporator (EVA) is not recirculated to the economizer (ECO) .

According to an alternative embodiment of the invention, the step II) of heat recovery is replaced by a step K) in which either each or both of said flow of Boil Off Gas (BOGa) and/or said flow of Boil Off Gas (BOGb) carries out an indirect heat exchange with the flow of the first organic fluid (FOA) .

More in particular, such a heat exchange occurs in the economizer of the cycle of the first organic fluid (ECO) .

More in detail, said step K) comprises the steps:

K' ) in which said flow of Boil Off Gas (BOGb) carries out a heat exchange with the first carrier fluid (FV1) in a first cooler (BOGC1) .

After the step K' ) there is a step K' ' ) in which said first carrier fluid (FV1) obtained in step K' ) carries out a heat exchange with the flow of organic fluid (FOA) in the economizer (ECO) of the cycle which uses the first organic fluid.

In a variant of the present invention, said step K) comprises the steps: K' ) in which said flow of Boil Off Gas (BOGb) carries out a heat exchange in a first cooler (BOGC1) with a first carrier fluid (FV1) which then carries out a heat exchange with the flow of organic fluid (FOA) in the economizer (ECO) of the cycle which uses the first organic fluid, and

K' ' ) in which said flow of Boil Off Gas (BOGa) carries out a heat exchange in a second cooler (BOGC2) with a second carrier fluid (FV2) which then carries out a heat exchange with the flow of Boil Off Gas BOGb in the first cooler (BOGC1) .

According to an additional embodiment of the present invention, the step II) of heat recovery is replaced by a step of superheating in which the flow of organic fluid (FOA1) is superheated by the heat of a gas produced by a further and different power cycle.

For the purposes of the present invention, after step II) of heat recovery, a portion of the Boil Off Gas (BOG2) can be either sent to the network or used in a power cycle.

In all the embodiments described in the present patent application, one or more (or none) of the steps chosen from the step d) of superheating, the step 4) of economization and the step 5) of evaporation may be carried out, in mutually independent manner, using one or more low-temperature heat sources.

Such sources may be mutually the same or not.

In particular, said low-temperature heat source may be seawater or air heating technologies.

Furthermore, according to the purposes of the present invention, the steps c) of heating and d) of superheating of the LNG may be carried out on the entire flow of LNG2 obtained after step b) or a portion of the LNG flow (LNG3) obtained after step b) may be regasified in a vaporization section which is either traditional or known in the prior art.

As shown in Figure 2, in the liquefied natural gas (LNG) is stored at atmospheric pressure and at a temperature of about -160°C in the tank.

As described above, there is also a quantity of Boil Off Gas inside the tank.

In particular, the liquefied gas tank may be located in a place or in a structure different from that of the regasification system, e.g. which may be onshore or offshore .

Exiting the tank, from which it is taken at a temperature of about -155°C and at almost atmospheric pressure, a flow LNG1 is subjected to a step a) of pumping.

Preferably, such a pumping takes the LNG to a pressure of about 60-80 bar. Such a step a) may comprise a sub-step al) operated by a low-pressure pump (PCBP) and a sub-step a2) operated by a high-pressure pump (PCAP) ; the two pumps operate in series .

In a preferred aspect, step al) allows to obtain about 7 bara, while step a2 ) allows to obtain about 60, 70 or 80 bara.

With regard to the consumption of the two pumps, the pump PCBP consumes, for example, about 400 kWe, while the pump PCAP consumes, for example, about 1 MWe, for a flow of LNG (LNG1) of about 139 t/h.

After the step al) of low-pressure pumping and before the step a2) of high-pressure pumping, a portion of the LNG flow (LNG1') is used in a step b) of recondensation of the Boil Off Gas in a recondenser (RECOND) ; in the recondenser, the LNG is heated, e.g. to about -142°C.)

The flow LNG2 exiting step a2) is subjected to a step c) of heating in a condenser (COND) and then to a step d) of superheating in a superheater (SUR) .

The LNG is heated to about +3°C in the superheater.

In an aspect of the invention, with lower capacity regasification lines, e.g. with flows up to 400 kTPA (about 48 t/h) , the superheater can use air heating technologies or other heat sources represented by low- temperature sources. After step (d) , the natural gas (regasified LNG) is fed into the network.

For the purposes of the present invention, the BOG flow recondensed in step b) is represented by the Boil Off Gas originated from the tank (TANK) of the LNG.

In particular, such a flow of Boil Off Gas (BOG1), after exiting the tank, is initially subjected to a step I) of compression.

More specifically, such a step I) comprises a sub step la) and a sub-step lb) , which operate in series.

The compression can reach, for example, about 7-15 bar .

After step I) of compression, the Boil Off Gas is subject to a step II) of heat recovery in a recuperator (REC) .

In an aspect of the invention, the flow of Boil Off Gas (BOGb) exiting from the recuperator (REC) is sent to the recondenser (RECOND) in a step III) (corresponding to step b) of the LNG circuit) .

A portion of the BOG flow obtained after compression (BOG2) may be used, with any further possible compression and possible heat recovery, for the following purposes:

1. internal uses (LP FG - Low-Pressure Fuel Gas - or recondenser or IGCE, corresponding to pressure levels of about 7-15 bara, MP FG Medium Pressure Fuel Gas for Heavy Duty GT with pressures of about 25-30 bara, HP FG - High Pressure Fuel Gas - for Aeroderivative GT requiring inlet pressure of about 55 bara) or

2. external uses (sending to network at MP (Medium Pressure) , with pressures in the range of about 20-25 bara or to network at HP (High Pressure) , with pressures in the range of about 70-90 bara) .

According to an aspect of the invention, step II) of heat recovery of the flow of Boil Off Gas (BOGb) is carried out in a recuperator (REC) which operates on an organic fluid cycle (FOA) .

For the purposes of the present invention, a flow of organic fluid FOA1 is subjected to a step 1) in the recuperator (REC) (step which corresponds to step II) of the Boil Off Gas cycle) and is then sent to a step 2) of expansion in a turbine (TURB) for the production of electricity .

Inside the turbine (TURB) , the organic fluid FOA1 may, for example, expand to about 0.8 bara and cool down to about -27°C.

Exiting the turbine (TURB) , the flow of organic fluid FOA1 implements a step 3) of condensation in a condenser (COND) (step which corresponds to step c) of the LNG circuit) .

Inside the condenser (COND) , the flow of organic fluid FOA1 condenses (with a heat exchange, for example, of about 19.8 MWt to reach a temperature of about -45 °C and a pressure of about 1 bara) .

The flow of organic fluid FOA1 is then sent to a step 4) in an economizer (ECO), possibly after a step of pumping by means of a pump (PFOA) .

The pump (PFOA) may compress the flow of organic fluid FOA1 up to a pressure of about 6 bara.

After step 4), the flow of organic fluid FOA1 is subjected to a step 5) of evaporation in an evaporator (EVA) .

Before being sent to the evaporator (EVA) , a pump may be provided to increase the pressure of the flow FOA1 ; such an increase in pressure is used to overcome the losses of pressure consisting mainly of the evaporator (EVA) and the upstream and downstream pipes.

The flow FOA1 receives heat in the evaporator (EVA) .

In an aspect of the present invention applied to smaller capacity regasification lines of up to 400 kTPA, the evaporator (EVA) may use air heating technologies or other heat sources represented by low-temperature sources .

After step 5) of evaporation, the flow of organic fluid FOA1 is sent to the recuperator (REC) .

In the recuperator (REC) , the flow of organic fluid FOA1 receives heat from the compression of the Boil Off Gas; for example, it can heat up to about 20°C and more by virtue of the contribution of about 1.5 MWt .

Exiting the evaporator (EVA) , a portion of the flow of organic fluid FOA2, separated with a mass split indicated by SM in figure 2, is recirculated in the economizer (ECO) .

In the economizer (ECO) , the flow of organic fluid FOA2 is mixed with the flow FOA1 and the temperature is increased, e.g. up to about -10°C with a minimum increase in pressure, e.g. up to about 6 bara.

In an aspect of the invention, the portion FOA2 represents about 10-20%, preferably 15% of the total flow of organic fluid FOA1.

The total organic fluid inside the circuit can, for example, have a flow of about 180-190 t/h, preferably about 185 t/h; such a flow can also be significantly reduced up to about 50% and more, with an appropriate choice of organic fluid (e.g. using ethane instead of propane) and of the operating conditions of the thermodynamic cycle.

The configuration described above with reference to Figure 2 allows treating LNG flows in the order of size from 50 to 1,500 kTPA.

According to an aspect shown in Figure 3, for example, the present invention can be used to modify existing plants or LNG regasification lines.

In such a case, the step c) of heating and the step d) of superheating of the LNG are carried out in by-pass condition to a traditional line and are carried out on a portion LNG2 exiting step a2) of a high-pressure pump ( PCAP ) .

The other portion of LNG (LNG3) may be subjected to a step e) of vaporization in a vaporization section according to the prior art.

After such a step (e) , the natural gas (NG) obtained is combined with the current exiting the superheater (SUR) and fed into the network.

For a regasification capacity of 400 kTPA, the net electrical power of an ORC cycle developed by applying the heat recovery of the BOG which is the object of the present invention is about 0.85 MWe, with the same flow of the BOG (about 8 t/h) , with an increase of 35% of the produced electricity compared to the same ORC cycle according to the prior art, i.e. without heat recovery of the BOG.

If the LNG flow is higher, in the order of about 1200 kTPA, it may be useful to use a circuit which operates with low-temperature, preferably renewable heat sources, instead of air heating technologies. For example, as shown in Figure 4, a circuit which employs seawater (200) can be used.

The usable flow of seawater 200 can be, for example, of about 4700 t/hour at a temperature of about 8-10°C.

The seawater, after a step of pumping at about 4 bar by means of a pump (PAM, which consumes 0.6 MWe) , can be sent to the evaporator (EVA) and/or to the superheater (SUR) .

For this purpose, the flow 201 can be divided into two portions 202 and 203.

In particular, the flow 202 is used in step 5) of evaporation of the organic fluid FOA inside the evaporator (EVA) (e.g. contributing 21 MWt) .

The flow 203, on the other hand, is used in the superheater (SUR) for step d) of superheating of the LNG; in this case, the seawater will provide about 7 MWt.

The flow of seawater exiting the evaporator (EVA) 206 and/or the flow exiting the superheater (SUR) 204 can be combined into a single 205 flow for re-entry into the sea.

In each of the steps in the evaporator and/or superheater, the seawater is cooled down to about 5°C.

For the purposes of the present invention, the flow of seawater 201 can be sent for about 60-80%, preferably about 70-75% (t/hour), to the evaporator (EVA) and for the rest to the superheater (SUR) . Alternatively, the flow of seawater 201 may be sent entirely to the evaporator (EVA) or to the superheater (SUR) .

If the seawater is used in the evaporator (EVA) , the organic fluid FOA may, for example, receive a quantity of heat of about 21 MWt and may, for example, exit at a temperature of about 7°C and at a pressure of about 6 bara .

Also for the solution described above, steps c) of heating and d) of superheating may be carried out on a portion of the LNG (LNG2) exiting step a2) of pumping with a high-pressure pump (PCAP) , while a second portion of the LNG3 is subjected to a step e) of vaporization according to the prior art (see figure 5) .

The net electrical power developed by the ORC cycle may be, for example, about 2.5 MWe, whereas without the use of the compression heat of the BOG it would be about 2.3 MWe (therefore with an increase of about 10%) .

An alternative embodiment of the present invention is shown in figure 6.

In particular, it is an embodiment in which a flow of organic fluid FOA operates two distinct heat recovery steps of the compression heat of the BOG (in a first recuperator -REC1- and a second recuperator -REC2-, respectively), of expansion in turbine (in a first turbine -TURB1- and in a second turbine -TURB2-, respectively) and of condensation (in a first condenser -CONDI- and in a second condenser -COND2-, respectively) .

As described in greater detail, exiting the tank, from which it is taken at a temperature of approximately - 155°C and at almost atmospheric pressure, a flow LNG1 is subjected to a step a) of pumping.

Such a step a) may comprise a sub-step al) operated by a low-pressure pump (PCBP) and a sub-step a2) operated by a high-pressure pump (PCAP) ; the two pumps operate in series .

After the step al) of low-pressure pumping and before the step a2) of high-pressure pumping, a portion of the LNG1 flow (LNG1') is used to recondense the BOG in a step b) of recondensation of the BOG in a recondenser (RECOND) , in which this LNG flow condenses a BOG flow.

The flow LNG2 exiting step a2) is subjected to a step c) of heating in a condenser (COND) and then to a step d) of superheating in a superheater (SUR) to be introduced to the network.

The flow of BOG recondensed in step b) is represented by the BOG originating from the tank (TANK) of the LNG.

In particular, such a flow of BOG (BOG1) is initially subjected to a step I) of compression, comprising a sub step la) and a sub-step lb) , which operate in series. After step I) of compression, the BOG is subjected to a step II) of heat recovery in a recuperator (REC) .

The flow BOGb exiting the recuperator (REC) is sent to the recondenser (RECOND) for a step III) of recondensation .

In this embodiment, the step c) of heating of the LNG comprises the further step c' ) of heating.

In the organic fluid circuit, according to a first mass split (SMI in figure 6) , the flow FOA1 not recirculated in the economizer (ECO) is used in a first step of heat recovery 1) in a first recuperator (REC1) with the flow of BOGb obtained after step lb) of compression of the BOG (corresponding to step II) of the BOG circuit) .

In a preferred aspect, such a step of low-temperature recovery is carried out, for example, at the temperature in the range between 50°C and 120°C.

After step 1) of heat recovery, the organic fluid FOA1 is expanded in step 2) in the first turbine (TURB1) for producing electricity.

The flow of organic fluid FOA1 exiting the turbine (TURB1) is sent to a step 3) of condensation in a condenser (CONDI) (corresponding to step c) of the LNG circuit) .

Exiting the condenser, the flow of organic fluid FOA1 is sent to step 4) of energy optimization in an economizer (ECO), possibly after pumping with a pump (PFOA1) .

Exiting the economizer (ECO) , the flow FOA1 is sent to a step 5) of evaporation in an evaporator (EVA) .

A flow of the organic fluid FOA2, according to a mass split (SMI as shown in figure 6) is not sent to the recuperator (REC1) and is recirculated in the economizer (ECO) instead.

According to another mass split (SM2 as shown in figure 6) , a portion FOA3 of the organic fluid expanded in the turbine (TURB1) is sent to a further step 1') of heat recovery in a recuperator (REC2) for the heat exchange with the flow of BOGa obtained after step la) of compression (corresponding to an additional step II') of the BOG circuit) .

In a preferred aspect, the step of low-temperature recovery is carried out at the temperature in the range of -30 to +20 ° C .

The flow of organic fluid FOA3 exiting the recuperator (REC2) is expanded in a second turbine (TURB2) for the production of electricity.

Exiting the turbine (TURB2), the flow of organic fluid FOA3 is sent to the second condenser (COND2) for a further step 3' ) of condensation (corresponding to step c' ) of additional heating of the LNG circuit.

Exiting the condenser (COND2), the flow of organic fluid FOA3 is combined with the flow FOA1, possibly after a step of pumping with a pump (PFOA2) .

The embodiment described above provides for the solution suggested by the present invention to be implemented for the regasification of a portion of the LNG next to a traditional line according to the prior art.

For the purposes of the present invention, however, the described solution may be applied for the construction of new plants or new lines for the regasification of LNG in existing plants.

In an embodiment, seawater circulating in a seawater circuit, as described above with reference to Figure 4, may be used in the evaporator (EVA) and/or superheater (SUR) .

Alternatively, air heating technologies may be used in the evaporator (EVA) and superheater (SUR) instead of a low-temperature energy source.

The present invention is not limited to the embodiments which include only one or two pressure levels, but it can find application for the number of pressure levels considered useful by those skilled in the art; equally, those skilled in the art will be able to evaluate and choose the most appropriate source of thermal energy, according to needs, flows to be treated and implementation costs . According to a further embodiment of the present invention shown, for example, in figure 7, two steps are carried out: of heat recovery, of expansion in the turbine for the production of electricity and of heating of the LNG, each of which uses a different organic fluid.

Each of the organic fluids operates on its own circuit, wherein the two circuits are integrated as described below.

In particular, the two organic fluids (FOA and FOB) operate two distinct steps of heat recovery (in recuperators REC1 and REC2, respectively), of expansion in turbine (TURB1 and TURB2) and of condensation (in CONDI and COND2 condensers, respectively) .

After the step al) of low-pressure pumping and before the step a2) of high-pressure pumping, a portion of the LNG1 flow (LNG1') is subjected to a step b) of recondensation of the BOG in a recondenser (RECOND) , in which this LNG flow condenses a BOG flow.

In particular, such a flow of BOG (BOG1) is initially subjected to a step I) of compression, which comprises a sub-step la) and a sub-step lb) , which operate in series.

After step I) of compression, the BOG is subjected to a step II) of heat recovery in a recuperator (REC) .

The flow BOG1 exiting the recuperator (REC) is sent to the recondenser (RECOND) in step III) .

According to a first mass split (SMI in figure 6) , a flow of the first organic fluid FOA1 not recirculated in the economizer (ECO) is used in a first heat recovery step 1) in a first recuperator (REC1) with the flow of Boil Off Gas (BOGb) obtained after the step lb) of compression of the BOG.

In a preferred aspect, such a step 1) corresponds to a step lib) of low-temperature recovery, which is carried out, for example, at a temperature in the range between 50 °C and 120°C.

After step 1) of heat recovery, the flow of organic fluid FOA1 is expanded in step 2) in the first turbine (TURB1) for producing electricity.

Exiting the condenser (CONDI), the flow of organic fluid FOA1 is sent to step 4) of energy optimization in an economizer (ECOl), possibly after pumping with a pump ( PFOA) .

Exiting the economizer (ECOl), the flow FOA1 is sent to a step 5) of evaporation in an evaporator (EVA1) .

A flow of the organic fluid FOA1 exiting the evaporator (EVA1) is not sent to the recuperator (REC1) and is recirculated in the economizer (ECO) instead.

After step 2) of expansion, a flow of the first organic fluid FOA3 (according to the mass split SM2 in figure 7) is not sent to the first condenser (CONDI) and is sent to a second evaporator (EVA2) instead.

As described above, such an evaporator (EVA2) is the integration point with the circuit of the second organic fluid (FOB) .

Exiting the evaporator (EVA2), the FOA3 flow is combined with the flow FOA1.

A step of heat exchange is implemented between the flow FOA3 and a flow of the second organic fluid FOB1 in the second evaporator (EVA2) .

Exiting the evaporator (EVA2), the flow FOB1 is sent to the second recuperator (REC2) for a step 1') of heat recovery with the Boil Off Gas flow (BOGa) obtained after step la) (corresponding to step II') of the BOG circuit) .

Exiting the recuperator (REC2), the flow FOB1 is expanded in the second turbine (TURB2) in a step 2') for the production of electricity.

Exiting the turbine (TURB2), the flow FOB1 is sent to the second condenser (COND2) for a step 3') of condensation .

After step 3' ) , the flow FOB1 is sent to an economizer for a step 4') of energy optimization in an economizer (EC02), possibly after a step of pumping with a pump (PFOB) .

Exiting the economizer (EC02), the flow FOB1 is sent to the evaporator (EVA2) for the step 5') of evaporation.

A portion of the second organic fluid FOB2, separated with a mass split (SM3 in figure 7) exiting the evaporator (EVA2), is not sent to the recuperator (REC2) and is recirculated to the economizer (EC02) instead.

The present invention is not limited to the embodiments which provides for the use of one or two organic fluids, but can be applied to more organic fluids according to that deemed useful by those skilled in the art according to needs, flows to be treated and implementation costs.

In an aspect of the invention, a flow of Boil Off Gas (BOG2) exiting the recuperator (REC1) can be used, with a possible additional compression and possible heat recovery, for the following purposes:

1. internal uses (LP FG - Low-Pressure Fuel Gas - or recondenser or IGCE, corresponding to pressure levels of about 7-15 bara, MP FG - Medium Pressure Fuel Gas - for Heavy Duty GT with pressures of about 25-30 bara, HP FG - High Pressure Fuel Gas - for Aeroderivative GT requiring inlet pressure of about 55 bara) or

According to an embodiment of the invention shown in figure 8, the heat exchange between the organic fluid and the Boil Off Gas is not implemented directly and is implemented indirectly by means of a carrier fluid, instead .

In particular, two (or more) carrier fluid circuits can be provided, which can operate on one or more steps of the BOG circuit.

Furthermore, the two carrier fluids can be either mutually the same or different.

According to an embodiment, the circuit of the first organic fluid and of the second organic fluid, described above, may not comprise a recuperator.

Furthermore, the recirculation of a portion of the first and/or second organic fluid to the economizer may not be included.

For the purposes of the present invention, instead, the Boil Off Gas circuit may comprise a cooler (BOGC1 in Figure 8) for the heat exchange between the flow of Boil Off Gas (BOGb) obtained after step lb) and the first carrier fluid (FV1) and a cooler (BOGC2 in Figure 8) for the heat exchange between the Boil Off Gas flow (BOGa) obtained after step la) and the second carrier fluid ( FV2 ) .

More specifically, the BOGC1 is part of a circuit of the first carrier fluid (FV1), which also comprises the economizer of the circuit of the first organic fluid (ECOl), with which it is integrated.

Therefore, the flow of Boil Off Gas (BOGb) obtained from step lb) carries out a heat exchange with the flow FOA1 of the first organic fluid in the economizer (ECOl) of the cycle of the first organic fluid.

Such a heat exchange is indirect.

More in detail, there is a high-temperature heat exchange inside the BOGC1, e.g. at the temperature in the range between 50°C and 120°C.

The BOGC2 is part of a circuit of the second carrier fluid (FV2), which also comprises the economizer of the circuit of the second organic fluid (EC02), with which it is integrated.

Therefore, the flow of Boil Off Gas obtained from step la) carries out an indirect heat exchange with the flow FOB1 of the second organic fluid in the economizer (EC02) of the cycle of the second organic fluid.

More in detail, in the BOGC2 there is a low- temperature heat exchange, e.g. at the temperature in the range between -30°C and +20°C.

In an aspect of the invention, a portion of the flow BOG2 exiting the cooler (BOGC2) is not sent to the recondenser (RECOND) and can be used, with a further possible compression and possible heat recovery, for the following purposes: 1. internal uses (LP FG - Low-Pressure Fuel Gas - or recondenser or IGCE, corresponding to pressure levels of about 7-15 bara, MP FG - Medium Pressure Fuel Gas - for Heavy Duty GT with pressures of about 25-30 bara, HP FG - High Pressure Fuel Gas - for Aeroderivative GT requiring inlet pressure of about 55 bara) or

Seawater may be used in the solution described above, as described above, e.g. in relation to Figure 4, or such use may be replaced in part or in full by the use of other low-temperature heat sources, as appropriate, where deemed possible by those skilled in the art.

Figure 9 is an alternative embodiment of the present invention, variant with respect to Figure 2, described above .

In this embodiment, the step II) of heat recovery between the flow of Boil Off Gas (BOGb) obtained after step lb) and the organic fluid is carried out indirectly by means a carrier fluid (PV) .

The carrier fluid (PV) is sent, possibly after a step of pumping with a pump (PFV) to a BOG cooler (BOGC) to a step of heat exchange with the Boil Off Gas (BOGb) flow obtained from step lb) .

Exiting the BOGC, before step II), the carrier fluid (PV) is subjected to a step of heat recovery in a carrier fluid recuperator (RECFV) .

Such a recuperator (RECFV) preferably uses a high- temperature heat source (RAT in figure 9) .

In an embodiment, the recirculation of the organic fluid FOA in the economizer (ECO) may not be included and this may possibly exploit a low-temperature source of heat energy (RBT) , as described above.

As for the evaporator (EVA) , this can exploit air heating technologies or a low-temperature source of thermal energy.

According to the further embodiment shown in Figure 10, it can be expected that the heat exchange between the Boil Off Gas and the organic fluid FOA will be indirectly implemented by means of a carrier fluid in the economizer of the organic fluid cycle.

For such a purpose, the step II) of heat recovery is replaced with a step in which the Boil Off Gas (BOGb) flow carries out a heat exchange with a first carrier fluid (FV1) in a first cooler (BOGC1) and said flow of Boil Off Gas (BOGa) carries out a heat exchange with a second carrier fluid (FV2) in a second cooler (BOGC2), and that said first carrier fluid (FV1) carries out a heat exchange with the flow of organic fluid (FOA) in the economizer (ECO) .

In particular, a first circuit for the carrier fluid (FV1) may be included, by virtue of which a first heat exchange between the first carrier fluid (FV1) and the first organic fluid (FOA) is carried out in the economizer of the cycle of the first organic fluid (ECO) and a second heat exchange between the first carrier fluid (FV1) and the flow of Boil Off Gas obtained after the step lb) (BOGb) in the first cooler of the circuit BOG (BOGC1) .

Furthermore, a second circuit may be provided for the carrier fluid (FV2) .

The carrier fluid of the first and second circuits (FV1 and FV2 ) may be mutually the same or not.

In particular, the carrier fluid of the second circuit (FV2) carries out a first heat exchange between the carrier fluid (FV2) and the Boil Off Gas flow obtained from the first step la) of compression (BOGa) and a second heat exchange between the carrier fluid (FV2) and the Boil Off Gas flow obtained from the second step lb) of compression (BOGb) .

In an aspect of the invention, a portion of the flow of Boil Off Gas (BOGb) exiting the cooler (BOGC1) is sent to the recondenser (RECOND) , while a second portion (BOG2) may be used, with a further possible compression and possible heat recovery, for the following purposes:

1. internal uses (LP FG - Low-Pressure Fuel Gas - or recondenser or IGCE, corresponding to pressure levels of about 7-15 bara, MP FG - Medium Pressure Fuel Gas - for Heavy Duty GT with pressures of about 25-30 bara, HP FG - High Pressure Fuel Gas - for Aeroderivative GT requiring inlet pressure of about 55 bara) or 2. external uses (sending to network at MP (Medium Pressure) , with pressures in the range of about 20-25 bara or to network at HP (High Pressure) , with pressures in the range of about 70-90 bara) .

A further embodiment of the present invention is shown in figure 11.

In this regard, the BOG circuit may comprise two coolers (BOGC1 and BOGC2) which operate, respectively, on the flow of Boil Off Gas obtained after step la) (BOGa) and on the flow of Boil Off Gas obtained after step lb) of compression (BOGb) .

Furthermore, the heat exchange between the Boil Off Gas and the organic fluid FOA occurs not directly, but by means of a carrier fluid PV, as described in relation to Figure 11, instead.

In particular, the heat exchange with the carrier fluid is carried out in the BOGC1 with the Boil Off Gas (BOGa) obtained after step la) and in BOGC2 with the Boil Off Gas (BOGb) obtained after step lb) .

In one aspect, the evaporator of the organic fluid circuit (EVA) operates with a low-temperature heat source, e.g. ambient air, which is then cooled.

The air thus cooled may be used in a gas turbine (GTG) , which may be fed with a portion of the Boil Off Gas obtained after compression (BOG2) . For the purposes of the present invention, the step II) of heat recovery of the organic fluid is replaced by a step of superheating in a superheater (SUR) which exploits the exhaust gases produced by the turbine.

In this embodiment, a flow of Boil Off Gas obtained after cooling in BOGC1 (BOG3) may be sent to the step of condensation .

From the description provided above, those skilled in the art will be able to understand the several advantages offered by the present invention.

First of all, although described with reference to the regasification of Liquefied Natural Gas, the present invention may be applied without any limitation to the regasification of liquid hydrogen and/or cryogenic storage of liquid hydrogen or technical gases.

That described above may be applied onshore, offshore and even aboard floaters; in particular, the latter two applications allow to have seawater easily available .

In any case, the solutions described allow the Boil Off Gas to be compressed at different pressure levels, also high for sending to the network or to power plants, recovering the compression heat of the Boil Off Gas itself, by means of a thermodynamic cycle which allows the regasification of the LNG at the same time. Furthermore, the process of the present invention allows a better operation of the recondenser and a higher turndown capacity (minimum sendout) .

Such solutions offer a wide flexibility in the management and Boil Off Gas both for internal and external use as described above, increasing plant efficiency.

The present invention has demonstrated that it can produce a quantity of electricity which makes the regasification line self-sufficient.

k k k

Claims

1. A process for the regasification of a flow of liquefied natural gas (LNG1), contained in a tank together with a quantity of BOG, and for the production of electricity comprising:

a step al) wherein said flow of LNG (LNG1) is subjected to a low pressure pumping step, thus obtaining a flow LNG2 ;

a step b) wherein a portion (LNG1') of said flow (LNG2) is heated in a Recondenser, thus obtaining a flow (LNGl^{, f}) subsequently combined to the flow (LNG2);

a step c) wherein said flow (LNG2) is heated in a condenser (COND) ;

a step d) wherein said flow (LNG2) is subjected to a superheating step in a superheater (SUR) , thus obtaining regasified LNG;

a step I) wherein a flow (BOG1) of the BOG contained in the tank is compressed in a first step la) , thus obtaining a flow BOGa, and in a second step lb) , thus obtaining a flow BOGb;

a step II) wherein said flow BOGb is cooled in a heat recovery step in a recuperator (REC, REC1, REC2); a step III) wherein said flow BOGb is recondensed in the Recondenser of step b) ;

wherein said heat recovery step II) and said condensation step c) are carried out respectively in a step 1) and in a step 3) of a cycle which employs a flow of an organic fluid (FOA1), which, after step 1) and before step 3), is subjected to an expansion step 2) in a turbine (TURB) for the production of electricity.

2 . A process according to the preceding claim, wherein, after the condensation step 3), said flow of organic fluid ( FOA1 ) is subjected to the steps of:

4) heating in an economizer (ECO),

5) evaporation in an evaporator (EVA) and subsequently to the heat recovery step in the recuperator (REC, REC1, REC2) for the heat exchange with the flow BOGb obtained from the compression step lb) .

3 . A process according to any one of the preceding claims, wherein, after the evaporation step 5) , a portion of the flow of organic fluid (FOA2) is recirculated in the economizer (ECO) .

4 . A process according to claim 2 or 3, wherein a portion of the flow of the organic fluid (FOA3) obtained after step 2) is subjected to the further steps of:

1' ) heat recovery in a second recuperator (REC2) with the flow BOGa obtained after the compression step la) ;

2') expansion in a second turbine (TURB2) for the production of electricity;

3') condensation in a second condenser (COND2) with the flow LNG2.

5 . A process according to any one of claims from 2 to 4, wherein a portion of the flow of the organic fluid obtained after step 2) (FOA3) is employed in an evaporation step in an evaporator (EVA2) of a cycle which employs a flow of a second organic fluid (FOB1) .

6. A process according to the preceding claim, wherein said flow of the second organic fluid (FOB1) is subjected to the steps of:

1' ' ) heat recovery in a second recuperator (REC2) with the flow BOGa obtained after the compression step la) ; 2'') expansion in a second turbine (TURB2) for the production of electricity;

3'') condensation in a second condenser (COND2) with the flow LNG2 ;

’’) heating in an economizer (EC02), possibly after a pumping step by means of a pump (PFOB) , after which said flow of the second organic fluid FOB1 is sent to the evaporator (EVA2) for heat exchange with the portion of the first organic fluid (FOA3) .

7 . A process according to the preceding claim, wherein a portion of the flow of the second organic fluid (FOB2) exiting the evaporator (EVA2) is recirculated in the economizer (EC02) .

8. A process according to any one of claims from 2 or from 4 to 7, when not dependent from claim 3, wherein step II) is replaced by a step X) wherein the flow BOGb carries out an indirect heat exchange with the flow of first organic fluid (FOA1) in the economizer (ECOl) by means of a first carrier fluid (FV1) .

9 . A process according to the preceding claim, wherein said step X) comprises the steps:

X' ) wherein said flow BOGb carries out a heat exchange with a first carrier fluid (FV1) in a first cooler (BOGC1 ) ,

X' ' ) wherein said first carrier fluid (FV1) obtained from step X' ) carries out a heat exchange with the flow of organic fluid (FOA1) in the economizer of the cycle of the first organic fluid (ECOl) .

10 . A process according to the preceding claim, wherein step II') is replaced by a step Y' ) wherein the flow BOGa carries out an indirect heat exchange with the flow of the second organic fluid (FOB1) in the economizer of the cycle of the second organic fluid (EC02) by means of a second carrier fluid (FV2) .

11 . A process according to the preceding claim, wherein said step Y) comprises the steps:

U' ) wherein said flow BOGb carries out a heat exchange with a second carrier fluid (FV2) in a second cooler

(BOGC2 ) , Y' ' ) wherein said second carrier fluid (FV2) obtained from step U' ) carries out a heat exchange with the flow of the second organic fluid (FOB1) in the economizer of the cycle of the second organic fluid (EC02) .

12. A process according to any one of claims from 8 to 11, wherein said first (FV1) and said second (FV2) carrier fluid may be the same or different.

13. A process according to any one of claims 2 or from 4 to 7, when not dependent from claim 3, wherein said step II) is replaced by a step Z) wherein said flow BOGb carries out an indirect heat exchange with the flow of the first organic fluid (FOA1) in the recuperator of the cycle of the first organic fluid (REC, REC1) .

14. A process according to the preceding claim, wherein said step Z) comprises the steps:

Z' ) wherein said flow BOGb carries out a heat exchange with a carrier fluid (FV) in a cooler (BOGC) ,

Z' ' ) wherein said carrier fluid (FV) obtained from step Z' ) carries out a heat exchange with the flow of the first organic fluid (FOA1) in the recuperator (REC) of the cycle of the first organic fluid.

15. A process according to the preceding claim, wherein, before said step Z' ' ) , said carrier fluid (FV) is subjected to a heat recovery step in a recuperator (RECFV) with a high temperature heat source.

16. A process according to any one of claims 2 or from 4 to 7, wherein said heat recovery step II) is replaced by a step K) wherein each or both of said flow BOGa and/or said flow BOGb carries out an indirect heat exchange with said flow of organic fluid (FOA1) .

17. A process according to claim 16, wherein said step K) comprises the steps:

K' ) wherein said flow BOGb carries out a heat exchange in a first cooler (BOGC1) with the first carrier fluid (FV1) which subsequently carries out a heat exchange with the flow of said first organic fluid (FOA1) in the economizer (ECO) of the cycle of the first organic fluid, and

K' ' ) wherein said flow BOGa carries out a heat exchange in a second cooler (BOGC2) with a second carrier fluid (FV2) which subsequently carries out a heat exchange with the flow BOGb in the first cooler (BOGC1) .

18. A process according to any one of claims 1 or 2 or from 4 to 7, wherein said heat recovery step II) is replaced by a superheating step wherein the flow of organic fluid (FOA1) is superheated by the heat of a gas produced by a further power cycle.

19. A process according to any one of the preceding claims, wherein the superheating step d) and/or the economization step and/or the evaporation step 5) are carried out, independently of one another, employing one or more low temperature heat sources, which may be equal with respect to one another.

20 . A process according to any one of the preceding claims, wherein the condensation step c) and the superheating step d) of the LNG are carried out on the whole flow of LNG2 obtained after step b) or a portion (LNG3), obtained after step b) , is regasified in a vaporization section represented by a vaporization bath, which may be of the Submerged Combustion Vaporizer (SCV) or of the Open Rack Vaporizer (ORV) type.