EP3548713A1

EP3548713A1 - Closed gas cycle in cryogenic applications or refrigerating fluids

Info

Publication number: EP3548713A1
Application number: EP17818621.9A
Authority: EP
Inventors: Salvatore DE RINALDIS; Luca Davide INGLESE; Alessandro LEPORE; Fabrizio MELONI; Gianluca Valenti; Ennio MACCHI; Marco ASTOLFI; Paolo Chiesa
Original assignee: Saipem SpA
Current assignee: Saipem SpA
Priority date: 2016-11-30
Filing date: 2017-11-28
Publication date: 2019-10-09
Also published as: WO2018100485A1; JP2020501071A; JP7018946B2; IT201600121407A1

Abstract

The object of the present invention is a regasification line for a liquefied gas comprising a closed gas cycle section, which operates with a working fluid, and which comprises a first heat exchanger (HE1), wherein the heat of the working fluid is transferred to the liquefied gas for its regasification, and a turbine (T1) for generating electrical current by means of said working fluid, said line further comprising a second heat exchanger (HE2), which is part of a first intermediate fluid circuit, and wherein said first intermediate fluid transfers heat to said working fluid.

Description

"CLOSED GAS CYCLE IN CRYOGENIC APPLICATIONS OR

REFRIGERATING FLUIDS"

Technical field of the invention

The present invention finds application in the energy sector, in particular for the reducing energy consumption required in the regasification terminals of a liquefied gas.

Prior art

Technologies for regasifying liquefied natural gas (LNG) are known.

The liquefied natural gas is a mixture of natural gas mainly consisting of methane and, to a lesser extent, of other light hydrocarbons such as ethane, propane, isobutane, Ώ-butane, pentane, and nitrogen, which is converted from the gaseous state, which is found at room temperature, to the liquid state, at about -160°C, to allow its transportation.

The liquefaction plants are located in the proximity of natural gas production sites, while the regasification plants (or "regasification terminals") are located in the proximity of the users.

Most of the plants (about 85%) are located onshore, while the rest (about 15%) offshore on platforms or ships .

It is common that each regasification terminal comprises several regasification lines, to satisfy the load of liquefied natural gas or the demands, as well as for flexibility or technical requirement reasons (for example, for maintenance of a line) .

Normally, the regasification technologies involve liquefied natural gas stored in tanks at atmospheric pressure at a temperature of -160°C and comprise the steps of gas compression up to about 70-80 bar and vaporization and overheating up to about 3°C.

The thermal power required for regasifying 139 t/h is about 27 MWt, while the electrical power is about 2.25 MWe (4.85 MWe if the other auxiliary loads of the plant are taken into account; 19.4 MWe electrical load maximum of the plant on 4 regasification lines) .

Among these, the most used, individually or in combination with each other, are the Open Rack Vaporizer (ORV) technology, used in about 70% of the regasification terminals, and Submerged Combustion Vaporizer (SCV) .

Open Rack Vaporizer (ORV)

This technology provides that the natural gas at liquid state (about 70-80 bar and at a temperature of - 160°C) is made to flow from the bottom upwards within aluminum tubes flanked to form panels; the vaporization progressively occurs as the fluid proceeds.

The heat carrier is the seawater which flowing from the top downwards on the outer surface of the tubes provides the heat required for vaporization by a difference in temperature.

In particular, the heat exchange is optimized by the design of the profile and of the superficial roughness of the tubes, which carry out a homogeneous distribution of the thin seawater film on the panel.

Submerged Combustion Vaporizer (SCV)

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

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

The same bath water is kept in circulation in order to ensure a homogeneous distribution of temperature.

On the other hand, the exhausted fumes are discharged by the venting stack of the SCV. The patent IT 1042793 ( Snamprogetti S.p.A.) describes a process for the regasification of LNG and for the simultaneous production of electrical energy by a nitrogen closed gas cycle (Brayton) which recovers heat from the discharge of a gas turbine.

However, such a process finds a limited application, as it produces a quantity of electrical energy greater than the requirement of the regasification terminal; the calculated yield of 55% produces 33 Mwe, 10 times greater than that required.

Furthermore, it may be used only limited to the availability of a gas turbine, with which to recover the heat from the discharge gases; it also requires a compression ratio equal to 10, therefore requiring the use of rather complex machines, compressors and multistage turbines which working at high temperatures (400÷700°C) also use expensive materials.

Other drawbacks and limitations are represented by the fact that the ratio between thermal and electrical load is strongly unbalanced towards the thermal part; therefore, to simultaneously cover the thermal and the electrical load, a large part of the heat recovered from the gas turbine would be discharged by the closed gas cycle, carrying out a closed gas cycle with poor efficiency; moreover, in conditions of reduced LNG flow rate it is necessary to release a part of the turbine discharge gases in the atmosphere, with further loss of efficiency or, still losing efficiency within the system, to choke the turbine load.

With particular reference to the Submerged Combustion Vaporizer (SCV) , such technology implies a fuel gas consumption equal to about 1.5% of the gas produced, produces carbon dioxide which lowers the pH of the water bath requiring treatments with caustic soda and determines a production of CO2 of about 50,000 t/year to regasify 139 t/h.

As regards instead the Open Rack Vaporizer, such technology may partially cause the freezing of the seawater in the outer part of the tubes, especially in the sections wherein the LNG is colder; furthermore: i) it may be exploited in the geographic regions and/or in the seasons where the seawater temperature is at least 5-9°C, mainly represented by the subtropical zones, ii) the seawater must be treated in advance to eliminate or reduce the content of heavy metals which could corrode the zinc coating of the tubes, iii) it implies an electrical energy consumption for the operating seawater pumps which must overcome a geodetic difference in level equal to the development in height of the ORV with additional consumption of 1.2 MWe per regasification line with respect to the SCV technology (total plant power equal to 24.2 MWe) , iv) finally, the technology is quite complex and is available at a limited number of suppliers and of sizes.

Therefore, in general, the conventional technologies do not allow producing the electrical energy required for the plant and lead to the loss of a great quantity of energy in the form of refrigeration units.

Summary of the invention

The authors of the present invention have surprisingly found that it is possible to introduce a closed gas cycle into a tradition regasification line.

Object of the invention

In a first object, a regasification line for liquefied natural gas (LNG) is described.

In another object, the invention describes a process for generating thermal energy and electrical energy.

In a further object, a regasification terminal is described comprising a regasification plant of liquefied natural gas (LNG) .

Brief description of the figures

Figure 1 shows a diagram of a regasification line according to the present invention; Figure 2 shows a plant comprising more regasification lines, wherein the concept of energy bypass is diagrammed;

Figure 3 shows a diagram of a regasification line according to an alternative embodiment of the present invention;

Figure 4 shows a diagram of a regasification line according to another alternative embodiment of the present invention;

Figures 5 (A and B) and 6 show some alternative configurations of portions of the regasification lines of the invention;

Figures 7 and 8 show the diagram of a regasification line according to further embodiments of the present invention .

Detailed description of the invention

The present invention is described in particular in relation to the regasification of liquefied natural gas (LNG) , but the regasification line, the regasification terminal and the regasification process hereinafter described are equally applicable for the regasification or vaporization of other liquefied fluids stored at low temperatures (lower than about 0°C) or at cryogenic temperatures (lower than -45°C) . In the following description, the term "liquefied gas" is intended to mean a fluid of mainly liquid composition .

The present invention will find equal application for the regasification or vaporization of a liquefied gas selected from the group comprising for example: air, nitrogen, hydrocarbon compounds, e.g. alkanes, such as for example propane and butane, or alkenes, such as for example ethylene or propylene, or the regasification or vaporization of hydrogen.

For simplicity of description, in the present description and in the figures reference shall be made to natural gas .

According to an object of the present invention, a regasification line for liquefied natural gas (LNG) is described .

The term "regasification line" is intended to mean the plant portion which comprises the structures, the equipment, the machinery and the systems for the regasification of liquefied natural gas (LNG) .

Such structures, equipment, machinery and systems originate, in particular, from the tank wherein the LNG is stored and terminates with the inlet point of the regasified LNG in the distribution network of the gas itself . More in detail, in the tank the liquefied natural gas (LNG) is stored at atmospheric pressure and at a temperature of about -160°C.

In particular, the liquefied gas tank may be located in a place or in a structure other than that of the regasification plant, which for example could be onshore or offshore or on floaters.

A circuit element is the bath of a submerged combustion vaporization (SCV) section.

Before entering in the vaporization bath, the LNG may be subjected to a preliminary compression step to bring it to a pressure of about 70÷80 bar.

The compression is operated by a low pressure pump (about 400 kWe) and by a high pressure one (about 1300 kWe) , which operate in series (PMP1 in figure 4) .

In figure 1 CMP1 represents the boil off gas compressors (BOG) .

In a preferred aspect, at the bath inlet of the SCV section, the liquefied gas may be at the supercritical state; for example, in the case of the liquefied natural gas, this may be at a pressure of about 70÷80 bar and at a temperature of about -155°C.

Within the SCV bath the liquefied natural gas is vaporized and superheated up to a temperature of about 3°C. Once regasified, the natural gas may be introduced into the natural gas distribution network.

According to a first object of the present invention, the regasification line (the base circuit) of the liquefied natural gas is modified so as to integrate a liquefied natural gas (LNG) by-pass circuit.

In particular, the integration between the two circuits is at the drawing connection of the liquefied natural gas from the base circuit and at the reintroducing connection of the liquefied natural gas regasified in the base circuit destined for the distribution network.

Preferably, the drawing connection is downstream of the cryogenic pumps and upstream of the vaporization bath (SCV) .

For the purposes of the present invention, the following are therefore described:

- a traditional regasification line, already existing, modified so as to integrate a natural gas regasification by-pass circuit (revamping) ; and

- a regasification line consisting of the by-pass circuit as the main line, for example for constructing new plants. Liquefied natural gas (LNG) by-pass circuit

A portion of the LNG flow (101) as output from the storage tank, optionally after the preliminary compression step, is withdrawn from the LNG base circuit and subjected to a heating and vaporizing step in a heat exchanger (HE1) .

In particular, such heating is operated up to a temperature of about 3°C.

The natural gas flow thus vaporized (102) is introduced into the natural gas network at a pressure of about 70 bar and 3°C.

According to an aspect of the invention, a portion (103) of the LNG as output from the exchanger HE1 is sent to a boiler (natural gas-fired boiler) .

If an initial LNG flow rate of about 139 t/h is considered, the quantity intended for the boiler circuit is of about 1-2 t/h.

According to a first object of the present invention, the liquefied natural gas (LNG) circuit comprising the base circuit and the by-pass circuit described above is modified by introducing (or integrating with) a closed gas cycle.

Closed gas cycle According to the present invention, the closed gas cycle operates with a fluid, called working fluid, which, preferably, is comprised of a monatomic gas.

In an even more preferred aspect, said gas is selected from the group comprising argon, nitrogen, helium and air.

For the objects of the present invention, such a working fluid is argon (Ar) .

The working fluid 1 at a temperature of about 70 °C and at a pressure of about 20 bar is subjected to a compression step, through a compressor Kl, up to about 42 bar, therefore making a compression ratio of about 2 (more precisely 2.09) .

In the closed gas cycles, the determining parameter is the compression ratio, while the minimum and maximum pressure (connected to each other by the compression ratio) are optimized in the design of turbomachinery (as the pressure increases, the size decreases since the volumetric flow rates decrease) and of equipment (as the pressure increases, the thickness of the tubes increases) .

The flow 2 thus obtained is heated up to about 4°C in a heat exchanger (HE3 figure 1) .

This step comprises a heat exchange equal to about 12 MWt. For the purposes of the present invention, the heat exchange step in the third exchanger HE3 is optional .

Subsequently, the heated flow (3 in figure 1) is heated, or optionally further heated, in a heat exchanger (HE2 in figure 1) obtaining a flow 4 at about 120°C.

This step comprises a heat exchange equal to about 18 MWt .

In a subsequent step, the working fluid flow 4 expands in a turbine T2 keyed to a generator Gl and to the compressor Kl up to about 21 bar and cooling down to about 40°C (flow 5 in figure 1), providing a net electrical power of about 2.25 MWe .

Finally, within the exchanger HE1 the working fluid of the closed gas cycle transfers thermal power to the LNG for about 27 MWt cooling down.

In a preferred aspect of the invention, the working fluid flow rate of the closed gas cycle circulating in the circuit is of about 137.8 t/h.

For the purposes of the present invention, a heat exchange occurs in the heat exchanger HE1 with which the working fluid of the closed gas cycle transfers thermal power to the liquefied natural gas (LNG) which is thus regasified. In such a step, a heat exchange corresponding to about 27 MWt occurs.

According to alternative aspects of the present invention shown in figure 5A (wherein C=compressor, Rl=first reducer, Tl=turbine, R2=second reducer and G=generator) the turbine and the closed gas cycle compressor may be directly keyed on the same shaft; moreover, they may have the same rotation velocity or not and they may transfer mechanical energy to one same electrical generator.

In another alternative aspect shown in figure 5B (wherein C=compressor, Rl=first reducer, Tl=turbine, T2=second turbine, R2=second reducer and G=generator) , the working fluid may expand in two turbines in series: Tl, which operates at high pressure, keyed to the compressor, and T2, which operates at low pressure, keyed to the generator.

In another alternative shown in figure 6, the compressor Kl is electrically operated and the turbine T2 is keyed to the only generator.

In another alternative not shown, a heat exchanger (recoverer) is inserted at the output of the turbine, wherein the working fluid after expanding in the turbine transfers heat to the working fluid output from the exchanger HE3 before receiving heat from the exchanger HE2.

According to a further aspect of the present invention, the working fluid circuit may be further integrated with additional circuits.

In particular, such circuits may comprise:

- a boiler circuit

- a circuit for recovering heat from a "Fuel Cell";

- a seawater circuit;

- a circuit for recovering compression heat from the BOG compressor .

According to a preferred aspect of the invention, the integration is possible with any one of or with more of those cycles listed above.

Boiler circuit or first high temperature circuit

The circuit is fed with water at a temperature of about 30°C (201 in figure 1) .

A water flow 202 arrives to the boiler at a pressure of about 3.82 bar, put in circulation by the circulation pump of the boiler PMP3 in figure 1; the flow 203 of the water heated in the boiler at about 140°C is cooled in a heat exchanger (HE2), wherein it cools down to about 30°C (201) .

According to a preferred aspect of the invention, the boiler circuit is integrated with the closed gas cycle at the exchanger HE2, within which the boiler circuit water transfers thermal power, cooling down, to the working fluid of the closed gas cycle which heats up to about 120°C.

Such a step comprises, in particular, a heat exchange corresponding to about 18 MWt.

In an alternative aspect of the invention, the boiler may be replaced by an equivalent heat source.

According to an alternative aspect of the present invention, the superheated water boiler circuit may be replaced with a diathermic oil circuit.

The choice of one or the other manner may be made based on the needs.

In an aspect of the invention shown in Figure 8, the boiler circuit operates with an intermediate fluid represented by discharge fumes of the boiler itself (203 in Figure 8) supplied with air.

In particular, a heat exchanger occurs in the exchanger HE2 with the fumes output from the boiler, producing fumes sent to the stack 201.

The working fluid output from the exchanger HE2 is heated in the boiler and subsequently the flow 4 is sent to the turbine T2.

In such a configuration, the heat exchange occurs by radiation in the boiler and by convection in the exchanger HE2 (integration point with the working fluid cycle) .

In the embodiment described above, the working fluid preferably used is nitrogen.

In an alternative aspect of the invention, the boiler, as a heat source, is a Fuel Cell, whose discharge fluids are capable of transferring heat.

The supply fluid of the Fuel Cell may be: hydrogen, ethanol, methane.

Seawater circuit or second low temperature circuit

The seawater is withdrawn at the seawater outlet at a temperature of about 9°C (301 in fig. 1) .

Subsequently, it is subjected to a pumping step up to a pressure of about 2 bar (302 in figure 1) with a pump PMP2 and then cooled in a third heat exchanger (HE3 ) down to about 4°C.

This cooling step in HE3 involves a transfer of thermal energy of about 12 MWt .

In these conditions the water flow (303) may be released into the sea.

Optionally, before the introduction into the circulation, the seawater is subjected to a filtering step in order to retain substances and organic material, for example algae, mollusks, and inorganic material such as sand or particulates. According to a preferred aspect of the invention, the integration with the closed gas cycle occurs at the third heat exchanger HE3, wherein the seawater transfers heat to the working fluid of the closed gas cycle.

Such a step, in particular, comprises a heat exchange corresponding to about 12 MWt.

It will be seen that the heat exchange step in the third heat exchanger (HE3) corresponds to the step described above of heating the working fluid of the closed gas cycle.

The integration of the closed gas cycle with the seawater circuit allows exploiting a second heat source at low temperature and therefore reducing the consumption of regasified natural gas.

In the present description, where reference is made to "seawater", this is meant to refer not only to pumped seawater, and suitably treated to remove sediments, but also more in general to fresh water, obtained from rivers, canals, wells, natural basins such as lakes, etc. or artificial basins.

In an alternative embodiment of the present invention, in place of the seawater, ambient air may be used as a source of heat at low temperature using for example air heating technologies. In such a configuration, an exchanger-coil may be provided through which passes ambient air naturally or by forced circulation, wherein the working fluid within the coil heats up and the air outside the coil cools down .

The structural modifications of the circuit in this context are within the scope of the person skilled in the art .

BOG cycle

According to a further aspect of the invention shown in figure 7, the seawater circuit may be replaced by or added to a BOG circuit.

For such purposes, in particular, a tempered water flow 301 is sent to the exchanger HE3 wherein the heat exchange occurs with the working fluid.

The flow output 101 from the exchanger HE3 303 is sent to the exchanger HE5 for the heat exchanger with the BOG output from the BOG compressor.

According to a further aspect of the invention not shown, the heat exchanger between the BOG after compression and the working fluid may directly occur in the exchanger HE3.

According to a further aspect of the invention not shown, the BOG compression may be carried out in more steps, in this condition at the output of every compression the heat may be transferred into more exchangers such as HE3 or single exchanger (more heat exchanges in a single body) .

Electrical circuit

As regards the electrical requirements, the system of the invention requires about 2.25 MWe to make a regasification line energetically independent and 4.85 MWe if 1/4 of the electrical load of the entire regasification terminal is to be covered.

In particular, the system of the invention entirely provides for the electrical requirements of a regasification line (2.25 MWe) or of 1/4 of the electrical load of the entire regasification terminal and feeds the low and high pressure cryogenic pumps

(PMP1), the boil off gas compressor (CMP1) and the pumps for pumping seawater (PMP2) and boiler circulation pumps

(PMP3) .

Therefore, according to the above description, the present invention describes a regasification line of liquefied natural gas (LNG) which comprises:

- a vaporization section of said liquefied natural gas (LNG) , and

a closed gas cycle section which operates with a working fluid and which in turn comprises a first heat exchanger (HE1), a compressor, a second exchanger (HE2), a third exchanger (HE3) and a turbine for generating electrical energy through said working fluid of the closed gas cycle.

More in particular, the heat of the working fluid of the closed gas cycle is transferred to the liquefied natural gas (LNG) within the first heat exchanger (HE1) .

For the purposes of the present invention, said working fluid of the closed gas cycle is selected from the group comprising: air, nitrogen, helium, argon.

According to the present invention, the closed gas cycle operates with a fluid, which, preferably, is comprised of a monatomic gas.

Preferably, the working fluid of the closed gas cycle is argon.

According to a preferred aspect of the invention, the described regasification line comprises two heat exchangers (respectively HE1, HE2) .

In an aspect of the invention, the second exchanger (HE2) is part of a circuit which operates with a first intermediate fluid.

Within said second exchanger (HE2), in particular, a heat exchange is carried out between said first intermediate fluid and said working fluid of the closed gas cycle, to which heat is transferred. In a preferred embodiment of the invention, in the second exchanger (HE2) said first intermediate fluid consists of discharge fumes of an endothermic engine, of a gas turbine or of an internal combustion engine or process recoveries (sources at high temperature) .

According to a further aspect, the regasification line of the present invention comprises a third heat exchanger (HE3) .

Such a third exchanger (HE3), in particular, is part of a circuit which operates with a second intermediate fluid.

Within said third exchanger (HE3), in particular, a heat exchange is carried out between said second intermediate fluid and said working fluid of the closed gas cycle, to which heat is transferred.

For the purposes of the present invention, the working fluid circuit may be integrated with the first intermediate fluid circuit or with the second intermediate fluid circuit or with both circuits.

In any case, according to a preferred aspect of the invention, the circuit which operates with the first intermediate fluid and the circuit which operates with the second intermediate fluid are circuits which exploit low temperature heat sources for example at temperatures lower than 180°C, preferably lower than 120°C. According again to a preferred aspect of the invention, the circuit which operates with the first intermediate fluid and the circuit which operates with the second intermediate fluid are circuits which exploit heat sources at high temperature for example at temperatures higher than 180°C, preferably higher than 300°C, even more preferably higher than 400°C, and low temperature, respectively.

For the objects of the present invention, the term "low temperature heat source" is intended to mean for example: ambient air, seawater, solar heating, process heat recoveries and/or low temperature machinery.

For the purposes of the present invention, the term "high temperature heat source" is intended to mean for example: solar heating, exhausted heat of a thermodynamic cycle, discharge gas of a gas turbine or internal combustion engine, process heat recoveries and/or high temperature machinery.

According to preferred aspects of the present invention, the first intermediate fluid is tempered/superheated water or diathermic oil and the respective circuit is a boiler circuit.

Therefore, the cooling of superheated boiler water or diathermic oil and the heating of working fluid of the closed gas cycle is performed in the second exchanger (HE2) .

According to a particular aspect, the cooling of the boiler water and the heating of the working fluid of the closed gas cycle output from the third heat exchanger (HE3) are performed in the second heat exchanger (HE2) (Fig. 4 and Fig. 1) .

However, according to an alternative aspect, in the second heat exchanger there are performed the cooling of the boiler water and the heating of the working fluid of the closed gas cycle output from the first heat exchanger (HE1) for regasifying liquefied natural gas (LNG) with said working fluid (HE2) (fig. 3) .

According to a preferred aspect of the present invention, the second intermediate fluid is seawater and the respective circuit is a seawater circuit.

According to the present invention, the regasification line comprises a vaporization section of liquefied natural gas which is of the Submerged Combustion Vaporizer (SCV) type.

According to a particularly preferred aspect of the invention, the turbine of the closed gas cycle is fed with the working fluid of the closed gas cycle heated in output from the second heat exchanger (HE2) or in output from the third (HE3) and from the second heat exchanger (HE2) for generating electrical energy.

In an aspect of the invention, the boiler of the boiler circuit is fed with a portion of regasified natural gas output from the first heat exchanger (HE1) in which the heat exchange between the closed gas cycle working fluid and the liquefied natural gas (LNG) is implemented .

For the purposes of the present invention, the regasification line of liquefied natural gas (LNG) further comprises a connection to the outer network for electrical energy supply, when available, or an electrical generating unit for example a gas turbine or internal combustion engine.

According to an alternative embodiment of the invention, the regasification line of liquefied natural gas is modified to further comprise a heat pump (HP in figure 3) .

More in particular, such an embodiment provides that the first intermediate fluid circuit is preferably a boiler circuit.

As regards the heat pump (HP) , this preferably comprises :

- a refrigerating fluid circuit, optionally comprising pumps for circulating said refrigerating fluid, and - a first and a second heat exchanger of the heat pump.

In particular, the refrigerating fluid circuit operates by means of a fluid preferably chosen from the group comprising, for example: water-glycol and other refrigerating fluids such as, for example, fluids R134a, R32, R143a, R125.

According to a preferred aspect of the present invention, said refrigerating fluid operates:

- a first heat exchange in the first heat exchanger of the pump, represented by an evaporator of the heat pump (VPC in figures 3 and 4), with which the refrigerating fluid acquires heat from a first intermediate fluid of the heat pump (HPF1);

- a second heat exchanges in the second heat exchanger of the pump, represented by a condenser of the heat pump (CPC in figures 3 and 4), with which the refrigerating fluid transfers heat from a second intermediate fluid of the heat pump (HPF2) .

For the purposes of the present invention, the first intermediate fluid (HPF1) is represented by seawater (or fresh water, as defined above) , which is extracted at a temperature of about 9°C and cooled down to about 4°C in the evaporator of the heat pump (VPC), with a heat exchange corresponding to about 4.4 MWt, considering the self-sufficiency of a regasification line and 9.8 MWt by that of 1/4 of the electrical load of a regasification terminal.

Optionally, before the use in the heat pump, the seawater is subjected to a filtering step in order to retain substances and organic material, for example algae, mollusks, and inorganic material such as sand or particulates .

In an alternative aspect of the invention, the first intermediate fluid of the heat pump (HPF1) may be represented by ambient air.

For the purposes of the present invention, the second intermediate fluid (HPF2) is tempered water, which is heated from about 18°C to about 23°C in the condenser of the heat pump (CPC) , with a heat exchange corresponding to about 5.1 MWt, considering the self- sufficiency of a regasification line and 11.4 MWt by that of 1/4 of the electrical load of a regasification terminal .

According to a particularly preferred aspect of the present invention, the second intermediate fluid circuit (HPF2) is integrated with the liquefied natural gas (LNG) regasification by-pass circuit.

In particular, such integration is implemented by a heat exchanger (HE4 in figure 3), wherein the second intermediate fluid (HPF2) transfers heat to the liquefied natural gas.

According to a preferred aspect, the liquefied natural gas flow object of the heat exchange with the second intermediate fluid (HPF2) is the LNG output from the first heat exchanger (HE1) and is, therefore, at least already partially regasified.

Furthermore, a portion of the regasified liquefied natural gas output from the heat exchanger (HE4) may be used for feeding the boiler of the boiler circuit.

According to an even more preferred aspect of the invention, a fraction of the electrical power produced by the turbine of the closed gas cycle feeds the heat pump in particular the compressor of the heat pump (CPC) .

According to a second object of the invention, a process for generating thermal energy and electrical energy is described.

For the purposes of the present invention, such a process is also meant as a process for the regasification of a liquefied gas and/or for heating (or superheating) a regasified gas.

One of such applications is for example the storage of a low temperature gas. In particular, such a process comprises a step 1) of operating a closed gas cycle with a working fluid.

Preferably, step 1) in turn comprises the steps of:

i) performing one or more thermal energy acquisition steps by the working fluid of the closed gas cycle,

ii) performing an electrical energy generating step by said working fluid, and

iii) performing a thermal energy transferring step from the working fluid of the closed gas cycle to a liquefied fluid.

In an aspect of the invention, such a liquefied fluid is liquefied natural gas (LNG) in a heat exchanger .

Preferably, the working fluid of the closed gas cycle is argon. As regards step ii) of generating electrical energy, this is preferably performed by a generator (Gl) connected to the turbine (T2) of the closed gas cycle.

Furthermore, such a step ii) is performed after step i) of acquiring heat and before step iii) of transferring thermal energy.

According to a preferred aspect of the invention, step i) described above of performing one or more heat acquisition steps by the working fluid of the closed gas cycle comprises a step A.

According to another aspect of the invention, step i) described above comprises a step A', as an alternative or in addition to step A.

Preferably, one or both said steps A and A' comprise the acquisition of thermal energy from a low temperature heat source.

Preferably, step A' comprises the acquisition of thermal energy from a high temperature heat source.

As described above, for the purposes of the present invention, the term "low temperature heat source" is intended to mean for example: ambient air, seawater, low temperature solar heating, exhausted heat of a low temperature thermo-dynamic cycle, process heat recoveries and/or low temperature machinery. It is understood that a low temperature source operates at temperatures lower than about 180°C and, preferably, lower than about 120°C.

For the purposes of the present invention, the term "high temperature heat source" is intended to mean for example: high temperature solar heating, exhausted heat of a high temperature thermodynamic cycle, discharge gas of a gas turbine or internal combustion engine, process heat recoveries and/or high temperature machinery .

It is understood that a high temperature source operates at temperatures higher than 180°C, preferably higher than 300°C and even more preferably higher than 400°C.

In a particularly preferred aspect of the present invention, step A is performed acquiring thermal energy from seawater.

In an alternative aspect, step A is performed as an alternative or in addition to the acquisition of thermal energy from tempered water heated by BOG after being compressed in the BOG compressor.

In another particularly preferred aspect of the present invention, step A' is performed acquiring thermal energy from the superheated water or from diathermic oil of a boiler circuit or from the fumes produced by a boiler.

As described above, step iii) comprises the transferring of thermal energy to the liquefied natural gas, which is thus regasified.

Such regasification, in particular, is performed in the heat exchanger (HE1) wherein the working fluid of the closed gas cycle operates the transferring of thermal energy.

In a particular aspect of the invention, the boiler of step A' is fed with a portion of the liquefied natural gas regasified in the heat exchanger (HE1) due to the transferring of heat operated by the working fluid of the closed gas cycle.

The process described above is preferably operated in a regasification line of the liquefied natural gas (LNG) modified according to the present invention as described above.

According to an alternative embodiment of the present invention, the process comprises further steps of:

2) actuating a heat pump (HP) by means of the steps of: a) implementing a first heat exchange between a refrigerating fluid and a first intermediate fluid (HPF1), wherein said intermediate fluid (HPF1) transfers thermal energy to said refrigerating fluid,

b) actuating a second heat exchange between said refrigerating fluid and a second intermediate fluid

(HPF2), wherein said refrigerating fluid transfers thermal energy to said second intermediate fluid (HPF2); and of

3) actuating a heat exchange between said second intermediate fluid (HPF2) and the liquefied natural gas (LNG) .

With reference to step 3), this is preferably actuated on a liquefied natural gas flow at least partially regasified in the first heat exchanger (HE1) .

According to a particularly preferred aspect of the process of the invention, the heat pump actuated in step 2) is fed by the electrical energy produced in step ii) and, in particular, by the generator Gl connected to the turbine T2.

In particular, the pumps for circulating refrigerating fluid will be fed.

In a further object, a regasification terminal is described comprising one or more regasification lines of liquefied natural gas (LNG) .

In particular, each regasification line is the line described above according to the present invention. A regasification terminal is meant as a plant and generally comprises common structures represented by:

- liquefied natural gas storage tank,

compression section comprising cryogenic pumps; generally, this is a low pressure pump (which consumes about 400 kWe) and a high pressure pump (which consumes about 1300 kWe) ,

- boil-off gas compressor (BOG compressor) ,

- connection to the outer network for electrical energy supply, when available, or an electrical generating unit as, for example, a gas turbine or internal combustion engine,

- vaporization section of liquefied gas for example by Submerged Combustion Vaporization technology or Open Rack Vaporizer with the air supply circuit thereof and relative compressor,

- and one or more traditional regasification lines and at least one according to the by-pass configuration described above, in order to satisfy the different requirements and to allow a good flexibility of the plant .

In an aspect of the invention, the terminal comprises from 2, 3, 4, 5 or 6 lines, preferably 4.

The different regasification lines operate in parallel . Such a structure therefore allows the adaptation of already existing plants with the technology proposed by the present invention (revamping) .

For the purposes of the present invention, a new embodiment of a regasification terminal may comprise one or more regasification lines according to the by-pass configuration described above, therefore without a "traditional" vaporization section, for example of the SCV type.

For plant technical requirements, it cannot be excluded that some elements of single circuits are common to more regasification lines.

The arrangement of an independent closed gas cycle for each line, in particular, allows modifying the efficiency of heat exchange within each line, thus allowing a wide working flexibility.

The possibility of realizing a plant comprising different regasification lines therefore allows actuating the process of the present invention in an independent way, simultaneously or not, in each regasification line, with clear advantages in terms of flexibility .

From the foregoing description, the person skilled in the art may understand the numerous advantages provided by the present invention. First of all, the advantage in terms of energy is significant, which achieves 11% and also 37% in the configuration which provides the use of the heat pump with seawater.

It should not be underestimated that the described process allows working with low temperature boilers of about 120-180°C while covering the electrical requirements of a gasification line and using a compression ratio of 2-3, thus limiting the number of stages of the compressor and of the turbine.

Furthermore, in the case of reduced regasification load, the flow rate of the circulating working fluid of the closed gas cycle may be regulated by an outer tank which operates at an intermediate pressure between drawing and delivering to the compressor; the closed gas cycle, therefore, may be regulated without decreasing the efficiency of the system.

The described technology allows working also in an energy by-pass configuration, in the presence of any disconnection of the closed gas cycle due to technical or maintenance problems.

The same energy by-pass configuration allows regulating the electrical and thermal loads of the plant without stopping the production, exploiting the electrical energy from the outer network for regasifying, or operating with the described modular system, withdrawing energy from the other lines in conditions of excess electrical production (electrical surplus) and avoiding the use of the outer network.

The same energy by-pass configuration allows providing electrical energy to the plant during the maintenance and/or mismanagement of the conventional regasification lines, thus operating on a fraction of the LNG flow rate.

Furthermore, the process parameters allow using constructively simple and readily available equipment, among the others requiring a conventional metallurgy; the whole, therefore, leads to a reduction of manufacturing costs of the plant.

The working fluid of the closed gas cycle used by the objects of the present invention is a monatomic gas.

The use of a monatomic gas allows the use of simpler turbomachinery with respect to those with polyatomic gas, wherein by simpler machines it is meant machines with little variable meridian profile.

In particular, the use of argon, besides the benefits of a monatomic gas, also allows the possibility to exploit the positive effects of real gas in proximity of the saturation curve, that is the compression work is less than that of a perfect gas; another benefit of argon is having a high molecular weight (40 kg/kmol), which allows having low enthalpy shifts and making turbomachinery with few stages and little mechanically stressed since they have low rotation velocity with possibility of direct coupling to an electrical generator .

It should also not be forgotten that it is chemically inert, it is non-flammable and, finally, it is widely available at low cost.

Furthermore, the use of argon makes the designing the turbomachinery and the sizing thereof on the basis of preliminary calculations easier.

The process entirely closes the electrical balance of a regasification line, of a fraction of the electrical power of the entire plant or of the entire regasification plant.

On the other hand, with respect to the specific technologies there is no thermal power consumption as in the SCV, and an efficiency of the cycle coupled to the regasification is achieved, expressed in terms of sum of the electrical power and of the thermal power for the regasification compared to the total heat inlet to the cycle, close to one, the fuel gas consumption is reduced with an advantage greater than 40% (Fuel Gas Saving - FGS= gas cycle consumption-SCV consumption) /SCV consumption) and, finally, a reduction of 40% of CO2 emissions .

Compared to the Open Rack Vaporizer, the present invention allows exploiting seawater even in conditions which would prevent the use of the ORV, as for example seawater temperature lower than 5°C and when the size for small LNG flow rates are not available; furthermore, it is less necessary to chemically treat the seawater and to pump it to overcome the difference in level due to the height of the panels and suppliers for equipment to be used are widely available and easy to find.

The embodiment which provides the use of ambient air in the exchanger HE3 through the air heating technology, allows improving the efficiency of the turbine due to the blowing of cooled air, due to the transferring of heat to the closed gas cycle, to the turbine itself and to avoid in this way the de-rating of the power.

Such an advantage is significant especially in cases wherein the ambient air temperature is already high (warm countries) and is also found in cases wherein the gas turbine covers part of the electrical load (e.g. plant base load) and is not integrated with the closed gas cycle. The embodiment which comprises the use of the BOG circuit has the particular advantage of carrying out a pre-cooling of the BOG before entering the BOG recondenser .

Furthermore, it allows further heating the working fluid and without the use of fuel.

It is also possible to gradually introduce the heat available after every BOG compression stage, in the case of polyphase compression, into the closed gas cycle, thus obtaining a gradual very efficient heating.

The embodiment of the invention which comprises the use of a heat pump offers further advantages.

First of all, a reduction of fuel gas consumption is obtain with respect to the SCV technology, with an advantage (expressed in terms of fuel gas saving (FGS)=(gas cycle consumption -SCV consumption) /SCV consumption) ) up to 35% in the case of the closed gas cycle integrated with a heat pump.

Furthermore, the heat pump is efficient, having coefficient of performance (COP) - which expresses the thermal power transferred to regasify LNG and the (electrical) power spent to transfer energy from the seawater to LNG to be regasified - up to 15.

Moreover, the heat pump works between seawater temperature in the interval 3°C - 12°C (and over) and temperature outlet from the exchanger HE4 up to 10°C; this allows achieving very high COP of the heat pump (in such a configuration, the heat pump operates as a chiller) .

Undoubtedly, the installation of the heat pump is flexible, which may be placed in proximity of the sea or in proximity of the regasification plant; such flexibility results in the possibility of optimizing the path seawater pipes, according to the specificity of the application .

The person skilled in the art may further easily understand how the technology described above may be applied not only to the construction of new regasification lines or plants, but also to the modification of existing plants (revamping) .

The regasification terminal described by the present invention allows satisfying several needs, such as, the need to adapt the plant flow rates to the needs of regasified or stored LNG and, on the contrary, to adapt the operation of the plant to any reduction of the LNG flow, technical requirements connected for example, to the routine and special maintenance of one or more lines, due to the undisputed management flexibility. In addition to what is described above, it is noted that the invention may be applied to base load and small scale plant tubes.

Moreover, it should be noted that the present invention is described in particular in relation to the regasification of liquefied natural gas (LNG) , but the regasification line, the regasification terminal and the regasification process herein described are equally applicable for the regasification or vaporization of other liquefied fluids stored at low temperatures (lower than about 0 °C) or at cryogenic temperatures (lower than -45 °C) .

For example, the present invention will find application for the regasification or vaporization of also other liquefied gases, such as air, nitrogen, hydrocarbon compounds, e.g. alkanes, such as for example propane and butane, or alkenes, such as for example ethylene, propylene or liquefied natural gas (LNG) , hydrogen .

Furthermore, the invention may be applied using as a cold well not a fluid to be regasified (nitrogen, hydrogen and other above gases) but also a liquid or solid cryogenic storage. On the other hand, in another application, it can be used for forming gaseous cryogenic storage, liquid or solid .

Claims

1. A regasification line for a liquefied gas comprising a closed gas cycle section, which operates with a working fluid, and which comprises a first heat exchanger (HE1), wherein the heat of the working fluid is transferred to the liquefied gas for its regasification, and a turbine (T2) for generating electrical current by means of said working fluid, said line further comprising a second heat exchanger (HE2), which is part of a first intermediate fluid circuit, and wherein said first intermediate fluid transfers heat to said working fluid.

2. A regasification line for a liquefied gas according to the preceding claim further comprising a third heat exchanger (HE3) which is part of a second intermediate fluid circuit, and wherein said second intermediate fluid transfers heat to said working fluid.

3. A regasification line for a liquefied gas according to the preceding claim 1 or 2, wherein said first intermediate fluid circuit is a boiler circuit or a circuit which operates with the fumes produced by the boiler of the boiler circuit.

4. A regasification line for a liquefied gas according to the preceding claim 1 or 2, wherein said second intermediate fluid circuit is a seawater circuit.

5. A regasification line for a liquefied gas according to any one of the preceding claims, wherein the cooling of the boiler water and the heating of the working fluid of the closed gas cycle output from the first heat exchanger (HE1) are performed in the second heat exchanger (HE2) .

6 . A regasification line for a liquefied gas according to any one of the preceding claims, wherein the cooling of the boiler water and the heating of the working fluid of the closed gas cycle output from the third heat exchanger (HE3) are performed in the second heat exchanger (HE2) .

7. A regasification line for a liquefied gas according to any one of the preceding claims from 2 to 6, wherein in the third heat exchanger (HE3) it is performed the cooling of the seawater and the heating of the working fluid of the closed gas cycle output from the heat exchanger (HE1) for regasifying the liquefied gas with said working fluid.

8. A regasification line for a liquefied gas according to any one of claims from 3 to 7, wherein the first intermediate fluid outlet from the exchanger HE2 is sent into the boiler of the boiler circuit for the heat exchange with the fumes produced by said boiler.

9 . A regasification line for a liquefied gas according to any one of the preceding claims, wherein said closed gas cycle turbine (T2) is fed with the working fluid of the heated closed gas cycle output from the second heat exchanger (HE2) .

10. A regasification line for a liquefied gas according to claim 8, wherein said turbine (T2) of the closed gas cycle is fed with the working fluid of the heated closed gas cycle in output from the boiler of the boiler circuit .

11. A regasification line for a liquefied gas according to any one of the preceding claims, wherein said working fluid of the closed gas cycle is selected from the group comprising: air, nitrogen, helium, argon, and is preferably argon.

12. A regasification line for a liquefied gas according to any one of the preceding claims, wherein the boiler circuit comprises a boiler fed with a portion of regasified gas output from the first heat exchanger (HE1) in which the heat exchange between the closed gas cycle working fluid and the liquefied gas is implemented .

13. A regasification line for a liquefied gas according to any one of the preceding claims, further comprising a heat pump (HP), which comprises:

- a refrigerating fluid circuit,

- a first heat exchanger of the heat pump (CPC) for the heat exchange between said refrigerating fluid and a first intermediate fluid of the heat pump (HPF1) and a second heat exchanger of the heat pump (VPC) , for the heat exchange between said refrigerating fluid and a second intermediate fluid of the heat pump (HPF2), and

- a further heat exchanger (HE4) for the heat exchange between said second intermediate fluid (HPF2) and the liquefied gas.

14. A regasification line for a liquefied gas according to the preceding claim, wherein said heat pump is fed by a generator (Gl) connected to the turbine (T2) of the closed gas cycle.

15. A regasification line for a liquefied gas according to any one of the preceding claims from 4 to 14, wherein said second intermediate fluid circuit is replaced or added to a BOG circuit which comprises a heat exchanger HE5 wherein a heat exchange between the seawater and the BOG occurs .

16. A regasification line for a liquefied gas according to any one of the preceding claims, wherein said liquefied gas to be regasified is selected from the group comprising for example: air, nitrogen, hydrocarbon compounds, e.g. alkanes, such as for example propane and butane, or alkenes, such as for example ethylene, propylene or liquefied natural gas (LNG) , hydrogen, and is preferably liquefied natural gas (LNG) .

17. A regasification terminal for a liquefied gas, comprising one or more regasification lines according to any one of the preceding claims.

18. The regasification terminal for a liquefied gas according to the preceding claim, wherein said regasification lines are in parallel.

19. The regasification terminal for a liquefied gas according to the preceding claim 17 or 18, further comprising a vaporization section of the Submerged Combustion Vaporizer (SCV) or Open Rack Vaporizer type.

20. A process for generating thermal energy and electrical energy in a regasification line of a liquefied gas comprising the steps of:

1) operating a closed gas cycle with a working fluid comprising :

i) one or more steps of acquiring thermal energy from part of said working fluid,

ii) a step of generating electrical energy by using said closed gas cycle working fluid, and iii) a step of transferring thermal energy from said working fluid to a liquefied gas in a first heat exchanger (HE1) .

21. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to the preceding claim, wherein said step i) comprises a step (step A) of acquiring thermal energy from seawater or from ambient air.

22. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to claim 20 or 21, wherein said step i) comprises a step (step A') of acquiring thermal energy from superheated water or from diathermic boiler oil .

23. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to the preceding claim, wherein said step A' ) is either alternative or in addition to said step A) .

24. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to any one of the preceding claims from 20 to 23, further comprising the steps:

2) actuating a heat pump (HP) by means of the steps of: a) implementing a first heat exchange between a refrigerating fluid and a first intermediate fluid of the heat pump (HPF1), wherein said first intermediate fluid (HPF1) transfers heat to said refrigerating liquid,

b) performing a second heat exchange between said refrigerating fluid and a second intermediate fluid of the heat pump (HPF2), wherein said refrigerating fluid transfers heat to said second intermediate fluid (HPF2); and the step of:

3) implementing a heat exchange between said second intermediate fluid (HPF2) and the liquefied gas.

25. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to the preceding claim, wherein the liquefied gas of step 3) is the partially regasified liquefied gas in the first heat exchanger (HE1) .

26. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to any one of the preceding claims from 20 to 25, comprising the step of supplying said heat pump (HP) with the electrical energy produced in step ii) .

27. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to any one of the preceding claims from 20 to 26, characterized in that said boiler is fed with a portion of the regasified gas according to step iii ) .

28. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to any one of the preceding claims from 20 to 27, characterized in that said working fluid is selected from the group comprising: argon, nitrogen, helium, air, and is preferably argon.

29. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to any one of the preceding claims from 20 to 28, which is performed independently on different regasification lines of a regasification terminal .

30. The process for generating thermal energy and electrical energy in a regasification line of a liquefied gas according to any one of the preceding claims from 20 to 29, wherein said liquefied gas is chosen from the group comprising for example: air, nitrogen, hydrocarbon compounds, e.g. alkanes, such as for example propane and butane, or alkenes, such as for example ethylene, propylene or liquefied natural gas (LNG) , and is preferably liquefied natural gas (LNG) .

31. The process according to any one of the preceding claims from 20 to 30, for forming a gaseous, liquid or solid cryogenic storage.