DESCRIPTION

"PROCESS FOR GENERATING ELECTRIC AND THERMAL ENERGY IN A POWER CYCLE WHICH USES A FLUID OBTAINED FROM MIXING LNG

AND LPG"

Technical field of the invention

The present invention is applied in the field of the regasification of liquefied natural gas (LNG) .

Background art

Technologies are known for the regasification of liquefied natural gas (LNG) .

Liquefied natural gas is a natural gas mixture mainly consisting of methane, and to a lesser extent, of other light hydrocarbons such as, for example, ethane, propane, iso-butane, n-butane, pentane and nitrogen, which mixture is converted from the gaseous state (which it is in at ambient temperature) to the liquid state, at about -160°C, to allow the transport thereof.

Liquefaction plants are located close to natural gas production sites while regasification plants (or "regasification terminals" are located close to the users .

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

It is common for each regasification terminal to comprise several regasification lines to meet the liquefied natural gas load or requests, and also for reasons of flexibility or of technical needs (for example, for servicing a line) .

Regasification technologies normally involve liquefied natural gas stored in drums at atmospheric pressure at the temperature of -160°C and provide the steps of compressing the gas up to about 70-80 bar, vaporizing and overheating up to about 3°C.

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

Among these, the open rack vaporizer (ORV) , used in about 70% of the regasification terminals, and the submerged combustion vaporizer (SCV) are the most used, individually or combined with one another.

Open Rack Vaporizer (ORV)

This technology provides for the liquid natural gas (about 70-80 bar and at the temperature of -160°C) to be caused to flow upward inside aluminum pipes placed side- by-side to form panels; the vaporization occurs progressively as the fluid proceeds.

The heat carrier is the seawater which flowing downward on the outer surface of the pipes, provides the heat required for the vaporization due to a difference in temperature.

The heat exchange is particularly optimized by the design of the profile and the surface roughness of the pipes, which obtain a homogeneous distribution of the thin seawater film over the panel.

Submerged Combustion Vaporizer (SCV)

Such a technology exploits a demineralized water bath heated by an immersed flame burner, as heat carrier; in particular, fuel gas (FG) is burned in the combustion section and the fumes generated pass through a coil of perforated pipes from which combusted gas bubbles are output, which heat the water bath, thus also transferring the condensation heat.

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

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

The exhausted fumes instead are exhausted from the SCV exhaust stack.

With particular reference to the submerged combustion vaporizer (SCV) , such a technology results in a fuel gas consumption equal to about 1.5% of the gas produced, it produces carbon dioxide which lowers the pH of the water bath, requiring treatments with caustic soda, and causes a production of CO2 of about 50,000 t/year to regasify 139 t/h.

Instead with regards to the open rack vaporizers, such a technology may partly cause the freezing of the seawater in the outer part of the pipes, especially in the sections in which the LNG is colder; moreover: i) it may be exploited in the geographical regions and/or seasons in which the temperature of the seawater is at least 5 to 9°C, mainly depicted by sub-tropical areas, ii) the seawater is to be treated beforehand to eliminate or reduce the content of heavy metals which could corrode the zinc coating of the pipes, iii) it results in a consumption of electric energy to operate the seawater pumps which is to exceed a geodetic difference of level equal to the development in height of the ORV, with the additional consumption of 1.2 MWe per regasification line with respect to the SCV technology (total plant power equal to 24.2 MWe), iv) lastly, the technology is rather complex and is available from a limited number of suppliers and at a limited number of sizes.

Therefore, the conventional technologies do not generally allow the electric energy required for the plant to be generated, and result in the loss of a large amount of energy in the form of cold energy.

Organic Rankine Cycle

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

Such cycles provide the possibility of selecting the working fluid among tens of possible fluids and allow efficient thermodynamic cycles to be achieved, also for low source temperatures and for small heat resources.

Moreover, the selection of a low boiling fluid allows a condensing cycle to be achieved at cryogenic temperatures without incurring freezing problems or too hard vacuum degrees.

American Patent Application US 2013/0160486 (Ormat Technologies Inc.) describes single- or two-level pressure cycles which operate with a single fluid, with and without heat exchanges within the cycle (regenerations) on both levels; in one embodiment, two cascading cycles are operated with two different fluids, in which the heat of a first cycle is used only for evaporating the second fluid and the liquefied natural gas is vaporized with the heat alone released by the cycle of the second fluid.

As is shown in figures 2 and 6 of the above- mentioned patent, the cycles described by Ormat operate using a pure substance as engine fluid; indeed, the vaporization/condensation curves indicate that the temperature remains constant and the substances mentioned as examples are all pure substances.

This results in a thermodynamic disadvantage which translates into a smaller power extractable from the cycle; an attempt is made in the configurations proposed in figures 7, 7A, 7D, 7E to obviate such a problem by extracting a portion of the working fluid from the expander so that the heating of the LNG may be adjusted on two heat levels, close to the LNG heating curve.

This operation has the effect of increasing the extractable power from the ORC but becomes unbalanced and complicates the expander or in order to obviate such a problem, it uses two separate expanders for generating two thermal levels required for approaching the ORC engine fluid condensation curve and the LNG vaporization curve .

Prior art document JP 2016 148001 describes a process for controlling the calorific value of the so- called city gas (a gaseous fuel) in order to reduce the evaporation and the formation of boil off gas (BOG) ; for this purpose, an amount of liquefied petroleum gas (LPG) is cooled and added to the liquefied natural gas (LNG) . Prior art document JP S57 164183 describes a method for continuously preparing an engine fluid to be used in a Rankine Power Generating Cycle from an ethane-enriched current, obtained by distilling the liquefied natural gas (LNG) to which propane and/or commercial butane and pentanes or the like are added as corrective additives.

Prior art document JP H05271671 describes a method for continuously purifying liquefied petroleum gas (LPG) by means of inverse osmosis within the scope of a method for correcting the calorific value of the city fuel gas (gaseous fuel) by means of mixing small amounts of liquefied petroleum gas (LPG) with liquefied natural gas (LNG) .

Prior art document CN 203 240278 describes a continuous method for mixing liquefied natural gas and liquefied petroleum gas in order to increase the calorific value of a fuel mixture.

Prior art document JP 2008 115842 describes a method for reducing the production of particulate in a diesel- powered diesel engine to which an amount of water is added in order to promote the catalytic combustion of the carbon particles.

Prior art document US 4,444,015 describes a method for generating power by means of two Rankine Cascade Cycles, which operates between a heat source and a cold well represented by LNG, which vaporizes; the use is described of a generic engine fluid represented by a mixture comprising nitrogen, hydrogen and hydrocarbons with a number of carbon atoms from 1 to 6 or equivalent halogenated atoms .

Therefore, the conventional technologies do not generally allow the electric energy required for the plant to be generated, and result in the loss of a large amount of energy in the form of cold energy.

Summary of the invention

The authors of the present invention have surprisingly found that a mixture of liquefied natural gas (LNG) and liquefied petroleum gas (LPG) may be used as working fluid in a power generating cycle (PGC) , which residual heat may be used for regasifying liquefied natural gas (LNG) .

Object of the invention

In a first object, it is described a process for preparing a working fluid (IMR) represented by a mixture of liquefied natural gas (LNG) and liquefied petroleum gas (LPG) .

The working fluid (IMR) comprising liquefied natural gas (LNG) and liquefied petroleum gas (LPG) obtained by such a process represents a second object of the present invention . In a third object it is described a process for regasifying liquefied natural gas (LNG) which uses the working fluid (IMR) of the invention.

In a fourth object it is described a liquefied natural gas (LNG) regasification line which uses the working fluid (IMR) of the invention.

According to a fifth object, the working fluid (IMR) which is used in the regasification process of liquefied natural gas (LNG) is used in a power cycle.

In a further object it is described a power generating cycle which uses the working fluid (IMR) of the invention.

Brief description of the drawings

Figure 1 shows the general simplified diagram of a regasification line according to the present invention, better detailed in figure 2;

Figure 3 shows an LNG regasification line on a small scale, with examples of heat sources which can be used independently of one another;

Figure 4 shows an alternative embodiment of the present invention, in which the heat of the fumes generated by a gas turbine, is recovered;

Figure 5 shows an embodiment in which a post combustor of the fumes of the gas turbine is added; Figure 6 shows a diagram of a regasification line according to another embodiment of the present invention, in the case of unavailability of the IMR turbo-expander;

Figure 7 shows a regasification line according to an embodiment of the present invention, which also uses the combustion air of the turbine as low temperature heat sources ;

Figure 8 shows a regasification line according to a further embodiment of the present invention, which uses a heat accumulator;

Figure 9 shows the vaporization curve of the LNG and the condensation curve of the IMR of the present invention;

Figure 10 shows the vaporization curve of various LNGs and the condensation curves of various IMRs according to the present invention as the molecular weight (molecular average) varies, where the chemical composition of the LNG remains constant;

Figure 11 shows a depiction of a thermodynamic cycle for IMR units according to the present invention;

Figure 12 shows the detail of an LPG cryogenic filter .

Detailed description of the invention According to a first object of the present invention, it is described a process for preparing a working fluid (hereinafter indicated as IMR) .

Said working fluid is a liquid mixture.

In particular, such a fluid is obtained by mixing commercial liquefied petroleum gas (LPG) and commercial liquefied natural gas (LNG) .

The term "commercial liquefied petroleum gas (LPG) " means a fuel, the features of which are well-defined, for the usual uses in the civil and industrial field, having the following properties:

vapor pressure at 100°F;

minimum temperature at which 95% in volume of a hypothetical sample is vaporized at atmospheric pressure, possibly by heating according to a precise methodology;

the percentage molar content of molecules having a number of carbon atoms greater than 4; for the purposes of the present invention, it indeed also contains hydrocarbons with 7 or >7 carbon atoms.

It is known how liquefied petroleum gases (LPG) are a cut of the crude oil and how they are separated from it due to refining in a topping column.

Various refining processes produce liquefied petroleum gas (LPG) ; for example, cracking produces liquefied petroleum gas (LPG) as a by-product.

For the purposes of the present invention, liquefied petroleum gas (LPG) preferably is defined as a combustible fluid which features fall within the limits defined in the following table:

(1) maximum temperature at which 95% evaporation of the volume of the sample being examined is obtained at atmospheric pressure

(2) content of molecules with at least 5 carbon atoms The term "commercial liquefied natural gas (LNG) " means a hydrocarbon fluid mainly in liquid state obtained by condensing natural gas at a sufficiently low temperature to keep it liquid also at atmospheric pressure .

It is known that natural gas mainly consists of methane and light hydrocarbons which rarely have a number of carbon atoms >5; it may also contain nitrogen in variable proportions.

For the purposes of the present invention, "IMR" is defined as any mixture of liquefied natural gas (LNG) and liquefied petroleum gas (LPG) obtained by mixing 1 volume of liquefied natural gas (LNG) with an amount of liquefied petroleum gas (LPG) between 0.25 and 1.2 volumes of liquefied natural gas (LNG) .

More in detail, the process of the present invention for preparing the working fluid comprises a step I) in which a first amount (101) of liquefied natural gas (LNG) from a drum (510) thereof is prepared in a first drum of the working fluid (530); practically, a suitable amount of a flow of liquefied natural gas (LNG) is loaded into a drum (530, IMR drum) .

In a step II), a suitable first amount (210) (or a flow) of liquefied petroleum gas (LPG) is added.

The contact between the liquefied natural gas (LNG) and the liquefied petroleum gas (LPG) with the formation of the IMR therefore occurs in said first drum (530, IMR drum) .

For the purposes of the present invention, the liquefied petroleum gas (LPG) is added to the liquefied natural gas (LNG) at ambient temperature.

In a step III), any volatile compounds are allowed to move away by evaporation.

Such an evaporation is promoted by the liquefied petroleum gas (LPG) being added to the liquefied natural gas (LNG) at ambient temperature.

In a step IV) , the pressure is reduced, if required.

In a preferred aspect, the pressure is decreased down to about 2 to 20 bar.

In a possible step V), one or more of the steps II), III) or IV) are repeated up to reaching the condensation temperature of the fluid, as is further detailed below.

In particular, in step I), the volume of liquefied natural gas (LNG) may be determined by those skilled in the art according to the size of a possible power cycle using the IMR as working fluid.

With regards to the liquefied natural gas (LNG) , an amount (100) which is sent to the regasification section (590), possibly after a high pressure pumping step by means of a pump (600), originates from the drum (510) in which it is stored.

After the pumping step, a portion preferably is separated of said first amount of liquefied natural gas (101) which is sent to the first drum (530, IMR drum) for preparing the working fluid, as described above.

The addition of step II) and the subsequent mixing of the liquefied petroleum gas (LPG) and liquefied natural gas (LNG) generate the heating of the IMR obtained and contained in the IMR drum; this causes the most volatile chemical compounds therein contained to move away by evaporation (step III), thus increasing the pressure in the IMR drum.

This advantageously allows reaching the pressure required in the first drum (530, IMR drum) for the purposes of operating the power cycle of which it is a part .

If the pressure is excessive, the excess vapors may be moved away in step IV) from the first drum (IMR drum) by means of a vent valve (not depicted in the drawing) .

For the purposes of the present invention, the mixing of step II) occurs by adding and without the need for any mixing equipment.

According to a particular aspect of the present invention, the total amount of liquefied petroleum gas (LPG) to be added to the liquefied natural gas (LNG) to obtain the working fluid varies within the above- described limits.

The final goal is to reach a given liquefaction point .

The final added amount may be determined by optimizing the process; in particular, it may be optimized on the basis of: performance of the regasification process of the liquefied natural gas (LNG) ; and/or

performance of the possible power generating cycle which uses the IMR as working fluid.

For example, an arbitrary volume (within the above- mentioned limits) of liquefied petroleum gas (LPG) may be added to a volume of liquefied natural gas (LNG) which is adequate to the size of the power generating cycle and subsequent circulating of the IMR thus obtained in the power cycle equipment.

By following the performance obtained, the composition of the IMR may be modified to have the desired performance.

Alternatively, the heat exchange curves of LNG may be determined on a laboratory scale, and of various IMR samples prepared by mixing a set volume of liquefied natural gas (LNG) with a volume of liquefied petroleum gas (LPG) (within the above-mentioned limits) in the possible field of IMR variability.

From a practical viewpoint, there is a need to fix the operating pressures of liquefied natural gas (LNG) and IMR, and also the related flow rates.

Once the mixing ratios most satisfying the plant engineering performance are determined, the process may be transposed onto industrial scale by then carrying out the required modifications.

As an alternative to the two methodologies disclosed above, should the chemical analyses of the liquefied natural gas (LNG) and of the liquefied petroleum gas (LPG) to be used in the specific plant and in the specific period desired be available, the suitable simulations may be carried out.

The first two methodologies allow the pressure and the temperature that the IMR may have in the IMR drum to be calculated, thus allowing the IMR to be prepared using a pressure indicator and temperature sensor rather than measuring volumes.

The process described by the present invention preferably is a batch type process.

According to an aspect of the present invention, in order to avoid the solidification of components such as water and heavy hydrocarbons possibly (but not necessarily) in the liquefied petroleum gas (LPG) , a purification step of the liquefied petroleum gas (LPG) may precede the mixing of the liquefied petroleum gas (LPG) with the liquefied natural gas (LNG) .

Such a step may be carried out by well-known methodologies, such as the use of molecular sieves for separating water and hydrocarbons. Alternatively, a cryogenic filter like that shown in figure 12, may be used.

The cryogenic filter shown in figure 12 consists of an external exchanger (620) at the first drum (530, IMR drum) and an internal coil (610) at the first drum (530, IMR drum) , and also a possible other solids filter (630) .

In particular, the external exchanger (620) is of the shell and tube condenser type.

In a step 1), a first purification amount (200) of liquefied petroleum gas (LPG) from the drum (520) of the liquefied petroleum gas is supplied to the shell side of the external exchanger (620) .

Thereby, by meeting a cold fluid flowing in the pipes, the liquefied petroleum gas (LPG) cools and allows the removal of the undesired components for solidification on the cold surface of the pipes, thus giving rise to a second purification amount (201) of liquefied petroleum gas.

In a successive step 2), the second purification amount (201) of liquefied petroleum gas (LPG) obtained output from the shell side is sent to the internal coil (610) to the first drum (IMR drum) .

Thereby, the liquefied petroleum gas (LPG) exchanges heat with the working fluid which implements the cooling thereof, thus obtaining a third purification (202) amount of the liquefied petroleum gas.

In a step 3), said third purification amount (202) of the liquefied petroleum gas (LPG) , output from the internal coil (610), is supplied to the pipes side in the external exchanger (620) where it constitutes the cold fluid which cools the above-mentioned first purification amount (200) of liquefied petroleum gas

(LPG) flowing in the shell side, thus obtaining a fourth purification amount (203) of liquefied petroleum gas.

A step 4) may possibly also be carried out, wherein said fourth amount (203) of liquefied petroleum gas

(LPG) output from the pipes side of the external exchanger (620) is further filtered in a solids filter (630) .

The first amount (210) of liquefied petroleum gas (LPG) is obtained from step 3) or 4), which is sent to the first drum ( IMR drum) for preparing the working fluid .

Advantageously, such a first amount (210) of liquefied petroleum gas (LPG) which is sent to the first drum of the working fluid (530, IMR drum) for preparing the working fluid has a reduced content of heavy, potentially solidifiable components.

In a preferred aspect of the invention, such an amount sent to the first drum (530, IMR drum) has a reduced content of pentanes.

In a preferred aspect of the invention, such a content is less than 0.1%.

From the above, it is apparent that the liquefied natural gas (LNG) and the liquefied petroleum gas (LPG) involved in purifying the liquefied petroleum gas (LPG) are the same used for preparing the working fluid (IMR), and therefore there is no need for external fluids.

The working fluid (IMR) obtained according to the above-described process represents a further object of the present invention.

In an aspect of the invention, such a working fluid (IMR) may have cooling properties (i.e., have a low liquefaction point at standard pressure) according to the temperature of the liquid with which heat is exchanged .

The present invention also describes a plant for preparing the above-described working fluid.

Such a plant comprises a first drum (530) for adding an amount (210) of liquefied petroleum gas to an amount (101) of liquefied natural gas so as to generate said working fluid (IMR), a second drum (510) for said liquefied natural gas and a third drum (520) for said liquefied petroleum gas. In an aspect of the invention, the plant further comprises a cryogenic filter (630) for purifying the liquefied petroleum gas (LPG) , as described above.

Obviously, the plant comprises ducts, pipes and valves .

According to a third object, the present invention describes a regasification line for liquefied natural gas (LNG) which comprises a vaporization section (590) of the liquefied natural gas inside of which a heat exchange occurs between the liquefied natural gas (LNG) and the working fluid of the present invention.

Although reference is particularly made to the regasification of liquefied natural gas (LNG) in the present invention, the regasification line, the regasification terminal and the regasification process hereinbelow described are equally applicable for regasifying or vaporizing other liquefied fluids stored at low temperatures (less than about 0°C) or at cryogenic temperatures (less than -45°C) .

Thus, the present invention is also applied to regasify or vaporize a liquefied gas selected from the group which comprises for example: air, nitrogen, hydrocarbon compounds such as alkanes, among which for example, propane and butane, or alkenes, among which for example, ethylene or propylene. In the following description, the term "liquefied gas" means a fluid having a prevalent liquid composition .

The term "regasification line" means that portion of plant which comprises the structures, equipment, machinery and the systems for regasifying the liquefied natural gas (LNG) .

Such structures, equipment, machinery and systems particularly originate from the second drum (510) in which the liquefied natural gas (LNG) is stored and the third drum (520) in which the liquefied petroleum gas is stored, and end with the introduction point of the regasified liquefied natural gas (LNG) into the distribution network of the gas itself.

In more detail, the liquefied natural gas (LNG) in the drum (510) is stored at atmospheric pressure and at a temperature of about -160°C;

in certain cases, for example for smaller plants, at a pressure between 3 bar g and 10 bar g and at a temperature between -150°C and -130°C.

The liquefied gas drum may be particularly located in a different place or structure from that of the regasification plant, which for example, could be onshore or offshore .

Once regasified in the regasification section, the natural gas may be introduced into the natural gas distribution network.

According to an aspect 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 reintroduction connection of the liquefied natural gas which was regasified in the base circuit for destination to the distribution network.

The drawing connection preferably is downstream of the cryogenic pumps and upstream of the vaporization bath .

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

an existing traditional regasification line, modified so as to integrate a natural gas regasification by-pass circuit (revamping) according to the present invention; and

a regasification line formed as main line of the line described by the present invention, for example for creating new plants. According to a fourth object of the invention, it is described a process for regasifying liquefied natural gas (LNG) comprising the step of carrying out a heat exchange between said liquefied natural gas (LNG) and the working fluid described by the present invention.

Such a working fluid may have cooling properties as detailed above.

For such purposes, performance constraints consist in obtaining a liquefied natural gas (LNG) which was regasified at the temperature and pressure required for operating the plant and at which the IMR, output from the liquefied natural gas (LNG) vaporizer, is completely condensed, or perhaps undercooled (to avoid IMR leaks), so the process may be cyclical.

In particular, the regasification process of liquefied natural gas (LNG) comprises the step of carrying out a heat exchange between an amount (100) of liquefied natural gas and an amount (310) of working fluid in a vaporization section (590) of the liquefied natural gas .

The amount of natural gas (NG) obtained as an output from the regasification section (590) is introduced into the distribution network of the natural gas itself at the required pressure and temperature (normally about 70 bar and 3°C) . In an aspect of the invention, the amount (300) of IMR used for regasifying the liquefied natural gas (LNG) comes from the IMR drum (530) .

According to an alternative aspect of the present invention, the amount of IMR used for vaporizing the liquefied natural gas (LNG) is an amount (310) which comes from a power generating cycle.

According to a further object of the present invention, it is described a power generating cycle which uses the above-described working fluid.

More specifically, such a fluid is subjected to a series of steps in the generating cycle.

According to an aspect of the invention, the amount (310) of working fluid (IMR) used for regasifying the liquefied natural gas (LNG) is an amount obtained from a heat exchange step between an amount (410) of working fluid (IMR) obtained from the steps in a power generating cycle with an amount (300) of working fluid (IMR) input into the power generating cycle (after the output from the IMR drum) .

For the purposes of the present invention, such an amount (310) of working fluid is subjected to one or more of the following steps:

heat transfer, and/or

heat acquisition, and/or expansion in turbine (570) with production of electric and/or mechanical energy (by means of suitable generator)

An example of a possible power generating cycle according to the present invention is detailed hereinbelow, and particularly comprises:

engine fluid collection drum (530, IMR drum), one or more pumps for pumping the working fluid (20, IMR pump) ,

a turbo-expander (570) for generating mechanical and possibly electric energy from the expansion of the working fluid,

a high temperature heat exchanger (550) and a low temperature heat exchanger (540) for recovering heat by means of heat exchange between portions of working fluid at various temperatures,

possibly one or more recuperators for recovering heat by exploiting low or high temperature heat sources, such sources may be for example, exhausted gases from an internal combustion engine,

possibly one or more pumps for pumping the engine fluid (not shown in the drawings) .

The power generating cycle further comprises the hot side of the regasification section (590) of the liquefied natural gas (LNG) .

For the purposes of the present invention, the amount (310) of the working fluid used for regasifying the liquefied natural gas (LNG) is obtained by means of a process which comprises the steps of:

a) heating;

b) expansion in a turbine (570);

c) partial cooling.

In particular, a first amount (400) of said working fluid in the process is subjected to the steps of:

a) heating, thus obtaining a second amount (430) of heated working fluid;

b) expansion in a turbine (570) with the generation of mechanical energy, thus obtaining a third amount (440) of expanded working fluid;

c) partial cooling, thus obtaining a fourth amount (310) of partially cooled working fluid.

For the purposes of the present invention, said step a) comprises the steps:

al) in which said amount (400) of working fluid is heated in a high temperature recuperator (550), thus obtaining an amount (420) heated at a high temperature, and a step a2) of heating from a high temperature heat source (560), thus obtaining said second heated amount (430) of working fluid. In an aspect of the present invention, prior to step al), a step aO) may be carried out in which a first portion (401) of said amount of the working fluid is heated by means of a low temperature heat source (580), thus obtaining a second heated portion (402) .

Such a second heated portion (402) is then joined to the first amount (400) of working fluid, thus obtaining a further amount (403) of working fluid.

According to another aspect of the present invention, said step c) comprises the steps:

cl) in which said third amount (440) of expanded working fluid partially transfers heat to said first amount (400) of step al) in the high temperature recuperator (550), thus obtaining a fifth amount (410) of the heated working fluid, and

c2) in which said fifth amount (410) of the working fluid is partially cooled in a low temperature recuperator (540) by means of heat exchange with an amount (300) of the working fluid output from the drum (530), thus obtaining a second cooled amount (310) of working fluid output from the drum and the first amount (400) of heated working fluid.

As depicted in figure 1, the amount (101) of liquefied natural gas (LNG) in the drum (530, IMR drum) forms a mixture (IMR) with an amount (210) of liquefied petroleum gas from a drum (520) thereof, possibly after the purification step as described above.

An amount (300) of working fluid is sent, possibly by means of pumping with a pump (20), from the drum (530, IMR drum) to a low temperature recuperator (540) in which it acquires heat, thus giving rise to the first amount (400) of heated working fluid for the power generating cycle.

Such a heat exchange particularly occurs with an amount (410) of working fluid output from a high temperature recuperator (550) .

An amount of working fluid (310) leaves the low temperature recuperator (540), which amount is sent to the regasification section (590) of the liquefied natural gas from which an amount (320) of cooled working fluid exits, which is then sent back to the drum (530, IMR drum) thereof.

The working fluid (400) as the output from the low temperature recuperator (540) is sent to a high temperature recuperator (550) .

In a preferred aspect of the present invention, prior to entering the high temperature recuperator (550), a first portion (401) of the first amount of working fluid is heated by a low temperature heat source (580), thus obtaining a second heated portion (402), then is joined to the first amount (400) of working fluid, thus obtaining a further amount (403) of working fluid .

For the purposes of the present invention, a low temperature heat source may be the heat discarded by a radiator of a combustion engine, or the heat obtained from the second cooling of the exhausted gases of a turbine, possibly post-combusted, or the combined series of a first heat recovery, obtained from the pre-cooling of the combustion air of a turbine, and the second cooling of the exhausted gases of a turbine, possibly post-combusted (580' in figure 3) .

Alternatively, a boiler or one or more renewable sources may be used, also combined with one another, such as, for example: solar energy, air/water, geothermal energy, graphite heat accumulator or molten salt .

According to an embodiment of the present invention, shown for example in figure 7, also a second low temperature heat source (581) may be exploited in an additional step a0' ) .

In a particular embodiment of the invention, such a step a0' ) replaces step aO) .

In another embodiment of the invention, step a2) is carried out due to a low temperature heat source. Therefore, the first amount (400) or the further amount (403) of working fluid is sent to the high temperature recuperator (550) .

The amount (420) of the working fluid heated at a high temperature is obtained as the output from the high temperature recuperator (550) in which it is heated, which amount is further heated by means of the heat recovered from a high temperature heat source (560) .

According to an embodiment of the present invention, shown for example in figure 7, such a high temperature heat source may be replaced with a low temperature heat source (581) .

For the purposes of the present invention, a high temperature heat source is the heat of the fumes of a combustion engine, or the heat obtained from the first cooling of the exhausted gases of a turbine, possibly post-combusted, (560' in figure 3) or alternatively, a boiler or one or more renewable sources, also combined with one another, such as for example: solar energy, air/water, geothermal energy, graphite heat accumulator or molten salt (560 in figure 3) .

After the heating step by the high temperature heat source (560), the second amount (430) of heated working fluid is expanded in a turbine (570) to generate mechanical (and possibly electric) energy with partial cooling .

A third expanded amount (440) of working fluid is obtained output from the turbine (570), which third expanded amount is sent to the high temperature recuperator (550), inside of which it transfers part of the residual heat thereof in order to pre-heat the amount (400) or further amount (403) of the working fluid .

Thus, the fifth amount (410) of the working fluid thus cooled in the high temperature recuperator (550) is obtained, which fifth cooled amount is sent to the low temperature recuperator (540), inside of which it transfers part of the heat thereof in order to pre-heat the amount (300) of working fluid output from the drum (530, IMR drum) thereof, thus giving rise to the first amount (400) of working fluid intended for the high temperature recuperator (550) .

According to an aspect of the invention, a by-pass of the turbine (570) may be provided, which is useful for the start-up operations and possible operation in case of stopped turbine; it is worth noting that the turbine may be also only partially by-passed by means of the above-mentioned by-pass line, thus adjusting the temperature of the third expanded working amount (440) .

As described above, the amount of liquefied petroleum gas may be subjected to a filtering step prior to the introduction into the working fluid drum (530, IMR drum) .

For this purpose, as shown in figure 12, a first purification amount (200) of liquefied petroleum gas output from the second drum (520) is subjected to a cooling step by means of the passage in the shell side of an external exchanger (620) .

Thereby, possible solidifiable contaminants are deposited on the outer side of the pipes, which in turn are crossed by an amount of return liquefied petroleum gas (LPG) from the inner coil (610) to the first drum (530, IMR drum), where the temperature of the liquefied petroleum gas (LPG) further decreases by heat exchange with the liquefied natural gas (LNG) therein loaded at the beginning of the working fluid production process.

The second purification amount (201) of liquefied petroleum gas (LPG) as an output from the exchanger (620) crosses the internal coil (610) in the first drum (530, IMR drum), thus cooling.

The third purification amount (202) of liquefied petroleum gas thus obtained is sent to the exchanger (620) by the above-mentioned passage in the pipes of the tube bundle and the fourth purification amount (203) of the liquefied petroleum gas thus obtained then passes in a filter (630, LPGFS-LPG solids filter) to separate any solids carried over.

The operation thus carried out has the advantage of not dispersing the heat of the liquefied petroleum gas (LPG) , which serves to cause the light components in the liquefied natural gas (LNG) to evaporate.

It is worth noting that the coil (610) (cryogenic coil) in the first drum (530, IMR drum) may be used both for the present operation and to keep the working fluid cold, should it be crossed by a liquefied natural gas (LNG) flow.

EXAMPLE 1

The goal of Example 1 is to regasify an LNG flow rate equal to 6.7 t/h

The chemical analysis of the LNG at hand is prepared, herein indicated:

The object is achieved by means of the diagram of accompanying figure 3, in which a power generating cycle (PGC) according to a particular embodiment of the present invention and a regasification line are depicted .

The LPG is imported into the plant in order to generate the IMR, of which LPG the chemical laboratory results are available, with the following results:

The chemical analyses of the LNG and of the LPG being available, the IMR is determined according to the above- described methodology.

The LNG and IMR operating pressures in the LNG vaporizer are set.

The LNG pressure is unequivocally determined by the specific needs of the regasification line, which in the present example, requires introduction in natural gas (NG) network at 74.5 bar g.

With regards to the IMR pressure, it is strictly associated with the design pressure of the equipment forming the power generating cycle, in particular the power generating operating machine (turbo-expander) .

The optimal operating pressure of said machine is of 76.5 bar g and the optimal expansion ratio is about 7; once the losses of load are calculated, the pressure of the IMR output from the LNG vaporizer is 9.5 bar g.

The losses of load are applied to both sides of the LNG regasifier, up to a maximum of 0.5 bar.

Once the LNG and IMR pressures are known, the virtual IMR samples are prepared, obtained by mixing LNG at the storage temperature, possibly kept at the storage pressure also in the IMR drum, and LPG at ambient temperature .

The mixing process results in the formation of a series of IMR samples having different molecular weight.

The family of heat exchange curves are generated for the IMR samples to the LNG to be regasified, thus obtaining results which are similar to those shown in figure 10. The IMR sample which maximizes the energy performance in selected while limiting the exchange surface required for the regasifier within the technical-economic feasibility limits; in the case at hand, the IMR will have an average molar molecular weight equal to 30.55 u .m. a .

According to the calculations, such an IMR sample has a boiling temperature of -117.5°C at 9.5 bar g.

The IMR is prepared by adding LPG to LNG up to reaching the aforesaid temperature of -117.5°C at the pressure of 9.5 bar g .

Operatively, the operation of the diagram presented is the following: a cylinder engine generating the power of 1.55 MWe and the thermal input of which is equal to 4 MW, is the heat source of the PGC thus operating:

- PGC: the fluid "01" (IMR) with flow rate 7.8 t/h and temperature of -117.5°C is collected in the IMR drum and pumped at a pressure (maximum of the cycle) of 78.5 bar g, then is heated in the low temperature recuperator at the expense of the heat transferred from the IMR current "08" up to a temperature of -27.6°C; then, the IMR pre- heated current "03" comes into thermal contact with the radiator of the cylinder engine (thermal engine) where it receives 760 kW of thermal power and is heated up to 60°C, to then undergo a successive pre-heating in the high temperature recuperator at the expense of the IMR output from the expander "07". The current thus obtained "05" has a temperature of 135°C and is ready for the final heating in the exhaust gas recuperator, where it meets the exhausted gases of the cylinder engine and cools them down to a temperature of 148 °C; it is output "06" therefrom at a temperature of 280°C and a pressure of 76.5 bar g, to enter the IMR turbo-expander where it performs work, being output "07" at 11 bar g and 187.5°C. Then, the IMR transfers heat in the high temperature recuperator, where it pre-cools "08" down to 80°C; the final cooling to 8°C follows in the low temperature recuperator, a temperature adapted to keep a minimum approach which is not less than 5°C in the LNG regasifier/IMR condenser.

The LNG regasifier, here called LNG regasifier/IMR condenser, heats supercritical LNG from a temperature of -145°C to 3°C by operating in pure countercurrent with the IMR stream. The mechanical power generated by the IMR turbo expander is equal to 455 kW which, net of the energy used by the IMR pump and equal to 35 kW, provides an available power of 420 kW with respect to a thermal power of 900 kW recuperated from the combustion fumes; this corresponds to a mechanical efficiency of 46.7%, much greater than the mechanical efficiency of a diesel engine of equal size (about 35%) .

- 80% of the thermal input to the cylinder engine is recovered, both in the form of energy generated and of heat used for regasifying LNG.

With respect to the processes from the known art: an ethane cycle (the fluid which provides a greater efficiency for cycles with pure components) has: a) an efficiency of the PGC which decreases from 46.7% to 32.9% b) a net mechanical power recovered, from 420 kW to only 240 kW c) an overall efficiency (energy recovered/energy introduced) at 76%

- A further comparison using the same configuration of the PGC based on the same thermal levels and the same pressure jumps of the turbo-expander, but in which the IMR is replaced with the ethane, has the following results : a) the efficiency decreases from 46.7% to 42.7% b) the net mechanical power recovered decreases from 420 kW to 375 kW (-10%) c) the overall efficiency (energy recovered/energy introduced) decreases to 78%

EXAMPLE 2

The goal of Example 2 is to regasify an LNG flow rate equal to 139 t/h

The chemical analysis of the LNG is prepared:

The object is achieved by means of the diagram of accompanying figure 7, in which a power generating cycle (PGC) according to a particular embodiment of the present invention and a regasification line are depicted .

LPG is imported into the plant in order to generate the working fluid, of which LPG the chemical laboratory results are available, with the following results:

The chemical analyses of both the LNG and the LPG being available, the IMR is prepared according to the above description .

The LNG and IMR operating pressures in the LNG vaporizer are set. The LNG pressure is unequivocally determined by the specific needs of the regasification line, which in the present example, requires introduction in natural gas (NG) network at 74.5 bar g.

With regards to the IMR pressure, it depends on the design pressure of the equipment forming the PGC, in particular the power generating operating machine (turbo-expander) .

Since the optimal operating pressure of said machine is of 76.5 bar g and the optimal expansion ratio is about 7, once the losses of load are calculated, the pressure of the IMR output from the LNG vaporizer is 9.5 bar g. The losses of load are applied to both sides of the LNG regasifier, up to a maximum of 0.5 bar.

Using a calculator, the virtual IMR samples are prepared, obtained by mixing LNG at the storage temperature, possibly kept at the storage pressure also in the IMR drum, and LPG at ambient temperature.

According to the above exhaustive description, the mixing process results in the formation of a series of IMR samples having different molecular weight.

Again, using the calculator, the family of heat exchange curves are generated for the IMR samples to the LNG to be regasified, thus obtaining results which are similar to those shown in figure 10. At this point, the IMR sample which maximizes the energy performance is selected while limiting the exchange surface required for the regasifier within the technical-economic feasibility limits; in the case at hand, the IMR will have an average molar molecular weight equal to 29.7 u.m.a.

From the calculations, such an IMR sample has a boiling temperature of -123.2°C at 9.5 bar g.

The IMR is produced up to reaching the aforesaid temperature of -123.2°C at the pressure of 9.5 bar g. Operatively, the operation of the diagram presented is the following:

a 24.5MWe gas turbine and the thermal input of which is equal to 75 MWt, is the thermal source of the PGC thus operating

- PGC: the fluid "01" (IMR) with flow rate 168 t/h and temperature of -123.2 °C is collected in the IMR drum and pumped at a pressure (maximum of the cycle) of 78.5 bar g, then is heated in the low temperature recuperator at the expense of the heat transferred from the IMR current "08" up to a temperature of -38.9°C; then, the pre heated IMR current "02" comes into thermal contact with the chiller of the combustion air of the turbine

(consider for example, air at 80% of relative humidity and 15°C cooled down to 5°C) , where it receives 1860 kW of thermal power and is heated up to -25°C) .

Then, the IMR enters "03" the first coil of the exhaust gas recuperator where it recovers the last part of the heat transferred by the exhausted turbine gases; it is output "04" at the temperature of 60°C, to then undergo a successive pre-heating in the high temperature recuperator at the expense of the IMR output from the expander "07". The current thus obtained "04" has a temperature of 138°C and is ready for the final heating in the exhaust gas recuperator, where it meets the exhausted gases just output from the turbine; the sum of the recoveries carried out by the exhaust gas recuperator lowers the temperature of the fumes down to 160 °C .

The IMR, now at a temperature of 280°C and a pressure of 76.5 bar g "06", enters the IMR turbo-expander where it performs work, being output "07" at 11 bar g and 186°C. Then, the IMR transfers heat in the high temperature recuperator, where it pre-cools "08" down to 80°C; the final cooling at 8°C follows in the low temperature recuperator, a temperature adapted to keep a minimum approach which is not less than 5°C in the LNG regasifier/IMR condenser. The LNG regasifier herein indicated heats supercritical LNG from a temperature of -162°C to 3°C by operating in pure countercurrent with the IMR flow.

The mechanical power generated by the IMR turbo expander is equal to 10 kW which, net of the energy used by the IMR pump and equal to 760 kW, provides an available power of 9300 kW with respect to a thermal power of 35.4 kW recuperated from the combustion fumes.

- 80% of the thermal input of the turbine is recovered, both in the form of energy generated and of heat used for regasifying LNG.

It is worth noting that the cooling of the turbine combustion air in this configuration is beneficial therefor, thus increasing the efficiency thereof.

EXAMPLE 3

The diagram in figure 4 is particularly adapted to medium- and large-sized applications.

EXAMPLE 4

The diagram in figure 5 indicates a variant of the diagram in figure 4 in which the same results are obtained by using a post-combustor of the exhausted turbine fumes in terms of LNG vaporization and cycle power, albeit a turbine with lesser power is installed. The possibility of modulating the post-combustion introduces a further flexibility which allows the minimum load of the plant to be regulated without heat waste; indeed in figure 4, the regulation of the heat provided to the ORC occurred by discharging part of the turbine exhausts into the atmosphere prior to the thermal recuperation, thus wasting part of the thermal input introduced into the system.

Those skilled in the art may understand the several advantages offered by the present invention from the description provided above.

Firstly, the present invention makes available a new mixture which may be used for regasifying liquefied natural gas (LNG) with excellent results in terms of energy due to the proximity of the vaporization curves of the liquefied natural gas (LNG) and the condensation curve of the working fluid (IMR) .

Moreover, the fact that it may be prepared from commercially available fluids significantly increases the procurement easiness and affordability of the process .

Indeed, the process of the invention for preparing the working fluid (IMR) does not require distillation steps, for example for preparing the two components of the mixture .

The liquefied natural gas (LNG) used may be that in the plant itself, while the liquefied petroleum gas (LPG) may be imported and of commercial grade.

Again, storing liquefied petroleum gas (LPG) at the plant may not be required because once the IMR has formed, the mixture may be "altered" by adding liquefied natural gas (LNG) (due to the natural tendency of the light components of the LNG to evaporate) .

Moreover, the system described is highly flexible, given that the composition of the IMR can be varied, also dynamically, to optimize the cycle performance.

The plant is easy to manufacture, with a single turbine and without the need for extractions, so as to increase the overall reliability of the plant with respect to plants with several turbines or with a more complex turbine.

In the embodiment with a post-combustor for the turbine fumes, the size of the turbine itself may advantageously be small.

The configuration in figure 6 may be particularly interesting for covering possible stand-by or start-up speeds; in the event of the unavailability of the turbine or stopped plant, the circulation of liquefied natural gas in the first drum (530, IMR drum) keeps the circuit cold.

Instead with respect to conventional technologies, it is worth noting how the process described results in a co-generation of electric energy and in the vaporization of the LNG with an efficiency which is greater than 75%, considering as total efficiency:

(mechanical or electric power + theoretical LNG vaporization heat )/thermal power introduced.

From an environmental viewpoint, a reduction of CO2 emissions is obtained which is proportionate to the reduction of the consumption of fuel gas to obtain the separate generation of the same mechanical or electric powers and the vaporization of the liquefied natural gas (LNG) by means of the conventional SCV or ORV technologies .

Those skilled in the art may also understand not only how the above-described technology may be applied to construct new regasification lines or plants, but also to modify existing plants (revamping) .

The regasification terminal described by the present invention allows multiple needs to be met, such as for example the need to adapt the plant flow rates to the requests of regasified or stored liquefied natural gas (LNG) and contrarily, to adapt the plant operability to a possible reduction of the amount of liquefied natural gas (LNG) , technical requirements associated for example, with routine or supplementary maintenance of one or more lines due to the undisputed management flexibility .

The solution proposed by the present invention also is highly adaptable to seasonal or daily weather conditions .

A further undoubted advantage is that the system may use heat sources at a different temperature, thus allowing the use of the source energy at a higher temperature to be maximized, which is made possible by the introduction of at least two thermal recuperators/regenerators (HTS, LTS).

It is also worth noting how the present invention is particularly described 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 regasifying or vaporizing other liquefied fluids stored at low temperatures (less than about 0°C) or at cryogenic temperatures (less than -45°C) .

For example, the present invention is also applied to regasify or vaporize other liquefied gases.

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