Methods for LNG vaporization and cryogenic power generation

Abstract

This invention describes a method for gasifying liquefied natural gas (LNG) and for generating electricity, which operates efficiently at low temperatures.

Description

Technical Field

[0001] This invention has been applied in the field of regasification and energy recovery of liquefied natural gas (LNG). Background Technology

[0002] Organic Rankine Cycle

[0003] Organic fluid Rankine cycle (ORC) is widely used in geothermal and industrial processes for biomass and waste heat recovery. It offers the possibility of selecting a working fluid from dozens of candidate fluids, thus enabling efficient thermodynamic cycles, even under conditions of low source temperature and limited heat availability.

[0004] Choosing a low-boiling-point fluid also allows for temperatures below room temperature, enabling condensation cycles at low temperatures without the risk of freezing or excessive vacuum.

[0005] From 1965 to 2013, ORMAT, RGJACKSON, Reickichi Nozawa, Fluor, and Exxon Mobil filed numerous patents related to ORCs applicable to LNG regasification.

[0006] Recently, Saipem also published its own ORC cycle patent, which works for a single fluid produced from LNG and LPG (WO2020 / 075112a1).

[0007] Based on a high-boiling-point working fluid (referred to as IMR), it requires the use of a high-temperature heat source and is designed to maximize the mechanical power that can be extracted from the source by using waste heat to evaporate the LNG stream (which is both a cooling fluid and a cold source).

[0008] The advantage of this idea is that it does not have a direct thermal impact on the environment and typically utilizes fuel, ensuring continuous power generation independent of environmental conditions; in addition, the IMR formulation is designed to make full use of the kilocalories contained in the evaporated LNG stream while using a simple cycle consisting of a single machine (expander) for the expansion of the working fluid.

[0009] However, unless the ORC cycle is combined with an expensive CO2 sequestration system, the use of fuel has the drawbacks of utilizing non-renewable energy sources and involving carbon dioxide emissions into the atmosphere.

[0010] Increasing sensitivity to environmental pollution related to greenhouse gas emissions is driving the market toward solutions that do not involve the use of fuel.

[0011] Inversed mixed refrigerant (IMR) is an readily available and inexpensive fluid with thermodynamic properties similar to LNG, and it condenses completely only at relatively high pressures at LNG storage temperatures; however, it may not completely evaporate at room temperature except at pressures slightly above the condensation pressure.

[0012] Between these two constraints, the expansion ratio available for power generation is reduced to the point that it is unsuitable for use in situations where only a room temperature source exists.

[0013] Prior art document US3.479.832 describes a process for evaporating liquefied natural gas, which separates liquid (28, 44) and gas (26, 4, 42) into single-component fractions, and for generating electricity by using a working fluid with variable composition. Summary of the Invention

[0014] The inventors of this patent application have developed a method for gasifying liquefied natural gas (LNG) and for generating electricity, which uses a working fluid obtained by mixing liquefied natural gas (LNG) and liquefied petroleum gas (LPG), and is particularly suitable for operation at cryogenic temperatures.

[0015] Purpose of the invention

[0016] In the first objective, the present invention describes a method for gasifying liquefied natural gas (LNG) and for generating electricity. Attached Figure Description

[0017] Figure 1 A diagram is shown illustrating a method for gasifying liquefied natural gas (LNG) and for generating electricity, as described in prior art document WO2020 / 075112A1.

[0018] Figure 2 A diagram illustrating a method according to a first embodiment of the present invention is shown.

[0019] Figure 3 A diagram illustrating a method according to a second embodiment of the present invention is shown. Detailed Implementation

[0020] IMR - Reverse-phase mixed refrigerant /

[0021] The IMR working fluid is a liquid mixture.

[0022] Specifically, this fluid is obtained by mixing commercial liquefied petroleum gas (LPG) and commercial liquefied natural gas (LNG).

[0023] The term "commercial liquefied petroleum gas (LPG)" refers to a fuel with clearly defined characteristics, commonly used in civil and industrial applications, and possessing the following properties:

[0024] - Vapor pressure at 100°F;

[0025] - Under atmospheric pressure, the lowest temperature at which 95% of the sample volume evaporates is likely determined by heating using precise methods;

[0026] - Mole percentage of molecules having more than 4 carbon atoms; for the purposes of this invention, it also contains hydrocarbons having 7 or more carbon atoms.

[0027] As is well known, liquefied petroleum gas (LPG) is blended into crude oil and separated from it by refining in a top tower.

[0028] Liquefied petroleum gas (LPG) is produced by various refining methods; for example, pyrolysis produces LPG as a byproduct.

[0029] For the purposes of this invention, liquefied petroleum gas (LPG) is preferably defined as a flammable fluid, the characteristics of which fall within the range defined in the table below:

[0030]

[0031]

[0032] (1) The highest temperature at which 95% of the volume of the sample under test is obtained under atmospheric pressure.

[0033] (2) The content of molecules with at least 5 carbon atoms.

[0034] The term "commercial liquefied natural gas (LNG)" refers to a hydrocarbon fluid that is primarily in a liquid phase, obtained by condensing natural gas at a sufficiently low temperature so that it remains liquid even at atmospheric pressure.

[0035] Natural gas is known to consist mainly of methane and light hydrocarbons, with soft hydrocarbons rarely having more than 5 carbon atoms; it may also contain a variable proportion of nitrogen.

[0036] For the purposes of this 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 a certain amount of liquefied petroleum gas (LPG) between 0.25 and 1.2 volumes.

[0037] The method for preparing the working fluid for IMR is described in detail in patent application WO2020 / 075112A1 (Saipem SpA), the contents of which are incorporated herein by reference in their entirety.

[0038] LNG vaporization pipeline

[0039] For the purposes of this invention, the liquefied natural gas (LNG) vaporization pipeline originates from liquefied natural gas (LNG). Figure 2 and 3 The LNG storage tanks, once vaporized, are fed into the network ( Figure 2 In NG).

[0040] In particular, gasification is achieved through several heating steps, which is compatible with the increased system complexity due to the increased efficiency of the method.

[0041] According to a preferred embodiment of the invention, three liquefied natural gas heating steps are provided, wherein the liquefied natural gas flow exchanges heat by acquiring heat from one or more flows.

[0042] More specifically, according to Figure 2 and 3 As shown, the liquefied natural gas stream 40 leaving the dedicated tank (LNG) undergoes a first heating step to obtain a partially regasified stream 41, which is further heated during a second step to obtain a regasified stream 42, followed by a third heating step that produces a fully regasified stream 43.

[0043] LIMR Cycle - Low Temperature Reverse Mixed Refrigerant

[0044] The LIMR cycle is implemented by utilizing a first working fluid (1MF or LIMR) and includes an expander ( Figure 2 EX in the middle), one or more low-temperature heat sources ( Figure 2 H1, H2) and each tank containing a second or third working fluid ( Figure 2 (V1, V2, and V3 in the text).

[0045] Specifically, the first canister V1 contains a certain amount of a second working fluid (2MF), which, in a preferred aspect of the invention, is an inverse mixed refrigerant (IMR).

[0046] The second tank V2 and the third tank V3 contain a certain amount of a third working fluid, which in a preferred aspect of the invention is liquefied natural gas (LNG).

[0047] Regarding the expander (EX), this is preferably a turbine used for power generation.

[0048] According to a first objective of the present invention, a method for gasifying liquefied natural gas (LNG) and for generating electricity is described, comprising the following steps:

[0049] 1) The first working fluid 1MF in the gas phase 1 is subjected to a first cooling step to obtain a cooled flow 2 of the first working fluid 1MF.

[0050] 2) The cooling flow 2 of the first working fluid 1MF is sent to the first tank V1 containing a certain amount of the second working fluid 2MF.

[0051] 3) Separate the first condensed fraction 3 and the first gaseous fraction 6.

[0052] 4) The first gaseous portion 6 is subjected to a second cooling step to obtain the first condensed portion 7.

[0053] 5) The first condensation section 7 is sent to the second tank V2 containing a certain amount of the third working fluid 3MF.

[0054] 6) Separate the second condensed fraction 8 and the second gaseous fraction 12.

[0055] 7) Subject the second gaseous portion 12 to a third cooling step to obtain the condensed final portion 13.

[0056] 8) The final condensate 13 is sent to a third tank V3 containing a certain amount of the third working 3MF, thereby obtaining the third condensate fraction 14.

[0057] 9) The first condensate 3 is subjected to a pumping step to obtain a first pumped condensate 4, and then subjected to a heat exchange step to obtain a first portion 5 for mixing the working fluid.

[0058] 10) The second condensed fraction 8 is subjected to a pumping step to obtain a second pumped condensed fraction 9, subjected to a first heat exchange step to obtain a second pumped and higher-temperature condensed fraction 10, and subjected to a second heat exchange step to obtain a second mixing portion 11 for the working fluid.

[0059] 11) The third condensate 14 is pumped to obtain a third pumped condensate 15, subjected to a first heat exchange to obtain a third pumped and higher-temperature condensate 16, and subjected to a second heat exchange to obtain a third mixed portion 17 for the working fluid.

[0060] 12) The first 5, second 11, and third 17 mixture portions for the first working fluid are mixed in mixer M to obtain the initial flow 18 of the first working fluid.

[0061] 13) The initial flow 18 of the first working fluid is heated by a second low-temperature heat source H2, thereby obtaining a heated flow 19 of the first working fluid.

[0062] 14) The heated flow 19 of the first working fluid is expanded into the power generation expander EX, thereby obtaining a first expanded and cooled working fluid flow 20.

[0063] 15) The flow 20 of the first expanding and cooling working fluid is heated by the first low-temperature heat source H1, thereby obtaining the flow of the first working fluid in the gas phase 1 in step 1).

[0064] According to one aspect of the invention, during step 1), the flow of the first working fluid 1 is primarily in the gas phase.

[0065] According to a particular aspect of the invention, during step 3), a first condensate fraction 3 is obtained by mixing the liquid fraction of the cooling stream 2 with the second working fluid 2MF contained in the first tank V1.

[0066] According to one aspect of the invention, during step 4), the first condensation portion 7 obtained is not completely condensed but only partially condensed.

[0067] According to another aspect of the invention, during step 6), a second condensate fraction 8 is obtained by mixing the liquid fraction of the first condensate fraction 7 with the third working fluid 3MF contained in the second tank V2.

[0068] According to one aspect of the invention, during step 11), the third pumped and higher-temperature condensate 16 may not be condensed.

[0069] For the purposes of this invention, steps 13) and 15) are performed using a low-temperature heat source.

[0070] Specifically, the low-temperature heat source can be: ambient air, seawater, low-temperature solar thermal energy, depletion heat from a low-temperature thermodynamic cycle, or heat recovery from methods and / or low-temperature machinery. Here, "seawater" refers not only to pumped seawater that has been properly treated to remove sediment, but more generally to ambient water obtained from rivers, canals, wells, natural basins (such as lakes), and artificial basins.

[0071] Typically, a low-temperature source is a source with a temperature between approximately 0 and 55°C.

[0072] When referring to a flow with “higher” temperature or “higher” pressure, it means that such a flow has undergone a heating or pumping step, resulting in an increased temperature or pressure compared to before.

[0073] Special reference Figure 2As shown in the diagram, during the heat exchange step, the flow 1 of the first working fluid is cooled.

[0074] Cooling determines the condensation of the heavy fraction 3 of the first working fluid, which is separated inside the first tank V1, containing the second working fluid 2MF.

[0075] Heavy fractions refer to liquid fractions with chemical compositions similar to IMR, and "similar" means that the molecular weight difference is about 40%.

[0076] The heavy fraction 3 is pumped by the first pump P1 to obtain the pumped heavy fraction 4, which, after the heating step, forms a first mixing portion for the first working fluid 5.

[0077] The same cooling also determined the separation of the first gaseous portion 6, which underwent a further heat exchange step, from which a further cooled first gaseous portion 7 was obtained.

[0078] This cooling determined the further condensation of heavy fraction 8, which was separated inside the second tank V2, containing liquefied natural gas (LNG) as the third working fluid 3MF.

[0079] The heavy fraction 8 is pumped by the second pump P2 to obtain the pumped heavy fraction 9, which is subjected to a first heating to provide a preheated flow 10, and subjected to a second heating to form a second mixing portion for the first working fluid 11.

[0080] The same cooling also determined the separation of the second gaseous portion 12, which underwent even further cooling steps, thus yielding the final condensed portion 13.

[0081] The final condensate section 13 is sent to the third tank V3, which contains liquefied natural gas (LNG) as the third working fluid 3MF.

[0082] The outflow from the third tank V3 then undergoes a first heat exchange step and a subsequent second heat exchange step to obtain a third mixing portion for the first working fluid 17.

[0083] Regarding the third mixing section for the first working fluid 17, this is then done in the mixer ( Figure 2 The interior of M) and the first and second mixing portions (corresponding to respectively) Figure 2 The streams 5 and 11 are mixed.

[0084] The working fluid 18 (LIMR) obtained from mixing inside mixer M is then subjected to a second low-temperature heat source ( Figure 2 The heating step of H2 in the middle, thereby obtaining the heating flow 19, which is then in the expander ( Figure 2 It expands in EX to generate energy.

[0085] After expansion, the expansion flow 20 is subjected to a first low-temperature heat source ( Figure 2 The heating step of H1 in the process is used to obtain an expanded and heated flow 1.

[0086] Such an expanded and heated flow 1 can therefore re-enter the circulation as described above as the first working fluid 1MF.

[0087] For the purposes of this invention, the liquefied natural gas stream 40 is vaporized in a heat exchange with one or more of the aforementioned streams.

[0088] More specifically, the flow of liquefied natural gas undergoes:

[0089] - Corresponding to the first heat exchange in step 7) mentioned above, thereby obtaining a stream 41 of partially regasified liquefied natural gas;

[0090] - Corresponding to the second heat exchange in steps 4) and 10) and 11) above, a stream 42 of liquefied natural gas is obtained that is further regasified;

[0091] - Corresponding to the third heat exchange in steps 1), 9), 10) and 11) above, a stream 43 of fully regasified natural gas is obtained.

[0092] According to embodiments of the present invention, for example in Figure 3 As shown, a third cryogenic heat source H3 may be further involved during the first heat exchange step, which is heated by means of an intermediate carrier fluid:

[0093] -The flow of natural gas 42 is further heated (after the second heating step).

[0094] - First pump delivers condensate fraction 4.

[0095] -Second pumping and higher temperature condensation fraction 10,

[0096] - Third pump and higher temperature condensate 16.

[0097] like Figure 3 As shown in the diagram, the flow of fluid 50 is actually pumped by the fourth pump P4, thereby obtaining a flow 51 at a greater pressure.

[0098] This higher pressure flow 51 releases heat during the first heat exchange step, thereby obtaining a cooling flow 52 for the carrier fluid.

[0099] From the above description, the advantages provided by the method of the present invention will be immediately apparent to those skilled in the art.

[0100] In particular, such a method utilizes a low-temperature heat source, which means a source at room temperature, such as, for example, seawater or a natural or artificial reservoir.

[0101] Compared to the method and power cycle described in patent application WO2020 / 075112, the power cycle of the present invention has the same effectiveness and the same system simplicity.

[0102] Advantageously, the cycle of the present invention can also be operated at low temperatures.

[0103] Since no fuel is required, the above methods do not rely on non-renewable energy sources and do not involve the production of carbon dioxide.

Claims

1. A method for gasifying liquefied natural gas (LNG) and for generating electricity, comprising the following steps: 1) The flow of the first working fluid 1MF in the gas phase (1) is subjected to a first cooling step to obtain a cooled flow (2) of the first working fluid 1MF. 2) The cooling flow (2) of the first working fluid 1MF is sent to the first tank V1 containing a certain amount of the second working fluid 2MF. 3) Separate the first condensed fraction (3) and the first gaseous fraction (6) from the first tank V1. 4) The first gaseous portion (6) is subjected to a second cooling step to obtain the first condensed portion (7). 5) The first condensation section (7) is sent to the second tank V2 containing a certain amount of the third working fluid 3MF. 6) Separate the second condensed fraction (8) and the second gaseous fraction (12) from the second tank V2. 7) Subject the second gaseous portion (12) to a third cooling step to obtain the condensed final portion (13). 8) The final portion (13) of the condensate is sent to a third tank V3 containing a certain amount of the third working 3MF, thereby obtaining the third condensate fraction (14). 9) The first condensate (3) is subjected to a pumping step to obtain a first pumped condensate (4), and subjected to a heat exchange step to obtain a first portion (5) for mixing the working fluid. 10) The second condensed fraction (8) is subjected to a pumping step to obtain a second pumped condensed fraction (9), subjected to a first heat exchange step to obtain a second high-pressure and higher-temperature condensed fraction (10), and subjected to a second heat exchange step to obtain a second portion (11) for mixing the working fluid. 11) The third condensate (14) is pumped to obtain a third pumped condensate (15), subjected to a first heat exchange to obtain a third pumped and higher-temperature condensate (16), and subjected to a second heat exchange to obtain a third portion (17) for mixing the working fluid. 12) Mix the first part (5), the second part (11), and the third part (17) to mix the first working fluid in the mixer M, thereby obtaining an initial flow (18) of the first working fluid. 13) The initial flow (18) of the first working fluid is heated by a second low-temperature heat source H2 to obtain a heated flow (19) of the first working fluid. 14) The heated flow (19) of the first working fluid is expanded into the power-generating expander EX, thereby obtaining an expanded and cooled flow (20) of the first working fluid. 15) The flow (20) of the first working fluid, which has expanded and cooled, is heated by a first low-temperature heat source H1, thereby obtaining the flow of the first working fluid in the gas phase (1) of step 1). in: - During step 7), heat exchange is performed with the liquefied natural gas stream (40) to obtain a partially regasified natural gas stream (41). - During steps 4), 10), and 11), heat exchange b) is performed with the partially regasified natural gas stream (41) to obtain a further regasified natural gas stream (42). - A third heat exchange is performed with the further regasified natural gas stream (42) during steps 1), 9), 10), and 11) to obtain a fully regasified stream (43), wherein: The second working fluid 2MF is a fluid obtained by adding a certain amount of liquefied petroleum gas (LPG) to a certain amount of liquefied natural gas (LNG), wherein the certain amount is such that 0.25 to 1.2 volumes of LPG are added to 1 volume of LNG, wherein... The third working fluid 3MF is liquefied natural gas (LNG).

2. The method according to claim 1, wherein, A low-temperature heat source is used during steps 13) and 15).

3. The method according to claim 1 or 2, wherein, A third low-temperature heat source (H3) is further employed during the heat exchange step described in step 1).

4. The method according to claim 3, wherein, The heat exchange with the third low-temperature heat source (H3) is carried out indirectly by means of a carrier fluid.

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