Method for regasification and distribution of natural gas

Abstract

Apparatus (1) and method for regasifying natural gas under low temperature conditions, comprising a cryogenic tank (10) and a capacitive tank (20) configured to store natural gas under low temperature conditions. The apparatus (1) further comprises a supply circuit (30) arranged for connection between the cryogenic tank (10) and the capacitive tank (20) and comprising a pump (31) configured to cause an increase in pressure and temperature of the natural gas. The apparatus (1) comprises a motor body (40) configured for generating mechanical energy and comprising at least one working chamber (41) having an inlet gap (42) arranged in fluid communication with the capacitive tank (20) and a discharge gap (43) connected to a spent natural gas discharge circuit (60), and a recirculation circuit (70), the motor body (40) being configured for generating mechanical energy and comprising at least one working chamber (41) having an inlet gap (42) arranged in fluid communication with the capacitive tank (20) and a discharge gap (43) arranged in fluid communication with the spent natural gas discharge circuit (60). The recirculation loop (70) is adapted to deliver a portion of the spent gas into the capacitive tank (20). The apparatus (1) comprises a delivery pipe connected to the discharge circuit (60) and to a network for transporting and distributing regasified natural gas.

Description

Technical Field

[0001] The present invention relates to a method for the regasification and distribution of natural gas. The term "natural gas" should be understood to mainly refer to methane. Background Art

[0002] It is known that liquefied methane (LNG) is transported by LNG carriers for the purpose of supplying distribution networks such as national networks. Specifically, the LNG carrier transports the liquefied natural gas from its production area to a predetermined delivery point. Once at the delivery point, the liquefied natural gas is returned to the gaseous state through a regasification process and is then introduced into the national transportation network.

[0003] It is known to use a heat source to regasify the liquefied natural gas. For example, devices that utilize heat obtained from seawater are known. Devices that use heat obtained from the combustion of a portion of the same regasified natural gas are also known.

[0004] The applicant has noted that even in their latest embodiments, the energy efficiency of the aforementioned transportation method by LNG carriers (paying particular attention to the regasification phase) is very poor. In fact, the energy used for liquefying the natural gas is not recovered at all during the regasification process. On the contrary, in the case of burning a portion of the gas itself, the overall efficiency of the process will be further impaired. As a result, liquefied natural gas is generally more expensive than natural gas transported by pipeline. Summary of the Invention

[0005] In this context, the technical task of the present invention is to propose a method for the regasification and distribution of natural gas that overcomes the above-mentioned drawbacks of the prior art.

[0006] Specifically, the object of the present invention is to provide a method for the regasification and distribution of natural gas that achieves an improvement in the energy efficiency of the entire process and thus reduces the selling cost of the natural gas itself.

[0007] Broadly speaking, the specified technical task and the specified object are achieved by a method for the regasification and distribution of natural gas according to one or more of the appended claims 1 and / or its dependent claims. Brief Description of the Drawings

[0008] Other features and advantages of the present invention will become more apparent from the indicative and thus non-limiting description of a preferred but non-exclusive embodiment of the method for the regasification and distribution of natural gas as shown in the drawings, in which:

[0009] Figure 1 A preferred embodiment of a natural gas regasification device for implementing the method for the regasification and distribution of natural gas according to the present invention is schematically shown;

[0010] Figures 2A - 2C shows the corresponding views of the components of the Figure 1 device;

[0011] Figures 3A - 3F shows the corresponding views of the Figures 2A - 2C components under different operating configurations;

[0012] Figure 4 shows the Figure 1 Mollier diagram of the open working cycle of the device. DETAILED DESCRIPTION

[0013] Referring to the accompanying drawings, the device for regasifying natural gas has been designated by the reference numeral "1".

[0014] The term "natural gas" is to be understood as preferably meaning methane. However, the present invention is applicable to common cryogenic liquids such as nitrogen, oxygen, ammonia, and common fluids having a critical temperature far below room temperature.

[0015] Referring to Figure 1 , the device 1 includes a cryogenic tank 10, a capacitive tank 20, a supply circuit 30 (which connects the cryogenic tank 10 to the capacitive tank 20 and includes a pump 31), a motor body 40, a discharge circuit 60, and a recirculation circuit 70. The device also includes a delivery pipe that is connected to the discharge circuit 60 and is configured to introduce the regasified natural gas into a network for the delivery and distribution of the regasified natural gas.

[0016] The cryogenic tank 10 is configured for the storage of natural gas under cryogenic conditions.

[0017] The term "cryogenic conditions" is understood to mean that the natural gas is in a cryogenic state, particularly at a temperature below the corresponding critical point temperature and at a low pressure substantially equal to atmospheric pressure. Preferably, the term "cryogenic conditions" is understood to mean the liquid state of natural gas under the aforementioned temperature and pressure conditions.

[0018] Under normal operating conditions, almost all of the natural gas in the cryogenic tank 10 is in the liquid state. However, as shown in the subsequent part of the present disclosure, a relatively small proportion of natural gas can be provided to be stored in the cryogenic tank 10 in the gaseous state, or if necessary, the natural gas can also be brought to the solid state.

[0019] Advantageously, since the natural gas is stored in the cryogenic tank 10 at a pressure substantially equal to the ambient pressure, problems associated with pressure tanks are solved.

[0020] In terms of size, the size of the cryogenic tank 10 can be "specially" determined based on the use of the device and based on the required space and autonomy requirements.

[0021] Advantageously, since almost all of the natural gas is stored substantially in a liquid state, it can be accumulated in large quantities.

[0022] In fact, for the same volume, the mass of liquid natural gas is even hundreds of times greater than that of the same natural gas in a gaseous state.

[0023] According to one aspect of the present invention, the cryogenic tank 10 may include a vacuum extraction pump 11 configured to extract a portion of the gaseous natural gas from the cryogenic tank 10, thereby obtaining a pressure below atmospheric pressure inside the cryogenic tank 10.

[0024] Specifically, the vacuum pump 11 is operably arranged at the upper part of the cryogenic tank 10 so as to extract a liquid portion of the natural gas from the overlying gaseous portion of the natural gas.

[0025] According to a preferred use of the vacuum pump 11, it can be used to create pressure and temperature conditions inside the cryogenic tank 10, thereby causing the thermodynamic state of the triple point of natural gas. Even more preferably, the vacuum pump 11 can be used such that pressures and temperatures lower than those determining the thermodynamic state of the triple point are reached in the cryogenic tank 10.

[0026] As a non - limiting example, this property can be advantageously used in the application of a ship, in which it is necessary to at least partially solidify the natural gas stored in the cryogenic tank 10 in such a way as to limit (if not eliminate) the resonance phenomenon to prevent the ship from capsizing.

[0027] This condition can be adjusted.

[0028] Downstream of the cryogenic tank 10, a supply circuit 30 is operably arranged to connect the cryogenic tank 10 to the capacitive tank 20.

[0029] Generally, the supply circuit 30 is configured to change the thermodynamic conditions of the natural gas. Specifically, the supply circuit 30 is configured to raise the temperature and pressure of the natural gas, so as to advantageously utilize the natural gas from an energy perspective. According to one aspect of the present invention, the supply circuit 30 is configured to raise the temperature and pressure of the natural gas, thereby promoting at least a partial transformation of the state of the natural gas (from liquid to gas), as will be clear in the following of the present invention.

[0030] The supply circuit 30 includes the aforementioned pump 31, which is arranged inside the cryogenic tank 10 or is in fluid communication with the cryogenic tank 10 by means of a conduit. Specifically, the pump 31 is operably arranged in such a way that it can extract liquid natural gas from the cryogenic tank 10.

[0031] A check valve 33 may also be provided between the cryogenic tank 10 and the pump 31. Advantageously, the check valve 33 allows the intermittent use of the pump 31 without creating a "backflow" towards the cryogenic tank 10 and thus without the pressure in the cryogenic tank 10 increasing due to natural gas returning from the supply circuit 30 to the cryogenic tank 10. This allows the cryogenic tank 10 to have an optimal size and optimally cope with thermal insulation.

[0032] According to one aspect of the invention, the pump 31 can be controlled and regulated according to the rate of the motor body 40.

[0033] Functionally, the pump 31 is configured to cause an increase in the pressure and temperature of the natural gas. Preferably, the pump 31 is configured to facilitate the transition of the natural gas to the supercritical state.

[0034] The term "supercritical state" is understood to mean that the natural gas reaches thermodynamic conditions such that the temperature of the natural gas is higher than its critical temperature while the pressure is higher than its critical pressure. Under these thermodynamic conditions, the properties of the substance are partly similar to those of a liquid and partly similar to those of a gas.

[0035] The work done on the natural gas by the pump 31 can be divided into two parts, identified on the Mollier diagram by section "A"-"B" and by section "B"-"C". Figure 4 in.

[0036] First, the pump 31 raises the pressure of the natural gas, thereby obtaining a liquid and high-pressure natural gas with a moderately increased temperature. Preferably, the natural gas is brought to a supercritical pressure value. This transformation is shown on the Mollier diagram by section "A"-"B". Figure 4 in.

[0037] Advantageously, by operating on a liquid that is substantially incompressible under the aforementioned cryogenic conditions, the pump 31 requires a negligible operating energy consumption compared to the mechanical (and thus electrical) energy generated by the equipment 1 as a whole.

[0038] Secondly, in section 32 of the supply circuit 30 between the pump 31 and the capacitive tank 20, the amount of natural gas accumulating under the aforementioned supercritical conditions continuously increases: the pump 31 continuously introduces more natural gas, such that in this section of the conduit 32, the pressure of the natural gas further increases. At the same time, the temperature of the natural gas increases significantly. In other words, the pump drive work raises the pressure and temperature of the natural gas. As a result of this drive work, the natural gas is in a supercritical state under high pressure and high temperature conditions. Such a transformation can be considered to be substantially adiabatic. This second part is shown on the Mollier diagram by section "B"-"C". Figure 4 in.

[0039] Preferably, a check valve 34 is arranged downstream of the pump 31, and the check valve 34 is operably interposed between the pump 31 and the aforementioned capacitive tank 20.

[0040] In summary, the natural gas stored in the cryogenic tank 10 is in cryogenic conditions, i.e., at a very low temperature (lower than the melting temperature of the corresponding natural gas) and at a pressure substantially equal to atmospheric pressure. In other words, the natural gas is in a condition such that it cannot be utilized in an energy - advantageous manner, and is identified by the reference numeral "A" on the Mollier diagram of Figure 4 which is not provided in the original text.

[0041] The supply circuit 30 switches the thermodynamic conditions of the natural gas from the initial cryogenic conditions to high - temperature and high - pressure thermodynamic conditions, which are represented by the reference numeral "C" on the Mollier diagram of Figure 4 which is not provided in the original text. Preferably, the thermodynamic condition "C" corresponds to the supercritical state of the natural gas. This condition will now be identified in the subsequent part of the present disclosure as the thermodynamic condition of "exliquid".

[0042] By using the supply circuit 30, the behavior of raising the pressure of the natural gas is taken by means of the pump 31, and then the temperature is raised by virtue of the aforementioned driving work until the natural gas in the "exliquid" condition is obtained.

[0043] According to an aspect of the present invention, the supply circuit 30 may include a metering tank 73, a valve 72 configured to isolate the supply circuit 30, and a valve 73 interposed between the metering tank 71 and the capacitive tank 20.

[0044] The capacitive tank 20 is configured to collect and mix a certain amount of "exliquid" natural gas from the supply circuit 30 with a relative amount of recycled natural gas recovered from the motor body 40 through the recirculation circuit 70, so as to optimally supply the motor body 40.

[0045] In other words, the capacitive tank 20 is appropriately dimensioned in a way to perform the function of mixing the "exliquid" natural gas and the recycled natural gas in order to obtain a certain amount of natural gas defined as "supply natural gas". As will be explained in the subsequent part of the present disclosure, the recycled natural gas is in a gaseous state at a lower pressure than the "exliquid" natural gas. Similarly, inside the capacitive tank 20, the "exliquid" natural gas from the supply circuit 30 causes complete evaporation particularly through its partial expansion.

[0046] The capacitive tank 20 is appropriately dimensioned in a way to perform the function of metering the supply natural gas to the motor body 40.

[0047] Note: There are some missing references in the original text for "on the Mollier diagram of " in ID=3, ID=8, ID=10, etc. The translation has been made as best as possible considering the available context.The natural gas defined as "feed natural gas" has pressure and temperature conditions that are average with respect to the pressure and temperature conditions of "liquefied" natural gas and recycled natural gas. Under these "feed" thermodynamic conditions, the natural gas is in the gaseous state. These "feed" conditions are indicated in Figure 4 by the reference numeral "E" in the drawings.

[0048] The characteristics of the recirculation loop 70 and the dosage ratio between the "liquefied" natural gas and the recycled natural gas will be described in detail in the following of this disclosure.

[0049] The "recycled" thermodynamic conditions are indicated in Figure 4 by the reference numeral "D" in the drawings.

[0050] The motor body 40 is configured to generate mechanical energy and includes at least one working chamber 41 having an inlet gap 42 and a discharge gap 43. The inlet gap 42 is arranged to be in fluid communication with the capacitive tank 20, and the feed natural gas is supplied from the inlet gap 42. The discharge gap 43 is connected to a discharge circuit 60 for natural gas in an exhausted condition (indicated by the reference numeral "F" in Figure 4 the drawings).

[0051] The expansion of the "liquefied" natural gas is indicated in Figure 4 by the section "E" - "F" in the drawings.

[0052] The working chamber 41 is configured to convert the expansion and / or movement of the feed natural gas into mechanical work by means of at least one movable wall 44.

[0053] Preferably, the movable wall 44 is constrained to translate between a top dead center and a bottom dead center. Alternatively, the movable wall 44 can be constrained to rotate about an axis.

[0054] The term "exhausted natural gas" should be understood to mean natural gas under the conditions after such conversion, in which the natural gas has a low enthalpy content and temperature and pressure conditions suitable for introduction into a transportation and distribution network.

[0055] The motor body 40 can be manufactured according to any type as long as it is suitable for the required purpose.

[0056] According to a preferred embodiment, the motor body 40 is of the reciprocating type.

[0057] Specifically, in a manner known per se, the motor body 40 includes at least one cylinder 45 defining a working chamber 41, the working chamber 41 having an inlet clearance 42 associated with a supply valve 46 and an exhaust clearance 43 associated with an exhaust valve 47. A piston 48 integral with a respective movable wall 44 and a connecting rod 49 constrained to the piston 48 are slidably constrained within the cylinder 45. Finally, the connecting rod 49 is constrained to the motor shaft 50.

[0058] Functionally, the motor body 40 is configured such that the conversion work of the supplied natural gas by the motor body 40 can be substantially divided into two different operating phases.

[0059] In a first operating phase, with the supply valve 46 open, there occurs a transfer of high-pressure supplied natural gas from the capacitive tank 20 to the working chamber 41 of the motor body 40, which causes a first movement of the movable wall 44 and thus a first movement of the motor shaft 50.

[0060] Since this is a mechanical phenomenon of mass transfer, in this first operating phase, the pressure, temperature, and enthalpy of the supplied natural gas can be considered to be substantially constant.

[0061] In other words, mechanical energy is generated due to the mass transfer of the supplied natural gas within the working chamber 41.

[0062] Nevertheless, in the first operating phase, the supplied natural gas does not undergo a thermodynamic conversion but remains substantially constant in pressure and enthalpy.

[0063] Once the first operating phase ends, the second operating phase begins. This second operating phase includes a transformation similar to a polytropic transformation that exchanges mechanical work with the movable wall 44 of the working chamber 41.

[0064] Specifically, in the second operating phase, a portion of the enthalpy of the supplied natural gas is converted into mechanical energy.

[0065] Specifically, the temperature and pressure of the supplied natural gas decrease, and the natural gas can be considered to be lean natural gas. In the second operating phase, since the transfer of the mass of the supplied natural gas from the capacitive tank 20 to the working chamber 41 has been completed, the mass of the natural gas inside the working chamber can be considered to be constant.

[0066] The mechanical energy obtained in this second expansion operating phase is negligible compared to the mechanical energy obtained in the first transfer operating phase.

[0067] In the following description, the movement cycle of the motor body 40 is described based on the angle presented by the motor shaft 50 during its clockwise rotation.

[0068] Specifically, it is assumed that the position of the motor shaft 50 where the movable wall 44 is at top dead center is at an angle of 0 degrees.

[0069] Specifically, in the first operating phase, the motor shaft 50 moves from 12 degrees to 50 degrees, while in the second operating phase, the motor shaft 50 moves from 50 degrees to 180 degrees.

[0070] According to another embodiment not shown in the drawings, the motor body 40 may be of the flow motor type.

[0071] In such an embodiment, the first operating phase and the second operating phase occur substantially simultaneously.

[0072] Once the operating phase is over, the spent natural gas is at least partially conveyed into the discharge circuit 60. The discharge circuit 60 is adapted to discharge the natural gas in the delivery pipe under the conditions indicated by the reference numeral "G" in the Figure 4 Mollier diagram. The discharge circuit 60 may include a spent natural gas collection tank 61 and a discharge conduit adapted to at least partially discharge the spent natural gas from the device 1.

[0073] The discharge circuit 60 may further include a discharge valve 62.

[0074] At the operating level, the discharge circuit 60 is connected to the delivery pipe and thus connected or connectable to the delivery and distribution network of the regasified natural gas. The discharge circuit 60 is configured to receive a portion of the spent natural gas from the motor body 40 and change its thermodynamic conditions so that it is suitable for introduction into the delivery and distribution network of the regasified natural gas.

[0075] According to another aspect of the present invention, the device 1 may include a stop system 80 to stop the operation of the motor body 40, and the stop system 80 is configured to interrupt the operation of the device 1.

[0076] Preferably, such a stop system 80 may be associated with the pump 31 so as to be able to prevent the extraction of natural gas from the cryogenic tank 10 and thus prevent the supply of the device 1.

[0077] The stop system 80 may also act through a valve 74 connected to the stop system 80.

[0078] According to one aspect of the present invention, the device 1 may include a supplementary circuit 90, the supplementary circuit 90 being associated with the discharge circuit and configured to supplement a portion of the spent natural gas passing through the discharge circuit 60 (in particular a portion of the spent natural gas passing through the collection tank 61) into the cryogenic tank 10.

[0079] Alternatively, the device 1 may include a supplementary circuit 90 associated with the supply circuit and configured to supplement a portion of the gaseous natural gas leaving the main heat exchanger 32 into the cryogenic tank 10.

[0080] Advantageously, thanks to the supplementary circuit 90, a pressure drop in the cryogenic tank 10 due to the pumping of liquefied natural gas by the pump 31 is avoided, thereby preventing an excessive pressure drop inside the cryogenic tank 10 and avoiding related problems such as natural gas solidification.

[0081] In fact, in addition to the liquefied natural gas extracted by the pump 31, the gaseous natural gas introduced into the cryogenic tank 10 by the supplementary circuit 90 keeps the pressure inside the cryogenic tank 10 substantially constant.

[0082] Furthermore, advantageously, the supplementary circuit 90 allows the pump to extract a certain amount from the cryogenic tank 10, thereby balancing the pressure drop caused by the instantaneous consumption of liquefied natural gas required for the operation of the device 1.

[0083] In other words, when the pump 31 withdraws natural gas from the cryogenic tank 10, the operating pressure in the cryogenic tank 10 is restored by replacing the volume of liquefied natural gas withdrawn by the pump 31 with the volume of supplementary gaseous spent natural gas.

[0084] In order to regulate the flow rates in the discharge circuit 60 and the supplementary circuit 90, slave shut-off and flow regulating valves are operably arranged.

[0085] According to a particular aspect of the present invention, the recirculation circuit 70 is adapted to convey in the capacitive tank 20 a part of the spent natural gas extracted from the working chamber 41 of the motor body 40.

[0086] Advantageously, thanks to the use of the recirculation circuit 70, the spent natural gas introduced into the delivery pipe from the discharge circuit 60 has temperature and pressure conditions such as being safe and sufficient for the delivery and distribution operations of the network itself. In other words, the spent natural gas is discharged without compromising the pressure and temperature of the device 1 and the delivery and distribution network of the regasified natural gas.

[0087] The recirculation circuit 70 is actually configured such that it extracts a part of the spent natural gas from the working chamber 41 and introduces it into the capacitive tank 20 after polytropic compression, as Figure 4 shown by the section "F" - "D" in the Mollier diagram in Figure 4 which raises the temperature and pressure. In the capacitive tank 20, the recirculated natural gas is mixed with the "overliquid" natural gas from the supply circuit 30. Inside the recirculation circuit, the natural gas has

[0088] the thermodynamic conditions denoted by the reference numeral "E" in the Mollier diagram in

[0089] The mixing of the recycled natural gas with the "liquefied" natural gas arriving from the supply circuit 30 takes place in a predetermined and controlled manner, thus defining the supplied natural gas. In other words, as will be explained in a subsequent part of the present disclosure, the amounts of recycled natural gas and "liquefied" natural gas arriving from the supply circuit 30 must follow a predetermined inverse relationship.

[0090] According to a preferred embodiment, this mass ratio between the recycled natural gas and the "liquefied" natural gas is 23 to 1.

[0091] Based on the embodiment of the device 1, the polytropic compression can be carried out by means of a dedicated compressor or advantageously by using the return stroke of the piston 48 from the bottom dead center to the top dead center of the motor body 40.

[0092] Hereinafter, two embodiments of the device 1 will be described in detail, paying particular attention to the technical characteristics of the motor body 40 and the recirculation circuit 70, since the characteristics of the cryogenic tank 10 and the supply circuit 30 are substantially the same.

[0093] The first embodiment is schematically shown in Figure 1 、 Figures 2A - 2C and Figures 3A - 3F shown.

[0094] In such an embodiment, the motor body is of the reciprocating type described above, as Figures 2A - 2C shown.

[0095] In such an embodiment, the motor body 40 is configured to:

[0096] - accommodate the supplied natural gas;

[0097] - preside over the expansion phase of the supplied natural gas;

[0098] - convert the displacement and / or expansion of the supplied natural gas into mechanical energy; and

[0099] - preside over the compression phase of the spent natural gas.

[0100] In other words, the motor body 40 is configured to perform the first operating phase, the second operating phase and the polytropic compression phase on the supplied natural gas.

[0101] Furthermore, in this embodiment, the motor body 40 is integrated with the recirculation circuit 70 and with the static mixing tank 20.

[0102] In other words, the capacitive tank 20 and the recirculation circuit 70 are obtained inside the motor body 40 and are defined by the operation and movement of its components.

[0103] Specifically, the motor body 40 has a supply chamber 51 and a discharge chamber 52, the supply chamber 51 and the discharge chamber 52 being provided in the cylinder and being respectively provided between the working chamber 41 and the inlet gap 42 and between the working chamber 41 and the discharge gap 43.

[0104] The supply chamber 51 and the discharge chamber 52 are respectively associated with a supply valve 46 and a discharge valve 47.

[0105] Specifically, each of the valves 46, 47 is mushroom-shaped and includes planar lower elements 46a, 47a and stems 46b, 47b, the planar lower elements 46a, 47a being configured to occlude the bottom portions of the respective chambers 51, 52, thereby defining a sealing interval with the working chamber 41, and the stems 46b, 47b being integral with the planar lower elements 46a, 47a.

[0106] Each of the valves 46, 47 is slidably constrained in the respective chambers 51, 52, thereby defining a translational movement with a linear trajectory.

[0107] The inlet gap 42 is present in the upper portion of the motor body 40 and is substantially transverse to the longitudinal axis of the supply chamber 51.

[0108] Similarly, the discharge gap 43 is present in the upper portion of the motor body 40 and is substantially transverse to the longitudinal axis of the discharge chamber 52.

[0109] According to a specific structural aspect of the supply valve 46, it has a chamber 46c present inside the stem 46b, the chamber 46c defining a first accommodation volume "V1". The stem 46b also has a through-hole 46d for such a chamber 46c, the through-hole 46d preferably being present transversely in the stem 46b.

[0110] The valve also has a closing element 46e for the chamber 46c.

[0111] Preferably, the closing element 46e is threaded and, depending on its degree of tightening in the chamber 46c, allows adjustment of the size of the first accommodation volume "V1".

[0112] The supply chamber 51 and the supply valve 46 together define a second accommodation volume "V2". In other words, the second accommodation volume "V2" is defined as the volume of the supply chamber 51 from which the space occupied by the supply valve 46 and the first accommodation volume "V1" are removed.

[0113] In this embodiment, the first accommodation volume "V1" and the second accommodation volume "V2" so defined define a capacitive tank 20.

[0114] According to another aspect of the present invention, the dimensional ratio between the first accommodation volume "V1" and the second accommodation volume "V2" is 1 to 23.

[0115] The supply valve 46 is movable within the supply chamber 51 such that it can assume four corresponding operating configurations.

[0116] Specifically, the supply valve 46 can assume a closed configuration, also defined as the first configuration shown in Figure 2c, in which the through-hole 46d faces the inlet gap 42 of the motor body 40, and in which the planar lower element 46a closes the lower supply chamber 51. Additionally, in this closed configuration, the rod 46b is substantially attached to the wall of the motor body 40, closing the upper supply chamber 51.

[0117] By lowering, the supply valve 46 can assume a second configuration in which the through-hole 46d does not face the inlet gap 42, the inlet gap 42 is closed by the rod 46b, and in which the planar lower element 46a closes the lower supply chamber 51. In such a configuration, the rod 46b still closes the upper part of the supply chamber 51 such that the first accommodation volume "V1" is not in fluid communication with the second accommodation volume "V2".

[0118] By further lowering, the supply valve 46 can assume a third configuration in which the through-hole 46d does not face the inlet gap 42, the inlet gap 42 is closed by the rod 46b, and in which the planar lower element 46a closes the lower supply chamber 51. In this configuration, the first accommodation volume "V1" is in fluid communication with the second accommodation volume "V2".

[0119] Finally, the supply valve 46 can assume an open configuration, also defined as the fourth configuration, in which the rod 46b closes the inlet gap 42 and in which the first accommodation volume "V1" and the second accommodation volume "V2" are in fluid communication with the working chamber 41.

[0120] The discharge valve 47 can alternatively assume two operating configurations.

[0121] Specifically, the discharge valve 47 can assume a closed configuration and an open configuration. In the closed configuration, the discharge valve 47 closes the supply chamber 52 and the lower discharge gap 43. In the open configuration, the discharge gap 43 is in fluid communication with the working chamber 41.

[0122] Advantageously, as shown in the drawings, according to another structural aspect, since in the open configuration the supply valve 46 or the discharge valve 47 can at least partially enter the working chamber 41, on the movable wall 44, the recess is at least partially made in a shape opposite to that of the supply valve 46 and the discharge valve 47 so as not to abut against them.

[0123] Hereinafter, the motion cycle of the embodiment of the motor body 40 just described will be described in detail.

[0124] In the following description, the motion cycle of the motor body 40 is described based on the angle presented by the motor shaft 50 during its clockwise rotation.

[0125] Specifically, the position of the motor shaft 50 where the movable wall 44 is located at top dead center is assumed to be at a 0-degree angle.

[0126] Specifically, Figure 3A An initial stage is shown, in which the supply valve 46 is in a closed configuration or a first configuration, and the discharge valve 47 is in a closed configuration.

[0127] In this stage, the recycled natural gas is contained in the second containment volume "V2".

[0128] The first containment volume "V1" is filled with "liquefied" natural gas from the supply circuit 30 via the inlet gap 42.

[0129] Preferably, according to the preferred use of the device 1, the mass ratio of the "liquefied" natural gas to the recycled natural gas is 1 to 23. Advantageously, this allows for very low consumption.

[0130] The movable wall 44 is close to top dead center.

[0131] In this stage, the motor shaft 50 moves from a 356-degree angle to a 6-degree angle.

[0132] Figure 3B A subsequent stage of the movement cycle is shown, in which the discharge valve 47 is in a closed configuration. In this stage, the supply valve 46 first switches to the second configuration, thereby closing the inlet gap 42, and then switches to the third configuration, thereby putting the first containment volume "V1" in fluid communication with the second containment volume "V2". In this configuration, the recycled natural gas can be mixed with the "liquefied" natural gas from the supply device 30 to obtain the supply natural gas.

[0133] This stage corresponds to the first operating stage of the motor body 40 described above.

[0134] In this stage, the movable wall 44 remains substantially close to top dead center, and the motor shaft 50 moves from a 6-degree angle to a 12-degree angle.

[0135] Figure 3C A stage is shown in which the supply valve 46 switches to an open configuration or a fourth configuration, while the discharge valve 47 is in a closed configuration.

[0136] In this stage, the first containment volume "V1" and the second containment volume "V2" are in fluid communication with the working chamber 41, such that the supply natural gas can be conveyed within the working chamber 41. This stage corresponds to the second operating stage of the motor body 40 described above. Under supply conditions, the movable wall 44 moves downward by the thrust of the natural gas. In this stage, the motor shaft 50 moves from a 12-degree angle to a 170-degree angle.

[0137] Figure 3DShows a stage of the movement cycle in which both the supply valve 46 and the discharge valve 47 are in the open configuration.

[0138] In this stage, an amount of spent natural gas corresponding to the amount of natural gas from the supply circuit 30 is conveyed into the discharge circuit 60 leaving the working chamber 41. The movable wall 44 is located near the bottom dead center.

[0139] In this stage, the motor shaft 50 moves from the 170 - degree angle to the 180 - degree angle.

[0140] Figure 3E Shows a stage of the movement cycle in which the supply valve 46 is in the open configuration or the first configuration, while the discharge valve 47 is switched in the closed configuration. In this stage, the spent natural gas is adiabatically compressed by means of the movable wall 44.

[0141] In this stage, the motor shaft 50 moves to the 180 - degree angle.

[0142] Furthermore, in this stage, the working chamber 41 contains a certain amount of natural gas corresponding to the recycled natural gas.

[0143] Finally, Figure 3F Shows the cycle stage of the movement cycle in which, after the polytropic compression, the recycled natural gas is located in the capacitive tank 20.

[0144] In this stage, the motor shaft 50 moves from the 180 - degree angle to the 356 - degree angle.

[0145] Advantageously, this embodiment has some advantages that make its use very efficient.

[0146] The first relates to the simplicity of the structure of the motor body 40. The motor body 40 is actually basically constructed as a general diesel motor.

[0147] In other words, advantageously, any existing diesel motor or Otto motor can be converted into such a motor body 40.

[0148] Specifically, the motor body 40 of the present invention can be obtained by modifying an existing diesel motor or Otto motor. In this case, the modification is limited to the head and the control of the valves that can be performed mechanically or electronically.

[0149] The second advantage relates to the compactness of the device 1. In fact, the recirculation circuit 70 and the capacitive tank 20 are present inside the motor body 40.

[0150] Now describe another embodiment of the device 1 not shown in the drawings.

[0151] In such an embodiment, the recirculation loop 70 is associated with the collection tank 61 of the discharge loop 60 and includes a compressor connected and moved by the motor body 60.

[0152] Basically, the compressor is configured to perform three different functions, specifically:

[0153] - Extract a portion of the lean natural gas from the collection tank 61 by means of a slave shut-off valve and a flow control valve, the volume of the exhausted natural gas of this portion having been calculated for recirculation and based on the desired discharge temperature of the device 1;

[0154] - Compress the natural gas;

[0155] - Transfer the compressed lean natural gas to the capacitive tank 20, where the pressure and temperature can be measured by appropriate measuring instruments.

[0156] Furthermore, a check valve can be provided between the compressor and the capacitive tank 20 so that the natural gas contained in the capacitive tank 20 does not return to the compressor.

[0157] According to one aspect of the invention, the operation of the device can depend on the rotation of the motor shaft 50 or on the control unit.

[0158] According to one aspect of the invention, the motor shaft 50 can be connected to an electric machine that converts the mechanical work available at the motor shaft 50 into electrical energy.

[0159] The invention also relates to a method for regasifying natural gas under cryogenic conditions, preferably capable of being carried out by the aforementioned device 1.

[0160] The method provides a preliminary stage in which a cryogenic tank 10 containing natural gas at a cryogenic temperature Tcryo and a pressure level Pcryo is provided. This state of the natural gas is Figure 4 represented in the Mollier diagram by the reference letter "A".

[0161] The method can include a previous stage in which the natural gas under cryogenic conditions is transported by special transport means (preferably an LNG carrier) and transferred to the cryogenic tank 10, which cryogenic tank 10 is preferably stationary and part of a fixed installation.

[0162] Alternatively, the method can be carried out by transferring (e.g., on an LNG carrier) after filling the cryogenic tank with gas under cryogenic conditions.

[0163] The method envisages a stage of cyclic operation.

[0164] Specifically, the method provides a stage in which, by means of the supply circuit 30 leaving the cryogenic tank, a predetermined flow rate of natural gas is extracted under cryogenic conditions. In the supply circuit 30, the pressure of the natural gas rises from the level Pcryo to the level Pproc, where Pproc is greater than Pcryo and greater than Prec, and the temperature of the natural gas rises from Tcryo to the process temperature Tproc, where Tproc is greater than Tcryo. These conditions are represented in the Mollier diagram of Figure 4 by the reference numeral "C".

[0165] Due to the foregoing work performed by the pump 31, these stages occur in the section 32 of the supply circuit 30.

[0166] Through these stages, the natural gas reaches a thermodynamic condition called the "liquefied" condition. Specifically, at high temperature and high pressure, especially at points arranged above the critical isotherm in the Mollier diagram, the natural gas reaches the supercritical state.

[0167] Then, the method provides a stage in which natural gas of mass M1 is supplied to the capacitive tank 20 at the temperature Tproc and the pressure level Pproc.

[0168] The recycled mass M2 of natural gas is also supplied to the capacitive tank 20 at the recycled temperature Trec and the pressure level Prev. This mass M2 of natural gas is in the recycled condition, which is represented in the Mollier diagram of Figure 4 by the reference numeral "D".

[0169] Preferably, the natural gas of mass M2 comes from the recirculation circuit 70, while the natural gas of mass M1 comes from the supply circuit 30.

[0170] At this time, the method provides a stage in which the natural gas of masses M1 and M2 (the "liquefied" mass M1 and the recycled mass M2 respectively) are mixed to obtain natural gas of mass M1 + M2 at the supply temperature Tfeed and the pressure level Pfeed.

[0171] The values of the pressure Pfeed and the temperature Tfeed are the weighted averages of the corresponding pressure values Pproc and Prec and the corresponding temperature values Tproc and Trec.

[0172] It should be remembered that preferably, the pressure Prec of the recycled natural gas is lower than the pressure Pproc of the natural gas from the supply circuit 30. Similarly, the temperature Trec of the recycled natural gas is preferably lower than the temperature Tfeed of the natural gas from the supply circuit 30.

[0173] Therefore, the value of the pressure Pfeed is lower than Pproc and higher than Prec. Similarly, the temperature value Tfeed is lower than Tproc and higher than Trec.

[0174] According to an alternative embodiment, the pressure Prec of the recycled natural gas is lower than the pressure Pproc of the natural gas from the supply circuit 30, but the temperature Trec of the recycled natural gas is higher than the temperature Tfeed of the natural gas from the supply circuit 30.

[0175] The mass M1+M2 is under the above-mentioned natural gas supply conditions. These conditions are indicated by the reference numeral "E" in the Figure 4 Mollier diagram.

[0176] Once the natural gas of mass M1+M2 is obtained, it is supplied from the capacitive tank 20 to the motor body 40 at the pressure level Pfeed and the supply temperature Tfeed.

[0177] Then, the method provides a stage in which the natural gas of mass M1+M2 expands in the motor body 40, thereby reducing the pressure from the Pfeed level to the Pex level, where Pex is lower than Pfeed, and thereby reducing the temperature from Tfeed to Tex, where Tex is lower than Feed, thereby generating mechanical energy.

[0178] This stage is indicated by the section "E"-"F" in the Figure 4 Mollier diagram. The end condition of the natural gas expansion is indicated by the reference numeral "F" in the Figure 4 Mollier diagram.

[0179] Finally, the method provides a stage of discharging the natural gas of mass M1' (corresponding to the initial mass M1) into the delivery pipe connected to the regasified natural gas transportation and distribution network. This stage is first carried out by means of the discharge circuit 60, then in the delivery pipe, and then introduced into the regasified natural gas transportation and distribution network connected thereto. The discharge conditions are indicated by the reference numeral "G" in the Figure 4 Mollier diagram.

[0180] The method further includes a stage in which the remaining mass of natural gas corresponding to the recycled mass "M2" is compressed, thereby increasing the pressure from the Pex level to the Prec level, and increasing the temperature from Tex to Trec, and supplying the mass M2 at the pressure level Prec and the supply temperature Trec of the capacitive tank 20. This stage is indicated by the reference numeral "F"-"D" in the Figure 4 Mollier diagram.

[0181] Preferably, the stage of compressing a mass M2 of natural gas so as to increase the pressure from level Pex to level Prec and increase the temperature from Tex to Trec and feeding the mass M2 at the pressure level Prec and supply temperature Trec of the capacitive tank 20 is carried out by means of the motor body 40, in particular by means of a return stroke opposite to the previous expansion, and the compressed natural gas is conveyed in the recirculation circuit 70.

[0182] According to a preferred embodiment of the method, the natural gas is methane. In this embodiment, the following pressure and temperature values are obtained:

[0183] - The pressure level Patm is approximately equal to atmospheric pressure; and

[0184] - The pressure level Pproc has a value between about 200 bar and about 220 bar;

[0185] - The pressure level Pfeed has a value between about 150 bar and about 200 bar;

[0186] - The pressure level Pex has a value between about 2 bar and about 4 bar;

[0187] - The temperature Tcryo is between about -130 °C and about -90 °C;

[0188] - The temperature Tproc is between about +300 °C and about +500 °C;

[0189] - The temperature Trec is between about +250 °C and about +350 °C;

[0190] - The temperature Tfeed is between about +280 °C and about +340 °C; and

[0191] - The temperature Tex is between about -20 °C and about +20 °C.

[0192] Advantageously, the present invention overcomes the drawbacks complained of in the prior art.

[0193] Specifically, one object achieved is to provide an apparatus 1 and a method for regasifying natural gas under cryogenic conditions, which allow high processing reliability while achieving a considerable improvement in the energy efficiency of the entire process.

[0194] This result is achieved thanks to the possibility of using the regasification of natural gas to generate mechanical and / or electrical energy, at least partially recovering the energy consumed in the previous liquefaction of the natural gas in order to be able to transport it more advantageously.

[0195] Furthermore, advantageously, from the point of view of processing and the environment, the apparatus 1 and the method are reliable because they do not require combustion and / or pollute the environment.

Claims

1. A method for regasification and distribution of natural gas, comprising the following stages: - Supplying natural gas of mass M0 at cryogenic temperature Tcryo and pressure level Pcryo to a cryogenic tank (10); - Extracting a mass M1 of natural gas from said cryogenic tank, where M1 is lower than M0, and increasing the pressure of the mass M1 from the pressure level Pcryo to the pressure level Pproc and increasing the temperature of the mass M1 from Tcryo to the process temperature Tproc by means of a supply circuit connected downstream of said cryogenic tank; - Supplying natural gas of mass M1 at temperature Tproc and pressure level Pproc to a capacitive tank (20) by means of said supply circuit, and supplying recycled natural gas of mass M2 at temperature Trec, in particular lower than the elevated temperature Tproc1, and at pressure level Prec, in particular lower than the elevated pressure Pproc, by means of a recirculation circuit (70); - Mixing the natural gas of mass M1 and M2 within said capacitive tank (20) to obtain natural gas of mass M1 + M2 at supply temperature Tfeed and at pressure level Pfeed; - Supplying natural gas of mass M1 + M2 at pressure level Pfeed and at supply temperature Tfeed to a motor body (40) connected downstream of said capacitive tank (20); - Expanding the natural gas of mass M1 + M2 in the motor body (40), thereby reducing the pressure from the pressure level Pfeed to the pressure level Pex and reducing the temperature from Tfeed to Tex, thereby generating mechanical energy; - Discharging a part M1’ of the natural gas of mass M1 + M2 at said temperature Tex and said pressure level Pex from said motor body (40) to a network for transporting and / or distributing natural gas connected downstream of said motor body (40); - Compressing the remaining mass of natural gas corresponding to the recycled mass M2 within said motor body (40), thereby increasing the pressure of the recycled mass M2 from the pressure level Pex to the pressure level Prec, and thereby increasing the temperature of the recycled mass from the temperature Tex to the temperature Trec; - Supplying said new mass M2 at pressure level Prec and supply temperature Trec to said capacitive tank (20) by means of said recirculation circuit (70) interposed between said motor body (40) and said capacitive tank (20).

2. The method according to claim 1, wherein, The temperature Tex and the pressure level Pex are suitable for introducing natural gas into the national transportation network and / or the natural gas distribution network; preferably, the temperature Tex is between -20 °C and 40 °C, and wherein the pressure level Pex is between 0.5 bar and 12 bar.

3. The method according to claim 1 or 2, wherein The temperature Tproc is between 300 °C and 500 °C, and wherein the pressure level Pproc is between 200 bar and 220 bar; preferably, the natural gas is in a supercritical state.

4. The method according to any one of the preceding claims, wherein, The temperature Trec of the recycled mass M2 is between +250 °C and +350 °C.

5. The method according to claim 4, in the case of being subordinate to claim 3, wherein the mass ratio of the mass M1 and the mass M2 is between 1:15 and 1:30, preferably having a value of 1:

23.

6. The method according to any one of the preceding claims, wherein, The temperature Tfeed is between 280 °C and 340 °C, and wherein the pressure level Pfeed is between 150 bar and 200 bar. Preferably, the stage of mixing the masses M1 and M2 of natural gas in the capacitive tank causes the expansion of the mass M1, in particular a transition from a supercritical state to a gaseous state.

7. The method according to any one of the preceding claims, wherein, The stage of increasing the pressure of the natural gas from the level Pcryo to the level Pproc and increasing the temperature of the natural gas from Tcryo to the process temperature Tproc is carried out by means of a pump operatively arranged in the supply circuit.

8. The method according to any one of the preceding claims, comprising a stage of transporting the cryogenic tank from the liquefaction point of the natural gas to the delivery point of the natural gas via a means of transport, in particular by means of an LNG carrier, said transport stage being between the stage of supplying the cryogenic tank and the stage of extracting the mass M1 from the cryogenic tank.

9. The method according to any one of claims 1 to 7 preceding, comprising a stage of transporting the mass M0 at the cryogenic temperature Tcryo and at the pressure level Pcryo from the liquefaction point of the natural gas to the delivery point of the natural gas via a means of transport, in particular by means of an LNG carrier, said transport stage being before the stage of supplying the cryogenic tank.

10. The method according to any one of the preceding claims, wherein, The cryogenic temperature Tcryo is between 180 °C and -140 °C, preferably equal to -160 °C, and wherein the pressure level Pcryo is substantially equal to atmospheric pressure.

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