Patent Description:
The term "cryogenic conditions" is intended to mean a carrier fluid in a low-temperature state, and in particular at a temperature lower than the respective critical point temperature of the carrier fluid, and in a low-pressure state, substantially equal to atmospheric pressure.

Moreover, the term "carrier fluid" is intended to mean fluids belonging to the family of cryogenic liquids such as, for example, nitrogen, oxygen, ammonia, as well as generic fluids having their critical temperature well below room temperature such as, for example, methane.

The present invention is used in various applications including, for example, electricity generation, propulsion (land, railway, naval), the handling of industrial machinery, or the high-efficiency re-gasification of fluids under cryogenic conditions (e.g., methane after transport on a methane tanker).

Engines powered by compressed air are known. A historical example is represented by the locomotives of the Naples-Portici railway line, whose pneumatic engines were powered by compressed air stored in a pressurized tank and taken by a distributor metering the quantity of compressed air required by the engine cycle and from which to obtain the mechanical energy.

A serious problem with this system is that it could only be fed at a relatively low pressure, up to <NUM> bar, due to safety problems. The low pressure allowed a limited amount of compressed air charge to be placed in the tank, thus resulting in a limited operating autonomy.

Moreover, the progressive bleeding of compressed air from the tank led to a decrease in the air pressure itself, with consequent reduction in functionality until the engine stopped.

A further problem was linked to the high consumption of air taken from the tank. In fact, the direct use of compressed air taken as a carrier gas did not allow any savings.

Another problem was the cost of supplying the compressed air supplied by a compressor which, as is known, has low efficiency and involves very high supply costs.

Moreover, in this solution, even if the air pressure were increased in order to increase the power obtainable from the engine, there would still be other problems linked to the use of compressed air.

The first problem is that the expansion of the air and the related decrease in temperature can generate condensation of water and carbon dioxide which, at certain values, can disrupt the operation of the engine. The second problem is linked to the low temperature reached by the exhaust gas at the engine exhaust, which can cause safety problems and/or environmental damage. For these reasons, the air is never compressed beyond <NUM>-<NUM> bar.

The success of compressed air engines is therefore limited to applications where, for safety reasons, the use of fuels and/or electric motors is not recommended such as, for example, in coal mines. Basically, this family of compressed air engines is that of pneumatic engines that have high consumption of compressed air. Document <CIT> discloses an energy producing plant with a cryogenic carier fluid as known in the art.

In this context, the technical task underlying the present invention is to propose a plant and a method for producing mechanical energy from a carrier fluid under cryogenic conditions, which overcome the above-mentioned drawbacks of the prior art.

In particular, it is an object of the present invention to provide a plant and a method for producing mechanical energy from a carrier fluid under cryogenic conditions in an efficient and continuous manner.

A further object of the present invention is to provide a plant and a method for producing mechanical energy from a carrier fluid under cryogenic conditions, which are free of condensation and/or "ice" problems at the exhaust of the plant itself.

A further object of the present invention is to provide a plant and a method for producing mechanical energy from a carrier fluid under cryogenic conditions apt to operate with very low consumption of carrier fluid.

A further object of the present invention is to provide a plant and a method for producing mechanical energy from a carrier fluid under cryogenic conditions, which do not affect the environment.

The specified technical task and objects are substantially achieved by means of a plant for producing mechanical energy from a carrier fluid under cryogenic conditions, comprising a cryogenic tank configured for storing said carrier fluid under said cryogenic conditions and a capacitive tank. The plant further comprises a supply circuit, arranged as a connection between the cryogenic tank and the capacitive tank and comprising a pump, configured to increase the pressure of the carrier fluid, and a main heat exchanger, arranged downstream of the pump and configured to promote a thermal exchange between a thermal source and the carrier fluid so as to increase the temperature of the carrier fluid and evaporate said carrier fluid. The plant provides an engine body, configured for producing mechanical energy and comprising at least one work chamber having an inlet port, arranged in fluid communication with the capacitive tank, and an outlet port connected to a discharge circuit for the spent carrier fluid, and a recirculation circuit designed to convey a portion of the spent carrier fluid into the capacitive tank.

Furthermore, the specified technical task and objects are substantially achieved by means of a method for producing mechanical energy from a carrier fluid under cryogenic conditions, comprising the preliminary steps of:.

The method also comprises the cyclical steps of:.

Further features of the present invention will become more apparent from the indicative, and therefore non-limiting description of a preferred, but not exclusive, embodiment of such a device, as illustrated in the accompanying drawings wherein:.

With reference to the accompanying figures, the reference numeral "<NUM>" indicates, as a whole, a plant for producing mechanical energy from a carrier fluid under cryogenic conditions.

Essentially, as shown in <FIG>, the plant <NUM> comprises a cryogenic tank <NUM>, a capacitive tank <NUM>, a supply circuit <NUM>, which connects the cryogenic tank <NUM> to the capacitive tank <NUM> and comprises a pump <NUM>, and a main heat exchanger <NUM>, an engine body <NUM>, a discharge circuit <NUM>, and a recirculation circuit <NUM>.

The cryogenic tank <NUM> is configured for storing the carrier fluid under the aforementioned cryogenic conditions.

Under normal operating conditions, almost all of the carrier fluid in the cryogenic tank <NUM> is in the liquid state. However, as will be seen hereinafter, a relatively small percentage of carrier fluid stored inside the cryogenic tank <NUM> can be provided in the gaseous state or, if necessary, the carrier fluid can be transformed into the solid state.

Advantageously, since the carrier fluid is stored in the cryogenic tank <NUM> at a pressure substantially equal to the ambient pressure, the problems concerning pressurized tanks are solved.

In terms of sizing, the size of the cryogenic tank <NUM> can be established "ad hoc" depending on the use of the plant and on the space and autonomy requirements.

Advantageously, since almost all of the carrier fluid is substantially stored in the liquid state, it is possible to accumulate a large amount thereof.

For the same volume, in fact, the carrier fluid in the liquid state has a mass as high as hundreds of times that of the same carrier fluid in the gaseous state.

According to one aspect of the present invention, the cryogenic tank <NUM> may comprise a suction vacuum pump <NUM> configured to extract a portion of carrier fluid in the gaseous state from the cryogenic tank <NUM> to obtain a pressure lower than the atmospheric pressure inside the cryogenic tank <NUM>.

In particular, said vacuum pump <NUM> can be operationally arranged in an upper portion of the cryogenic tank <NUM>, so as to draw from the gaseous portion of the carrier fluid which lies above the liquid portion of the carrier fluid.

According to a preferred use of said vacuum pump <NUM>, it can be used to create pressure and temperature conditions inside the cryogenic tank <NUM> such as to determine the triple point thermodynamic state of the carrier fluid.

Even more preferably, the vacuum pump <NUM> can be used so that in the cryogenic tank <NUM> a pressure and a temperature lower than the pressure and temperature determining the triple point thermodynamic state are reached.

This feature can be advantageously used, by way of non-limiting example, in naval applications, where it is necessary to solidify - at least partially - the carrier fluid stored inside the cryogenic tank <NUM>, so as to limit or even eliminate the resonance phenomena, preventing the ship from overturning. This condition is adjustable.

The supply circuit <NUM>, which connects the cryogenic tank <NUM> to the capacitive tank <NUM>, is operationally arranged downstream of the cryogenic tank <NUM>.

Generally, the supply circuit <NUM> is configured to modify the thermodynamic conditions of the carrier fluid so as to make it advantageously usable from the energy point of view.

The supply circuit <NUM> comprises the pump <NUM>, configured to increase the pressure of the carrier fluid, and the main heat exchanger <NUM>, operationally arranged downstream of the pump <NUM> and configured to promote a thermal exchange between a thermal source and the carrier fluid so as to increase the temperature of the carrier fluid and evaporate the carrier fluid, preferably evaporate the carrier fluid completely.

The pump <NUM> may be operationally arranged inside the cryogenic tank <NUM>, or may be operationally arranged in fluid communication with the cryogenic tank <NUM> via a conduit.

Specifically, the pump <NUM> is operationally arranged so that it can draw the carrier fluid in a liquid state from the cryogenic tank <NUM>.

A check valve <NUM> may also be provided between the cryogenic tank <NUM> and the pump <NUM>.

Advantageously, this check valve <NUM> allows the pump <NUM> to be used intermittently without causing "regurgitation" towards the cryogenic tank <NUM>, and therefore pressure increases in the cryogenic tank <NUM> due to the carrier fluid going back from the supply circuit <NUM> to the cryogenic tank <NUM>.

This allows the cryogenic tank <NUM> to be sized and the thermal insulation to be addressed in an optimal way.

Advantageously, by operating on a substantially incompressible liquid, the pump <NUM> requires a negligible operating energy cost compared to the mechanical energy produced by the plant <NUM> as a whole.

According to a further aspect, the pump <NUM> can be controlled and adjusted according to the speed of the engine body <NUM>.

Functionally, as will be explained in detail hereinafter, the pump <NUM> causes an increase in the pressure of the carrier fluid, so as to obtain a high-pressure carrier fluid in the liquid state.

Preferably, the carrier fluid is brought to a normally supercritical pressure value.

This transformation is shown in <FIG> on the Mollier diagram by segment AB.

A check valve <NUM> may be arranged between the pump <NUM> and the main heat exchanger <NUM>.

The check valve <NUM> can be configured to remove the load on the pump <NUM> caused by possible regurgitation of the carrier fluid in the gaseous state returning from the heat exchanger <NUM> and by actions on the carrier fluid that flows through the supply circuit <NUM> due to the effect of the pump <NUM>. The main heat exchanger <NUM> is configured to heat the high-pressure, liquid carrier fluid and promote a change of state thereof.

In particular, the main heat exchanger <NUM> is configured to promote a change of state of the carrier fluid from the liquid state to the gaseous state, preferably to a supercritical gas phase.

Specifically, the main heat exchanger <NUM> causes the temperature reached by the carrier fluid to be higher than the respective critical temperature. Furthermore, the main heat exchanger <NUM> is configured to maintain the pressure of the carrier fluid substantially constant with respect to the value acquired following the work of the pump <NUM>.

In the present description, the term "thermal source" is intended to mean any heat source having a temperature higher than the carrier fluid at the outlet of the pump <NUM> and preferably higher than the critical temperature of the carrier fluid.

This thermal source may be of any nature, provided it is suitable for the purpose.

According to an exemplary and therefore non-limiting embodiment, atmospheric air or sea water can be used as in the known methane re-gasification applications.

According to a further embodiment, the main heat exchanger <NUM> can be associated, for example, with a solar collector plant which acts as a thermal source, so as to obtain thermal energy substantially at zero cost. According to a further embodiment, the plant <NUM> can comprise an auxiliary plant for producing mechanical energy, not shown in the figures, associated with or associable with the main heat exchanger <NUM>, which transfers its own thermal waste, which acts as a cold thermal source, to the main heat exchanger <NUM>.

Preferably, this auxiliary plant for producing mechanical energy comprises a Stirling engine.

In particular, the Stirling engine is placed between the thermal source and the main heat exchanger <NUM>.

Specifically, the Stirling engine uses the heat from the thermal source to supply energy to a respective expansion chamber of the Stirling engine, whereas it uses the main heat exchanger <NUM> to subtract energy from a respective compression chamber of the Stirling engine. In other words, the carrier fluid acts as a cold source, extracting heat from the Stirling engine. In the presence of the Stirling engine, it may be particularly advantageous to provide a thermal source at a higher temperature than the atmospheric air and/or sea water. For example, the thermal source may comprise solar collectors or a low-enthalpy plant for heat recovery from other production cycles.

Structurally, the main heat exchanger <NUM> can be made according to any known type of construction, provided it is suitable for the purpose.

Functionally, inside the main heat exchanger <NUM>, the heating of the carrier fluid basically takes place in two steps.

In a first step, the high-pressure, liquid carrier fluid receives heat from the thermal source by means of the main heat exchanger and undergoes a change of state, passing from the liquid to the gaseous state.

This change of state allows the high-pressure, gaseous carrier fluid to create the "hydraulic press" effect.

In fact, the volume of the carrier fluid in the liquid state is hundreds of times less than the volume occupied by the same mass of carrier fluid in the gaseous state.

Therefore, in the second heating step, this amplifying effect is used so as to further increase the temperature of the high-pressure, gaseous carrier fluid.

This transformation is shown in <FIG> on the Mollier diagram by segment BC.

Functionally, therefore, the supply circuit <NUM> transforms the low-pressure, liquid carrier fluid from the cryogenic tank <NUM> into a high-pressure, gaseous carrier fluid.

In summary, the carrier fluid stored in the cryogenic tank <NUM> is under cryogenic conditions, i.e., at very low temperatures, above the melting temperature of the respective carrier fluid and at a pressure substantially equal to atmospheric pressure.

In other words, the carrier fluid under cryogenic conditions is not in such conditions as to be used advantageously and directly to obtain mechanical work.

By using the supply circuit <NUM>, the pressure of the carrier fluid is increased by means of the pump <NUM>, and the temperature is changed by means of the main heat exchanger <NUM>. In addition, the main heat exchanger <NUM> promotes a change of state, from liquid to gas, of the carrier fluid.

In this way, the carrier fluid at the outlet of the supply plant is in the "ex-liquid" condition, i.e., in the gaseous state at high pressure. This condition is shown in <FIG> by the reference "C".

The capacitive tank <NUM> is operationally arranged downstream of the main heat exchanger <NUM> and in fluid communication therewith.

As shown in <FIG>, moreover, the supply circuit <NUM> can comprise a metering tank <NUM>, a valve <NUM> configured to insulate the supply circuit <NUM>, and a valve <NUM> placed between the metering tank <NUM> and the capacitive tank <NUM>.

The capacitive tank <NUM> is configured to collect and mix a given quantity of "ex-liquid" carrier fluid from the supply circuit <NUM> with a respective quantity of recirculation carrier fluid recovered from the engine body <NUM> by means of the recirculation circuit <NUM>, in order to advantageously supply the engine body <NUM>.

In other words, said capacitive tank <NUM> is suitably sized to mix the "ex-liquid" carrier fluid and the recirculation carrier fluid so as to obtain a given quantity of carrier fluid defined as the "supply carrier fluid".

Moreover, said capacitive tank <NUM> is suitably sized to meter the supply carrier fluid with which the engine body <NUM> is to be to supplied.

This carrier fluid defined as the "supply carrier fluid" has pressure and temperature conditions averaged with respect to the pressure and temperature conditions of the "ex-liquid" carrier fluid and recirculation carrier fluid. This "supply" condition is shown in <FIG> by the reference "E".

The features of the recirculation circuit <NUM> as well as the dosage ratio between the "ex-liquid" carrier fluid and the recirculation carrier fluid will be illustrated in detail hereinafter.

The "recirculation" condition is instead shown in <FIG> by the reference "D".

The engine body <NUM> is configured for producing mechanical energy and comprises at least one work chamber <NUM> having an inlet port <NUM> arranged in fluid communication with the capacitive tank <NUM>, from which it is supplied with the supply carrier fluid, and an outlet port <NUM> connected to the discharge circuit <NUM> for the spent carrier fluid, shown in <FIG> by the reference "G".

The expansion of the "ex-liquid" carrier fluid is shown in <FIG> by the reference "EG".

The work chamber <NUM> is configured to transform the expansion and/or movement of the supply carrier fluid into mechanical work by means of at least one movable wall <NUM>.

Preferably, the movable wall <NUM> is bound to translate between an upper dead centre and a lower dead centre. Alternatively, the movable wall <NUM> can be bound to rotate about an axis.

The term "spent carrier fluid" is intended to mean the carrier fluid under conditions subsequent to this transformation, in which the carrier fluid has low enthalpy and temperature and pressure conditions suitable for emission into the environment.

The engine body <NUM> can be made according to any type, provided it is suitable for the required purpose.

According to a preferred embodiment, the engine body <NUM> is of the reciprocating motion type.

In particular, in a manner known per se, the engine body <NUM> comprises at least one cylinder <NUM> defining the work chamber <NUM> having the inlet port <NUM>, associated with a supply valve <NUM>, and the outlet port <NUM>, associated with a discharge valve <NUM>. The cylinder <NUM> houses a piston <NUM>, which is slidingly constrained therein and integral with the respective movable wall <NUM>, and a connecting rod <NUM>, which is constrained to the piston <NUM>. Lastly, the connecting rod <NUM> is constrained to a drive shaft <NUM>.

Functionally, the engine body <NUM> is configured such that the transformation work of the engine body <NUM> on the supply carrier fluid can be substantially divided into two distinct operating steps.

In the first operating step, with the supply valve <NUM> open, high-pressure supply carrier fluid from the capacitive tank <NUM> is conveyed to the work chamber <NUM> of the engine body <NUM>, which causes a first movement of the movable wall <NUM> and therefore a first movement of the drive shaft <NUM>.

Since this is a mechanical mass transport phenomenon, in this first operating step, the pressure, temperature and enthalpy of the supply carrier fluid can be considered substantially constant.

In other words, mechanical energy is generated as a result of the transfer of a mass of the supply carrier fluid into the work chamber <NUM>.

Furthermore, in the first operating step, the supply carrier fluid does not undergo thermodynamic transformations, but maintains the pressure and enthalpy substantially constant.

After the first operating step has been completed, a second operating step begins. This second operating step consists of a transformation similar to a polytropic transformation, which exchanges mechanical work with the movable wall <NUM> of the work chamber <NUM>.

In particular, in the second operating step, part of the enthalpy of the supply carrier fluid is transformed into mechanical energy.

In particular, the temperature and pressure of the supply carrier fluid are reduced and the carrier fluid can be considered as spent carrier fluid.

In the second operating step, since the transfer of the mass of supply carrier fluid from the capacitive tank <NUM> to the work chamber <NUM> is finished, the mass of the carrier fluid within the work chamber can be considered constant.

The mechanical energy obtained in this second, expansion operating step is negligible compared to the mechanical energy obtained in the first, transfer operating step.

In the following description, a movement cycle of the engine body <NUM> is described as a function of the angle assumed by the drive shaft <NUM> during its rotation, which occurs in a clockwise direction.

In particular, the position of the drive shaft <NUM> in which the movable wall <NUM> is in the upper dead centre is assumed as an angle of <NUM> degrees.

In particular, in the first operating step, the drive shaft <NUM> is moved from <NUM> degrees to <NUM> degrees, whereas in the second operating step, the drive shaft <NUM> is moved from <NUM> degrees to <NUM> degrees.

According to a further embodiment, not shown in the accompanying figures, the engine body <NUM> may be of the flow engine type.

In this embodiment, the first operating step and the second operating step occur substantially simultaneously.

Once the operating steps have been completed, the spent carrier fluid is conveyed - at least partially - into the discharge circuit <NUM>. The discharge circuit <NUM> is designed to discharge the carrier fluid into the environment under the conditions indicated by the reference "F" in the Mollier diagram in <FIG>. The discharge circuit <NUM> may comprise a collection tank <NUM> for the spent carrier fluid and a discharge duct designed to at least partially expel the spent carrier fluid from the plant <NUM>.

The discharge circuit <NUM> may further comprise a discharge valve <NUM>.

According to a further aspect of the present invention, the plant <NUM> can comprise a system <NUM> for stopping the operation of the engine body <NUM> configured to stop the operation of the plant.

Preferably, the stopping system <NUM> can be associated with the pump <NUM> so as to be able to block the extraction of carrier fluid from the cryogenic tank <NUM> and therefore the supply to the plant <NUM>.

The stopping system <NUM> can also act through the valve <NUM>, connected to the stopping system <NUM>.

According to one aspect of the present invention, the plant <NUM> can comprise a replenishment circuit <NUM> associated with the discharge circuit and configured to replenish the cryogenic tank <NUM> with a portion of the spent fluid passing through the discharge circuit <NUM>, and in particular with a portion of spent fluid passing through the collection tank <NUM>.

Alternatively, the plant <NUM> may comprise a replenishment circuit <NUM> associated with the supply circuit and configured to replenish the cryogenic tank <NUM> with a portion of the gaseous carrier fluid exiting the main heat exchanger <NUM>.

Advantageously, the replenishment circuit <NUM> prevents the pressure decrease in the cryogenic tank <NUM>, due to the bleeding of liquid carrier fluid exerted by the pump <NUM>, from excessively decreasing the pressure inside the cryogenic tank <NUM>, thus avoiding problems related, for example, to the solidification of the carrier fluid.

In fact, the carrier fluid in the gaseous state introduced into the cryogenic tank <NUM> by the replenishment circuit <NUM> maintains the pressure inside the cryogenic tank <NUM> substantially constant, net of the carrier fluid in the liquid state extracted by the pump <NUM>.

Advantageously, moreover, the replenishment circuit <NUM> allows the pump to draw from the cryogenic tank <NUM> quantities such as to balance the pressure decrease caused by the instantaneous consumption of carrier fluid in the liquid state required for the operation of the plant <NUM>.

In other words, as the pump <NUM> withdraws carrier fluid from the cryogenic tank <NUM>, the operating pressure in the cryogenic tank <NUM> is restored by replacing the volume of carrier fluid in the liquid state, withdrawn by the pump <NUM>, with a volume of the spent carrier fluid in a re-integrated gaseous state.

Pilot-operated valves for flow interception and regulation can be operationally arranged for the regulation of the flows in the discharge circuit <NUM> and replenishment circuit <NUM>.

According to a particular aspect of the present invention, the recirculation circuit <NUM> is designed to convey a portion of the spent carrier fluid, drawn from the work chamber <NUM> of the engine body <NUM>, into the capacitive tank <NUM>.

Advantageously, the use of the recirculation circuit <NUM> allows the spent carrier fluid, discharged into the atmosphere from the discharge circuit <NUM>, to have such temperature and pressure conditions as to be safe and suitable for the environment. In other words, the spent carrier fluid is discharged at such a pressure and temperature as not to damage the plant <NUM> and the environment.

The recirculation circuit <NUM> is in fact configured so as to draw part of the spent carrier fluid from the work chamber <NUM> and introduce it into the capacitive tank <NUM> following a polytropic compression, indicated in the Mollier diagram in <FIG> by the reference "GD", which increases the temperature and pressure thereof. In the capacitive tank <NUM>, the recirculating carrier fluid mixes with the "ex-liquid" carrier fluid from the supply circuit <NUM>, thereby increasing the pressure and temperature thereof. This state of the carrier fluid is indicated in the Mollier diagram in <FIG> by the reference "D".

In fact, the temperature of the recirculating carrier fluid, following the polytropic compression, is higher than the temperature of the "ex-liquid" carrier fluid from the supply circuit <NUM>.

In contrast, the pressure of the recirculating carrier fluid is lower than the pressure of the "ex-liquid" carrier fluid from the supply circuit <NUM>.

The mixing of the recirculating carrier fluid with the "ex-liquid" carrier fluid from the supply circuit <NUM> takes place in a predetermined and controlled manner, so as to define the supply carrier fluid.

In other words, the quantities of recirculating carrier fluid and carrier fluid from the supply circuit <NUM> must meet a predetermined reciprocal ratio, as will be explained hereinafter.

According to a preferred embodiment, this mass ratio between the recirculating carrier fluid and the "ex-liquid" carrier fluid is <NUM> to <NUM>.

The polytropic compression, depending on the embodiment of the plant <NUM>, can be carried out by means of a suitable compressor or advantageously by means of the engine body <NUM>, using the return stroke from the lower dead centre to the upper dead centre of the piston <NUM>.

Two embodiments of the plant <NUM> will be described in detail below, with particular attention to the technical characteristics of the engine body <NUM> and recirculation circuit <NUM>, since the characteristics of the cryogenic tank <NUM> and supply circuit <NUM> are substantially the same.

A first embodiment is schematically shown in <FIG>, <FIG>, and <FIG>.

In this embodiment, the engine body is of the aforesaid reciprocating motion type, shown in <FIG>.

In this embodiment, the engine body <NUM> is configured to:.

In other words, the engine body <NUM> is configured to carry out the first and second operating steps and the polytropic compression step on the supply carrier fluid.

In this embodiment, moreover, the engine body <NUM> is integral with the recirculation circuit <NUM> and with the stilling and mixing tank <NUM>.

In other words, the capacitive tank <NUM> and the recirculation circuit <NUM> are formed inside the engine body <NUM> and defined by the operation and movement of the components thereof.

In detail, the engine body <NUM> has a supply chamber <NUM> and a discharge chamber <NUM>, which are formed in the cylinder and placed between the work chamber <NUM> and the inlet port <NUM> and between the work chamber <NUM> and the outlet port <NUM>, respectively.

The supply valve <NUM> and the discharge valve <NUM> are associated with the supply chamber <NUM> and the discharge chamber <NUM>, respectively.

In particular, each of the valves <NUM>, <NUM> is a poppet valve and comprises a lower planar element 46a, 47a configured to close a bottom portion of the respective chamber <NUM>, <NUM> so as to define a hermetic separation from the work chamber <NUM>, and a stem 46b, 47b, integral with the lower planar element 46a, 47a.

Each of the valves <NUM>, <NUM> is slidingly constrained in the respective chamber <NUM>, <NUM> so as to define a translation movement with a linear trajectory.

The inlet port <NUM> is formed in the engine body <NUM> in an upper portion thereof and is substantially transverse to a longitudinal axis of the supply chamber <NUM>.

Likewise, the outlet port <NUM> is formed in the engine body <NUM> in an upper portion thereof and is substantially transverse to a longitudinal axis of the discharge chamber <NUM>.

The supply valve <NUM>, according to a particular structural aspect, has a cavity 46c formed inside the stem 46b, which defines a first containment volume "V1". The stem 46b also has a through hole 46d for said cavity 46c, preferably formed transversely in the stem 46b.

The valve also has a closing element 46e for closing the cavity 46c. Preferably, this closing element 46e is threaded and, depending on how tight it is in the cavity 46c, allows the size of the first containment volume "V1" to be adjusted.

The supply chamber <NUM>, together with the supply valve <NUM>, defines a second containment volume "V2". In other words, this second containment volume "V2" is defined as the volume of the supply chamber <NUM> from which the bulk of the supply valve <NUM> and the first containment volume "V1" are subtracted.

In this embodiment, the thus defined first containment volume "V1" and second containment volume "V2" define the capacitive tank <NUM>.

According to a further aspect of the present invention, the dimensional ratio between the first containment volume "V1" and the second containment volume "V2" is <NUM> to <NUM>.

The supply valve <NUM> is movable inside the supply chamber <NUM> so that it can assume four respective operating configurations.

In particular, the supply valve <NUM> can assume a closed configuration, also defined as the first configuration, shown in <FIG>, in which the through hole 46d faces the inlet port <NUM> of the engine body <NUM> and in which the lower planar element 46a closes the supply chamber <NUM> at the bottom. Moreover, in this closed configuration, the stem 46b, substantially adhering to the walls of the engine body <NUM>, closes the supply chamber <NUM> at the top.

When the supply valve <NUM> is lowered, it can assume a second configuration, in which the through hole 46d does not face the inlet port <NUM>, which is closed by the stem 46b, and in which the lower planar element 46a closes the supply chamber <NUM> at the bottom. In this configuration, the stem 46b still closes the supply chamber <NUM> at the top so that the first containment volume "V1" is not in fluid communication with the second containment volume "V2".

When the supply valve <NUM> is lowered still further, it can assume a third configuration, in which the through hole 46d does not face the inlet port <NUM>, which is closed by the stem 46b, and in which the lower planar element 46a closes the supply chamber <NUM> at the bottom. In this configuration, the first containment volume "V1" is in fluid communication with the second containment volume "V2".

Lastly, the supply valve <NUM> can assume an open configuration, also defined as the fourth configuration, in which the stem 46b closes the inlet port <NUM> and the first "V1" and second "V2" containment volumes are in fluid communication with the work chamber <NUM>.

The discharge valve <NUM>, on the other hand, can assume two operating configurations.

In particular, the discharge valve <NUM> can assume a closed configuration, in which the discharge valve <NUM> closes the supply chamber <NUM> and the outlet port <NUM> at the bottom, and an open configuration, in which the outlet port <NUM> is in fluid communication with the work chamber <NUM>.

Advantageously, as shown in the attached figures, according to a further structural aspect, since in the open configuration the supply valve <NUM> or the discharge valve <NUM> could at least partially enter the work chamber <NUM>, a number of recesses are formed on the movable wall <NUM>, the recesses being at least partially shaped complementarily to the supply and discharge valves <NUM>, <NUM> so as not to abut against them.

A movement cycle of the above embodiment of the engine body <NUM> will be described in detail hereinafter.

In particular, <FIG> shows an initial step in which the supply valve <NUM> is in the closed configuration, or first configuration, and the discharge valve <NUM> is in the closed configuration.

In this step, the recirculating carrier fluid is within the second containment volume "V2".

The first containment volume "V1" is filled with the "ex-liquid" carrier fluid from the supply circuit <NUM> through the inlet port <NUM>.

Preferably, according to a preferred use of the plant <NUM>, the mass ratio between the "ex-liquid" carrier fluid and the recirculating carrier fluid is <NUM> to <NUM>. Advantageously, this allows very low consumption.

The movable wall <NUM> is close to the upper dead centre.

During this step, the drive shaft <NUM> is moved from the angle of <NUM> degrees to the angle of <NUM> degrees.

<FIG> shows a subsequent step of the movement cycle in which the discharge valve <NUM> is in the closed configuration. During this step, the supply valve <NUM> is first switched to the second configuration so as to close the inlet port <NUM>, and then switched to the third configuration so that the first containment volume "V1" is in fluid communication with the second containment volume "V2". In this configuration, the recirculating carrier fluid can mix with the "ex-liquid" carrier fluid from the supply circuit <NUM>, thereby obtaining the supply carrier fluid.

This step corresponds to the first operating step of the engine body <NUM> described above.

During this step, the movable wall <NUM> is still substantially close to the upper dead centre and the drive shaft <NUM> is moved from the angle of <NUM> degrees to the angle of <NUM> degrees.

<FIG> shows a step in which the supply valve <NUM> is switched to the open configuration, or fourth configuration, whereas the discharge valve <NUM> is in the closed configuration.

During this step, the first containment volume "V1" and the second containment volume "V2" are in fluid communication with the work chamber <NUM> so that the supply carrier fluid can move into the work chamber <NUM>. This step corresponds to the second operating step of the engine body <NUM> described above. The movable wall <NUM> is moved downwards by the thrust of the carrier fluid in the supply conditions. During this step, the drive shaft <NUM> is moved from the angle of <NUM> degrees to the angle of <NUM> degrees.

<FIG> shows a step of the movement cycle in which both the supply valve and the discharge valve <NUM>, <NUM> are in the open configuration.

During this step, a quantity of spent carrier fluid, corresponding to the quantity of carrier fluid coming from the supply circuit <NUM>, is conveyed into the discharge circuit <NUM> from the work chamber <NUM>. The movable wall <NUM> is close to the lower dead centre.

<FIG> shows a step of the movement cycle in which the supply valve <NUM> is in the open configuration, or first configuration, whereas the discharge valve <NUM> is switched to the closed configuration. During this step, the spent carrier fluid undergoes the adiabatic compression by the movable wall <NUM>.

During this step, the drive shaft <NUM> is moved to the angle of <NUM> degrees. During this step, moreover, the work chamber <NUM> contains a quantity of carrier fluid corresponding to the recirculating carrier fluid.

Lastly, <FIG> shows a step of the movement cycle in which, following the polytropic compression, the recirculating carrier fluid is in the capacitive tank <NUM>.

Advantageously, this embodiment has several advantages which make its use extremely efficient.

The first relates to the structural simplicity of the engine body <NUM>. In fact, the engine body <NUM> is substantially structured as a generic Diesel engine. Advantageously, in other words, any existing Diesel or Otto engine can be converted into said engine body <NUM>.

In particular, the engine body <NUM> of the invention can be obtained by modifying an existing Diesel or Otto engine. In this case, the modifications are limited to the cylinder head and to the control of the valves, which can be done mechanically or electronically.

The second advantage is linked to the compactness of the plant <NUM>. In fact, the recirculation circuit <NUM> and the capacitive tank <NUM> are formed inside the engine body <NUM>.

A further embodiment of the plant <NUM>, not shown in the accompanying figures, will now be described.

In this embodiment, the recirculation circuit <NUM> is associated with the collection tank <NUM> of the discharge circuit <NUM> and comprises a compressor connected and moved by the engine body <NUM>.

Essentially, the compressor is configured to perform three distinct functions, in particular:.

Moreover, a check valve can be arranged between the compressor and the capacitive tank <NUM>, so that the carrier fluid contained in the capacitive tank <NUM> does not return to the compressor.

According to one aspect of the present invention, the operation of the plant can be entrusted to the rotation of the drive shaft <NUM> or to a control unit. The present invention also relates to a method for producing mechanical energy from a carrier fluid under cryogenic conditions, which can be preferably carried out by means of the aforesaid plant <NUM>.

The method comprises preliminary steps of preparing the cryogenic tank <NUM> containing a carrier fluid at a cryogenic temperature Tcryo and a pressure level Pcryo. This state of the carrier fluid is indicated in the Mollier diagram in <FIG> by the reference "A".

The method also comprises the preliminary steps of preparing the capacitive tank <NUM> and the engine body <NUM> designed to host an expansion phase and a compression phase.

The method further comprises the preliminary step of supplying the capacitive tank <NUM> with a mass M2 of carrier fluid at a recirculation temperature Trec and at the pressure level Prec. This mass M2 of carrier fluid in the aforementioned recirculation conditions is indicated in the Mollier diagram in <FIG> by the reference "D".

At this point, the method comprises cyclical steps.

In particular, the method comprises a step wherein the pressure of the carrier fluid is raised from the Pcryo level to the Pproc level, where Pproc is greater than Pcryo and greater than Prec. This condition is indicated in the Mollier diagram in <FIG> by the reference "B".

Preferably, the step of raising the pressure of the carrier fluid from the Pcryo level to the Pproc level is carried out by means of the pump <NUM>.

Next, the method comprises a step wherein the temperature of the carrier fluid is raised from Tcryo to a first process temperature Tproc1, where Tproc1 is greater than Tcryo, and a step wherein the temperature of the carrier fluid is raised from Tproc1 to a second process temperature.

Tproc2, where Tproc2 is greater than Tproc1.

This condition is indicated in the Mollier diagram in <FIG> by the reference "C".

These steps are preferably carried out by the main heat exchanger <NUM>. Moreover, in these steps, the carrier fluid is transformed from liquid to gas, thereby obtaining the carrier fluid in the aforementioned "ex-liquid" conditions.

The method then comprises a step wherein the capacitive tank <NUM> is supplied with a mass M1 of working fluid at the temperature Tproc2 and pressure level Pproc.

Preferably, the mass M2 of the carrier fluid comes from the recirculation circuit <NUM>, whereas the mass M1 of the carrier fluid comes from the supply circuit <NUM>.

At this point, the method comprises a step wherein the masses M1 and M2, "ex-liquid" and recirculating, respectively, of the carrier fluid are mixed, thereby obtaining a mass M1+M2 of the carrier fluid at the supply temperature Tfeed and pressure level Pfeed.

It is recalled that the pressure Prec of the recirculating carrier fluid is lower than the pressure Pfeed of the supply carrier fluid. Furthermore, the temperature Trec of the recirculating carrier fluid is higher than the temperature Tfeed of the supply carrier fluid.

This mass M1+M2 is in the aforesaid supply carrier fluid conditions. This condition is indicated in the Mollier diagram in <FIG> by the reference "E".

Once the mass M1+M2 of the carrier fluid has been obtained, it is supplied from the capacitive tank <NUM> to the engine body <NUM> at the pressure level Pfeed and supply temperature Tfeed.

The method then comprises a step of expanding the mass M1+M2 of carrier fluid in the engine body <NUM>, so as to lower the pressure from the level Pfeed to the level Pex, wherein Pex is less than Pproc, and to lower the temperature from Tfeed to Tex, wherein Tex is less than Tfeed, thereby producing mechanical energy.

This step is indicated in the Mollier diagram in <FIG> by the reference "EG".

The condition of end of expansion of the carrier fluid is indicated in the Mollier diagram in <FIG> by the reference "G".

Lastly, the method comprises a step of discharging the mass M1 of fluid towards an external environment.

This step is preferably carried out with the discharge circuit <NUM>. The discharge conditions are indicated in the Mollier diagram in <FIG> by the reference "F".

The method further comprises a step of compressing the mass M2 of fluid so as to raise the pressure from the level Pex to the level Prec and so as to raise the temperature from Tex to Trec and supply the capacitive tank <NUM> with the mass M2 at the pressure level Prec and supply temperature Trec. This step is indicated in the Mollier diagram in <FIG> by the reference "GD".

Preferably, the step of compressing the mass M2 of fluid so as to raise the pressure from the level Pex to the level Prec and to raise the temperature from Tex to Trec and supply the capacitive tank <NUM> with the mass M2 at the pressure level Prec and supply temperature Trec is carried out by means of the recirculation circuit <NUM>.

According to one embodiment of the method, the carrier fluid spent is nitrogen. In this embodiment, the pressure and temperature values are the following:.

According to a further embodiment of the method, the carrier fluid is methane. In this embodiment, the pressure and temperature values are the following:.

Advantageously, the present invention overcomes the drawbacks encountered in the prior art.

In particular, an achieved object is that of providing a plant and a method for producing mechanical energy from a carrier fluid under cryogenic conditions, which are free of condensation and/or "ice" problems at the discharge of the plant itself.

This result is achieved by the presence of the recirculation circuit <NUM>, which allows a temperature of the spent carrier fluid at the outlet of the plant <NUM> sufficient to prevent the formation of condensation and/or ice.

A further achieved object is that of providing a plant and a method for producing mechanical energy from a carrier fluid under cryogenic conditions, which are capable of operating with very low consumption of carrier fluid.

This result is achieved by means of the recirculation circuit <NUM>, which allows very low consumption of carrier fluid.

A further achieved object is that of providing a plant and a method for producing mechanical energy from a carrier fluid under cryogenic conditions, which do not affect the environment.

Claim 1:
A plant (<NUM>) for producing mechanical energy from a carrier fluid under cryogenic conditions, comprising:
- a cryogenic tank (<NUM>) configured for storing said carrier fluid under said cryogenic conditions;
- a capacitive tank (<NUM>);
- a supply circuit (<NUM>), connecting said cryogenic tank (<NUM>) to said capacitive tank (<NUM>) and comprising a pump (<NUM>), configured to increase the pressure of said carrier fluid, and a main heat exchanger (<NUM>), arranged downstream of said pump (<NUM>) and configured to promote a thermal exchange between a thermal source and said carrier fluid so as to increase the temperature of said carrier fluid and evaporate said carrier fluid;
- an engine body (<NUM>), configured for producing said mechanical energy and comprising at least one work chamber (<NUM>) having an inlet port (<NUM>), arranged in fluid communication with said capacitive tank (<NUM>), and an outlet port (<NUM>) connected to a discharge circuit (<NUM>) for the spent carrier fluid;
characterised in that it comprises a recirculation circuit (<NUM>) designed to convey a portion of said spent carrier fluid into said capacitive tank (<NUM>).