IT202100004295A1 - VOLUMETRIC DRIVE MACHINE FUEL WITH HYDROGEN AND LIQUID OXYGEN - Google Patents

Description

VOLUMETRIC DRIVE MACHINE FUEL WITH HYDROGEN AND LIQUID OXYGEN

DESCRIPTION

Technical Sector of the Invention

The present invention ? relating to an innovative volumetric driving machine which adopts a thermodynamic cycle similar to a diesel cycle. The car ? preferably fueled with hydrogen in quality? of fuel and with liquid oxygen in quality? of comburent, and usable, therefore, for the generation of energy from a source of combined hydrogen and oxygen.

In particular, the energy produced may be used, by way of example, in electricity storage systems in the phase of returning energy to the grid and/or for the mechanical propulsion of units? naval vessels, for example ships for the transport of hydrogen.

Advantageously, the thermal energy produced by the combustion gases will be able to be used as a thermal source in plants for the production of additional electricity, for example in organic Rankine cycle (ORC) plants.

The volumetric machine, according to the present invention, will be? free of harmful emissions to the exhaust, sar? equipped with a good thermodynamic efficiency and sar? competitive from an economic point of view compared to other sources of ?clean? energy? powered by hydrogen, such as fuel cell systems.

Known technique

How?? known, hydrogen and oxygen are available in large-scale energy storage systems, based on the production of hydrogen by electrolysis of water. These two products are often stored on site as compressed gas or as liquefied gas. Storage as liquid ? more easy for oxygen, which can? be liquefied at a temperature pi? higher than hydrogen and requires a smaller storage volume. The concept of energy storage with hydrogen involves the steps of:

? hydrogen production using cheap energy during periods of excess energy production from renewable energy systems (for example, photovoltaic fields and wind turbine clusters);

? storage in tanks, both in the liquid phase and as compressed gas, of the hydrogen produced, or both of the hydrogen and of the oxygen, should the latter also be used;

? power generation in periods of high power demand, using stored gas.

For the production of electricity, among others, the following solutions can be adopted: (i) hydrogen fueled gas turbines in combined cycle configuration, (ii) fuel cells and (iii) hydrogen fueled internal combustion engines . The latter have a lower cost per kW installed and are suitable for relatively small installations. However currently the typical efficiency ? lower than other solutions and the cost of maintenance? greater.

Are they known why? used or at least proposed in the literature, some internal combustion engines fueled by hydrogen characterized by the compression of a mixture of air and hydrogen and by the adoption of spark ignition. The cycle implemented ? a Otto cycle, having a volumetric compression ratio limited to approximately V (max) / v (min) = 10, for the necessity? to avoid the dreaded detonation phenomena (?knocking?, according to the well-known English terminology), inside a fluid containing both the gaseous fuel, i.e. hydrogen, and the comburent, i.e. air. Some examples of hydrogen fueled internal combustion engines are described in some patent documents.

In US 3,608,529A ? described an internal combustion engine powered by hydrogen or petrol and provided with a system for recovering and recirculating the water coming from the exhaust duct.

Document US 3,862,624A discloses an internal combustion engine that uses oxygen and excess hydrogen and has a substantially closed exhaust system that recirculates the gaseous portion of the exhaust through the engine and expels only water.

Finally, document US4112875A describes an internal combustion engine fueled by hydrogen-oxygen, which uses an inert gas, such as argon, as the working fluid to increase engine efficiency, eliminate pollution and facilitate the operation of a closed-loop energy system.

Basically, the adoption of hydrogen as a fuel involves, compared to engines powered by natural gas, a lower energy content of the air/fuel mixture introduced into the machine: in fact, hydrogen has a density lower than other gaseous fuels, only partially compensated by the higher energy per unit? mass.

This difference can be partially compensated for by increasing the compression ratio of the turbocharger upstream of the internal combustion engine. However, the limit inherent in the fact that the starting pressure upstream of the turbocharger remains? necessarily atmospheric pressure.

There is therefore the need to define an innovative volumetric drive machine powered preferably with hydrogen, capable of supplying power in the energy return phase in periodic storage plants, rather than for propulsion systems and which is favorable from the point of view costs, dimensions and energy efficiency.

Summary of the Invention

In order to substantially solve the technical problems highlighted above, an object of the present invention is define an innovative volumetric driving machine which operates according to a thermodynamic cycle similar to a Diesel cycle, which is preferably fueled with hydrogen as a? of fuel and that uses oxygen in the liquid phase as a comburent, in order to increase the specific power per unit? of engine displacement.

Alongside this result, the present invention also proposes to increase the overall efficiency of the energy transformation thanks to the adoption of the Diesel scheme with a high compression ratio, to reduce the cost per kWh of the electric energy produced and to further reduce the emission of pollutants (already minimal) from reciprocating engines powered by hydrogen, thanks to the use of liquid oxygen instead of air. What? by operating, in fact, you avoid having any type of nitrogen oxide emission at the exhaust.

In addition to the dedicated power storage systems described above, another important field of application ? the use of hydrogen for marine propulsion: the adoption of the present invention would require a suitable supply of liquid oxygen in addition to the supply of hydrogen. However, compared to a supply of liquid hydrogen, the supply of cryogenic oxygen (about -180?C and with a density close to that of water or diesel) is ? less demanding, since? does liquid oxygen show a lower volume and a cooler storage temperature? high compared to liquid hydrogen.

In particular, future liquid hydrogen carrier tankers could be a good field of application for the invention.

Accordingly, according to the present invention there is provided a volumetric driving machine which operates according to a thermodynamic cycle similar to a Diesel cycle, preferably fueled by hydrogen and using compressed oxygen in a pump in the liquid phase as comburent, the volumetric driving machine having the characteristics stated in independent claim, attached to the present description.

Further embodiments of the invention, preferred and/or particularly advantageous, are described according to the characteristics set forth in the attached dependent claims.

Brief Description of the Drawings

The invention will come now described with reference to the attached drawings, which illustrate some non-limiting embodiments, in which:

- figure 1 schematically illustrates a volumetric Diesel cycle driving machine in a four-stroke configuration, provided with an auxiliary system for recovering heat energy at the exhaust, according to a first embodiment of the present invention,

- figure 2 schematically illustrates, in a second embodiment of the present invention, a volumetric Diesel cycle driving machine in a two-stroke configuration, equipped with an organic Rankine cycle plant (Organic Rankine Cycle, acronym ORC) for the recovery of ?thermal energy at the exhaust,

- figure 3 schematically illustrates a diesel cycle volumetric driving machine in a two-stroke configuration and with one or more? controlled valves, provided with an auxiliary system for recovering the thermal energy at the exhaust, according to a third embodiment of the present invention,

- figure 4 schematically illustrates a volumetric Diesel cycle driving machine in a four-stroke configuration, equipped with an organic Rankine cycle plant for the recovery of thermal energy at the exhaust, the ORC plant operating according to a plurality of of thermodynamic cycles in cascade, according to a fourth embodiment of the present invention,

- figure 5 illustrates the counter-current heat exchange curves between the oxygen to be liquefied and the hydrogen to be gasified,

- figure 6 represents the scheme of the plant which allows to obtain the heat exchange process of figure 5,

- figure 7 illustrates a variant of the plant diagram of figure 6, in which ? present further heating of the evaporated hydrogen, followed by expansion in the turbine,

- figure 8 represents a plant diagram for the production of liquid oxygen based on a fractional distillation process of air, - figure 9 represents the same plant of figure 8 in which separate heat exchangers are highlighted respectively for air heat exchange /nitrogen and for air/hydrogen heat exchange, e

- figure 10 schematically illustrates an example of use of the volumetric driving machine, according to one of the embodiments of the invention, in an electric network provided with renewable/random energy sources.

Detailed Description

By way of a purely non-limiting example, the present invention will be now described with reference to the aforementioned figures.

Object of this invention ? a volumetric driving machine in which a cycle equivalent to the well-known Diesel cycle takes place. In fact, in the Diesel cycle, a first reactant, essentially made up of air, is introduced into a closed casing (for example, a cylinder in which a piston moves) and is compressed thanks to a closure of the casing in which the reactant ? content (closure that can? occur through the closing of valves, or through the movement of walls that block the admission and/or exhaust ports as occurs, for example, in certain 2-stroke engines or in machines like? Wankel?, or , again, in capsulism engines) associated with a progressive decrease in the volume of the casing. A volumetric compression ratio is identified as the ratio between the initial volume of the first reactant charge and the final volume at the end of the reduction process of the volume contained in the envelope, R=Vi/Vf. In the absence of the limit imposed by the phenomenon of detonation in a scheme type Diesel, the compression ratio will be able? typically be elevated in the 10-20 range. A compression ratio more? high can correspond to a higher energy efficiency. The compression takes place in a short time so that the heat exchange with the casing? a small fraction of the energy required for compression. Is it done like this? a compression close to an adiabatic transformation, for which the temperature of the end of compression ? much more higher than the initial one. Around the compression end point (typically with a certain advance compared to the point itself), it is introduced through a duct called an injector, with a much higher pressure? higher than that of the first reactant contained in the shell, a second reactant, hydrocarbon or other fuel, which rapidly mixes with the first reactant. Thanks to the high temperature reached by the first reactant due to the compression, a reaction starts between the two reactants, which leads to the formation of third compounds, with development of the reaction energy. In many machines, the injection of the second reagent takes place with a modality? modulated over time, to obtain a good completeness of the reaction. Furthermore ? is it possible that they are introduced more? reagents, for example to overcome the difficulty? triggering of the reaction of the reactants (technique adopted, for example, in ?dual fuel? engines, in which a fraction of reactant (typically fuel gas) is added to the air introduced into the casing and the start of the oxidation reaction is guaranteed by the injection, at the end of the compression, of a small quantity of liquid fuel with easy ignition characteristics.

This is followed by the expansion inside the casing, with collection of the expansion energy of the high temperature gas resulting from the reaction, and the expulsion of the reaction products, through suitable valves or openings.

As described, in the event that the first reactant is air and at least one second reactant is a fuel or in any case a substance that can? putting in place an oxidation reaction by the oxygen present in the air, constitutes the well-known functioning of a Diesel cycle machine.

In the present invention however, according to a preferred embodiment, the first reactant admitted to the container is not? air but? substantially hydrogen (H2) while the second reactant ? substantially oxygen (O2), compressed in the liquid state, at pressure pi? high pressure in the casing and started for introduction into the cylinder through the injector. The injection proceeds until obtaining the introduction of the quantity? established O2, possibly also with mode? discontinuous or in any case with a modulated flow rate.

Hydrogen and oxygen react, also thanks to the high temperature resulting from the compression which can be assimilated to an adiabatic compression, and give rise to products of the reaction with a very high temperature, in the range of 2000-3000 degrees C. The product of the reaction? consisting substantially of water in the form of vapor at a supercritical temperature.

The quantity? introduced of oxygen? preferably lower than the quantity? stoichiometric, so at the end of the reaction ? present a fraction of H2 that is not ? been oxidized. The oxidized part? present as water vapour, H2O.

The gas extracted from the casing, still characterized by a high temperature, is cooled by a heat exchange system which transfers the heat to a thermal user. During cooling, the condensation of as much greater part of the water vapor produced by the reaction as less? the temperature reached at the end of cooling. The condensed fraction? separated and extracted as liquid water. The non-condensed fraction, substantially composed of hydrogen and water vapour, is preferably sent back to the admission to the enclosure, possibly through a machine (compressor or expander) capable of modifying the pressure. Alternatively, can be discharged into the atmosphere after purification and/or oxidation according to known techniques.

With reference to figure 1, the schematic diagram of a four-stroke volumetric driving machine 10 is now described, equipped with cylinder 8, piston 9 - operating with periodic motion inside the casing/cylinder so as to generate a chamber inside ? inside the casing with a volume that varies periodically between a minimum volume V1 and a maximum volume V2 -, at least one inlet opening 3 with relative intake valve, at least one discharge opening 4 with relative discharge valve and a collection system and conferring to a rotating shaft the mechanical power collected by the piston 9 thanks to the alternation of the pressures acting on it in the various phases of the thermodynamic cycle carried out in the machine itself, according to the known technique of internal combustion engines and therefore not shown in the figure.

In the suction phase, a quantity of hydrogen enters the cylinder 8 from any source 1 (for example, evaporation of liquefied gas, gas from cylinders or suitably expanded cylinder wagons, gas from hydrogen gas pipelines, gaseous hydrogen from chemical processes, gas from gasholder etc.) through the intake valve 3. The gas pressure is not ? necessarily linked to the atmospheric pressure as in the case of the classic Diesel which draws air from the environment at atmospheric pressure. Advantageously, can? be appropriate to work with the inlet pressure pi? high to get more power per unit? of displacement. Furthermore, a fraction of return gas from the machine 10 itself is added to the aspirated hydrogen, through the duct 2.

At the end of the compression (with a certain degree in advance) an injection system 5a (essentially comprising a manifold 7 which is the source of the liquid oxygen, an injection pump 6 and at least one injector 5) introduces the right quantity? of oxygen, in the form of a high-velocity jet. Essential characteristic of the present invention, ? the compression of oxygen in the liquid phase, necessary to reach adequate injection pressures (for example, in the order of 200-500 bar) for effective mixing in the combustion chamber. Based on the capacity? of thermal insulation of the injection ducts, which will have to maintain cryogenic temperatures, from the nozzle of the injector 5 will be? injected liquid oxygen or high pressure gas.

If oxygen is injected in the gaseous phase, it is necessary to optimize the law of variation of the areas in the nozzle (for example, divergent nozzle, plug nozzle, etc.) and take into account the fact that the modulation of the flow rate is affected by the compressibility? of the gas. Moreover, ? preferable the injection of liquid both to avoid the drawbacks exposed above, and why? ? greater capacity? penetration of the drops. Proper cryogenic tracing of the pipes and pump is an effective solution.

At this point, in the presence of the two phases, fuel and oxidizing agent mixed at least locally, the oxidation reaction starts naturally in the presence of a high temperature of the compressed gas. Alternatively, the start of the oxidation reaction could be assisted by the presence of a pre-chamber or by a plurality of? of walls (as in a ?hot head? engine), i.e. high temperature environments in which to inject the oxygen, compressed in the liquid phase starting from the pump 6.

The subsequent oxidation reaction leads to the achievement of a final temperature and pressure, the values of which depend primarily on the H2/O2 ratio, ie? by how much excess hydrogen that does not participate in the reaction goes through the cycle. A very high temperature can lead to an excess of thermal flow dissipated through the walls (even if the emissive power of the gases should be lower than that of conventional diesel due to the absence of carbonaceous particles). Can? also lead to excessively high discharge temperatures, which are difficult to manage for the downstream thermal utilization plant, for example an ORC plant.

Advantageously, the compression phase and the expansion phase can be differentiated through a timing of the valves which reduces the quantity? of gas introduced, in order to obtain a greater expansion and therefore a lower temperature at the exhaust.

The gases leaving through the exhaust duct 12 pass through a heat exchanger forming part of a heat exchange system 13 designed to generate further mechanical power (for example, an ORC plant) and to dispose of the residual heat towards an external cold source 14. Alternatively, the exhaust gases are sent to a thermal user of another nature.

The exhaust gas cooling takes place in a first part with the characteristics of cooling a gas mixture, in a second part starting from the dew point temperature of the water contained, the cooling curve therefore changes in relation to the progressive condensation of the water content. Will the power production system be? realized in such a way as to obtain the maximum efficiency of the recovery (between? 8% and 35% of the power to? shaft of the volumetric driving machine), for example, by adopting ORC systems with more? layers, or cascading ORC systems.

Does the cooled gas pass through a further conduit 15 carrying with it? liquid water (condensate). Preferably, the condensate can? be separated in a separator 16 with liquid subtraction 18.

The cycle closes with the return duct 19 which re-introduces the fraction of hydrogen discharged in excess from the engine into the engine. This duct can include a machine 19a, for example, a compressor with external drive, or a turbocharger, whose turbine ? driven by exhaust gases.

If necessary, can a vent 17 must also be provided to remove any excess non-condensables and to maintain the optimum pressure level in the return duct 19.

With reference to figure 2, in this second embodiment of the invention the volumetric driving machine 19a is comparable to a Diesel cycle engine in a two-stroke configuration, also in this case equipped with a heat exchange system, which in this configuration ? explicitly shown as an ORC system (the use of this form of recovery through ORC is to be understood also applicable to the 4-stroke machine of Fig.1 as well as the form of recovery illustrated in Fig.1 can also be applied to the solution of Fig.2). In particular, figure 2 schematises all the main components of an ORC organic Rankine cycle plant: a feed pump 25, a heat exchanger 26 with the function of preheater, evaporator and possible superheater of the organic fluid, a turbine 27 (with an electric generator 28 coupled to it or other operating machine) and a capacitor 29. The two-stroke volumetric machine 20 will have? similar characteristics to the previous four-stroke volumetric machine 10 and, according to the prior art, will have? at least one washing port 21 and at least one discharge port 22 facing the cylinder 23. ? to note that this machine not having substantially any gaseous discharge into the atmosphere ? less problematic than the classic two-stroke diesel engines, which must minimize the production and subsequent expulsion of particulate matter.

Referring to figure 3, ? schematically illustrated is a two-stroke Diesel cycle displacement engine 30 in configuration, which differs from the two-stroke displacement engine 20 of Figure 2 in that it has a controlled exhaust valve 31 in the head. Also in this case ? provided, an auxiliary plant 32 for the recovery of the thermal energy at the exhaust. This scheme can be more advantageous in terms of power per unit? of displacement, as the ?washing?, cio? the expulsion of burnt gas and the introduction of new gas? more effective when made in a one-way flow pattern with actuated valve.

Finally, and with reference to figure 4, ? illustrated is a volumetric Diesel cycle driving machine 40 and in a four-stroke configuration, provided with a turbine expander 41 on the exhaust, to produce power and pre-cool the exhaust gases before accessing the heat recovery, as well as? of a heat exchange system for the recovery of heat energy at the exhaust. In this case, by way of example, we are dealing with an organic Rankine cycle plant 42 operating according to a plurality of of thermodynamic cycles on different temperature levels, fed by heat exchangers 43, 44, preferably in series on the discharge path, which can? also include a 45 aftercooler.

In all the configurations presented, the crankcase of the machine or rather the volume present under the piston (9 in Fig.1.) will receive? certainly a flow of leakage through the piston rings, therefore it is necessary to prevent the crankcase from receiving oxygen from the outside to avoid the formation of a dangerous atmosphere. The Applicant believes that the best solution is pressurization with inert gas, preferably Argon, to prevent leakage towards the cylinder leading to the formation of nitrogen oxides (NOx), as could occur if nitrogen were used for pressurization of the crankcase and other potential leak points, such as valve cases.

As an alternative to feeding with substantially pure hydrogen as fuel, the proposed volumetric machine can be fueled advantageously with other fuels whose composition also contains carbon atoms in addition to hydrogen atoms.

In particular, you can dealing with hydrogen-natural gas, hydrogen-gaseous hydrocarbon mixtures, suspensions or vapor of liquid hydrocarbons and gaseous hydrocarbons.

In case you adopt a power supply with a fuel containing in some form also carbon or hydrocarbons, it will be? it is essential to adopt a vent flow to the outside that is adequate to avoid the accumulation in the casing of CO2, CO and carbonaceous particles formed in the oxidation reaction at high temperature. For the purpose, can the vent 17, previously described, can be used.

For an effective elimination of harmful compounds before venting into the atmosphere ? appropriate the adoption of suitable components to obtain a complete oxidation and more? in general a purification of the exhaust gases, such as catalytic mufflers and particulate filters, a known technique in the field of internal combustion engines fed with air (Air Breathing Engines). The gas coming out of the vent 17 can be advantageously brought to a suitable temperature for the correct functioning of these components through a heat exchange in counter-current with the exhaust gases from the manifold 12. ? it is also possible that, in relation to the particular fuel used, it is preferable to adopt an oxygen flow rate in excess of the stoichiometric ratio, contrary to what is indicated for feeding substantially with hydrogen.

Among the fuels of potential interest are methylcyclohexane (MCH), studied for example by Chiyoda, a company of Japanese engineering, which compound is suitable for the transport and accumulation of hydrogen through a liquid hydrocarbon at room temperature, as well as? alcohols such as methanol.

In a further meaning, liquid fuels and MCH in particular can also be injected by a further injector into the cylinder, during or at the end of the compression phase.

With reference to the feeding of the hydrogen and oxygen reactants to the volumetric driving machine object of the invention, ? essential to minimize the energy consumption for the supply of the reagents themselves. Therefore, the aforementioned volumetric driving machine, advantageously, also includes a plant for the production of gaseous hydrogen and oxygen in the liquid phase, as will be the case? better described below.

For example, in the case of feeding the machine with hydrogen kept in the liquid state and gaseous oxygen pressurized in containers (for example, in tank trailers), an efficient solution for obtaining gaseous hydrogen and liquid oxygen suitable for pressurization in the pump 6, on the other hand, consists in carrying out a substantially counter-current heat exchange between hydrogen to be gasified and oxygen to be liquefied, possibly assisted by expansion phases in the valve (thanks to the Joule-Thompson effect) or in the turbine (adiabatic cooling), optimized according to known techniques.

Figure 5 illustrates the heat exchange curves representing the temperature trend of the two fluids as a function of the exchanged power, between the oxygen to be liquefied and the hydrogen to be gasified and shows one of the possible situations of counter-current heat exchange, with pressurization of both streams. In the figure the following values are adopted: 10 bar abs for hydrogen and 20 bar abs for oxygen.

Figure 6 shows the scheme of plant 70 which allows to obtain the process mentioned in figure 5. In figure ? reported a first tank of gaseous oxygen 71, a second tank of liquid hydrogen 72, hydrogen which ? driven by a pump 73 towards a heat exchanger 74 where in counter-current it receives heat from the oxygen, obtaining the liquefaction of the oxygen and the gasification of the hydrogen. L?Oxygen in the liquid phase? collected in a third tank 75 and from there? ? pushed by means of the pump 6 to the injector 5.

Figure 7 adds further heating of the hydrogen evaporated in the heat exchanger 76, followed by expansion in the turbine 77 to obtain mechanical/electrical power, thus recovering part of the energy expended for the gasification of the hydrogen itself. The thermal energy for heating can? come from the cylinder liners cooling system, possibly with integration with the heat available at the exhaust.

In a further sense can you? obtain the necessary liquid oxygen from the liquefaction and fractional distillation of atmospheric air, which uses the evaporation of the hydrogen fed to the machine as a cold source. In this case ? it is necessary that the nitrogen fraction, which remains gaseous downstream of the oxygen condensation, is isolated with a suitable separator (such as one or more distillation columns) and sent back to cool the incoming air, with a regenerative type scheme.

The process scheme for this solution? shown in figure 8 in which in the plant 80 are represented in addition to the components already note a source of compressed and purified air 81, a single heat exchanger 82, preferably of the plate type with a plurality of of heat exchanger flows (?multi-stream plate-fin heat exchangers?) often used in the cryogenic field, in which the air? counter-current cooled both by hydrogen and by the flow, substantially formed by nitrogen, which comes from the separator 83, which can? include one or more distillation columns.

The same pattern? shown in figure 9, in which, instead of the single heat exchanger, two separate heat exchangers are highlighted, a first heat exchanger 84 for the air/nitrogen return flow heat exchange and a second heat exchanger 85 for the air/hydrogen heat exchange.

Advantageously, the air flow coming from the air source 81 (line 96) can be cooled beforehand in a heat exchanger 86. The air flow 87 leaving the heat exchanger 86 can? be separated into two distinct flows by a flow divider 87a: a first flow 88 ? sent to the heat exchanger 84 and a second flow 89 ? started to the heat exchanger 85. Altres? advantageously at the outlet from the heat exchangers 84 and 85, the air flow combined in a single flow 90 can be cooled in a heat exchanger 91. The heat removed from the air is transferred in this exchanger to the flow of incoming hydrogen coming from the tank 72 and from the pump 73. At the exit from the exchanger 91 the air flow contains oxygen in a good part condensed. A separator 92 possibly equipped with a distillation column sends the liquid oxygen to the line 94 and the aeriform fraction, consisting substantially of nitrogen, to the exchanger 84 through the line 93. Other exchangers can advantageously complete the heat exchange, in particular an exchanger in counter-current between the two ducts 97 and 96, respectively fed by nitrogen and by incoming air, suitably purified in 81 as seen above.

AND? it should be noted, in general, that the liquefaction of the oxygen component of the air is part of a known cryogenic technique which includes solutions aimed at avoiding damage to the process due to the presence of elements or compounds, even in small quantities? in the supply air, such as water, argon and other noble gases, CO2. In the proposed system it is necessary to take account of said known techniques and solutions.

? it should be noted that the two flows of oxygen and air have flow rates, in terms of fraction of oxygen transported, substantially corresponding to the stoichiometric ratio in combustion. However can? be advantageous to keep a certain amount? of liquid oxygen accumulated upstream of the pump 6 which feeds the injectors 5 of the engine, to compensate for any deficiencies in the flow rate fed to the pump itself, especially in transients.

In general, the production of liquid oxygen from air can be of great interest why? it allows to drastically reduce the logistics costs of supply and storage of the reagents. This, in the presence of significant incentives for the use of hydrogen, can? make feasible systems distributed throughout the territory, e.g. for cogeneration in nursing homes, industries, district heating plants.

With reference to figure 10, an example of use of the volumetric driving machine 10 is now described, according to one of the embodiments of the invention, in an electric network 100 provided with renewable/random energy sources. The electrical network 100 will be able deliver or absorb electric power according to the demand for electric power. In the diagram illustrated in the figure, can be provided for an electrolyser 110, which will absorb? electrical power from network 100 to produce hydrogen and oxygen from the electrolysis of water. Hydrogen and oxygen in the gaseous phase will be able to feed fuel cells 120, which will supply electrical power to the grid 100. The volumetric driving machine 10 will also be? in electrical connection with the network 100 and can? be dedicated to absorbing the electrical power demand peaks required by the grid. The electrical power supplied by the fuel cells and by the volumetric machine can approximately be of the order of 100 MW. Possibly, the volumetric driving machine 10 will be able to? also deliver thermal power contained in its exhaust gases for a thermal user 130. The basic components, already? described, for feeding the volumetric machine 10: in particular, a first tank 140 containing liquid hydrogen, a second tank 150 containing liquid oxygen, as well as a first machine 160 and a second machine 170 for liquefaction or regasification, respectively, of hydrogen and oxygen. These machines will be able to work according to one of the two functions, depending on the needs of the network 10. For example, if there will be? request for electrical power from the fuel cells 120, the machines 160, 170 will be able to work as regasifiers for hydrogen and oxygen, respectively. If, however, there will be request for electric power from the volumetric machine 10, the machine 160 can work as a regasifier of? hydrogen, while the machine 170 potr? carry out the liquefaction of the oxygen. On the other hand, when a tank 140, 150 reaches a minimum level of liquid contained therein, respectively hydrogen or oxygen, the corresponding machine 160, 170 will be able to perform the liquefaction of? hydrogen or? oxygen, also in relation to the forecast of availability? of electricity and according to the expected cost for the same.

Finally, in the scheme of figure 10 ? a tank 180 is also provided for the possible supply (or integration of the supply) of the volumetric machine 10 by means of hydrocarbons (with possible enrichment of hydrogen). In the example in figure 10, the mixture ? made up of natural gas and hydrogen.

The case of ships for the transport of liquid hydrogen? also very interesting, especially if we take into account the use of the boil-off fraction of the hydrogen reserve that can? be fed into ducts 1, 2, 19. In particular, ? the application to submersible vessels is interesting, also in the unmanned version, preferably intended for the transport of liquids or gases such as hydrogen and oxygen or for the implementation of mining operations and/or cleaning of the seabed.

The characteristics of the volumetric drive according to the present invention, in particular, in comparison with fuel cell plants fed by hydrogen and oxygen, for sizes 10-50 MW and for a time horizon of about twenty years, should be as follows: ? Significantly lower cost per installed kW

? Similar electrical efficiency

? Better tolerance towards impurities? in the gas

? Global volume occupied by the lower system

? Power generation with alternator, therefore with the presence of rotating reserve in the network, and better quality? of the energy produced? Less use of precious and/or strategic materials

? Easy recycling at end of life

? Availability of waste heat at various thermal levels.

In addition to the embodiment of the invention, as described above, it is to be understood that numerous other variations exist. It is also to be understood that such embodiments are exemplary only and do not limit or the scope of the invention, n? its applications, n? its possible configurations. On the contrary, although the above description allows the skilled technician to implement the present invention at least according to an exemplary embodiment thereof, it must be understood that many variants of the components described are possible, without thereby departing from the scope of the invention, as defined in the appended claims, which are construed literally and/or according to their legal equivalents.

Claims (33)

1. Volumetric driving machine (10, 20, 30, 40) operating according to an operating sequence substantially equivalent to the cycle of Diesel engines, hereinafter referred to as ?Diesel cycle? and including: - at least one casing (8, 23) for containing a fuel element and a comburent element, - at least one piston (9) operating with periodic motion inside the enclosure (8, 23), so as to generate a chamber inside the enclosure with a volume that varies periodically between a minimum volume (V1) and a maximum volume (V2), - inlet openings (3, 21) for the intake of the fuel element and exhaust openings (4, 22, 31) for the discharge of burnt gases produced by the combustion of the fuel element with the comburent element, - a system of injection (5a) for the injection of the comburent element in the enclosure (8, 23), - at least one supply duct (1) of the fuel element and at least one exhaust duct (12) of the burnt gases, - a system for collecting and transferring to a rotating shaft the mechanical power collected by the piston (9) thanks to the alternation of the pressures acting on it in the various phases of the thermodynamic cycle carried out in the machine itself, the volumetric driving machine (10, 20, 30, 40) being characterized by the fact that the comburent element ? compressed oxygen in the liquid phase by one or more? pumps (6) before introduction into the casing (8, 23). 2. Volumetric driving machine (10, 20, 30, 40) according to claim 1, wherein the fuel element is? hydrogen in the gaseous phase. 3. Volumetric driving machine (10, 20, 30, 40) according to claim 2, wherein the hydrogen is present in excess of the stoichiometric value of the oxidation reaction between hydrogen and oxygen. 4. Volumetric driving machine (10, 20, 30, 40) according to claim 2 or 3, wherein the fuel element comprises hydrogen added with hydrocarbons. 5. Volumetric driving machine (10, 20, 30, 40) according to claim 1, wherein the fuel element comprises hydrocarbons. Displacement engine (10, 20, 30, 40) according to claim 5, wherein the hydrocarbons consist wholly or partly of methylcyclohexane (MCH). 7. Volumetric driving machine (10, 20, 30, 40) according to one of the preceding claims, wherein the mechanical power supplied by the machine feeds an electric generator. 8. Volumetric driving machine (10, 20, 30, 40) according to one of claims 1 to 6, wherein the mechanical power delivered by the machine feeds a propulsion line of a motor vehicle. 9. Volumetric driving machine (10, 20, 30, 40) according to claim 8, wherein said motor vehicle is a vessel, vessel or other water vehicle. 10. Volumetric driving machine (10, 20, 30, 40) according to one of the preceding claims, wherein said at least one supply duct (1) of the fuel element and at least one exhaust duct (12) of the burnt gases are connected between them in order to optimize the corresponding flows of the fuel element and the burnt gases. 11. Volumetric driving machine (10, 20, 30, 40) according to one of the preceding claims, comprising a further injector configured to inject into the casing (8, 23), during the compression phase, at least a part of the fuel elements in liquid. 12. Volumetric driving machine (10, 40) according to one of the preceding claims, wherein the operating sequence substantially equivalent to a Diesel cycle? a four-stroke cycle and the inlet ports (3) and exhaust ports (4) are controlled by controlled valves. 13. Volumetric driving machine (20, 30) according to one of claims 1 to 11, wherein the operating sequence substantially equivalent to a diesel cycle? a two-stroke cycle. Positive driving machine (30) according to claim 13, wherein the discharge openings (31) are controlled by controlled valves. Volumetric driving machine (10, 20, 30, 40) according to one of the preceding claims, further comprising a heat exchange system (13) for recovering the heat of the exhaust gases passing through the exhaust pipe (12). 16. Volumetric driving machine (10, 20, 30, 40) according to claim 15, wherein the heat exchange system (13) is? an organic rankine cycle (ORC) plant. 17. Volumetric power machine (10, 20, 30, 40) according to claim 16, wherein the organic Rankine cycle (ORC) operates on multiple? temperature levels (42) or with cascade cycles. Positive driving machine (10, 20, 30, 40) according to one of the preceding claims, further comprising an exhaust gas condensate separator (16). 19. Volumetric driving machine (10, 20, 30, 40) according to claim 18, wherein the separator (16) is? equipped with a vent (17) to remove non-condensable gases or other aeriforms. 20. Volumetric drive (10, 20, 30, 40) according to one of the preceding claims, further comprising a duct (19) for recirculation of the residual gas downstream of the separator (16), substantially comprising unburnt hydrogen. 21. Volumetric driving machine (10, 20, 30, 40) according to claim 20, wherein along the recirculation duct (19) ? allocated an operating machine (19a) to compress the hydrogen at pressures higher than the pressure in an admission duct (1). 22. Volumetric driving machine (10, 20, 30, 40) according to one of the preceding claims, provided with a turbine expander (41) located on the exhaust duct (12) for producing mechanical power and pre-cooling the exhaust gases. 23. Volumetric driving machine (10, 20, 30, 40) according to one of the preceding claims, provided with a casing pressurized with inert gas. 24. Volumetric driving machine (10, 20, 30, 40) according to claim 23, wherein said inert gas ? argon. 25. Volumetric driving machine (10, 20, 30, 40) according to one of the preceding claims, further comprising a plant (70) for producing hydrogen in the gaseous phase and compressed oxygen in the liquid phase starting from hydrogen in the liquid and oxygen in the gaseous phase, said plant being equipped with: - a first tank (71) containing gaseous oxygen, - a second tank (72) containing liquid hydrogen, - a pump (73) which moves the hydrogen, - a heat exchanger (74) between hydrogen and oxygen which, as a result of the heat exchange, carries out the liquefaction of the oxygen and the gasification of the hydrogen, - a third tank (75) which contains oxygen in the liquid phase. 26. Volumetric engine (10, 20, 30, 40) according to claim 25, wherein the system (70) comprises a further heat exchanger (76) for further heating of the hydrogen and a turbine (77) for the expansion of hydrogen gas and to obtain mechanical/electrical power. 27. Volumetric driving machine (10, 20, 30, 40) according to one of claims 1 to 24, further comprising a plant (80) for producing hydrogen in the gaseous phase and compressed oxygen in the liquid phase starting from hydrogen in the liquid phase and from air, said plant being equipped with: - a source of compressed and purified air (81), - a tank (72) containing liquid hydrogen, - a pump (73) which moves the hydrogen, - a single heat exchanger (82) in which the air? counter-current cooled both by hydrogen and by the return flow, substantially formed by nitrogen, which comes from a nitrogen/oxygen separator (83). 28. Volumetric driving machine (10, 20, 30, 40) according to claim 27, wherein the system (80) comprises, instead of the single heat exchanger (82), at least two separate heat exchangers, a first heat exchanger (84) for air/nitrogen backflow heat exchange and a second heat exchanger (85) for air/hydrogen heat exchange. 29. Method for the production of hydrogen in the gaseous phase, in quality? of fuel element, and compressed oxygen in the liquid phase, in quality? of comburent element, the method being implemented in a volumetric driving machine (10, 20, 30, 40) according to one of the preceding claims, the method being characterized by the following steps: - storage of hydrogen in the liquid state and pressurized gaseous oxygen in containers accessible to the volumetric engine, - heat exchange, essentially in counter-current, between the hydrogen to be gasified and the oxygen to be liquefied. 30. A method according to claim 29, wherein the heat exchange step is followed by expansion phases in throttling valves or turbines. 31. Method for the production of hydrogen in the gaseous phase, in quality? of fuel element, and compressed oxygen in the liquid phase, in quality? of comburent element, the method being implemented in a volumetric driving machine (10, 20, 30, 40) according to one of claims 1 to 28, the method being characterized by the following steps: - supply of liquid hydrogen and air purified from water and particulates, - heat exchange, substantially in counter-current, between hydrogen to be gasified and air, - separation of the nitrogen fraction, which remained gaseous, from the condensed oxygen, - heat exchange between nitrogen fraction and air. 32. Electricity grid (100) provided with renewable energy sources and electrical consumers, including at least: - an electrolyser (110), for the production of hydrogen and oxygen in the gaseous phase, - fuel cells (120), for the supply of electrical power to the grid (100), e - a volumetric driving machine (10, 20, 30, 40), according to one of the claims from 1 to 28, in electrical connection with the network (100) and configured to deliver electric power slaved to the absorption of peaks of electric power demand requested by the network (100). The electrical network (100) according to claim 32, further comprising: - a first tank (140) containing liquid hydrogen and a second tank (150) containing liquid oxygen, - a first machine (160) for liquefaction or regasification of hydrogen and a second machine (170) for liquefaction or regasification of oxygen, and - a feed comprising a mixture of natural gas and hydrogen.