WO2011080782A1

WO2011080782A1 - Method and device for preparing a homogeneous gaseous mixture starting from a flow of gas and from a flow of liquid

Info

Publication number: WO2011080782A1
Application number: PCT/IT2009/000601
Authority: WO
Inventors: Massimiliano Antonini; Andres Salvidia; Guido Saracco; Corrado Farina; Simone Solaro; Marco Mori; Massimiliano Anastasi
Original assignee: Hysytech S.R.L.
Priority date: 2009-12-30
Filing date: 2009-12-30
Publication date: 2011-07-07

Abstract

The present invention relates to a method for preparing a homogeneous gaseous mixture (ALu) starting from a flow of gas (A) and from a flow of liquid (L). In particular, the method according to the invention allows the preparation of a gaseous mixture in predetermined temperature conditions. The method provides for heating of a metal body (10) in which a hydraulic circuit (5) is defined to a predetermined temperature and passing a two-phase mixture formed of the flow of liquid (L) and of the flow of gas (A) through said circuit (5). In particular, the metal body (10) is heated with a thermal power (3) such as to ensure heating and vaporization of the liquid part of the two-phase mixture.

Description

METHOD AND DEVICE FOR PREPARING A HOMOGENEOUS GASEOUS MIXTURE STARTING FROM A FLOW OF GAS AND FROM A FLOW OF LIQUID

FIELD OF THE INVENTION

The present invention falls within the scope of processes for liquid evaporation in controlled conditions. More precisely the present invention relates to a method for preparing a homogeneous gaseous mixture starting from a flow of gas and from a flow of liquid. In particular, the method according to the invention allows the preparation of a gaseous mixture in predetermined temperature conditions. The gaseous mixture that can be obtained through the method according to the invention comprises a first part corresponding to the flow of evaporated liquid and a second part corresponding to the initial flow of gas. In the field of fuel cells, the method according to the invention can be used to humidify the anode and cathode flows involved by electrochemical reactions. The method according to the invention can also be used to produce steam in controlled conditions starting from a flow of steam and from a flow of water. The present invention also relates to a device for the implementation of this method.

STATE OF THE ART

As it is known in the industrial field, vaporization of a liquid and humidification of a gas in controlled conditions still presents some partially unsolved problems. In particular, current methods and relative plants provided for these purposes still prove to be somewhat unsatisfactory, both in terms of efficiency and in terms of structure and operation.

Within the field of fuel cells, for example, there is the need to humidify the anode and cathode flows involved by electrochemical reactions. A first known solution consists in mixing these flows, in a mixing unit, with a flow of steam produced in a separate boiler. This solution has proved somewhat inconvenient as it requires a plant of large dimensions and consequently having high maintenance costs.

To overcome this limit, humidifying devices of smaller dimensions have been developed. An example of these devices is described in the patent application US 2006/0097412. In particular, in this solution the humidifier comprises a main housing body, positioned inside which is a finned heat exchanger, which is heated through a high temperature fluid. A flow of gas to be humidified and a flow of water to be vaporized are introduced through relative feed ducts. Contact of the water with the hot surfaces of the heat exchanger produces steam that is mixed with a flow of gas. The gas-steam mixture exits from the main housing body to be subsequently sent to the fuel cells.

Just as others of similar concept, this solution has some drawbacks, the first of which lies in the fact that vaporization of the liquid takes place in conditions with limited control. This vaporization is in fact substantially immediate and this causes the continuous formation of "cold spots" which determine disturbances and pulsations in the vaporization. In practice, a homogeneous gas-steam mixture both in terms of composition and temperature cannot be obtained with this type of device.

Another example of devices used to humidify a flow of gas is described in the patent application WO 2009053034. In particular, in this further example, the device comprises a main body comprising a lower chamber into which water to be evaporated is introduced. This chamber is heated through a heat exchanger which in practice allows it to evaporate. The gas to be humidified is introduced into the main body and is destined to be mixed with the water vapor coming from the lower chamber. The gas-steam mixture passes through a predetermined path before being delivered from the main body for subsequent use. While passing through this path, the mixture is heated through the same heat exchanger used to evaporate the water.

This second device and others of similar concept do not allow a homogeneous gas-steam mixture to be obtained, above all in terms of composition. In other words, the steam flow rate destined to be mixed with the flow of gas to be humidified is difficult to control. Naturally, this prevents a gaseous mixture of homogeneous composition from being obtained.

On the basis of these considerations, the need emerges for new technical solutions that make it possible to overcome the limits and drawbacks of prior art. In particular, there is the need to provide a new method for preparing, in controlled conditions, a gaseous mixture staring from a flow of gas and from a flow of liquid. Therefore, the main aim of the present invention is to provide a method and a device that allow this result to be achieved. Within this aim, a main object of the present invention is to provide a method and a device that allow the preparation of a homogeneous gaseous mixture in terms of composition and at a predetermined temperature starting from a flow of gas and a flow of liquid.

Another object of the present invention is to provide a method and a device for preparing a gaseous mixture which are reliable and relatively easy to produce at competitive costs.

SUMMARY OF THE INVENTION

The present invention relates to a method for preparing a homogeneous gaseous mixture starting from a flow of gas and from a flow of liquid. The method provides for the provision of a metal body, inside which a hydraulic circuit is defined for the passage of a two-phase mixture formed of said flow of liquid and said flow of steam. The method provides for heating of the metal body to a predetermined heating temperature and introducing the two-phase mixture into the hydraulic circuit of the metal body to allow vaporization of the liquid part while it passes through the circuit. With this solution the gaseous mixture obtained is formed partly by the flow of gas introduced into the circuit and partly by the flow of liquid evaporated inside the hydraulic circuit.

It has been found that the liquid part of the two-phase mixture is vaporized while passing through the hydraulic circuit in a gradual and non-immediate manner, as it is conveyed by the flow of gas. In other words, the flow of gas acts as a carrier for this liquid part, allowing a homogeneous and gradual evaporation.

According to the ratio between the flow rates of the liquid and gas that form the two-phase mixture introduced into the hydraulic circuit, the method can also be considered as a method of evaporating a liquid or alternatively as a method of humidifying a gas. More precisely, for example, in the case in which the liquid flow rate is greater than the gas flow rate, then the method will in fact allow a gaseous mixture to be obtained formed for the greater part of vaporized liquid and for the remaining part of the gas introduced. Vice versa, when the flow rate of the gas introduced is established considerably greater than that of the liquid, then the method will in fact allow a gaseous mixture to be obtained at a predetermined temperature humidified by means of vaporization of the liquid. According to a preferred embodiment of the invention, the metal body is heated through heating means positioned inside this body. In a possible embodiment, these means comprise electric heating elements in the form of cartridges or in the form of an electric coil inserted inside the metal body.

The present invention also relates to a device for preparing a homogeneous gaseous mixture starting from a flow of liquid and from a flow of gas. In particular, the device according to the present invention comprises a metal body inside which a hydraulic circuit is defined, susceptible to be passed through by a two-phase mixture formed by the flow of liquid and by the flow of gas. The device according to the invention comprises heating means to heat the metal body to a predetermined heating temperature and suitable to vaporize the liquid part of the two-phase mixture. The device according to the present invention has a configuration that is particularly compact and easy to produce, to the advantage of final manufacturing costs.

According to a first possible embodiment, the metal body has the form of a cylinder made of metal material and the hydraulic circuit comprises a plurality of longitudinal passages that extend between a first and a second transverse surface of the cylinder. The hydraulic circuit comprises a plurality of first connecting passages that connect, in proximity of the first transverse surface, two adjacent longitudinal passages. The hydraulic circuit also comprises a plurality of second connecting passages that connect, in proximity of the second connecting surface, other, two longitudinal passages at least one of which differing from the preceding ones.

Preferably, the first connecting passages are staggered with respect to the second connecting passages so that a first of said longitudinal passages is connected to a second longitudinal passage through one of the first connecting passages and so that it is connected to a third longitudinal passage through one of the second connecting passages.

According to another embodiment of the device according to the invention, the metal body is formed by a cylinder made of metal material and by a metal liner which covers the outside of this cylinder. In this embodiment the hydraulic circuit comprises a circulation channel defined by a helical groove produced on the outer surface of the cylinder and by the inner surface of the metal liner. The hydraulic circuit comprises an axial inlet to allow introduction of the two-phase mixture into the circulation channel and an axial outlet passage connected to the circulation channel through a radial connection.

According to a further embodiment, the metal body is formed by a casting of metal material. In this case the hydraulic circuit is defined by a hydraulic coil embedded inside said casting and provided with an inlet element and with an outlet element for said two-phase mixture. In this further solution, the metal body can be heated through an electric coil embedded inside the metal body in a position substantially coaxial with the first coil in which the two-phase mixture circulates. Alternatively, heating can be produced through a radiant burner provided with a combustion chamber coaxial with the metal body so as to transfer the heat generated by the internal combustion through the relative walls.

LIST OF FIGURES

Further features and advantages of the present invention shall be apparent from the description of particular embodiments of the present invention shown by way of non-limiting example in the accompanying drawings, wherein:

- Fig. 1 shows a first block diagram relative to a method according to the present invention;

- Fig. 1A shows a second block diagram relative to a method according to the present invention;

- Fig. 2 relates to a first embodiment of a device according to the invention:

- Fig. 3 is a sectional view according to the line Ill-Ill of Fig. 2;

- Fig. 4 is a sectional view according to the line IV-IV of Fig. 2;

- Fig. 5 is a sectional view according to the line V-V of Fig. 2;

- Fig. 6 relates to a second embodiment of a device according to the invention;

- Fig. 7 is a sectional view according to the line VII-VII of Fig. 6;

- Fig. 8 is a sectional view according to the line Vlll-Vlll of Fig. 6;

- Fig. 9 is a sectional view according to the line IX-IX of Fig. 6;

- Fig. 10 relates to a third embodiment of a device according to the present invention;

- Fig. 11 is a sectional view according to the line Xl-Xl of Fig. 10; - Fig. 12 is a sectional view according to the line XII-XII of Fig. 10;

- Fig. 13 is a perspective view relative to a group of components of the device of Fig. 10;

- Fig. 14 is a perspective view relative to a further embodiment of a device according to the present invention;

- Fig. 15 is a longitudinal sectional view of the device of Fig. 13.

DETAILED DESCRIPTION

With reference to aforesaid figures, the method according to the present invention provides for the provision of a metal body, for example made of steel or aluminum, inside which a hydraulic circuit is defined for circulation of a two-phase mixture formed by a flow of liquid and by a flow of gas. The method provides for heating of the metal body through a heating system of adequate power, capable of allowing evaporation of the flow of liquid while it passes through the hydraulic circuit, and capable of taking the system (formed by the body and by the circuit) to a heating temperature Tp sufficient to obtain the delivery of a gaseous mixture at the design temperature conditions.

The two-phase liquid-steam mixture is mixed prior to or simultaneously to being introduced into the hydraulic circuit. After being introduced into the hydraulic circuit, the gaseous part of the two-phase mixture transports the liquid part, allowing gradual evaporation thereof. The heated thermal body allows all points of the circuit to be maintained at a constant temperature at all times, so as to prevent the formation of cold spots during evaporation of the liquid. It has been found that through this solution it is in fact possible to obtain a homogeneous gaseous mixture both in terms of temperature and composition. The gaseous mixture obtainable through the method according to the invention will be formed by a part corresponding to the evaporated liquid and a part corresponding to the initial flow of gas.

Fig. 1 schematically shows a block diagram of the method according to the invention. The metal body is indicated with the reference 10, while the hydraulic circuit defined in this body is indicated with the reference line 5. The block with the reference 3 indicates the heating means used to heat the metal body 10. The initial flow of gas is indicated with the reference A, while the flow of liquid is indicated with the reference L. The (single-phase) homogeneous mixture delivered from the hydraulic cireuit is indicated with the reference ALu, while the two-phase mixture formed by the flow of gas A and by the flow of liquid L is indicated with ALi. As shown, the heating means 3 are operatively positioned inside the metal body so as to optimize transmission of the thermal power W required to maintain the body at the predetermined temperature. For this purpose, the heating means can comprise electric heating elements, for example in the form of cartridges or coils, or also a radiant burner positioned inside the metal body.

With reference to the schematic diagram of Fig. 1A, according to a possible embodiment of the method according to the invention, the flow of gas A is obtained through partial evaporation of the flow of liquid L. In particular, the flow of liquid is preheated inside the metal body 10 to reach pressure and temperature conditions suitable to be partially evaporated through an evaporation unit comprising, for example, an evaporation nozzle or other functionally equivalent means. Evaporation of a part of the liquid L generates the flow of gas A which, together with the remaining part of liquid, forms the two-phase mixture introduced into the circuit 5.

In the event in which, for example, the flow of liquid L is formed by water, the water is preheated inside the metal body 10 to take it to the pressure and temperature conditions sufficient to allow evaporation thereof through the evaporation nozzle. The water vapor generated through this nozzle forms the gaseous part (flow A) which mixes with the remaining part of liquid, not vaporized, to form the two-phase mixture ALi introduced into the hydraulic circuit 5. From the description above, it can be understood that the method according to the invention in this case can also be considered as a method for evaporating a flow of liquid, for example water in the case considered above.

According to another possible embodiment of the method, the flow rate of the flow of gas (steam in the case of water) is chosen significantly higher than the flow rate of the flow of liquid. In this case, the method according to the invention can be used as method to humidify the flow of gas A through evaporation of the liquid part L. In both cases considered, and in all the embodiments of the method, the boundary conditions (such as temperature of use of the gaseous mixture delivered ALu, flow rates of the flows forming the two-phase mixture ALi, etc.) define the power necessary to reach the specifications required, which can be calculated by means of an energy balance. A first portion of this power takes account of the sensible heat required to take the liquid to evaporation condition, a second portion instead takes account of the latent evaporation heat, and the last portion takes account of the sensible heat to take the vapor phase to the required temperature condition.

The present invention also relates to a device 2,2B,2C,2D that allows implementation of the method according to the present invention. In particular, this device allows the preparation of a homogeneous gaseous mixture at a predetermined temperature starting from a flow of gas and from a flow of liquid. The device 2,2B,2C,2D according to the invention can be used as an evaporation device of a liquid, for example, in cases in which the flow of gas (such as water vapor) is chosen of the same nature as the liquid (water). The device 2,2B,2C,2D according to the invention can also be used as humidifier in the case in which it is necessary to provide a flow of gas A with a certain degree of humidity which is reached through controlled evaporation of the flow of liquid L.

Figures 2 to 5 are relative to a first possible embodiment of a device 2 according to the present invention. In this embodiment, the metal body 10 is in the form of a steel cylinder which extends along a longitudinal axis between a first and a second transverse surface which are substantially orthogonal to the axis X. Purely to simplify the description, the metal body 10 will also be indicated hereafter with the expression "cylinder 10".

In this embodiment, the hydraulic circuit 5 is defined by a plurality of longitudinal passages 8A,8B,8C which extend between the first and the second transverse surface of the cylinder 10. These longitudinal passages 8A,8B,8C are distributed according to a circumference concentric to the axis of the cylinder 10. The circuit also comprises a plurality of first connecting passages 7 that connect two adjacent longitudinal passages in proximity of the first transverse surface of the cylinder 10 and a plurality of second connecting passages 7B which connect two adjacent longitudinal passages in proximity of the second transverse surface of the cylinder. The first connecting passages 7 are staggered with respect to the second passages 7B so that a first longitudinal passage 8A is connected to a second longitudinal passage ·8Β through one of the first connecting passages 7 and so that it is connected to a third longitudinal passage 8C through one of the second connecting passages 7B.

With reference to the sectional view of Fig. 3, the hydraulic circuit 5 also comprises an axial passage 13 and a radial passage 12 which connects one of the second connecting passages 7B to the axial passage 13. The first 7 and the second passages 7B are defined by a milling operation performed respectively on the first and on the second transverse surface of the cylinder 10. For this purpose, Fig. 3 shows the configuration and the arrangement of the milled parts which define the first passages 7, while Fig. 5 allows us to observe the arrangement of the milled parts defining the second passages 7B. By comparing Figs. 3 and 5, the staggered arrangement between the first 7 and the second passages 7B is evident. These passages 7,7B are closed axially through a first 9 and a second flange 9B which is connected permanently to the cylindrical body 10.

With reference once again to Figs. 3 to 5, it can be seen that the cylindrical body 10 comprises a plurality of longitudinal seats 17, positioned inside which are electric heating cartridges (not shown) used as heating means to heat the cylindrical body 10. Further longitudinal seats 18 are instead used to position thermocouples to read the temperature of the cylinder 10.

From an operational viewpoint, the metal cylinder 10 is heated through the electric cartridges so that it can maintain a predetermined heating temperature. At the inlet of the hydraulic circuit 5 the flow of gas is mixed with the flow of liquid to form the two-phase mixture ALi which passes through the hydraulic circuit 5. In particular, the mixture is sent from one longitudinal passage 8A,8B,8C to the adjacent one by means of the first 7 and of the second connecting passages 7,7B. In practice, the mixture passes longitudinally through the cylinder 10 first in one direction and then in the other until completing the circuit, or until reaching the radial passage 12 which conveys the homogeneous gaseous mixture ALu into the axial passage 13. Through this the mixture ALu is take directly to the user.

Figs. 6 to 9 relate to a second embodiment of a device 2B according to the present invention which differs from the previous embodiment due to a different configuration of the hydraulic circuit. More in detail, the device 2B once again comprises a cylindrically shaped metal body 10 (hereafter also indicated with the expression metal cylinder 10) on the outer surface of which a helical groove 19 is produced. The metal cylinder 10 is covered externally by a liner 10B also made of metal material. The inner surface of the metal liner 10B closes the helical groove externally so as to define a substantially helical circulation channel for the two- phase mixture. This mixture is introduced into the circulation channel through an axial inlet 19A indicated in Fig. 6 and also visible in Fig. 9. After passing through the circulation channel, the mixture is conveyed through a radial connection 19B (see Fig. 7) into the axial passage 13, through which it can be conveyed to a user through a suitable connecting element 27 (Fig. 6).

Just as for the previous solution described, also in this second case the cylindrical body 10 is heated from the inside through electric cartridges 36. These cartridges 36 are arranged along a perimeter circumference concentric to the cylindrical body. It has been found that this arrangement allows a substantially uniform temperature to be obtained over the entire cylindrical body 10. From a constructional viewpoint, the sectional views in Figs. 7 to 9 allow observation of the possible configuration of the circulation channel or of the hydraulic circuit 5 through which evaporation of the liquid part of the two-phase mixture takes place. It has been found that the helical configuration of the circulation channel facilitates flow of the two-phase mixture inside the cylindrical body 10 and consequently optimizes the vaporization process.

Figs. 10 to 13 relate to a third embodiment of a device 2C according to the present invention which can be used, for example, as evaporator to evaporate a flow of water. In this further solution, the metal body 10 is composed of a casting of metal material, inside which a hydraulic coil 41 defining the hydraulic circuit for the two- phase mixture is placed in an outer position and an electric coil 42 for heating the metal body is placed in an inner position. In this embodiment the device 2C also comprises a further coil 47 (see Fig. 13) which acts as preheater for the flow of liquid L as better specified below. From the constructional viewpoint, therefore, the three coils 41 ,42,47 are first positioned so that they are preferably coaxial, as clearly shown in Fig.13. Subsequently, a casting of metal material, such as aluminum, is produced around the coils so as to configure the cylindrical heating body 10.

With reference to Fig. 13, the preheating coil 47 has an inlet 47A into which a flow of water (flow of liquid L) is introduced. The outlet 47B of the coil 47 is operativeiy connected, through a flanged connection 48, to an inlet 43 of the hydraulic coil 41 in which the two-phase mixture is destined to circulate. In proximity of the flanged connection 48 an evaporation nozzle (not shown in the figures) is operativeiy positioned to allow evaporation of a part of the flow of liquid. More precisely, while passing through the preheating coil 44 the liquid L reaches pressure and temperature conditions that allow it to partially evaporate while passing through the nozzle. In this manner, a two-phase mixture ALi is generated downstream of the nozzle, whose gaseous part A is composed of the vaporized liquid part and whose liquid part L is formed by the remaining part of unvaporized liquid.

With reference in particular to the sectional view of Fig. 11 , the outer coil 41 comprises an outlet element 44 through which the homogeneous gaseous mixture ALu exits from the metal body 10 following vaporization of the liquid part to reach an environment or a user. It can be seen that from a constructional viewpoint this third embodiment of the device according to the invention advantageously does not require any mechanical machining of the metal body, with consequent reduction in final manufacturing costs. As indicated above the metal body 10 can be composed of a casting of aluminum or alternatively another metal material with high coefficient of thermal conduction.

Figs.14 and 15 relate to a further embodiment of a device 2D according to the present invention which differs from the device 2C shown in Figs. 9 to 11 due to a different configuration of the heating means. Unlike the previous case, heating of the metal body 10 is in this case (device 2D) produced through the use of a radial burner. This expression is intended to indicate a burner 100 provided with a combustion chamber 101 whose walls 118 transfer the heat generated by combustion directly to the metal body 0 by thermal conduction.

The longitudinal sectional view of Fig. 14 shows in detail a preferred embodiment of the radial burner 100 which is formed by a tubular element 115 positioned coaxial with the metal body 10. More precisely, the tubular element 118 extends along a longitudinal direction X and comprises an axial operating cavity. This cavity is open on at -least a first side and is limited on the opposite side by a housing wall 112 of a cap element 113 connected to the end of the tubular element 1 15 . A first portion of the operating cavity defines the combustion chamber 101 indicated above.

The burner 100 comprises first feed means to introduce an oxidizer into the operating cavity in a first oxidizer intake position P1 and second feed means to introduce a fuel into the operating cavity in a fuel intake position P2. Preferably, the first feed means are configured so as to introduce a flow of oxidizer according to a tangential direction so as to impart a substantially spiral motion to this flow inside the axial cavity. The second feed means are instead configured so as to introduce a flow of fuel which extends along a direction substantially parallel to the longitudinal axis of the cavity.

The axial operating cavity comprises a second portion 111 between the oxidizer intake position P1 and the fuel intake position P2, which defines a stabilization chamber for the flow of oxidizer introduced by the first feed means. In other words, this chamber advantageously stabilizes the spiral motion of the oxidizer ensuring constant feed and a constant combustion stoichiometric ratio.

As can be seen again in Fig. 15, the second feed means preferably comprise a lance element 130 which extends through the cap element 113 being preferably connected thereto. A first portion 130A of the lance element 130 is outside the tubular element 5. This first portion is in communication, for example through a supply pipe 131 , with a fuel source, not shown in the figures, which can, for example, be a bottle of methane or other pressurized gaseous fuel. A second portion 130B of the lance element 130 is inside and substantially coaxial with the axial operating cavity and terminates with an emission end 133 through which the fuel C exits. The axial extension of this first portion in practice defines the axial extension LT of the stabilization chamber as it stabilizes the distance between the intake position of the first oxidizer and that of the fuel. It has been found that particularly appreciable results in terms of flame stability are obtained when the combustion chamber 101 and the stabilization chamber 1 1 have the same diametric extension. The radial burner comprises combustion ignition means which are advantageously positioned inside the -operating cavity. More in detail, in the case illustrated these means comprise a spark igniter 140 positioned inside the lance element 130. The spark igniter 140 comprises a part made of insulating material which is coaxial with the inside of the lance element 130. This body comprises an ignition end 140B, also called tip, which emerges with respect to the fuel delivery end 133 of the lance element 130. This emerging position of the tip allows the spark to strike in a region which undoubtedly contains flammable mixture generated by the constant mixing of combustion air coming from the stabilization chamber 11 A and from the lance element 130.

The technical solutions adopted for the method and the device according to the invention allow the aim and the objects set to be fully achieved. In particular, the method and the devices described allow the preparation of a homogeneous gaseous mixture both in terms of composition and in terms of temperature.

The method and the device thus conceived are susceptible to numerous modifications and variants, all falling within the scope of the inventive concept; moreover all details can be replaced by other technically equivalent details.

In practice, the materials used and the contingent dimensions and forms can be any, according to requirements and to the state of the art.

Claims

1. A method for preparing a homogeneous gaseous mixture (ALu) starting from a flow of gas (A) and from a flow of liquid (L), said method comprising the steps of:

- providing a metal body (10) inside which a hydraulic circuit (5) is defined for passage of a two-phase mixture (ALi) formed by the mixture of said flow of gas (A) and of said flow of liquid (L);

- heating said metal body (10) to a heating temperature (Tp) at least sufficient to allow vaporization of the liquid part of said two-phase mixture (ALi);

- introducing said two-phase mixture (ALi) into said hydraulic circuit so as to vaporize said liquid part of said two-phase mixture (AL).

2. The method according to claim 1 , wherein said flow of liquid (L) and said flow of gas (A) are mixed before entering said hydraulic circuit.

3. The method according to claim 1 , wherein said flow of liquid (L) and said flow of gas (A) are mixed upon introduction into said hydraulic circuit.

4. The method according to claim 1 , wherein said flow of gas (A) is formed by a part of the vaporized flow of liquid (L).

5. The method according to claim 1 , wherein said metal body is heated through heating means positioned inside this body.

6. The method according to claim 5, wherein said heating means are formed by electric heating elements.

7. A device (2) for preparing a homogeneous gaseous mixture (ALu) starting from a flow of gas (A) and from a flow of liquid (L), said device being characterized in that it comprises a metal body (10) inside which at least one hydraulic circuit (5) is defined, destined to be passed through by a two-phase mixture formed by said gas and by the liquid part to be vaporized, said device comprising heating means (41 ,36) to heat said metal body (10) to a predetermined heating temperature (Tp) so as to vaporize the liquid part of said two-phase mixture.

8. The device (2) according to claim 7, wherein said metal body (10) is in the form of a cylinder made of metal material and wherein said hydraulic circuit (5) comprises a plurality of longitudinal passages (8A,8B,8C) which extend between a first and a second transverse surface of the cylinder, said circuit (5) comprising a plurality of first connecting passages (7) that connect, in proximity of said first surface, two adjacent longitudinal passages (5A) and a plurality of second connecting passages (7B) that connect, in proximity of said second connecting surface, another two different adjacent longitudinal passages.

9. The device (2) according to claim 8, wherein said first connecting passages (7) are staggered with respect to the second passages (7B) so that a first of said longitudinal passages (8A) is connected to a second longitudinal passage (8B) through one of said first connecting passages (7) and so that it is connected to a third longitudinal passage (8C) through one of the second connecting passages (7B).

10. The device according to claim 8 or 9, wherein said heating means comprise electric heating elements positioned axially inside said cylindrical body (10).

11. The device (2B) according to claim 7, wherein said metal body comprises a cylinder made of metal material ( 0) and a liner (10B) which covers the outside of said cylinder (10), said hydraulic circuit (5) comprising a circulation channel defined by a helical groove produced on the outer surface of said cylinder and by the inner wall of said liner (10B), said hydraulic circuit (5) comprising an axial inlet (19A) for introducing said two-phase mixture into said channel and an axial outlet passage (13) connected to said channel through a radial connection (19B).

12. The device (2B) according to claim 11 , wherein said heating means comprise a plurality of electric cartridges (36) positioned axially inside said metal body (10).

13. The device (2C) according to claim 7, wherein said metal body (10) is formed by a casting of metal material, said hydraulic circuit (5) being defined by a hydraulic coil (41) embedded inside said casting and comprising an inlet element (43) and an outlet element (44) for said two-phase mixture (ALu).

14. The device (2C) according to claim 13, wherein said heating means comprise an electric heating coil (42) embedded inside said casting in a position substantially coaxial with said first coil (41).

15. The device (2C) according to claim 13 or 14, wherein said device (2C) comprises a preheating coil (47) to heat said liquid to the temperature and pressure conditions sufficient to allow partial evaporation thereof in an evaporation nozzle positioned at the outlet of said preheating coil (47) and at the inlet of said hydraulic coil (41).

16. The device (2C) according to claims 13 to 15, wherein said metal body is made of aluminum.

17. The device (2D) according to one of claims 13 to 16, wherein said heating means comprise a radiant burner (100) comprising a combustion chamber (101) positioned inside said metal body (10).

18. The device (2D) according to claim 17, wherein said metal body (10) has a substantially cylindrical form and wherein said radiant burner ( 00) comprises a tubular element (115), a portion of which defines said combustion chamber (101), said tubular element (115) being positioned inside said metal body (10) so that said combustion chamber is substantially coaxial with said metal body (10). ^'