A rotary machine for heating a gas stream, in particular as a chemical reactor

Abstract

The present disclosure concerns a rotary machine (10) for increasing the energy of a gas stream, in particular a reactant gas stream (S, S', S", …, Sn), characterised in that the rotary machine (10) comprises one or more stages (11), each stage (11) comprising a. a first rotor (12) comprising a plurality of rotor blades configured to convert the mechanical energy of the rotary machine (10) into kinetic energy of the gas stream (S, S', S", …, Sn) by increasing the pressure, temperature and velocity of the gas stream (S, S', S", …, Sn), b. a second rotor (13) comprising a plurality of rotor blades configured to convert the mechanical energy of the rotary machine (10) and the kinetic energy of the gas stream (S, S', S", …, Sn) into internal energy of the gas stream by reducing the pressure of the gas stream (S, S', S", …, Sn), provided downstream the first rotor (12), the first rotor (12) and the second rotor (13) of each stage (11) being fixed to a shaft (15) or part of a same radial extension (151) of the shaft (15). The disclosure also concerns a method for increasing the energy of a gas stream, in particular a reactant gas stream, the method comprising: a. providing a stream (S) of a gas to the rotary machine (10) defined above, b. providing energy to the gas stream (S, S', S", …, Sn) by alternatively i. increasing pressure, temperature and velocity of the gas stream (S, S', S", …, Sn) by means of the rotor blades of the first rotor (12), and ii. reducing pressure of the gas stream (S, S', S", …, Sn), converting the stage rothalpy to increase the temperature of the gas stream (S, S', S", …, Sn) by means of the rotor blades of the second rotor (13).

Description

A rotary machine for heating a gas stream, in particular as a chemical reactorDescriptionTECHNICAL FIELD

[0001] The present disclosure pertains to the technical field of mechanical engineering, in particular of chemical engineering, specifically to the design and operation of rotary machines used for heating a gas stream, in particular for the chemical reaction of reactant gases. The invention involves a rotary machine that comprises at least one stage, which includes a first rotor comprising a plurality of centrifugal, axi-centrifugal or axial rotor blades and a second rotor comprising a plurality of centripetal, axi-cen- tripetal or axial rotor blades. These blades are designed to manipulate the pressure and temperature of the gas stream, thereby facilitating the chemical reaction process. The invention may include multiple stages, catalysts, and temperature-resistant materials. It also provides methods for maintaining optimal chemical reaction conditions, in particular optimal cracking conditions. This technology can be applied in various industrial processes where chemical reaction of a gas stream is required.BACKGROUND ART

[0002] Traditionally, endothermic chemical reactions, such as the cracking of a reactant gas to produce smaller final products, need to be provided with heat to reach the activation energy of the chemical reaction and maintain a sufficient energy of the reaction until the reaction completes. In particular, ethylene, propylene and other light olefins are produced in tubular reactors in a fired heater, that is a radiant box with burners. In fact, since the involved reactions are endothermic, energy, in particular heat must be provided from external sources to the reactor, not only for reaching the activation energy of the chemical reaction, but also to allow the reaction to continue until the full conversion of the reactant gas is obtained or at least until the kinetic equilibrium is reached. This technology bums a fuel in order to obtain heat needed for the reaction. The problems with this technology include the production of carbon dioxide, a greenhouse gas, the deposition of coke and exergy losses.

[0003] Recently, a step to energy saving and reduced production of greenhouse gas was the shift from surface heat exchange (primarily radiative) to a more direct meansof energy transfer to the feedstock. To this aim, turbomachines were proposed for ethylene production, and more in general for endothermic reactions, in order to add energy to the reaction mixture from inlet conditions to outlet conditions including energy required for the reaction. In essence the radiant box with burner system was replaced by a turbomachine that supplies the duty that is absorbed in the radiant cell. The reaction proceeds inside the turbomachine producing valuable products. These turbomachines are called turbo-reactors and allow to improve the yield of the reaction and to improve exergy efficiency of -43% with respect to typical cracking furnaces. Turbo-reactors could potentially reduce greenhouse gas emissions by at least 70% for a cracking plant, whilst providing the required cracking energy with -500 smaller volume than that of a conventional radiant section.

[0004] More in detail, according to this known technology, the heat for the reaction is generated by means of gas dynamics (compression and shock waves). First, the process fluid is accelerated to supersonic velocity with the use of a jet tube. Then, shock waves are produced by decelerating a supersonic stream to subsonic velocity. This results in an instantaneous increase in the temperature of the reactants, typically methane or ammonia, which accelerates the pyrolysis. After the pyrolysis, the mixture is quenched. This results in a high yield and selectivity of H2.

[0005] In general, the design objective of the pyrolytic reactors of the prior art is to increase the yield of the primary product (H2) while minimizing side reactions. This can be achieved by reducing the residence time and increasing the temperature / heating rate. The turbo reactors of the prior art allow to achieve this aim because stator blades (guide vanes) rapidly accelerate, pre-condition and pre-swirl the flow before entering the rotor. Then, the transonic ultra-high loading impellers impart mechanical energy to the flow. Finally, the transonic diffuser transforms kinetic into internal energy by decelerating the high-speed flow using a shockwave system.

[0006] Advantages of the turbo-reactors of the prior art are: direct mechanical energy transfer, controllability and intense mixing, lower residence time and higher yield, unfavourable environment for coking.

[0007] In particular, direct mechanical energy transfer is obtained because the turbomachines directly impart the rotor shaft’s mechanical energy (i.e. pure exergy) tothe process fluid by aerodynamic action through rotating blades. This direct energy transfer vs. surface heat exchange increases the exergy efficiency of the process. Moreover, since the process fluid is the hottest part of the turbo-reactor, an effective thermal protection technology could minimize irreversible losses due to heat transfer. Direct mechanical energy transfer is also obtained because the turbomachine transforms the kinetic energy into internal energy over a short distance.

[0008] Another advantage of the turbo-reactors of the prior art is controllability and intense mixing. In fact, through careful aerothermal design and operational control (e.g. varying the rotational speed), turbomachines can control the temperature and pressure distributions, enthalpy increase, mass flow rate, reaction rate, residence time, and turbulent mixing of species.

[0009] Lower residence time and higher yield can also be obtained through the turboreactors of the prior art, since the process fluid can attain higher temperatures without reaching the critical melting temperature of the walls. This allows shorter residence times and therefore a higher yield.

[0010] Unfavourable environment for coking is obtained by the turbo-reactors of the prior art because of high surface viscous shear stresses, a low temperature level and gradient on the wall plus a reduction in the residence time. Moreover, the turbo-reactors of the prior art allow for the possibility of using anti-coking and anti-corrosion inner-wall surface coatings.

[0011] However, the turbo-reactors of the prior art still face some challenges and disadvantages that require improvements. Specifically, in addition to the fact that shock waves can potentially result in mechanical problems of the blades, when the turbo-reactors are used to achieve cracking of a stream of a reactant gas, where the number of product molecules exceeds the number of reactant molecules, an extra problem arises from the pressure increase, which demands suitably sized equipment.

[0012] Accordingly, an improved turbo-reactor configured to impart heat to a gas stream, in particular to a cracking reaction of a stream of reactant gas while maintaining its pressure and temperature substantially constant would be beneficial and would be welcomed in the technology.SUMMARY

[0013] In one aspect, the subject matter disclosed herein is directed to a rotary machine for increasing the energy of a gas stream, in particular a reactant gas stream. The rotary machine comprises one or more stages, each stage including a first rotor with a plurality of rotor blades configured to convert the mechanical energy of the rotary machine into kinetic energy of the gas stream by increasing the pressure, temperature, and velocity of the gas stream, and a second rotor with a plurality of rotor blades configured to convert the mechanical energy of the rotary machine and the kinetic energy of the gas stream into internal energy of the gas stream by reducing the pressure of the reactant gas stream, provided downstream of the first rotor, the first rotor and the second rotor of each stage being fixed to a shaft or part of the same radial extension of the shaft.

[0014] In one aspect, the profile of the rotor blades of the first rotor and / or of the rotor blades of the second rotor changes along a direction proceeding from the root to the tip of the blades, while the angle of incidence of the rotor blades of the second rotor is comprised between -70° and -5° or between 5° and 30°, preferably between -50° and -10° or between 7° and 20°.

[0015] In accordance with other aspects, each stage is an axial stage, where the first rotor is an axial rotor and the second rotor is an axial rotor, additionally configured to reduce the velocity of the reactant gas stream.

[0016] In yet other aspects, each stage is a centrifugal centripetal stage, with the first rotor being a centrifugal impeller and the second rotor being a centripetal impeller, wherein the centripetal impeller of each centrifugal centripetal stage is additionally configured to increase the temperature of the reactant gas stream.

[0017] In further aspects, a connection channel is present downstream of the first rotor and upstream of the second rotor of each stage. In additional aspects, the rotary machine comprises a plurality of stages in series. In other aspects, the rotary machine comprises two or more stages, with at least two stages arranged on the same shaft. In yet other aspects, the rotary machine comprises two or more stages, with at least two stages being integrally geared.

[0018] In accordance with further aspects, the one or more stages are configured to increase the energy of the reactant gas stream at least up to the activation energy of the chemical reaction. In other aspects, the one or more stages are configured to increase the temperature of the reactant gas stream at least up to 850°C. In yet other aspects, the one or more stages are configured to provide an energy amount higher than the activation energy of the chemical reaction. In further aspects, the one or more stages are configured to provide an energy amount corresponding at least to the activation energy of an endothermic chemical reaction and subsequent temperature loss due to the reaction kinetic. In accordance with additional aspects, the rotary machine comprises one or more stages configured to increase the energy of the gas stream at least up to the activation energy of the chemical reaction and one or more subsequent stages configured to provide the gas stream with an additional energy amount. In other aspects, the one or more subsequent stages are configured to provide the gas stream with an additional energy amount at least equal to the temperature loss due to the reaction kinetic.

[0019] In yet other aspects, the geometrical parameters of the rotary machine are configured to control the residence time of the gas stream within the rotary machine.

[0020] In further aspects, the connection channel is configured to connect the exit of the first rotor and the inlet of the second rotor of each stage without reducing the module of velocity of the reactant gas stream. In accordance with additional aspects, the connection channel comprises a stationary external side wall on the external side of the connection channel with respect to the shaft. In other aspects, the connection channel also comprises a stationary inside side wall on the internal side of the connection channel with respect to the shaft. In yet other aspects, the rotary machine further comprises cylindrical elements provided between the external side wall and the internal side wall of the connection channel.

[0021] In further aspects s, the rotary machine further comprises vanes provided between the external side wall and the internal side wall of the connection channel. In particular, the angle of incidence of the vanes is comprised between -70° and -5° or between 5° and 30°, preferably between -50° and -10° or between 7° and 20°. In accordance with additional aspects, the rotary machine comprises, upstream of the first of the one or more stages and / or downstream of the last of the one or more stages, aplurality of vanes. In other embodiments, the vanes upstream of the first of the one or more stages are inlet guide vanes (IGV) and the vanes downstream of the last of the one or more stages are discharge guide vanes (DGV). In particular, when a plurality of vanes is present upstream of the first of the one or more stages, then the angle of incidence of the rotor blades of the first rotor is comprised between -70° and -5° or between 5° and 30°, preferably between -50° and -10° or between 7° and 20°. In yet other aspects, the rotary machine comprises a plenum upstream of the first of the one or more stages or, if present, upstream of the vanes. In further embodiments, the rotary machine comprises a discharge scroll downstream of the last of the one or more stages or, if present, downstream of the vanes. In accordance with additional aspects, the rotary machine comprises one or more of the following: variable speed electrical drivers, recycle loops, throttling valves, inlet guide vanes (IGV), and discharge guide vanes (DGV) to enhance the reaction and machine control to the optimal working conditions.

[0022] In other aspects, the rotary machine comprises a catalyst. In yet other embodiments, at least part of the surfaces of the plenum or vanes and / or first rotor and / or second rotor are covered with a catalytic material. In further aspects, the plenum or inlet guide vanes and / or first rotor and / or second rotor and / or connection channels and / or discharge guide vanes and / or discharge are made of temperature-resistant materials. In accordance with additional aspects, the rotary machine comprises a cooling system configured to cool the one or more stages. In other aspects, the cooling system comprises one or more cooling channels inside the structure of the rotoric components and / or statoric components of the one or more stages. In yet other embodiments, the shaft is connected to a turbomachine or an electrical device.

[0023] In accordance with further aspects, a method is provided for increasing the energy of a gas stream, in particular a reactant gas stream. The method comprises providing a gas stream to the rotary machine as previously defined, and providing energy to the gas stream by alternatively increasing the pressure, temperature, and velocity of the gas stream by means of the rotor blades of the first rotor, and reducing the pressure of the gas stream, converting the stage rothalpy to increase the temperature of the gas stream by means of the rotor blades of the second rotor.

[0024] In other aspects, the method comprises providing energy to the gas stream atleast up to the activation energy of a chemical reaction, in particular a cracking reaction, to react at least part of the gas stream.

[0025] According to other aspects, the method comprises providing an energy amount to the gas stream higher than the activation energy of the chemical reaction, in particular the cracking reaction.

[0026] In other aspects, the method comprises providing an energy amount to the gas stream at least equal to the activation energy of an endothermic chemical reaction, in particular a cracking reaction and subsequent energy loss due to the reaction kinetic, to react part or the whole of the gas stream. In one aspect, the method comprises a step of controlling the residence time of the gas stream within the rotary machine. According to one aspect, the method comprises a step of controlling the speed of the gas stream within the rotary machine. In one aspect, the method comprises a step of maintaining a low hydrocarbon partial pressure of the gas stream within the rotary machine.

[0027] According to other aspects, the method further comprises a step of maintaining an optimal cracking temperature of the gas stream within the rotary machine. According to still other aspects, the method further comprises a step of cooling said one or more stages, in particular the step of cooling comprises flowing a cooling fluid inside one or more cooling channels inside the structure of the rotoric components and / or statoric components of said one or more stages.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. l illustrates a schematic view of part of a rotary machine for increasing the energy of a gas stream, in particular for reacting, more in particular cracking of a reactant gas, according to a first embodiment;Fig.2 illustrates a sectional schematic view of part of a rotary machine for increasing the energy of a gas stream, according to a second embodiment;Fig. 3 illustrates a sectional schematic view of an upper half of a centrifugal- centripetal stage of the rotary machine for increasing the energy of a gas, according to a third embodiment, the lower half being symmetrical with respect to the axis;Fig. 4 illustrates a sectional schematic view of an upper half of a centrifugal- centripetal stage of the rotary machine for increasing the energy of a gas, according to a fourth embodiment, the lower half being symmetrical with respect to the axis;Fig. 5 illustrates a sectional schematic view of an upper half of a centrifugal- centripetal stage of the rotary machine for increasing the energy of a gas, according to a fifth embodiment, the lower half being symmetrical with respect to the axis;Fig. 6 illustrates a sectional schematic view of an upper half of a centrifugal- centripetal stage of the rotary machine for increasing the energy of a gas, according to a sixth embodiment, the lower half being symmetrical with respect to the axis; andFig. 7 illustrates a sectional schematic view of an upper half of an axial rotary machine for increasing the energy of a gas, according to a seventh embodiment, the lower half being symmetrical with respect to the axis.DETAILED DESCRIPTION OF EMBODIMENTS

[0029] According to one aspect, the present subject matter is directed to a rotary machine for increasing the energy of a gas stream, in particular a reactant gas stream, wherein the rotary machine comprises one or more stages, each stage comprising a. a first rotor comprising a plurality of rotor blades configured to convert the mechanical energy of the rotary machine into kinetic energy of the gas stream by increasing the pressure, temperature and velocity of the gas stream, b. a second rotor comprising a plurality of rotor blades configured to convert the mechanical energy of the rotary machine and the kinetic energy of the gas stream into internal energy of the gas stream by reducing the pressure of the reactant gas stream, provided downstream the first rotor, the first rotor and the second rotor of each stage being fixed to a shaft or part of a same radial extension of the shaft.

[0030] In one aspect, the profile of the rotor blades of the first rotor and / or of the rotor blades of the second rotor changes along a direction proceeding from the root to the tip of the blades, in order to optimize the aerodynamics of the rotor.

[0031] In one aspect, the angle of incidence of the rotor blades of the second rotor is comprised between -70° and -5° or between 5° and 30°, preferably between -50° and -10° or between 7° and 20°. As commonly accepted in the field, a negative value of the angle of incidence indicates that the incoming gas flow moves towards the pressure side of the blade, while a positive value of the angle of incidence indicates that the incoming gas flow moves towards the suction side of the blade. This misalignment can cause aerodynamical inefficiencies and performance losses in the rotary machine, which is done by purpose with the aim of increasing the entropy of the gas. However, the angle of incidence must be less than the maximum limits of the ranges, in order to avoid the formation of stagnation zones. In particular, the formation of stagnation zones must be avoided when the gas is natural gas or a gas rich in hydrocarbons, to prevent the formation of coke.

[0032] In one aspect, each stage is an axial stage, the first rotor is an axial rotor and the second rotor is an axial rotor, additionally configured to reduce the velocity of the reactant gas stream.

[0033] In yet other aspects, each stage is a centrifugal centripetal stage, with the first rotor being a centrifugal impeller and the second rotor being a centripetal impeller, wherein the centripetal impeller of each centrifugal centripetal stage is additionally configured to increase the temperature of the reactant gas stream.

[0034] In further aspects, a connection channel is present downstream of the first rotor and upstream of the second rotor of each stage. In additional aspects, the rotary machine comprises a plurality of stages in series. In other aspects, the rotary machine comprises two or more stages, with at least two stages arranged on the same shaft. In yet other aspects, the rotary machine comprises two or more stages, with at least two stages being integrally geared.

[0035] In different embodiments, the rotary machine is designed to increase the energy of a gas stream. In certain embodiments, the rotary machine comprises one or more stages, each stage including a first rotor with a plurality of rotor blades configured to increase the pressure, temperature, and velocity of the gas stream. The first rotor and the second rotor of each stage are fixed to a shaft or are part of the same radial extension of the shaft. The rotary machine may include a connection channeldownstream of the first rotor and upstream of the second rotor of each stage. The machine can also comprise a plurality of stages in series, with at least two stages arranged on the same shaft or integrally geared. The stages are configured to increase the energy of the gas stream up to the activation energy of the cracking reaction, in particular, in case of reaction of a low hydrocarbon to obtain ethylene and propylene with the capability to increase the temperature of the gas stream to at least 850°C. The stages can provide an energy amount higher than the activation energy of the cracking reaction, accounting for subsequent temperature loss due to reaction kinetics.

[0036] In one embodiment, each stage is an axial stage, where the first rotor is an axial rotor and the second rotor is an axial rotor, additionally configured to reduce the velocity of the gas stream. In another embodiment, each stage is a centrifugal centripetal stage, with the first rotor being a centrifugal impeller and the second rotor being a centripetal impeller, where the centripetal impeller is also configured to increase the temperature of the gas stream.

[0037] The rotary machine can include stages configured to increase the energy of the gas stream up to the activation energy of the cracking reaction and subsequent stages to provide additional energy. The geometrical parameters of the machine are designed to control the residence time of the reactant gas stream within the machine. In the case of centrifugal centripetal stages, the connection channel is configured to connect the exit of the first rotor and the inlet of the second rotor without reducing the velocity module of the reactant gas stream. This connection channel may include a stationary external side wall and a stationary inside side wall, with cylindrical elements or vanes provided between these walls. In particular, the angle of incidence of the vanes is comprised between -70° and -5° or between 5° and 30°, preferably between - 50° and -10° or between 7° and 20°.

[0038] The rotary machine may also feature vanes upstream of the first stage and / or downstream of the last stage, which can be inlet guide vanes (IGV) and discharge guide vanes (DGV), respectively. Additionally, the machine can include a plenum upstream of the first stage or vanes, and a discharge scroll downstream of the last stage or vanes. The machine may incorporate variable speed electrical drivers, recycle loops, throttling valves, IGVs, and DGVs to optimize reaction and machine control. In particular, when a plurality of vanes is present upstream of the first of the one or morestages, then the angle of incidence of the rotor blades of the first rotor is comprised between -70° and -5° or between 5° and 30°, preferably between -50° and -10° or between 7° and 20°.

[0039] The rotary machine can include a catalyst, with catalytic material covering at least part of the surfaces of the plenum, vanes, first rotor, and second rotor. The components of the machine, such as the plenum, IGVs, first rotor, second rotor, connection channels, DGVs, and discharge, are made of temperature-resistant materials. The machine may also feature a cooling system with cooling channels inside the structure of the rotoric and statoric components of the stages.

[0040] The shaft of the rotary machine can be connected to a turbomachine or an electrical device.

[0041] The method for increasing the energy of a reactant gas stream involves providing the gas stream to the rotary machine, increasing its pressure, temperature, and velocity using the first rotor, and reducing its pressure to increase its temperature using the second rotor. The method can provide energy up to or higher than the activation energy of the cracking reaction, control the residence time and speed of the gas stream, maintain low hydrocarbon partial pressure, and ensure optimal cracking temperature. The method may also include cooling the stages by flowing a cooling fluid inside cooling channels within the rotoric and statoric components.

[0042] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment s). Further, the particular features, structures or characteristics may be combined in anysuitable manner in one or more embodiments.

[0043] When introducing elements of various embodiments the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0044] Referring now to the drawings, Fig.1 shows a schematic of part of an exemplary rotary machine 10, comprising a plurality of centrifugal -centripetal stages 11 sharing a common shaft 15. Each centrifugal-centripetal stage 11 comprises rotoric components and statoric components, the rotoric components comprising a centrifugal impeller 12, which comprises a plurality of centrifugal or axi-centrifugal rotor blades and a centripetal impeller 13, which comprises a plurality of centripetal or axi-centrip- etal rotor blades. The centrifugal impeller 12 of each centrifugal-centripetal stage 11 is fluidly connected to the centripetal impeller 13 through a connection channel 14. In particular, the connection channel 14 can be vaned or vaneless and connects the exit of the centrifugal impeller 12 and the inlet of the centripetal impeller 13.

[0045] In particular, each centrifugal-centripetal stage 11 is designed to alternatively work in the first and second quadrant. Namely, the centrifugal impeller 12 is configured to work in the first quadrant, to increase both pressure and temperature of a reactant gas stream S, while the centripetal impeller 13 is configured to work in the second quadrant, to reduce pressure and contemporary increase the temperature of the gas stream S, converting the stage rothalpy into gas enthalpy and entropy.

[0046] By way of explanation of the disclosure, not limitation of the disclosure, a reactant gas stream S of ethane with a flow rate of 30000 kg / h was delivered to the rotary machine 10 of Fig. 1, the reactant gas stream having a temperature of 700°C and a pressure of 1.5 bara. Through the first centrifugal impeller 12 of the first centrifugal-centripetal stage 11 both pressure and temperature of a reactant gas stream S increased, the temperature at the exit of the first centrifugal impeller 12 being approximately 740°C, the pressure being approximately 2 bara. The gas stream was then directed, through the first connection channel 14, to the first centripetal impeller 13 of the first centrifugal-centripetal stage 11 at substantially the same temperature and pressure. In the centripetal impeller 13 the temperature of the reactant gas stream increasedup to approximately 800°C, while the pressure decreased down to approximately 1,5 bara. The gas stream S’ was then directed to the second centrifugal-centripetal stage 11, the temperature and pressure of the gas stream at the exit of the centrifugal impeller 12 being respectively 835°C and 2 bara, while the temperature and pressure of the gas stream at the exit of the centripetal impeller 12 was respectively 850°C and 1,5 bara.

[0047] The rotary machine 10 achieved the aim of increasing the temperature of the gas stream while maintaining an approximately constant pressure, despite the cracking reaction caused an increase in the number of moles of the gas.

[0048] Several embodiments of possible centrifugal-centripetal stage arrangements will be described below with reference to the following Figs 2, 3, 4, 5 and 6.

[0049] With continuing reference to Fig.1, Fig.2 shows a schematic of part of another exemplary rotary machine 10, comprising two centrifugal-centripetal stages 11 sharing a common shaft 15. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Fig.l and described above, and which will not be described again. According to the embodiment of Fig.2, each centrifugal-centripetal stage 11 comprises a centrifugal impeller 12 and a centripetal impeller 13, which are part of a same radial extension 151 of the shaft 15. A radial-axial connection channel 152 is also shown between the exit of the centripetal impeller 13 of the first centrifugal -centripetal stage 11 and the inlet of the centrifugal impeller 12 of the subsequent centrifugal-centripetal stage 11.

[0050] With continuing reference to Fig.l and 2, Fig.3 illustrates an embodiment of a centrifugal-centripetal stage 11 of the rotary machine 10 for cracking of a reactant gas, according to the present disclosure. In the embodiment of Fig.3, the rotor shaft 15 rotates around its axis together with the centrifugal impeller 12, of which a centrifugal rotor blade 121 is shown, and the centripetal impeller 13, of which a centripetal rotor blade 131 is shown. The rotation of the centrifugal rotor blades 121 cause an increase of the velocity of the gas stream and of its total and static temperature. Thus, in the centrifugal impeller 12, the mechanical energy of the rotary machine 10 is converted into kinetic energy of the gas stream. The centripetal rotor blades 131 cause a decrease of the velocity of the gas stream and a consequent increase of its static temperature. Thus, in the centripetal impeller 13, the mechanical energy of the rotary machine 10and the kinetic energy of the gas stream is converted into internal energy of the gas stream.

[0051] The connection channel 14 comprises a stationary external side wall 141 on the external side with respect to the shaft 15 and a stationary internal side wall 142 on the internal side with respect to the shaft 15. A plurality of cylindrical elements 143 is provided between said external side wall 141 and said internal side wall 142. The connection channel 14 is therefore a completely stationary connection channel, inside which the velocity of the gas stream remains constant or increases and the static temperature of the gas stream remains constant or lowers. Therefore, inside the connection channel 14, the kinetic energy of the gas stream is not converted into internal energy of the gas stream.

[0052] Finally, the embodiment shown in Fig.3 also comprises inlet vanes 16, which are stationary components of the rotary machine 10, upstream the centrifugal impeller 12.

[0053] With continuing reference to Figs.1, 2 and 3, a further embodiment of a centrifugal-centripetal stage 11 of the rotary machine 10 for cracking of a reactant gas is shown in Fig.4. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Fig.3 and described above, and which will not be described again. The centrifugal -centripetal stage 11 of Fig.4 differs from the centrifugal-centripetal stage of Fig.3 only in that vanes 144 are provided between the external side wall 141 and the internal side wall 142 of the connection channel 14. Therefore, also according to this embodiment, the connection channel 14 is a completely stationary connection channel, inside which the velocity of the gas stream remains constant or increases and the static temperature of the gas stream remains constant or lowers and therefore, inside the connection channel 14, the kinetic energy of the gas stream is not converted into internal energy of the gas stream.

[0054] With continuing reference to Figs.l, 2, 3 and 4, a further embodiment of a centrifugal-centripetal stage 11 of the rotary machine 10 for cracking of a reactant gas is shown in Fig.5. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Fig.3 and 4 and described above, and which will not be described again. The centrifugal-centripetal stage 11 of Fig.5differs from the centrifugal-centripetal stage of Figs.3 and 4 in that the connection channel 14 does not comprise an internal wall separating it from the rotating components of the machine 10. As a consequence, the connection channel 14 is only partially stationary. Therefore, inside the connection channel 14, an additional quote of the mechanical energy of the rotary machine 10 is converted into internal energy of the gas stream, as secondary effect of the friction between the rotating components and the gas stream across the connection channel 14.

[0055] Additionally, with continuing reference to Figs.1, 2, 3, 4 and 5, a further embodiment of a centrifugal-centripetal stage 11 of the rotary machine 10 for cracking of a reactant gas is shown in Fig.6. The centrifugal-centripetal stage 11 of Fig.6 differs from the centrifugal -centripetal stage of Fig.5 only in that inlet vanes are not provided upstream the centrifugal impeller 12.

[0056] Finally, with continuing reference to Figs. l, 2, 3, 4, 5 and 6, a schematic of part of an exemplary rotary machine 10, comprising a plurality of axial stages 11’ sharing a common shaft 15 is shown in Fig.7. Each axial stage 11’ comprises rotoric components and statoric components, the rotoric components comprising a first axial rotor, comprising a plurality of axial rotor blades 12’ and a second axial rotor, comprising a plurality of axial rotor blades 13’. The rotor blades 12’ of the first axial rotor are configured to increase the pressure, temperature and velocity of a gas stream while the rotor blades 13’ of the second axial rotor are configured to reduce the pressure and the velocity of the gas stream.

[0057] While aspects of the invention have been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirt and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

Claims

CLAIMS1. A rotary machine (10) for increasing the energy of a gas stream (S, S’, S”, Sn), in particular a reactant gas stream (S, S’, S”, ..., Sn), characterised in that the rotary machine (10) comprises one or more stages (11), each stage (11) comprising a. a first rotor (12) comprising a plurality of rotor blades configured to convert the mechanical energy of the rotary machine (10) into kinetic energy of the gas stream (S, S’, S”, . . ., Sn) by increasing the pressure, temperature and velocity of the gas stream (S, S’, S”, ..., Sn), b. a second rotor (13) comprising a plurality of rotor blades configured to convert the mechanical energy of the rotary machine (10) and the kinetic energy of the gas stream (S, S’, S”, . . ., Sn) into internal energy of the gas stream by reducing the pressure of the gas stream (S, S’, S”, ..., Sn), provided downstream the first rotor (12), the first rotor (12) and the second rotor (13) of each stage (11) being fixed to a shaft (15) or part of a same radial extension (151) of the shaft (15).

2. A rotary machine (10) according to claim 1, characterised in that the profile of the rotor blades of the first rotor (13) and / or of the rotor blades of the second rotor (13) changes along a direction proceeding from the root to the tip of the blades.

3. A rotary machine (10) according to claim 1 or 2, characterised in that the angle of incidence of the rotor blades of the second rotor (13) is comprised between -70° and -5° or between 5° and 30°.

4. A rotary machine (10) according to the previous claim, characterized in that the angle of incidence of the rotor blades of the second rotor (13) is comprised between -50° and -10° or between 7° and 20°.

5. A rotary machine (10) according to any of the previous claims, characterized in that each stage (11) is an axial stage, the first rotor (12) is an axial rotorand the second rotor (13) is an axial rotor, additionally configured to reduce the velocity of the gas stream (S, S’, S”, ..., Sn).

6. A rotary machine (10) according to one or more of claims 1-4, characterised in that each stage (11) is a centrifugal centripetal stage (11), said first rotor(12) is a centrifugal impeller (12) and said second rotor (13) is a centripetal impeller(13), wherein the centripetal impeller (13) of each centrifugal centripetal stage (11) is additionally configured to increase the temperature of the gas stream (S, S’, S”, ..., Sn).

7. A rotary machine (10) according to any of the preceding claims, wherein a connection channel (14) is present downstream of the first rotor (12) and upstream of the second rotor (13) of each stage (11).

8. A rotary machine (10) according to any of the preceding claim, characterised in comprising a plurality of stages (11) in series.

9. A rotary machine (10) according to any of claims 1-8, comprising two or more stages (11), characterised in that at least two stages (11) are arranged on a same shaft (15).

10. A rotary machine (10) according to any of claims 1-8, comprising two or more stages (11), characterised in that at least two stages (11) are integrally geared.

11. A rotary machine (10) according to any of the previous claims, characterised in that said one or more stages (11) are configured to increase the energy of a reactant gas stream (S, S’, S”, ... , Sn) at least up to the activation energy of a chemical reaction.

12. A rotary machine (10) according to the preceding claim, characterised in that said one or more stages (11) are configured to increase the temperature of the reactant gas stream (S, S’, S”, ..., Sn) at least up to 850°C.

13. A rotary machine (10) according to claim 11 or 12, characterised in that said one or more stages (11) are configured to provide an energy amount higher than the activation energy of the cracking reaction.

14. A rotary machine (10) according to the previous claim, characterised in that said one or more stages (11) are configured to provide an energy amount corresponding at least to the activation energy of the cracking reaction and subsequent temperature loss due to the reaction kinetic.

15. A rotary machine (10) according to any of the previous claims, characterised in comprising one or more stages (11) configured to increase the energy of the gas stream (S, S’, S”, ..., Sn) at least up to the activation energy of the cracking reaction and one or more subsequent stages (11) configured to provide to the gas stream (S’, S”, ...) an additional energy amount.

16. A rotary machine (10) according to the previous claim, characterised in that said one or more subsequent stages (11) are configured to provide to the gas stream (S’, S”, ...) an additional energy amount at least equal to the temperature loss due to the reaction kinetic.

17. A rotary machine (10) according to any of the previous claims, characterised in that the geometrical parameters of the rotary machine (10) are configured to control the residence time of the reactant gas stream (S, S’, S”, ..., Sn) within the rotary machine (10).

18. A rotary machine (10) according to claim 7, characterised in that said connection channel (14) is configured to connect the exit of the first rotor (12) and the inlet of the second rotor (13) of each stage (11) without reducing module of velocity of the reactant gas stream (S, S’, S”, ..., Sn).

19. A rotary machine (10) according to claim 18, characterised in that said connection channel (14) comprises a stationary external side wall (141) on the external side of the connection channel (14) with respect to the shaft (15).

20. A rotary machine (10) according to claim 19, wherein said connection channel (14) also comprises a stationary inside side wall (142) on the internal side of the connection channel (14) with respect to the shaft (15).

21. A rotary machine (10) according to claim 20, further comprising cylindrical elements (143) provided between said external side wall (141) and said internal side wall (142) of the connection channel (14).

22. A rotary machine (10) according to claim 20, further comprising vanes (144) provided between said external side wall (141) and said internal side wall (142) of the connection channel (14).

23. A rotary machine (10) according to claim 22, characterized in that the angle of incidence of the vanes (144) is comprised between -70° and -5° or between 5° and 30°.

24. A rotary machine (10) according to claim 22, characterized in that the angle of incidence of the vanes (144) is comprised between -50° and -10° or between 7° and 20°.

25. A rotary machine (10) according to any of the previous claims, characterised in comprising, upstream the first of said one or more stages (11) and / or downstream the last of said one or more stages (11), a plurality of vanes.

26. A rotary machine (10) according to the previous claim, characterised in that said vanes upstream the first of said one or more stages (11) are inlet guide vanes (IGV) and said vanes downstream the last of said one or more stages (11) are discharge guide vanes (DGV).

27. A rotary machine (10) according to claim 25 or 26, characterised in that the angle of incidence of the rotor blades of the first rotor (12) is comprised between -70° and -5° or between 5° and 30°.

28. A rotary machine (10) according to the preceding claim, characterized in that the angle of incidence of the rotor blades of the first rotor (12) is comprised between -50° and -10° or between 7° and 20°.

29. A rotary machine (10) according to any of the previous claims, characterised in comprising a plenum upstream the first of said one or more stages (11) or, if present, upstream said vanes.

30. A rotary machine (10) according to any of the previous claims, characterised in comprising a discharge scroll downstream the last of said one or more stages (11) or, if present, downstream said vanes.

31. A rotary machine (10) according to any of the previous claims, characterised in comprising one or more of the following: variable speed electrical drivers, recycle loops, throttling valves, inlet guide vanes (IGV) and discharge guide vanes (DGV) to enhance the reaction and machine control to the optimal working conditions.

32. A rotary machine (10) according to any of the previous claims, characterized in that it comprises a catalyst.

33. A rotary machine (10) according to the previous claim, characterized in that at least part of the surfaces of the plenum or vanes and / or first rotor (12) and / or second rotor (13) are covered with a catalytic material.

34. A rotary machine (10) according to any of the previous claims, characterized in that said plenum or inlet guide vanes and / or first rotor (12) and / or second rotor (13) and / or connection channels (14) and / or discharge guide vanes and / or discharge are made of temperature resistant materials.

35. A rotary machine (10) according to any of the previous claims, characterized in that it comprises a cooling system configured to cool said one or more stages (11).

36. A rotary machine (10) according to claim 35, characterized in that the cooling system comprises one or more cooling channels inside the structure of the rotoric components and / or statoric components of said one or more stages (11).

37. A rotary machine (10) according to any of the previous claims, characterized in that the shaft (15) is connected to a turbomachine or an electrical device.

38. A method for increasing the energy of a gas stream, the method com- prising: a. providing a stream (S) of a gas to the rotary machine (10) of any of claims 1-37, b. providing energy to the gas stream (S, S’, S”, . . ., Sn) by alternatively i. increasing pressure, temperature and velocity of the gas stream (S, S’, S”, . . . , Sn) by means of the rotor blades of the first rotor (12), and ii. reducing pressure of the gas stream (S, S’, S”, . . ., Sn), converting the stage rothalpy to increase the temperature of the gas stream (S, S’, S”, . . ., Sn) by means of the rotor blades of the second rotor (13).

39. A method according to the previous claim, wherein the method comprises providing energy to the gas stream (S, S’, S”, ... , Sn) at least up to the activation energy of a chemical reaction, in particular a cracking reaction, to react at least part of the gas stream (S, S’, S”, ..., Sn).

40. A method according to the previous claim, wherein the method comprises providing an energy amount to the gas stream (S, S’, S”, ..., Sn) higher than the activation energy of the cracking reaction.

41. A method according to the previous claim, wherein the method comprises providing an energy amount to the gas stream (S, S’, S”, ..., Sn) at least equal to the activation energy of the cracking reaction and subsequent energy loss due to the reaction kinetic, to react part or the whole of the gas stream (S, S’, S”, ..., Sn).

42. A method according to any of claims 38-41, wherein the method comprises a step of controlling the residence time of the gas stream (S, S’, S”, ..., Sn) within the rotary machine (10).

43. A method according to any of claims 38-42, wherein the method comprises a step of controlling the speed of the gas stream (S, S’, S”, ..., Sn) within the rotary machine (10).

44. A method according to any of claims 38-43, wherein the method comprises a step of maintaining a low hydrocarbon partial pressure of the gas stream (S, S’, S”, ..., Sn) within the rotary machine (10).

45. A method according to any of claims 38-44, wherein the method further comprises a step of maintaining an optimal cracking temperature of the gas stream (S, S’, S”, ..., Sn) within the rotary machine (10).

46. A method according to any of claims 38-45, wherein the method further comprises a step of cooling said one or more stages (11).

47. A method according to claim 46, characterized in that the step of cooling comprises flowing a cooling fluid inside one or more cooling channels inside the structure of the rotoric components and / or statoric components of said one or more stages (11).

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