A device for cracking a gas

Abstract

The present disclosure concerns a turbomachine for cracking a gas. Embodiments disclosed herein specifically concern a turbomachine comprising one or more compressors to compress the gas and consequently increase its temperature up to the cracking temperature of the gas, wherein at least one of the compressors is coupled through a planetary gear type system with an integrally geared rotating system, which is driven by a driving rotating machine. An expander can be advantageously connected downstream of the compressors and is configured to recover energy from the compressed gas, the expander being preferably additionally coupled with the integrally geared rotating system. The compressors can also be combined with one or more catalytic sections, one or more wave rotors and one or more separating apparatuses downstream of the compressors and / or the wave rotors and / or the expander, to separate the products of the cracking reaction.

Description

A device for cracking a gasDescriptionTECHNICAL FIELD

[0001] The present disclosure concerns a turbomachine for cracking a gas. Embodiments disclosed herein specifically concern a turbomachine comprising one or more compressors to compress the gas and consequently increase its temperature up to the cracking temperature of the gas, wherein at least one of the compressors is coupled through a planetary gear type system with an integrally geared rotating system. More in particular, embodiments disclosed herein specifically concern a turbomachine for cracking a gas, in particular in a system for CCL-free pyrolysis of gaseous fluids to produce cracked products, mainly for hydrogen and / or olefins production without using external heating sources.BACKGROUND ART

[0002] Thermal decomposition of a chemical compound to obtain simpler molecules is commonly used in the treatment of organic materials. This technology is known as pyrolysis or thermal cracking. In particular, cracking is the process whereby complex organic molecules such as long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. Thermal decomposition can also be applied to non-organic molecules.

[0003] In particular, thermal decomposition of methane from natural gas or ammonia is recently getting more and more importance as a technology to produce hydrogen. For example, with reference to the thermal decomposition of methane into carbon and hydrogen (CH4 + Heat — > C + 2H2) with trace quantities of other hydrocarbons, this process (methane pyrolysis or methane cracking) is based on the heating of methane to temperatures in which the kinetics of the reaction produce high conversions in a reasonable time. The governing reaction is endothermic, thus the necessary energy input should be provided from an energy source. A main characteristic of this process is the absence of oxygen, which eliminates CO2 and CO by-products. Additionally, nowater is consumed, and the produced carbon may have qualities that can be marketed and used in a variety of traditional and novel applications, or it can be securely stored for future use.

[0004] According to the prior art, one or more compressors can be used to compress the gas to be cracked and consequently increase its temperature up to the cracking temperature of the gas.

[0005] Recently, shock-wave compression has been proposed as an energy source or temperature multiplier for direct thermal methane decomposition [Akbari, P., Copeland, C. D., Tuchler, S., Davidson, M., and Mahmoodi-Jezeh, S. V, “ShockWave Heating: A Novel Method for Low-Cost Hydrogen Production” ASME Paper IMECE2021-69775, 2021], In this approach, a wave rotor [Akbari, P., Nalim, M. R., and Muller, N., “A Review of Wave Rotor Technology and Its Applications,” ASME Journal of Engineering for Gas Turbines and Power, Vol. 128, No. 4, 2006, pp. 717- 735] is used to generate shock and rarefaction waves for exchanging energy between fluid streams. This technology is considered very promising in order to produce hydrogen without any undesirable by-product, such as in particular carbon dioxide. In particular, this technology is favorably applicable to produce hydrogen to be used as feedstock for a gas turbine operating as the driver of a compressor in a booster station for natural gas pipelines, in order to counteract the pressure drop of the natural gas along the pipeline [Pejman et al, “The Use of Wave Machinery for Power Generation and Production of Hydrogen as Gas Turbine Fuel”, AIAA Scitech Forum, 29 December 2021}. This solution allows the wave rotor to use a little fraction of the natural gas from the pipeline to produce hydrogen to be used as fuel for the gas turbine, by leveraging the pressure already present in the natural gas pipeline to use the natural gas as the driver gas of the wave rotor. At the same time, the low-pressure natural gas at the driver gas outlet of the wave rotor is sent back to the wave rotor as the driven gas, being heated up to the cracking temperature, to obtain hydrogen.

[0006] Additionally, always according to the prior art, gas cracking turbomachine combining together one or more compressors with one or more wave rotors have been disclosed. The use of catalysts has also been disclosed in combination with the compressors and / or the wave rotor in order to improve the conversion rate or selectivity or both of the pyrolysis reaction.

[0007] More in general, the possibility of using wave rotors to increase the temperature of a gas up to its thermal decomposition can be applied to different kind of gases. However, the use of compressors to heat a gas stream up to its decomposition temperature can still be improved in order to reduce or even eliminates the need for external heating sources by extending the versatility of the process to a broad spectrum of cracking reactions.

[0008] Therefore, there is a need for improved designs of a compressor based cracking system that can address these challenges and provide efficient and reliable performance in various industrial applications.

[0009] Accordingly, an improved compressor based gas cracking system to address the issues of flexibility of the systems of the current art would be beneficial and would be welcomed in the technology.SUMMARY

[0010] In one aspect, the subject matter disclosed herein is directed to a turbomachine for cracking a gas, the turbomachine comprising one or more compressors, configured to compress the gas and consequently increase its temperature up to the cracking temperature, wherein at least one of the compressors is coupled through a planetary gear type system with an integrally geared rotating system, which is driven by a driving rotating machine.

[0011] In one aspect, the disclosure concerns a turbomachine for cracking a gas wherein an expander is connected downstream of the compressors and is configured to recover energy from the compressed gas, the expander being preferably additionally coupled through the same or a different planetary gear type system with the integrally geared rotating system. In particular, a bull gear is used in case the speed ratio is greater than 7.

[0012] In another aspect, the compressors can be combined with one or more catalytic sections, one or more wave rotors and one or more separating apparatuses downstream of the compressors and / or the wave rotors and / or the expander, to separate the products of the cracking reaction.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 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 scheme of the mechanical connection of the components of a turbomachine for cracking a gas, according to a first embodiment;Fig.2 illustrates a scheme of the mechanical connection of the components of a turbomachine for cracking a gas, according to a second embodiment;Fig.3 illustrates a scheme of the mechanical connection of the components of a turbomachine for cracking a gas, according to a third embodiment;Fig.4 illustrates a block diagram of a turbomachine for cracking a gas, according to a fourth embodiment;Fig.5 illustrates a section view of a turbomachine for cracking a gas, according to a fifth embodiment; andFig.6 illustrates an exploded perspective view of a turbomachine for cracking a gas, according to a sixth embodiment.DETAILED DESCRIPTION OF EMBODIMENTS

[0014] According to one aspect, the present subject matter is directed to a turbomachine for cracking a gas, the turbomachine comprising one or more compressors, with a gas inlet and with a compressed gas outlet, the inlet being connected to a feedstock of a gas to be cracked. The compressors are configured to compress the gas and consequently increase its temperature up to the cracking temperature. In particular, at least one of the compressors is coupled through a planetary gear type system with an integrally geared rotating system, which is driven by a driving rotating machine. The planetary gear type system and the integrally geared rotating system allow to obtain cracking of the components of the gas with a compact system, with a reduced footprint, standing to offer a solution that significantly reduces or even eliminates the need for external heating sources. Their versatility can be extended to a broad spectrum of cracking reactions. The system can further comprise components configured to combine with the compressors to increase efficiency and rate of conversion of the cracking reaction, such as wave rotors arranged downstream of the compressors, separatingmeans arranged downstream or inside the wave rotors, energy recovery means (such as an expander) configured to recover energy after cracking and provide such energy in the form of heat to the cracking reaction and / or electricity to the wave rotors and / or the compressors. Advantageously, the wave rotors of the system can be additionally integrated through the same or a different planetary gear type system to the same integrally geared rotating system of the compressors.

[0015] 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 any suitable manner in one or more embodiments.

[0016] 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.

[0017] Referring now to the drawings, Fig.1 shows a schematic of an exemplary turbomachine for cracking a gas, the turbomachine comprising one or more compressors 10, with a gas inlet and with a compressed gas outlet, the inlet of a first compressor 10 being connected to a feedstock of a gas to be cracked by means of a feed line 11. The compressed gas outlet of the first compressor is connected to the inlet of a second compressor 10 by means of a line 12. A catalytic section 13 is arranged along the line 12. The compressors 10 are configured to compress the gas and consequently increase its temperature up to the cracking temperature of the gas, the catalytic sections 13 amongst two compressors being configured to increase the conversion rate of thecracking reaction or improve selectivity (yield) of the reaction. The compressed gas outlet of the last compressor 10 is connected to a cracked gas outlet line 14. The compressors 10 are integrated in a planetary gear type system 100, namely by means of a common bull gear 102, which is driven by a driving rotating machine (not shown).

[0018] Several embodiments of possible wave rotor system arrangements will be described below with reference to the following Figs 2, 3, 4, 5, and 6.

[0019] In particular, with continuing reference to Fig.1, Fig.2 illustrates a second embodiment of a turbomachine of the present disclosure. In Fig. 2, 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 this exemplary embodiment, two wave rotors are integrated in the system, the wave rotors 15 being coupled to the same bull gear 102 of the compressors 10. Generally, the wave rotors 15 are arranged downstream the compressors 10, which pressurize the gas to be reacted at the pressure required by the wave rotor 15. However, it is also possible to arrange a compressor 10 downstream the driver outlet of a wave rotor, to restore the pressure of the driver gas. Therefore, the cracking reaction can initiate inside the compressor 10 if the process fluid is further accelerated to the supersonic velocity and then decelerated to subsonic velocity in the statoric part of the compressor 10, which brings the fluid to its thermal cracking conditions. The heat required for the pyrolysis reaction is supplied by the system composed by the compressors 10 and the wave rotors 15, without the need for external heating sources.

[0020] With continuing reference to Figs. 1 and 2, a further embodiment of a turbomachine for cracking a gas according to the present disclosure is shown in Fig. 3. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Figs. 1 and 2 and described above, and which will not be described again. The wave rotor system of Fig. 3 differs from the wave rotor system of Figs. 1 and 2 in that it comprises both compressors 10 and wave rotors 15, but also a catalytic section 13 along the lines 12 connecting a compressor 10 to another compressor 10 and / or to a wave rotor 15, mounted on the same bull gear 102. Alternatively, the catalytic section can be arranged inside the compressors 10 and / or inside the wave rotors 15 (by way of example inside at least a portion of one or more of the channels of the at least one wave rotor in the form of a solid bulk catalyst, a monolith, a catalytic metal foam and / or a coating of at least part of the walls of the channel or channels).

[0021] With continuing reference to Figs. 1 and 3, Fig. 4 illustrates a further embodiment of a wave rotor system. The same reference numbers used in Figs. 1, 2 and 3 are used in Fig. 4 to designate the same or corresponding parts, components or elements, which will not be described again. The embodiment of Fig. 4 comprises a compressor 10 with a gas feed line 11. A catalytic pre-cracking reactor 16 is arranged downstream the compressor 10 and upstream of a wave rotor 15. The driver gas inlet of the wave rotor 15 is fed by the compressed gas from the compressor 10, while the driven gas inlet is connected to the feed line 11 through a by-pass line 17. A second catalytic reactor 18 is arranged downstream the wave rotor 15. Further, means for recovering energy, such as an expander 19, and separating means to separate the products of the cracking reaction, such as a pressure swing adsorber 20, are arranged downstream the catalytic reactor 16. According to this embodiment, a gas to be pyrolyzed is fed to the compressor 10 through the feed line 11. The compressor 10 increases the pressure of the gas, and correspondingly its temperature, before it is passed through a catalytic pre-cracking reactor 16 and subsequently fed as a driver gas to the wave rotor 15. A portion of the low-pressure stream from the gas feed line 11 is delivered as a driven gas directly to the wave rotor 15 through a by-pass line 17. Additional flexibility of the compressor 10 is allowed by integrating the compressor 10 into a planetary gear type system. The high temperature and high pressure gas from the wave rotor 15 is directed to the second catalytic reactor 18. According to this embodiment, the compressor 10 and the wave rotor 15 can be used to simply compress the gas to be pyrolyzed or also to perform a pre-cracking of the gas, which is subsequently completed by the second catalytic reactor 18. The second catalytic reactor 18 can be a fixed or fluidized bed reactor. In case the second catalytic reactor 18 is a fixed bed catalytic reactor, it can be filled with solid catalyst or catalytic metal foams or monolith or with catalytic membrane for in situ separation / purification of the desired products the further improves the yield or the reaction or moderate the reaction temperature for a given conversion rate. The catalyst can be integrated also in the compressor 10 and / or in the wave rotor 15, for example, as metal foams, monolith or coatings. The catalytic reactors 16, 18 can be operated adiabatically without external heating sources. Alterna-tively, they can be operated isothermally using external sources such as electrical heaters or plasma or microwave or exhaust stream of a gas turbine or other high temperature fluid streams. The pyrolyzed gas from the second catalytic reactor 18 is then directed, to the expander 19. In particular, the expander 19 is implemented for energy recovery, the recovered energy 21 being supplied to the wave rotor 15 in the form of heat through the heat line 21’ and / or to the compressor 10 through the heat line 21” and / or to the catalytic reactor 18 through the heat line 21’”. The gas downstream the expander 19 is directed to the pressure swing adsorber 20. In case the gas to be pyrolyzed by the wave rotor system is cracked into two gas products in addition to a fraction of unreacted gas, then the pressure swing adsorber 20 is composed of two sections, to respectively separate a first and a second gas product, non-reacted gas being recycled back to either compressor inlet or low-pressure side of the wave rotor. According to alternative embodiments, different types of separating means can be used in place of the pressure swing adsorber, such as a temperature swing adsorber or a membrane.

[0022] With continuing reference to Figs. 1, 2, 3 and 4, a further embodiment of the turbomachine for cracking a gas is disclosed in Fig. 5. The same reference numbers used in Figs. 1, 2, 3 and 4 are used in Fig. 5 to designate the same or corresponding parts, components or elements, which will not be described again. In particular, Fig. 5 shows the upper half portions of two overhung impeller centrifugal compressors 10 coupled to a bull gear 102.

[0023] Referring to Fig.6, with continuing reference to Figs. 1, 2, 3, 4 and 5, a further embodiment of the turbomachine for cracking a gas is disclosed. The same reference numbers used in Figs. 1, 2, 3, 4 and 5 are used in Fig. 6 to designate the same or corresponding parts, components or elements, which will not be described again. The embodiment of Fig. 6 is shown as an exploded perspective view of a compressor 10 and a wave rotor 15 that are coupled by a common bull gear. In particular, a bull gear is needed in case the speed ratio is greater than 7.

[0024] The planetary gear type system and the integrally geared rotating system can also comprise one or more idle gears (free wheels), which are used to increase the rotor span, thus avoiding interference among the statoric parts of the compressor stages or any of the rotating machines being part of the planetary gear type system.

[0025] While aspects of the invention has 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 se- quence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

Claims

CLAIMS1. A turbomachine for cracking a gas, the turbomachine comprising one or more compressors (10), with a gas inlet and with a compressed gas outlet, the inlet being connected to a feedstock of a gas to be cracked, the compressors (10) being configured to compress the gas and consequently increase its temperature up to the cracking temperature of the gas, wherein at least one of the compressors (10) is coupled through a planetary gear type system with an integrally geared rotating system (100), which is driven by a driving rotating machine.

2. The turbomachine of claim 1, wherein an expander (19) is connected downstream of the compressed gas outlet of the compressors (10) and configured to recover energy from the compressed gas.

3. The turbomachine of claim 1, wherein the expander (19) is coupled through the same or a different planetary gear type system with the integrally geared rotating system (100).

4. The turbomachine of any of the preceding claims, wherein a catalytic section is arranged downstream of the compressors (10).

5. The turbomachine of any of the preceding claims, wherein the compressors (10) are connected in series, the inlet of a compressor (10) being connected to the outlet of the preceding compressor (10).

6. The turbomachine of claim 5, wherein the catalytic section is arranged between the outlet of one compressor (10) and the inlet of the downstream compressor (10).

7. The turbomachine of any of the preceding claims, wherein the turbomachine comprises one or more separating apparatuses (20) downstream the compressors (10) and / or downstream the expander (19).

8. The turbomachine of any of the preceding claims, wherein at least one wave rotor (15) is connected downstream the compressors (10), the driver gas inlet of the wave rotor (15) being connected to the compressed gas outlet of a compressor (10).

9. The turbomachine of claim 8, wherein the driven gas inlet of the wave rotor (15) is directly connected to the feedstock of the gas to be cracked through a by-pass line (17).

10. The turbomachine of claim 8 or 9, wherein the catalytic section is arranged downstream of the compressor (10) and upstream of the wave rotor (15).

11. The turbomachine of claims 8-10, wherein the turbomachine comprises a plurality of wave rotors (15).

12. The turbomachine of claim 11, wherein the catalytic section is arranged between two wave rotors (15).

13. The turbomachine of any of claims 8-12, wherein the wave rotors(14) are coupled through a planetary gear type system with an integrally geared rotating system (100).

14. The turbomachine of any of claims 8-13, wherein the turbomachine comprises one or more separating apparatuses (20) downstream the wave rotors (15) or between two wave rotors (15).

15. The turbomachine of any of the preceding claims, wherein the integrally geared rotating system (100) comprises a common bull gear (102), at least one of the compressors (10) and / or the expander (19) and / or at least one of the wave rotors(15) being coupled to the common bull gear (102).

16. The turbomachine of any of the preceding claims, wherein the integrally geared rotating system (100) comprises one or more idle gears.

17. The turbomachine of any of the preceding claims, wherein one or more of the compressors (10) coupled through a planetary gear type system with the integrally geared rotating system (100) are overhung-impeller centrifugal compressors(10).

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