Plant and process for the high-efficiency production of hydrogen by pyrolysis

Abstract

A plant (10) for producing hydrogen by pyrolysis of hydrocarbons, comprising : at least one reactor (1) comprising at least one longitudinally-developing hollow vessel along which there are sequentially at least a first zone (1105) for pre-heating an inlet gas flow (FG) comprising hydrocarbons and cooling an outlet flow of solid particles (42), a second zone (1104) for heating and reacting a pre-heated gas flow (FC) and passing a flow of pre-heated solid particles (42), a third zone (1103) for pre-heating an inlet flow of solid particles (42) and cooling an outlet gas flow comprising hydrogen, at least one electrically conductive element (1111) extending longitudinally at least at one longitudinal section of the second zone (1104), wherein said electrically conductive element (1111) has two ends (1112) configured to be placed at an electric potential difference such that it is carrying current being heated, and wherein the electrically conductive element (1111) is configured and arranged to transmit the heat generated by it to the solid particles (42) and / or the gas flow passing through the second zone (1104).

Description

[0001] PLANT AND PROCESS FOR THE HIGH-EFFICIENCY PRODUCTION OF

[0002] HYDROGEN BY PYROLYS IS

[0003] The present invention relates to a plant for the high-ef ficiency production of hydrogen by pyrolysis .

[0004] The invention further relates to a proces s for the high-ef ficiency production of hydrogen by pyrolysis .

[0005] In more detail , the invention refers to the production of hydrogen by pyrolysis reactions of hydrocarbons .

[0006] As is known, hydrogen production solutions known in the state of the art are classi fied in categories depending on the basic chemical reaction used to obtain the hydrogen molecule . A colour is attributed for "disclosure" purposes to the hydrogen produced with di f ferent methodologies ; in particular, the following can be mentioned :

[0007] "Grey" hydrogen, in which the production occurs by steam reforming of methane , a technology involving a signi ficant impact in terms of CO2 emissions ;

[0008] "Blue" hydrogen, in which steam reforming of methane is operated with capturing CO2 ;

[0009] "Green" hydrogen, in which the production occurs by water electrolysis using electrical energy produced from renewable sources ;

[0010] "Turquoise" hydrogen, which involves a direct pyrolysis of methane ( and / or other hydrocarbons ) .

[0011] This last technology, compared to the others mentioned, requires a lower amount of energy (being up to seven times less energy-intensive , for example , than the process for producing green hydrogen) . The production of "turquoise" hydrogen has recently developed mainly through three technologies: a first technology based on the use of bubbles in a molten bath (bubbles in a molten bath) , a second technology based on the use of plasma (plasma based) and a third technology based on a catalytic bed of pellets (catalytic bed of pellets) .

[0012] From US2982622, a plant and a process for converting hydrocarbons by pyrolysis are known, in which a reactor is traversed in countercurrent by a flow of solid particles (e.g., of coal, coke) and by a gas flow comprising hydrocarbons. At the pyrolysis zone, there are pairs of electrodes immersed in the moving bed of solid particles. By applying a potential difference to the electrodes of each pair, electric current passes directly through the moving bed of solid particles (coke) . However, the electrical resistance of the moving bed of solid particles is poorly controllable, and the electric current passes where it finds the least resistance, with uncontrollable paths (and thus heating zones) .

[0013] The main object of the present invention is to provide a plant and a process for the high-efficiency production of hydrogen, in particular turquoise hydrogen, which overcomes the drawbacks of the prior art .

[0014] In the scope of this general object, the present invention aims to provide a plant and a process for the high-efficiency production of hydrogen, in particular turquoise hydrogen, which allow for precise and reliable control of the heat input required for pyrolysis.

[0015] These objects are achieved according to the invention by a plant according to claim 1 .

[0016] The invention further relates to a process for the high-ef ficiency production of hydrogen according to claim 10 .

[0017] Further features are speci fied in the dependent claims .

[0018] The solution proposed according to the present invention diverges from the three above-mentioned production typologies ("bubbl es in mol ten ba th, " "plasma based, " and " ca talyti c bed of pell ets" ) in that it uses , as a heating means , a zone of a reactor comprising a plurality of electrically conductive elements , which are arranged in an assembly configured in such a way as to allow the passage of gas and heat exchange solid particles , as better detailed below . At this zone of the reactor, the electrically conductive elements are configured to be connected to a power supply plant and thus to be passed through by electric current , being heated by Joule ef fect . When an electric current flows through these electrically conductive elements , they provide the solid particles and / or the gas transiting through the corresponding zone o f the reactor with the thermal energy required for pyrolysis .

[0019] Thus , the subj ect of the present invention is a plant for producing hydrogen by pyrolysis of hydrocarbons , comprising :

[0020] - at least one reactor comprising at least one longitudinally-developing hollow vessel along which there are sequentially at least :

[0021] - a first zone for pre-heating an inlet gas flow comprising hydrocarbons and for cooling an outlet flow of solid particles ; - a second zone for heating and reacting the gas flow pre-heated in the f irst zone , and for passing a flow of pre-heated solid particles ;

[0022] - a third zone for pre-heating an inlet flow of solid particles and for cooling an outlet gas flow comprising hydrogen; at least one electrically conductive element extending at a longitudinal section of said second zone , wherein said at least one electrically conductive element has two ends configured to be placed at an electric potential di f ference such that said electrically conductive element is passed through by electric current and heats up, and wherein said at least one electrically conductive element is configured and arranged to transmit the heat generated by it to the solid particles and / or the gas flow passing through said second zone .

[0023] Preferably, the first , second, and third zones are vertically sequential to each other from the lower end to the upper end of the reactor . At the first zone , there are at least one inlet of the inlet gas flow and at least one outlet of the outlet flow of solid particles .

[0024] At the third zone , there are at least one inlet of the inlet flow of solid particles and at least one outlet of the outlet gas flow .

[0025] Preferably, each electrically conductive element extends longitudinally along its respective longitudinal section of the second zone .

[0026] Preferably, each electrically conductive element i s integrated into walls contained in or forming at least a portion of said vessel .

[0027] That is , the electrically conductive element i s integrated into walls at least partially delimiting said longitudinal section of the second zone of the vessel itsel f .

[0028] Such walls comprise lateral walls at least partially delimiting the internal cavity of the vessel itsel f and / or separating walls delimiting the internal cavity of the vessel into a plurality of passage conduits for the flow of solid particles and / or the gas flow .

[0029] Preferably, such walls , whether lateral wall s and / or separating walls , are made of thermally conductive material .

[0030] Advantageously, such walls , whether lateral wall s and / or separating walls , are made of thermally conductive and electrically insulating material .

[0031] In a possible embodiment , the electrically conductive element comprises at least one succession o f electrically conductive refractory bricks , consecutive to and in contact with each other . Preferably, such a succession forms for example at least one column . An example of electrically conductive refractory bricks , of possible arrangements and electrical connections thereof , is known from US 11877346B2 .

[0032] In a further pos sible embodiment , the electrically conductive element comprises at least one resistor . By way of example only, the resistor can be of the wiretype .

[0033] Preferably, the reactor comprises a plurality o f electrically conductive elements , each of which extends at least at a longitudinal section of the second zone o f the vessel .

[0034] The electrically conductive elements of the plurality of electrically conductive elements can extend at the same longitudinal section of the second zone and / or at two or more subsequent longitudinal sections thereof .

[0035] In a possible embodiment , two or more electrically conductive elements are connected in parallel with each other .

[0036] In another possible embodiment , di f ferent potential di f ferences are applied to two or more electrically conductive elements . This would allow di f ferent portions of the second zone to be supplied di f ferently and, with the same electrically conductive element , di f ferentiate the heating . This could be achieved by making electrically conductive elements having di f ferent electrical resistances and applying the same potential di f ference to each of them .

[0037] In general , the electrically conductive elements equipping the second zone can be equal to or di f ferent from each other ; in particular, they can have equal or di f ferent electrical resistance .

[0038] Preferably, the plant according to the present invention comprises at least one power supply plant or at least one voltage generator connected to the ends o f said at least one electrically conductive element .

[0039] The present invention also relates to a process for producing hydrogen by pyrolysis of hydrocarbons , comprising :

[0040] - flowing a flow of solid particles in contact with and in countercurrent to a gas flow comprising hydrocarbons through a heating and reaction zone that is defined in the internal cavity of a vessel forming a reactor, and at least at a longitudinal section of which there is at least one electrically conductive element , which electrically conductive element has two ends configured to be placed at an electric potential di f ference such that the electrically conductive element itsel f is passed through by electric current and heats up, and wherein such electrically conductive element is configured and arranged to transmit the heat generated by it to the solid particles and / or the gas flow passing through the heating and reaction zone ,

[0041] - heating at least a fraction o f the flow of solid particles and / or the gas f low as they flow along the heating and reaction zone , by supplying electrical energy to the electrically conductive element , which is thus passed through by electric current being heated by Joule ef fect .

[0042] It is noted that , unlike a solution as known from US2982622 , according to the present invention, the input of thermal energy to the solid particles and / or gases flowing through the heating and reaction zone is not due to the electric current passing through the moving bed of solid particles , which is actually avoided, but is due to the electric current passing through electrically conductive elements ( " electrically active elements" ) inserted into the corresponding longitudinal section o f the reactor (vessel ) .

[0043] According to the present invention, the electric current does not pass through the solid particles flowing through the reactor, and in particular in the heating and reaction zone thereof . This allows to improve control of the heat input required for pyrolysis .

[0044] The present invention will now be described, by way of illustration but not limitation, according to some preferred embodiments , with particular reference to the figures of the attached drawings , in which :

[0045] Figure 1 is a schematic view of the gas flows in a plant according to the invention for performing a process according to the invention;

[0046] Figure 2 schematically shows a diagram of the temperature evolution of the gas flow in a plant according to the invention;

[0047] Figure 3 schematically and non-limitingly shows a possible embodiment of a reactor of a plant according to the present invention for performing the process according to the present invention;

[0048] Figure 4 schematically shows a longitudinal section of a reactor according to the scheme of Figure 3 ;

[0049] Figures 4A and 4B show, schematically and in an enlarged scale , the detail highlighted in Figure 4 according to two possible embodiments of an electrically conductive element ;

[0050] Figures 5a, 5b, and 5c show, schematically and in cross section according to plane V-V of Figure 4 , various possible embodiments of the walls of the vessel of the reactor at the second zone (heating and reaction zone ) thereof ;

[0051] Figure 6 is a view like that of Figure 4 , in which the bed of solid particles is schemati zed;

[0052] Figure 7 schematically shows a possible embodiment of a plant according to the invention for performing the process according to the invention .

[0053] With reference to Figure 1 , it is observed that the plant 10 according to the invention comprises :

[0054] - a reactor 1 (R) ,

[0055] - a solid-gas separator 2 ( SGS ) and

[0056] - a gas-gas separator 3 ( GGS ) . Figure 1 schematically shows the gas flows in the plant 10 according to the invention.

[0057] In particular, there is an inlet of inlet gas flow or supply flow "FG" (Feed Gas) of gas or gas mixture, comprising hydrocarbons, for example methane or mixtures of CxHycompounds in the gas or vapor state. Optionally, the inlet gas flow can be at least partially of nonfossil origin, being for example produced from renewable sources, for example, it can comprise or consist of biogas or biomethane. In the remainder of the description, reference will mainly be made to methane, comprising the alternatives mentioned above.

[0058] The passage of the gas flow in the reactor 1, operating at high temperature ( 1200 °-2000 °C, preferably 1200°- 1500°C) and in a substantially oxygen-free environment, allows known pyrolysis reactions of the inlet gas flow FG to be performed.

[0059] As a result of these reactions, there is an outlet gas flow exiting the reactor 1, comprising a gas mixture whose composition is enriched in hydrogen H2. That is, the hydrogen H2 concentration in the gas mixture forming the outlet gas flow is greater than the hydrogen concentration H2 in the inlet gas flow FG. In addition to hydrogen H2, the outlet gas flow consists of acetylene C2H2, as well as gas residues (whose composition substantially depends on the components of the inlet gases and the transit in the reactor 1) , and solid residues, predominantly carbon in the solid state (hereinafter "Solid Carbon", abbreviated as SC) , with different crystalline and aggregation forms, including black carbon or Carbon Black. According to the invention, the inlet gas flow FG to be converted and comprising hydrocarbons, in particular methane, is pre-heated in a first section or zone of the same reactor 1, as will be further illustrated below. In a second section or zone of the reactor 1 following the first one, the pre-heated gas flow SI is heated to perform the pyrolysis reaction. Then, the high-temperature gas flow S2 of the gases produced by the pyrolysis reaction (hydrogen, gas residues typically including acetylene and methane, as well as a solid part consisting of carbon in powder form or similar) is conveyed outward by transiting in a third section or zone of the reactor 1, at which it is cooled, as will be better illustrated below. Finally, the cooled gas flow S3 extracted from the reactor 1 passes through a gas / solid separator 2 (SGS) to remove the solid fraction (SC) . Subsequently, the gas flow S4, purified from the solid fraction and exiting the gas / solid separator 2 (SGS) , is sent to a gas / gas separator 3 (GGS) to remove the residues of other gases resulting from the pyrolysis reaction (including methane and acetylene) and / or originally present in the inlet gas flow FG, obtaining a main gas flow S51 predominantly consisting of hydrogen, and a residual gas flow S52 comprising methane, acetylene, and / or other gases (as described above) , which can optionally be recycled by redirecting it into the inlet gas flow FG to be converted.

[0060] In summary, the process according to the invention provides three steps (as illustrated in Figure 2) : - a step of pre-heating the inlet gas flow (e.g., methane) , a heating and reaction step (heating-pyrolysis of the pre-heated gas flow) , and a step of cooling the outlet gas flow, now rich in hydrogen .

[0061] It is speci fied that in the present description, "conversion" means the at least partial conversion o f the inlet gas flow into hydrogen, or more precisely, the performance of pyrolysis reactions on the inlet gas flow such as to obtain a hydrogen concentration in the outlet gas flow that is greater than the hydrogen concentration in the inlet gas flow .

[0062] Figure 3 schematically shows a possible embodiment of a reactor 1 according to the invention . The reactor 1 comprises the three above-mentioned sections or zones for pre-heating, heating-pyrolysis and cooling the inlet gas flow FG, which comprises , as described above , gas hydrocarbons CxHy, in particular methane .

[0063] In the embodiment schematically depicted in Figure 3 , the reactor 1 comprises a longitudinally-developing hollow vessel inside which there i s a moving bed o f sol id particles or solid elements 42 . In the attached figures , the di f ferent backgrounds by which the solid particles 42 are depicted correspond to di f ferent temperatures thereof : lighter backgrounds correspond to lower temperatures , while denser backgrounds correspond to higher temperatures .

[0064] In the attached figures , the solid particles or solid elements 42 are depicted in the shape of spheres . The spherical or otherwise rounded shape is a possible and preferred embodiment ; however, the solid particles or solid elements 42 could have a di f ferent shape , provided that they are adapted to forming a moving bed that extends in the vertical direction, whose solid elements are introduced from above and descend downward by gravity . The solid particles 42 , hereinafter also referred to as spherical elements 42 , are preferably made of a hard material , resistant to temperatures higher than 1200 ° C, advantageously higher than 1500 ° C, and even more advantageously higher than 2000 ° C . Depending on the maximum process temperature , alumina can be a material usable to make the spherical elements 42 .

[0065] The reactor 1 comprises a longitudinally-developing hollow vessel along which there are sequentially at least three sections or zones :

[0066] - a first zone for pre-heating an inlet gas flow FG comprising hydrocarbons and for cooling an outlet flow of solid particles ;

[0067] - a second zone for heating and reacting the gas f low pre-heated in the first zone or section, and for passing a flow of pre-heated solid particles ;

[0068] - a third zone for pre-heating an inlet flow of solid particles and for cooling an outlet gas flow comprising hydrogen and coming from the second zone or section .

[0069] The reactor 1 is general ly configured and arranged such that the first zone is at a lower height than the second zone , and the latter is at a lower height than the third zone .

[0070] The third zone is therefore defined at an upper section 43 of the reactor 1 .

[0071] The first zone, instead, is defined at a lower section 41 of the reactor 1 .

[0072] The second zone , finally, is an intermediate section 40 between the lower 41 and the upper 43 sections of the reactor 1 .

[0073] As will become clearer from the following description, the two lower 41 and upper 43 sections are "passive" sections, at which there is no heat input from the outside, whereas the intermediate section 40 is an "active" section, at which heat is supplied from the outside by employing electrical energy.

[0074] The spherical elements 42 descend by gravity from the upper section 43 (third zone) , passing through the intermediate section 40 (second zone) , where they are heated, and then through the lower section 41 (first zone) , with a motion regulated by regulation elements placed at the lower outlet of the reactor 1, as better illustrated below.

[0075] Simultaneously, the inlet gas flow FG is introduced into the reactor 1 at the lower section 41 (first zone) , flows over the spherical elements 42 therein, being thus pre-heated and, ascending upward, first reaches the intermediate section 40 (second zone) , at which it is further heated until reaching pyrolysis temperatures, and then flows through the upper section 43 (third zone) , at which the outlet gas flow S2, which comprises the gases produced by the pyrolysis reaction, is cooled by heating the spherical elements 42 introduced into the reactor 1 and descending by gravity toward the lower section 41 (first zone) . Subsequently, the gas flow comprising the gases produced by pyrolysis, and thus cooled, escapes from the upper section 43 (third zone) to be conveyed toward the subsequent stations of the plant 10 (for example, the solid / gas separator 2, the gas / gas separator 3) .

[0076] The reactor 1 is thus a "moving bed" reactor, meaning the mass of solid particles 42 moving along it (in particular, descending in a controlled manner by gravity) , and operates in countercurrent .

[0077] According to the present invention, at the intermediate section 40 ( second zone or active section) , there are one or more electrically conductive elements 1111 which, when electric current flows through them, are able to provide thermal energy through the Joule ef fect both to the spherical elements 42 at the intermediate section and, generally, transiting downward, and to the inlet gas f low FG, already preheated as it passes through the lower section 41 ( first zone ) and ascending upward, which will be heated at such intermediate section 40 until preferably reaching temperatures between 1000 ° C and 1500 ° C .

[0078] The electrically conductive elements 1111 are configured and arranged so as to allow both the spherical elements 42 to transit downward and simultaneously the gas flow FG to transit upward .

[0079] Preferably, the electrically conductive elements 1111 comprise resistive elements inserted into thermally conductive and preferably electrically insulating material , such that , when electric current flows through them, they generate heat by Joule ef fect , which is then transmitted to the gas flow FG and the spherical elements 42 present in or transiting through the intermediate section 40 .

[0080] In a possible embodiment , outside the reactor 1 , there can be an assembly for recirculating the spherical elements 42 from the lower section 41 to the upper section 43 ( in Figure 7 it is depicted only schematically by the dashed track) . Such a recirculation assembly i s optional ; it can be advantageously adapted to further cool the spherical elements 42 and / or to clean them by removing solid particulate residues ( Solid Carbon) therefrom . The hot gases produced by the pyrolysis reaction are indeed rich in suspended solid residues SC, which deposit at least partially on the spherical elements 42 from which they must be removed at least periodically .

[0081] In more detail , and with particular reference to the attached figures , the reactor 1 ("moving bed" of spherical elements 42 or other solid particles o f suitable shape ) comprises a longitudinally-developing hollow vessel .

[0082] The reactor 1 , or the vessel defining it , comprises an external metallic containment structure , which is internally coated with one or more coating layers , some of which are made of refractory material , and others o f thermally insulating material . The coating layers can consist of materials even di f ferent from each other and can have di f ferent mechanical and thermal features ( insulating or refractory) . In particular, the refractory material used can be alumina-based .

[0083] The internal cavity of the reactor 1 forms at least one conduit 1100 for transiting the spherical elements 42 as well as the gas flow FG therethrough .

[0084] Preferably, the conduit 1100 extends longitudinally in a substantially vertical direction between two opposite ends , respectively between an upper end and a lower end, at which at least one first inlet 1101 and at least one first outlet 1102 are respectively defined .

[0085] Preferably, the first inlet 1101 and the first outlet 1102 are provided for entering and exiting the flow of solid particles 42 therethrough .

[0086] Along the longitudinal extension of the conduit 1100 , the following sections can be identified sequentially from its lower end toward its upper end :

[0087] - a lower section 1105 forming a first zone for preheating an inlet gas flow FG comprising hydrocarbons and for cooling an outlet flow of solid particles ( spherical elements 42 ) ;

[0088] - an intermediate section 1104 or active section forming a second zone for heating and reacting a pre-heated gas flow, and for passing a flow of pre-heated solid particles ( spherical elements 42 ) ;

[0089] - an upper section 1103 forming a third zone for preheating an inlet flow of solid particles ( spherical elements 42 ) and for cooling an outlet gas flow S2 comprising hydrogen .

[0090] The spherical elements 42 enter through at least one supply conduit 1101 ' , advantageously with a diameter lower than that of the conduit 1100 , which supply conduit 1101 ' extends through the wall at the upper end o f the reactor 1 , inside the conduit 1100 , for a section having a length Hl .

[0091] The reactor 1 further comprises at least one second outlet 1120 for exiting therethrough the gas flow S2 treated ( at least partially converted, or enriched, in H2 ) in the reactor 1 .

[0092] Preferably, the second outlet 1120 is defined at the upper section 1103 .

[0093] Preferably, the second outlet 1120 is obtained in the longitudinal section of the reactor 1 between the lower end of the supply conduit 1101 ' and the wall at the upper end of the reactor 1 .

[0094] The gas flow transiting in the upper section 1103 releases heat , being cooled, to the spherical elements 42 which, by gravity, transit downward along the supply conduit 1101 ' .

[0095] The reactor 1 further comprises a second inlet 1130 for entering therethrough the gas flow FG to be treated ( converted) . Preferably, the second inlet 1130 is defined at the lower section 1105 . The second inlet 1130 can be single , as depicted in the figures , or can be configured, as readily understandable by those skilled in the art , with a plurality of outlet openings inside the conduit 1100 , which are advantageously uni formly distributed along at least a cross section of the conduit 1100 . In a possible embodiment , the outlet openings o f the second inlet 1130 can be distributed on two or more cross sections of the conduit 1100 arranged at di f ferent heights .

[0096] In this way, the inlet gas flow FG receives heat , being heated, from the spherical elements 42 that were previously heated as they passed first through the upper section 1103 and then the intermediate or active section 1104 ; the spherical elements 42 , therefore , while passing through the lower section 1105 until reaching the first outlet 1102 , are cooled by releasing heat to the inlet gas flow FG, which travels the reactor 1 in the opposite direction .

[0097] As a function of the process parameters , which include the temperature of the spherical elements 42 at the inlet of the lower section 1105 and the flow rate of the inlet gas flow FG, the gas to be treated can reach temperatures higher than 400 ° C-600 ° C, thus allowing partial cracking of hydrocarbons already in the lower section 1105 of the reactor 1 .

[0098] As depicted in Figures 4 and 6 , in a preferred but non-exclusive embodiment , the terminal portion of the lower section 1105 can be shaped as an inverted f rustoconical shape .

[0099] The intermediate or active section 1104 is equipped with one or more electrically conductive elements 1111 , through which, when the electric current pas ses through them, thermal energy is provided to perform pyrolysis reactions of the gas mixture forming the gas flow FG to be treated .

[0100] The electrically conductive elements 1111 extend, preferably longitudinally, at least at one longitudinal section of the intermediate section 1104 ( second zone ) and have each two ends 1112 configured to be placed at an electric potential di f ference such that each electrically conductive element 1111 is passed through by electrical current and heats up by Joule ef fect . The electrically conductive elements 1111 are configured and arranged to transmit the heat generated by them to the solid particles ( spherical elements 42 ) and / or to the gas flow traveling in countercurrent through the intermediate section 1104 .

[0101] Preferably, the electrically conductive elements 1111 are integrated into walls contained in or forming at least a portion of the vessel forming the reactor 1 .

[0102] That is , the electrically conductive elements 1111 are integrated into walls contained in or forming at least a portion of the vessel , which delimit at least in part the respective longitudinal section of the second zone ( intermediate section 1104 ) of the vessel itsel f .

[0103] Such walls can comprise both lateral walls at least partially delimiting the internal cavity of the vessel itsel f , and / or separating walls delimiting the internal cavity of the vessel into a plurality of passage conduits 1106 for the flow of solid particles ( spherical elements 42 ) and / or the gas flow .

[0104] Preferably, such walls , whether lateral wall s and / or separating walls , are made of thermally conductive material .

[0105] Advantageously, such walls , whether lateral wall s and / or separating walls , are made of thermally conductive and electrically insulating material .

[0106] Such walls , i . e . , the walls into which the electrically conductive elements 1111 are integrated, can for example be made of ceramic materials suitable to withstand high temperatures , preferably equal to or higher than 1800 ° C .

[0107] In other words , the electrically conductive elements 1111 are at least partially coated with materials , advantageously and preferably thermally conductive and electrically insulating, so as to be integrated into walls .

[0108] In a possible first embodiment , the electrically conductive elements comprise at least one respective resistor . By way of example only, the resistor can be o f the wire-wound type .

[0109] Such a possible first embodiment is schemati zed in Figure 4A: the electrically conductive elements 1111 are formed by resistors 1111a inserted into electrically insulating and thermally conductive materials 1111b, so as to be integrated into walls . Thermally conductive and electrically insulating materials 1111b into which the electrically conductive elements 1111 are advantageously integrated can be , for example, ceramic materials capable of withstanding high temperatures , preferably above 1800 ° C, as well as impacts and wear caused by the transit , even in contact , of the spherical elements 42 . The electrically conductive elements 1111 are positioned and connected to each other such that the resistors 1111a form a continuous electric circuit through which electric current can flow .

[0110] In this first embodiment, it is optionally poss ible to provide catalysts that allow to perform pyrolysis of hydrocarbons ( e . g . , methane ) at lower-than-usual temperatures , for example around 1000 ° C, thereby expanding the selection of the resi stors 1111a suitable for use . Possible catalysts for methane pyrolysis comprise : carbon; nickel , iron, cobalt and / or their oxides ; platinum; palladium .

[0111] The catalyst can be deposited on the surface of the spherical elements 42 and / or on the surface of the electrically conductive elements 1111 , or the walls into which they are integrated (material 1111b ) , the gas flow FG to be treated flowing over said surface

[0112] Optionally, the spherical elements 42 themselves can be made at least partially of a pyrolysis-catalysing material .

[0113] In a possible second embodiment , the electrically conductive elements 1111 comprise at least one succession of electrically conductive refractory bricks or blocks , consecutive to each other and in contact with each other . Preferably, such a succession forms at least one column . An example of electrically conductive refractory bricks or blocks , of possible arrangements and electrical connections thereof , is known from US 11877346B2 . As described in such document , the bricks or blocks are made of electrically conductive refractory material , doped with compounds such as metal oxides .

[0114] Such bricks or blocks ef fectively form resistors capable of withstanding high temperatures and high dissipated electric powers ; they can be used to make structures or matrixes suitable for heating, in particular fluids flowing therethrough .

[0115] Such a possible second embodiment is schemati zed in Figure 4B : each electrically conductive element 1111 comprises a succession 1111c, for example a columnshaped portion, made of electrically conductive refractory bricks or blocks , as described above . Advantageously, such column-shaped portion 1111c is coated, at the surface facing the inside of the conduit 1100 , with a coating portion l l l ld made of refractory material , preferably electrically non-conductive , and even more preferably electrically non-conductive and thermally conductive . The electrically conductive elements 1111 are thereby integrated into walls .

[0116] The electrically conductive elements 1111 are positioned so that the electrically conductive portions 1111c are in contact with each other, so as to form a continuous electric circuit through which electric current can pass through . The bricks or blocks forming each electrically conductive element 1111 are arranged in succession consecutively to and in contact with each other, so as to make a continuous resistor, at whose opposite ends an electric potential di f ference can be applied, so that each electrically conductive element 1111 is passed through by electric current .

[0117] The coating portion or the electrically insulating part l l l ld can be made separately, with additional electrically insulating bricks or blocks , or directly "en bloc" to each brick or block, i . e . , by making only a central portion of each brick or block conductive and leaving the portion thereof forming its lateral faces electrically non-conductive , while the portions thereof forming the upper and lower faces are also electrically conductive at the central portion . In this second case , in order to make the electric circuit , the bricks or blocks must be arranged, indeed, so that the electrically conductive portions 1111c thereof are in contact with each other .

[0118] In this second embodiment , employing pyrolysis catalysts is generally not necessary, due to the ability to reach, without particular problems , temperatures in the order of 1800 ° C .

[0119] Preferably, as exempli fied in the attached figures , the electrically conductive elements 1111 , or the lateral and / or intermediate walls into which they are integrated, are arranged so as to form a plurality o f passage conduits 1106 for the flow of solid particles ( spherical elements 42 ) and / or the treated gas flow . The passage conduits 1106 advantageously have a vertical axial extension .

[0120] Inside each passage conduit 1106 , both the descending flow of the spherical elements 42 and the ascending gas flow FG being treated transit simultaneously; the latter penetrates through the interstices between the spherical elements 42 . Both the spherical elements 42 and the gas f low FG to be treated are heated by the heat dissipated by Joule ef fect from the electrically conductive elements 1111 when electric current flows through them .

[0121] In any case , the surface of the electrically conductive elements 1111 , or of the walls into which they are integrated, facing the inside of each of the passage conduits 1106 is coated with and / or made of an electrically insulating material ( 1111b, l l l ld) , such that , even i f the spherical elements 42 were electrically conductive , conditions for a short circuit through the spherical elements 42 themselves cannot occur .

[0122] Each electrically conductive element 1111 comprises a pair of ends 1112 configured to be placed at an electric potential di f ference , such that electrical current flows through the respective electrically conductive element 1111 and the latter heats up .

[0123] The ends 1112 of the electrically conductive elements 1111 are adapted to be connected to a power supply plant 1110 ( e . g . , at least one voltage generator ) .

[0124] Two or more electrically conductive elements 1111 can be connected in parallel to the same power supply plant 1110 ; alternatively, or additionally, each electrically conductive element 1111 can be connected to a respective power supply plant 1110 . As will be immediately clear to those skilled in the art , the ends 1112 of the electrically conductive elements 1111 are in electrical contact with them, i . e . , with their conductive portions ( resistors 1111a, 1111c ) , and are electrically insulated from the internal volume of the reactor 1 in which the spherical elements 42 transit , in order to avoid any short-circuit problem as mentioned above .

[0125] Advantageously, depending on the embodiment , the reactor 1 can comprise a structural support element 1113 suitable for withstanding the weight and mechanical stresses exerted on the group of electrically conductive elements 1111 . The structural support element 1113 i s also shaped to allow both the spherical elements 42 to transit downward and the gas flow FG to pass upward .

[0126] The passage conduits 1106 , at least partially formed by the electrically conductive elements 1111 , or the walls into which they are integrated, can have di f ferent shapes and arrangements . Figures 5a, 5b, and 5c show, schematically and in cross section, several possible shapes of the structure overall made by the assembly of passage conduits 1106 through which the spherical elements 42 and the gas f low FG to be treated transit .

[0127] With reference to Figure 7 , it shows a plant 10 further comprising :

[0128] - a system for controlled loading of the solid particles entering the reactor 1 , and a system for controlled unloading of the solid particles exiting the reactor .

[0129] At the first outlet 1102 of the reactor 1 , a device 1303 for regulating the flow of spherical elements 42 exiting the reactor 1 i s provided; such a device can be made , for example , by a rotary valve of a known type (hereinafter referred to as valve 1303 ) .

[0130] The mode for managing the reactor 1 provides that the entire flow of spherical elements 42 is regulated solely by the valve 1303 , and that there are never sections inside the conduit 1100 along which the spherical elements 42 are in free fall . The geometry of the parts inside the reactor 1 is shaped to keep a mas s flow such as to optimi ze the heat trans fer between gas and solid particles ( spherical elements 42 ) .

[0131] In particular ( see Figure 6 ) : the supply conduit 1101 ' is constantly filled with spherical elements 42 , at least in the section between the wall at the upper end of the reactor 1 and the lower end of the supply conduit 1101 ' ; - the upper section 1103 is constantly filled with spherical elements 42 up to the lower end of the supply conduit 1101 ' ; the intermediate or active section 1104 is constantly filled with spherical elements 42 ; - the lower section 1105 is constantly filled with spherical elements 42 up to the lower end of the intermediate section 1104 .

[0132] In this way, at least one plenum zone A i s created between the external wall of the supply conduit 1101 ' and the corresponding internal lateral surface of the conduit 1100 .

[0133] The outlet gas flow S2 , enriched in hydrogen following the pyrolysis reactions of the mixture forming the inlet gas flow FG, is suctioned from plenum A. Advantageously, it is necessary to ensure that at the upper section 1103 of the reactor 1 , substantially the entire gas flow transiting therethrough ( gas flow which has undergone pyrolysis and which releases heat , being cooled, to the descending flow of entering spherical elements 42 ) exits the reactor 1 through the second outlet 1120 and does not instead escape through the inlet path of the spherical elements 42 themselves ( supply conduit 1101 ' , first inlet 1101 ) .

[0134] Advantageously, it is further necessary to ensure that the loading of the spherical elements 42 entering the reactor 1 occurs without introducing oxygen or gas oxidizing mixtures (e.g., air) into the reactor 1.

[0135] In the embodiment illustrated in the attached figures (Figure 7) , these objects are achieved by a system for controlled loading of spherical elements 42, which comprises, in sequence from top to bottom as depicted in Figure 7 : a first container 1201 of spherical elements 42, for example a silo or hopper; a first sealing valve 1301 (open-close) for passing / blocking spherical elements 42 and gases; a second container 1202 of spherical elements 42, for example a closed silo, connected to a system 1202' for controlling the internal atmosphere of the second container 1202, with the possibility of making vacuum and / or controlled atmosphere conditions (e.g., inert, nitrogen, etc . ) ; a second sealing valve 1302 (open-close) for passing / blocking the spherical elements 42 and gases; a third container 1203 of the spherical elements 42, for example a closed silo, directly connected to the reactor 1 through the supply conduit 1101' .

[0136] With this configuration of plant 10, it is possible to supply the spherical elements 42 into the reactor 1 itself by a method comprising the steps of: a) closing the first valve 1301 and loading the first container 1201 with a quantity not lower than the capacity of the second container 1202; b) when the second container 1202 is empty, closing the second valve 1302, opening the first valve 1301, and filling the second container 1202; c ) closing the first valve 1301 and, while keeping the second valve 1302 closed, making, in the second container

[0137] 1202 , controlled atmosphere conditions (vacuum, inert atmosphere , etc . ) by the system 1202 ' ; d) opening the second valve 1302 to unload the contents of the second container 1202 into the third container

[0138] 1203 , from which the spherical elements 42 flow into the reactor 1 through the supply conduit 1101 ' , with a continuous flow regulated by the valve 1303 .

[0139] In this way, in the section downstream of the second valve 1302 , the presence of a controlled atmosphere and a quantity of spherical elements 42 adapted to ensure a constant flow rate are always ensured, while simultaneously preventing the escape of gases (hydrogen) from the supply conduit 1101 ' of the spherical elements 42 and preventing oxygen from entering the reactor 1 : the first and third containers 1201 and 1203 contain a variable level of spherical elements 42 , and there is never a condition without spherical elements 42 in the third container 1203 ; the second container 1202 alternates between a fully filled condition (when it receives the load from the first container 1201 ) and a fully emptied condition (when pouring the load into the third container 1203 ) .

[0140] There are further possible variants of the abovedescribed sequence, which allow to achieve the same ob j ects .

[0141] As observed in the figures and already described above , in the reactor 1 there is an intermediate or active section 1104 , through which the spherical elements 42 pass from the upper section 1103 ( or third zone , at which the spherical elements 42 receive heat from the treated gas flow ascending from the intermediate section 1104 ) to a lower section 1105 ( or first zone , at which the spherical elements 42 release heat pre-heating the inlet gas flow FG to be treated) .

[0142] In such intermediate or active section 1104 , it is necessary to ensure :

[0143] - the correct transit o f the gas f low being treated from the lower section 1105 to the upper section 1103 ;

[0144] - the correct transit o f the spherical elements 42 from the upper section 1103 to the lower section 1105 ;

[0145] - the correct heat exchange of both the gas flow to be treated and the spherical elements 42 with the electrically conductive elements 1111 described above , as well as with each other .

[0146] This result can be achieved by selecting a suf ficiently small average si ze of the spherical elements 42 , both in absolute terms and with respect to the minimum dimension of the pathway within the reactor 1 .

[0147] Preferably, the average diameter of spherical elements 42 is lower than 50 mm, more preferably lower than 25 mm, still more preferably lower than 10 mm, and even more preferably lower than 5 mm, down to 1 mm . For example , the average diameter of the spherical elements 42 is 6 mm or 5 mm .

[0148] In order to ensure a suitable flow of spherical elements 42 through the intermediate or active section 1104 , without causing blockages , the minimum diameter o f the passages (passage conduits 1106 ) in this section must be at least ten times the average diameter of the spherical elements 42 . At the upper section 1103 of the reactor 1, the spherical elements 42, in addition to receiving heat from the gas flow ascending from the intermediate section 1104, can accumulate on their surface at least a part of the solid particulate SC (Solid Carbon) suspended in the gas flow itself.

[0149] Continuing their descending motion, the spherical elements 42, after passing through the intermediate section 1104, reach the lower section 1105, at which they release heat to the inlet gas flow FG to be treated, pre-heating it, and being cooled from a temperature in the range of 1200°C, 1500°C, or 2000°C at the inlet of the lower section 1105 to a temperature in the range of 100°C to 400°C at the outlet of the lower section 1105. Therefore, there are spherical elements 42 exiting the reactor 1 which are covered with a layer of solid particulate SC and are at a relatively high temperature. Under these conditions, if exposed to an oxidizing agent (e.g., air) , there would be a significant risk of ignition of the solid particulate SC.

[0150] In order to avoid this risk, downstream of the valve 1303 for regulating the flow of spherical elements 42, an unloading system is advantageously provided, suitable for allowing a controlled transition, in terms of composition and temperature, of the spherical elements 42 toward an oxidizing atmosphere such as air. Such unloading system can be made similarly in concept to the system for controlled loading of the spherical elements 42 entering the reactor 1, and comprise, respectively:- a first container 1204 still receiving the flow of spherical elements 42 from the valve 1303; a first sealing valve 1304 (open-close) for passing / blocking the spherical elements 42 and gases; a second container 1205, connected to a system 1205' for controlling the internal atmosphere, and receiving the spherical elements 42 from the first container 1204; a second sealing valve 1305 (open-close) for passing / blocking the spherical elements 42 and gases.

[0151] With such an unloading system, it is possible to unload the spherical elements 42 from the reactor 1 by a method comprising the steps of: a) closing the first valve 1304 and loading the first container 1204 with a quantity of spherical elements 42 not lower than the capacity of the second container 1205; b) closing the second valve 1305, opening the first valve 1304, and filling the second container 1205 with spherical elements 42; c) closing the first valve 1304 and making, in the second container 1205, controlled atmosphere conditions (vacuum, inert gas, etc.) by the system 1205'; d) opening the second valve 1305 to unload the contents of second container 1205; e) closing the second valve 1305 and restoring a controlled atmosphere inside the second container 1205.

[0152] Advantageously, during step c) , cooling of the spherical elements 42 in the second container 1205 is operated, which can be performed for example by a cooled inert gas stream.

[0153] With an unloading method as described above, in the section upstream of the first valve 1304, the maintenance of a controlled atmosphere and an available volume adapted to receive the (constant) flow rate of spherical elements 42 from the valve 1303 is ensured, while simultaneously preventing air from entering the reactor 1 .

[0154] It is emphasized that when implementing such an unloading method : the first container 1204 contains a variable level of spherical elements 42 ; the second container 1205 alternatively assumes a fully filled condition (when receiving the load from the first container 1204 ) and a fully emptied condition (when unloading the load through the second valve 1305 ) .

[0155] In this way, it is possible to ef fectively unload the spherical elements 42 from the reactor 1 at a safe temperature to prevent the uncontrolled combustion of the solid particulate SC in air .

[0156] There are other sequences that allow to achieve the same result , for example , it is possible to start with the first valve 1304 open and the second valve 1305 closed . When the second container 1205 is full , close the first valve 1304 and activate the system 1205 ' to inert the material in the second container 1205 . At the end, open the second valve 1305 to unload the contents of the second container 1205 . Then close the second valve 1305 and inert the second container 1205 . At this point , the system is ready to repeat the cycle .

[0157] Downstream of the second valve 1305 , the spherical elements 42 can be stored in air for their subsequent use in the reactor 1 , after an appropriate cleaning step to remove solid particulate SC residues .

[0158] Furthermore , as mentioned above , a recirculation system can be provided for recirculating the spherical elements 42 entering the reactor 1 in a controlled atmosphere , which can comprise a cooling assembly and / or a cleaning assembly for removing solid particulate SC while recovering the same .

[0159] As can be understood from the above description, the reactor 1 described is particularly advantageous in terms of constructive simplicity and safety, since , apart from the required inlets and outlets for process gases and the spherical elements 42 , which are adequately managed as described above , there are no other components passing through the containment case of the reactor .

[0160] The simplicity of the intermediate or active section 1104 makes it well-suited for scale-up based on the desired productivity, as well as for precise control , which is essentially based on the power delivered to the electrically conductive elements 1111 in combination with the flow rates of the transiting gas flows and the flow of the spherical elements 42 , regulated by the valve 1303 .

[0161] Furthermore , the solution according to the invention achieves a maximi zation of hydrogen yield, an inj ection of gas , particularly methane, into a zone with uni form and controlled temperature , and an ef ficient recycle of unconverted gases .

[0162] Furthermore , according to the invention, a possibility of partial separation of solid carbon ins ide the reactor 1 itsel f is achieved . Indeed, solid carbon, in addition to remaining suspended in the outlet gas flow ( for which the use of the gas / solid separator 2 visible in Figure 1 is provided) , partially remains on the surface of the spherical elements 42 and partially deposits on the surface of the electrically conductive elements 1111 or on the walls into which they are integrated; the latter deposition is however limited due to the mechanical action exerted by the transit of the spherical elements 42 .

[0163] Finally, the solution according to the present invention allows to achieve the thermal recovery from high-temperature gases , with consequent consumption reduction, directly inside the reactor 1 itsel f .

[0164] This integration allows to achieve a particularly high ef ficiency, due to the possibility of recovering heat not only from the gases but also , at least partially, from the solid carbon, through the particular structure of the reactor, and ef fectively using such heat for pre-heating the entering gas .

[0165] The present invention has been described, by way o f illustration but not limitation, according to its preferred embodiments , but it should be understood that variations and / or modi fications can be made by a person skilled in the art without departing from the related scope of protection as defined in the attached claims .

Claims

CLAIMS1) Plant (10) for producing hydrogen by pyrolysis of hydrocarbons comprising: at least one reactor (1) comprising at least one longitudinally-developing hollow vessel along which there are sequentially at least:- a first zone (1105) for pre-heating an inlet gas flow (FG) comprising hydrocarbons and cooling an outlet flow of solid particles (42) ;- a second zone (1104) for heating and reacting a pre-heated gas flow (FG) and passing a flow of pre-heated solid particles (42) ;- a third zone (1103) for pre-heating an inlet flow of solid particles (42) and cooling an outlet gas flow comprising hydrogen;- at least one electrically conductive element (1111) longitudinally extending at least at one longitudinal section of said second zone (1104) , wherein said at least one electrically conductive element (1111) has two ends (1112) configured to be placed at an electric potential difference so that said electrically conductive element is carrying current, heating itself, and wherein said at least one electrically conductive element (1111) is configured and arranged to transmit heat generated by it to the solid particles (42) and / or the gas flow passing through said second zone (1104) .2) Plant (10) according to claim 1, wherein said at least one electrically conductive element (1111) is integrated into walls contained in or forming at least a portion of said vessel ( 1 ) .3) Plant (10) according to claim 2, wherein said walls comprise lateral walls delimiting the internal cavity ofsaid vessel and / or separating walls delimiting the internal cavity of said vessel into a plurality of passage conduits (1106) for said flow of solid particles (42) and / or said gas flow (FG) .4) Plant (10) according to claim 2 or 3, wherein said walls are made of thermally conductive material (1111b, lllld) .5) Plant (10) according to any one of claims 2 to 4, wherein said walls are made of electrically insulating material (1111b, lllld) .6) Plant (10) according to one or more of the preceding claims, wherein said at least one electrically conductive element (1111) comprises at least one succession (1111c) of electrically conductive refractory bricks consecutive to each other.7) Plant (10) according to one or more of the preceding claims, wherein said at least one electrically conductive element (1111) comprises at least one resistor (1111a) .8) Plant (10) according to one or more of the preceding claims, comprising a plurality of said electrically conductive elements (1111) each of which extends at least at one longitudinal section of said second zone (1104) , wherein said electrically conductive elements (1111) of said plurality of electrically conductive elements extend at the same longitudinal section of said second zone (1104) and / or at two or more subsequent longitudinal sections of said second zone (1104) .9) Plant (10) according to claim 8, wherein two or more of said electrically conductive elements (1111) are connected in parallel.10) Process for producing hydrogen by pyrolysis ofhydrocarbons comprising:- flowing a flow of solid particles (42) in contact with and in countercurrent to a gas flow (FG) comprising hydrocarbons through a heating and reaction zone (1104) of a reactor (1) at least at one longitudinal section of which there is at least one electrically conductive element (1111) having two ends (1112) configured to be placed at an electric potential difference such that said electrically conductive element (1111) carrying current, being heated, and wherein said at least one electrically conductive element (1111) is configured and arranged to transmit the heat generated by it to the solid particles (42) and / or the gas flow (FG) passing through said heating and reaction zone (1104) ,- heating at least a fraction of said flow of solid particles (42) and / or said gas flow (FG) while flowing along said heating and reaction zone (1104) by supplying electrical energy to said at least one electrically conductive element (1111) .

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