System for producing solid carbon from co2 and related method

Abstract

A system (100) for producing solid carbon C from carbon dioxide CO2, for example from CO2 captured from a power plant. The system comprises: a methanation unit (110) fluidly coupled to the carbon capture system and configured to receive carbon dioxide CO2 and perform methanation of the carbon dioxide CO2 to produce at least methane CH4 and heat; and a pyrolysis unit (120) configured to receive methane CH4 and heat and to perform pyrolysis of methane CH4 to produce hydrogen H2 and solid carbon C, where the methanation unit (110) and the pyrolysis unit (120) are thermally and fluidly coupled such that at least gaseous hydrogen H2 is supplied from the pyrolysis unit (120) to the methanation unit (110) and heat is provided from the methanation unit (110) to the pyrolysis unit (120).

Description

[0001] manual Technical Field

[0002] The subject matter disclosed herein relates to a system and associated methods for producing solid carbon from CO2. Background Art

[0003] In order to achieve the goals of the Paris Agreement and limit future temperature increases to 1.5°C, efforts to reduce emissions have been intensified, as have the development of technologies for removing carbon dioxide (CO2) from the atmosphere, which are known as carbon capture (=CC) and carbon capture and storage (=CCS). Generally speaking, carbon dioxide (CO2) can be captured before or after combustion. In particular, CO2 is removed after combustion of fossil fuels (capturing or "scrubbing" CO2 from exhaust or "flue" gases). Typically, CO2 is captured at the emission source, such as power plants, natural gas processing facilities and industrial processes (however, capture from the open atmosphere is also possible).

[0004] CCS involves capturing carbon dioxide (CO2) at the source of emissions, transporting the captured CO2, and then storing it in suitable deep underground locations; however, these locations are often unavailable.

[0005] After capture, the CO2 must be transported to a suitable storage location. Pumping CO2 through pipelines is a well-known and reliable technology. However, pipeline safety is a key aspect, especially in densely populated areas or areas with frequent seismic activity. In addition, pumping CO2 through pipelines requires CO2 compression stations in order to increase the CO2 pressure and carry out CO2 transportation, and the interaction of CO2 with water vapor can also cause pipeline corrosion. Finally, gaseous CO2 can be used, for example, to perform enhanced oil recovery (=EOR), or it can be converted into a high-pressure, liquid form, called "supercritical CO2", and injected directly into sedimentary rocks to store it. Therefore, capturing and using / storing the captured CO2 requires a lot of energy.

[0006] It is desirable to have a system that allows for more convenient transport and storage of CO2 after CO2 capture. In particular, it is desirable to have a system provided with a carbon capture system that does not require CO2 compression and / or CO2 liquefaction to perform CO2 storage (i.e., does not require energy-intensive CO2 conversion). Summary of the Invention

[0007] According to one aspect, the subject matter disclosed herein relates to a system for producing solid carbon C from carbon dioxide, CO2, such as CO2 captured from exhaust gases of a power plant or other CO2 sources. The system includes a methanation unit fluidly coupled to a carbon capture system and configured to receive the carbon dioxide, CO2, to perform methanation of the carbon dioxide, CO2, to produce at least methane, CH4, and heat; and a pyrolysis unit configured to receive the methane, CH4, and heat and to perform pyrolysis of the methane, CH4, to produce hydrogen, H2, and solid carbon C, wherein the methanation unit and the pyrolysis unit are thermally and fluidly coupled such that at least gaseous hydrogen, H2, is supplied from the pyrolysis unit to the methanation unit, and heat is provided from the methanation unit to the pyrolysis unit.

[0008] According to another aspect, the subject matter disclosed herein relates to a method for producing solid carbon (C) from carbon dioxide (CO), comprising the steps of performing pyrolysis of methane (CH) in a pyrolysis unit to produce hydrogen (H) and solid carbon (C), and performing methanation of the carbon dioxide (CO) in a methanation unit to produce at least methane (CH) and heat. The heat generated by the methanation is used to perform the pyrolysis of the methane (CH), and the hydrogen (H) generated by the pyrolysis is used to perform the methanation of the carbon dioxide (CO). BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A more complete appreciation thereof will be readily obtained as the disclosed embodiments of the present invention and many of its attendant advantages become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0010] Figure 1 shows a schematic diagram of a first embodiment of an innovative system for generating solid carbon C from carbon dioxide CO2,

[0011] Figure 2 Shown Figure 1 A more detailed schematic diagram of the methanation unit,

[0012] Figure 3 Shown Figure 1 A more detailed schematic diagram of the pyrolysis unit,

[0013] Figure 4 shows a schematic diagram of a second embodiment of the innovative system for generating solid carbon C from carbon dioxide CO2,

[0014] Figure 5 A flow chart of an embodiment of a method for producing solid carbon C from carbon dioxide CO2 is shown. DETAILED DESCRIPTION

[0015] According to one aspect, the subject matter disclosed herein relates to an innovative alternative to perform CCS by eliminating the energy-intensive processes and infrastructures required for compression, storage and transportation of carbon dioxide. This is achieved by producing solid carbon from the captured CO2 using a pyrolysis and methanation process. The solid carbon is produced by the methane through a pyrolysis process which also produces hydrogen as a product. It is noted that the pyrolysis process is an endothermic process, thus heat is required to carry out the reaction. The heat is provided by the methanation process which is an exothermic process, thus heat is generated during the reaction. The methanation process produces methane from carbon dioxide and hydrogen, which are supplied by the carbon capture system and the pyrolysis process, respectively. Advantageously, the methane produced by the methanation process can be recycled to the pyrolysis process in order to perform the pyrolysis of methane and / or to produce additional heat for the pyrolysis process by burning the methane.

[0016] Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. The examples and drawings are provided to explain the present disclosure and should not be understood to limit the present disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the scope or spirit of the present disclosure. In the following description, like reference numerals are used to illustrate the drawings of the embodiments to indicate elements performing the same or similar functions. Moreover, some references can not be repeated in all the drawings for the sake of clear illustration.

[0017] In Figure 1 , a simplified diagram of a first embodiment of an innovative system for generating solid carbon (= C) from carbon dioxide (= CO2), hereinafter referred to as “system 100”, is shown. Without limitation with reference to Figure 1 , the system 100 comprises a methanation unit 110 and a pyrolysis unit 120, which are thermally and fluidly coupled to each other, as will be better described below. The system 100 can advantageously be arranged downstream of a power plant, in particular of a process / plant producing a flue gas comprising CO2; more advantageously, the system 100 can be arranged downstream of a carbon capture system of a power plant, in particular fluidly coupled to the carbon capture system, in order to receive the captured CO2 from the carbon capture system. It is noted that there are several methods and systems known to perform CO2 capture from a flue gas, in order to separate the CO2 and discharge the flue gas without CO2 to the atmosphere. According to the scope of the present disclosure, any known carbon capture system can be used in order to separate a gaseous carbon dioxide CO2 stream from which solid carbon C can be produced.

[0018] The methanation unit 110 is configured to receive at least gaseous carbon dioxide CO2 and to perform a methanation of the carbon dioxide CO2 to produce at least gaseous methane CH4 and heat Q. In fact, the methanation reaction of carbon dioxide CO2 is known to be:

[0019]

[0020] And it is an exothermic reaction, so heat (=Q) is generated as it proceeds.

[0021] In particular, without limitation, reference is made to Figure 2 , the methanation unit 110 includes a pretreatment unit 130 configured to receive gaseous carbon dioxide at a second inlet 111. Advantageously, the second inlet 111 is fluidly coupled to a carbon capture system so that the carbon capture system can supply gaseous carbon dioxide to the pretreatment unit 130. The pretreatment unit 130 also includes a first inlet 113 and is configured to receive gaseous hydrogen H2 from the pyrolysis unit 120, as will be better described below. Advantageously, the pretreatment unit 130 is configured to perform:

[0022] - purification of carbon dioxide and / or hydrogen;

[0023] - compression of carbon dioxide and / or hydrogen;

[0024] - Mixing carbon dioxide and hydrogen.

[0025] Advantageously, carbon dioxide and hydrogen can be mixed with one another in the stoichiometric ratio required for the methanation reaction.

[0026] Non-restrictive reference Figure 2 The methanation unit 110 further comprises a reactor unit 140 fluidically coupled to the pretreatment unit 130; in particular, the reactor unit 140 has a main inlet 141 configured to receive a stream of carbon dioxide and hydrogen from the pretreatment unit 130. Advantageously, the carbon dioxide and / or hydrogen are pre-compressed to meet the inlet pressure conditions of the reactor unit 140. The reactor unit 140 further comprises a catalyst and is configured to perform a methanation reaction of the carbon dioxide CO2; in other words, in the reactor unit 140, a methanation reaction occurs between CO2 and H2 in the presence of the catalyst, in particular to produce methane CH4 and possibly other reaction byproducts.

[0027] As already described above, the methanation reaction of carbon dioxide is an exothermic reaction; therefore, heat Q is generated in the reactor unit 140. With non-limiting reference to Figure 1The heat Q produced by the methanation of carbon dioxide CO2 by the methanation unit 110 is provided to the pyrolysis unit 120 and used to perform the pyrolysis of the methane CH4. Advantageously, water H2O is supplied from the second inlet 115 to the reactor unit 140 to take away the heat Q, thereby producing hot water and / or steam H2O / S which is supplied by the second outlet 114 of the reactor unit 140. Advantageously, as will become apparent from the below, the hot water and / or steam H2O / S from the second outlet 114 is supplied to the pyrolysis unit 120.

[0028] Reference is made, without limitation, Figure 2 , to the first embodiment shown in Fig. 1, the methanation unit 110 further comprises a post-treatment unit 150 fluidly coupled to the reactor unit 140; in particular, the post-treatment unit 150 has a main inlet 151 configured to receive the methane CH4 and the by-products from the reactor unit 140. The post-treatment unit is configured to perform a separation between the methane CH4 and the by-products. In particular, the post-treatment unit 150 has a first outlet 112 configured to supply the methane CH4 (in particular gaseous methane CH4), and a second main outlet 116 configured to discharge the by-products (such as unreacted CO2 / H2 and / or H2O). For example, the post-treatment unit 150 can be a distillation column or an adsorption column or a separation unit.

[0029] According to Figure 1 the first embodiment shown in Fig. 1, the pyrolysis unit 120 is configured to receive the gaseous methane CH4 and the heat Q, and to perform the pyrolysis of the methane to produce gaseous hydrogen H2 and solid carbon C. The pyrolysis reaction of methane is known to be:

[0030]

[0031] and is an endothermic reaction, thus requiring heat (= Q) to proceed.

[0032] As described above, the hot water and / or steam H2O / S produced in the methanation unit 110 is supplied to the pyrolysis unit 120; in other words, at least a portion of the heat Q required to perform the pyrolysis of the methane (advantageously all the heat Q) is provided by the methanation unit 110 in the form of hot water and / or steam H2O / S. As will be better described by means of Figure 4 the second embodiment, at least another portion of the heat Q required to perform the pyrolysis of the methane is provided by the methanation unit 210 in the form of methane CH4 to be combusted in the pyrolysis unit 220 to generate additional heat Qi (see for example Figure 3 ). Advantageously, all the heat Q required to perform the pyrolysis of the methane is provided by the methanation unit 110 both in the form of hot water and / or steam H2O / S and in the form of methane CH4 to be combusted. It is noted that, Figure 4The elements 210, 211, 212, 213, 214, 220, 221, 222 and 224 in the Figure 1 The elements 110 (methanation unit), 111 (second inlet), 112 (first outlet), 113 (first inlet), 114 (second outlet), 120 (pyrolysis unit), 121 (first inlet), 122 (first outlet) and 224 (second outlet) in the

[0033] In particular, with non-limiting reference to Figure 3 The pyrolysis unit 120 comprises a pre-treatment unit 160 configured to receive gaseous methane CH4 at the first inlet 121. It is noted that the first inlet 121 can be fluidly coupled to a methane pipeline. It is noted that the gaseous methane CH4 from the methane pipeline can be used to perform the pyrolysis of the methane CH4 and / or can be combusted to generate additional heat Qi in the pyrolysis unit 120, in particular to perform the pyrolysis reaction. Advantageously, according to the embodiment shown in Figure 4 The pre-treatment unit can further comprise a second inlet 223 configured to receive gaseous methane CH4; in particular, the second inlet 223 can be fluidly coupled to the methanation unit 210 (in particular to the first outlet 212 of the post-treatment unit 150 of the methanation unit 210) and can be configured to receive the methane CH4, in particular gaseous methane CH4, produced by the methanation unit 210. It is noted that the gaseous methane CH4 from the methanation unit 210 can be used to perform the pyrolysis of the methane CH4 and / or can be combusted to generate additional heat Qi in the pyrolysis unit 220, in particular to perform the pyrolysis reaction.

[0034] Advantageously, the pre-treatment unit 160 is configured to perform:

[0035] - purifying the gaseous methane CH4;

[0036] - pre-heating the gaseous methane CH4.

[0037] In particular, the pre-treatment unit 160 has a second inlet 123 fluidly coupled to the second outlet 114 of the reactor unit 140, so as to receive the hot water and / or steam H2O / S and to perform the pre-heating of the gaseous methane CH4. Advantageously, the pre-treatment unit 160 is configured to transfer heat from the hot water and / or steam H2O / S to the gaseous methane CH4, and thus to supply heated gaseous methane CH4 from the first outlet 162 and cold water from the second outlet 126.

[0038] With non-limiting reference to Figure 3, the pyrolysis unit 120 further comprises a pyrolysis reactor 170 and a burner unit 180 thermally coupled to each other; in particular, the burner unit 180 is configured to provide additional heat Qi (see the large arrow in Figure 3 ) to the pyrolysis reactor in order to perform a pyrolysis reaction. Advantageously, both the pyrolysis reactor 170 and the burner unit 180 are fluidically coupled to the pre-treatment unit 160; in particular, the heated gaseous methane CH4supplied by the first outlet 162 of the pre-treatment unit 160 is advantageously split between the pyrolysis reactor 170 and the burner unit 180. Non-limitingly with reference to Figure 3 , the burner unit 180 has a first inlet 181 configured to receive a portion of the heated gaseous methane CH4from the pre-treatment unit 160 to be used as fuel, a second inlet 182 configured to receive an oxidizing agent, for example air, and is configured to generate additional heat Qi by burning the heated gaseous methane CH4and the oxidizing agent. Advantageously, as will be apparent from the following, the burner unit 180 can also have a third inlet 183 configured to receive any unutilized gaseous methane CH4, preferably unutilized heated gaseous methane CH4, to be used as fuel in the burner unit 180.

[0039] Non-limitingly with reference to Figure 3 , the pyrolysis reactor 170 has a first inlet 171 configured to receive a portion of the heated gaseous methane CH4from the pre-treatment unit 160 to perform a pyrolysis of the methane according to the previously described pyrolysis reaction; in other words, in the pyrolysis reactor 170, the pyrolysis reaction of the methane CH4occurs thanks to the heat Q provided by the methanation unit 110 and possibly the additional heat Qi provided by the burner unit 180, in particular to produce hydrogen H2and solid carbon C at the outlet 172 of the pyrolysis reactor 170. However, it should be noted that some gaseous methane CH4may not be utilized (i.e. not reacted) and is supplied at the outlet 172 together with the hydrogen H2and the solid carbon C.

[0040] Non-limitingly with reference to Figure 3 , the pyrolysis unit 120 further comprises a post-treatment unit 190 fluidically coupled to the pyrolysis reactor 170; in particular, the post-treatment unit 170 has a main inlet 191 fluidically coupled to the outlet 172 and configured to receive the hydrogen H2and the solid carbon C from the pyrolysis reactor 170 and possibly the unutilized methane CH4. In particular, the post-treatment unit 190 has a first outlet 122 fluidically coupled to the first inlet 113 and configured to supply gaseous hydrogen H2to the methanation unit 110, and a second outlet 124 configured to supply the solid carbon C. For example, the post-treatment unit 190 can be a separation unit, such as a cyclone or an adsorption vessel performing PSA (= Pressure Swing Adsorption).

[0041] Advantageously, the post-treatment unit 190 is further configured to separate any unutilized gaseous methane CH4from the hydrogen H2and the solid carbon C. In particular, the post-treatment unit 190 has a third outlet 192 fluidically coupled to the third inlet 183 of the combustor unit 180 and configured to supply the unutilized gaseous methane CH4to be used as fuel in the combustor unit 180. Even more advantageously, the unutilized gaseous methane CH4from the post-treatment unit 190 can be heated before being supplied to the combustor unit 180. In particular, the pyrolysis unit 190 can further comprise a heat exchanger 175 arranged downstream of the outlet 172 of the pyrolysis reactor 170 and fluidically coupled to the outlet 172 and the third outlet 192 of the post-treatment unit 190. Advantageously, the heat exchanger 175 is configured to transfer heat from the stream of hydrogen H2, solid carbon C and possibly unutilized methane CH4supplied at the outlet 172 to the unutilized gaseous methane CH4provided at the third inlet 183.

[0042] According to another aspect, the subject matter disclosed herein relates to a method 300 for producing solid carbon C from gaseous carbon dioxide CO2, in particular from gaseous carbon dioxide CO2captured by a carbon capture system. With non-limiting reference to Figure 5 , the method 300 comprises the following steps:

[0043] - performing 320 a methanation of the carbon dioxide CO2in a methanation unit 110e 210 to produce at least gaseous methane CH4and heat Q, and

[0044] - performing 310 a pyrolysis of the methane CH4in a pyrolysis unit 120 and 220 to produce gaseous hydrogen H2and solid carbon C.

[0045] According to the method 300, the heat Q produced at step 320 is used to perform the pyrolysis of methane CH4 in step 310, and the gaseous hydrogen produced at step 310 is used to perform the methanation of carbon dioxide CO2 in step 320. According to one possibility, the methane CH4 used to perform the pyrolysis of methane CH4 in 310 can be supplied by a methane pipeline. According to another possibility, the method 300 can further comprise a step 330 of supplying the gaseous methane CH4 produced by the methanation of carbon dioxide CO2 at step 320 to the pyrolysis unit 220. In particular, the gaseous methane CH4 supplied to the pyrolysis unit 220 is used to perform the pyrolysis of methane CH4 in 310 and / or is combusted to produce additional heat Qi in the pyrolysis unit 220; in other words, at least a part (possibly all) of the methane CH4 supplied to the pyrolysis unit 220 is produced in step 310. In particular, the gaseous methane CH4 supplied to the pyrolysis unit (which can be supplied by a methane pipeline and / or the methanation unit) can be used to perform the pyrolysis of methane CH4 in 310 and / or can be combusted to produce additional heat Qi in the pyrolysis unit, in particular to carry out the pyrolysis reaction.

Claims

1. A system (100, 200) for producing solid carbon (C) from gaseous carbon dioxide (CO2), the system (100, 200) comprising: - a methanation unit (110, 210) configured to receive at least gaseous carbon dioxide (CO2) and to perform a methanation of the carbon dioxide (CO2) to produce at least gaseous methane (CH4) and heat (Q); and - a pyrolysis unit (120, 220) configured to receive gaseous methane (CH4) and heat (Q) and to perform a pyrolysis of the methane (CH4) to produce gaseous hydrogen (H2) and solid carbon (C), wherein the methanation unit (110, 210) is fluidly coupled to a carbon capture system, wherein the methanation unit (110, 210) and the pyrolysis unit (120, 220) are fluidly coupled such that at least gaseous hydrogen (H2) is supplied to the methanation unit (110, 210), wherein the methanation unit (110, 210) and the pyrolysis unit (120, 220) are thermally coupled such that heat (Q) is provided to the pyrolysis unit (110, 210).

2. The system (100, 200) according to claim 1, wherein the pyrolysis unit (120, 220) has a first outlet (122, 222) configured to supply gaseous hydrogen (H2), wherein the methanation unit (110, 210) has a first inlet (113, 213) configured to receive gaseous hydrogen (H2), wherein the first outlet (122, 222) and the first inlet (113, 213) are fluidly coupled.

3. The system (100, 200) according to claim 1, wherein the heat (Q) produced by the methanation of carbon dioxide (CO2) by the methanation unit (110, 210) is received by the pyrolysis unit (110, 210) and used to perform the pyrolysis of methane (CH4).

4. The system (100, 200) according to claim 1, wherein the methanation unit (110, 210) has a second inlet (111, 211) configured to receive gaseous carbon dioxide (CO2) from the carbon capture system.

5. The system (100, 200) according to claim 1, wherein the pyrolysis unit (120, 220) has a first inlet (121, 221) configured to receive gaseous methane (CH4) from a methane pipeline, wherein the gaseous methane (CH4) from the methane pipeline is used to perform the pyrolysis of methane (CH4) and / or is combusted to produce additional heat (Qi) in the pyrolysis unit (120, 220).

6. The system (200) of claim 1, wherein the methanation unit (210) has a first outlet (212) configured to supply gaseous methane (CH4), wherein the pyrolysis unit (220) has a second inlet (223) configured to receive gaseous methane (CH4), wherein the first outlet (212) and the second inlet (223) are fluidly coupled, wherein the gaseous methane (CH4) from the methanation unit (210) is used to perform pyrolysis of methane (CH4).

7. The system (200) of claim 1, wherein the methanation unit (210) has a first outlet (212) configured to supply gaseous methane (CH4), wherein the pyrolysis unit (220) has a second inlet (223) configured to receive gaseous methane (CH4), wherein the first outlet (212) and the second inlet (223) are fluidly coupled, wherein the gaseous methane (CH4) from the methanation unit (210) is combusted to generate additional heat (Qi) in the pyrolysis unit (220).

8. The system (200) of claim 1, wherein the methanation unit (210) has a first outlet (212) configured to supply gaseous methane (CH4), wherein the pyrolysis unit (220) has a second inlet (223) configured to receive gaseous methane (CH4), wherein the first outlet (212) and the second inlet (223) are fluidly coupled, wherein a portion of the gaseous methane (CH4) from the methanation unit (210) is used to perform pyrolysis of methane (CH4) and a portion of the gaseous methane (CH4) from the methanation unit (210) is combusted to generate additional heat (Qi) in the pyrolysis unit (220).

9. A method (300) for producing solid carbon (C) from gaseous carbon dioxide (CO2), the method comprising the steps of: - performing (320) methanation of carbon dioxide (CO2) in a methanation unit (110, 210) to produce at least gaseous methane (CH4) and heat (Q), - performing (310) pyrolysis of methane (CH4) in a pyrolysis unit (120, 220) to produce gaseous hydrogen (H2) and solid carbon (C), wherein the heat (Q) produced by methanation is used to perform pyrolysis of methane (CH4), wherein the gaseous hydrogen (H2) produced by pyrolysis is used to perform methanation of carbon dioxide (CO2).

10. The method (300) of claim 9, further comprising the step of supplying (330) gaseous methane (CH4) produced by methanation of carbon dioxide (CO2) to the pyrolysis unit (220).

11. The method (300) of claim 10, wherein the gaseous methane (CH4) supplied to the pyrolysis unit (220) is used to perform (310) pyrolysis of methane (CH4).

12. The method (300) of claim 10, wherein the gaseous methane (CH4) supplied to the pyrolysis unit (220) is combusted to generate additional heat (Qi) in the pyrolysis unit (220).

13. The method (300) of claim 10, wherein a portion of the gaseous methane (CH4) supplied to the pyrolysis unit (220) is used to perform (310) pyrolysis of methane (CH4), and a portion of the gaseous methane (CH4) supplied to the pyrolysis unit (220) is combusted to generate additional heat (Qi) in the pyrolysis unit (220).

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