Use of co2-rich flue gas as purge gas in electrolysis units

Abstract

A gas heating section and reforming section are provided in which flue gas is used as an anode (oxygen) purge gas in an electrolysis unit. The resulting combined gas stream is fed as a combustion gas stream to the gas heating / reforming section. By continuously feeding the combined gas stream to the at least one combustor and combusting, a flue gas stream with high purity CO2 can be obtained. The invention also provides a chemical plant, and a method for providing a syngas stream.

Description

Technical Field

[0001] The present invention relates to a gas heating section, more specifically to a reforming section, wherein flue gas is used as anode (oxygen) purge gas in an electrolysis unit. The resulting combined gas stream is returned to the gas heating section / reforming section as a combustion gas stream. By continuously supplying the combined gas stream to the at least one burner and burning it, a flue gas stream with high purity CO2 can be obtained. The present invention also provides a chemical plant and a method for providing a synthesis gas stream. Background Art

[0002] In industrial chemical plants and processes, there is growing interest in the production of gaseous streams such as oxygen or hydrogen by electrolysis, both due to environmental concerns and due to the increasing opportunities to use electricity from renewable sources.

[0003] Industrial-scale electrolysis processes, such as those carried out in solid oxide electrolysis cells (SOECs), produce an oxygen stream that is usually considered a waste product and discharged directly to the atmosphere. To effectively utilize the oxygen stream produced by such industrial-scale electrolysis processes, a technique known as "purge gas" (also known as "flushing gas" or "scavenging gas") is usually used. The purge gas is introduced into the anode side of the electrolysis unit, mixed with the oxygen produced at the anode to form a combined gas stream containing oxygen, which is then discharged from the electrolysis unit. The use of a purge gas can increase the pressure of the combined gas stream to a higher pressure than the oxygen stream produced by the electrolysis unit itself, and can be used, for example, to adjust the chemical and physical composition of the oxygen stream for a specific application. The use of a purge gas can also improve operating safety by diluting the oxygen.

[0004] Atmospheric air is often used as a purge gas and has the advantage of being readily available. However, if the oxygen-containing combined gas stream produced by the electrolysis unit is recycled, the use of atmospheric air as a purge gas can result in the accumulation of inert nitrogen in the flue gas. Therefore, when atmospheric air is used as a purge gas in an electrolysis unit, a CO2 removal step is required on the resulting flue gas. This process is not ideal due to the high cost of the CO2 removal unit. Therefore, the CO2 to be stored must reach a high purity level in accordance with government regulations.

[0005] The use of carbon dioxide as a flushing gas has been disclosed in US2015038741 and WO2013 / 164172. US8496908 discloses a steam methane reforming process that produces a hydrogen product while capturing CO2 from the process.

[0006] It is an object of the present invention to provide a method for efficient reuse of flue gas streams from fired reformers and gas heaters with the aim of reducing or eliminating the need for flue gas cleaning / scrubbing treatments. Another object of the present invention is to provide efficient gas purge for electrolysis units. These and other objects are solved by the present invention. Summary of the invention

[0007] The inventors of the present invention have found that by generating pure oxygen in the electrolysis unit and using the flue gas produced by combustion as a purge gas, a synergistic effect between the gas heating section / reforming section and the electrolysis unit can be achieved. At the same time, a flue gas flow can be provided as a high-purity CO2 flow. Therefore, the present invention provides the possibility of avoiding the CO2 removal step on the flue gas.

[0008] Therefore, in a first aspect, the present invention relates to a gas heating section comprising:

[0009] - a combustion chamber comprising at least one burner;

[0010] - a heating chamber arranged in thermal communication with said combustion chamber,

[0011] - electrolysis unit;

[0012] - reactant feed to the electrolysis unit;

[0013] - a fuel supply to said at least one burner;

[0014] - a flow of combustion gases to said at least one burner;

[0015] - a first gas feed to the heating chamber;

[0016] wherein the combustion chamber is arranged to receive the fuel supply and the combustion gas stream, to carry out combustion in the at least one burner, and to output a flue gas stream enriched with carbon dioxide,

[0017] wherein the heating chamber is configured to receive heat energy from the combustion chamber and output a heated first gas flow,

[0018] wherein the electrolysis unit is configured to electrolyze the reactant feed into at least one anode product gas; and wherein

[0019] at least a first portion of the flue gas stream from the combustion chamber is arranged to be supplied to the anode of the electrolysis unit as a purge gas for the anode product gas to output a combined gas stream comprising carbon dioxide and the anode product gas from the electrolysis unit; and

[0020] Wherein at least a portion of the combined gas flow is arranged to be supplied to at least one burner of a combustion chamber as at least a portion of the combustion gas flow.

[0021] The present invention also provides a reforming section, comprising the gas heating section described herein, wherein the first gas stream is a first hydrocarbon feed, and wherein the heating chamber comprises a reforming catalyst configured to convert the first hydrocarbon feed into a synthesis gas stream.

[0022] The present invention also provides a chemical equipment, preferably a hydrogen production equipment, which includes the gas heating section described herein or the reforming section described herein.

[0023] Furthermore, a method for providing a synthesis gas stream in a reforming section according to the invention is provided.

[0024] Further details of the technique are provided in the accompanying dependent claims and the drawings.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The technology of the present invention is illustrated by the following schematic diagram, wherein:

[0027] Figure 1 shows a gas heating section according to the present invention;

[0028] Figure 2 shows a reforming section according to the invention;

[0029] Figure 3 A SOEC according to the invention is shown with a purge gas input. DETAILED DESCRIPTION OF THE INVENTION

[0031] Unless otherwise stated, all percentages of gas contents are by volume.

[0032] For the avoidance of doubt, the term "feed" refers to a means, such as a pipe, pipeline, etc., for supplying a gas to a suitable section, stage, reactor or unit.

[0033] The term “syngas” (short for synthesis gas) refers to a gas containing hydrogen, carbon monoxide, carbon dioxide, water vapor and small amounts of other gases (such as argon, nitrogen, methane, etc.).

[0034] The term "purge gas" refers to a gas supplied to the electrolysis unit as a carrier for carrying O2 out of the electrolysis unit, and the chemical composition of the purge gas will not undergo any chemical reaction or conversion when passing through the electrolysis unit.

[0035] Typically, reformers or fired heaters use air for combustion. This results in the introduction of significant amounts of nitrogen into the flue gas, necessitating downstream processing steps (e.g. CO2 capture).

[0036] The technology of the present invention simultaneously addresses at least two problems with a single solution - efficient utilization of the flue gas from the reformer / fired heater, and effective purging of oxygen from the electrolysis unit.

[0037] In a first aspect, a gas heating section is provided, such as Figure 1 The gas heating section generally includes:

[0038] - a combustion chamber comprising at least one burner;

[0039] - a heating chamber arranged in thermal communication with said combustion chamber,

[0040] - electrolysis unit;

[0041] - reactant feed to the electrolysis unit;

[0042] - a fuel supply to said at least one burner;

[0043] - a flow of combustion gases to said at least one burner;

[0044] - A first gas feed to said heating chamber.

[0045] Combustion Chamber

[0046] The combustion chamber defines a space contained within the housing in which the fuel is burned. A fuel supply provides fuel to at least one burner disposed within the combustion chamber. The fuel supply is typically a hydrocarbon-rich gas (such as natural gas). A combustion gas stream is also provided to the at least one burner, the combustion gas stream comprising an oxidant (such as oxygen) that can be combined with the fuel supply to be burned together.

[0047] The combustion chamber is configured to receive a fuel supply and a combustion gas flow, burn through the at least one burner, and output a flue gas flow. The flue gas flow is rich in CO2 (i.e., the CO2 content exceeds 50%, preferably exceeds 75%, and more preferably exceeds 90%). After multiple recirculations, the CO2 content of the flue gas flow can reach more than 99%.

[0048] Professional engineers can design the combustion chamber and burner as needed to achieve optimal combustion and heating.

[0049] If the oxygen content of the combustion gas stream is insufficient, additional oxygen may be added.Thus, in one aspect, provision is also made for supplying an oxygen-enriched supplementary feed to at least one burner, preferably in admixture with the combined gas stream.

[0050] The fuel supply delivered to the combustion chamber may be purified as required before entering the combustion chamber.

[0051] Heating chamber

[0052] The heating chamber is arranged to be in thermal communication with the combustion chamber. The heating chamber is arranged to receive heat energy from the combustion chamber and output a heated first gas stream. The heating chamber defines a space contained in the shell, where the first gas feed is heated. The relative arrangement of the heating chamber and the combustion chamber can be designed by those skilled in the art. A suitable arrangement is a shell and tube reactor, wherein the heating chamber comprises one or more pipelines arranged in the combustion chamber shell, or vice versa.

[0053] The first gas feed is arranged to be delivered to the heating chamber for heating. Thus, the heating chamber is arranged to receive heat energy from the combustion chamber and output a heated first gas stream.

[0054] Electrolysis unit

[0055] The electrolysis unit is arranged to electrolyze the reactant feed into at least an anode product gas. Preferably, the electrolysis unit is one or more solid oxide electrolysis cells (SOECs). The design and construction of SOECs are known, for example, from WO2013 / 164172, the contents of which are incorporated herein by reference. Alternatively, the electrolysis unit of the apparatus of the present invention may be an alkaline electrolyzer or a proton exchange membrane (PEM) electrolyzer.

[0056] At least a first portion of the flue gas stream from the combustion chamber is arranged to be supplied to the anode of the electrolysis unit as a purge gas for the anode product gas (typically oxygen) so that a combined gas stream comprising carbon dioxide and the anode product gas is output from the electrolysis unit.

[0057] At least a portion of the combined gas flow is arranged to be supplied to at least one burner of the combustion chamber as at least a portion of the combustion gas flow.

[0058] Reactant feed

[0059] A reactant feed is supplied to the electrolysis unit. The electrolysis unit is configured to electrolyze the reactant feed into at least an anode product gas.

[0060] In a preferred aspect, the reactant feed is a water-rich feed, and the electrolysis unit is configured to electrolyze the reactant feed into oxygen (as anode product gas) and hydrogen (as cathode product gas). On the other hand, the reactant feed is a CO2-rich feed, and the electrolysis unit is configured to electrolyze the reactant feed into oxygen (as anode product gas) and carbon monoxide (as cathode product gas).

[0061] The present technology allows the flue gas to be recycled as a purge gas for oxygen in the electrolysis unit. By continuously supplying the combined gas stream to the at least one burner and burning it, a flue gas stream with high purity CO2 (e.g., containing >99% CO2, preferably >99.9% CO2) can be obtained. This can reduce the need for expensive CO2 removal units (such as amine wash units) at the flue gas outlet.

[0062] It may be beneficial to purify the flue gas stream (either in its entirety or a first portion thereof) before feeding it to the electrolysis unit. Flue gases originating from the combustion of hydrocarbons may contain water, dust, metal ions and / or sulphides (such as H2S).

[0063] The gas heating stage may comprise one or more recirculation compressors, for example located in the first part of the flue gas stream fed to the electrolysis unit, or in the combined gas stream output from the electrolysis unit.

[0064] The gas heating section may produce excess flue gas (ie more than is required to purge the electrolysis unit anodes). Therefore, a second portion of the flue gas stream may be directed from the gas heating section. Preferably, this portion is high purity (>99%) CO2.

[0065] If the electrolysis is CO2 electrolysis (ie the reactant feed is a CO2 feed), it may be taken from the flue gas stream. Thus, a third portion of the flue gas stream may be provided as a CO2-rich feed to the electrolysis unit.

[0066] Reorganization section

[0067] In a preferred embodiment, the gas heating section described herein can be used as a reforming section. The reforming section converts the hydrocarbon gas feed into synthesis gas (syngas) by using a reforming catalyst. This process is an endothermic reaction.

[0068] In this embodiment, the reforming section comprises the gas heating section as described above, and is provided with several additional components. In the reforming section, the first gas stream is a first hydrocarbon feed, and the heating chamber is a reforming reactor containing a reforming catalyst, which is configured to convert the first hydrocarbon feed into a synthesis gas stream.

[0069] In one aspect of the reforming stage, the reforming reactor is a steam methane reforming (SMR) reactor and the water-rich co-feed is supplied to the SMR reactor.

[0070] The present invention also provides a method for providing a synthesis gas stream in a reforming section as described herein, the method comprising the steps of:

[0071] - providing a fuel supply and a combustion gas stream to the combustion chamber and causing them to be combusted in said at least one burner, thereby outputting a flue gas stream rich in carbon dioxide,

[0072] - electrolyzing a reactant feed in said electrolysis unit into at least an anode product gas, preferably oxygen;

[0073] - supplying at least a first portion of the flue gas stream from the combustion chamber to the anode of the electrolysis unit as a purge gas for the anode product gas, thereby outputting a combined gas stream comprising carbon dioxide and anode product gas from the electrolysis unit;

[0074] - supplying at least a portion of the combined gas flow as at least a portion of the combustion gas flow to at least one burner of the combustion chamber; and

[0075] - allowing heat energy to transfer from the combustion chamber to a reforming reactor and converting the first hydrocarbon feed into a synthesis gas stream in the reforming reactor.

[0076] Preferably, in the method, the flue gas stream is continuously recycled as a purge gas for oxygen and supplied as a combined gas stream to the at least one burner and burned until a flue gas stream containing >99% (preferably >99.9%) CO2 is obtained.

[0077] In another embodiment, a chemical plant (preferably a hydrogen production plant) is provided, which comprises the gas heating section described herein, or the reforming section described herein.

[0078] In a specific embodiment of the chemical plant, the reactant feed is a water-rich feed, and the electrolysis unit is configured to electrolyze the reactant feed into oxygen as an anode product gas and hydrogen as a cathode product gas, and the hydrogen cathode product gas is supplied as a feed to at least one reactor in the chemical plant.

[0079] The present technology can be used to modify existing chemical plants that use combustion heaters to provide heat or use combustion reformers. Modifications made in this way can simultaneously increase the production of hydrogen used inside the plant and reduce the need for CO2 separation / capture at the flue. Such modifications include the steps of replacing one or more combustion heaters in the existing plant with one or more gas heating sections described in the present invention. Alternatively, or in addition, such modifications may include replacing one or more combustion reformers in the existing plant with one or more reforming sections according to the present invention.

[0080] Although the invention has been described with reference to several aspects and embodiments, those skilled in the art may combine these aspects and embodiments within the scope of the appended claims.All documents cited herein are incorporated by reference. DETAILED DESCRIPTION

[0081] Figure 1A gas heating section (10) is shown. Figure 1 The details are as follows:

[0082] - Combustion chamber (12)

[0083] - a burner (12a);

[0084] -Heating chamber (220)

[0085] - an electrolysis unit (20);

[0086] - a reactant feed (18) to an electrolysis unit (20);

[0087] - a fuel supply (5) to the burner (12a);

[0088] - a combustion gas flow (7) to a burner (12a);

[0089] - a first gas feed (1) to a heating chamber (220);

[0090] The combustion chamber (12) receives a fuel supply (5) and a combustion gas stream (7). These are combusted together in a burner (12a) and a flue gas stream (19) is discharged from the combustion chamber (12). Heat energy (indicated by the large arrow) is transferred from the combustion chamber (12) to a heating chamber (220). The first gas feed (1) is thereby heated in the heating chamber (220) to output a heated first gas stream (221).

[0091] A reactant feed (18) is supplied to an electrolysis unit (20) where it is electrolyzed into at least an anode product gas (typically oxygen). The cathode product gas is typically hydrogen. A first portion (19a) of a flue gas stream (19) from a combustion chamber (12) is supplied to the anode of the electrolysis unit (20) as a purge gas for the anode product gas. A combined gas stream (21) output from the electrolysis unit (20) comprises carbon dioxide and the anode product gas. At least a portion of the combined gas stream (21) is used as at least a portion of a combustion gas stream (7) and is supplied to at least one burner (12a) of the combustion chamber (12).

[0092] A second portion (19b) of the flue gas stream (19) may be directed from the gas heating section (10). A third portion (19c) of the flue gas stream (19) may be arranged to be provided as a CO2-rich feed to an electrolysis unit. A fourth portion (19d) of the flue gas stream (19) may be arranged to be mixed with a combined gas stream (21) and then supplied to at least one burner (12a) of a combustion chamber (12).

[0093] Figure 2The reforming section (100) according to the present invention is shown. The reforming section (100) comprises Figure 1 The same components as those of the gas heating section (10) shown in FIG. Figure 1 The same as described in. Figure 2 In the invention, the first gas stream (1) is a first hydrocarbon feed (1'), and the heating chamber (220) is a reforming reactor (223) containing a reforming catalyst, which is configured to convert the first hydrocarbon feed (1') into a synthesis gas stream (222).

[0094] Figure 3 A SOEC (20) according to the invention is shown provided with a reactant feed (18), a purge gas input (a first portion 19a of the flue gas stream) and a combined gas stream (21).

[0095] based on Figure 1 The gas heating section shown is simulated.

[0096]

[0097]

[0098] It can be seen that the flue gas stream (19) from the burner is a high purity CO2 stream containing 97.77% CO2 and a small amount of O2. The flue gas stream is split into a first part (19a) and a second part (19b). The first part (19a) is used as a purge gas in the anode side of the SOEC (20), and the second part (19b) is derived from the gas heating section (10). The output combined gas stream (21) contains about 21 mol% oxygen and about 79 mol% CO2, and contains almost no other components.

[0099] The oxygen content of the stream (21) is high enough to allow it to be used as the combustion gas stream (7) in the burner (12a). Furthermore, the only other significant component in the gas stream (21) is CO2, which means that the accumulation of inert materials such as nitrogen can be effectively reduced, and the combustion of the stream in the burner produces a high purity CO2 stream.

Claims

1. A gas heating section (10), the gas heating section (10) comprising: - a combustion chamber (12) comprising at least one burner (12a); - a heating chamber (220) arranged in thermal communication with the combustion chamber (12), - an electrolysis unit (20); - a reactant feed (18) to the electrolysis unit (20); - a fuel supply (5) to the at least one burner (12a); - a flow (7) of combustion gases to the at least one burner (12a); - a first gas feed (1) to the heating chamber (220); wherein the combustion chamber (12) is arranged to receive the fuel supply (5) and the combustion gas flow (7), combust them in the at least one burner (12a) and output a flue gas flow (19) rich in carbon dioxide, The heating chamber (220) is configured to receive heat energy from the combustion chamber (12) and output a heated first gas flow (221), wherein the electrolysis unit (20) is configured to electrolyze the reactant feed (18) into at least one anode product gas; and among them At least a first portion (19a) of the flue gas stream (19) from the combustion chamber (12) is arranged to be supplied to the anode of the electrolysis unit (20) as a purge gas for the anode product gas, so as to output a combined gas stream (21) comprising carbon dioxide and anode product gas from the electrolysis unit (20); and Wherein at least a portion of the combined gas flow (21) is arranged to be supplied to at least one burner (12a) of a combustion chamber (12) as at least a portion of the combustion gas flow (7).

2. The gas heating section (10) according to claim 1, wherein the electrolysis unit (20) comprises one or more solid oxide electrolysis cells (SOEC).

3. The gas heating section (10) according to any of the preceding claims, wherein a second portion (19b) of the flue gas flow (19) is led out of the gas heating section (10).

4. A gas heating section (10) according to any one of the preceding claims, wherein an oxygen-enriched supplementary feed (31) is also provided to at least one burner (12a), preferably mixed with the combined gas flow (21).

5. A gas heating section (10) according to any one of the preceding claims, wherein the reactant feed (18) is a water-rich feed, and wherein the electrolysis unit (20) is arranged to electrolyze the reactant feed (18) into oxygen as anode product gas and hydrogen as cathode product gas.

6. A gas heating section (10) according to any one of the preceding claims, wherein the reactant feed (18) is a CO2-rich feed, and wherein the electrolysis unit (20) is configured to electrolyze the reactant feed (18) into oxygen as an anode product gas and carbon monoxide as a cathode product gas.

7. A gas heating section (10) according to any one of the preceding claims, wherein a third portion (19c) of the flue gas stream (19) is arranged to be supplied to the electrolysis unit as CO2-rich feed.

8. A gas heating section (10) according to any of the preceding claims, wherein a fourth portion (19d) of the flue gas flow (19) is arranged to be mixed with the combined gas flow (21) before supplying the combined gas flow (21) to at least one burner (12a) of the combustion chamber (12).

9. A reforming section (100) comprising a gas heating section (10) according to any one of the preceding claims, wherein the first gas flow (1) is a first hydrocarbon feed (1'), and wherein the heating chamber (220) is a reforming reactor (223) containing a reforming catalyst, and the reforming reactor (223) is configured to convert the first hydrocarbon feed (1') into a synthesis gas flow (222).

10. The reforming section (100) according to claim 9, wherein the reforming reactor (223) is a steam methane reforming (SMR) reactor, and wherein a water-rich co-feed is supplied to the SMR reactor.

11. A chemical equipment, preferably a hydrogen production equipment, comprising a gas heating section (10) according to any one of claims 1 to 8, or a reforming section (100) according to any one of claims 9 to 10.

12. A chemical plant according to claim 11, wherein the reactant feed (18) is a water-rich feed, and wherein the electrolysis unit (20) is configured to electrolyze the reactant feed (18) into oxygen as an anode product gas and hydrogen as a cathode product gas, and wherein the cathode product gas hydrogen is supplied as a feed to at least one reactor in the chemical plant.

13. A method for providing a synthesis gas stream in a reforming section according to any one of claims 9-10, the method comprising the steps of: - supplying a fuel supply (5) and a combustion gas stream (7) to the combustion chamber (12) and causing them to burn in the at least one burner (12a) thereby outputting a flue gas stream (19) rich in carbon dioxide, - electrolyzing a reactant feed (18) into at least an anode product gas, preferably oxygen, in said electrolysis unit (20); - supplying at least a first portion (19a) of the flue gas stream (19) from the combustion chamber (12) as a purge gas for the anode product gas to the anode of the electrolysis unit (20), thereby outputting a combined gas stream (21) comprising carbon dioxide and anode product gas from the electrolysis unit (20); - supplying at least a portion of the combined gas flow (21) as at least a portion of the combustion gas flow (7) to at least one burner (12a) of the combustion chamber (12); as well as - allowing heat energy to be transferred from the combustion chamber (12) to the reforming reactor (223) and converting the first hydrocarbon feed (1') into a synthesis gas stream (222) in the reforming reactor (223).

14. A method according to claim 13, wherein the flue gas stream (19) is continuously recirculated as a purge gas for oxygen and is supplied to the at least one burner (12a) as a combined gas stream (21) and burned until a flue gas stream (19) with a CO2 content of >99%, preferably >99.9%, is obtained.

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