Method and system for forming syngas

Abstract

A method for forming syngas, the method comprising: providing a first feed gas stream containing carbon dioxide; providing a second feed gas stream containing hydrogen; heating the first feed gas stream and / or the second feed gas stream; after heating, mixing the first feed gas stream and the second feed gas stream in a mixing zone lined with refractory ceramic material and / or formed of nickel-chromium alloy to form a heated mixed feed gas stream containing carbon dioxide and hydrogen; and feeding the heated mixed feed gas stream from the mixing zone into a countercurrent gas shift reactor containing a countercurrent gas shift catalyst to form a crude syngas product stream by converting at least a portion of the carbon dioxide into carbon monoxide, wherein the mixing zone and the countercurrent gas shift reactor are connected via a connecting pipe lined with refractory ceramic material and / or formed of nickel-chromium alloy, or the mixing zone is formed by a connecting pipe leading to the countercurrent gas shift reactor.

Description

Technical Field

[0001] This specification relates to methods and systems for forming syngas (synthesis gas) comprising carbon monoxide and hydrogen, and also to methods and systems for producing liquid hydrocarbons from syngas. Background Technology

[0002] The Fischer-Tropsch process converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. These reactions occur in the presence of a metal catalyst, typically at temperatures ranging from 150°C to 300°C and pressures from one atmosphere to tens of atmospheres. The Fischer-Tropsch process involves a series of chemical reactions that produce a variety of hydrocarbons, ideally possessing the formula (C... n H 2n+2 A more useful reaction is the following to produce alkanes:

[0003]

[0004] Where n can be 1 to 100 or higher. The formation of methane (n=1) is not required. In addition to the formation of alkanes, the competing reaction also produces small amounts of alkenes, as well as alcohols and other oxidized hydrocarbons. Because the standard enthalpy of reaction (ΔH) is -165 kJ / mol CO, the Fischer-Tropsch reaction is a highly exothermic reaction.

[0005] The syngas fed into the Fischer-Tropsch process can be derived from a variety of feedstocks; for example, natural gas reformed by steam reforming and / or autothermal reforming, municipal solid waste and biomass gasified at high temperatures, or carbon dioxide and hydrogen produced via the reverse water-gas shift reaction. The reverse water-gas shift reaction can be described as follows:

[0006]

[0007] Syngas production using the reverse water-gas shift reaction can be advantageous because it utilizes carbon dioxide that may have been intended to be released into the atmosphere.

[0008] WO2022079408 describes a method for producing a gaseous stream containing carbon monoxide, wherein the method involves feeding a gas mixture containing carbon dioxide and hydrogen into a burner disposed in a reverse-flow gas shift vessel and burning it together with a substoichiometric oxygen feed to form a combustion gas mixture containing carbon monoxide, carbon dioxide, hydrogen, and steam. The mixture is then passed through a reverse-flow gas shift catalyst to form a crude product gas containing carbon monoxide, carbon dioxide, hydrogen, and steam. The gas is then cooled so that moisture condenses and can be separated and removed; the gas stream is then passed to a carbon dioxide removal unit to remove carbon dioxide, which can be recycled back to the feed gas mixture in the reverse-flow gas shift vessel to produce syngas containing carbon monoxide and hydrogen.

[0009] WO2022079408 also discloses that the gas feed stream into the reverse-flow gas shifter can be preheated. The preheating temperature of the feed gas to the reverse-flow gas shifter can be in the range of 400°C to 1000°C or 450°C to 800°C to maintain combustion. The hydrogen and carbon dioxide feed streams can be premixed before preheating or preheated and mixed. The feed can be preheated to its preheating temperature by exchanging with the crude product gas mixture and / or by steam heating, or by using a calcination heater, or by electric heating, or by a combination of both or more of these. Preferably, the feed gas mixture containing carbon dioxide and hydrogen is heated by exchanging with the crude product gas mixture.

[0010] This specification relates to an improved method and system for producing syngas, with particular focus on the preheating of feed gas leading to a reverse water gas shift reactor. Summary of the Invention

[0011] As described in the background section, WO2022079408 teaches that preheating the carbon dioxide and hydrogen feed gases leading to the reverse water gas shift reactor (RTG) may be advantageous, and the carbon dioxide and hydrogen feed streams can be premixed before preheating or preheated and mixed. From a production system perspective, the simplest and seemingly preferred method is to mix the hydrogen and carbon dioxide feed gases and then preheat the gas mixture before passing it to the RTG. However, it has been surprisingly found that under certain preheating conditions, the carbon dioxide and hydrogen feed gas mixture may be more reactive than previously thought, and that the RTG reaction can be initiated at least partially when the mixed feed gases are preheated before entering the RTG. This can be problematic because such a reaction may generate a gas mixture containing CO / H2 / CO2 / H2O in the preheater equipment and pre-reactor piping system, and this gas mixture may degrade standard preheater equipment and piping systems via material damage mechanisms such as carburization and metal dusting. This could shorten the lifespan of these components and require their replacement, leading to increased equipment costs and longer factory downtime.

[0012] The aforementioned problems may be further exacerbated by the following: metallic structural materials catalyzing the reverse water-gas shift reaction in the preheater and / or piping system preceding the reverse water-gas shift reactor. For example, heating the mixed gas feed above a large metallic heat exchange surface in the preheater may catalyze the reverse water-gas shift reaction.

[0013] Furthermore, preheating the mixed gas feed can also trigger an exothermic methanation reaction, which is exothermic and causes a temperature rise. Methanation can also be catalyzed by metallic structural materials, and when heat release is faster than heat removal, it can lead to a runaway reaction. This can cause temperatures to rise and exceed the design temperature of the preheater or piping system, resulting in equipment damage and downtime.

[0014] One solution to these problems is to preheat the carbon dioxide and hydrogen mixture at a lower temperature and / or pressure to avoid initiating the reverse water gas shift (and / or methanation) reaction before it enters the reverse water gas shift reactor. However, this approach may reduce the efficiency of the reverse water gas shift system.

[0015] Another approach is to use a preheater comprising components made of an alloy more resistant to degradation caused by gases containing CO / H2 / CO2 / H2O. However, components made of such alloys tend to be expensive and harder to procure, resulting in longer delivery cycles, more costly construction, and less spare parts availability. Furthermore, such components may still have a limited lifespan due to eventual failure from carburization and / or metallization.

[0016] Another approach is to preheat the carbon dioxide and hydrogen feed gases separately, which is envisioned as an alternative in WO2022079408. However, if these separately heated feed gas streams are subsequently mixed before entering the reverse water-gas shift reactor (RTP), the RTP reaction may occur in the mixing zone before entering the RTP reactor. To avoid this problem, the separately preheated carbon dioxide and hydrogen feed streams can be fed separately into the RTP reactor and mixed only within the reactor. However, this would require modifications to the RTP reactor design and could potentially lead to suboptimal mixing of reactants and / or increased reactor complexity.

[0017] In view of the foregoing, this specification provides an alternative / improved method that avoids at least some of the problems outlined above. The method includes:

[0018] Provide a first feed gas stream containing carbon dioxide;

[0019] Provide a second feed gas stream containing hydrogen;

[0020] Heating the first feed gas stream and / or the second feed gas stream;

[0021] After heating, the first feed gas stream and the second feed gas stream are mixed in a mixing zone lined with refractory ceramic material and / or formed of nickel-chromium alloy to form a heated mixed feed gas stream containing carbon dioxide and hydrogen; and

[0022] A heated mixed feed gas stream from the mixing zone is fed into a counter-current gas shift reactor containing a counter-current gas shift catalyst to form a crude syngas product stream by converting at least a portion of the carbon dioxide into carbon monoxide.

[0023] The mixing zone and the reverse water gas shift reactor are connected by a connecting pipe lined with refractory ceramic material and / or made of nickel-chromium alloy, or the mixing zone is formed by a connecting pipe leading to the reverse water gas shift reactor.

[0024] This specification also provides a system for performing the above methods, the system comprising:

[0025] One or more heaters for heating a first feed gas stream containing carbon dioxide and / or a second feed gas stream containing hydrogen;

[0026] A mixing zone, lined with refractory ceramic material and / or formed of nickel-chromium alloy, is used to mix the heated first and second feed gas streams to form a heated mixed feed gas stream containing carbon dioxide and hydrogen; and

[0027] A reverse-flow gas shift reactor, comprising a reverse-flow gas shift catalyst, is configured to receive a heated mixed feed gas stream from a mixing zone and pass the heated mixed feed gas stream through the reverse-flow gas shift catalyst within the reactor to form a crude syngas product stream by converting at least a portion of carbon dioxide into carbon monoxide.

[0028] The mixing zone and the reverse water gas shift reactor are connected by a connecting pipe lined with refractory ceramic material and / or made of nickel-chromium alloy, or the mixing zone is formed by a connecting pipe leading to the reverse water gas shift reactor.

[0029] This method heats the carbon dioxide and hydrogen feed streams separately to prevent them from reacting in the preheater. Therefore, it avoids the risks of metallization and carburization in the preheater (feed heater) without requiring it to be made of an expensive metallization-resistant alloy. It also avoids the risk of exothermic methanation reactions occurring in the preheater. Furthermore, the separately heated feed streams are then mixed in a mixing zone lined with refractory ceramic material and / or nickel-chromium alloy, ensuring that the mixing zone is resistant to metallization and carburization should any counter-current gas shift reaction occur there. This also allows the carbon dioxide and hydrogen feed streams to be mixed before entering the counter-current gas shift reactor, eliminating the need for reactor modifications to receive separate carbon dioxide and hydrogen feed streams. The mixing zone and the counter-current gas shift reactor are connected via a connecting pipe lined with refractory ceramic material and / or nickel-chromium alloy, or the mixing zone is formed by a connecting pipe leading to the counter-current gas shift reactor. Therefore, this method can provide a system that is robust to degradation and can provide optimal levels of feed gas preheating at desired gas pressures, while avoiding costly modifications to preheating equipment and / or reverse water-gas shift reactors. This simplifies the procurement of capital equipment, increases equipment life, and minimizes unexpected downtime by eliminating the risk of system material damage. Attached Figure Description

[0030] Figure 1 A flowchart of a method for forming crude syngas is shown.

[0031] Figure 2 It shows how to... Figure 1 The flowchart shows a method for forming syngas by combining it with Fischer-Tropsch units to form a hydrocarbon product feed stream.

[0032] Figure 3 A flowchart of a method for forming crude syngas, not according to this specification, is shown.

[0033] Figure 4 (a) shows the relationship between CO content and temperature for a heated feed mixture of carbon dioxide and hydrogen.

[0034] Figure 4 (b) shows that Figure 4 (a) is a curve obtained by extrapolating from the 500°C test data to show the trend of CO formation up to 650°C.

[0035] Figure 5 A flowchart of a method for forming crude syngas according to this specification is shown, and a flowchart (such as...) is also shown. Figure 3 The flowchart shown can be modified to implement this invention.

[0036] The table below provides an overview of the reference numerals used in the accompanying drawings.

[0037] Detailed Implementation

[0038] Figure 1 A flowchart of a method for forming crude syngas is shown. The method includes heating a first feed gas 2 containing carbon dioxide using a heater 4 to form a heated carbon dioxide feed gas stream 6. A second feed gas 8 containing hydrogen is separately heated using a heater 10 to form a heated hydrogen feed gas stream 12. The heated carbon dioxide feed gas stream 6 and the heated hydrogen feed gas stream 12 are then mixed in a mixing zone 14 lined with a refractory ceramic material (and / or formed of a nickel-chromium alloy) to form a heated mixed feed gas stream 16 containing carbon dioxide and hydrogen. Subsequently, the heated mixed feed gas stream 16 is fed from the mixing zone 14 into a counter-current gas shift reactor 18 containing a counter-current gas shift catalyst, and the heated mixed feed gas stream is passed through the counter-current gas shift catalyst within the counter-current gas shift reactor 18 to form a crude syngas product stream 20 by converting at least a portion of the carbon dioxide into carbon monoxide.

[0039] The first and second heaters for separately heating the carbon dioxide and hydrogen feed streams can be provided by separate heaters. This configuration allows for the selection of heating the carbon dioxide and hydrogen feed streams at different temperatures. Alternatively, the first and second heaters can be provided by a single heater unit. An important feature is that the carbon dioxide and hydrogen feed streams remain as separate streams during the preheating process. This can be achieved by guiding the two separate streams through the same heating unit or by using two separate heaters. An alternative option is to heat only one of the feed streams. In this case, one of the feed streams needs to be heated to a sufficiently high temperature so that the mixed feed stream is hot enough after mixing with the other unheated feed stream.

[0040] Mixing zone 14 may be formed by a container or piping system configured to receive and mix heated carbon dioxide and hydrogen streams 6, 12. If the container or piping system 14 is then connected to the countercurrent gas shift reactor 18 via another connecting pipe 16, this other connecting pipe is also lined with refractory ceramic material (and / or formed of nickel-chromium alloy). Alternatively, mixing zone 14 may be formed within the connecting pipe 16 leading to the countercurrent gas shift reactor 18, without requiring a separate mixing container.

[0041] As described in the Summary of the Invention, a key feature of this specification is the separate heating of the carbon dioxide and hydrogen feed streams, followed by mixing in a region with a refractory ceramic lining (and / or formed of a nickel-chromium alloy). The heated mixed feed gases in the mixing zone are at the temperature and pressure required to initiate a reverse water-gas shift reaction to form a mixture of carbon dioxide, hydrogen, carbon monoxide, and water. The refractory ceramic lining (and / or nickel-chromium alloy) in the mixing zone prevents the gas mixture from degrading the metal components. Furthermore, to avoid such metal degradation downstream of the mixing zone, downstream system components may also be lined with refractory ceramic materials and / or made of degradation-resistant alloys. For example, one or more components of a reverse water-gas shift reactor may be lined with refractory ceramic materials and / or made of degradation-resistant alloys. In this respect, the reverse water-gas shift reactor has been designed to withstand the damage of the reverse water-gas shift reaction. A key feature of certain configurations in this specification is that they can be implemented using standard heaters and reactors if preheating of the reactants before they enter the reverse water-gas shift reactor is sufficient to initiate the reaction, while avoiding the problems of existing configurations.

[0042] As described in the Summary of the Invention, an alternative to the above method is to mix carbon dioxide and hydrogen before heating and then maintain the temperature of the gas mixture low enough that the reverse water-gas shift reaction is not initiated before entering the reverse water-gas shift reactor. However, this results in low efficiency within the reverse water-gas shift reactor. Another alternative to the above method is to mix carbon dioxide and hydrogen before heating and then use a heater specifically configured to withstand degradation caused by the gas mixture containing carbon dioxide, hydrogen, carbon monoxide, and water formed at the initiation of the reverse water-gas shift reaction. However, this method requires such a heater to be manufactured from expensive alloy and / or ceramic-coated components resistant to metal dust. This method is advantageous because it allows the use of more standard heating equipment to heat the feed gas while still avoiding the problem of heating equipment degradation. Providing a ceramic-lined mixing zone / container / pipeline is much easier than providing a heater with custom-made corrosion-resistant components. Therefore, this method can be implemented in cases where a heater and / or feed pipe is used to heat the first feed gas and the second feed gas and feed them into the mixing zone, wherein the heater and / or feed pipe is not lined with refractory ceramic material or is not formed of expensive metal dust resistant alloys (e.g., nickel-chromium alloys, such as nickel-chromium-only alloys, nickel-chromium-aluminum alloys or nickel-chromium-copper alloys).

[0043] For configurations where the mixing zone is lined with refractory ceramic material, the refractory ceramic material can be selected from any ceramic material that is resistant to degradation caused by a mixture of carbon dioxide, hydrogen, carbon monoxide, and water at the process temperatures and pressures required for optimal feeding of the process gas into the countercurrent water-gas shift reactor. For example, the refractory ceramic material can be an oxide, carbide, or nitride of one or more of the following elements: silicon, aluminum, magnesium, calcium, boron, chromium, and zirconium.

[0044] For configurations where the mixing zone is formed of an alloy resistant to metal dust (such as a nickel-chromium alloy), the nickel-chromium alloy can be selected from nickel-chromium alloys only, nickel-chromium-aluminum alloys, or nickel-chromium-copper alloys. For example, the nickel-chromium alloy can be selected from alloys such as 310, 310S, 310Si, 800 / H / HT, RA 330, 600 / H, 625, 890, RA330, RA230, X alloy, CT15C, Paralloy CR39W, H39WMR, H39WM+, HK40, HPW, HPNb, HP Microalloy, 601 alloy, 602 CA, 603XL, 617, 671, 690, 693, 803, and NEXAGE. ™ 696, VDM ® ALLOY 699 XA, HAYNES ® HR-235 ® One or more of the following alloys are preferred: HR214, HR120, HR160, H46M, RA253MA, RA333, RA353MA, 45TM, Paralloy OPTIM-AL, H46M, or H48T. Preferred alloys include 600 / H alloy, 625, 890, RA330, RA230, X alloy, CT15C, Paralloy CR39W, H39WMR, H39WM+, HK40, HPW, HPNb, and HP Microalloy. Most preferred alloys include 601 alloy, 602 CA, 603XL, 617, 671, 690, 693, 803, and NEXAGE. ™ 696, VDM ® ALLOY 699 XA, HAYNES ® HR-235 ® HR214, HR120, HR160, H46M, RA253MA, RA333, RA353MA, 45TM, Paralloy OPTIM-AL, H46M, and H48T. The alloys can also provide pressure retention in the mixing zone, or they can form a coating with another metal that provides mechanical support for pressure retention in the mixing zone.

[0045] In addition, nickel-chromium alloys may include coatings to increase corrosion resistance. The coating may be selected from aluminum diffusion coatings, chromium diffusion coatings, silicon coatings (e.g., silicon CVD coatings), or catalytic coatings.

[0046] To further reduce corrosion, corrosion inhibitors can be added to one or more feed streams before the mixing zone. For example, corrosion inhibitors can be sulfur-based, such as H₂S or disulfides. Such agents create a protective sulfur atmosphere on the metal surface, which preferentially prevents carbon from being absorbed onto the surface. Therefore, to increase corrosion protection, low levels of reactive sulfur substances, such as H₂S or disulfides, can be provided in the process environment. Sulfur content less than 10 ppm (e.g., in the range of 1 to 10 ppm) is sufficient to mitigate metal dusting.

[0047] Regarding process gas conditions, one or both of the first and second feed gases may be heated to the following temperatures: at least 300°C, 400°C, 450°C, 500°C, 600°C, or 700°C; not exceeding 1500°C, 1300°C, 1200°C, 1100°C, 1000°C, 900°C, or 850°C; or within any combination of the aforementioned lower and upper limits. Furthermore, one or more of the first feed gas, second feed gas, heated carbon dioxide feed gas stream, heated hydrogen feed gas stream, and heated mixed feed gas stream may have the following pressures: at least 5, 10, 15, or 20 bar absolute pressure; not exceeding 60, 50, 40, or 30 bar absolute pressure; or within any combination of the aforementioned lower and upper limits.

[0048] The heaters used to heat the first and second feed gases can be of any suitable type to achieve the desired operating temperature. For example, the first and / or second feed gases can be heated using heater types selected from the following: heat exchange heaters; turbomachinery heaters; electric heaters; radiant heaters; or resistance heaters. Heat source options for the heaters can include geothermal, nuclear (fusion / fission), rotary kinetic heating, concentrated solar energy, infrared, microwave, radio waves, induction, resistance, electric arc, plasma, microwave, ultrasonic, or industrial waste heat, or any of the above utilized via a heat storage medium such as molten salt or a high-temperature thermal storage device.

[0049] The reverse-flow gas shift reactor can be a self-heating reverse-flow gas shift reactor, wherein further heating to the reaction temperature is provided by burning a portion of the heated mixed feed gas with the oxygen feed stream in a burner within the reactor. In this case, the burner advantageously may include nozzles also lined with refractory ceramic material. Alternatively, the reverse-flow gas shift reactor can be an electrically heated reactor or an adiabatic reactor. For example, the feed gas may be fully preheated to the reaction temperature (e.g., electrically) before passing over the catalyst in the reverse-flow gas shift reactor.

[0050] Figure 2 It shows how to... Figure 1 The flowchart illustrates a method for forming syngas by combining it with Fischer-Tropsch units to generate hydrocarbon product streams. The crude syngas product stream 20 is related to the above-mentioned... Figure 1 The same process is described, and for the sake of brevity, these steps / parts will not be repeated.

[0051] The crude syngas from the reverse water-gas shift reactor is advantageously treated to remove water and carbon dioxide before being fed to the Fischer-Tropsch unit. Thus, the crude syngas 20 can be passed to the water removal unit 22 to form a separated water stream 24 and a water-lean syngas 26. The separated water stream 24 can be fed into the electrolyzer 28 to produce a hydrogen stream 30, which is recycled to a second feed gas 8 containing hydrogen. The electrolyzer 28 can also produce an oxygen stream 32, which is fed to the burner of the reverse water-gas shift reactor 18.

[0052] exist Figure 2 In this process, the hydrogen stream 30 is recirculated upstream of the heater 10 to the second feed gas 8 containing hydrogen. Alternatively, the hydrogen stream 30 may be recirculated to the feed gas downstream of the heater 10. For example, the hydrogen stream 30 may be directly recirculated to the mixing zone 14. In this case, the hydrogen stream 30 may optionally be heated separately from the second feed gas 8.

[0053] The crude syngas (advantageously after water removal) is fed into the carbon dioxide removal unit 34 to form a separated carbon dioxide stream 36 and a carbon dioxide-lean syngas 38. The separated carbon dioxide stream 36 can be recycled back to the first feed gas 2 containing carbon dioxide. Figure 2 In this process, the carbon dioxide stream 36 is recirculated upstream of the heater 4 into the first feed gas 2 containing carbon dioxide. Alternatively, the carbon dioxide stream 36 can be recirculated into the feed gas downstream of the heater 4. For example, the carbon dioxide stream 36 can be directly recirculated into the mixing zone 14. In this case, the carbon dioxide stream 36 can optionally be heated separately from the first feed gas 2.

[0054] After removing water and carbon dioxide, and optionally further processing to remove other contaminants, the syngas can then be passed to the Fischer-Tropsch unit 40 to produce a hydrocarbon product stream 42 and a tail gas stream 44. Advantageously, the tail gas stream 44 is recycled to the reverse water-gas shift reactor 18. In this case, the tail gas stream can pass through the re-enrichment reactor 46 to form a methane-containing stream 48, which is fed back into the reverse water-gas shift reactor 18. Both the reverse water-gas shift reaction and the steam methane reforming reaction can occur within the reverse water-gas shift reactor 18 to produce crude syngas. Figure 2 In this embodiment, the methane-containing feed stream 48 is illustrated as being directly recycled to the reverse water-gas shift reactor 18. However, as an alternative, the methane-containing feed stream 48 may be recycled to one of the first feed stream and the second feed streams 2, 8 or to the mixing zone 14.

[0055] To illustrate the benefits of this method, a counterexample is described below, followed by a summary of experiments that led to revisions in this specification.

[0056] Figure 3 An example flowchart of a method for forming crude syngas, not according to this specification, is shown. Carbon dioxide feed gas 2 is mixed with hydrogen feed gas 8. The mixed feed gas 50 is passed through a mixed feed gas exchanger 52 to heat the mixed feed gas using the hot syngas product stream from the countercurrent gas shift reactor. For example, the mixed feed gas at this stage may be at a temperature of about 400°C (398°C in the illustrated example). The mixed feed gas is then passed through a mixed feed gas heater 54 to further increase the temperature of the mixed feed gas. For example, in the illustrated embodiment, the mixed feed gas is heated to 550°C. The heated mixed feed gas 56 is then fed to the countercurrent gas shift reactor 18.

[0057] The tail gas stream 44 (e.g., recycled from a downstream hydrocarbon synthesis unit) is passed through a tail gas exchanger 58 to heat the tail gas using a hot syngas product stream from the reverse water gas shift reactor. The tail gas is then passed through a reverse enrichment reactor 46 to produce a methane-containing gas stream 48, which is mixed with a heated mixed feed gas stream 56. In the illustrated example, the temperature of the methane-containing gas stream from the reverse enrichment reactor is 530°C, the temperature of the heated mixed H2 / CO2 stream is 550°C, and the temperature of the feed gas is 548°C when the two streams are mixed and fed into the reverse water gas shift reactor. It can be noted that the heating element of the feed gas heater will be at a higher temperature than the process gas temperature.

[0058] Oxygen feed 60 is also fed into the reverse-flow gas shift reactor 18 and combusted to further increase the temperature of the reactants, thereby driving the reverse-flow gas shift reaction and producing a crude syngas product stream. In the illustrated embodiment, the temperature of the crude syngas leaving the reactor is 900°C. The hot crude syngas can be used to generate steam in the syngas boiler 62, and then passed through the tail gas exchanger 58 and the H2 / CO2 feed gas exchanger 52.

[0059] The inventors have determined that the mixed feed gas heater 54 and the gas pipeline 56 from the heater 54 to the reverse water gas shift reactor 18 may be susceptible to damage under certain operating conditions and during prolonged operation. Figure 3 (Highlighted area in the image). This is because CO may form in this area, leading to metal degradation.

[0060] Regarding the above, experiments have been conducted to determine how much CO can be formed when the preheated and mixed H2 and CO2 feed is introduced before entering the reverse water-gas shift reactor. Figure 3 The flowchart illustrates the process. A mixed H2 and CO2 feed was preheated from 300°C to 500°C in an empty reactor. The reactor was preheated with nitrogen before switching to the H2 and CO2 mixture. Each temperature test was conducted for 1 hour, then gradually switched to higher temperatures within the test temperature range. The amount of CO was measured at each test temperature. The test conditions are summarized below:

[0061] •H2 – 70.1 mol%, CO2 – 29.9 mol%

[0062] • Test pressure – 24.7 gauge pressure

[0063] • Reactor tube material – 800 HT aluminized

[0064] • Reactor ID (inner diameter) – 28mm

[0065] • Sample the gas at the reactor outlet and measure the CO content.

[0066] The result is Figure 4 As shown in (a), a graph depicts CO content (mol%) versus temperature. The amount of CO remains relatively low between 300°C and 400°C, a temperature range corresponding to... Figure 3 The temperature range of the mixed feed gas between the feed exchanger 52 and the heater 54. However, as the temperature rises to 500°C or higher, the CO content increases significantly, corresponding to a temperature... Figure 3 The temperature of the mixed feed gas in the heater 54 and the gas line 56 leading to the reactor. In another test conducted at 600°C, a CO content as high as 10 mol% was measured. Figure 4(b) shows that Figure 4 (a) is a curve obtained by extrapolating from the 500°C test data to show the trend of CO formation up to 650°C.

[0067] Therefore, these experiments will show that, at least under these operating conditions, CO generation in heater 54 and gas line 56 may be a potential problem if the mixed feed gas conditions and construction materials are not properly managed.

[0068] Furthermore, there is some evidence in the literature that certain metallic alloys used in the manufacture of reactor equipment can influence the amount of CO2 converted to CO through the reverse water-gas shift reaction. For example, in F. Bustamante and RM Enick's "High-Temperature Kinetics of the Homogeneous Reverse Water–Gas Shift Reaction", AICHE Journal, vol. 50, No. 5, May 2004, pg 1039, a comparison was made between the reverse water-gas shift reaction in an Inconel 600 (nickel-chromium alloy) reactor and a quartz reactor. This paper found that Inconel 600 catalyzed the reverse water-gas shift reaction compared to an inert quartz reactor and showed some evidence of CO2 conversion in a temperature range of 538 °C, similar to... Figure 3 The flowchart shows the temperature of the heated mixed feed gas stream 56. Therefore, it is conceivable that alloy materials typically used in the feed heater 54 and gas line 56 could contribute to driving the reverse water gas shift reaction in the heater and gas line 56 to produce CO before it enters the reverse water gas.

[0069] The formation mechanisms of carbon and metal dust include the following:

[0070] H2 + CO2 CO + H₂O [CO is formed by the RWGS reaction]

[0071] 2 CO C + CO2 [CO forms carbon via Boudouard carbon]

[0072] CO + H2 C + H₂O [CO is reduced to carbon]

[0073] Methane cracking (e.g., in the de-enriched tail gas of a recycle) can also form carbon. Carbon formation can cause metal dusting, a form of corrosion that occurs when vulnerable materials are exposed to an environment with high carbon activity. Metal components may corrode over time, potentially leading to equipment failure. While not bound by theory, initial data suggest that in... Figure 3 Under the current conditions of the heated mixed feed gas in heater 54 and gas line 56, carbon formation via CO reduction is more likely to be problematic than carbon formation via the Boudouard route. Thermodynamically, the feed gas composition falls into the carbon formation region via CO reduction. This means that the feed gas composition can thermodynamically form carbon. However, the extent to which this may be problematic in practice will also depend on the kinetics of the carbon formation process. Below 400°C to 450°C, the process kinetics are slow enough that metal dusting is generally not a problem. However, the lower feed heater temperature of the syngas production process of the present invention reduces process efficiency. Therefore, from a process efficiency perspective, it is desirable to preheat the feed gas to a temperature exceeding 500°C.

[0074] Figure 5 A modified flowchart addressing this problem is shown. In this flowchart, the carbon dioxide and hydrogen feed streams 2 and 8 are heated separately so that they do not react in the electric preheater. The heated tail gas, hydrogen, and CO2 feed streams are then combined in refractory-lined tubes 14 and 68 at the inlet of the reverse-flow gas shift reactor 18. No CO is formed in the separate hydrogen and CO2 feed streams. Therefore, the feed lines and electric heaters can be designed using standard / lower-cost metallurgy suitable for the operating conditions and gas composition. Figure 3 Compared to the previous configuration, this configuration does require some additional equipment. Although Figure 3 The configuration includes a single exchanger and heater for mixing H2 / CO2 feeds, but Figure 5 The configuration requires two exchangers and two heaters for the H2 / CO2 feed, namely an exchanger 64 and an electric heater 4 for the CO2 feed stream, and an exchanger 66 and an electric heater 10 for the hydrogen feed stream. Figure 5 The configuration also requires pipes 14 and 68 to have refractory linings. In other aspects, Figure 5 The flowchart configuration corresponds to Figure 3 The flowchart configuration is shown, and the same parts are labeled with the same reference numerals.

[0075] While the invention has been specifically shown and described with reference to certain examples, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for forming syngas, the method comprising: Provide a first feed gas stream containing carbon dioxide; Provide a second feed gas stream containing hydrogen; Heating the first feed gas stream and / or the second feed gas stream; After heating, the first feed gas stream and the second feed gas stream are mixed in a mixing zone lined with refractory ceramic material and / or formed of nickel-chromium alloy to form a heated mixed feed gas stream containing carbon dioxide and hydrogen. as well as The heated mixed feed gas stream from the mixing zone is fed into a counter-current gas shift reactor containing a counter-current gas shift catalyst to form a crude syngas product stream by converting at least a portion of the carbon dioxide into carbon monoxide. The mixing zone and the reverse-flow gas shift reactor are connected via a connecting pipe lined with refractory ceramic material and / or formed of nickel-chromium alloy, or the mixing zone is formed by a connecting pipe leading to the reverse-flow gas shift reactor.

2. The method according to claim 1, Both the first feed gas stream and the second feed gas stream are heated by separate heaters.

3. The method according to any of the preceding claims, The first feed gas and / or the second feed gas are heated by a heater and / or a feed pipe and fed into the mixing zone. The heater and / or the feed pipe are not lined with refractory ceramic material or are not formed of nickel-chromium alloy.

4. The method according to any of the preceding claims, The mixing zone is lined with a refractory ceramic material, which is an oxide, carbide, or nitride of one or more of the following elements: silicon, aluminum, magnesium, calcium, boron, chromium, and zirconium.

5. The method according to any one of claims 1 to 3, The mixing zone is formed of a nickel-chromium alloy selected from nickel-chromium alloys only, nickel-chromium-aluminum alloys, or nickel-chromium-copper alloys.

6. The method according to claim 5, The nickel-chromium alloys mentioned are selected from alloys such as 310, 310S, 310Si, 800 / H / HT, RA 330, 600 / H, 625, 890, RA330, RA230, X alloy, CT15C, Paralloy CR39W, H39WMR, H39WM+, HK40, HPW, HPNb, HPMicroalloy, 601 alloy, 602 CA, 603XL, 617, 671, 690, 693, 803, and NEXAGE. ™ 696, VDM ® ALLOY 699XA, HAYNES ® HR-235 ® One or more of the following: HR214, HR120, HR160, H46M, RA253MA, RA333, RA353MA, 45TM, ParalloyOPTIM-AL, H46M or H48T.

7. The method according to claim 5 or 6, The nickel-chromium alloy mentioned above includes a coating.

8. The method according to claim 7, The coating is an aluminum diffusion coating, a chromium diffusion coating, a silicon coating, or a catalytic coating.

9. The method according to any of the preceding claims, Corrosion inhibitors are added to one or more feed streams before the mixing zone.

10. The method according to claim 9, The corrosion inhibitors mentioned above are sulfur-based corrosion inhibitors.

11. The method according to any of the preceding claims, The feed gas is heated to one or both of the first feed gas and the second feed gas to the following temperatures: at least 300°C, 400°C, 450°C, 500°C, 600°C or 700°C; not exceeding 1500°C, 1300°C, 1200°C, 1100°C, 1000°C, 900°C or 850°C; or within any combination of the lower and upper limits described above.

12. The method according to any of the preceding claims, One or more of the first feed gas, the second feed gas, the heated carbon dioxide feed gas stream, the heated hydrogen feed gas stream, and the heated mixed feed gas stream have the following pressures: at least 5, 10, 15, or 20 bar absolute pressure; not exceeding 60, 50, 40, or 30 bar absolute pressure; or within the range defined by any combination of the lower and upper limits above.

13. The method according to any of the preceding claims, The heated mixed feed gas in the mixing zone is at the temperature and pressure that triggers the reverse water-gas shift reaction to form a mixture of carbon dioxide, hydrogen, carbon monoxide and water.

14. The method according to any of the preceding claims, The first feed gas and / or the second feed gas are heated using a heater type selected from the following: heat exchange heater; turbomachinery heater; electric heater; resistance heater; radiation heater.

15. The method according to any of the preceding claims, The aforementioned reverse water gas shift reactor is a self-heating reverse water gas shift reactor, an electrically heated reverse water gas shift reactor, or an adiabatic reverse water gas shift reactor.

16. The method according to claim 15, The aforementioned reverse-flow gas shift reactor is a self-heating reverse-flow gas shift reactor, in which heating to the reaction temperature is provided by burning a portion of the heated mixed feed gas together with the oxygen feed stream in a burner within the reverse-flow gas shift reactor.

17. The method according to claim 16, The burner mentioned above includes a nozzle lined with refractory ceramic material.

18. The method according to any one of the preceding claims, further comprising: The crude syngas is passed to a water removal unit to form a separated water stream and a water-poor syngas stream; as well as The separated water stream is fed into an electrolyzer to generate hydrogen, which is then recycled into the second feed gas containing hydrogen.

19. The method according to claim 18, The electrolytic cell produces oxygen, which is fed into the burner of the reverse water gas shift reactor.

20. The method according to any one of the preceding claims, further comprising: The crude syngas is fed into a carbon dioxide removal unit to form a separated carbon dioxide stream and a carbon dioxide-lean syngas. as well as The separated carbon dioxide stream is recycled back into the first feed gas containing carbon dioxide.

21. The method according to any of the preceding claims, The synthesis gas is transferred from the reverse-flow gas shift reactor to the Fischer-Tropsch unit to generate a hydrocarbon product stream and a tail gas stream, and the tail gas stream is recycled back to the reverse-flow gas shift reactor.

22. The method according to claim 21, The exhaust gas stream is mixed with one or more of the first feed gas stream, the second feed gas stream, and the heated mixed feed gas stream.

23. A system for performing the method according to any preceding claim, the system comprising: One or more heaters, the one or more heaters being used to heat a first feed gas stream containing carbon dioxide and / or a second feed gas stream containing hydrogen; A mixing zone, lined with refractory ceramic material and / or formed of nickel-chromium alloy, is used to mix the heated first feed gas stream and the second feed gas stream to form a heated mixed feed gas stream containing carbon dioxide and hydrogen. as well as A reverse-flow gas shift reactor, comprising a reverse-flow gas shift catalyst, is configured to receive a heated mixed feed gas stream from a mixing zone and pass the heated mixed feed gas stream through the reverse-flow gas shift catalyst within the reactor to form a crude syngas product stream by converting at least a portion of the carbon dioxide into carbon monoxide. The mixing zone and the reverse-flow gas shift reactor are connected via a connecting pipe lined with refractory ceramic material and / or formed of nickel-chromium alloy, or the mixing zone is formed by a connecting pipe leading to the reverse-flow gas shift reactor.

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