EA040289B1 - SYSTEM AND METHOD FOR PRODUCING SYNTHESIS GAS - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a system for producing synthesis gas. The present invention also relates to a process for producing synthesis gas. More specifically, the present invention relates to a system and process for producing low H2/CO synthesis gas.

State of the art of the present invention

The catalytic production of synthesis gas by steam reforming of hydrocarbon feedstocks has been known for several decades. The endothermic steam reforming reaction is typically carried out in a steam reformer (SMR). The steam reformer or methane steam reformer comprises a series of catalyst-filled tubes located in a furnace or fired heater to provide heat for the endothermic reaction. The tubes typically have a length of 10 to 14 m and an internal diameter of 7 to 15 cm. Heat for the endothermic reaction is provided by burning fuel in burners in a furnace. The temperature of the synthesis gas at the outlet of the steam reformer depends on the use of synthesis gas, but is usually in the range from 65 to 980°C.

It is known that the formation of soot on the catalyst used for the catalytic production of synthesis gas by steam reforming is a problem, in particular for the production of synthesis gases having a relatively low H ₂ /CO ratio. Thus, soot resistant catalysts are required for such synthesis gases. Such soot resistant catalysts are, for example, noble metal catalysts, partially passivated nickel catalysts, and promoted nickel catalysts. In addition, the reforming of a CO2 rich gas on an industrial scale generally requires a co-introduction of water to reduce the gas's tendency to form soot. From a thermodynamic point of view, the presence of a high concentration of CO2 and a low concentration of steam in the feedstock is advantageous in order to produce syngas with a low H2/CO ratio. However, operation under such conditions may not be feasible due to the possibility of soot formation on the catalyst.

An alternative production of syngas with a low H2/CO ratio by steam reforming is the sulfur passivated reforming (SPARG) process, which can be used to produce syngas with a relatively low H2/CO ratio. This process requires the desulfurization of the produced synthesis gas in order to obtain a synthesis gas free of sulfur.

A more detailed description of the various methods for producing low H2/CO synthesis gas can be found in the article Experience in Industrial Scale Steam Reforming of CO2 Rich Gas, P.M. Mortensen and I. Dybkjsr, Applied Catalysis A: General, 495 (2015), 141-151.

Autothermal reforming (ATR) processes represent an alternative route to syngas production, particularly when a low hydrogen to carbon monoxide ratio is required. The main elements of the ATR reactor are a burner, a combustion chamber and a catalyst bed contained within a shell lined with refractory material and resistant to high pressure. In the ATR reactor, after partial combustion of the feed hydrocarbon stream in a substoichiometric amount of oxygen, steam reforming of the partially combusted feed occurs in a fixed bed of steam reforming catalyst. Steam reforming also occurs to some extent in the combustion chamber due to the high temperature. The steam reforming reaction is followed by a water gas shift reaction. Typically, at the outlet of the reactor, the gas is at or near equilibrium with respect to the steam reforming and water gas shift reactions. The outlet gas temperature is typically in the range of 850 to 1100°C. Additional details of the ATR and a full description can be found in the literature, such as the article Generating Syngas for Fischer-Tropsch Synthesis, Chapter 4, Studies in Surface Science and Catalysis, 2004, Volume 152, p. 258-352.

The ATR uses oxygen and steam, and optionally carbon dioxide, which react with the hydrocarbon feed stream to form synthesis gas. The ratio of hydrogen and carbon monoxide in the exit gas depends on the selected process conditions, including the amount of steam and carbon dioxide introduced into the original hydrocarbon stream and/or the ATR reactor. Increasing the amount of carbon dioxide will decrease the ratio of hydrogen to carbon monoxide in the produced synthesis gas, but will increase the oxygen consumption as well as the reactor size due to the increase in flow.

In addition, it is known in the art that steam reforming can be carried out by means of heat exchange reforming. In heat exchange reforming, a hot product stream from a steam reformer or an ATR reactor is used as a heat source for the steam reforming reaction. For example, EP-0033128 and EP-0334540 describe parallel configurations in which a hydrocarbon feed stream is introduced in parallel into a radiant furnace and a heat exchange reformer. The partially reformed gas from the radiant furnace is then used as a heat source for the reforming reactions in the heat exchange reforming reactor.

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Other parallel configurations combine heat exchange reforming and autothermal reforming. European Patents EP0983963, EP1106570 and EP0504471 describe processes in which a hydrocarbon feed stream is introduced in parallel into a heat exchange reformer and an autothermal reformer. The hot synthesis gas obtained from the autothermal reforming reactor is used as a heat exchange medium for the reforming reactions taking place in the heat exchange reforming reactor.

The heat exchange reformer may also be located upstream and in series with the steam reformer or ATR reactor.

In most cases, the resulting synthesis gas leaving the heat exchange reforming reactor has a temperature of from 500 to 750°C.

Heat exchange reforming has the potential to increase overall plant efficiency as well as fuel and/or oxygen savings. However, a problem in heat exchange reforming, particularly for producing CO rich synthesis gas, is metal dusting when the hot product stream from the steam reformer or ATR reactor is cooled to provide heat for the steam reforming reaction. Metallic dusting is known in the art (see, for example, the article Production of synthesis gas for Fischer-Tropsch synthesis, chapter 4, section 2.3.4.3., Studies in Surface Science and Catalysis, 2004, volume 152, pp. 304-305 ) and is a type of corrosion that can occur when metals come into contact with CO-containing gases at temperatures between 400 and 800°C.

The object of the present invention is to provide a system and method for producing synthesis gas with a lower H ₂ /CO ratio than is normally possible in an SMR or ATR reactor, while eliminating the risk of soot formation on the catalyst used in the SMR and reducing oxygen flow rate and reactor size if an ATR reactor is used. In addition, the object of the present invention is to provide a system and method that can be used to improve existing systems and methods (based on the ATR or SMR reactor) with increased productivity. It is a further object of the present invention to provide a system and method that is more efficient than the SMR or ATR reactor. A further object of the present invention is to provide a CO-enriched synthesis gas which is a synthesis gas having an H ₂ /CO ratio below 2.5, preferably below 2.0 and more preferably below 1.8 or even below 1.6 . The term CO-enriched synthesis gas is synonymous with the term synthesis gas with a low H2/CO ratio. The term synthesis gas is used to refer to a gas containing hydrogen, carbon monoxide, and possibly also carbon dioxide and small amounts of other gases such as argon, nitrogen, etc.

The term reforming is used to refer to steam reforming according to one or more of the following reactions:

CH ₄ + H ₂ O θ CO + ZN ₂ (i)

CH ₄ + 2H ₂ O θ CO ₂ + 4H ₂ (ii)

CH ₄ + CO ₂ θ 2CO + 2H ₂ (iii)

Reactions (i) and (ii) are steam methane reforming reactions, while reaction (iii) are dry methane reforming reactions.

For higher hydrocarbons C _n Hm, where n>2, m>4, equation (i) takes the general form:

C _n Hm + pN ₂ O -► pSO + (n + t / 2) H ₂ (iv), where n> 2, m> 4.

As a rule, reforming is accompanied by a water gas shift reaction (v):

The term methane steam reforming is used to refer to reactions (i) and (ii) proceeding in the direction of the arrow from left to right, while the term methanation is used to refer to reactions that are the reverse of reactions (i) and (ii) and proceed in the direction of the arrow from right to left. Thus, the term methane steam reforming and methanation reactions is used to denote reactions (i) and (ii) proceeding in the direction of equilibrium. The term reverse water gas shift is used to denote the conversion according to reaction (v) which proceeds in the direction of the arrow from right to left. In most cases, all of these reactions are in equilibrium or close to equilibrium at the outlet of the catalytic bed or catalytic zone of the reactor in question.

Brief summary of the present invention

The following describes embodiments of the present invention. However, it should be understood that the present invention is not limited to the specific embodiments described. On the contrary, any combination of the following features and elements, whether related to various embodiments or not, is intended to carry out and practice the present invention.

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Moreover, according to various embodiments of the present invention, numerous advantages are provided over the prior art. However, while embodiments of the present invention may provide advantages over other possible solutions and/or over the prior art, the achievement of a particular advantage by this embodiment does not limit the present invention. Thus, the following aspects, features, embodiments, and advantages are merely illustrative and do not constitute elements or limitations of the appended claims, except where specifically mentioned in the claim(s). Likewise, reference to the present invention should not be construed as a generalization of any subject matter disclosed herein, and should not be construed as an element or limitation of the appended claims, except as specifically mentioned in a claim(s).

One aspect of the present invention relates to a system for producing synthesis gas. The system comprises a synthesis gas producing reactor configured to produce a first synthesis gas from a feed hydrocarbon stream, and a final converter containing a shell containing a catalyst, the catalyst exhibiting catalytic activity in methane steam reforming, methanation, and water gas reverse reforming reactions. . The final converter comprises a conduit for supplying a CO2-enriched gas stream to the mixing zone of the final converter, the mixing zone being located upstream of the catalyst of the final converter. The CO2 _- enriched gas stream in the pipeline upstream of the mixing zone is in heat exchange communication with the produced synthesis gas from the catalyst of the final converter, the gas flowing over the catalyst located downstream of the mixing zone, and/or the mixed gas . In addition, the system includes a pipeline for supplying at least a portion of the first synthesis gas from the synthesis gas producing reactor to the mixing zone of the final converter, as a result of which at least a portion of the first synthesis gas and a CO ₂ enriched gas stream are combined to form mixed gas, and the mixing zone is located upstream of the catalyst.

Finally, the final converter contains an outlet for removing produced synthesis gas from the final converter. Preferably, the conduit is wholly or substantially wholly or contained within the final converter.

The first synthesis gas is mixed with the CO2 _- rich gas stream inside the mixing zone of the final converter, and as a result, a mixed gas is obtained, after which the CO2-rich gas stream is heated by heat exchange with the obtained synthesis gas from the catalyst of the final converter, the gas flowing over the catalyst, and /or mixed gas. Thereafter, the mixed gas is passed through the catalyst bed or zone, and as a result, a second synthesis gas is obtained, which is the final synthesis gas. The catalyst is located inside the shell of the final converter and outside the pipeline, i.e. between pipeline and shell. The catalyst is present in the form of a layer or zone of catalytic material. As an alternative configuration, the catalyst is inside the shell of the final converter and outside of several pipelines, i.e. between the plurality of pipelines and the shell. A plurality of conduits serve as several points of introduction of CO ₂ . The catalyst is present in the form of a layer or zone of catalytic material. As another alternative configuration, the catalyst is within one or more tubes of the final converter while the CO2 rich gas is passed through such catalyst-filled tubes and in heat exchange communication with such catalyst-filled tubes. The final converter is heated indirectly using heat from the synthesis gas, such that the CO2-enriched gas stream is heated by heat exchange with the produced synthesis gas before being introduced into the mixing zone. As a result of this, the energy consumption of the process as a whole is reduced, for example, compared to obtaining a similar synthesis gas directly from a fired reformer. In addition, the addition of a CO ₂ rich gas to the mixing zone helps to suppress the Boudoir reaction, i.e. reactions 2CO ^ CO ₂ + C. Thus, the use of heat exchange by synthesis gas over the catalyst becomes possible without unduly increasing the risk that lowering the temperature of the gas in the mixing zone will increase the likelihood of soot formation on the downstream catalyst. Finally, since the heat exchange is carried out within the final converter, the need for an individual or separate heat exchanger is reduced or even eliminated. This makes the configuration suitable for upgrading an existing synthesis gas plant.

The term conduit is used to refer to any appropriate conduit, conduit, conduit, or other means for directing hot gas from one reactor to another. The term mixing zone upstream of the reverse reformer catalyst is used to denote that the mixing zone is located upstream of the catalyst when viewed from the direction of flow of the CO2-enriched gas stream and/or when viewed from the direction of flow of the mixed gas. The term final converter is

- 3 040289 is used to designate a reactor located downstream of a synthesis gas producing reactor, such as a methane steam reforming reactor, with steam reforming, methanation and reverse reforming of water gas proceeding towards equilibrium in the final converter. In the final converter, the synthesis gas from the synthesis gas production reactor is converted into final synthesis gas, the final synthesis gas having a lower H2/CO ratio than the synthesis gas from the synthesis gas production reactor.

In an embodiment, the synthesis gas producing reactor is a methane steam reforming reactor. The combination of a methane steam reforming reactor producing a first synthesis gas in a parallel configuration with a final converter having a conduit for supplying a CO2-enriched gas stream in heat exchange communication with a catalyst inside the final converter makes it possible to change the composition of the produced synthesis gas to produce a gas that was considered would be critical for soot formation in a typical steam methane reformer configuration, but is not critical according to the concept of the present invention. Thus, the H2/CO ratio of the resulting synthesis gas may be less than the _H2 /CO ratio only possible with a steam reformer.

According to another embodiment, the synthesis gas producing reactor is an autothermal reactor (ATR reactor). The combination of the ATR reactor producing the first synthesis gas in a parallel configuration with a final converter having a pipeline for supplying a CO ₂ enriched gas stream in heat exchange communication with a catalyst inside the final converter makes it possible to increase the amount of carbon monoxide produced per unit of oxygen consumed, and also makes it possible to reduce the size of the ATR reactor per unit of produced carbon monoxide compared to what is possible with the ATR reactor.

According to the present invention, the CO2-enriched gas stream is heated by heat exchange with the produced synthesis gas from the catalyst of the final converter, the gas flowing over the catalyst, and/or the mixed gas, and as a result, the obtained synthesis gas from the final converter is cooled compared to the case of no a pipeline configured to supply a CO ₂ enriched gas stream to the mixing zone. Therefore, at least part of the heat load required to heat the CO ₂ -rich gas stream to a temperature obtained immediately upstream of the mixing zone is supplied indirectly by cooling the first synthesis gas. Thus, this heat load required to heat the CO2-enriched gas stream need not necessarily be provided, for example, by burning natural gas. As a result, the overall efficiency of the process is increased compared to other more conventional processes where the heat load is provided by combustion. In addition, the gas flowing through the catalyst has a lower thermodynamic potential for metal dusting compared to the first synthesis gas produced in the ATR or SMR reactor due to the addition of CO2.

In addition, the temperature of the gas flowing through the catalyst is preferably from 700 to 1000°C, preferably above 800, preferably above 850 and most preferably above 900°C. At these temperatures, the thermodynamic potential for metal dusting, as expressed, for example, by the Boudoir reaction, is low compared to conditions in a conventional heat exchange reformer, thus reducing the risk of metal dusting of the catalyst material used in the final converter. The relatively high temperature of the gas flowing through the catalyst is also an advantage, since the methane content decreases as the temperature increases. Generally, the maximum temperature of the CO2 gas entering the mixing zone does not exceed a temperature that is approximately 40°C lower than the temperature of the first synthesis gas that exits the synthesis gas producing reactor, since a small difference would result in the need for a large heat exchange zone within the final converter. Preferably, the maximum temperature of the CO ₂ gas entering the mixing zone does not exceed a temperature that is approximately 60° C. lower than the temperature of the first synthesis gas that exits the synthesis gas producing reactor.

Heat exchange between the CO ₂ rich gas stream and the gas inside the final converter preferably ensures that the temperature of the CO ₂ rich gas stream at the mixing point is from about 500 to 1000°C, more preferably from 700 to 1000°C and most preferably from 800 to 1000°C . It turns out to be advantageous that the temperature of the CO2-enriched gas stream is high at the mixing point, in order to ensure that the temperature of the mixed gas in the mixing zone and thus the mixed gas in the catalyst bed or zone is high, and thus the formation of soot on the catalyst in the final converter. The temperature of the catalyst depends on the process conditions, but, as a rule, is above 750, preferably above 800, preferably 850 and most preferably above 900°C. A typical maximum catalyst temperature is approximately 1000°C.

Thus, the present invention provides an increase in the capacity of the syngas producing reactor, with the final converter providing an increase in the production of carbon monoxide. In addition, the system provides control of the composition of the synthesis gas, since the addition of a CO2-enriched gas stream allows for lower H2/CO ratios than the ratios

H2/CO typically produced in a single syngas producing reactor.

The term low H2/CO synthesis gas is synonymous with the term CO rich synthesis gas and is used to refer to synthesis gas having an H2/CO ratio below 2.5, preferably synthesis gas having an H2/CO ratio below 2.0, preferably syngas having an H2/CO ratio below 1.8, and even more preferably syngas having an H2/CO ratio below 1.6. In addition, the term CO2 rich gas is used to refer to a gas stream in which the dry CO ₂ content is at least 50 mol%, for example at least 70 mol%, including at least 90 mol%.

In this context, the term O/C or O/C ratio is an abbreviation for the atomic ratio of oxygen and carbon. The ratio of oxygen to carbon is the ratio of the number of moles of oxygen and the number of moles of carbon in the gas. In addition, the term H/C or H/C ratio is an abbreviation for the atomic ratio of hydrogen and carbon. The ratio of hydrogen to carbon is the ratio of the number of moles of hydrogen and the number of moles of carbon in the gas. In addition, the term S/C or S/C ratio is an abbreviation for the ratio of steam and carbon. The vapor to carbon ratio is the ratio of the number of moles of vapor and the number of moles of carbon in hydrocarbons in the gas. Thus, S/C is the total number of moles of vapor divided by the total number of moles of carbon in hydrocarbons in the gas. It should be noted that the term C in the S/C ratio is thus different from the term C in the H/C and O/C ratios, since in the S/C ratio the term C means only carbon in the composition of hydrocarbons, while in the ratios O/C and H/C The term C means all the carbon in the gas.

The resulting synthesis gas discharged from the final converter may be subjected to further processing steps downstream of the final converter, such as separation in a separation unit. For example, CO ₂ can be isolated from the resulting synthesis gas. The separating unit may be a contact degassing unit, a pressure swing adsorption (PSA) block, a temperature swing pressure swing adsorption (TSA) block, a membrane block, a _CO2 washing block, or a combination of a CO2 separation block and a refrigeration block. A refrigeration block is defined as a cryogenic process for separating a mixture of H ₂ , CO and other gases into a stream of relatively pure CO, a stream of relatively pure H ₂ and the remainder of the stream containing what remains of the original stream.

The term contact degassing means a phase separating unit in which a stream is separated into liquid and gas phases according to thermodynamic phase equilibrium at a given temperature.

The term CO2 washing unit means a unit that uses a method such as chemical absorption to separate CO2 from the process gas. In a chemical absorption process, a CO ₂ containing gas is passed over a solvent which reacts with the CO ₂ and thus binds it. In most cases, chemical solvents are amines classified as primary amines such as monoethanolamine (MEA) and diglycolamine (DGA), secondary amines such as diethanolamine (DEA) and diisopropanolamine (DIPA), or tertiary amines such as triethanolamine (TEA ) and methyldiethanolamine (MDEA), but ammonia and solutions of alkali metal carbonates such as K ₂ CO ₃ and Na ₂ CO ₃ can also be used.

The term swing adsorption unit means an adsorption unit that separates heavier gases (such as CO2) from less heavy gases (such as H2). In equipment of this type, a dynamic balance is established between the adsorption and desorption of heavy gases on the adsorbent material. Adsorption can be caused by steric, kinetic or equilibrium effects. The exact mechanism will be determined by the adsorbent used and the equilibrium saturation will depend on temperature and pressure. Typically, the adsorbent material is treated in the process gas near saturation and regeneration is required thereafter. Regeneration can be carried out by changing the pressure or temperature. In practice, this means carrying out the process using two reactors, wherein the adsorbent is saturated at high pressure or low temperature first in one reactor, and then the reactor is switched to now desorb heavy gases from the same reactor by decreasing the pressure or increasing the temperature.

Membrane separation means a method carried out on at least a partially permeable barrier, for example made of a polymer, where the transport of individual gas particles occurs at different rates determined by their permeability. This ensures that the component is concentrated or diluted in the membrane retentate.

Cryogenic separation means a process using the phase change of various particles in a gas in order to isolate the individual components from a gas mixture by controlling the temperature.

The synthesis gas producing reactor comprises a first inlet for introducing a feed hydrocarbon stream, possibly together with carbon dioxide and steam, into the synthesis gas producing reactor, and possibly with a separate inlet for introducing an oxygen-containing stream, and an outlet for removing the first synthesis -gas. The system may include a device that allows at least a portion of the first synthesis gas to bypass the final converter. This bypass of the first synthesis gas may then be combined with the resulting synthesis gas from the final converter, resulting in a second production synthesis gas.

The term hydrocarbon feed stream is used to refer to a feed stream containing a hydrocarbon gas containing one or more hydrocarbons and possibly other constituents such as CO2 and/or steam. Examples of hydrocarbon gas may be natural gas, city gas, methane, or a mixture of methane and higher hydrocarbons. Typically, the original hydrocarbon stream is a hydrocarbon gas stream containing small amounts of hydrogen, carbon monoxide, carbon dioxide, nitrogen, argon, or combinations thereof, which supplement the steam and possibly carbon dioxide added to the hydrocarbon gas.

For reforming processes, an example of a hydrocarbon gas stream and steam is, for example, a mixture containing methane, steam, and optionally other gaseous oxidizers such as carbon dioxide. Another example of a hydrocarbon gas stream and steam is a desulfurized and pre-reformed natural gas and steam stream.

The term hydrocarbon feed stream is used to refer to a gas stream containing a hydrocarbon gas stream and possibly also steam, carbon dioxide, or other gases.

Typically, the hydrocarbon feed stream must be desulfurized to remove any sulfur contained in the feed, thereby preventing deactivation of the catalysts used in the process.

Optionally, the original hydrocarbon stream can also be subjected to adiabatic pre-reforming according to reaction (iv) in a temperature range of approximately 350 to 550°C, to convert higher hydrocarbons as an initial process step. Adiabatic pre-reforming typically occurs downstream of desulfurization. Pre-reforming eliminates the risk of higher hydrocarbon soot formation on the catalyst in downstream process steps. An example of a hydrocarbon feed stream is a desulfurized and pre-reformed natural gas and steam stream.

It should be understood that the terms inlet and outlet are not intended to be limiting. Thus, these terms also include the possibility that the units, for example producing synthesis gas reactor, contain more than one inlet and/or outlet.

In other embodiments, the synthesis gas producing reactor of the system is a thermal partial oxidation reactor or a catalytic partial oxidation reactor.

In the case of a thermal partial oxidation (TPOX) reactor, the hydrocarbon feed stream and the oxidizer are reacted thermally without a catalyst in a refractory lined reactor at high temperature. The temperature of the synthesis gas exiting the TROX reactor often exceeds 1200 to 1300° C. or higher. No catalyst is present. Little or no steam or carbon dioxide is added to the hydrocarbon feed stream, as this may contribute to the formation of soot. An autothermal reformer and a thermal partial oxidation reactor are particularly preferred as syngas producing reactors due to the high temperature attainable of the first syngas leaving the reactor.

Thus, the present invention can be used when an SMR reactor, an ATR reactor, a thermal partial oxidation reactor, or a catalytic partial oxidation reactor is combined with a gas-heated final converter. The present invention can also be used where the synthesis gas producing reactor comprises an SMR reactor located upstream and in series with the ATR reactor.

According to an embodiment, the conduit comprises a first portion configured to introduce the CO ₂ -rich gas stream into heat exchange communication with the produced synthesis gas. As a result, the CO ₂ -enriched gas stream is heated by heat exchange through the part of the final converter where the catalyst is located, and through the first part of the pipeline. The first conduit portion is an upstream portion of the conduit where the gas within the conduit is in heat exchange relationship with the gas flowing over the catalyst as seen from the direction of flow of the CO2 rich gas stream.

According to an embodiment, the conduit comprises a second portion configured to introduce the CO2-enriched gas stream into heat exchange communication with the mixed gas in the mixing zone. As a result, the CO2-enriched gas stream is heated by heat exchange through the part of the final converter where the catalyst is located, and through the second part of the pipeline. The second part of the pipeline is the downstream

- 6 040289 part of the pipeline where the gas inside the pipeline is in heat exchange relationship with the gas flowing over the catalyst, as seen from the direction of movement of the CO2-enriched gas stream.

According to an embodiment, the CO2-enriched gas stream is heated in a fired heater, in an electric heater, by heat exchange with at least a portion of the produced synthesis gas exiting the final converter and/or by heat exchange with superheated steam before entering the final converter. The temperature of the CO2-enriched gas stream before entering the final converter is, for example, 200 to 600°C, more preferably 300 to 500°C. When the CO ₂ rich gas stream is heated before entering the final converter, the Boudoir reaction is suppressed. As a result, the risk of metal dusting is reduced.

In an embodiment, the catalyst is a steam reforming catalyst. The steam reforming catalyst is also referred to as methane steam reforming catalyst or methane reforming catalyst. Examples of steam reforming catalysts are Ni/MgAl2O4, Ni/Al ₂ O ₃ , Ni/CaAkO4, Ru/MgAl2O4, Rh/MgAl2O4, Ir/MgAl2O4, M02C, W2C, CeO2, Al ₂ O ₃ supported noble metal, but are other catalysts suitable for reforming are also acceptable. The steam reforming catalyst is configured to catalyze the steam reforming reaction of methane; however, since the gas entering the final converter is a synthesis gas stream containing hydrogen and carbon monoxide, all reactions of methane steam reforming, methanation, and reverse reforming of water gas occur in the final converter, and the total content of methane, steam, and carbon monoxide in gas discharged from the final converter.

Another aspect of the present invention relates to a process for producing synthesis gas, comprising: obtaining a first synthesis gas from a hydrocarbon feed stream in a synthesis gas producing reactor;

feeding the CO2-enriched gas stream to the mixing zone of the final converter through a pipeline, wherein the CO2 _- rich gas stream in the pipeline upstream of the mixing zone is in heat exchange communication with the gas flowing over the catalyst, before mixing the CO2 _- rich gas stream, at least least with a portion of the first synthesis gas in the mixing zone;

supplying at least a portion of the first synthesis gas from the synthesis gas producing reactor to the mixing zone of the final converter through a conduit, thereby combining at least a portion of the first synthesis gas and a CO2-enriched gas stream to form a mixed gas, the final converter comprising a shell inside which the catalyst is located, and the catalyst exhibits catalytic activity in the reactions of steam reforming of methane, methanation and reverse conversion of water gas, and the mixing zone is located upstream of the catalyst;

obtaining the obtained synthesis gas from the mixed gas by carrying out the reactions of methane steam reforming, methanation and reverse shifting of water gas over a catalyst; and discharging the resulting synthesis gas from the final converter.

The method and its embodiments provide similar benefits as described with respect to the system of the present invention. Thus, they will not be described in further detail herein.

Brief description of the figures

An embodiment of the present invention is explained by way of example with reference to the drawing. It should be noted that the accompanying drawing illustrates only an exemplary embodiment of the present invention and thus should not be construed as limiting the scope of the present invention as it may allow for other embodiments of equal effectiveness.

The drawing is a schematic drawing of a system for producing synthesis gas according to an embodiment of the present invention.

Detailed disclosure of the present invention

The drawing shows a system 100 for producing produced synthesis gas 12. The system 100 includes a synthesis gas producing reactor 10 configured to produce a first synthesis gas 5 from a feed hydrocarbon stream 3. According to the embodiment shown in the drawing, the synthesis gas producing reactor 10 is an autothermal reforming reactor (ATR).

The hydrocarbon feed stream 3 to the ATR reactor 10 consists of a hydrocarbon gas stream 1, such as natural gas, with which steam and possibly CO2 stream 2 is combined. The combination of hydrocarbon gas stream 1 and steam stream 2 and possibly CO2 is the original hydrocarbon stream 3 introduced into the ATR 10 reactor.

An oxygen-containing stream 4, such as air, a steam and oxygen stream, an oxygen-enriched stream or substantially pure oxygen, is introduced into the ATR 10 reactor through an inlet. In the ATR 10 reactor after

- 7 040289 partial combustion of the original hydrocarbon stream 3 with a substoichiometric amount of oxygen in the oxygen-containing stream 4, steam reforming of the partially burnt source material in the fixed bed 11 of the steam reforming catalyst is carried out, and as a result, the first synthesis gas 5 is obtained containing hydrogen, carbon monoxide and dioxide carbon. The first synthesis gas 5 exiting the ATR 10 typically has a temperature of from about 900 to about 1100°C, including about 1000°C.

In addition, the system 100 contains the final converter 20 containing the shell 22, which contains the catalyst layer 21.

The system 100 includes a conduit (not shown) for supplying at least a portion of the first synthesis gas 5 from the synthesis gas producing reactor to the mixing zone 20c of the final converter 20. The final converter 20 also has a conduit 23 for supplying CO ₂ enriched gas flow 6 to the mixing zone 20c of the final converter 20, such that the CO2-enriched gas stream in the conduit upstream of the mixing zone 20c is in heat exchange communication with the gas flowing over the catalyst 21, i.e. downstream of the mixing zone, prior to mixing with at least a portion of the first synthesis gas 5 in the mixing zone 20c. According to the embodiment shown in the drawing, the catalyst 21 is located inside the shell of the final converter 20 and outside the conduit 23, i.e. between shell 22 and pipeline 23.

In the final converter 20, there are three zones or parts: a mixing zone 20c, a catalyst zone 20b, and a product gas zone 20a. Accordingly, three parts are present in conduit 23: the first part, where the CO2-enriched gas stream 6 is passed inside conduit 23 in heat exchange communication with the produced synthesis gas in the produced gas zone 20a; the second part, where the CO2-enriched gas stream 6 is passed inside the conduit 23 in heat exchange communication with the gas in the catalyst zone 20b; and the third part, where the CO2-enriched gas stream 6 is passed inside the conduit 23 in heat exchange communication with the mixed gas in the mixing zone 20c. The length of the mixing zone 20c and/or the product gas zone 20a in the direction of the longitudinal axis (not shown in the drawing) can be relatively small, for example in the case where the catalyst zone 20b is relatively large.

The final converter 20 also includes an outlet for removing produced synthesis gas 12 from the final converter 20.

In system 100, the first synthesis gas 5 is used as a heat source in the final converter 20. However, the CO2-enriched gas stream 6 may be preheated before being introduced into the final converter 20 via conduit 23.

Catalyst 21 carries out the reactions of methane steam reforming, methanation and water gas reverse reforming of the mixed gas, and as a result, produces a final synthesis gas 12. pipeline parts 23.

Arrows 25 show the direction of movement of the CO ₂ -rich gas stream 6 from inside conduit 23. In the mixing zone 20c, the first synthesis gas 5 and the CO2-rich gas stream 6 are mixed to form a mixed synthesis gas.

Example

An approximate technological calculation is presented below in table. 1. An initial hydrocarbon stream containing hydrocarbon gas, CO2 and steam and having an S/C ratio of 0.6 is introduced into the ATR 10 reactor according to the present invention, as shown in the drawing. The original hydrocarbon stream is heated to 650° C. before being introduced into the ATR reactor 10. The oxygen enriched stream 4 is added and its quantity is adjusted so that the temperature of the first synthesis gas 5 is 1050° C. The first synthesis gas 5 is produced in the ATR 10 reactor.

The total flow of all components in all streams entering the ATR reactor, and the flow of all components in the first synthesis gas 5 are presented in the column under the heading ATR 10 in table. 1.

The CO2 _- enriched gas stream is introduced into the pipeline and heated in the pipeline to a temperature of 988° C. by heat exchange with the gas flowing between the pipeline and the shell in the mixing zone 20c, the catalyst zone 20b and the product gas zone 20a. The CO ₂ -rich gas stream is mixed with the first synthesis gas to obtain a mixed synthesis gas having a temperature of 1038°C.

Within the catalyst zone 20b of the final converter 20, the combined stream is brought into equilibrium, i. e. balance the reactions of water gas reverse shift, methanation and reforming. At the outlet, the temperature of the resulting synthesis gas 12 leaving the final converter 20 is approximately 995° C., which is well below the methane decomposition equilibrium temperature for the gas (1349° C.) and above the Boudouard reaction equilibrium temperature for the gas (860° C.). Therefore, the resulting synthesis gas 12 does not have the potential to form soot.

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Table 1

Reactor ATR 10 CO ₂ rich gas stream 6 Catalytic layer of the final converter 20 Output from final converter 20 Temperature at 650 180 1038 inlet [°C] Temperature at 1050 988 995 853 outlet [°C] Gauge 35.5 35.5 34.5 34 pressure on inlet [kg/ ^cm2 ] Gauge 34.5 34.5 34 33.5 pressure on release [kg / cm ² ] Temperature - - 1349 decomposition methane on outlet [°C] Temperature 891 - 860 Boudoir reactions outlet [°C] Inlet: N ₂ [Nm ³ /h] 26 245 CO ₂ [Nm ³ /h] 8487 11615 17583 CH ₄ [Nm ³ /h] 18695 373 N ₂ [Nm ³ /h] 394 31372 H ₂ O [Nm ³ /h] 11321 16988 CO [Nm ³ /h] 0 20842 Oxygen inlet: About ₂ [Nm ³ /h] 10735 N ₂ [Nm ³ /h] 219 Temperature 371 oxygen on inlet [°C] Release: N ₂ [Nm ³ /h] 245 245 245 CO ₂ [Nm ³ /h] 5968 11615 12720 12720 CH ₄ [Nm ³ /h] 373 392 392 N ₂ [Nm ³ /h] 31372 26451 26451 H ₂ O [Nm ³ /h] 16988 21870 21870 CO [Nm ³ /h] 20842 25685 25685 Full flow on 75788 outlet [Nm ³ /h]

Thus, when the system and method is used, it is possible to provide the resulting synthesis gas having a relatively high CO content. In the example of Table. 1, the H2/CO ratio is 1.0, while the H/C and O/C ratios are 2.5 and 1.9, respectively.

In this context, the decomposition temperature of methane (T(MDC)) is calculated as the temperature at which the equilibrium constant of the reaction of decomposition of methane to form graphite (CH ₄ ^C+2H ₂ ) is equal to the reaction coefficient (QC) of the gas. The formation of carbon in the form of graphite can occur when the temperature is higher than this temperature.

The reaction coefficient QC is defined as the ratio of the square of the partial pressure of hydrogen and the partial pressure of methane, i.e.

QC \u003d P ² n ₂ / Rsn ₄ .

The Boudouard reaction temperature (T(BOU)) is calculated in a similar manner, but for the Boudoir reaction (2CO^C+CO ₂ ), in which case the formation of carbon in the form of graphite can occur when the temperature is lower than this Boudoir reaction temperature.

In table. 2 shows a comparative example of the corresponding values for producing a similar synthesis gas in a system with an ATR reactor but without an adiabatic final converter, which is referred to here as a stand-alone ATR reactor. In this case, all CO2 is introduced in advance into the ATR reactor, which is operated at an S/C ratio of 0.6. A comparison of examples shows that more oxygen is required for a stand-alone reactor.

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Claims (11)

From Table. 1 and 2 it can be seen that the discharge stream from the ATR in the case of the present invention is less than in the case of a stand-alone ATR. This means that by using the ideas of the present invention, a smaller ATR reactor can be designed. This also means that in the case of improvements, the production of carbon monoxide can be increased without the need to increase the given ATR reactor. This is done by introducing a final converter to form the system and applying the method according to the present invention. The oxygen consumption (calculated as the ratio of O ₂ consumed to CO produced [Nm ³ /Nm ³ ]) is 0.418 compared to 0.457 for the stand-alone ATR. Therefore, according to the present invention, oxygen is saved, which reduces the capital cost of an air separation unit to produce oxygen. CLAIM 1. A system for producing synthesis gas, comprising: producing synthesis gas reactor, configured to obtain the first synthesis gas from the original hydrocarbon stream; and a final converter containing a shell inside which is a catalyst, and the aforementioned catalyst exhibits catalytic activity in the reactions of methane steam reforming, methanation and reverse conversion of water gas; wherein the aforementioned final converter comprises a conduit for supplying a CO ₂ enriched gas stream to a mixing zone of the aforementioned final converter, wherein the aforementioned mixing zone is located upstream of the aforementioned catalyst, while the aforementioned CO ₂ enriched gas stream in the aforementioned pipeline is located upstream of the aforementioned mixing zone in heat exchange relationship with the gas flowing over the aforementioned catalyst, located - 10 040289 downstream of the mixing zone, wherein said system further comprises a conduit for supplying at least a portion of said first synthesis gas from said synthesis gas producing reactor to said mixing zone of said final converter, and as a result whereby at least a portion of said first synthesis gas and said CO2-enriched gas stream are combined to form a mixed gas, said final converter further comprising an outlet for removing produced synthesis gas from said final converter. 2. The system of claim 1, wherein said synthesis gas producing reactor is an autothermal reformer, a thermal partial oxidation reactor, a catalytic partial oxidation reactor, or a steam methane reformer. 3. The system according to claim 1 or 2, wherein said conduit comprises a first portion configured to introduce said CO2-enriched gas stream into heat exchange communication with said produced synthesis gas. 4. A system according to any one of claims 1 to 3, wherein said conduit comprises a second portion configured to introduce said CO2 _- enriched gas stream into heat exchange communication with a mixed gas in said mixing zone. 5. A system according to any one of claims 1 to 4, wherein the catalyst is a steam reforming catalyst. 6. A method for producing synthesis gas, including: obtaining a first synthesis gas from the original hydrocarbon stream in producing synthesis gas reactor; supplying a CO2-enriched gas stream to the mixing zone of the final converter through a pipeline, wherein the aforementioned final converter comprises a shell inside which the catalyst is located, while the aforementioned CO2-enriched gas stream in the aforementioned pipeline upstream of the aforementioned mixing zone is in heat exchange communication with the gas flowing above a catalyst, before mixing the aforementioned CO ₂ rich gas stream with at least a portion of the first synthesis gas in the aforementioned mixing zone; feeding at least a portion of said first synthesis gas from said synthesis gas producing reactor into a mixing zone of said final converter via a conduit and thereby combining at least a portion of said first synthesis gas and said CO2-enriched gas stream with forming a mixed gas, wherein in the aforementioned final converter, the aforementioned catalyst exhibits catalytic activity in the reactions of methane steam reforming, methanation, and water gas reverse shift, and wherein the aforementioned mixing zone is located upstream of the aforementioned catalyst; obtaining as a product of synthesis gas from the aforementioned mixed gas by carrying out the reactions of methane steam reforming, methanation and reverse shifting of water gas over the aforementioned catalyst; and discharging said produced synthesis gas from said final converter. 7. The method of claim 6, wherein said synthesis gas producing reactor is an autothermal reforming reactor, a partial oxidation reactor, a catalytic partial oxidation reactor, or a steam methane reforming reactor. 8. The method according to claim 6 or 7, wherein said CO2-enriched gas stream is introduced into heat exchange communication with said synthesis gas produced upstream of said catalyst. 9. The process according to any one of claims 6 to 8, wherein said CO2-enriched gas stream is introduced into heat exchange communication with a mixed gas in said mixing zone downstream of said catalyst. 10. A process according to any one of claims 6 to 9, wherein said CO2-enriched gas stream is heated in a fired heater, in an electric heater, by heat exchange with at least a portion of the produced synthesis gas leaving the final converter, and/or by heat exchange with superheated steam before entering the final converter. 11. A process according to any one of claims 6 to 10, wherein the catalyst is a steam reforming catalyst. -