Method for producing synthesis gas using exogenous CO2 without carbon fuel

Abstract

A process for producing a synthesis gas having an H2 / CO ratio of 0.5 to 3.5 comprising: a) combusting hydrogen and oxygen in an H2 burner in the presence of steam to produce steam, b) quenching the effluent of step a); c) electrolyzing the steam of step b) in a solid oxide electrolysis cell (SOEC), thereby obtaining hydrogen and oxygen, d) cooling the wet hydrogen of step c) and removing moisture by condensation; e) performing a reverse water-gas shift reaction on the hydrogen in the step d) and CO2 from an external source to obtain synthesis gas; f) cooling the wet synthesis gas of step e) and removing moisture by condensation, thereby obtaining a dry synthesis gas.

Description

Field of the Invention

[0001] The present invention relates to a method for producing synthesis gas using only CO2 from an external source as a carbon source.

[0002] The conventional method of producing synthesis gas is typically in the presence of large amounts of methane, which is a reactant in a typical reforming reaction:

[0003] CH4+CO2→2CO+2H2

[0004] CH4+H2O→CO+3H2

[0005] It is also the fuel needed for combustion reactions.

[0006] CH4+2O2→CO2+2H2O

[0007] Provides the energy required for the above-mentioned endothermic reforming reaction, and provides part of the steam and CO2 used as reactants in the above-mentioned reaction.

[0008] However, it is now considered necessary to produce syngas to reduce carbon fuels that produce large amounts of greenhouse CO2. Summary of the invention

[0009] The Applicant has now discovered that the disadvantages of conventional methods for producing synthesis gas using as the sole carbon source waste CO2 separated from flue gases or from other production processes (such as calcination in cement or steel production) can be overcome by the process of the present invention.

[0010] The method of the present invention comprises the following steps:

[0011] a) Combustion of hydrogen and oxygen in a H2 burner in the presence of steam at a temperature above 1000°C and a pressure of 10 to 40 bar to generate steam according to the following reaction scheme:

[0012] [R1]H2+0.5O2→H2O

[0013] b) quenching and optionally further cooling the effluent of step a) at a temperature of 800 to 900° C.;

[0014] c) electrolyzing the steam from step b) in a solid oxide electrolysis cell (SOEC) at a temperature of 800 to 900° C. and a pressure of 10 to 40 bar to obtain hydrogen and oxygen;

[0015] d) cooling the wet hydrogen from step c) and removing water by condensation;

[0016] e) according to the following reaction scheme, the hydrogen from step d) and an external source of CO2 Perform the reverse water gas shift reaction:

[0017] [R2]CO2+H2=CO+H2O

[0018] Synthesis gas is thus obtained, provided that the hydrogen is fed in the step in an amount of 0.5 to 3 moles relative to CO2;

[0019] f) cooling the wet synthesis gas of step e) and removing water, thereby obtaining a dry synthesis gas having the desired H2 / CO ratio. Another subject of the present invention is an apparatus for implementing the process according to the invention, comprising:

[0020] A) a H2 burner unit for performing step a), which is in direct fluid communication with a steam quencher for performing step b),

[0021] B) a steam quench for performing step b), which is in fluid communication with the H2 burner and the solid oxide electrolysis cell (SOEC) unit,

[0022] C) a solid oxide electrolysis cell for performing step c), in fluid communication with a H2 burner unit and a reverse water gas shift reaction unit;

[0023] D) The water-gas shift reaction unit is in fluid communication with the H2 burner and the solid oxide electrolysis cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural diagram of the method of the present invention.

[0025] Figure 2 is a schematic diagram of a particularly preferred embodiment of the device according to the invention.

[0026] Figure 3 is a graph where the left ordinate represents the reported power in kWh / kg H2 produced, the abscissa represents the outlet temperature of the SOEC, the right ordinate represents the inlet temperature of the SOEC, and x represents the mole fraction of steam converted after electrolysis.

[0027] Figure 4 is a schematic diagram of another preferred form of apparatus according to the invention.

[0028] Figure 5 A steam spreadsheet obtained by Aspen Hysys v11 simulation of the equipment reported in the figure above is reported.

[0029] Figure 6 A further preferred embodiment of the device according to the invention is reported.

[0030] Figure 7 A further preferred embodiment of the device according to the invention is reported.

[0031] Figure 8 A further preferred embodiment of the device according to the invention is reported. DETAILED DESCRIPTION

[0032] For the purposes of the present invention, the term "comprising" does not exclude the possibility of taking into account further components / steps that are not explicitly mentioned in the list following the wording.

[0033] The words “consisting of” exclude this possibility.

[0034] The term "equipment" comprises one or more units selected from separators or splitters, heat exchange systems, waste heat boilers, water condensers and reactors (such as H2 burners, SOECs, reverse water gas shift reactors) or units that internally include one or more of the above reaction units, heat exchange systems, etc.

[0035] For the purposes of the present invention, as exogenous CO 2 , CO 2 from an external source refers to waste CO 2 from flue gases or calcination, which has been separated beforehand in an absorption tower, a pressure swing absorption unit or the like.

[0036] Figure 1 The block diagram of the method and apparatus of the present invention is reported.

[0037] Step a) of the process according to the invention is preferably carried out in an H2 burner at a temperature above 1100° C., even more preferably at a temperature of 1100 to 1300° C. It is preferably carried out at a pressure of 30 bar.

[0038] In step a), steam is added in a molar amount preferably in the range of 1 to 4 relative to the sum of the molar amounts of hydrogen and oxygen supplied.

[0039] In step b), the hot effluent is cooled to a temperature of 850° C. at a pressure of 30 bar.

[0040] Step b) can be carried out in a quench unit by using a cooler steam stream as cooling fluid. In this case, the quench steam stream can preferably be further cooled in a boiler, wherein a pressurized cold water stream, preferably at a pressure of 30 bar, is used as cooling fluid.

[0041] In an alternative, when only quenching is carried out in step b), it is carried out in a quencher in which the hot effluent of step a) is directly contacted with a pressurized cold water stream at a pressure of 10 to 40 bar, preferably 30 bar.

[0042] The electrolysis step carried out in the SOEC unit is preferably carried out at 850°C, which is reported by M. Hillestad et al. in "Improving carbon efficiency and profitability of the biomass to liquid process with hydrogen from renewable power" Fuel 234 (2018) 1431–1451 Figure 2 The optimum temperature is derived from the graph.

[0043] The oxygen produced in step c) is pure oxygen and is preferably partially recycled in step a) while the remainder is stored for sale as high purity oxygen.

[0044] The hydrogen is preferably completely consumed: a part is used as feed to an H2 burner to generate the required steam, while the remainder is fed in step e) to a reverse water-gas shift reactor, where there will also be an exogenous CO2 feed.

[0045] The hydrogen leaving the SOEC is wet, so before being subjected to the reverse water gas shift reaction it is cooled in step d) and the water is removed by condensation.

[0046] The process can produce a synthesis gas with a H2 / CO ratio between 0.5 and 3.5.

[0047] In this case, 0.5 to 3.5 mol (relative to CO 2 ) of H 2 has to be fed to the reverse water gas shift reactor.

[0048] In order to obtain a H2 / CO ratio preferably in the range of 1 to 3.5, hydrogen must be added in an amount of 1 to 3.5 mol relative to the molar amount of CO2 in reaction [R2], and in order to obtain a synthesis gas with a H2 / CO ratio of 2 to 3.5 in the same step, H2[R2] is preferably added in an amount of 2 to 3.5 mol relative to CO2.

[0049] The process of the invention preferably comprises, in step b), dividing the steam stream leaving the boiler or the steam stream leaving the quencher into two streams, wherein the first stream is sent to the SOEC and the second stream is sent to a turbine and expanded, or alternatively, is recycled to step a) after prior cooling.

[0050] According to a particularly preferred embodiment of the device of the present invention, Figure 3 As shown, wherein units A), B) and D) are contained in a single unit, which unit comprises:

[0051] i) as the shell of the H2 burner, coinciding with unit A);

[0052] ii) the housing surrounds the tube bundle coinciding with unit C);

[0053] iii) the housing comprises a steam quench unit, coinciding with unit B),

[0054] The unit also features:

[0055] Three inlets for H2, O2 and steam on the shell side;

[0056] · Shell side hot effluent outlet;

[0057] The shell side cold water inlet (CW) is in fluid communication with the quench unit;

[0058] inlets for introducing reactants on the tube side, and

[0059] Synthesis gas outlet formed on the tube side.

[0060] Preferably, the quencher or quench unit iii) is of direct type selected from a nozzle crown, or of indirect type selected from a heat exchanger or a waste heat boiler.

[0061] Preferably, the outlet of the shell side effluent is located at the top of the unit, the inlet of the tube side reactants is located at the top of the unit, and the outlet of the tube side effluent is located at the bottom of the unit, and the steam quench unit is located at the top of the unit, such as Figure 3 shown.

[0062] In this case, the process of the invention is carried out according to the following steps: oxygen, hydrogen and steam enter from the bottom of the shell side, while CO2 and H2 enter from the top of the tube side of the unit. The tubes are heated by the exothermic reaction occurring on the shell side, whereby the endothermic reverse water-gas shift reaction occurs, and the synthesis gas produced leaves the unit from the bottom, while the steam used to mitigate the combustion occurring on the shell side and the hot effluent formed in said combustion enter the cooling zone, where the temperature is adjusted by contact with cold water through the nozzle crown, before leaving the unit and being partly supplied to the SOEC.

[0063] According to another embodiment of the present apparatus, the outlet for the shell side effluent is located at the bottom of the unit, the inlet for the tube side reactant is located at the bottom of the unit, and the outlet for the tube side effluent is located at the top of the unit, and the shell side steam quenching unit is located at the bottom of the unit.

[0064] Figure 4Another embodiment of the device is reported, in which H2 (H2 fuel) O2 (O2 inlet, O2 IN) and steam (steam input, STEAM IN) are burned to produce heat and additional steam (flue gas, FLUE GAS). The flue gas contains only steam and a very small amount of residual (exceeding the stoichiometric) oxygen. Due to the high temperature of the flue gas flow, it is necessary to use steam for quenching (steam quenching, STEAM QUENCH). The steam leaving the quenching unit is then further cooled in boiler 1 to 850°C, which is the steam temperature of the SOEC feed. The released heat is used to generate steam (steam 1, STEAM1). The cooled steam (to separator, TO SPLITTER) is then sent to a steam separator. Part of the superheated steam is expanded in the turbine unit, and the remaining part (to SOEC) is sent to the SOEC unit. The oxygen thus produced (O2 SOEC) is in serious excess with respect to the oxygen required in the H2 burner. The wet hydrogen gas stream (wet H2, WET H2) is sent to a cooling system (boiler 2, BOILER 2), and then to a dehydration flash condenser (H2 dehydration, DEWAT H2).

[0065] Dry hydrogen (H2) is split into a first stream (TO BURNER) and recycled back to the burner to maintain the flame, while the other stream (H2 RWGS) is mixed with an external CO2 stream. The resulting stream (RWGS mixture, RWGSMIX) is preheated in HE1 and the warm stream is fed to the RWGS unit where an endothermic reverse water gas shift reaction occurs. The resulting wet syngas is cooled in boiler 3 and dehydrated in a dehydration unit.

[0066] Remove moisture. The pretreated syngas has the best SN and H2 / CO>3 for methanol synthesis. Through heat recovery, excess steam (STEAM EXCESS) can be collected, which is combined with steam 1 (STEAM1) to meet the steam demand (STEAM IN) in the H2 burner (H2 BURNER).

[0067] Figure 5 The simulation of the Figure 4 Report the corresponding steam flows obtained from the simulations performed on the equipment in a spreadsheet.

[0068] Figure 6 yes Figure 4 Another preferred embodiment of the device disclosed in Figure 4 The difference of the equipment is that the flue gases are no longer quenched by an indirect method, but by direct contact with pressurized water.

[0069] Figure 7A similar Figure 4 Public devices, but with the following two differences:

[0070] Flue gas steam is quenched by direct contact with cold pressurized water.

[0071] • In addition, since the turbine is removed, the SH STEAM is a free steam flow, which can be further cooled and then recirculated to the H2 BURNER.

[0072] Figure 8 Public Figure 4 Another preferred embodiment of the device, which Figure 4 The plant reported in the invention differs in that there is no turbine, therefore the superheated steam (SH STEAM) is free steam which can be further cooled and then recycled to H2 Burner (H2 BURNER).

Claims

1. A method for producing synthesis gas having a H2 / CO ratio of 0.5 to 3.5, comprising: a) Combustion of hydrogen and oxygen in the presence of steam in a H2 burner to produce steam at a temperature above 1000°C (preferably above 1100°C, more preferably between 1200 and 1300°C) and a pressure of 20 to 40 bar (preferably 30 bar) according to the following reaction scheme: [R1]H2+0.5O2→H2O b) quenching and optionally further cooling the effluent of step a) at a temperature of 800 to 900° C., preferably at 850° C., at a pressure of 10 to 40 bar, preferably 30 bar; c) electrolyzing the steam from step b) in a solid oxide electrolysis cell (SOEC) at a temperature of 800 to 900° C. and a pressure of 10 to 40 bar, preferably 30 bar, to obtain hydrogen and oxygen; d) cooling the wet hydrogen from step c) and removing water by condensation; e) subjecting the hydrogen from step d) to a reverse water gas shift reaction with CO2 from an external source according to the following reaction scheme: [R2]CO2+H2=CO+H2O Synthesis gas is thereby obtained, provided that the hydrogen is fed in the reactor in an amount of 0.5 to 3.5 moles relative to CO2, thereby obtaining wet synthesis gas; f) cooling the wet synthesis gas of step e) and removing moisture, thereby obtaining a dry synthesis gas having a desired H2 / CO ratio.

2. The method according to claim 1, wherein in step e), hydrogen is fed in an amount of 1 to 3.5 moles relative to the molar amount of CO2, thereby producing a synthesis gas with a H2 / CO ratio of 1 to 3.

5.

3. The process according to claim 1 or 2, wherein in step e), hydrogen is fed in an amount of 2 to 3.5 moles relative to the molar amount of CO2, thereby producing a synthesis gas with a H2 / CO ratio of between 2 and 3.

5.

4. The method according to any one of claims 1 to 3, wherein in step a), steam is added in an amount ranging from 1 to 4 moles relative to the sum of the molar amounts of hydrogen and oxygen supplied.

5. The method according to any one of claims 1 to 4, wherein in step b), quenching is carried out in a quenching unit by passing a steam stream alone as a cooling fluid, and the quenched effluent is further cooled in a boiler, wherein cold water and a pressurized cold water stream at a pressure of 10 to 40 bar, preferably at 30 bar, are used as cooling fluid.

6. The process according to any one of claims 1 to 4, wherein in step b), cooling is carried out only in a quench unit by direct contact with a pressurized cold water stream at a pressure of 10 to 40 bar, preferably 30 bar.

7. The method according to any one of claims 1 to 6, wherein a portion of the oxygen produced in the electrolysis step c) is recycled in step a), while the remaining portion of the pure oxygen is stored for sale as high-purity oxygen.

8. The process according to any one of claims 1 to 7, wherein the dry hydrogen from step d) is divided into two streams, wherein the first stream is recycled to step a), and the second stream is mixed with external CO2, heated and sent to step e), where a reverse water gas shift is performed.

9. The method according to any one of claims 4 to 8, wherein the steam stream leaving the boiler or the steam stream leaving the quencher is divided into two streams, wherein the first stream is sent to the SOEC and the second stream is sent to a turbine and expanded, or recycled to step a) after prior cooling.

10. The method for performing steps a)-b) and e) according to any one of claims 1 to 9, comprising a shell for performing steps a) and b) and a tube bundle for performing step e), wherein: Oxygen, hydrogen and steam enter from the bottom of the shell side, CO2 and H2 enter the tubes at the top of the tube side, where the tubes are heated by the exothermic reaction occurring on the shell side, thereby an endothermic reverse water-gas shift reaction occurs, and the synthesis gas produced leaves the unit from the bottom, and the steam produced on the shell side enters the quench unit, where the temperature is adjusted by contact with cold water, and then leaves the unit and is partially provided to the SOEC.

11. An apparatus for implementing the method according to any one of claims 1 to 9, comprising: A) a H2 burner unit for carrying out step a), said unit being in direct fluid communication with a steam quencher for carrying out step b), B) a steam quench for carrying out step b), said unit being in fluid communication with a H2 burner and a solid oxide electrolysis cell (SOEC) unit, C) a solid oxide electrolysis cell for carrying out step c), said unit being in fluid communication with a H2 burner unit and a reverse water gas shift reaction unit; D) The reverse water gas shift reaction unit is connected to the H2 burner and the solid oxide electrolysis cell via fluid.

12. The device according to claim 10, wherein units A), B) and D) are contained in a single unit, said unit comprising: i) as the shell of the H2 burner, coinciding with unit A); ii) the housing surrounds the tube bundle coinciding with unit C); iii) said shell contains a steam quench, coinciding with unit B), The unit also features: Three inlets for H2, O2 and steam on the shell side; · outlet of hot effluent on the same shell side; The shell side cold water inlet (CW) is in fluid communication with the quench unit; Inlet for introducing reactants on the tube side, · Syngas outlet formed on the tube side.

13. The apparatus according to claim 12, wherein the steam quencher iii) is of a direct type selected from a nozzle crown, or of an indirect type selected from a heat exchanger or a waste heat boiler.

14. An apparatus according to claim 12 or 13, wherein the outlet for the shell side effluent is located at the top of the unit, the inlet for the tube side reactants is located at the top of the unit, the outlet for the tube side effluent is located at the bottom of the unit, and the steam quench unit is located at the top of the unit.

15. The apparatus according to any one of claims 12 or 13, wherein the outlet for the shell side effluent is located at the bottom of the unit, the inlet for the tube side reactants is located at the bottom of the unit, and the outlet for the tube side effluent is located at the top of the unit, and the shell side steam quenching unit is located at the bottom of the unit.

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