PROCESS AND PLANT FOR PROVIDING SYNTHESIS GAS AND FOR PRODUCING METHANOL

Abstract

The present invention specifies a process and a plant for production of a synthesis gas stream which makes it possible to produce the synthesis gas stream with a stoichiometry number suitable for the methanol synthesis or other syntheses. To this end an electrolytically produced hydrogen stream is admixed with a hydrocarbon-containing input gas stream and the resulting hydrogen-containing and hydrocarbon-containing input gas stream is reacted in the presence of oxygen to afford synthesis gas in a reforming step. The process mode according to the invention has the advantage that the electrolytically produced hydrogen stream need not be treated, in particular no oxygen need be removed from the electrolytically produced hydrogen stream. The invention further includes a process and a plant for production of methanol including the process according to the invention and the plant according to the invention for production of the synthesis gas stream.

Claims

1. A process for producing synthesis gas, comprising: (a) providing a hydrocarbon-containing input gas stream; (b) providing an electrolytically produced hydrogen stream; (c) supplying at least a portion of the electrolytically produced hydrogen stream to the hydrocarbon-containing input gas stream to obtain a hydrogen-containing input gas stream; and (d) reacting the hydrogen-containing input gas stream in the presence of oxygen as oxidant in a reforming step thereby producing a synthesis gas stream.

2. The process according to claim 1, wherein the reforming step comprises an autothermal reforming (ATR) or a partial oxidation (PDX) of the hydrogen-containing input gas stream.

3. The process according to claim 1, wherein an amount of electrolytically produced hydrogen stream supplied to the hydrocarbon-containing input gas stream according to step (c) is adjusted such that a synthesis gas stream having a stoichiometry number SN of 1.9 to 2.5 is obtained according to step (d), wherein $SN=\frac{n\left(H_2\right)-n\left({\mathrm{CO}}_2\right)}{n\left(\mathrm{CO}\right)+n\left({\mathrm{CO}}_2\right)},\mathrm{with}n\mathrm{in}\left[\mathrm{mol}\right].$

4. The process according to claim 1, wherein the electrolytically produced hydrogen stream contains oxygen as an impurity and the oxygen present as an impurity is not removed before the supplying of the electrolytically produced hydrogen stream to the hydrocarbon-containing input gas stream according to step (c).

5. The process according to claim 1, wherein the electrolytically produced hydrogen stream contains 0.01% to 5% by volume of oxygen as an impurity.

6. The process according claim 1, wherein the process comprises providing an electrolytically produced oxygen stream, wherein the electrolytically produced oxygen stream is used as oxidant in step (d).

7. The process according to claim 1, wherein the process comprises providing an oxygen stream produced by air separation, wherein the oxygen stream produced by air separation is used as oxidant in step (d).

8. The process according to claim 1, wherein a steam stream is supplied to the hydrocarbon-containing input gas stream or the hydrogen-containing input gas stream.

9. The process according to claim 1, wherein the hydrocarbon-containing input gas stream is a natural gas stream or a biogas stream.

10. A process for producing methanol comprising the process for producing synthesis gas according to claim 1, further comprising the step of reacting the synthesis gas stream over a solid methanol synthesis catalyst to afford raw methanol, wherein the raw methanol comprises at least methanol (CH.sub.3OH) and water.

11. The process according to claim 10, wherein the raw methanol is separated into pure methanol and water in a thermal separation process.

12. The process according to claim 10, wherein the water separated in the thermal separation process is used as starting material for the electrolytically produced hydrogen.

13. The process according to claim 10, wherein reacting the synthesis gas stream over the solid methanol synthesis catalyst to afford raw methanol generates a residual gas stream containing synthesis gas unconverted into raw methanol, wherein a portion of the residual gas stream is separated as a purge gas stream and wherein the purge gas stream is supplied to a hydrogen recovery apparatus to produce a non-electrolytically produced hydrogen stream and the non-electrolytically produced hydrogen stream is at least partially supplied to the hydrocarbon-containing input gas stream in addition to the electrolytically produced hydrogen stream to obtain the hydrogen-containing input gas stream according to step (c) and/or the non-electrolytically produced hydrogen stream is at least partially supplied to the synthesis gas stream obtained according to step (d).

14. A plant for producing synthesis gas, wherein the plant comprises the following components in fluid connection with one another: (a) a means configured for providing a hydrocarbon-containing input gas stream; (b) an electrolyzer configured for providing an electrolytically produced hydrogen stream; (c) a means configured for supplying at least a portion of the electrolytically produced hydrogen stream to the hydrocarbon-containing input gas stream which make it possible to produce a hydrogen-containing input gas stream; (d) a reactor configured for reacting the hydrogen-containing input gas stream in the presence of oxygen as oxidant in a reforming step which makes it possible to produce a synthesis gas stream.

15. The plant according to claim 14, wherein the reactor is an autothermal reformer or a reactor configured for a partial oxidation.

16. The plant according to claim 14, wherein the means (c) are configured such that an amount of electrolytically produced hydrogen stream suppliable to the hydrocarbon-containing input gas stream is adjustable such that a synthesis gas stream having a stoichiometry number SN of 1.9 to 2.5 is producible according to (d), wherein $SN=\frac{n\left(H_2\right)-n\left({\mathrm{CO}}_2\right)}{n\left(\mathrm{CO}\right)+n\left({\mathrm{CO}}_2\right)},\mathrm{with}n\mathrm{in}\left[\mathrm{mol}\right].$

17. The plant according to claim 14, wherein the plant includes no means for removing oxygen occurring as an impurity from the electrolytically producible hydrogen stream.

18. The plant according to claim 14, wherein the electrolyzer is configured for providing an electrolytically produced oxygen stream and the plant comprises means for using the oxygen stream as oxidant in the reactor (d) for reacting the hydrogen-containing input gas stream to afford the synthesis gas stream.

19. The plant according claim 14, wherein the plant comprises an apparatus for air separation, wherein the apparatus for air separation makes it possible to produce an oxygen stream and the plant comprises means for using the oxygen stream as oxidant in the reactor for reacting the hydrogen-containing input gas stream to afford the synthesis gas stream.

20. A methanol plant for producing methanol comprising a plant for producing synthesis gas according claim 14, wherein the methanol plant comprises a methanol synthesis reactor, wherein the methanol synthesis reactor is configured for reacting the synthesis gas producible by the plant to afford raw methanol, wherein the raw methanol contains at least methanol (CH.sub.3OH) and water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0100] The invention is more particularly elucidated hereinbelow by way of working examples and numerical examples without in this way limiting the subject-matter of the invention. Further features, advantages and possible applications of the invention will be apparent from the following description of the working examples in connection with the drawings and the numerical examples. In the figures, functionally and/or structurally identical or at least similar constituents are given identical reference numerals.

[0101] In the figures:

[0102] FIG. 1 shows a block flow diagram of a process for synthesis gas production and methanol production according to the prior art using PSA hydrogen,

[0103] FIG. 2 shows a block flow diagram of a process for synthesis gas production and methanol production according to the prior art using electrolytically produced hydrogen,

[0104] FIG. 3 shows a block flow diagram of a process for synthesis gas production and methanol production according to the invention and

[0105] FIG. 4 shows a block flow diagram of a further process for synthesis gas production and methanol production according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0106] FIG. 1 shows a highly simplified block flow diagram of an example of a process 1 for synthesis gas production and subsequent methanol production according to conventional processes from the prior art. 30 A hydrocarbon-containing input gas stream, here a natural gas stream, is supplied via conduit 20 and initially compressed in compressor 10. The compressed input gas is subsequently sent on via conduit 21 and freed of undesired concomitants in a unit for purification of natural gas 11. Purification unit 11 comprises for example a hydrodesulfurization plant for removal of sulfur compounds. The purified input gas is sent on via conduit 22 and mixed with steam supplied via conduit 31. The mixture of input gas and steam is subsequently reacted in an autothermal reformer 12 to afford a synthesis gas stream. The autothermal reformer is supplied with air, oxygen-enriched air or pure oxygen via a conduit (not shown). The synthesis gas produced in the autothermal reformer is sent on via conduit 23 and cooled in a unit for heat recovery 13. The unit for heat recovery 13 simultaneously converts process water from conduit 30 into steam which is sent on via conduit 31 and, as mentioned, combined with the hydrocarbon-containing input gas stream in conduit 22.

[0107] The cooled synthesis gas stream exiting the unit for heat recovery 13 has a stoichiometry number of markedly below 2.0 and therefore cannot be immediately employed for a subsequent methanol synthesis. For this reason a substream is removed from the synthesis gas stream of conduit 24 via conduit 25 and sent to a unit for pressure swing adsorption 14. The unit for pressure swing adsorption 14 produces a stream of largely pure hydrogen which is discharged from the pressure swing adsorption unit 14 via conduit 26. The unit for pressure swing adsorption 14 simultaneously produces a tail gas stream (not shown) which may for example be partially employed in the autothermal reformer 12 or else used for under-firing in a separate fired heater.

[0108] The hydrogen stream discharged from the unit for pressure swing adsorption 14 via conduit 26 is combined with the synthesis gas stream from conduit 24, thus resulting in a hydrogen-enriched synthesis gas stream which is sent on via conduit 27. The hydrogen-enriched synthesis gas stream in conduit 27 has a stoichiometry number of above 2.0 and may therefore be used for a subsequent methanol synthesis. Accordingly the synthesis gas stream is introduced into a unit for methanol synthesis 15 via conduit 27. The unit for methanol synthesis 15 may comprise one or more serially connected methanol synthesis reactors. In the methanol synthesis reactor(s) the hydrogen and the carbon oxides from the hydrogen-enriched synthesis gas stream are reacted over a solid methanol synthesis catalyst to afford raw methanol, a mixture of methanol and water. The raw methanol is subsequently sent on via conduit 28 and supplied to a distillation unit 16. Distillation unit 16 comprises a rectification column for example. The distillation unit separates the methanol from water and undesired byproducts. A stream of pure methanol is discharged from the distillation unit 29 via conduit 29 in addition to a stream of process water which is discharged via conduit 30. The process water in conduit 30 is converted into steam in the unit for heat recovery 13.

[0109] FIG. 2 shows a highly simplified block flow diagram of an example of a process 2 for synthesis gas production and subsequent methanol production according to the principle as described in EP 3 658 494 B1.

[0110] Compared to process 1 the hydrogen required for adjusting the stoichiometry number of the synthesis gas produced by reforming is produced by an electrolyzer 18. It is accordingly unnecessary to divert a substream from the cooled synthesis gas stream in conduit 24 and produce hydrogen therefrom in a unit for pressure swing adsorption, as described for FIG. 1.

[0111] Accordingly, a raw water stream is supplied via conduit 32 and purified, for example desalinized, in a unit for water treatment 7. The resulting pure water stream is sent on via conduit 33 and subjected to a water electrolysis in the electrolyzer 18, thus producing an electrolytically produced hydrogen stream and an electrolytically produced oxygen stream. The electrolysis may for example be a PEM electrolysis or an alkaline electrolysis. An oxygen stream is withdrawn from the electrolyzer 18 via conduit 35 and used in the autothermal reformer 12 and therefore supplied thereto as oxidant. The electrolytically produced hydrogen stream likewise produced in the electrolyzer is sent on via conduit 34. The hydrogen stream in conduit 34 contains oxygen as an impurity, for example 1% by volume, and optionally residual amounts of water not removed in the gas-liquid separator of the electrolyzer 18. The hydrogen stream is therefore supplied to a unit for purifying electrolysis hydrogen 19. In this purification unit 19 the oxygen present as an impurity is initially catalytically reacted with hydrogen of the hydrogen stream to afford water. This catalytically produced water and the abovementioned residual water is subsequently bound by adsorption, for example on a molecular sieve. The electrolytically produced hydrogen stream exiting the purification unit 19 is accordingly free from oxygen and dry, i.e. anhydrous. This purified hydrogen stream is sent on via conduit 36 and combined with the cooled synthesis gas stream from conduit 24. This results in a hydrogen-enriched synthesis gas stream having a stoichiometric number of more than 2.0 and which can therefore be used for the subsequent methanol synthesis in the unit for methanol synthesis 15.

[0112] FIG. 3 shows a highly simplified block flow diagram of an example of a process 3 for synthesis gas production and subsequent methanol production according to the invention.

[0113] The process mode according to process 3 differs from process 2 especially in that the hydrogen stream electrolytically produced by the electrolyzer 18 is supplied to the purified hydrocarbon-containing input gas stream in conduit 22 via conduit 38. As described in detail for FIG. 1 a hydrocarbon-containing input gas stream, here a natural gas stream, is supplied via conduit 20 according to process 3 too. The hydrocarbon-containing input gas stream is subsequently compressed via compressor 10, sent on via conduit 21 and purified in the unit for purifying the input gas 11. The purification unit 11 includes a hydrodesulfurization plant for removing sulfur compounds from the input gas stream. The purified, hydrocarbon-containing input gas stream is sent on via conduit 22 and as described above combined with the electrolytically produced hydrogen stream from conduit 38. The resulting hydrogen-containing and hydrocarbon-containing input gas stream (hydrogen-containing input gas stream in the context of the invention) is further admixed with steam from conduit 39. This results in conduit 22 in a steam-containing, hydrocarbon-containing and hydrogen-containing input gas stream. This stream is converted into synthesis gas in the autothermal reformer. The autothermal reformer is also supplied with electrolytically produced oxygen as oxidant via conduit 35. The autothermal reformer is moreover supplied via a conduit (not shown) with the still-lacking oxygen for the reaction, in the form of air, oxygen-enriched air or pure oxygen.

[0114] Since hydrogen reacts with oxygen in the autothermal reformer only to a small extent, if at all, to afford water, the synthesis gas at the outlet of the autothermal reformer has a high stoichiometry number SN of more than 1.9. Since the autothermal reformer in any case requires oxygen as oxidant it is not necessary to purify the electrolytically produced hydrogen stream in conduit 38 as described for process 2. Since a steam stream is supplied to the hydrogen-containing input gas stream/steam is produced (and reacted) in the course of the partial oxidation in the autothermal reformer 12 it is not necessary to dry the electrolytically produced hydrogen stream either. Inventive process 3 accordingly requires no purification unit 19 as described for FIG. 2.

[0115] The synthesis gas stream which has a stoichiometry number of more than 1.9 is sent on via conduit 23 and cooled in the unit for heat recovery 13. The cooled synthesis gas stream is sent on via conduit 40 and may subsequently be directly used for producing methanol in the unit for methanol synthesis 15.

[0116] The process shown in FIG. 3 further represents an optimization and alternative to the use of the process water generated in the distillation unit 16. According to the process shown in FIG. 3 the process water is supplied to a water treatment unit 17. According to the quality thereof it may also be directly employed as feed for the electrolyzer, thus bypassing the water treatment unit 17. In this case the process water is directly supplied via conduit 37 to conduit 33 (not shown). In any case the required amount of raw water (conduit 32) and/or pure water (conduit 33) is reduced. Depending on the available amount of process water from distillation unit 16 this may additionally be used for producing steam in the heat recovery unit 13 (not shown in FIG. 3).

[0117] FIG. 4 shows a highly simplified block flow diagram of an example of a further process, here process 4, for synthesis gas production and subsequent methanol production according to the invention.

[0118] The process mode according to process 4 shown in FIG. 4 differs from process 3 especially in that a purge gas stream is withdrawn from the methanol synthesis 15 via conduit 41 and sent to an apparatus for pressure swing adsorption (PSA) 9. The purge gas stream is separated from a residual gas stream (not shown) which substantially contains synthesis gas unconverted in the methanol synthesis 9. The apparatus for pressure swing adsorption 9 produces a hydrogen stream and a tail gas stream (tail gas stream not shown). The hydrogen stream, in the context of the invention a non-electrolytically produced hydrogen stream, is sent on via conduit 42 and in conduit 40 combined with the synthesis gas stream produced in the autothermal reformer 12.

[0119] Alternatively or in addition the hydrogen stream withdrawn from the PSA 9 could also be supplied to the hydrocarbon-containing input gas stream in conduit 22 in addition to the electrolytically produced hydrogen stream (see dashed conduit 42).

[0120] Utilizing the purge gas to produce hydrogen by pressure swing adsorption allows the electrolyzer to be made correspondingly smaller since accordingly said electrolyzer need not produce as much hydrogen for adjusting the stoichiometry number of the synthesis gas stream.

[0121] The following numerical examples are based on simulation data and serve to further elucidate the invention. The simulation data were generated using the software AspenPlus.

[0122] The following table shows simulation data for two comparative examples P1 and P2 and two inventive examples P3 and P4, in each case for a process mode with a PDX reactor. P1 in principle corresponds to the process mode of FIG. 1 with production of a hydrogen stream by pressure swing adsorption of reformed synthesis gas. P2 in principle corresponds to the process mode of FIG. 2 with production of a hydrogen stream by electrolysis and supply of the hydrogen stream downstream of the PDX reactor. P3 and P4 in principle correspond to the process mode of FIG. 3 (inventive) with production of a hydrogen stream by electrolysis and supply of the hydrogen stream upstream of the PDX reactor.

[0123] Streams are often reported as mole flows in kilomol per hour (kmol/h).

TABLE-US-00001 P1 P2 P3 P4 (comparative) (comparative) (inventive) (inventive) Natural gas stream 404.0 316.0 316.0 316.0 (kmol/h) Electrolyzer n/a 120.0 120.0 150.0 hydrogen stream (kmol/h) Oxygen stream 300.0 239.0 249.9 252.7 (t/h) Synthesis gas 21.5% n/a n/a n/a stream to PSA Synthesis gas 1031.3 1032.2 1007.7 1031.8 stream (kmol/h) Stoichiometry 1.99 1.97 1.91 1.98 number SN

[0124] The required natural gas stream is markedly higher for P1 since a relatively large proportion of the produced synthesis gas stream (21.5%) needs to be diverted for producing the hydrogen stream by pressure swing adsorption (PSA).

[0125] The comparison between P2 and P3 shows that when supplying the same hydrogen stream upwards of the PDX reactor (P3) a slightly lower synthesis gas amount is produced and the resulting synthesis gas exhibits a slightly lower stoichiometry number. Compensating this effect requires increasing the hydrogen stream amount from 120 kmol/hr to 150 kmol/hr (according to P4). The increase in operating costs (OPEX) brought about thereby can be compensated by the corresponding reduction of the capital costs (CAPEX) since according to the invention no purification unit connected downstream of the electrolyzer is required for removal of oxygen. Such a purification unit also increases the operating costs (OPEX) of the corresponding plant.

[0126] The following table shows simulation data for two comparative examples A1 and A2 and an inventive example A3, in each case for a process mode with an autothermal reformer (ATR reactor). A1 in principle corresponds to the process mode of FIG. 1 with production of a hydrogen stream by pressure swing adsorption (PSA) of reformed synthesis gas. In addition and not shown in FIG. 1, a further hydrogen stream is produced by a PSA utilizing a purge gas stream generated in the methanol synthesis. This non-electrolytically produced hydrogen stream is supplied to the synthesis gas stream downstream of the autothermal reformer and upstream of the methanol synthesis.

[0127] A2 corresponds to the process mode of FIG. 2 with production of a hydrogen stream by electrolysis and supply of this hydrogen stream downstream of the autothermal reformer. In addition and not shown in FIG. 2, a further hydrogen stream is produced by a PSA through utilization of the purge gas stream generated in the methanol synthesis. This non-electrolytically produced hydrogen stream is supplied to the synthesis gas stream downstream of the autothermal reformer and upstream of the methanol synthesis.

[0128] A3 corresponds to the process mode according to FIG. 4 (inventive) with production of a hydrogen stream by electrolysis and supply of this hydrogen stream upstream of the autothermal reformer. In addition, a further hydrogen stream is produced by a PSA utilizing the purge gas stream generated in the methanol synthesis. This non-electrolytically produced hydrogen stream is supplied to the synthesis gas stream downstream of the autothermal reformer and upstream of the methanol synthesis.

[0129] The examples A1 to A3 also show the synthesis of methanol from the produced synthesis gas in a synthesis loop with a water-cooled reactor at a recycle ratio of 1.6. The recycle ratio (RR) represents the quotient of the stream of recycle gas (residual gas unconverted at the outlet and recycled to the reactor inlet) and freshly supplied synthesis gas.

[0130] Streams are often reported as mole flows in kilomol per hour (kmol/h).

TABLE-US-00002 A1 A2 A3 (comparative) (comparative) (inventive) Natural gas stream 7741 7394 7408 (kmol/h) Hydrogen stream from n/a 880 1000 electrolyzer (kmol/h) Hydrogen stream 1650 650 700 from PSA (kmol/h) Oxygen stream 137 127 128 (t/h) Synthesis gas 1800 n/a n/a stream to PSA (kmol/h) Synthesis gas stream 22 943 23 001 23 038 (kmol/h) Stoichiometry 2.4 2.4 2.5 number SN Methanol product 5001 5004 5001 (t/d)

[0131] The comparison between A2 and A3 shows that when supplying the hydrogen stream to the natural gas stream upstream of the autothermal reformer a larger hydrogen amount is required to produce the same methanol amount (i.e. synthesis gas amount). The increase in operating costs (OPEX) brought about thereby can be compensated by the corresponding reduction of the capital costs (CAPEX) since according to the invention no purification unit connected downstream of the electrolyzer is required for removal of oxygen. Such a purification unit also increases the operating costs (OPEX) of the corresponding plant.

LIST OF REFERENCE SYMBOLS

[0132] 1, 2, 3 Process

[0133] 9 Pressure swing adsorption

[0134] 10 Compressor

[0135] 11 Input gas purification

[0136] 12 Autothermal reformer

[0137] 13 Heat recovery

[0138] 14 Pressure swing adsorption

[0139] 15 Methanol synthesis

[0140] 16 Distillation

[0141] 17 Water treatment

[0142] 18 Electrolyzer

[0143] 19 Electrolysis hydrogen purification

[0144] 20 to 42, 42 Conduit

[0145] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.