Plant and process for producing synthesis gas

Abstract

A synthesis gas plant for producing synthesis gas, said synthesis gas plant including an electrically heated reforming reactor system including a first catalyst active for catalyzing steam methane reforming reaction, said electrically heated reforming reactor system being arranged to receive a feed gas comprising hydrocarbons and outletting a first synthesis gas stream. The synthesis gas plant also includes a post converter downstream the electrically heated reforming reactor system, said post converter housing a second catalyst active for catalyzing steam methane reforming/methanation reactions and reverse water gas shift reaction, said post converter being arranged to receive at least part of said first synthesis gas stream and outletting a second synthesis gas stream. Furthermore, the synthesis gas plant includes means for adding a heated CO.sub.2 rich gas stream to the at least part of the first synthesis gas stream upstream the post converter and/or into the post converter.

Claims

1. A synthesis gas plant for producing a synthesis gas, said synthesis gas plant comprising: a reforming reactor system comprising a first catalyst bed comprising an electrically conductive material and a catalytically active material, said catalytically active material being arranged for catalyzing steam reforming of a feed gas comprising hydrocarbons to produce a first synthesis gas stream, said reforming reactor system further comprising a pressure shell housing said first catalyst bed, a heat insulation layer between said first catalyst bed and said pressure shell, and at least two conductors electrically connected to said electrically conductive material and to an electrical power supply placed outside said pressure shell, wherein said electrical power supply is dimensioned to heat at least part of said first catalyst bed to a temperature of at least 500° C. by passing an electrical current through said electrically conductive material, wherein said pressure shell has a design pressure of between 15 and 200 bar, a post converter downstream said reforming reactor system, said post converter housing a second catalyst active for catalyzing steam methane reforming, methanation and reverse water gas shift reactions, said post converter being arranged to receive at least part of said first synthesis gas stream and outletting a second synthesis gas stream; and means for adding a heated CO.sub.2 rich gas stream to the at least part of the first synthesis gas stream upstream said post convertor and/or into said post convertor.

2. The synthesis gas plant according to claim 1, wherein said first catalyst bed comprises a structured catalyst comprising a macroscopic structure of electrically conductive material, said macroscopic structure supporting a ceramic coating, wherein said ceramic coating supports a catalytically active material.

3. The synthesis gas plant according to claim 2, wherein the first catalyst bed comprises an array of macroscopic structures.

4. The synthesis gas plant according to claim 2, wherein said macroscopic structure(s) has/have a plurality of parallel channels, a plurality of non-parallel channels and/or a plurality of labyrinthic channels.

5. The synthesis gas plant according to claim 2, wherein said macroscopic structure(s) is/are extruded and sintered structure(s).

6. The synthesis gas plant according to claim 1, wherein the resistivity of the electrically conductive material is between 10.sup.−5Ω.Math.m and 10.sup.−7 Ω.Math.m.

7. The synthesis gas plant according to claim 2, wherein the material of the macroscopic structure is chosen as a material arranged to generate a heat flux of 500 to 50000 W/m.sup.2 by resistance heating of the material.

8. The synthesis gas plant according to claim 2, wherein the connection between the macroscopic structure(s) and said at least two conductors is a mechanical connection, a welded connection, a brazed connection or a combination thereof.

9. The synthesis gas plant according to claim 1, wherein said pressure shell further comprises one or more inlets close to or in combination with at least one fitting in order to allow a cooling gas to flow over, around, close to, or inside at least one conductor within said pressure shell.

10. The synthesis gas plant according to claim 1, wherein the electrically conductive material comprises a resistor embedded in the catalytically active material of the first catalyst bed.

11. The synthesis gas plant according to claim 10, wherein said embedded resistor supports a ceramic coating, wherein said ceramic coating supports said catalytically active material.

12. The synthesis gas plant according to claim 1, wherein the reforming reactor system further comprises a bed of a third catalyst material upstream said first catalyst bed within said pressure shell.

13. The synthesis gas plant according to claim 1, further comprising a gas separation system downstream the post converter, said gas separation system comprising one or more of the following units: flash separation, a CO.sub.2 wash unit, a temperature swing adsorption unit, a pressure swing adsorption unit, a membrane, and/or a cryogenic separation unit.

14. The synthesis gas plant according to claim 1, further comprising a first heating unit for heating the feed gas upstream said reforming reactor system.

15. The synthesis gas plant according to claim 1, wherein said first heating unit is a fired heater, a heat exchange unit or an electric preheating unit.

16. The synthesis gas plant according to claim 1, further comprising a second heating unit arranged to heat a CO.sub.2 rich gas stream to said heated CO.sub.2 rich gas stream by heat exchange within the second heating unit.

17. The synthesis gas plant according to claim 1, further comprising means for heating a CO.sub.2 rich gas stream to said heated CO.sub.2 rich gas stream by heat exchange with at least part of the second synthesis gas exiting the post converter and/or by heat exchange with superheated steam upstream the post converter.

18. The synthesis gas plant according to claim 1, wherein said post converter is an adiabatic post converter.

19. The synthesis gas plant according to claim 1, said synthesis gas plant further comprising a gas purification unit and/or a prereforming unit upstream said reforming reactor system.

20. The synthesis gas plant according to claim 1, wherein said reforming reactor system further comprises a control system arranged to control the electrical power supply to ensure that the temperature of the first synthesis gas stream exiting the pressure shell of the reforming reactor system lies in a predetermined range and/or to ensure that the conversion of hydrocarbons in the feed gas lies in a predetermined range and/or to ensure the dry mole concentration of methane lies in a predetermined range and/or to ensure the approach to equilibrium of the steam reforming reaction lies in a predetermined range.

21. A process for producing synthesis gas, said process comprising the steps of: a) in a reforming reactor system, comprising a first catalyst active bed comprising an electrically conductive material and a catalytically active material, said catalytically active material being arranged for catalyzing steam reforming of a feed gas comprising hydrocarbons to produce a first synthesis gas stream, said reforming reactor system further comprising a pressure shell housing a first catalyst bed, a heat insulation layer between said first catalyst bed and said pressure shell, and at least two conductors electrically connected to said electrically conductive material and to an electrical power supply placed outside said pressure shell, wherein said pressure shell has a design pressure of between 15 and 200 bar, receiving said feed gas comprising hydrocarbons, passing an electrical current through said electrically conductive material thereby heating at least part of said first catalyst bed to a temperature of at least 500° C. by, letting said feed gas comprising hydrocarbons react over the first catalyst bed and outletting a first synthesis gas stream; b) in a post converter downstream the reforming reactor system, said post converter housing a second catalyst active for catalyzing steam methane reforming, methanation and reverse water gas shift reactions, receiving at least part of said first synthesis gas stream, carrying out steam methane reforming, methanation and reverse water gas shift reactions and outletting a second synthesis gas stream; and c) adding a heated CO.sub.2 rich gas stream to the at least part of the first synthesis gas stream upstream the post converter and/or into the post converter.

22. The process according to claim 21, further comprising the step of heating said feed gas comprising hydrocarbons in a first heating unit upstream the reforming reactor system.

23. The process according to claim 22, wherein said first heating unit is a fired heater, a heat exchange unit or an electric preheating unit.

24. The process according to claim 21, further comprising the step of heating a CO.sub.2 rich gas stream to said heated CO.sub.2 rich gas stream by heat exchange within said first heating unit.

25. The process according to claim 21, further comprising the step of heating a CO.sub.2 rich gas stream to said heated CO.sub.2 rich gas stream, by heat exchange with superheated steam upstream the post converter.

26. The process according to claim 21, further comprising the step of heating a CO.sub.2 rich gas stream to said heated CO.sub.2 rich gas stream by heat exchange with at least part of the second synthesis gas exiting the post converter.

27. The process according to claim 21, wherein said post converter is an adiabatic post converter.

28. The process according to claim 21, further comprising a step of separation of CO.sub.2 from the second synthesis gas.

29. The process according to claim 21, wherein the second catalyst is a steam reforming catalyst.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention are explained, by way of example, and with reference to the accompanying drawings. It is to be noted that the appended drawings illustrate only examples of embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

(2) FIGS. 1 and 2 are schematic drawings of systems for producing a synthesis gas according to the invention.

DETAILED DESCRIPTION

(3) The following is a detailed description of embodiments of the invention depicted in the accompanying drawings. The embodiments are examples and are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

(4) FIG. 1 is a schematic drawing of a synthesis gas plant 100 for producing a synthesis gas according to the invention. The synthesis gas plant 100 comprises an electrically heated reforming reactor system 20 and a post converter 30. The post converter 30 may e.g. be an adiabatic post converter. The synthesis gas plant 100 also comprises an optional first heating unit 10 upstream the electrically heated reforming reactor system 20.

(5) Feed streams to the synthesis gas plant 100 comprises a feed gas comprising hydrocarbons 1, which is optionally heated in the optional first heating unit 10 to a preheated feed gas comprising hydrocarbons 2. In the case where the synthesis gas plant 100 does not comprise the first heating unit 10, the feed gas comprising hydrocarbons 1 is fed directly to the electrically heated reforming reactor system 20. The feed gas comprising hydrocarbons 1 is e.g. a stream of natural gas with steam added in order to facilitate steam methane reforming.

(6) The electrically heated reforming reactor system 20 comprises means for electrically heating the catalyst housed within the electrically heated reforming reactor system 20, such as by resistance heating. The electrically heated reforming reactor system 20 moreover comprises one or more inlets for letting the preheated feed gas comprising hydrocarbons 2 and steam 3 into contact with the first catalyst housed within the electrically heated reforming reactor system 20, and an outlet for outletting a first synthesis gas stream 4 comprising at least partly reformed gas from the electrically heated reforming reactor system 20. The first synthesis gas stream 4 exiting the electrically heated reforming reactor system 20 typically has a temperature of between about 650° C. and about 1050° C., such as about 950° C.

(7) The first synthesis gas streams 4 is led into a post converter 30 comprising a second catalyst active for catalyzing steam methane reforming/methanation and reverse water gas shift reactions. The post converter 30 may be an adiabatic reactor or an electrically heated unit. The post converter 30 comprises an outlet for letting out a second synthesis gas stream 5. A heated CO.sub.2 rich gas stream 7 is also led into the post converter 30. The heated CO.sub.2 rich gas stream 7 may be combined with the first synthesis gas stream 4 prior to being inlet into the post converter 30, or the heated CO.sub.2 rich gas stream 7 and the first synthesis gas stream 4 are input separately into the post converter 30.

(8) Within the post converter 30, the first synthesis gas stream 4 is reacted towards equilibrium by the reverse water gas shift and steam methane reforming/methanation reactions. The second synthesis gas stream 5 is close to equilibrium with respect to the steam methane reforming/methanation reactions and the reverse water gas shift reaction at the outlet of the post converter 30. The steam methane reforming reaction is endothermic, the reverse water gas shift reaction is mildly endothermic, whilst the methanation reaction is exothermic.

(9) Therefore, in the case where the post converter 30 is an adiabatic unit, the temperature of the second synthesis gas stream 5 exiting the post converter 30 may be lower than the temperature of the first synthesis gas stream 4 or it may have the same temperature as the first synthesis gas stream 4. The second synthesis gas stream 5 exiting the post converter 30 may be further processed downstream the third reactor, or the second synthesis gas stream may be the product synthesis gas stream from the synthesis gas plant 100.

(10) The synthesis gas plant 100 moreover comprises a second heating unit 40 for preheating of a CO.sub.2 rich gas stream 6 to a heated CO.sub.2 rich gas stream 7. The second heating unit 40 may also compress the CO.sub.2 rich gas stream 6, so that the resultant CO.sub.2 rich gas stream 7 is a heated and compressed CO.sub.2 rich gas stream 7.

(11) Optionally, only a part of the first synthesis gas stream 4 is led from the electrically heated reforming reactor system 20 to the post converter 30. In this case, the part of the first synthesis gas stream 4 bypassing the post converter 30 may be combined with the second synthesis gas stream 5 downstream the post converter 30.

(12) FIG. 2 is a schematic drawing of a synthesis gas plant 101 for producing synthesis gas according to the invention. The synthesis gas plant 101 comprises the units/components of the synthesis gas plant 100 shown in FIG. 1 as well as further units. Similar units are denoted by similar reference numbers and will not be described in detail here. The synthesis gas plant 101 thus also comprises the first and second heating units 10, 40 of the synthesis gas plant 100 as well as a third and fourth heating units 10′ and 10″, respectively.

(13) Within the synthesis gas plant 101, the third heating unit 10′ is arranged to preheat a feed gas comprising hydrocarbons 1 to a preheated feed gas 1a and a desulfurization unit 8 arranged to desulfurize the preheated feed gas 1a to a desulfurized (and preheated) feed gas 1b. The feed gas comprising hydrocarbons 1 is e.g. a stream of natural gas, such as natural gas, town gas, or a mixture of methane and higher hydrocarbons, with steam added to facilitate steam methane reforming. Typically, the feed gas comprising hydrocarbons 1 is a feed gas comprising hydrocarbons and comprising minor amounts of hydrogen, carbon monoxide, carbon dioxide, nitrogen, argon or combinations thereof, in addition to the hydrocarbon gasses therein, and in addition to steam added to facilitate steam methane reforming.

(14) The desulfurized feed gas 1b is heated in the fourth heating unit 10″ to provide the desulfurized and heated feed gas 1c which is fed into a prereforming unit 9 arranged to prereform the desulfurized and heated feed gas 1c together with heated steam 11′ to a prereformed feed gas 1d. The prereformed feed gas 1d is fed to a further heating unit 10, also denoted “a first heating unit 10”, for heating the prereformed feed gas 1d to a preheated and prereformed feed gas 2. The preheated and prereformed feed gas 2 is fed to an electrically heated reforming reactor system 20, optionally together with further steam 3. Within the electrically heated reforming reactor system 20 the preheated and prereformed feed gas 2 and the steam 3 undergo steam methane reforming, thereby producing a first synthesis gas stream 4 which is led to a post converter 30, in the form of an adiabatic post converter. The second synthesis gas stream 5 outlet from the post converter 30 typically has a temperature of about 600-900° C. and it is led to a waste heat recovery section 50 wherein steam is heated by the second synthesis gas stream 5 to heated steam 11, and the cooled second synthesis gas is outlet from the waste heat recovery unit 50 as a cooled second synthesis gas stream 12. The heated steam 11 may be further heated in the first heating unit 10 to form a stream of superheated steam. The stream of superheated steam is split up into a first stream 11′ of superheated steam led into the prereforming unit 9 and a second stream 11″ of superheated steam which is a byproduct of the process outlet from the synthesis gas plant 101.

(15) A condensation unit 60 is arranged to receive the cooled second synthesis gas stream 12 and condense steam within the second synthesis gas stream to a condensate stream 14. The remaining dried second synthesis gas stream 13 is subsequently fed to a CO.sub.2 separation unit 70 in the form of a unit with a membrane, a CO.sub.2 wash unit or a CO.sub.2 stripper. The CO.sub.2 separation unit 70 outputs a CO.sub.2 rich stream 16 and a CO.sub.2 lean product synthesis gas 15. The CO.sub.2 rich stream 16 may be fed to the second heating unit 40 for compression and preheating of CO.sub.2. The second heating unit 40 typically receives an additional stream 6 of CO.sub.2 rich gas stream in order to provide sufficient heated CO.sub.2 rich gas stream 7 to the post converter 30.

Example

(16) An example calculation of the process is given in Table 1 below. A feed gas comprising hydrocarbons comprising a hydrocarbon gas, CO.sub.2 and steam, and having a S/C ratio of 1.0 fed to the electrically heated reforming reactor system 20 of the invention as shown in FIG. 1. The feed gas comprising hydrocarbons is heated in the first heating unit 10 to 450° C. prior to being let into the electrically heated reforming reactor system 20. Within the electrically heated reforming reactor system 20 the gas is reformed and exits electrically heated reforming reactor system 20 as the first synthesis gas stream 4 having a temperature of 1000° C.

(17) A CO.sub.2 gas is preheated to 260° C. and led into first heating unit 10 in the form of an electric CO.sub.2 heating unit 10, where it is further preheated to 1000° C. The CO.sub.2 gas preheated to 1000° C. and the first synthesis gas stream 4 at a temperature of 1000° C. are led into the post converter 30 at a temperature of 1000° C. The CO.sub.2 gas and the first synthesis gas stream 4 may be combined to a single gas, having a temperature of 1000° C., before being led into the post converter 30.

(18) Within the post converter 30, the CO.sub.2 gas and the first synthesis gas stream 4 are equilibrated, viz. undergo reverse water gas shift, methanation and reforming reactions. The exit temperature of the gas stream exiting the post converter 30 is 853° C.

(19) TABLE-US-00001 TABLE 1 Electrically heated Electric CO.sub.2 Post reforming reactor heating unit converter system 20 10 30 Inlet T [° C.] 450 260 1000 Outlet T [° C.] 1000 1000 853 Pressure [barg] 27 27 26 S/C 1 — — CH.sub.4 feed addition 11741 — — [Nm.sup.3/h] H.sub.2O feed addition 11973 — — [Nm.sup.3/h] CO.sub.2 feed addition 0 19660 — [Nm.sup.3/h] H.sub.2 out [dry mol %] 63.5 — 28.7 CO out [dry mol %] 19.8 — 29.0

(20) Thus, when the synthesis gas plant and process of the invention are used, it is possible to provide a synthesis gas stream having a relative high amount of CO. In the example of Table 1, the H.sub.2/CO ratio is 1.0, while the normalized H.sub.2O/CH.sub.4 is ca. 1.0 corresponding to H/C and O/C ratios of 2.3 and 1.9, respectively. This would be more difficult in a steam methane reforming reactor without encountering problems with carbon formation on the catalyst and/or leading to very large reactor sizes. This is illustrated by the example in Table 2, where production of a synthesis gas of a H.sub.2/CO ratio of 1.0 is produced in a single SMR from the amount of methane as the example in Table 1. For comparison, in an SMR without a post converter, here denoted “a stand-alone SMR”, much more CO.sub.2 and H.sub.2O is added to the processes, signifying the larger steam methane reforming reactor size. See Table 2.

(21) TABLE-US-00002 TABLE 2 Stand-alone SMR Inlet T [° C.] 450 Outlet T [° C.] 950 Pressure [barg] 27 S/C 2.3 CH.sub.4 feed addition [Nm.sup.3/h] 11741 H.sub.2O feed addition [Nm.sup.3/h] 27004 CO.sub.2 feed addition [Nm.sup.3/h] 29572 H.sub.2 out [dry mol %] 25.1 CO out [dry mol %] 25.1