Process and system for producing synthesis gas

1. A process for producing synthesis gas, said process comprising the steps of:

a) in a reforming reactor comprising a first catalyst, reacting a hydrocarbon feed stream together with an oxidant gas stream, thereby producing a first synthesis gas stream;

b) providing a heated CO 2 rich gas stream to an adiabatic post converter comprising a second catalyst active for catalyzing steam methane reforming, methanation and reverse water gas shift reactions; and

c) in said adiabatic post converter, letting at least a part of the first synthesis gas stream and said heated CO 2 rich gas stream undergo steam methane reforming, methanation and reverse water gas shift reactions to thereby provide a product gas stream, said product gas stream being a synthesis gas stream.

2. The process according to claim 1 , wherein the reforming reactor is an autothermal reforming reactor.

3. The process according to claim 1 , wherein the reforming reactor is a steam methane reforming reactor.

4. The process according to claim 1 , wherein the product gas stream is a synthesis gas stream with an H 2 /CO ratio below 1.8.

5. The process according to claim 1 , wherein said at least part of the first synthesis gas stream and said heated CO 2 rich gas stream are combined to a combined gas stream upstream the adiabatic post converter.

6. The process according to claim 1 , wherein the heated CO 2 rich gas stream has a temperature of between about 500° C. and 1100° C. prior to combination with said at least part of the first synthesis gas stream and/or prior to being inlet into said adiabatic post converter.

7. The process according to claim 1 , further comprising the step of heating a CO 2 rich gas stream to form said heated CO 2 rich gas stream in a fired heater.

8. The process according to claim 1 , further comprising the step of heating a CO 2 rich gas stream to form said heated CO 2 rich gas stream in an electrically heated heater.

9. The process according to claim 1 , further comprising the step of heating a CO 2 rich gas stream to form said heated CO 2 rich gas stream by heat exchange with superheated steam.

10. The process according to claim 1 , further comprising the step of heating a CO 2 rich gas stream to said heated CO 2 rich gas stream by heat exchange with at least part of the product gas stream exiting the adiabatic post converter.

11. The process according to claim 1 , wherein the mole ratio between carbon dioxide in said heated CO 2 rich gas stream and hydrocarbons in the hydrocarbon feed stream is larger than 0.1.

12. The process according to claim 1 , wherein said hydrocarbon feed stream comprises steam and the S/C ratio in said hydrocarbon feed stream is between 0.2 and 2.

13. The process according to claim 2 , wherein the amount of steam, oxygen and carbon dioxide led into the reforming reactor and/or added to said at least part of the first synthesis gas stream upstream or in said adiabatic post converter is adjusted to provide a predetermined H 2 /CO ratio of said product gas stream.

14. The process according to claim 1 , wherein the amount and temperature of the heated CO 2 rich gas stream are adjusted to ensure that the temperature of said product gas stream is at least 800° C.

15. The process according to claim 1 , wherein the second catalyst is a steam reforming catalyst.

16. A system for producing synthesis gas, said system comprising:

a reforming reactor comprising a first catalyst and being arranged to at least partially react a hydrocarbon feed together with an oxidant gas stream thereby producing a first synthesis gas stream,

an adiabatic post converter comprising a second catalyst active for catalyzing steam methane reforming, methanation and reverse water gas shift reactions,

a conduit for leading at least part of the first synthesis gas stream into said adiabatic post converter,

means for adding a heated CO 2 rich gas stream to said at least part of the first synthesis gas stream upstream or in said adiabatic post converter; and

an outlet from said adiabatic post converter for letting out a product gas stream, said product gas stream being a synthesis gas stream.

17. The system according to claim 16 , wherein the reforming reactor is an autothermal reforming reactor.

18. The system according to claim 16 , wherein the reforming reactor is a steam methane reforming reactor.

19. The system according to claim 16 , wherein the product gas stream is a synthesis gas stream with an H 2 /CO ratio below 1.8.

20. The system according to claim 16 , further comprising a fired heater, wherein said means for adding a heated CO 2 rich gas stream comprises means for heating a CO 2 rich gas stream by heat exchange within the fired heater.

21. The system according to claim 16 , further comprising an electrically heated heater, wherein said means for adding a heated CO 2 rich gas stream comprises a means for heating a CO 2 rich gas stream by heat exchange within the electrically heated heater.

22. The system according to claim 16 , further comprising a second heat exchange unit allowing heating a CO 2 rich gas stream by heat exchange with superheated steam.

23. The system according to claim 16 , further comprising a third heat exchange unit allowing heating a CO 2 rich gas stream to said heated CO 2 rich gas stream by heat exchange with at least part of the product gas stream exiting said adiabatic post converter.

24. The system according to claim 16 , wherein the second catalyst is a steam reforming catalyst.