In revamps of existing plants the existing reactors, re ^¬ formers etc. may put restraints on the possibilities for the updated process and/or plant. For example the catalyst volume in an existing plant may provide a limit for a pro ^¬ cess which means that the revamp cannot in an advantageous setup result in a need for an increased catalyst volume. Thus in existing plants or other situations where con ^¬ straints are made on reformers, reactors etc. there is a need for alternative processes and plants which increase efficiency without increasing the capacity needs above the available .

In a first object of the present process and plant is pro ^¬ vided means for improving the amount and composition of a synthesis gas without increasing the need for reform ^¬ er/reactor/catalyst volume.

These and other advantages are achieved by a production plant comprising

a synthesis gas generation step arranged to receive a hydrocarbon or carboneous feed stock and in a synthesis gas generation process provide a syngas

a production step arranged to receive the syngas and produce a product stream

a reverse water gas shift step arranged to receive a ¾ rich gas stream and a CO ₂ feed and in a RWGS process ob- tain a reverse shifted gas stream, and

means for adding said reverse shifted gas stream to the synthesis gas stream whereby a plant which enable the production of a mixed synthesis gas stream having an improved CO/CO ₂ ratio without resulting in an increase in the needed duty of the synthesis gas generation step for exam ^¬ ple comprising a reformer and/or an increased catalyst vol- ume/heat transfer area in the production step.

The production step can be a methanol synthesis loop ar ^¬ ranged to receive the syngas/reverse shifted gas mixture and produce a Methanol-rich product stream

The production step may also e.g. be a purification unit producing a product gas rich in Carbonmonoxide .

The synthesis gas generation step can in some advantageous embodiments be a reforming step, a gasification step, or a partial oxidation step depending on what feed is provided and/or on the production step. I.e. the synthesis genera ^¬ tion step can be selected to provide an optimized inlet gas to the production step.

If the reverse shifted gas stream is provided downstream the synthesis gas generation step the synthesis gas genera ^¬ tion step does not need to be dimensioned to receive the reverse shifted gas stream. This may be highly desirable in setups wherein volume/capacity of the synthesis gas genera ^¬ tion step is an issue, which for example can be the case in revamps of existing plants.

If the RWGS step comprises a hydrogen recovery unit up- stream the RWGS process the stream which enters the RWGS process has an increased ¾ ratio and a decreased content of other substances compared to the stream which enters the RWGS step.

Depending on the setup used the hydrogen recovery unit can be of different types such as a membrane unit, PSA unit or cryogenic unit.

From the recovery unit a residual gas stream may be provid ^¬ ed e.g. to burners etc.

For example the ¾ rich gas stream can be a purge gas from the Methanol production loop. The purge gas can contain various substances which advantageously may be removed in which cases the purge gas can be passed through a hydrogen recovery unit as described above before it is fed to the

RWGS process. Alternatively the ¾ rich stream may be sent directly to the RWGS step.

The CO2 feed can be provided by various means. For example the CO2 can be provided from underground natural CO2 rich gas reservoir.

The CO2 can also be provided from a purification unit

(amine wash, PSA, etc.) removing CO2 from a synthesis gas, flue gas, or natural gas depending on which sources of CO2 are available or otherwise desirable in a given setup.

The RWGS step can be arranged in different ways with a range of suited catalysts. For example, the RWGS step may comprise a High Temperature Shift Catalyst (e.g. Tops0e SK- 201 or SK-501) or an UltraHigh Temperature Shift Catalyst for the RWGS process. In setups where the production unit is a purification unit producing a CO stream or CO-rich stream the production unit may for example be a membrane unit or a cryogenic unit.

Also provided is a process for adjusting the CO/CO ₂ ratio in a synthesis gas, said process comprising

in a production loop producing a product stream from a synthesis gas,

- in an RWGS reactor producing a reverse shifted gas stream at least from a CO ₂ feed and a ¾ rich gas stream, and

adding the produced reversed shifted gas stream to the synthesis gas upstream the production loop. I.e. in the present process a RWGS production step is used to provide a stream with an increased CO content, which stream with an increased CO content is added to the synthesis gas to ob ^¬ tain a mixed synthesis gas with a higher CO content thereby optimizing the production in the production loop.

The production loop can for example be a methanol produc ^¬ tion unit producing a methanol rich product stream or e.g. be a CO production/purification unit producing a CO rich stream.

If the ¾ rich gas stream is a purge gas from a Methanol loop a highly effective process is achieved wherein the off gas from the methanol production is used to optimize the composition of the syngas used in the methanol production.

In the process the RWGS shifted gas stream can advanta ^¬ geously be produced over a High Temperature Shift Catalyst (e.g. Tops0e SK-201 or SK-501) or a UltraHigh Temperature Shift Catalyst.

The RWGS inlet temperature can be in the range of 250 - 750 °C. Often higher temperatures may be preferred as the RWGS conversion is favoured by higher temperatures. E.g. the inlet temperature can be 350°C or above, such as 500°C or above. As the reverse water gas shift reaction is an endothermic reaction the outlet temperature in an adiabatic reactor will be lower than the inlet temperature, typically the temperature drop will be in the range 50-250°C, such as 60 - 125.

In several advantageous embodiments the reverse shift reac ^¬ tion converts 5-75% of the CO ₂ into CO, resulting in a re ^¬ verse shifted gas which has a CO/CO ₂ ratio of 0.05 - 3, such as above 0.1 and/or below 2.

Generally the syngas may mainly comprise Hydrogen, Car- bonmonoxide, Carbondioxide, Methane, and Water (small amounts of f.inst. Nitrogen, Argon, and Helium may also be present) In the case of methanol production the syngas may comprise

H ₂ 65-75 vol

CO 12-25 vol

C0 ₂ 5-10 vol-

CH ₄ 0-10 vol-

H ₂ 0 Saturated If the production step is a CO purification step the syngas generally comprises Hydrogen, Carbonmonoxide, Methane, Wa ^¬ ter, and Carbondioxide (small amounts of for example Nitro ^¬ gen, Argon, and Helium may also be present) before the CO ₂ removal step where the reverse shifted gas advantageous can be added

H ₂ 50-70 vol

CO 20-35 vol

C0 ₂ 5-10 vol-

CH ₄ 0-5 vol-%

H ₂ 0 Saturated

The ¾ rich gas stream may e.g. comprise Hydrogen, Carbonmonoxide, Carbondioxide, Water, and Methane. In case of a methanol loop purge gas the ¾ rich stream comprises

H ₂ 70-85 vol

CO 0-8 vol-%

C0 ₂ 2-10 vol-

CH ₄ 5-20 vol-

Methanol 0.3-1 vol

The present process and plant may advantageously be part of a revamp of an existing plant such as a methanol production plant . An example of parameters for the RWGS step is given below:

Fig. 1 shows a diagram of the plan/process according to the present invention wherein a synthesis gas generation step 1 is arranged to receive a hydrocarbon or carboneous feed stock 2 and in a synthesis gas generation process provide a syngas 3. A production step 4 is arranged to receive the syngas and produce a product stream (5) . A reverse water gas shift step 6 is arranged to receive a ¾ rich gas stream 7 and a CO ₂ feed 8 and in a RWGS process obtain a reverse shifted gas stream 9. The plant/process furthermore has means 10 for adding said reverse shifted gas stream to the synthesis gas stream. Upstream the reverse water gas shift process a ¾ recovery unit 11 can be arranged to pro ^¬ vide a gas stream 7 which has an increased ¾ concentration compare to what is received from the production step 4. Such a ¾ recovery unit may for example be used where a purge 12 from the production step 4 is used to provide the ¾ rich stream. From the recovery unit a residual gas stream 13 may be provided e.g. to burners etc. Thus according to the present invention is provided a pro ^¬ cess and a plant by which a mixture of CO ₂ and ¾ stream is send to a reactor with a catalyst active towards the Water Gas Shift Reaction, a RWG shift (C0 ₂ + H ₂ -» CO + H ₂ 0) can be obtained, improving the CO/CO ₂ ratio, and thus the reac- tivity of the synthesis gas, reducing the required catalyst volume and/or heat transfer area in the production step, such as a methanol synthesis reactor. The present process and plant may be a particular advantage for revamp pro ^¬ jects, where the size of reformer and/or Methanol reactor is given by existing structures.