METHOD FOR THE PREPARATION OF SYNTHESIS GAS

Abstract

Method for the preparation of synthesis gas combining electrolysis of water, tubular steam reforming and autothermal reforming of a hydrocarbon feed stock in parallel.

Claims

1. Method for the preparation of synthesis gas comprising the steps of: (a) providing a hydrocarbon feed stock; (b) preparing a separate hydrogen containing stream and a separate oxygen containing stream by electrolysis of water and/or steam; (c) steam reforming a first part of the hydrocarbon feed stock from step (a) in a tubular steam reformer to a tubular steam reformed gas comprising hydrogen, carbon monoxide and carbon dioxide; (d) autothermal reforming a second part of the hydrocarbon feed stock in an autothermal reformer with at least part of the oxygen containing stream obtained in step (b) to an autothermal reformed gas stream comprising hydrogen, carbon monoxide and carbon dioxide; (e) combining the steam reformed gas from step (c) with the autothermal reformed gas from step (d); (f) adding at least part of the separate hydrogen containing stream from step (b) into the hydrocarbon feed stock from step (a) and/or into the steam reformed gas stream from step (c) and/or into the autothermal reformed gas stream from step (d) and/or into the combined steam reformed gas and autothermal reformed gas stream from step (e); and (g) withdrawing the synthesis gas.

2. The method of claim 1, wherein carbon dioxide in flue gas from the tubular steam reformer is recovered and added to the steam reforming in step (c).

3. The method of claim 1, wherein the electrolysis of water and/or steam in step (b) is powered by renewable energy.

4. The method of claim 1, wherein the hydrogen stream is added to the combined tubular steam reformed gas and autothermal reformed gas stream in an amount to provide a module M=(H.sub.2−CO.sub.2)/(CO+CO.sub.2) in the synthesis gas withdrawn in step (g) of between 1.9 and 2.2.

5. The method of claim 1, wherein the module M=(H.sub.2−CO.sub.2)/(CO+CO.sub.2) in the synthesis gas withdrawn in step (g) is in the range from 2 to 2.1.

6. The method of claim 1, comprising the further step of heat exchange reforming a part of the hydrocarbon feedstock from step (a) and/or the tubular steam reformed gas from step (c).

7. The method of claim 1, wherein the hydrocarbon feed stock comprises natural gas, methane, LNG, naphtha or mixtures thereof either as such or pre-reformed and/or desulfurized.

8. The method of claim 1, wherein the synthesis gas withdrawn in step (g) is in a further step converted to a methanol product.

Description

[0011] Thus, this invention provides a method for the preparation of synthesis gas comprising the steps of

[0012] (a) providing a hydrocarbon feed stock;

[0013] (b) preparing a separate hydrogen containing stream and a separate oxygen containing stream by electrolysis of water and/or steam;

[0014] (c) steam reforming a first part of the hydrocarbon feed stock from step (a) in a tubular steam reformer to a tubular steam reformed gas comprising hydrogen, carbon monoxide and carbon dioxide;

[0015] (d) autothermal reforming a second part of the hydrocarbon feed stock in an autothermal reformer with at least part of the oxygen containing stream obtained in step (b) to an autothermal reformed gas stream comprising hydrogen, carbon monoxide and carbon dioxide;

[0016] (e) combining the steam reformed gas from step (c) with the autothermal reformed gas from step (d);

[0017] (f) adding at least part of the separate hydrogen containing stream from step (b) into the hydrocarbon feed stock from step (a) and/or into the steam reformed gas stream from step (c) and/or into the autothermal reformed gas stream from step (d) and/or into the combined steam reformed gas and autothermal reformed gas stream from step (e); and

[0018] (g) withdrawing the synthesis gas.

[0019] Tubular steam reforming creates CO.sub.2 in the flue gas from the burners in the tubular steam reforming. The Co.sub.2 in the flue gas is in an embodiment of the invention recovered and added to the tubular steam reforming process.

[0020] Thereby, the CO.sub.2 footprint of the method according to the invention is advantageously lowered when the added CO.sub.2 is utilized in the production methanol.

[0021] To minimize CO.sub.2 emissions further, a part of the feedstock can be heat exchange reformed in a heat exchange reformer downstream the tubular steam reformer and/or the tubular steam reformed gas can be additionally heat exchange reformed to reduce fuel consumption.

[0022] The electrolysis can be performed by various means known in the art such as by solid oxide based electrolysis or electrolysis by alkaline cells or polymer cells (PEM).

[0023] When the power for the electrolysis is produced (at least in part) by sustainable sources, the CO.sub.2-emissions is per unit of product produced by the method reduced.

[0024] Preferably, the electrolysis of water and/or steam is powered solely by renewable energy.

[0025] As already mentioned above, all the oxygen from the electrolysis unit is added to the autothermal reformer in step (d) and an ASU for the preparation of oxygen by separation of air is avoided.

[0026] The method according to the invention is preferably employed for the production of methanol synthesis gas.

[0027] Methanol synthesis gas has preferably a composition corresponding to a so-called module (M=(H2−CO2)/(CO+CO2)) of 1.90-2.20 or more preferably slightly above 2 (eg. 2.00-2.10).

[0028] Thus when the method according to the invention is used in the preparation of methanol synthesis gas, the amount of hydrogen added to the feed stock upstream to the SMR or the ATR or to the reformed gas downstream step (e) can be tailored such that when the hydrogen is mixed with the synthesis gas generated by the reforming steps and the optionally CO.sub.2 addition recovered from the tubular steam reformer a desired value of M of between 1.90 and 2.20 or preferably between 2.00 and 2.10 is achieved.

[0029] In general, suitable hydrocarbon feedstocks for use in the various embodiments of the invention comprise natural gas, methane, LNG, naphtha or mixtures thereof either as such or pre-reformed and/or desulfurized.

[0030] The method according to the invention can also be employed for producing synthesis gas for other applications where it is desirable to increase the hydrogen concentration in the feed gas and where the hydrogen and oxygen is favorably produced by electrolysis.