PROCESS AND PLANT FOR PRODUCING RENEWABLE FUELS

Abstract

Process and plant for producing methanol, the process comprising the steps of: a) providing a raw synthesis gas stream; b) water gas shifting at least a portion of the raw synthesis gas stream, thereby producing a shifted synthesis gas; c) preparing a separate hydrogen containing stream and a separate oxygen containing stream by electrolysis of a water feedstock; d) introducing at least a portion of the separate hydrogen containing stream into shifted synthesis gas, thereby producing a methanol synthesis gas; and e) converting the methanol synthesis gas into said methanol.

Claims

1. A process for producing methanol, comprising the steps of: a) providing a raw synthesis gas stream; b) water gas shifting (WGS) at least a portion of the raw synthesis gas stream, thereby producing a shifted synthesis gas; c) preparing a separate hydrogen containing stream and a separate oxygen containing stream by electrolysis of a water feedstock; d) introducing at least a portion of the separate hydrogen containing stream into the shifted synthesis gas, thereby producing a methanol synthesis gas, wherein the methanol synthesis gas has a module M=(H.sub.2CO.sub.2)/(CO+CO.sub.2) in the range 1.80-2.40, and a molar ratio CO/CO.sub.2 greater than 2; and e) converting the methanol synthesis gas into said methanol.

2. The process according to claim 1, wherein the module M=(H.sub.2CO.sub.2)/(CO+CO.sub.2) is in the range 1.95-2.10, and the molar ratio CO/CO.sub.2 is 10 or higher.

3. The process according to claim 1, wherein a portion of the raw synthesis gas bypasses the water gas shifting and is then combined with the shifted synthesis gas and the at least a portion of the separate hydrogen containing stream.

4. The process according to claim 1, wherein the process further comprises a cleaning step for providing the raw synthesis gas.

5. The process according to claim 4, wherein the process further comprises, prior to said step a), a thermal decomposition of a renewable feed stream for producing a crude synthesis gas stream, and subsequently subjecting the crude synthesis gas stream to said cleaning step for removing impurities, thereby producing the raw synthesis gas stream.

6. The process according to claim 5, wherein the thermal decomposition is gasification which is optionally conducted in a plasma gasifier, and the renewable feed stream is refused derived fuel (RDF).

7. The process according to claim 1, wherein in said step c) the electrolysis is conducted in: an alkaline and/or polymer electrolyte membrane electrolysis unit; or a solid oxide electrolysis cell unit (SOEC unit).

8. The process according to claim 1, wherein: in said step c) the electrolysis is conducted in a solid oxide electrolysis cell unit (SOEC unit), steam is generated in said step e) i.e. the methanol conversion step, and the water feedstock for the SOEC unit comprises at least a portion of the steam generated in said step e).

9. The process according to claim 1, wherein the process is free of any steam reforming step for producing the raw synthesis gas stream.

10. A plant for carrying out the process of claim 1, the plant comprising: a water gas shift (WGS) section configured to receive a raw synthesis gas stream and to provide a shifted synthesis gas; an electrolysis unit configured to receive a water feedstock and to provide a separate hydrogen containing stream and a separate oxygen containing stream; a mixing point configured to introduce at least a portion of the separate hydrogen containing stream into the shifted synthesis gas, thereby producing a methanol synthesis gas; wherein the methanol synthesis gas has a module M=(H.sub.2CO.sub.2)/(CO+CO.sub.2) in the range 1.80-2.40, and a molar ratio CO/CO.sub.2 greater than 2; and a methanol synthesis section configured to receive the methanol synthesis gas and convert the methanol synthesis gas into methanol; optionally, a cleaning unit arranged upstream said WGS section, and configured to receive a crude synthesis gas stream and provide said raw synthesis gas; optionally, a thermal decomposition unit arranged upstream said WGS section or upstream said cleaning unit, and configured to receive a renewable feed stream and provide said crude synthesis gas stream.

11. The process according to claim 1, wherein the process is free of any CO.sub.2-removal step after said step b).

12. The plant according to claim 10, wherein the plant is free of any CO.sub.2-removal section downstream of the water gas shift (WGS) section.

Description

[0071] FIG. 1 shows a schematic process and plant layout in accordance with the prior art.

[0072] FIG. 2 shows a schematic process and plant layout in accordance with an embodiment of the present invention.

[0073] With reference to FIG. 1, a schematic layout 10 in accordance with the prior art is shown, in which a raw synthesis gas 1 is used to produce a methanol product 11. A portion 1 of the raw synthesis gas is conducted to a water gas shift (WGS) step in WGS section 12 under the addition of water 19 by steam import, thereby producing shifted synthesis gas 3, 3.3. A portion 3 of the shifted synthesis gas is conducted to a step of acid gas removal, typically CO.sub.2-removal in CO.sub.2-removal section 14, thereby producing a CO.sub.2-stream 7 which is vented to the atmosphere, as well as a shifted and CO.sub.2-depleted synthesis gas 5. A portion 1 of the raw synthesis gas bypasses the WGS step and is combined with shifted synthesis gas 3 which bypasses the CO.sub.2-removal step, and which is then combined with the shifted and CO.sub.2-depleted synthesis gas 5 to produce methanol synthesis gas 9. This syngas 9 is then conducted to a methanol conversion step in a methanol synthesis section 16 comprising methanol synthesis loop 16 (methanol loop) including a methanol synthesis reactor (not shown) for producing a raw methanol stream, and methanol distillation section 16 thereby producing methanol product 11, suitably with a purity of 98 wt % methanol or higher. Steam 13 produced in the methanol loop 16 may be directed to a steam generation section 18, which thus generates steam 15, 15 used in the WGS section 12 and methanol distillation section 16. Boiler feed water 21 is suitably also added to the methanol loop 16.

[0074] Now with reference to FIG. 2, a schematic layout 100 in accordance with an embodiment of the present invention is shown. A raw synthesis gas 101, suitably produced in a prior thermal decomposition step in thermal decomposition unit such as a gasification unit being fed with a renewable feed stream, is used to produce methanol product 113. A portion 101 of the raw synthesis gas is conducted to a water gas shift (WGS) step in WGS section 112 under the addition of water 107 by steam import, thereby producing shifted synthesis gas 103. There is no acid gas removal, such as CO.sub.2-removal in a downstream CO.sub.2-removal section. A portion 101 of the raw synthesis gas bypasses the WGS step and is combined with shifted synthesis gas 103, together with a separate hydrogen containing stream 109, thereby producing methanol synthesis gas 111. The hydrogen containing stream 109 is prepared by electrolysis of steam 105, 107 in solid oxide electrolysis cell unit (SOEC unit) 120. The stream 105 is for instance demineralized water (DMW). The methanol synthesis gas 111 is then conducted, as in connection with FIG. 1, to a methanol conversion step in a methanol synthesis section 116 comprising methanol synthesis loop 116 (methanol loop) including a methanol synthesis reactor (not shown) for producing a raw methanol stream, and methanol distillation section 116 thereby producing e-methanol as the methanol product 113, suitably with a purity of 98 wt % methanol or higher. Steam 115 produced in the methanol loop 116 may be directed to a steam production section 118, which thus generates steam 117, 117 used in the WGS section 112 and methanol distillation section 116. Boiler feed water 121 is suitably also added to the methanol loop 116.

EXAMPLE

[0075] The table below shows a comparison of the process/plant scheme according to FIG. 1 (prior art) vs the process/plant scheme according to FIG. 2 (embodiment of the invention). By the invention there is more than 40% additional methanol production while at the same time eliminating the amount of carbon dioxide vented to the atmosphere (CO.sub.2 vent) from about 10000 tons per year, to zero:

TABLE-US-00001 Stream no. Stream no. FIG. 1 FIG. 2 FIG. 1 FIG. 2 (Prior art) (Invention) Methanol syngas 9 111 4450 4450 (Nm.sup.3/h) Hydrogen (Nm.sup.3/h) 109 0 1620 Steam: Medium pressure 19 107 1030 606 (MP) steam import (kg/h) Low pressure (LP) 17 119 759 1861 steam import (kg/h) CO.sub.2 vent (Nm.sup.3/h) 604 0 CO.sub.2 vent (tons per 9894 0 year)* Methanol: (kg/h) 1748 2487 Methanol (MTPD) 42.0 59.7 Additional 0 42 methanol production (%) *Assuming 365 days/year with a carbon dioxide density of 1.87 kg/m.sup.3