Process for producing ammonia synthesis gas and a method for revamping a front-end of an ammonia plant

Patent metadata

Field	Value
Publication number	US-10954124-B2
Application number	US-201415035151-A
Country	US
Kind code	B2
Filing date	Oct 13, 2014
Priority date	Nov 8, 2013
Publication date	Mar 23, 2021
Grant date	Mar 23, 2021

Abstract

A process for producing ammonia make-up synthesis gas and a procedure for revamping a front-end of an ammonia plant for producing ammonia make-up synthesis gas are disclosed, wherein the make-up synthesis gas is produced by means of steam reforming of a hydrocarbon gaseous feedstock; said front-end includes a primary reformer, a secondary reformer, a shift conversion section, a CO2 removal section and optionally a methanation section; a shell-and-tube gas-heated reformer is installed after said secondary reformer, and a portion of the available feedstock is reformed in the tubes of said gas-heated reformer, and heat is provided to the shell side of said gas-heated reformer by at least a portion of product gas leaving the secondary reformer, possibly mixed with product gas leaving the tubes of said gas-heated reformer.

First claim

The invention claimed is:

1. A procedure for revamping a front-end of an ammonia plant, said front-end being arranged to produce ammonia synthesis gas containing hydrogen and nitrogen by steam reforming of a hydrocarbon gaseous feedstock, said front-end including a primary reformer, a secondary reformer, a shift conversion section, and a CO 2 removal section, said procedure including at least:
installation of a gas-heated reformer after said secondary reformer, said gas-heated reformer being a shell-and-tube heat exchanger having a tube side and a shell side, and providing a catalytic reforming of a first gas current passing in the tube side and indirect heating of said first gas current by a second current traversing the shell side,
said first current including a portion of the available hydrocarbon feedstock, the remaining portion of said feedstock being directed to said primary reformer, and said second current comprising at least a portion of a product gas effluent from said secondary reformer,
said secondary reformer being an air-fired secondary reformer, and the procedure including the step of modifying said secondary reformer to operate with O 2 -enriched air, and
wherein said front-end includes a methanation section and said procedure provides for the addition of nitrogen to a product gas flowing in said methanation section or to a product gas effluent from said methanation section, or wherein the procedure provides for the installation of a final purification section after said CO 2 removal section, for the removal of inert gases from CO 2 -depleted product gas effluent from said CO 2 removal section, and nitrogen is added to a product gas flowing in said final purification section or to a product gas effluent from said final purification section.

2. The procedure of claim 1 , wherein said first current is a portion of a mixed flow comprising steam and the available hydrocarbon feedstock, which is redirected to said gas-heated reactor while the remaining portion is directed to said primary reformer.

3. The procedure of claim 2 , said mixed flow having a steam-to-carbon ratio of between 2 and 3.5.

4. The procedure of claim 1 , said second current comprising product gas effluent from said secondary reformer or autothermal reformer, and also comprising product gas leaving said tube side of said gas-heated reformer.

5. The procedure of claim 1 , said 02-enriched air being obtained by adding an oxygen flow to ambient air.

6. The procedure of claim 5 , said oxygen flow being in an amount to provide a molar concentration of oxygen in the enriched air between 25% and 70%.

7. The procedure of claim 5 , said oxygen flow being delivered by an air-separation unit.

8. The procedure of claim 7 , further comprising the provision and the installation of said air-separation unit.

9. The procedure of claim 1 , further including the revamping of said shift conversion section and/or the revamping of said CO 2 removal section.

10. The procedure of claim 9 , including the revamping of said shift conversion section by means of one or more of the following: the conversion of one or more existing axial-flow shift converters into axial-radial shift converters; adding one or more shift converters in parallel to the existing ones; replacing one or more existing adiabatic high-temperature shift converters with one or more isothermal medium-temperature shift converters.

11. The procedure of claim 10 , including the provision of one or more isothermal medium-temperature shift converters or the modification of one or more existing shift converters to operate as medium shift converters, wherein said medium-temperature shift converters include a copper-based catalyst, and comprise a heat exchanger immersed in the catalyst, to remove the heat produced by the exothermic shift conversion.

12. The procedure of claim 11 , said medium temperature being in the range of 200-300° C.

13. The procedure of claim 1 , said purification section including a methanation section.

14. The procedure of claim 1 , said purification section including a nitrogen wash section or a cryogenic condensation section for condensation of nitrogen and inerts, or a PSA unit.

15. The procedure of claim 14 , said purification section including a nitrogen wash section or a cryogenic condensation section, said procedure including the provision of a nitrogen line for addition of nitrogen before or into said nitrogen wash section or said cryogenic condensation section, and said nitrogen being in an amount suitable to obtain a purified synthesis gas containing hydrogen and nitrogen in a molar ratio around 3 to 1.

16. A process for producing ammonia synthesis gas containing hydrogen and nitrogen by steam reforming of a hydrocarbon gaseous feedstock, including:
mixing said hydrocarbon gaseous feedstock with steam,
reforming a first portion of the so obtained mixed flow of gaseous feedstock and steam in a primary reformer and then in a secondary reformer or in an autothermal reformer, obtaining a first product gas,
reforming a second portion of said mixed flow in a gas-heated reactor, obtaining a second product gas,
said gas-heated reactor being heated by a current of product gas comprising at least a portion said first product gas, wherein:
said secondary reformer operates with O 2 -enriched air, and
nitrogen is added to a product gas flowing in a final purification step or to a product gas effluent from said final purification step.

17. The process of claim 16 , said secondary reformer or autothermal reformer operating with O 2 -enriched air having a concentration of oxygen between 25% and 70% molar.

18. The process of claim 16 , further comprising the treatment of product gas comprising: shift conversion, removal of carbon dioxide, and purification of CO 2 -depleted product gas after said removal of carbon dioxide, and said purification including at least one of the following: a methanation process; nitrogen wash; cryogenic condensation; pressure-swing adsorption (PSA).

Assignees

• Casale Sa

Inventors

• Filippi Ermanno
• Ostuni Raffaele

Classifications

• C01B13/0229

  Purification or separation processes · CPC title

• C01B2203/0445

  Selective methanation · CPC title

• C01B3/382

  Processes with two or more reaction steps, of which at least one is catalytic, e.g. steam reforming and partial oxidation · CPC title

• C01B2203/0844

  the non-combustive exothermic reaction being another reforming reaction as defined in groups C01B2203/02 - C01B2203/0294 · CPC title

• C01B2203/068

  Ammonia synthesis · CPC title