Process for Producing Ammonia Synthesis Gas

• US 20100303703A1
• Filed: 11/06/2008
• Published: 12/02/2010
• Est. Priority Date: 11/27/2007
• Status: Active Grant

• Current Assignee: Casale SA
• Original Assignee: Ammonia Casale, S.A.
• Inventors: Filippi, Ermanno, Skinner, Geoffrey Frederick, Badano, Marco
• Granted Patent: US 9,040,011 B2
• Time in Patent Office: Days
• US Class Current: 423/359
• CPC Class Codes: C01B 2203/0233 the reforming step being a steam reforming step
• CPC Class Codes: C01B 2203/0244 the reforming step being an autothermal reforming step, e.g. secondary reforming processes
• CPC Class Codes: C01B 2203/025 containing a partial oxidation step
• CPC Class Codes: C01B 2203/0415 Purification by absorption in liquids
• CPC Class Codes: C01B 2203/042 Purification by adsorption on solids
• CPC Class Codes: C01B 2203/0435 Catalytic purification
• CPC Class Codes: C01B 2203/047 the impurity being carbon monoxide
• CPC Class Codes: C01B 2203/0475 the impurity being carbon dioxide
• CPC Class Codes: C01B 2203/068 Ammonia synthesis
• CPC Class Codes: C01B 2203/1235 Hydrocarbons
• CPC Class Codes: C01B 2203/142 At least two reforming, decomposition or partial oxidation steps in series
• CPC Class Codes: C01B 2203/147 Three or more purification steps in series
• CPC Class Codes: C01B 3/025 Preparation or purification of gas mixtures for ammonia synthesis
• CPC Class Codes: C01B 3/382 Multi-step processes
• CPC Class Codes: C01B 3/48 followed by reaction of water vapour with carbon monoxide
• CPC Class Codes: C01C 1/0405 from N2 and H2 in presence of a catalyst

Abstract

The present invention concerns a process for producing ammonia synthesis gas from the reforming of hydrocarbons with steam in a primary reformer (1) equipped with a plurality of externally heated catalytic tubes and then in a secondary reformer (2) together with an oxidant gas. In this process, the reaction of said hydrocarbons with said steam in said primary reformer (1) is performed at an operating pressure of at least 45 bar in the catalytic tubes and a flow of essentially pure oxygen or oxygen-enriched air is added to said secondary reformer as oxidant gas for substantially reforming together with said all the hydrocarbons content of said product gas exiting the primary reformer (1). In the case essentially pure oxygen is used as oxidant gas, a flow of nitrogen is added downstream the secondary reformer (2) to reach a N2/H2 molar ratio corresponding to or close to the stoichiometric ratio for ammonia synthesis. This process allows to obtain high synthesis gas production capacities and lower investment and energy costs.

Claims

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

feeding a gas flow comprising hydrocarbons and a gas flow comprising steam to a primary reformer equipped with a plurality of externally heated catalytic tubes,

reacting said hydrocarbons with said steam in the catalytic tubes of said primary reformer at an operating pressure of at least 45 bar in the catalytic tubes, obtaining a product gas,

feeding said product gas and a flow of oxidant gas to a secondary reformer,

subjecting said product gas to reaction with said oxidant gas and then to secondary reforming so as to substantially reform all the hydrocarbons content of said product gas exiting the primary reformer and obtain a reformed gas comprising hydrogen, carbon oxides and unreacted steam and also having a content of nitrogen from 0 to the content required for a H₂/N₂ molar ratio in said reformed gas close to the stoichiometric ratio for ammonia synthesis,

removing carbon oxides from said reformed gas, obtaining a synthesis gas suitable for synthesis of ammonia,

characterized in that wherein said oxidant gas is oxygen-enriched air having an appropriate N₂/O₂ molar ratio to substantially reform all the hydrocarbons content of said product gas exiting the primary reformer and to obtain a reformed gas with H₂/N₂ molar ratio close to the stoichiometric ratio for ammonia synthesis.

2. The process according to claim 1, said oxygen-enriched air having a O₂ content from 22 to 50 in mol % and being supplied to the secondary reformer in a ratio of 0.35 to 0.5 mol of oxygen content of the enriched air stream per mol of carbon in hydrocarbons entering the primary reformer or a pre-reformer if used.

3. The process according to claim 1 said operating pressure in the catalytic tubes of the primary reformer being in the range of 45-100 bar, preferably in the range of 60-80 bar.

4. The process according to claim 1, the outlet temperature of said gas product from the tubes of the primary reformer being in the range of 650-850°

C.

5. The process according to claim 4, said outlet temperature being in the range of 700-770°

C.

6. The process according to claim 1, said step of removing carbon oxides from said reformed gas comprising the following operative stages:

substantially removing carbon monoxide from said reformed gas by catalytic conversion with unreacted steam into carbon dioxide and hydrogen, so obtaining a reformed gas essentially deprived of carbon monoxide and some steam,

substantially removing carbon dioxide from reformed gas essentially deprived of carbon monoxide and some steam to obtain a reformed gas still including traces of carbon oxides,

removing said traces of carbon dioxide by catalytic conversion to methane.

7. The process for producing ammonia from ammonia synthesis gas, the process comprising the steps of obtaining ammonia synthesis gas according to claim 1, and reacting said synthesis gas in an ammonia synthesis loop under conditions effective to obtain ammonia.

8-12. -12. (canceled)