Plant and process for ammonia production with cryogenic purification, and related method of revamping

Patent metadata

Field	Value
Publication number	US-10514203-B2
Application number	US-201515527989-A
Country	US
Kind code	B2
Filing date	Nov 25, 2015
Priority date	Dec 23, 2014
Publication date	Dec 24, 2019
Grant date	Dec 24, 2019

Abstract

Process for the synthesis of ammonia from a make-up gas containing hydrogen and nitrogen, said process comprising: generation of a synthesis gas (8) containing hydrogen and nitrogen in a molar ratio lower than 3, inside a front-end section (2); a first cryogenic purification, designed to remove nitrogen and raise said molar ratio; conversion of the synthesis gas into ammonia (13) inside a high-pressure synthesis loop (6), with extraction from said loop of a purge stream (14) containing hydrogen and inert gases; wherein at least a portion of said purge stream (14) undergoes a further purification in order to recover at least part of the hydrogen contained therein, obtaining at least one stream (15, 15a, 16, 18) containing recovered hydrogen which is recycled to the process.

First claim

The invention claimed is:

1. A process for the synthesis of ammonia from a make-up gas containing hydrogen and nitrogen, said process comprising the steps of:
production of a synthesis gas containing hydrogen and nitrogen in a molar ratio lower than 3, inside a front-end section;
a first cryogenic purification of said synthesis gas, suitable to remove nitrogen and raise the hydrogen/nitrogen molar ratio of said gas to a predetermined value;
compression of the purified synthesis gas to a synthesis pressure;
conversion of synthesis gas into ammonia inside a synthesis loop, with extraction from said loop of a purge stream containing hydrogen and inert gases; and
performing a second purification of at least one portion of said purge stream, by means of a process suitable to recover at least part of the hydrogen contained therein, with the production of at least one stream containing recovered hydrogen and of at least one waste stream,
recycling said at least one stream containing recovered hydrogen to said process, in order to increase the ammonia production,
wherein at least a part of said at least one stream containing recovered hydrogen is recycled by means of joining with the gas stream undergoing said first cryogenic purification step.

2. The process according to claim 1 , wherein said synthesis gas from the front-end section contains an excess of nitrogen of at least 25% with respect to the hydrogen/nitrogen molar stoichiometric ratio of 3.

3. The process according to claim 1 , wherein at least 50% of said purge stream undergoes said second purification.

4. The process according to claim 1 , wherein said second purification comprises at least one of the following: a cryogenic separation process; a permeation process through a membrane permeable to hydrogen and impermeable to said inert gases; a process of adsorption with a material having high affinity for said inert gases and low affinity for hydrogen.

5. The process according to claim 4 , wherein said second purification is performed by means of a multi-stage process involving cryogenic separation or permeation through membrane, the process comprising, respectively, a plurality of cryogenic or permeation separation stages operating at different pressures, and resulting in a plurality of streams containing recovered hydrogen at pressures different from each other.

6. The process according to claim 1 , wherein a part of said at least one stream containing recovered hydrogen is recycled by means of direct feeding to the synthesis step.

7. The process according to claim 1 , wherein a portion of the synthesis gas stream from the front-end section is subjected to said first cryogenic purification, and a remaining portion of said stream is directly subjected to said second purification, together with the purge stream extracted from the synthesis loop, said second purification comprising a process of cryogenic separation.

8. The process according to claim 7 , wherein said second cryogenic purification comprises a low-pressure purification stage, carried out at a pressure higher than the minimum pressure among the incoming stream of the first purification, the outgoing stream of the first purification and the intake of a stage for compression of the synthesis gas, and said remaining portion of the stream is fed to said low-pressure purification stage.

9. The process according to claim 1 , wherein a portion of said waste stream from the second purification step is recycled, being combined with the gas stream from the front-end section.

Assignees

• Casale Sa

Inventors

• Filippi Ermanno
• Ostuni Raffaele

Classifications

• F25J2230/32

  Compression of the product stream · CPC title

• F25J3/0219

  Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature · CPC title

• C01B2203/046

  Purification by cryogenic separation · CPC title

• C01B2203/0405

  Purification by membrane separation · CPC title

• C01B3/506

  at low temperatures · CPC title