Production of ammonia make-up syngas with cryogenic purification

Patent metadata

Field	Value
Publication number	US-10273155-B2
Application number	US-201715601690-A
Country	US
Kind code	B2
Filing date	May 22, 2017
Priority date	Sep 2, 2009
Publication date	Apr 30, 2019
Grant date	Apr 30, 2019

Abstract

A process and a related equipment for making ammonia make-up synthesis gas are disclosed, where: a hydrocarbon feedstock is reformed obtaining a raw ammonia make-up syngas stream; said raw syngas is purified in a cryogenic purification section refrigerated by a nitrogen-rich stream produced in an air separation unit; the nitrogen-rich stream at output of said cryogenic section is further used for adjusting the hydrogen/nitrogen ratio of the purified make-up syngas; an oxygen-rich stream is also produced in said air separation unit and is fed to the reforming section.

First claim

The invention claimed is:

1. A process for making ammonia make-up synthesis gas, comprising the steps of:
reforming a hydrocarbon feedstock, followed by steps of shift, CO 2 removal and methanation, to obtain a raw ammonia make-up synthesis gas stream comprising hydrogen and nitrogen;
treating said raw ammonia make-up synthesis gas in a cryogenic purification section obtaining a purified synthesis gas stream;
feeding a liquid nitrogen-rich stream at a cryogenic temperature to said cryogenic purification section;
providing an indirect heat exchange between said raw ammonia make-up synthesis gas and/or a partially purified ammonia make-up synthesis gas and said liquid nitrogen-rich stream in the cryogenic section, said liquid nitrogen-rich stream being at least partly evaporated to provide refrigeration of said cryogenic section; and
treating an air stream in an air separation unit, obtaining said liquid nitrogen-rich stream and an oxygen-rich stream.

2. The process according to claim 1 , where said liquid nitrogen-rich stream, after at least a partial evaporation through the cryogenic section, is recovered at an output of said cryogenic section, and mixed with the purified synthesis gas to provide at least a portion of the nitrogen required to adjust the hydrogen/nitrogen ratio of the ammonia make-up synthesis gas.

3. The process according to claim 1 , where said air separation unit provides said liquid nitrogen-rich stream, and a second nitrogen-rich stream at ambient temperature and in a gaseous state, and where the amount of nitrogen required to adjust the HN ratio of the ammonia make-up synthesis gas is provided partly by the evaporated liquid nitrogen-rich stream recovered at the output of the cryogenic section and partly by said nitrogen-rich stream at ambient temperature.

4. The process according to claim 1 , where said oxygen-rich stream is used as further oxidant in the reforming process, by injection of said oxygen-rich stream into a secondary reformer of the reforming section.

5. The process according to claim 1 , wherein:
said raw synthesis gas is cooled down to a cryogenic temperature in a main heat exchanger of the cryogenic section, obtaining a cooled raw synthesis gas;
said cooled raw synthesis gas is fed to a contacting device where a liquid fraction containing impurities is obtained by cryogenic liquefaction and separated from the synthesis gas;
a purified synthesis gas is recovered from said contacting device and is further cooled and purified in a condenser which is refrigerated by at least partial evaporation of said liquid nitrogen-rich stream;
a further purified synthesis gas is taken at the output of said condenser and re-heated in said main heat exchanger, by heat exchange with the incoming raw synthesis gas and with evaporated nitrogen stream taken from said condenser.

6. The process according to claim 5 , wherein said liquid fraction containing impurities is further used as a refrigerating medium for the main heat exchanger of the cryogenic section.

7. The process according to claim 1 , wherein said liquid nitrogen-rich stream and/or a second nitrogen-rich stream at ambient temperature are substantially pure nitrogen.

8. An equipment for producing ammonia make-up synthesis gas comprising:
a front-end section comprising a reforming section adapted to reform a hydrocarbon feedstock and to produce a raw ammonia synthesis gas stream;
a cryogenic purification section treating the raw synthesis gas produced in the front-end;
an air separation unit feeding a liquid nitrogen-rich stream at a cryogenic temperature to said cryogenic purification section, for use as a heat exchange medium to refrigerate said cryogenic purification section; and
at least one indirect heat exchanger between said raw ammonia make-up synthesis gas and/or a partially purified ammonia make-up synthesis gas and said liquid nitrogen-rich stream in the cryogenic section, said liquid nitrogen-rich stream being at least partially evaporated in said heat exchanger(s) to provide refrigeration of said cryogenic section;
wherein said air separation unit further delivers a first liquid nitrogen-rich stream and a second stream of nitrogen at ambient temperature for HN ratio adjustment, and additionally delivers an oxygen-rich stream which is fed as oxidizer to the reforming section; and
wherein the front-end section further comprises equipment for shift, CO 2 removal and methanation.

9. The equipment according to claim 8 , further comprising a line for recovering the evaporated nitrogen-rich stream at an output of the cryogenic purification section, and for mixing said nitrogen-rich stream with purified synthesis gas, to provide at least a portion of nitrogen required for adjusting the hydrogen/nitrogen ratio of the ammonia make-up synthesis gas.

10. The equipment according to claim 9 , the front-end comprising a primary reformer, a secondary reformer, and equipment for shift, CO 2 removal and methanation, said oxygen-rich stream being fed to the secondary reformer of the reforming section.

11. The equipment according to claim 8 , the cryogenic section comprising:
a cryogenic condenser column;
a condenser receiving a partially-purified synthesis gas obtained in the cryogenic condenser column, said condenser being refrigerated by the liquid nitrogen-rich stream;
a main heat exchanger where the incoming raw synthesis gas is cooled by heat exchange with one or more of the following: the nitrogen stream evaporated in said condenser, the purified synthesis gas, a bottom effluent of said cryogenic condenser column.

12. The method for revamping the front-end of an ammonia plant, said front-end section comprising a reforming section with at least a primary reformer and a secondary reformer for converting a hydrocarbon feedstock into ammonia raw make-up synthesis gas, the method comprising at least the steps of:
installing an air separation unit in parallel to said front-end;
providing a cryogenic section for treatment of the raw synthesis gas, if not present in the original plant;
providing a line for feeding a liquid nitrogen-rich stream produced in said air separation unit to said cryogenic section, for use as refrigerating medium;
providing at least one indirect heat exchanger between said raw ammonia make-up synthesis gas and/or a partially purified ammonia make-up synthesis gas and said liquid nitrogen-rich stream in the cryogenic section, said liquid nitrogen-rich stream being at least partially evaporated in said heat exchanger(s) to provide refrigeration of said cryogenic section; and
providing a line feeding oxygen-rich stream produced in said air separation unit to the secondary reformer, in order to increase the capability of said reforming section.

Assignees

• Casale Sa

Inventors

• Filippi Ermanno
• Skinner Geoffrey Frederick

Classifications

• C01B2203/1241

  Natural gas or methane · CPC title

• C01B3/506

  at low temperatures · CPC title

• C01B2203/047

  the impurity being carbon monoxide · CPC title

• C01B3/38

  using catalysts · CPC title

• C01B3/34 Primary

  by reaction of hydrocarbons with gasifying agents · CPC title