Systems and methods for improving ammonia synthesis efficiency

• US 8,617,270 B2
• Filed: 12/03/2008
• Issued: 12/31/2013
• Est. Priority Date: 12/03/2008
• Status: Active Grant

• Current Assignee: Kellogg Brown & Root LLC (KBR Incorporated)
• Original Assignee: Kellogg Brown & Root LLC (KBR Incorporated)
• Inventors: Haque, Israr Ul
• Primary Examiner(s): Akram, Imran
• Application Number:
  US12/327,249
• Publication Number:
  US 20100132259A1
• Time in Patent Office: 1,854 Days
• Field of Search: 48 61-1185, 481/271, 481/279, 48197 R-197 A, 422129-242, 429400-535
• US Class Current: 48/197.R
• CPC Class Codes: C01B 2203/0233 the reforming step being a steam reforming step
• CPC Class Codes: C01B 2203/0261 containing a catalytic partial oxidation step [CPO]
• CPC Class Codes: C01B 2203/0283 containing a CO-shift step, i.e. a water gas shift step
• CPC Class Codes: C01B 2203/044 Selective oxidation of carbon monoxide
• CPC Class Codes: C01B 2203/0445 Selective methanation
• CPC Class Codes: C01B 2203/0475 the impurity being carbon dioxide
• CPC Class Codes: C01B 2203/068 Ammonia synthesis
• CPC Class Codes: C01B 2203/1241 Natural gas or methane
• CPC Class Codes: C01B 2203/146 At least two 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 3/384 the catalyst being continuously externally heated
• CPC Class Codes: C01B 3/48 followed by reaction of water vapour with carbon monoxide
• CPC Class Codes: Y02P 20/52 using catalysts, e.g. selective catalysts

Abstract

Systems and methods for producing syngas are provided. In at least one specific embodiment, a hydrocarbon can be reformed in the presence of steam and one or more first catalysts in a first reaction zone to provide an effluent containing a portion of the hydrocarbon, carbon monoxide, carbon dioxide, and hydrogen at a first temperature. The first reaction zone can include one or more catalyst-containing tubes. The effluent can be indirectly heated from the first temperature to a second temperature. The effluent at the second temperature can be reformed in the presence of one or more oxidants and one or more second catalysts at conditions sufficient to provide a syngas comprising hydrogen, carbon monoxide, carbon dioxide, and less than about 5% mol, dry basis, methane. The syngas can be used to indirectly heat the effluent from the first temperature to the second temperature.

Claims

1. A method for producing syngas, comprising:

reforming a hydrocarbon in the presence of steam and one or more first catalysts in a first reaction zone to provide an effluent comprising a portion of the hydrocarbon, carbon monoxide, carbon dioxide, about 8% mol to about 12% mol methane, and hydrogen at a first temperature, wherein the first reaction zone comprises one or more catalyst-containing tubes, and wherein a ratio of steam to the hydrocarbon in the first reaction zone is 2.5 to 3.5;

indirectly heating the effluent from the first temperature to a second temperature;

reforming the effluent at the second temperature and at a pressure of about 4,000 kPa to about 5,500 kPa in the presence of one or more oxidants and one or more second catalysts at conditions sufficient to provide a syngas having a temperature of about 1,030°

C. or more and comprising hydrogen, carbon monoxide, carbon dioxide, and less than 0.3% mol, dry basis, methane, wherein the syngas is used to indirectly heat the effluent from the first temperature to the second temperature;

converting at least a portion of the carbon monoxide in the syngas used to indirectly heat the effluent to provide a converted syngas comprising carbon dioxide and 1% mol dry basis or less carbon monoxide;

removing at least a portion of the carbon dioxide of the converted syngas to provide a lean syngas comprising 1% mol dry basis or less carbon dioxide and carbon monoxide;

converting at least a portion of any carbon dioxide, carbon monoxide, or both contained in the lean syngas to methane;

separating at least a portion of the water from the lean syngas;

separating at least a portion of nitrogen in the lean syngas to provide an ammonia syngas having a hydrogen to nitrogen ratio of about 2.9;

1 to about 3.2;

1; and

reacting at least a portion of the hydrogen and nitrogen in the ammonia syngas to provide an ammonia product.

2. The method of claim 1, wherein the first temperature is about 700°

C. or more.

3. The method of claim 1, wherein the second temperature is about 850°

C. or more.

4. The method of claim 1, wherein the hydrocarbon comprises methane.

5. The method of claim 1, wherein the temperature of the syngas after indirectly heating the effluent from the first temperature to the second temperature is about 880°

C. or more.

6. The method of claim 1, wherein heat is indirectly exchanged from the syngas after the syngas is used to indirectly heat the effluent to a condensate to provide high pressure steam.

7. The method of claim 1, wherein reacting at least a portion of the hydrogen and nitrogen in the ammonia syngas to provide an ammonia product occurs in an ammonia converter, the ammonia converter comprising:

a first shell having two or more discrete catalyst beds disposed therein;

a second shell disposed about the first shell;

a first heat exchanger disposed external to the first shell and in fluid communication therewith;

a second heat exchanger disposed external to the second shell and in fluid communication therewith; and

a flow path disposed within the first shell, wherein the two or more discrete catalyst beds within the first shell are disposed about the flow path, wherein a first portion of the ammonia syngas is introduced to the first shell and a second portion of the ammonia syngas is introduced to the second shell.

8. The method of claim 1, wherein the effluent comprises about 35% mol to about 39% mol hydrogen, about 4% mol to about 5% mol carbon monoxide, about 6% mol to about 8% mol carbon dioxide, about 8% mol to about 10% mol methane, and about 42% mol to about 47% mol steam.

9. The method of claim 1, wherein the temperature of the hydrocarbon and steam is monotonically increased to the first temperature.

10. The method of claim 1, wherein the syngas has a temperature of about 1,050°

C. or more.

11. The method of claim 1, wherein the syngas has a temperature from about 1,030°

C. to about 1,050°

C.

12. The method of claim 1,

wherein separating the at least a portion of the nitrogen in the lean syngas to provide the ammonia syngas comprises:

cooling the lean syngas in a cross-exchanger to obtain a cooled syngas;

introducing the cooled syngas to a distillation column;

expanding a liquid bottoms stream from the distillation column through a liquid expander to form a cooled waste fluid;

rectifying vapor in the distillation column to form an overhead having a reduced nitrogen content;

cooling the overhead vapor in indirect heat exchange with the cooled waste fluid to form the ammonia syngas.

18. The method of claim 1, wherein the temperature of the syngas after the syngas is used to indirectly heat the effluent is about 860°

C. to about 900°

C.

13. A method for producing syngas, comprising:

reforming a hydrocarbon in the presence of steam and one or more first catalysts in a first reaction zone to provide an effluent comprising a portion of the hydrocarbon, carbon monoxide, carbon dioxide, about 8% mol to about 12% mol methane, and hydrogen at a first temperature, wherein the temperature of the hydrocarbon and steam is monotonically increased to the first temperature, and wherein a ratio of steam to the hydrocarbon in the first reaction zone is 2.5 to 3.5;

indirectly heating the effluent at the first temperature to provide an effluent at a second temperature; and

reforming the effluent at the second temperature and at a pressure of about 4,000 kPa to about 5,500 kPa in the presence of one or more oxidants and one or more second catalysts to provide a syngas, wherein the syngas has a temperature of about 1,030°

C. or more and comprises hydrogen, carbon monoxide, carbon dioxide, nitrogen, less than 0.3% mol, dry basis, methane, and water, and wherein the syngas is used to indirectly heat the effluent at the first temperature to the second temperature;

converting at least a portion of the carbon monoxide in the syngas used to indirectly heat the effluent to provide a converted syngas comprising carbon dioxide and 1% mol dry basis or less carbon monoxide;

removing at least a portion of the carbon dioxide of the converted syngas to provide a lean syngas comprising 1% mol dry basis or less carbon dioxide and carbon monoxide;

converting at least a portion of any carbon dioxide, carbon monoxide, or both contained in the lean syngas to methane;

separating at least a portion of the water from the lean syngas;

separating at least a portion of the nitrogen in the lean syngas to provide an ammonia syngas having a hydrogen to nitrogen ratio of about 2.9;

1 to about 3.2;

1; and

reacting at least a portion of the hydrogen and nitrogen in the ammonia syngas to provide an ammonia product.

14. The method of claim 13, wherein reacting at least a portion of the hydrogen and nitrogen in the ammonia syngas to provide an ammonia product occurs in an ammonia converter, the ammonia converter comprising:

a first shell having two or more discrete catalyst beds disposed therein;

a second shell disposed about the first shell;

a first heat exchanger disposed external to the first shell and in fluid communication therewith;

a second heat exchanger disposed external to the second shell and in fluid communication therewith; and

a flow path disposed within the first shell, wherein the two or more discrete catalyst beds within the first shell are disposed about the flow path, wherein a first portion of the ammonia syngas is introduced to the first shell and a second portion of the ammonia syngas is introduced to the second shell.

15. The method of claim 14, wherein the effluent comprises about 35% mol to about 39% mol hydrogen, about 4% mol to about 5% mol carbon monoxide, about 6% mol to about 8% mol carbon dioxide, about 8% mol to about 10% mol methane, and about 42% mol to about 47% mol steam.

16. The method of claim 13, wherein the first temperature is about 700°

C. or more.

17. The method of claim 13, wherein the second temperature is about 850°

C. or more.

19. The method of claim 13, wherein the temperature of the syngas after indirectly heating the effluent from the first temperature to the second temperature is about 880°

C.

20. A method for producing syngas, comprising:

reforming a hydrocarbon in the presence of steam and one or more first catalysts comprising about 15 wt % to about 20 wt % nickel in a first reaction zone to provide an effluent comprising a portion of the hydrocarbon, carbon monoxide, carbon dioxide, about 8% mol to about 12% mol methane, and hydrogen at a first temperature, wherein the first reaction zone comprises a plurality of catalyst-containing tubes, each having an inside diameter of about 40 mm to about 115 mm, and wherein a ratio of steam to the hydrocarbon in the first reaction zone is 2.5 to 3.5;

indirectly heating the effluent from the first temperature to a second temperature; and

reforming the effluent at the second temperature and at a pressure of about 4,000 kPa to about 5,500 kPa in the presence of one or more oxidants and one or more second catalysts comprising about 10 wt % to about 15 wt % nickel in a second reaction zone at conditions sufficient to provide a syngas having a temperature greater of about 1,050°

C. or more and comprising hydrogen, carbon monoxide, carbon dioxide, and less than 0.3% mol, dry basis, methane, wherein the syngas is used to indirectly heat the effluent from the first temperature to the second temperature;

indirectly exchanging heat from the syngas after the syngas is used to indirectly heat the effluent to a condensate to provide high pressure steam;

converting at least a portion of the carbon monoxide in the syngas used to indirectly heat the condensate to provide a converted syngas comprising carbon dioxide 1% mol dry basis or less carbon monoxide;

removing at least a portion of the carbon dioxide of the converted syngas to provide a lean syngas comprising 1% mol dry basis or less carbon dioxide and carbon monoxide;

converting at least a portion of any carbon dioxide, carbon monoxide, or both contained in the lean syngas to methane;

separating at least a portion of the water from the lean syngas;

separating at least a portion of nitrogen in the lean syngas to provide an ammonia syngas having a hydrogen to nitrogen ratio of about 2.9;

1 to about 3.2;

1; and

reacting at least a portion of the hydrogen and nitrogen in the ammonia syngas to provide an ammonia product.

21. The method of claim 20, wherein the one or more second catalysts further comprises one or more noble metals.

22. The method of claim 20, wherein the temperature of the syngas after the syngas is used to indirectly heat the effluent is about 880°

C. to about 900°

C.

23. The method of claim 20, wherein the effluent comprises from about 35% mol to about 39% mol hydrogen, from about 4% mol to about 5% mol carbon monoxide, from about 6% mol to about 8% mol carbon dioxide, from about 8% mol to about 10% mol methane, and from about 42% mol to about 47% mol steam.