A METHOD FOR REVAMPING AN AMMONIA PLANT

Abstract

A method for revamping an ammonia plant including a steam system, said steam system comprising at least a high-pressure section operating at a first pressure and a medium-pressure section operating at a second pressure lower than said first pressure, the revamping including: the provision of at least one additional heat recovery by means of a steam flow at a third pressure which is intermediate between said first and second pressure, and the provision of a steam export line arranged to export outside the ammonia plant at least a portion of said steam flow at said third pressure.

Claims

1. A method for revamping an ammonia plant including a steam system, said steam system comprising at least a high-pressure section operating at a first pressure and a medium-pressure section operating at a second pressure lower than said first pressure, the revamping including: the provision of at least one additional heat recovery by means of a steam flow at a third pressure which is intermediate between said first and second pressure, and the provision of a steam export line arranged to export outside the ammonia plant at least a portion of said steam flow at said third pressure.

2. The method according to claim 1, wherein: said ammonia plant is part of an installation including other ammonia plants, and said steam is exported to another ammonia plant of the installation, having a medium-pressure steam section operating at said third pressure.

3. The method according to claim 2, including: the installation of a new high-pressure steam user in the high-pressure section of the steam system, said steam user having a steam input taken from the high-pressure section, and said steam flow at intermediate pressure being taken from a steam outlet of said new steam user.

4. The method according to claim 3, wherein operation of an existing medium-pressure steam user of the steam system is discontinued, and the discontinued steam user is replaced by said new high-pressure steam user.

5. The method according to claim 3, said new high-pressure steam user being a steam turbine, comprising a steam extraction to provide said steam flow at said third pressure.

6. The method according to claim 4, wherein operation of an existing steam turbine of the ammonia plant, fed with steam at said second pressure, is discontinued, and said existing steam turbine is replaced by said new steam turbine.

7. The method according to claim 5, wherein said new steam turbine is a multi-stage turbine, and said steam extraction being taken after one or more stage(s) of the turbine.

8. The method according to claim 1, wherein said third pressure is at least 5 bar above said second pressure.

9. The method according to claim 1, wherein said second pressure is less than 40 bar and said third pressure is 40 to 60 bar.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0019] FIG. 1 is a scheme of an ammonia plant.

[0020] FIG. 2 is an exemplary scheme of a portion of a steam system of the ammonia plant of FIG. 1, before revamping.

[0021] FIG. 3 is the scheme of FIG. 2 after a revamping which is carried out in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

[0022] FIG. 1 is a basic scheme of an ammonia plant including a primary reforming section 1, a secondary reforming section 2, a purifying section 3, a syngas compressor 4, an air compressor 5 and an ammonia synthesis loop 6.

[0023] Natural gas 7 is steam reformed the primary and secondary reforming sections with the help of steam 8 and air 9 admitted to the secondary section. In some embodiments said air 9 may be enriched or replaced with oxygen. The purified syngas 10 is compressed and sent to loop 6 for production of ammonia 11.

[0024] The scheme of FIG. 1 is well known and needs no further description.

[0025] The plant of FIG. 1 comprises a steam system and some components of said steam system are shown in FIG. 2.

[0026] The steam system comprises a high-pressure section 12 operating for example at 100 bar and a medium-pressure section 13 operating for example at 35 bar.

[0027] The high-pressure section 12 comprises a main steam header 14 feeding a steam turbine 15 which drives the syngas compressor 4. In the example, the steam turbine 15 includes a first stage 15′ and a second stage 15″, and part of steam extracted from the first stage is sent to the medium-pressure section 13.

[0028] The medium-pressure section 13 comprises a main steam header 16 feeding other steam users such as, for example, a steam turbine 17 driving the air compressor 5; a steam turbine 18 driving a feed water pump; a steam turbine 19 driving a refrigerant compressor.

[0029] The numerals 15c, 17c, 18c and 19c denote condensers of the turbines 15, 17, 18 and 19 respectively.

[0030] The steam system comprises also a low-pressure header 20. Steam may pass from the high to medium pressure and from medium to low pressure via lines 21 and 22 including a let-down valve 23, 24.

[0031] The line 25 denotes medium-pressure steam sent to the front-end, and line 26 denoted steam which is imported at a pressure higher than the medium pressure, for example 45 bar. This steam 26 can be imported from another ammonia plant having a medium pressure steam section at said pressure level of 45 bar. It can be noted that said steam, despite being available at 45 bar must be let down in the valve 27, to connect the line 26 to the steam header 16 at a lower pressure. Hence, a significant amount of energy of steam of line 26 is lost.

[0032] FIG. 3 shows the scheme after revamping. The medium-pressure turbine 19 is discontinued and replaced by a new high-pressure turbine 28 including stages 28′ and 28″, fed through line 29 with a portion of the high-pressure steam of header 14. A portion of the steam leaving the first stage 28′ is extracted via line 30 after expansion (steam extraction), while the remaining portion is sent to the second stage 28″ with line 31 for further expansion.

[0033] The extracted steam portion of line 30 is then exported at a pressure higher than the design pressure of the MP section 3, for example 50 bar. More preferably this pressure is substantially the same as the pressure of a medium-pressure section of the steam system of another ammonia plant of the same facility. Hence the steam of line 30 can be efficiently exported from the revamped ammonia plant to this another ammonia plant. Part or all of the steam of line 30 may also return via the line 26 after use. The outlet of the second stage 28″ is sent to the condenser 19c previously connected with the medium-pressure turbine 19.