A PLANT, SUCH AS AMMONIA PLANT, COMPRISING AN ABSORPTION REFRIGERATION UNIT

Abstract

A chemical plant comprising a refrigeration system including an absorption refrigeration unit, and a steam system including one or more steam producers, steam users, and at least one steam condenser, wherein a heat exchanger is arranged to intercept at least part of a steam flow directed to said steam condenser, and said heat exchanger transfers heat to a working fluid of said absorption refrigeration unit to provide at least part of a heat input required for operation of said refrigeration system.

Claims

1-14. (canceled)

15. A chemical plant, comprising: a refrigeration system including at least an absorption refrigeration unit; a steam system including one or more steam producers, steam users, and at least one steam condenser; and a heat exchanger is arranged to intercept at least part of a steam flow directed to said steam condenser; said heat exchanger transfers heat to a working fluid of said at least one absorption refrigeration unit to provide at least part of a heat input required for operation of said refrigeration system.

16. The chemical plant of claim 15, wherein said heat exchanger is fitted within a steam duct directed to said at least one steam condenser.

17. The chemical plant of claim 15, wherein said heat exchanger includes a coil or tube bundle exposed to the steam and internally traversed by said working fluid.

18. The chemical plant of claim 15, wherein steam at an inlet of said heat exchanger has a temperature in a range of 60 to 90 C,.

19. The chemical plant of claim 18, wherein the temperature is in a range of 75 to 85 C.

20. The chemical plant of claim 15, wherein said working fluid of the at least one absorption refrigeration unit includes a binary solution of a refrigerant and an absorbent.

21. The chemical plant of claim 20, wherein said binary solution includes lithium bromide and water.

22. The chemical plant of claim 15, which is suitable for synthesis of ammonia and further comprising: a front-end section for generation of a make-up synthesis gas; and a synthesis section for conversion of said make-up synthesis gas into an ammonia-containing product; wherein the generation of said make-up synthesis taking place by reforming of a hydrocarbon feedstock, and said reforming taking place in a presence of process air.

23. The chemical plant of claim 22, wherein said at least one absorption refrigeration unit is used for refrigeration of said make-up synthesis gas, said ammonia-containing product, or said process air.

24. The chemical plant of claim 15, which is suitable for the synthesis of methanol.

25. A method for revamping a chemical plant, said chemical plant including a refrigeration system and a steam system, wherein said steam system includes one or more steam producers, steam users, and at least one steam condenser, the method comprising: installing an absorption refrigeration unit to said refrigeration system; and installing a heat exchanger arranged to intercept at least part of a steam flow directed to said at least one steam condenser; wherein said heat exchanger transfers heat to a working fluid of said absorption refrigeration unit to provide at least part of a heat input required for operation of said refrigeration system.

26. The method of claim 25, wherein installing said heat exchanger includes: removing a steam duct originally directed to the steam condenser and installing a new steam duct of smaller length; and installing the heat exchanger between the newly installed steam duct and the condenser.

27. The method of claim 25, wherein installing said heat exchanger includes: removing a portion of a steam duct directed to the steam condenser, said portion being in proximity of said steam condenser; and installing the heat exchanger in the place of said removed portion.

28. The method of claim 25, wherein said heat exchanger includes an inlet and an outlet for said working fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 is a simplified block scheme of an ammonia plant according to a preferred embodiment of the invention.

[0050] FIG. 2 shows a simplified block scheme of the absorption refrigeration unit of the plant shown in FIG. 1, according to a preferred embodiment of the invention.

[0051] FIG. 3 shows a steam exhaust condenser of an ammonia plant according to the prior art.

[0052] FIG. 4 shows a steam exhaust condenser of an ammonia plant according to an embodiment of the invention.

DETAILED DESCRIPTION

[0053] FIG. 1 illustrates a simplified scheme of an ammonia plant 100.

[0054] A hydrocarbon feedstock 1 is reformed in a front-end section 101 producing a make-up synthesis gas 2. Said synthesis gas 2 is obtained at a pressure of 15-30 bar or greater in the front-end section 101 and is fed to a synthesis loop 102 via a multi-stage syngas compressor 103. The synthesis loop 102 works at a synthesis pressure of about 80-300 bar.

[0055] The synthesis loop 102 produces an ammonia-containing product 3. Said synthesis loop 102 contains a chiller 104, which is supplied with a cold liquid refrigerant 5 provided by an absorption refrigeration unit 105 and contributes to the chilling of the ammonia-containing product 3. The resulting hot liquid refrigerant 6 then returns to said absorption refrigeration unit 105.

[0056] The ammonia plant 100 also comprises a steam system which typically includes steam generators and steam turbines. Steam generators include for example heat exchangers which remove heat from the front-end section 101, e.g. from hot reformed gas. Steam turbines include for example a turbine 106 coupled to said multi-stage syngas compressor 103 and supplied with steam 7. For the sake of simplicity, in the example of the figure only the steam turbine 106 is illustrated.

[0057] The steam system further comprises a steam exhaust condenser 107 which receives the steam discharged from the one or more steam turbines, e.g. steam 13.

[0058] The steam system can further provide steam 9 which furnishes a heat input to the absorption refrigeration unit 105 and said unit 105 can return steam 10 with a lower heat content.

[0059] At least part of the heat input to said absorption refrigeration unit 105 is furnished by steam 8 before its condensation in the steam exhaust condenser 107, through a heat exchanger 108.

[0060] More in detail, the absorption refrigeration unit 105 operates with a working fluid. Said working fluid requires heat to be regenerated, according to the known technique of the absorption machines. In the example of FIGS. 1 to 4, reference will be made to an aqueous solution of LiBr, wherein LiBr acts as absorbent and water acts as refrigerant.

[0061] In the example of FIG. 1, the working fluid 11 enters, preferably via a pump (not shown), the heat exchanger 108 wherein it is heated by the steam 8. The heated working fluid 12 so-obtained returns to the absorption refrigeration unit 105, and steam 13 leaving the heat exchanger 108 with low thermal content is sent to the steam exhaust condenser 107. Said steam exhaust condenser 107 provides a steam condensate 14.

[0062] As shown in FIG. 2, said absorption refrigeration unit 105 essentially comprises a regenerator 201, a condenser 202, an evaporator 203 and an absorber 204.

[0063] After being pre-heated into said heat exchanger 108, said working fluid 12 is flashed through a valve 205, then enters the regenerator 201 wherein water vapours 23 are separated from a LiBr rich solution 24. Said rich solution 24 is recycled to the absorber 204.

[0064] According to the example of FIG. 2, steam 9 is furnished as additional heat input to the regenerator 201 to better regenerate the working fluid, and steam 10 with a lower heat content is exported from the absorption refrigeration unit 105.

[0065] The water vapours 23 extracted from said regenerator 201 are sent to the condenser 202, wherein they are condensed by a cooling medium 25 (e.g cooling water), providing a condensate 26. Said condensate 26 is supplied to the evaporator 203 through a valve 206. Said evaporator 203 is also supplied with the hot liquid refrigerant 6 obtained from the chiller 104, wherein it is regenerated. Accordingly, inside said evaporator 203, the condensate 26 is evaporated at lower pressure providing water vapours 27, and said liquid refrigerant 6 is cooled down thus being again available for the refrigerating process in the chiller 104.

[0066] Said water vapours 27 are supplied to the absorber 204, wherein they are absorbed by said LiBr rich solution 24 with the help of a cooling water 28. The absorber 204 provides a lean LiBr solution 11, which feeds the heat exchanger 108 wherein it is heated by steam 8, obtaining the stream 12.

[0067] According to another embodiment of the invention, said absorption refrigeration unit directly cools the ammonia-containing product 3 without providing the liquid refrigerant 5 to a chiller.

[0068] A preferred embodiment of said heat exchanger 108 is depicted in FIG. 4. This embodiment may advantageously result from the revamping of the system shown in FIG. 3.

[0069] According to FIG. 3, the condenser 107 receives steam from a plurality of conduits 109, 110, 111, e.g. the discharge tubes of steam turbines, and provides the steam condensate 14. The cooling medium 15 used in the condenser 107 is for example cooling water.

[0070] The method of revamping according to the embodiment shown in FIG. 4 comprises: replacing one or more of the conduits 109-111, e.g. the conduit 109, with a new discharge tube 109a of smaller length; installing the heat exchanger 108 between the tube 109a and a nozzle 113 of the condenser 107; installing a coil or a tube bundle 114 inside the shell 112 of said heat exchanger 108 for the circulation of the working fluid 11 coming from the absorption refrigeration unit 105.

[0071] According to another embodiment, the method of revamping may comprise the removal of a portion of conduit 109 and the subsequent installation of the heat exchanger 108 in place of said removed portion.

[0072] According to the invention, the heat content of the steam 8 extracted from the steam turbines of the ammonia plant is recovered and advantageously employed in the absorption refrigeration unit 105, instead of being discharged via condensation of the steam 8 into the steam exhaust condenser 107. Accordingly, it is the steam 13 discharged from the heat exchanger 108, which has smaller heat content than the steam 8, to be condensed inside the steam exhaust condenser 107, thus providing the steam condensate 14.