Ammonia production process utilizing enhanced boiling surface in refrigeration zone
First Claim
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1. In a process for producing ammonia which comprises:
- (a) reacting a nitrogen-hydrogen ammonia synthesis gas stream in the presence of an ammonia synthesis catalyst at conditions effecting partial conversion to ammonia; and
(b) cooling the reacted synthesis gas stream to a temperature below the dewpoint of ammonia so as to condense said ammonia by indirect heat exchange with ammonia refrigerant in at least two or more stages of cooling wherein each successive stage cools the reacted synthesis gas to a lower temperature with the last stage of cooling providing the lowest reacted synthesis gas temperature T, said indirect heat exchange having an overall heat transfer coefficient Uo, and wherein the ammonia refrigerant is provided by a compressor having at least two or more stages of compression, each stage of compression requiring a corresponding respective amount of compression energy to compress the ammonia such that a total amount of energy E is expended for compression and each stage of compression having an inlet suction pressure and an outlet discharge pressure;
the improvement which comprises decreasing the amount of compression energy expended per unit amount of ammonia produced in the process by;
(i) providing heat exchange apparatus for cooling the reacted synthesis gas with ammonia refrigerant having a thermally conductive wall with an enhanced boiling surface on one side of said wall in at least the last stage of cooling such that the ammonia refrigerant is in contact with the said enhanced boiling surface during the indirect heat exchange; and
(ii) increasing the suction pressure to at least the first stage of compression.
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Abstract
This invention pertains to the field of producing ammonia. More specifically, the present invention relates to reducing the costs of producing a unit amount of ammonia, particularly the energy costs, by the utilization of an enhanced boiling surface in the refrigeration zone of the process.
7 Citations
35 Claims
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1. In a process for producing ammonia which comprises:
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(a) reacting a nitrogen-hydrogen ammonia synthesis gas stream in the presence of an ammonia synthesis catalyst at conditions effecting partial conversion to ammonia; and (b) cooling the reacted synthesis gas stream to a temperature below the dewpoint of ammonia so as to condense said ammonia by indirect heat exchange with ammonia refrigerant in at least two or more stages of cooling wherein each successive stage cools the reacted synthesis gas to a lower temperature with the last stage of cooling providing the lowest reacted synthesis gas temperature T, said indirect heat exchange having an overall heat transfer coefficient Uo, and wherein the ammonia refrigerant is provided by a compressor having at least two or more stages of compression, each stage of compression requiring a corresponding respective amount of compression energy to compress the ammonia such that a total amount of energy E is expended for compression and each stage of compression having an inlet suction pressure and an outlet discharge pressure; the improvement which comprises decreasing the amount of compression energy expended per unit amount of ammonia produced in the process by; (i) providing heat exchange apparatus for cooling the reacted synthesis gas with ammonia refrigerant having a thermally conductive wall with an enhanced boiling surface on one side of said wall in at least the last stage of cooling such that the ammonia refrigerant is in contact with the said enhanced boiling surface during the indirect heat exchange; and (ii) increasing the suction pressure to at least the first stage of compression. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. The method for decreasing energy expended per unit amount of ammonia produced in an ammonia production process which comprises:
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(a) reacting a nitrogen-hydrogen ammonia synthesis gas stream in the presence of an ammonia synthesis catalyst at conditions effecting partial conversion to ammonia; (b) passing the reacted synthesis gas containing gaseous ammonia through two or more stages of cooling by indirect heat exchange with ammonia refrigerant to a temperature below the dewpoint of the ammonia to obtain condensed ammonia product;
wherein at least the last stage of cooling contains a thermally conductive wall with an enhanced boiling surface on the side which is in contact with the ammonia refrigerant, said last stage of cooling having an overall heat transfer coefficient Uo, and wherein the ammonia refrigerant is provided by a compressor having two or more stages of compression requiring an input of compression energy for each stage of compression, each stage of compression having an inlet suction pressure and an outlet discharge pressure;(c) increasing the suction pressure to at least the first stage of the compressor such that a percentage increase in ammonia condensation is greater than the corresponding percentage increase in compressor energy consumption. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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33. In a process for producing ammonia which comprises:
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(a) reacting a nitrogen-hydrogen ammonia synthesis gas stream in the presence of an ammonia synthesis catalyst at conditions effecting partial conversion to ammonia; and (b) cooling the reacted synthesis gas stream containing gaseous ammonia to a temperature T below the dewpoint of the ammonia to obtain a condensed liquid ammonia product by indirect heat exchange with ammonia refrigerant in at least two or more stages of cooling, wherein the ammonia refrigerant is provided by a compressor having at least two or more stages of compression, each stage of compression requiring a corresponding amount of compression energy to compress the ammonia; the improvement which comprises reducing the energy expended per unit amount of ammonia produced by increasing the amount of ammonia condensed while maintaining or reducing the overall compressor energy consumption by; (i) providing heat exchange apparatus for cooling the reacted synthesis gas with ammonia refrigerant having a thermally conductive wall with an enhanced boiling surface on one side of said wall in at least the last stage of cooling such that the ammonia refrigerant is in contact with the said enhanced boiling surface during the indirect heat exchange; and (ii) cooling the reacted synthesis gas to a temperature below T so as to condense more ammonia; and (iii) increasing the suction pressure in at least the first stage of the compressor so as to maintain or reduce the overall compressor energy consumption.
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34. In a process for producing ammonia which comprises;
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(a) reacting a nitrogen-hydrogen ammonia synthesis gas stream in the presence of an ammonia synthesis catalyst at conditions effecting partial conversion to ammonia; and (b) cooling the reacted synthesis gas stream containing gaseous ammonia to a temperature T below the dewpoint of the ammonia to obtain a condensed liquid ammonia product by indirect heat exchange with ammonia refrigerant in at least two or more stages of cooling, wherein the ammonia refrigerant is provided by a compressor having at least two or more stages of compression, each stage of compression requiring a corresponding amount of compression energy to compress the ammonia; the improvement which comprises reducing the energy expended per unit of ammonia produced by maintaining the ammonia obtained substantially constant while reducing the overall compressor energy consumption by; (i) providing heat exchange apparatus for cooling the reacted synthesis gas with ammonia refrigerant having a thermally conductive wall with an enhanced boiling surface on one side of such wall in at least the last stage of cooling such that the ammonia refrigerant is in contact with the said enhanced boiling surface during the indirect heat exchange; and (ii) cooling the reacted synthesis gas to essentially the same temperature T so as to obtain a substantially constant amount of ammonia condensation; and (iii) increasing the suction pressure in at least the first stage of the compressor so as to decrease the overall compressor energy consumption.
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35. In a process for the production of ammonia comprising:
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(a) compressing a hydrogen-nitrogen ammonia synthesis gas stream to a pressure greater than about 1800 psia; (b) combining the compressed synthesis gas with a reacted synthesis gas stream containing hydrogen, nitrogen, and gaseous ammonia from step (i); (c) passing a first portion of the combined stream to a heat exchanger which is in indirect heat exchange with a vapor phase stream containing hydrogen, nitrogen, and gaseous ammonia obtained from step (g) to cool the first portion of the combined stream; (d) passing a second portion of the combined stream to at least one cooling stage cooled with ammonia refrigerant; (e) recombining the cooled first and second portions of combined stream; (f) passing the recombined stream to a final cooling stage to reduce the temperature of the recombined stream to a temperature T1 and providing a mixture containing liquid ammonia, gaseous ammonia, hydrogen, and nitrogen; (g) separating the liquid ammonia from the vapor portion of the mixture in a first separating zone to form a vapor phase of gaseous ammonia, hydrogen and nitrogen and a liquid ammonia phase; (h) passing the vapor phase in indirect heat exchange with the first portion of the combined stream in accordance with step (c); (i) reacting the vapor phase in the presence of an ammonia synthesis catalyst at conditions effecting conversion of the hydrogen and nitrogen to gaseous ammonia and form the reacted synthesis gas stream of step (b); wherein the ammonia refrigerant in the cooling stages is provided by a compressor having at least two or more stages of compression; the improvement which comprises reducing the energy expended per unit of ammonia produced by; (i) providing at least the final ammonia refrigerant cooling stage with a thermally conductive wall having an enhanced boiling surface on the side which is in contact with the ammonia refrigerant said that the overall heat transfer coefficient is increased by a factor of at least 2.0 to 3.0; (ii) reducing the temperature of the recombined stream to a temperature T2 which is less than T1 such that more ammonia is condensed; (iii) increasing the amount of the first portion of the combined stream passed to the heat exchanger; and (iv) increasing the suction pressure to at least the first stage of the compressor.
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Specification