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CN-117545713-B - Dual pressure system for producing nitric acid and method of operating the same

CN117545713BCN 117545713 BCN117545713 BCN 117545713BCN-117545713-B

Abstract

The present disclosure discloses a system for producing nitric acid with reduced power, the system being a standard dual pressure nitric acid plant, characterized in that the system further comprises means for splitting the off gas stream into a first off gas stream and a second off gas stream, the first off gas stream being in fluid communication with an oxygen enriched gas upstream of an ammonia mixing unit, and means for regulating the amount of off gas split into the first off gas stream and the second off gas stream, such that an air compressor is not required for operating the nitric acid plant. The present disclosure further relates to a method for operating the system, the use of the system of the present disclosure for carrying out the method of the present disclosure, and a method for retrofitting a standard dual pressure nitric acid plant to the system of the present disclosure.

Inventors

  • BENT VIGELAND
  • Halvo Erin
  • Peter Fouconier
  • ANDRE DESMET

Assignees

  • 亚拉国际有限公司

Dates

Publication Date
20260508
Application Date
20220825
Priority Date
20210825

Claims (20)

  1. 1. A production facility for producing nitric acid with reduced power consumption and reduced emissions, comprising: A source of oxygen-enriched gas; Mixing means downstream of said source of oxygen-enriched gas for mixing a first oxygen-containing gas with the ammonia gas stream to produce an ammonia/oxygen-containing gas mixture; an ammonia converter for oxidizing ammonia in the ammonia/oxygen-containing gas mixture to produce a NOx gas/steam mixture comprising water and nitrogen oxides; means for adjusting the ammonia concentration and/or oxygen concentration in the ammonia converter for maintaining the oxygen to ammonia molar ratio inside the ammonia converter at a ratio of at least 1.2; A first gas cooler/condenser downstream of the ammonia converter to produce an aqueous dilute nitric acid mixture and a gaseous NO x stream; A NO x gas compressor for compressing the gaseous NO x stream to produce a compressed NO x gas stream at pressure P2; An absorber for absorbing NO x gas in water from the compressed NO x gas stream to produce a crude nitric acid stream containing residual NO x gas and a tail gas comprising NO x gas, the absorber comprising an absorber tail gas outlet for evacuating the tail gas; a heat exchange system upstream of the gas cooler/condenser for exchanging heat between the NO x gas/steam mixture and the tail gas; a second gas cooler/condenser for separating and condensing steam from the compressed NO x gas stream; A supply of a second oxygen-containing gas having (i) a pressure equal to or higher than P1 and up to P2 for supplying oxygen downstream of the ammonia converter and upstream of the NOx gas compressor, or (ii) a pressure higher than P2 for supplying oxygen to the compressed NOx gas stream; Means for controlling the flow of said second oxygen-containing gas such that the tail gas stream contains at least 0.5% by volume of oxygen, and A first pressure relief device downstream of the heat exchange system for expanding the tail gas stream downstream of the absorber column to produce a first expanded tail gas at a pressure equal to or greater than P1 and less than P2, wherein the first pressure relief device may at least partially power the NO x gas compressor; characterized in that the production device further comprises: Means for splitting the tail gas into a first tail gas stream and a second tail gas stream, wherein the first tail gas stream is in fluid communication with the oxygen-enriched gas, and wherein mixing of the oxygen-enriched gas with the first tail gas stream provides the first oxygen-containing gas.
  2. 2. A production apparatus for producing nitric acid according to claim 1, comprising a source of pressurized air in fluid communication with a system for pressurizing the system comprising: A source of oxygen-enriched gas; mixing means downstream of said source of said oxygen-enriched gas for mixing a first oxygen-containing gas with an ammonia gas stream to produce an ammonia/oxygen-containing gas mixture; means for measuring the oxygen concentration in the first oxygen-containing gas; Means for adjusting the oxygen concentration in the first oxygen-containing gas such that the molar ratio of oxygen to ammonia at the inlet of the ammonia converter is at least 1.2 or at least 1.25; Means for regulating the supply of said ammonia gas to said mixing means; an ammonia converter operable at a pressure P1 for oxidizing ammonia in the ammonia/oxygen-containing gas mixture to produce a NO x gas/steam mixture comprising water and nitrogen oxide; Means for measuring the temperature in the ammonia converter; a first gas cooler/condenser downstream of the ammonia converter to produce an aqueous dilute nitric acid mixture and a gaseous NOx stream; A NOx gas compressor for compressing the gaseous NOx stream to produce a compressed NOx gas stream at a pressure P2; An absorber for absorbing NOx gases in water from the compressed NOx gas stream to produce a crude nitric acid stream containing residual NOx gases and a tail gas comprising NO x gases, the absorber comprising an absorber tail gas outlet for evacuating the tail gas; Means for measuring the oxygen concentration in the tail gas stream downstream of the absorber; A heat exchange system upstream of the gas cooler/condenser for exchanging heat between the NOx gas/steam mixture and the exhaust gas; A second additional gas cooler/condenser for separating and condensing steam from the compressed NOx gas stream to produce a compressed NOx gas stream; a supply of a second oxygen-containing gas having (i) a pressure equal to or higher than P1 and up to P2 for supplying oxygen upstream of the NO x gas compressor, or (ii) a pressure higher than P2 for supplying oxygen to the compressed NOx gas stream such that the tail gas contains at least 0.5% by volume of oxygen, and A tail gas expander downstream of the heat exchange system for expanding a tail gas stream downstream of the absorber column to produce a first expanded tail gas at a pressure P1, wherein the tail gas expander may at least partially power the NO x gas compressor; Characterized in that the system further comprises: means for splitting the tail gas stream downstream of the absorber into a first tail gas stream and a second tail gas stream in fluid communication with the oxygen-enriched gas, and Means for adjusting the amount of tail gas split into said first tail gas stream and said second tail gas stream.
  3. 3. The production facility of claim 1 or 2, wherein the system further comprises one or more of: A steam turbine, wherein the steam turbine may at least partially power the NOx gas compressor; A heat exchanger for exchanging heat between the first expanded tail gas and a cooler tail gas stream, wherein the first expanded tail gas exits the heat exchanger, and wherein the means for diverting is positioned downstream of the heat exchanger and in fluid communication with the first expanded tail gas; A NO-removing x treatment unit, and Second pressure relief means for expanding said second tail gas stream to atmospheric pressure to produce a second expanded tail gas.
  4. 4. The production plant of any one of claims 1 or 2 further comprising a bleach for bleaching the crude nitric acid stream containing residual NOx gas to provide a bleached nitric acid stream, the bleach having an inlet for oxygen-enriched bleaching gas and an outlet for exhaust gas, the exhaust gas being in fluid communication with any gas stream downstream of the ammonia converter and upstream of the NOx gas compressor if the bleach is operated at a pressure equal to or higher than P1 and up to equal to P2, or with any stream downstream of the NOx gas compressor and upstream of the absorber column if the bleach is operated at a pressure higher than P2, such that the supply of the second oxygen-containing gas is at least partially from the exhaust gas.
  5. 5. The production facility of claim 4, wherein a portion of the oxygen-enriched gas or a portion of the first oxygen-containing gas or a portion of the tail gas is in fluid communication with the inlet of the bleach such that the oxygen-enriched bleach gas is at least partially provided by the oxygen-enriched gas portion, by the first oxygen-containing gas portion, or by a portion of a tail gas stream.
  6. 6. The production facility of any one of claims 1 or 2, further comprising a stream of a second oxygen-containing gas in direct fluid communication with any off-gas stream.
  7. 7. The production plant according to any one of claims 1 or 2, wherein the oxygen-enriched gas, the second oxygen-containing gas, the oxygen-enriched bleaching gas and the bleach effluent gas are all at least partially provided by a water electrolysis cell.
  8. 8. The production facility of any one of claims 1 or 2 wherein the fluid communication between the pressurized air source and the system is in direct fluid communication with the oxygen-enriched gas.
  9. 9. The production plant according to claim 1 or 2, wherein the source of oxygen-enriched gas is a source of pressurized oxygen-enriched gas.
  10. 10. The production plant according to claim 1 or 2, wherein the source of oxygen-enriched gas is a high pressure water electrolyzer.
  11. 11. The production plant according to claim 1, wherein the means for adjusting the ammonia concentration and/or oxygen concentration in the ammonia converter is means for controlling the flow of the oxygen enriched gas and/or means for controlling the flow of the ammonia gas stream.
  12. 12. The production facility of claim 1, wherein the heat exchange system is configured to heat an exhaust gas stream with heat from the NOx gas/steam from the ammonia converter.
  13. 13. The production facility of claim 1 wherein the first pressure relief device is a tail gas expander.
  14. 14. The production plant of claim 2 wherein the means for adjusting the oxygen concentration in the first oxygen-containing gas is such that the molar ratio of oxygen to ammonia at the inlet of the ammonia converter is between 1.2 and 9 or between 1.25 and 9.
  15. 15. A method for producing nitric acid with reduced power consumption and reduced emissions in a production plant according to any of claims 1 or 2, the method comprising the steps of: Providing or preparing an oxygen-enriched gas and a first oxygen-containing gas, and providing an ammonia gas stream, prior to step c); c) Supplying the ammonia gas stream and a first oxygen-containing gas to the mixing device, thereby producing an ammonia/oxygen-containing gas mixture; d) Oxidizing ammonia in the ammonia/oxygen-containing gas mixture in the ammonia converter to produce a gaseous NOx gas/steam mixture comprising water and nitrogen oxides; e) Cooling the NOx gas in the gaseous NOx gas/steam mixture in the heat exchange system and in a first gas cooler/condenser to produce an aqueous lean nitric acid mixture and a gaseous NOx stream; f) Compressing the gaseous NO x stream in the NO x gas compressor, thereby providing a pressurized NOx compressed gas stream having a pressure P2; g) Absorbing a pressurized gaseous NO x stream in said absorber column, thereby providing said crude nitric acid stream containing residual NOx gases and said tail gas comprising NO x gas; h) Heating the tail gas in the heat exchange system using heat from the NO x gas/steam mixture from the ammonia converter; i) Cooling the pressurized NOx gas stream in the second gas cooler/condenser to provide a pressurized NO x gas stream, and J) Expanding at least part of the tail gas obtained in step h) in a first pressure relief device, thereby providing a first expanded tail gas; characterized in that the method further comprises the steps of: k) Splitting the tail gas stream into a first tail gas stream and a second tail gas stream and mixing the first tail gas stream with the oxygen-enriched gas using a first means for splitting, thereby providing the first oxygen-containing gas; m) adjusting the flow of the oxygen-enriched gas or the flow of the ammonia gas stream mixed in step k) such that the molar ratio of oxygen to ammonia at the inlet of the ammonia converter is maintained at a ratio of at least 1.2 or at least 1.25, and Q) adjusting the flow of the oxygen-enriched gas upstream of the NO x gas compressor at a pressure equal to or higher than P1 and up to P2 or downstream of the NO x gas compressor at a pressure higher than P2 such that the oxygen concentration in the tail gas stream is maintained at a concentration of at least 0.5% by volume.
  16. 16. The method for producing nitric acid with reduced power consumption and reduced emissions according to claim 15 comprising the steps of: c) Supplying the ammonia gas stream and a first oxygen-containing gas to the mixing device, thereby producing an ammonia/oxygen-containing gas mixture; d) Oxidizing ammonia in the ammonia/oxygen-containing gas mixture in the ammonia converter to produce a gaseous NOx gas/steam mixture comprising water and nitrogen oxides; e) Cooling the NOx gas in the gaseous NOx gas/steam mixture in the heat exchange system and in a first gas cooler/condenser to produce an aqueous lean nitric acid mixture and a gaseous NOx stream; f) Compressing the gaseous NOx stream in the NOx gas compressor to provide a pressurized NOx compressed gas stream having a pressure P2; g) Absorbing a pressurized gaseous NO x stream in said absorber column, thereby providing said crude nitric acid stream containing residual NOx gases and said tail gas comprising NO x gas; h) Heating the tail gas in the heat exchange system using heat from the NO x gas/steam mixture from the ammonia converter; i) Cooling the pressurized NO x gas stream in the second gas cooler/condenser to provide a pressurized NO x gas stream, and J) Expanding the tail gas obtained in step h) in the tail gas expander, thereby providing a first expanded tail gas; characterized in that the method further comprises the steps of: k) Splitting the tail gas stream into a first tail gas stream and a second tail gas stream and mixing the first tail gas stream with the oxygen-enriched gas using means for splitting to provide the oxygen-containing gas; l) measuring the oxygen concentration in the oxygen-containing gas; m) if the oxygen concentration measured in step l) is such that the oxygen to ammonia molar ratio in the ammonia converter is less than 1.2 or 1.25, adjusting the supply of the oxygen-enriched gas, e.g. the oxygen-enriched gas has a pressure P2 and is mixed in step k), or adjusting the supply of the ammonia gas stream in step c) such that the oxygen to ammonia molar ratio at the inlet of the ammonia converter is at least 1.2 or 1.25; n) measuring the temperature in the ammonia converter; o) if the temperature measured in step n) is outside the range of 800 ℃ to 950 ℃, adjusting the volume of the first tail gas stream mixed in step k) or the volume of the ammonia gas stream supplied in step C) such that the temperature in the ammonia converter is maintained in the range of 800 ℃ to 950 ℃; p) measuring the oxygen concentration in the tail gas downstream of the absorber; q) if the oxygen concentration measured in step P) is less than 0.5 vol.% oxygen, regulating the supply of the oxygen-enriched gas at a pressure equal to or higher than P1 and up to P2 upstream of the NO x gas compressor or at a pressure higher than P2 downstream of the NO x gas compressor, or regulating the flow of the second oxygen-containing gas such that the off-gas contains at least 0.5 vol.% oxygen; r) repeating steps c) to q).
  17. 17. The method according to claim 15 or 16, wherein the first tail gas stream mixed in step k) is obtained after step j), and wherein the method further comprises the steps of: s) heating a stream of offgas which is colder than the first expanded offgas with the first expanded offgas in the heat exchanger, in particular before step k), so that the first expanded offgas reaches a temperature of less than 300 ℃, and heating the offgas obtained in step g) with the first expanded offgas obtained in step j) in the heat exchanger, so that the offgas to be mixed in step k) reaches a temperature of less than 300 ℃; t) treating the tail gas stream in the NO-removal x treatment unit; u) expanding said second tail gas stream in said second pressure relief device to provide a second expanded tail gas, and V) recovering at least part of the steam generated in the ammonia converter in the steam turbine.
  18. 18. The method according to any one of claims 15 or 16, further comprising the step of: w) bleaching said crude nitric acid stream comprising residual NO x gas in said bleach to produce a bleached nitric acid stream.
  19. 19. The method of claim 18, further comprising the step of: w 1) supplying a portion of the oxygen-enriched gas or a portion of the first oxygen-containing gas obtained in step k) or a portion of the tail gas obtained in step g) to the inlet of the bleach in step w).
  20. 20. The method according to any one of claims 15 or 16, further comprising the step of: x) supplying a stream of oxygen-enriched gas to the tail gas stream.

Description

Dual pressure system for producing nitric acid and method of operating the same Technical Field The present disclosure relates to the field of nitric acid production in dual pressure equipment. Introduction to the invention Pure nitric acid is a transparent colorless liquid with strong odor. Nitric acid is produced in large quantities mainly by catalytic oxidation of ammonia (Ostwald process). Ammonia is converted to nitric acid in several stages. Ammonia is first oxidized in an ammonia burner on a platinum wire mesh (commonly referred to as an ammonia converter) or cobalt balls, producing nitrogen oxides (also referred to as Nitric Oxide (NO) in this disclosure) and water: 4NH3(g)+5O2(g)→4NO(g)+6H2O(g) (1) The reaction product nitrogen oxide from (1) is then oxidized after cooling to nitrogen dioxide (NO 2) and further to dinitrogen tetroxide N 2O4 (g) in an oxidation zone: 2NO(g)+O2(g)→2NO2(g) (2) 2NO2(g)→N2O4(g) (3) The cooling of the nitrogen oxide gas is accomplished first via the use of a waste heat recovery system that recovers heat from the conversion of ammonia to nitrogen oxide, then via the use of a chiller condenser in which condensed nitric acid is separated from the nitrogen oxide, nitrogen dioxide and dinitrogen tetroxide and nitric acid gas (collectively referred to as NO x gas), and finally by heating the tail gas released at the outlet of the absorption column where NO x gas is absorbed. Nitrogen dioxide and dinitrogen tetroxide are converted to nitric acid and nitric oxide by absorption in water, followed by compression via a NO x gas compressor: 3NO2(g)+H2O(l)→2HNO3(aq)+NO(g) (4) 3N2O4(g)+2H2O(l)→4HNO3(aq)+2NO(g) (5) up to 68% of weak nitric acid (azeotrope) is obtained. The concentration of nitric acid can be increased up to 99% concentrated nitric acid via the rectification process. The total reaction is given by: NH3+2O2→HNO3+H2O (6) The main process units in the nitric acid production plant include an ammonia converter (converting ammonia to nitrogen oxide over a suitable catalyst using oxygen), an oxidation stage (converting nitrogen oxide to nitrogen dioxide and tetraoxide), an absorber unit (for absorbing NO x gas into water), and a bleach unit (removing unreacted dissolved gases, particularly dissolved gases containing NO x gas, from aqueous nitric acid, giving it a typical brown color). The production process of nitric acid can be classified into single-pressure (single-pressure) and double-pressure (partial pressure) processes. In a dual pressure process, the absorber unit is operated at a higher operating pressure than the ammonia converter. Modern dual pressure processes are characterized by low pressure ammonia converters typically operating at 2 to 6bara and high pressure absorber units operating at 9 to 16 bara. The dual pressure process requires an air compressor to feed low pressure air (which includes about 21vol% oxygen) to the converter and an NO x gas compressor to feed high pressure NO x gas to the absorber unit. The operating pressure of the air compressor is from 2bara to 6bara inclusive and the operating pressure of the NO x gas compressor is from 9bara to 16bara inclusive. The driving force of the air compressor typically originates from an exhaust gas turbine and a steam turbine or a power source such as an electric motor. Thus, the compressor train of a dual pressure nitric acid production plant typically includes an air compressor, a NO x gas compressor, an exhaust gas turbine, and a steam turbine or a power source such as an electric motor. In more detail, referring to fig. 1, the dual press apparatus and process according to the related art operates in the following manner. The gaseous ammonia 32, optionally preheated in a preheater unit (not shown), is mixed in a mixing device 35 with compressed air 34 pressurized to low pressure using an air compressor 36, and the resulting ammonia/oxygen enriched air mixture 14 is fed to an ammonia converter 37 operating at low pressure, wherein the ammonia is oxidized over a suitable catalyst, obtaining an LP NO x gas/steam mixture 15 comprising water and Nitrogen Oxide (NO). The heat of the mixture exiting the ammonia converter is recovered, after which the NO x gas/stream mixture is subsequently cooled in a gas cooler/condenser 38 to a temperature at which water is condensed, and the aqueous dilute nitric acid mixture 17 is separated from the gaseous NO x stream 22. Gaseous NO x stream 22 is sent to NO x gas compressor 40 where its pressure is raised from low pressure to high pressure, approximately equal to the absorber unit 41 operating pressure, and pressurized gaseous NO x stream 24 is also sent to absorber unit 41, commonly referred to as an absorber column. The pressurized NO x gas stream 24 is further oxidized to further convert NO to NO 2 and N 2O4, cooled in an additional gas cooler/condenser 39, and then also directed to the absorber column 41. Inside the absorber column 41, the pressurized NO x gas st