US20180017321A1 - Method for recovering gaseous nitrogen from the waste nitrogen stream of an air separation unit - Google Patents
Method for recovering gaseous nitrogen from the waste nitrogen stream of an air separation unit Download PDFInfo
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- US20180017321A1 US20180017321A1 US15/647,948 US201715647948A US2018017321A1 US 20180017321 A1 US20180017321 A1 US 20180017321A1 US 201715647948 A US201715647948 A US 201715647948A US 2018017321 A1 US2018017321 A1 US 2018017321A1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/08—Separating gaseous impurities from gases or gaseous mixtures or from liquefied gases or liquefied gaseous mixtures
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
- F25J3/04012—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling
- F25J3/0403—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling of nitrogen
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
- F25J3/04048—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams
- F25J3/0406—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams of nitrogen
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
- F25J3/04284—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
- F25J3/0429—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams of feed air, e.g. used as waste or product air or expanded into an auxiliary column
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
- F25J3/04375—Details relating to the work expansion, e.g. process parameter etc.
- F25J3/04393—Details relating to the work expansion, e.g. process parameter etc. using multiple or multistage gas work expansion
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/044—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a single pressure main column system only
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/04—Mixing or blending of fluids with the feed stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2215/00—Processes characterised by the type or other details of the product stream
- F25J2215/42—Nitrogen or special cases, e.g. multiple or low purity N2
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2220/00—Processes or apparatus involving steps for the removal of impurities
- F25J2220/44—Separating high boiling, i.e. less volatile components from nitrogen, e.g. CO, Ar, O2, hydrocarbons
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/30—Compression of the feed stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2245/00—Processes or apparatus involving steps for recycling of process streams
- F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2245/00—Processes or apparatus involving steps for recycling of process streams
- F25J2245/42—Processes or apparatus involving steps for recycling of process streams the recycled stream being nitrogen
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2270/00—Refrigeration techniques used
- F25J2270/04—Internal refrigeration with work-producing gas expansion loop
Definitions
- the present invention relates to a distillation separation process and plant.
- it relates to a process and an apparatus for production of a gaseous nitrogen stream having a high purity with reduced capital investments.
- the usual solution to provide a gaseous nitrogen stream with a high purity is to purify air.
- the process is based on fractionated air distillation at cryogenic temperature in a single column. It involves five steps: compression, purification, heat exchange, distillation and cold production.
- EP-A-0299364 discloses a process in which a nitrogen-rich gas flow from the head of the medium-pressure column of a double column is fed to a column having a head condenser and a flow of high pressure nitrogen is withdrawn at the top of this column.
- U.S. Pat. No. 5,934,106 discloses an air separation apparatus for the production of nitrogen in a single column having a top condenser.
- the vaporized rich liquid is expanded in a turbine having the same inlet temperature as the air turbine and the vaporized rich liquid turbine is coupled to a cold vapor compressor from an intermediate level of the single column.
- GB-A-2126700 discloses an air separation apparatus for the production of nitrogen in a single column having a top condenser. According to one mode of operation, the vaporized rich liquid is expanded in a turbine having the same inlet temperature as the air turbine and the relaxed air and the vaporized rich liquid relaxed are sent to air.
- the present invention is directed to a process that satisfies at least one of these needs.
- a method is provided for increasing the nitrogen production of an existing air separation apparatus by using at least a portion of the waste nitrogen as a feedstock for a separate cryogenic distillation system.
- a stream of dry enriched nitrogen (typically above 90%) is coming out of the cold box and is usually used for the regeneration of the dryers, for the precooling section as a cooling medium in the chiller tower or simply vented. If there is a need of extra gaseous nitrogen or liquid nitrogen in a facility close to an already existing air separation unit and there is no extra capacity available on this existing asset, one solution is to use the previously mentioned enriched nitrogen stream (“Waste nitrogen”) as a feed to a cryogenic purification unit to produce a gaseous or liquid nitrogen stream at the required purity.
- Waste nitrogen enriched nitrogen
- An advantage of certain embodiments of the invention is that there is no need to include a separate purification step as there is no significant carbon dioxide or water amount to be removed. Moreover, the feed is more enriched in nitrogen than air so the distillation is made easier compared with the typical process scheme using air. This waste nitrogen is typically at lower pressure, and therefore, embodiments of the invention include a feed compressor to boost the waste nitrogen feedstock up to a suitable pressure for rectification within the distillation column of the nitrogen generator.
- FIG. 1 provides an embodiment of the present invention.
- FIG. 2 provides an additional embodiment of the present invention.
- FIG. 3 provides yet another embodiment of the present invention.
- a stream of dry enriched nitrogen (typically above 90%) is coming out of the cold box and is usually used for: (1) the regeneration of the dryers, (2) the precooling section as a cooling medium in the chiller tower, or (3) simply venting to the atmosphere.
- dry enriched nitrogen typically above 90%
- one solution is to use the previously mentioned enriched nitrogen stream (“Waste nitrogen”) as a feed to a cryogenic purification unit to produce a gaseous or liquid nitrogen stream at the required purity.
- a particular advantage of the invention is that there is no need to include an additional water/carbon dioxide purification step for this enriched nitrogen stream, as there is no significant carbon dioxide or water amount to be removed. Moreover, the feed is more enriched in nitrogen than air, which allows for an easier distillation compared with the typical process scheme using air.
- the ASU cold box produces gaseous nitrogen, liquid nitrogen, gaseous oxygen, liquid oxygen and liquid argon as products.
- the ASU cold box also produces waste nitrogen, which is typically vented or used for other purposes and sent to waste nitrogen users.
- waste nitrogen is typically vented or used for other purposes and sent to waste nitrogen users.
- at least a portion of the waste nitrogen from the ASU cold box can be diverted to a separate nitrogen generator in order to produce a purified gaseous and/or liquid nitrogen product.
- the nitrogen generator will also produce a small amount of waste nitrogen (e.g., enriched nitrogen stream), which can either be vented or sent to the waste nitrogen users.
- FIG. 2 provides a more detailed flow diagram of the nitrogen generator.
- the waste nitrogen from the ASU is at a lower pressure as this waste nitrogen stream typically originates from the top of the low pressure column of the ASU, and therefore, the nitrogen stream is compressed in nitrogen compressor before being cooled in a heat exchanger that is separate from the heat exchanger in the ASU.
- the nitrogen is introduced into a single distillation column. Nitrogen vaporizes and accumulates near the top of the column, while other impurities such as oxygen and argon accumulate in the column bottoms.
- the liquid is removed from the column bottom, expanded across a valve, and then introduced into the top condenser to provide reflux duty (e.g., condense nitrogen in the top condenser coming from the top of the column).
- the enriched liquid vaporizes in the top condenser and is then warmed in the subcooler and the heat exchanger. To provide additional refrigeration, a portion of this stream can be expanded and then re-warmed in the heat exchanger. The resulting warmed enriched gas is still predominantly nitrogen and can either be vented to the atmosphere or used as a waste gas.
- Purified gaseous nitrogen is removed from the top of the distillation column and warmed in the heat exchanger to produce the final gaseous product. If liquid nitrogen is desired, liquid nitrogen can be withdrawn from the condensing nitrogen stream from the top condenser (not shown).
- FIG. 3 provides an optional embodiment in which a portion of the enriched nitrogen stream (e.g., waste nitrogen from nitrogen generator) can be recycled to the waste nitrogen compressor in order to further improve the overall recovery of the system.
- the turbine can be configured to at least partially power the waste nitrogen compressor.
- “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
- Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
- Optional or optionally means that the subsequently described event or circumstances may or may not occur.
- the description includes instances where the event or circumstance occurs and instances where it does not occur.
- Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
Abstract
Description
- This application is a non-provisional application of U.S. Provisional Applicant No. 62/361,823, filed Jul. 13, 2016, which is herein incorporated by reference in its entirety.
- The present invention relates to a distillation separation process and plant. In particular, it relates to a process and an apparatus for production of a gaseous nitrogen stream having a high purity with reduced capital investments.
- The usual solution to provide a gaseous nitrogen stream with a high purity is to purify air. The process is based on fractionated air distillation at cryogenic temperature in a single column. It involves five steps: compression, purification, heat exchange, distillation and cold production.
- EP-A-0299364 discloses a process in which a nitrogen-rich gas flow from the head of the medium-pressure column of a double column is fed to a column having a head condenser and a flow of high pressure nitrogen is withdrawn at the top of this column.
- U.S. Pat. No. 5,934,106 discloses an air separation apparatus for the production of nitrogen in a single column having a top condenser. The vaporized rich liquid is expanded in a turbine having the same inlet temperature as the air turbine and the vaporized rich liquid turbine is coupled to a cold vapor compressor from an intermediate level of the single column.
- GB-A-2126700 discloses an air separation apparatus for the production of nitrogen in a single column having a top condenser. According to one mode of operation, the vaporized rich liquid is expanded in a turbine having the same inlet temperature as the air turbine and the relaxed air and the vaporized rich liquid relaxed are sent to air.
- On air separation units which are not intended for the production of pure nitrogen, it is of course not possible to make nitrogen gas and/or pure liquid a posteriori without making very significant changes to devices.
- Therefore, the methods known heretofore fail to provide a simple and economical way of producing pure liquid and/or gaseous nitrogen from a nitrogen-enriched gas from a main air separation apparatus.
- The present invention is directed to a process that satisfies at least one of these needs. In certain embodiments of the invention, a method is provided for increasing the nitrogen production of an existing air separation apparatus by using at least a portion of the waste nitrogen as a feedstock for a separate cryogenic distillation system.
- In a typical air separation unit, a stream of dry enriched nitrogen (typically above 90%) is coming out of the cold box and is usually used for the regeneration of the dryers, for the precooling section as a cooling medium in the chiller tower or simply vented. If there is a need of extra gaseous nitrogen or liquid nitrogen in a facility close to an already existing air separation unit and there is no extra capacity available on this existing asset, one solution is to use the previously mentioned enriched nitrogen stream (“Waste nitrogen”) as a feed to a cryogenic purification unit to produce a gaseous or liquid nitrogen stream at the required purity.
- An advantage of certain embodiments of the invention is that there is no need to include a separate purification step as there is no significant carbon dioxide or water amount to be removed. Moreover, the feed is more enriched in nitrogen than air so the distillation is made easier compared with the typical process scheme using air. This waste nitrogen is typically at lower pressure, and therefore, embodiments of the invention include a feed compressor to boost the waste nitrogen feedstock up to a suitable pressure for rectification within the distillation column of the nitrogen generator.
- These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.
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FIG. 1 provides an embodiment of the present invention. -
FIG. 2 provides an additional embodiment of the present invention. -
FIG. 3 provides yet another embodiment of the present invention. - While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalence as may be included within the spirit and scope of the invention defined by the appended claims.
- In a typical air separation unit, a stream of dry enriched nitrogen (typically above 90%) is coming out of the cold box and is usually used for: (1) the regeneration of the dryers, (2) the precooling section as a cooling medium in the chiller tower, or (3) simply venting to the atmosphere. If there is a need of extra gaseous nitrogen or liquid nitrogen in a facility close to an already existing air separation unit and there is no extra capacity available on this existing asset, one solution is to use the previously mentioned enriched nitrogen stream (“Waste nitrogen”) as a feed to a cryogenic purification unit to produce a gaseous or liquid nitrogen stream at the required purity.
- A particular advantage of the invention is that there is no need to include an additional water/carbon dioxide purification step for this enriched nitrogen stream, as there is no significant carbon dioxide or water amount to be removed. Moreover, the feed is more enriched in nitrogen than air, which allows for an easier distillation compared with the typical process scheme using air.
- In
FIG. 1 , air enters an ASU cold box under conditions effective for the rectification of air. In the embodiment shown, the ASU cold box produces gaseous nitrogen, liquid nitrogen, gaseous oxygen, liquid oxygen and liquid argon as products. In addition to these products, the ASU cold box also produces waste nitrogen, which is typically vented or used for other purposes and sent to waste nitrogen users. In the embodiment shown, at least a portion of the waste nitrogen from the ASU cold box can be diverted to a separate nitrogen generator in order to produce a purified gaseous and/or liquid nitrogen product. The nitrogen generator will also produce a small amount of waste nitrogen (e.g., enriched nitrogen stream), which can either be vented or sent to the waste nitrogen users. -
FIG. 2 provides a more detailed flow diagram of the nitrogen generator. In this embodiment, the waste nitrogen from the ASU is at a lower pressure as this waste nitrogen stream typically originates from the top of the low pressure column of the ASU, and therefore, the nitrogen stream is compressed in nitrogen compressor before being cooled in a heat exchanger that is separate from the heat exchanger in the ASU. After cooling, the nitrogen is introduced into a single distillation column. Nitrogen vaporizes and accumulates near the top of the column, while other impurities such as oxygen and argon accumulate in the column bottoms. The liquid is removed from the column bottom, expanded across a valve, and then introduced into the top condenser to provide reflux duty (e.g., condense nitrogen in the top condenser coming from the top of the column). The enriched liquid vaporizes in the top condenser and is then warmed in the subcooler and the heat exchanger. To provide additional refrigeration, a portion of this stream can be expanded and then re-warmed in the heat exchanger. The resulting warmed enriched gas is still predominantly nitrogen and can either be vented to the atmosphere or used as a waste gas. - Purified gaseous nitrogen is removed from the top of the distillation column and warmed in the heat exchanger to produce the final gaseous product. If liquid nitrogen is desired, liquid nitrogen can be withdrawn from the condensing nitrogen stream from the top condenser (not shown).
-
FIG. 3 provides an optional embodiment in which a portion of the enriched nitrogen stream (e.g., waste nitrogen from nitrogen generator) can be recycled to the waste nitrogen compressor in order to further improve the overall recovery of the system. In an additional embodiment, the turbine can be configured to at least partially power the waste nitrogen compressor. - While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
- The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
- “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
- “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
- Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
- Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
- All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.
Claims (5)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US15/647,948 US20180017321A1 (en) | 2016-07-13 | 2017-07-12 | Method for recovering gaseous nitrogen from the waste nitrogen stream of an air separation unit |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US201662361823P | 2016-07-13 | 2016-07-13 | |
US15/647,948 US20180017321A1 (en) | 2016-07-13 | 2017-07-12 | Method for recovering gaseous nitrogen from the waste nitrogen stream of an air separation unit |
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