CN109564060B - Method for producing air gas by cryogenic separation of air - Google Patents

Method for producing air gas by cryogenic separation of air Download PDF

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Publication number
CN109564060B
CN109564060B CN201780048225.6A CN201780048225A CN109564060B CN 109564060 B CN109564060 B CN 109564060B CN 201780048225 A CN201780048225 A CN 201780048225A CN 109564060 B CN109564060 B CN 109564060B
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pressure
air
product
air stream
conduit
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CN109564060A (en
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保罗·孔
范惠明
温迪·伊普
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Priority claimed from US15/382,902 external-priority patent/US10267561B2/en
Priority claimed from US15/382,896 external-priority patent/US10302356B2/en
Application filed by LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude filed Critical LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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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
    • F25J3/04406—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 dual pressure main column system
    • F25J3/04412—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 dual pressure main column system in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column
    • 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
    • F25J3/04078—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression
    • F25J3/04084—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression of nitrogen
    • 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
    • F25J3/04078—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression
    • F25J3/0409—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression of oxygen
    • 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
    • F25J3/04296—Claude expansion, i.e. expanded into the main or high pressure column
    • 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
    • F25J3/04521—Coupling of the air fractionation unit to an air gas-consuming unit, so-called integrated processes
    • F25J3/04527—Integration with an oxygen consuming unit, e.g. glass facility, waste incineration or oxygen based processes in general
    • 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
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04769—Operation, control and regulation of the process; Instrumentation within the process
    • F25J3/04812—Different modes, i.e. "runs" of operation
    • F25J3/04836—Variable air feed, i.e. "load" or product demand during specified periods, e.g. during periods with high respectively low power costs
    • 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
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/60—Details about pipelines, i.e. network, for feed or product distribution

Abstract

A method and apparatus for producing air gas by cryogenic separation of air may include the steps of: sending a purified and compressed air stream to a cold box under conditions effective to use a column system to cryogenically separate the air stream into an oxygen product and nitrogen, wherein the purified and compressed air stream is at a feed pressure upon entering the column system; withdrawing the oxygen product at a product pressure; delivering the oxygen product to an oxygen conduit at a delivery pressure, wherein the oxygen conduit has a conduit pressure; wherein during the second mode of operation, the method may include monitoring the line pressure; and reducing the difference between the tubing pressure and the delivery pressure. By operating in a dynamic manner, energy savings can be achieved in situations where the line pressure deviates from its highest value.

Description

Method for producing air gas by cryogenic separation of air
PCT patent application
RELATED APPLICATIONS
This application claims priority to U.S. provisional application serial No. 62/356,962, filed on 30/6/2016, which is hereby incorporated by reference in its entirety.
Technical Field
The present invention relates generally to a method and apparatus for efficiently operating an air separation plant that feeds at least one of its products into a pipeline.
Background
Air separation plants separate atmospheric air into its main components: nitrogen and oxygen, and occasionally argon, xenon and krypton. These gases are sometimes referred to as air gases.
A typical cryogenic air separation process may include the following steps: (1) filtering the air to remove large particulates that may damage the main air compressor; (2) compressing the pre-filtered air in a main air compressor and using inter-stage cooling to condense some water from the compressed air; (3) passing the compressed air stream through a front end purification unit to remove residual water and carbon dioxide; (4) cooling the purified air in a heat exchanger by indirect heat exchange with a process stream from a cryogenic distillation column; (5) expanding at least a portion of the chilled air to provide refrigeration to the system; (6) introducing cold air into the distillation column for rectification therein; (7) nitrogen (usually as a gas) is collected from the top of the column and oxygen as a liquid is collected from the bottom of the column.
In some cases, an air separation unit ("ASU") may be used to supply one of its air gases to a nearby pipeline (e.g., an oxygen or nitrogen pipeline) to supply one or more customers that are not located in close proximity to the ASU. In a typical ASU supplying local piping, it is common to use a process configuration that utilizes an internal compression (pumping) cycle, which in the case of an oxygen pipeline means that liquid oxygen produced from a lower pressure column is pumped from low pressure to a pressure above that of the pipeline and vaporized within a heat exchanger, most commonly against a high pressure air stream from a booster air compressor ("BAC") or main air compressor ("MAC"). As used herein, a booster air compressor is a secondary air compressor located downstream of the purification unit that is used to boost a portion of the main air feed for the purpose of efficiently vaporizing the product liquid oxygen stream.
Under normal conditions, an ASU feeding oxygen to an oxygen pipeline is designed to produce oxygen at a constant pressure. This is because the ASU operates most efficiently under steady state conditions. However, the pipe cannot be operated at a constant pressure. For example, it is not uncommon for an oxygen pipeline to operate between 400 and 600psig (i.e., a pressure change of about 200 psig) within a day. This may occur due to variable customer demand and/or variable supply to the pipeline.
In the prior art known to date, ASUs are typically designed to provide oxygen at a constant pressure above the highest pressure expected for the pipeline. To address the problems associated with variations in conduit pressure, the pressure of the gaseous oxygen is typically reduced across a control valve just prior to introduction of the oxygen into the conduit to approximately match the pressure of the conduit. However, this approach suffers from inefficiencies whenever the pipeline pressure is below the design pressure of the ASU. It would therefore be advantageous to provide methods and apparatus that operate in a more efficient manner.
Disclosure of Invention
The present invention is directed to a method and apparatus that meets at least one of these needs.
In one embodiment, the present invention may include a method for regulating one or more production pressures of air gases (e.g., nitrogen and oxygen) to correspond with a pipeline pressure, thereby reducing power consumption when the pipeline pressure is reduced.
In one embodiment, such inefficiencies may be minimized by: the equipment used in the ASU (e.g., main heat exchanger, liquid oxygen ("LOX") pump, BAC, MAC, etc.) is designed with sufficient flexibility to be able to deliver gaseous oxygen ("GOX") at different pressure levels based on pipeline pressure. In another embodiment, the method and apparatus can include a process control strategy to automatically and continuously adjust the GOX product pressure exiting the main heat exchanger to conform to the line pressure.
In another embodiment, since the GOX product pressure can be adjusted to match the oxygen line, the BAC exit pressure can be adjusted to match the heating profile of the pressurized LOX. Those skilled in the art will also recognize that the MAC discharge pressure can be adjusted in a similar manner if the unit does not use BAC.
In one particular embodiment, the apparatus may include an automated pipeline GOX feed valve set to 100% open, wherein GOX flow is controlled by a flow indicator controller ("FIC") operable to effect changes with LOX pump speed. The BAC discharge pressure may be based on the actual ASU GOX pressure through a control loop, preferably a feed forward control loop. As the line pressure decreases, the discharge pressure of the BAC and LOX pumps will decrease, providing significant energy savings.
Furthermore, the stability of the overall ASU process is not affected by these dynamic process conditions. This is mainly due to the fact that ASUs have faster kinetics than pipelines, since pipelines often contain such large amounts of gas; relatively, the pressure changes slowly.
In other embodiments, the conduit may be a nitrogen conduit fed by high pressure gaseous nitrogen ("GAN") produced by an internal compression process. The control strategy may also be implemented using any alternative control scheme that may allow GOX and/or GAN pressures to automatically conform to the pipe. For example, the ASU product pressure may be adjusted to conform to a pipeline by controlling the pressure differential across the product control valve to the pipeline. In one embodiment, the pressure differential across the product control valve is less than 5 psi. In another embodiment, the ASU product pressure is within 5psi of the pipeline pressure, allowing the product control valve to remain fully open, resulting in minimal pressure loss across the product control valve.
In one embodiment, a method for producing air gas by cryogenic separation of air may comprise the steps of:
a) compressing air to a pressure suitable for cryogenic rectification of the air to produce a compressed humid air stream having a first pressure Po；
b) Purifying the compressed humid air stream from water and carbon dioxide within a front end purification system to produce a dry air stream having a reduced amount of water and carbon dioxide as compared to the compressed humid air stream;
c) compressing a first portion of the dry air stream in a booster compressor to form a boosted pressure air stream having a first boost pressure PB1；
d) Introducing a second portion of the dry air stream and the pressurized air stream into a cold box under conditions effective to separate air to form an air gas product, wherein the air gas product is selected from the group consisting of oxygen, nitrogen, and combinations thereof;
e) extracting the air gas product from the cold box, the air gas product having a first product pressure PP1；
f) Introducing the air gas product into a conduit, wherein the conduit is configured to deliver the air gas product to a location downstream of the conduit, wherein the conduit is at a conduit pressure PPLOperating under conditions in which the air gas product is delivered at a first delivery pressure PD1Is introduced into the conduit;
g) monitoring the pipeline pressure P in the pipelinePL(ii) a And
h) based on the pipeline pressure PPLOne or more pressure set points within the cold box are adjusted.
In an optional embodiment of the method of producing air gas by cryogenic separation of air:
the one or more pressure set points of step h) is the first product pressure PP1；
Adjusting the first boost pressure PB1So that the first delivery pressure PD1With the pipe pressure PPLThe difference between them is below a given threshold;
the threshold is less than 5psi, preferably less than 3 psi;
the cold box comprises a main heat exchanger, a column system with a double column consisting of a lower pressure column and a higher pressure column, a condenser arranged at the bottom of the lower pressure column, and a liquid oxygen pump;
the air gas product is oxygen and the conduit is an oxygen conduit;
liquid oxygen pump pressurises liquid oxygen from the lower pressure column to a first product pressure PP1；
Pipeline pressure P based on monitoringPLAdjusting the first product pressure PP1；
Based on the first product pressure PP1Adjusting the first boost pressure PB1(ii) a And/or
The air gas product is nitrogen and the pipeline is a nitrogen pipeline.
In another aspect of the invention, a method of producing an air gas by cryogenic separation of air may include a first mode of operation and a second mode of operation, wherein during the first mode of operation and the second mode of operation, the method includes the steps of: sending a purified and compressed air stream to a cold box under conditions effective to cryogenically separate the air stream using a column system to form an air gas product, wherein the purified and compressed air stream is at a feed pressure P upon entering the cold boxFWherein the air gas product is selected from the group consisting of oxygen, nitrogen, and combinations thereof; at product pressure PPOExtracting the air gas product; at delivery pressure PDODelivering the air gas product to an air gas pipeline, wherein the air gas pipeline has a pipeline pressure PPL(ii) a Wherein during the second mode of operation, the method further comprises the steps of: monitoring pipeline pressure PPL(ii) a And reducing the pipe pressure PPLAnd delivery pressure PDOThe difference between them.
In an optional embodiment of the method of producing air gas by cryogenic separation of air:
reducing the pipe pressure PPLAnd delivery pressure PDOThe step of adjusting the difference between further comprises adjusting the product pressure PPO；
Reducing the pipe pressure PPLAnd delivery pressure PDOThe step of adjusting the difference between further comprises adjusting the feed pressure PFA step (2);
product pressure PPOAnd delivery pressure PDOAre substantially the same;
the air gas product is oxygen, wherein the cold box comprises a main heat exchanger, a column system with a double column consisting of a lower pressure column and a higher pressure column, a condenser arranged at the bottom of the lower pressure column, and a liquid oxygen pump;
the cold box further comprises a Gaseous Oxygen (GOX) feed valve, wherein the GOX feed valve is in fluid communication with the outlet of the liquid oxygen pump and the inlet of the air gas conduit;
reducing the pipe pressure PPLAnd delivery pressure PDOThe step of difference therebetween comprises not adjusting the GOX feed valve;
reducing the pipe pressure PPLAnd delivery pressure PDOThe step of difference between comprises keeping the GOX feed valve fully open;
the method may further comprise the step of providing a main air compressor upstream of the cold box, wherein the pipeline pressure P is reducedPLAnd delivery pressure PDOThe step of adjusting the difference between further comprises the step of adjusting the operation of the liquid oxygen pump and the operation of the main air compressor such that the product pressure P is adjustedPOAnd a feed pressure PF(ii) a And/or
The method may further comprise the step of providing a booster compressor downstream of the main air compressor and upstream of the cold box, wherein the pipeline pressure P is reducedPLAnd delivery pressure PDOThe step of adjusting the difference between further comprises the step of adjusting the operation of the liquid oxygen pump and the operation of the booster compressor such that the product pressure P is adjustedPOAnd a feed pressure PF。
In another aspect of the invention, an apparatus is provided. In this embodiment, the apparatus may comprise:
a) a main air compressor configured to compress air to a pressure suitable for cryogenic rectification of air to produce a compressed humid air stream having a first pressure Po；
b) A front end purification system configured to purify the compressed humid air stream from water and carbon dioxide to produce a dry air stream having a reduced amount of water and carbon dioxide as compared to the compressed humid air stream;
c) a booster compressor in fluid communication with the front end purification system, wherein the booster compressor is configured to compress a first portion of the dry air stream to form a boosted pressure air stream having a first boost pressure PB1；
d) A cold box comprising a main heat exchanger, a column system having a dual column comprised of a lower pressure column and a higher pressure column, a condenser disposed at the bottom of the lower pressure column, and a liquid oxygen pump, wherein the cold box is configured to receive a pressurized air stream and a second portion of a dry air stream under conditions effective to separate air to form an air gas product, wherein the air gas product is selected from the group consisting of oxygen, nitrogen, and combinations thereof;
e) apparatus for monitoring the pressure of a conduit, wherein the conduit is in fluid communication with a cold box such that the conduit is configured to receive an air gas product from the cold box, the air gas product having a first product pressure PP1(ii) a And
f) means for adjusting one or more pressure set points of the plant based on the monitored pipeline pressure, wherein the one or more pressure set points of the plant are selected from the group consisting of a discharge pressure of the liquid oxygen pump, a discharge pressure of the booster air compressor, a discharge pressure of the main air compressor, and combinations thereof.
In an optional embodiment of the plant for producing air gas by cryogenic separation of air:
regulating the first product pressure PP1So that the first product pressure PP1And a first delivery pressure PD1The difference between them is below a given threshold;
the threshold is less than 5psi, preferably less than 3 psi;
the air gas product is oxygen and the conduit is an oxygen conduit;
liquid oxygen pump pressurises liquid oxygen from the lower pressure column to a first product pressure PP1；
Based on the first product pressure PP1Adjusting the first boost pressure PB1(ii) a And/or
The air gas product is nitrogen and the pipeline is a nitrogen pipeline.
In another aspect of the invention, an apparatus for producing an air gas by cryogenic separation of air may include a cold box configured to cryogenically separate an air stream in an efficient use of a column system to form airReceiving a purified and compressed air stream under gaseous product conditions, wherein the purified and compressed air stream is at a feed pressure P upon entering the cold boxFWherein the air gas product is selected from the group consisting of oxygen, nitrogen, and combinations thereof, and wherein the cold box is configured to be at a product pressure PPOProducing an air gas product; means for transferring the air gas product from the cold box to an air gas duct; a pressure monitoring device configured to monitor a pipeline pressure PPL(ii) a And a controller configured to control the flow of the fluid based on the line pressure PPLRegulating the product pressure P of the gaseous product of the air coming out of the cold boxPO。
In an optional embodiment of the plant for producing air gas by cryogenic separation of air:
the air gas product is oxygen, wherein the cold box comprises a main heat exchanger, a column system with a double column consisting of a lower pressure column and a higher pressure column, a condenser arranged at the bottom of the lower pressure column, and a liquid oxygen pump;
the controller is also configured to reduce the line pressure PPLAnd delivery pressure PDOThe difference between them;
the controller is further configured to communicate with the liquid oxygen pump and regulate a discharge pressure of the liquid oxygen pump;
product pressure PPOAnd delivery pressure PDOAre substantially the same;
the controller is in communication with the pressure monitoring device;
the device may be absent being configured to reduce the pipeline pressure PPLAnd delivery pressure PDOGOX feed valve of the difference between;
the plant may have a Gaseous Oxygen (GOX) feed valve, wherein the GOX feed valve is in fluid communication with an outlet of the liquid oxygen pump and an inlet of the air gas conduit, wherein the GOX feed valve is maintained in a fully open position;
the apparatus may have a main air compressor arranged upstream of the cold box, wherein the controller is further configured to regulate a discharge pressure of the main air compressor; and/or
The apparatus may include a booster compressor downstream of the main air compressor and upstream of the cold box, wherein the controller is further configured to regulate a discharge pressure of the booster compressor.
Drawings
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. It is to be noted, however, that the appended drawings illustrate only several embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG. 1 provides an embodiment of the present invention.
Fig. 2 provides another embodiment of the present invention.
FIG. 3 provides a data diagram for one embodiment of the present invention.
Detailed Description
While the invention will be described in conjunction with several embodiments, it will be understood that they are not intended to limit the invention to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
Returning now to fig. 1. Air 2 is introduced into the main air compressor 10 and compressed, preferably to a pressure of at least 55psig to 75psig (or about 5psig above the pressure of the higher pressure column). The resulting compressed humid air stream 12 is then purified of water and CO in a front end purification system 202Thereby generating a flow of drying air 22. In one embodiment, all of the dry air stream 22 enters the cold box 40 via line 26. The pressure of the drying air stream 22 is measured by a first pressure indicator PI1 a. Within the cold box 40, the air is cooled and cryogenically treated to separate the air into an air gas product 42. The air gas product 42 is then removed from the cold box 40 and passed through the product control valve 50 before entering the air gas duct 60. In a preferred embodiment, the pressure and flow rate of the air gas product 42 may be measured by a second pressure indicator PI2 and a flow indicator FI1, respectively. The pressure of the air gas line 60 may be indicated by a pressure indicator PI3.
In one embodiment, the various pressure and flow indicators/sensors are configured to communicate (e.g., wirelessly or wired) with the process controller 55 so that the various flow rates and pressures can be monitored by the process controller 55, which is configured to adjust various settings throughout the process based on the measured flow and pressure.
In addition, embodiments of the present invention may also include a booster air compressor 30. This embodiment is indicated by a dashed line, as it is an optional embodiment. In this embodiment, a portion of the dry air stream 22 is sent via line 24 to a booster air compressor 30 and further compressed to form a booster air stream 32 prior to introduction into a cold box 40. The addition of the pressurized air compressor 30 allows for additional degrees of freedom in fine tuning the process, as will be explained in more detail below. In this embodiment, the first pressure indicator PI1b is located on line 32 instead of line 26. Similarly, the pressure controller 14b is in communication with the charge air compressor 30, as compared to the pressure controller 14a of the main air compressor 10. While the embodiment of FIG. 1 shows the booster air compressor 30 as a single compressor, one of ordinary skill in the art will recognize that the booster air compressor 30 may be more than one physical compressor. Furthermore, the charge air compressor 30 may also be a multi-stage compressor.
Although these figures illustrate direct communication lines from the various pressure and flow indicators to the process controller 55, embodiments of the present invention should not be so limited. Rather, one of ordinary skill in the art will recognize that embodiments of the present invention may include situations where certain indicators are in direct communication with an associated pressure controller.
FIG. 2 provides a more detailed view of the cold box 40 for an optional embodiment that includes a booster air compressor 30. In this embodiment, the cold box 40 further comprises a heat exchanger 80, a turbine 90, a valve 100, a twin column 110, a higher pressure column 120, an auxiliary heat exchanger 130, a lower pressure column 140, a condenser/reboiler 150, and a liquid oxygen pump 160. Turbine 90 may be attached to supercharger 70 via a common shaft. As in FIG. 1, air 2 is introduced into the main air spaceGas compressor 10 and compresses, preferably to a pressure of at least 55psig to 75psig (or about 5psig above the pressure of the higher pressure column). The resulting compressed humid air stream 12 is then purified of water and CO in a front end purification system 202Thereby generating a flow of drying air 22. A first portion 24 of the dry air stream is sent to a booster air compressor 30 and the remaining portion 26 of the dry air stream enters a cold box 40 where it is fully cooled in a heat exchanger 80 before being introduced into a higher pressure column 120 for separation therein. After pressurization in the charge air compressor 30, the charge air stream 32 is preferably fully cooled in heat exchanger 80 before being introduced into the bottom of the higher pressure column 120 and then expanded across valve 100.
Preferably, a portion of the charge air stream 37 is removed from an inner stage of the charge air compressor 30 prior to further compression in the supercharger 70, and then cooled in an aftercooler 75 to form a second charge air stream 72. The second boosted pressure stream 72 undergoes partial cooling in heat exchanger 80 where it is extracted from an intermediate portion of heat exchanger 80 and then expanded in turbine 90 to form an expanded air stream 92, which may then be combined with the second portion 26 of the drying air stream before being introduced into the higher pressure column 120.
The higher pressure column 120 is configured to allow air rectification therein to produce an oxygen-rich liquid at the bottom and a nitrogen-rich gaseous stream at the top. An oxygen-rich liquid 122 is withdrawn from the bottom of the higher pressure column 120 before exchanging heat with the low pressure waste nitrogen 114 and the low pressure nitrogen product 112 in an auxiliary heat exchanger 130, and then expanded across a valve and introduced into the lower pressure column 140. As is well known in the art, the higher pressure column 120 and the lower pressure column 140 are part of a dual column 110, and these two columns are thermally coupled via a condenser/reboiler 150 that condenses the rising nitrogen-rich gas from the higher pressure column 120 and vaporizes the liquid oxygen collected at the bottom of the lower pressure column 140. In the illustrated embodiment, two nitrogen-rich liquid streams 126, 128 are withdrawn from the higher pressure column 120, exchange heat with the low pressure nitrogen product 112 and the low pressure waste nitrogen 114, are subsequently expanded across their respective valves, and are then introduced into the lower pressure column 140. Higher pressure nitrogen product 129 may also be withdrawn from higher pressure column 120 and then heated in heat exchanger 80.
Liquid oxygen is collected at the bottom of the lower pressure column 140 and is withdrawn by a liquid oxygen pump 160 and pressurized to an appropriate pressure to form a liquid oxygen product 162. The liquid oxygen product 162 is then vaporized within the heat exchanger 80 to form the air gas product 42. The pressure and flow rate of the air gas product 42 may be measured via second pressure sensors PI2 and FI1, respectively. As shown in fig. 1, the air gas product 42 flows across the product control valve 50 and into the air gas conduit 60.
As noted previously, the pressure of the air gas line 60 tends to drift over time. In the methods known so far, this problem is solved by adjusting the opening degree of the product control valve 50 to generate an appropriate pressure drop. However, this is inefficient. Instead, embodiments of the present invention may adjust a pressure set point within the cold box, for example, the discharge pressure of the liquid oxygen pump 160. By reducing this pressure by an appropriate amount, the product control valve 50 can be kept fully open, resulting in minimal expansion losses across the product control valve 50. In one embodiment, a suitable amount produces a difference between PI2 and PI3 of less than 5psi, preferably less than 3 psi.
In another embodiment, by varying the pressure of the liquid oxygen product 162, its vaporization temperature will also vary. Further, it is preferred that the liquid oxygen product 162 be vaporized against a condensing air stream (e.g., the pressurized air stream 32). Likewise, in the preferred embodiment, the discharge pressure of the booster air compressor 30 is also changed by an appropriate amount. In one embodiment, the appropriate amount is preferably an amount that results in an improved heating profile between the liquid oxygen product 162 and the pressurized air stream 32.
In embodiments where the air gas product is nitrogen, this embodiment may include withdrawing higher pressure nitrogen product 129 as a liquid from higher pressure column 120 and pressurizing it to an appropriate pressure using a liquid nitrogen pump (not shown) prior to heating in heat exchanger 80. The resulting heated nitrogen product is then introduced into a nitrogen line in a similar manner as described for the gaseous oxygen product. Alternatively, the liquid nitrogen stream may be removed from the lower pressure column instead of the higher pressure column.
FIG. 3 provides a graphical representation of pressure as a function of time for an embodiment of the present invention. As can be seen in FIG. 3, the ASU GOX pressure is maintained slightly above (e.g., between 3-4 psi) the GOX pipe pressure. This is accomplished by both varying the LOX discharge pressure from the LOX pump and varying the charge air compressor (BAC) discharge pressure. By operating the LOX pump and BAC in a variable speed mode, embodiments of the present invention are able to save power consumption without any loss of flow rate production and thus present an incredible advantage over heretofore known methods.
Tables I and II below show comparative data for each stream for oxygen production at 610psig and 400 psig.
Figure BDA0001966150460000101
Table II: 400psig GOX
Figure BDA0001966150460000111
As shown in the above table, as the line pressure changes, the pressure of streams 32, 37, 42 and 162 can be adjusted while keeping all other conditions substantially the same. As will be readily appreciated, being able to reduce the compression requirements on LOX pump 160 and BAC 30 can result in significant energy savings. Furthermore, this is done without any production loss in terms of flow rate and without any significant disturbance to the operating conditions of the double column.
The terms "nitrogen-rich" and "oxygen-rich" will be understood by those skilled in the art as referring to the composition of air. Likewise, nitrogen-rich encompasses fluids having a nitrogen content greater than that of air. Similarly, oxygen-rich encompasses fluids having an oxygen content greater than that of air.
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 invention can suitably comprise, consist or consist essentially of the disclosed elements, and can be practiced in the absence of an element that is not disclosed. Furthermore, if there is language referring to the order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, one skilled in the art will recognize that certain steps may be combined into a single step.
The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.
The term "comprising" in the claims is an open transition term that means that the subsequently identified claim elements are a nonexclusive list (i.e., anything else can be additionally included and kept within the scope of "comprising"). Unless otherwise indicated herein, the term "comprising" as used herein may be replaced by the more limited transitional terms "consisting essentially of and" consisting of.
In the claims, "providing" is defined as meaning supplying, making available, or preparing something. Steps may be performed by any actor in the absence of such express language in the claims to the contrary.
Optional or optionally means that the subsequently described event or circumstance may or may not occur. This description includes instances where the event or circumstance occurs and instances where it does not.
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 the range.
All references identified herein are each hereby incorporated by reference in their entirety and for any specific information for which each reference is incorporated by reference.

Claims (17)

1. A method for producing air gas by cryogenic separation of air, the method comprising the steps of:
a) compressing (10) air (2) to a pressure suitable for cryogenic rectification of the air to produce a compressed humid air stream (12) having a first pressure Po；
b) Purifying the compressed humid air stream from water and carbon dioxide within a front end purification system (20) to produce a dry air stream (22) having a reduced amount of water and carbon dioxide as compared to the compressed humid air stream (12);
c) a first portion (24) of the drying air stream is compressed in a booster compressor (30) to form a boosted pressure air stream (32) having a first boosted pressure PB1；
d) The second portion (26) of the drying air stream and the boosted pressure air stream are introduced into a cold box (40) under conditions effective to separate air to form an air gas product (42) having a first product pressure PP1Wherein the air gas product is selected from the group consisting of oxygen, nitrogen, and combinations thereof;
e) withdrawing the air gas product from the cold box;
f) introducing the air gas product into a conduit (60), wherein the conduit is configured to deliver the air gas product to a location downstream of the conduit, wherein the conduit is at a conduit pressure PPLOperating under conditions in which the air gas product is delivered at a first delivery pressure PD1Is introduced into the conduit;
g) monitoring the pipeline pressure P in the pipelinePL(PI 3); and
h) based on the pipeline pressure PPLAdjusting one or more pressure set points, wherein the one or more pressure set points are selected from the first boost pressure P of step c)B1The first pressure P of step a)oAnd combinations thereof.
2. The method of claim 1, further comprising monitoring a pipeline pressure P based on the monitored pipeline pressurePLAdjusting the first product pressure PP1The step (2).
3. A method as set forth in claim 1 wherein the first boost pressure P is adjustedB1So that the first delivery pressure PD1And the pressure P of the pipelinePLThe difference between them is below a given threshold.
4. The method of claim 3, wherein the given threshold is less than 5 psi.
5. The method of claim 3, wherein the given threshold is less than 3 psi.
6. The method of claim 1, wherein the cold box comprises a main heat exchanger (80), a column system (110) having two columns consisting of a lower pressure column (140) and a higher pressure column (120), a condenser (150) arranged at the bottom of the lower pressure column, and a liquid oxygen pump (160).
7. The method of claim 6, wherein the air gas product is oxygen and the conduit is an oxygen conduit, and wherein the liquid oxygen pump pressurizes liquid oxygen from the lower pressure column to the first product pressure PP1。
8. The method of claim 1, wherein the pipeline pressure P is monitored based on the measured pressurePLAdjusting the first product pressure PP1。
9. The method of claim 8, wherein based on the first product pressure PP1Adjusting the first boost pressure PB1。
10. The method of claim 6, wherein the air gas product is nitrogen and the conduit is a nitrogen conduit.
11. A method for producing air gas by cryogenic separation of air, the method comprising a first mode of operation and a second mode of operation, wherein during the first mode of operation and the second mode of operation the method comprises the steps of:
compressing air to a pressure suitable for cryogenic rectification of the air to produce a compressed humid air stream having a first pressure Po；
Purifying the compressed humid air stream from water and carbon dioxide within a front end purification system to produce a dry air stream having a reduced amount of water and carbon dioxide as compared to the compressed humid air stream;
compressing a first portion of the dry air stream in a booster compressor to form a boosted pressure air stream having a first boost pressure PB1；
Passing the charge air stream to a cold box (40) under conditions effective to cryogenically separate the charge air stream using a column system (110) to form an air gas product (42), wherein the air gas product is selected from the group consisting of oxygen, nitrogen, and combinations thereof;
at product pressure PPOWithdrawing the air gas product from the cold box;
at delivery pressure PDODelivering the air gas product to an air gas duct (60), wherein the air gas duct has a duct pressure PPL；
Wherein during the second mode of operation, the method further comprises the steps of:
monitoring the pipeline pressure PPL(PI 3); and
reducing the pipeline pressure PPLAnd the delivery pressure PDOThe difference between the values of the two signals,
wherein the line pressure P is reducedPLAnd the delivery pressure PDOThe step of difference between further comprises basing the line pressure P on the differencePLAdjusting one or more pressure set points, wherein the one or more pressure set pointsThe point is selected from the first boost pressure PB1A first pressure PoAnd combinations thereof.
12. The method of claim 11, wherein the line pressure P is reducedPLAnd the delivery pressure PDOThe step of adjusting the difference between further comprises adjusting the product pressure P while in the cold boxPO。
13. The method of claim 11, wherein the product pressure PPOAnd the delivery pressure PDOAre substantially the same.
14. An apparatus for producing air gas by cryogenic separation of air, the apparatus comprising:
a) a main air compressor (10) configured to compress air (2) to a pressure suitable for cryogenic rectification of the air to produce a compressed humid air stream (12) having a first pressure Po；
b) A front end purification system (20) configured to purify the compressed humid air stream from water and carbon dioxide to produce a dry air stream (22) having a reduced amount of water and carbon dioxide as compared to the compressed humid air stream;
c) a booster compressor (30) in fluid communication with the front end purification system, wherein the booster compressor is configured to compress a first portion (24) of the dry air stream to form a boosted pressure air stream having a first boosted pressure PB1；
d) A cold box (40) comprising a main heat exchanger (80), a column system (110) having a dual column comprised of a lower pressure column (140) and a higher pressure column (120), a condenser (150) disposed at the bottom of the lower pressure column, and a liquid oxygen pump (160), wherein the cold box is configured to receive the pressurized air stream (32) and a second portion (26) of the drying air stream under conditions effective to separate air to form an air gas product, wherein the air gas product is selected from the group consisting of oxygen, nitrogen, and combinations thereof;
e) means for monitoring a pressure (PI3) of a conduit (60), wherein the conduit is in fluid communication with the cold box such that the conduit is configured to receive an air gas product from the cold box, the air gas product having a first product pressure PP1Wherein the air gas product is at a first delivery pressure PD1Lower is introduced into the conduit; and
f) means for adjusting one or more pressure set points of the plant (55) based on the monitored pipeline pressure, wherein the one or more pressure set points of the plant are selected from the group consisting of a discharge pressure of the liquid oxygen pump (160), a discharge pressure of the booster compressor (30), a discharge pressure of the main air compressor (10), and combinations thereof.
15. The apparatus of claim 14, wherein the first product pressure P is adjustedP1So that the first product pressure PP1And the first delivery pressure PD1The difference between them is below a given threshold.
16. The apparatus of claim 15, wherein the given threshold is less than 5 psi.
17. The apparatus of claim 15, wherein the given threshold is less than 3 psi.
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