CA2589334A1 - Air separation process and apparatus - Google Patents

Air separation process and apparatus

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Publication number
CA2589334A1
CA2589334A1 CA 2589334 CA2589334A CA2589334A1 CA 2589334 A1 CA2589334 A1 CA 2589334A1 CA 2589334 CA2589334 CA 2589334 CA 2589334 A CA2589334 A CA 2589334A CA 2589334 A1 CA2589334 A1 CA 2589334A1
Authority
CA
Grant status
Application
Patent type
Prior art keywords
column
nitrogen
air separation
air
separation unit
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
CA 2589334
Other languages
French (fr)
Inventor
Jean-Renaud Brugerolle
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Air Liquide SA
Original Assignee
Air Liquide SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00Combustion technologies with mitigation potential
    • Y02E20/10Combined combustion
    • Y02E20/14Combined heat and power generation [CHP]

Abstract

In an integrated power generation system, part of the air from a gas turbine compressor is separated in a single nitrogen wash column to remove oxygen and gaseous nitrogen produced at the top of the column is sent back to a point upstream of the expander of the gas turbine. The wash column may be fed with liquid nitrogen from an independent air separation unit, in which air is separated by cryogenic distillation. Liquid from the bottom of the wash column may be fed back to the air separation unit

Description

INTEGRATED APPARATUS FOR GENERATING POWER AND/OR OXYGEN
ENRICHED FLUID, PROCESS FOR THE OPERATION THEREOF AND AIR
SEPARATION PROCESS AND APPARATUS

io TECHNICAL FIELD OF THE INVENTION
The present invention relates to an integrated apparatus for generating power and/or oxygen-enriched fluid and a process for the operation thereof.
The invention also relates to an air separation apparatus and process.

BACKGROUND OF THE INVENTION
Oxygen production facilities typically extract oxygen from air. Air has the advantage of being free and available everywhere. One of the drawbacks is that because air is at atmospheric pressure, it contains a lot of water and CO2 at low partial pressure. And pressure drops in process cycles are energy-intensive close to atmospheric pressure. This is the reason why most oil, chemical or petrochemical processes operate in the range of from 10 to 40 bar. Pressure drops are less costly, heat exchange is easier, and the size of plants is reduced, drastically decreasing overall cost.
In the case of oxygen production, as air contains 80% nitrogen, a low pressure waste gas containing nitrogen is normally produced. In case of cryogenic distillation, cold heat contained in the waste nitrogen must be recuperated through heat exchangers which are costly both in investment and related energy needs.
Some oxygen plants operate at higher than normal pressure with some means and additional investment to recover the energy lost in the waste nitrogen.
Figure 1 shows a basic power gas turbine arrangement in which an air compressor I sends air 3 at from about 8 to about 35 bar to a combustor 5 fed by fuel 6. The combustion gas 7 mixed with dilution air 4 forms mixture stream 8 which is expanded in gas turbine 9 having an inlet temperature from about 900 to about 1400 C and generates power. To achieve good combustion in the burner, a close to stoichiometric mixing is necessary to use fuel efficiently and produce minimum pollution. But in this case, combustion produces a hot gas at temperatures higher than 2000 C, well above what any kind of hot turbine can accept. For this reason, quench type cooling takes place by mixing this very hot flue gas 7 with compressed dilution air 4 from the compressor at the same pressure as stream 3 but much lower temperature. The dilution air flow 4 is of the same order of magnitude as the combustion air flow 3.
Because this dilution air 4 does not participate in the combustion, oxygen is not necessary. So it is possible to extract the oxygen contained in the dilution air 4 as shown in Figure 2. Air 4 is cooled, purified and distilled in separation unit 12 producing oxygen 10 and nitrogen 11. Nitrogen 11 is mixed with combustion gas 7.
Generally the separation unit used is a double column comprising a thermally linked high pressure column and low pressure column. However, it is known to use a single column with a top condenser and a bottom reboiler for this purpose.
If the amount of nitrogen 11 is limited, it may alternatively be mixed with air stream 3 and sent to combustor 5 as described in US Patent No. 4,224,045.
Another option is to send the nitrogen to be mixed with the fuel stream 6.
It is an object of the invention to provide a integrated apparatus for generating power and/or oxygen-enriched fluid, a process for the operation thereof and to an air separation apparatus and process which possess advantages over the known art.

SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided an integrated apparatus for generating oxygen-enriched fluid and/or power comprising a first air separation unit, a gas turbine comprising a combustor and an expander, a first compressor, means for sending air from the first compressor to the combustor and optionally to the first air separation unit, means for sending combustion gases from the combustor to the expander, means for sending a nitrogen-enriched gas from the first air separation unit to a point upstream of the expander and means for either compressing the nitrogen-enriched gas sent to a point upstream of expander, further compressing the air sent to the first air separation unit from the first compressor or expanding the air sent to the combustor from the first compressor, wherein the first air separation unit lo comprises at least one column and the apparatus comprises means for sending nitrogen-enriched liquid from an external source to the top of the column, the external source not being a condenser fed by gaseous nitrogen from the single column, and means for removing the nitrogen-enriched gas from the top of the single column and for removing oxygen-enriched fluid from the bottom of the column.
According to another aspect of the present invention, there is provided a process for generating power and/or oxygen-enriched fluid using an integrated system comprising the steps of compressing air in a first compressor, sending air from the first compressor to a combustor and optionally to a first air separation unit, sending a nitrogen-enriched gas from the first air separation unit to a point upstream of an expander of a gas turbine, sending fuel to the combustor, sending combustion gas from the combustor to the expander and either compressing the nitrogen-enriched gas sent to a point upstream of expander, further compressing the air sent to the first air separation unit from the first compressor or expanding the air sent to the combustor from the first compressor, wherein the first air separation unit comprises at least one column and the process comprises feeding a column of the first separation unit with air, sending nitrogen-enriched liquid from an external source to the top of the column, the external source not being a condenser fed by gaseous nitrogen from the column and removing nitrogen-enriched gas from the top of the column and an oxygen-enriched fluid from the bottom of the column.
According to a further aspect of the present invention, there is provided an air separation apparatus comprising a first compressor, means for sending air from the first compressor to the air separation unit following cooling and purification, an air separation unit, means for removing a nitrogen-enriched fluid and an oxygen-enriched fluid from the air separation unit, wherein the apparatus comprises a further column, means for sending nitrogen-enriched liquid from the air separation unit to the top of the further column, means for sending compressed air to the bottom of the further column and means for removing nitrogen-enriched gas from the top of the further column and for removing lo oxygen-enriched fluid from the bottom of the further column and sending it to the air separation apparatus.
According to yet another aspect of the present invention, there is provided an air separation process comprising compressing air in a first compressor, sending air from the first compressor to a first air separation unit, removing a nitrogen-enriched fluid and an oxygen enriched fluid from the first air separation unit and feeding the bottom of a further column with air, wherein the process comprises sending nitrogen-enriched iiquid from the first air separation unit to the top of the further column, and removing nitrogen enriched gas from the top of the further column and an oxygen-enriched liquid from the bottom of the further column and sending the oxygen-enriched liquid to the air separation unit.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in further detail with reference to the Figures 3 to 6 which are schematic flow sheets of an integrated air separation unit for use in an integrated power generation system and with reference to Figures 7 and 8 which are schematic flow sheets of air separation units according to the invention. It will be appreciated that the units of Figures 7 and 8 could be used as integrated air separation unit for supplying nitrogen enriched gas to a gas turbine or another application.
DETAILED DESCRIPTION OF THE INVENTION
Cryogenic technology is the basic technology for large air separation plants.
In the process of Figure 3, air is compressed to from about 8 to about 35 bara in compressor 1. Air stream 3 is sent to combustor 5 where it is burnt with fuel 6.

Air stream 4 is cooled in heat exchanger 8, purified in purifying unit 14 and then cooled in heat exchanger 13 to a temperature suitable for cryogenic distillation. It is then sent to a first air separation unit, in this case a wash column 15 which is a single column fed at the top by a liquid nitrogen wash stream 17 which may be pure or contain up to 5% oxygen. Various sources for the liquid are shown in 1o Figures 4 to 6.
The single column 15 contains a number of separation stages, which may be composed of trays or structured packing.
Liquid 37 containing from about 27 to about 40 mol.% oxygen is removed from the bottom of column 15.
Nitrogen-enriched gas 21 containing from about 85 to about 100 mol.%
nitrogen is removed from the column at a pressure in the range of from about 8 to about 25 bara, warmed in exchangers 13, 8, reactivates air purification 14, compressed and sent to the combustion chamber 5 or else mixed either with the combustion gas as shown or with air stream 3. The mixture thus formed is sent to expander 9 producing external work. The nitrogen is compressed in a booster 16 at ambient temperature but may be compressed at sub-ambient or super-ambient temperatures so as to make up for the pressure drop in the exchangers and column.
Alternatively, air stream 4 may be boosted to the operating pressure of column 15 any of the temperatures described.
A less economical option would be to expand the feed air 3 slightly before sending it to the combustor. .
When the air separation from our gas turbine by-pass is performed using a liquid nitrogen wash column 15 (Figure 3), the following advantages are obtained:

- all heat exchanges (hot and cold) and purification are carried out at elevated pressure thus reducing investment and energy drop cost.
- the nitrogen wash column 15 is fed by nitrogen-enriched liquid 17, and very impure oxygen 37 is removed in liquid-rich phase. These liquids easily can be pumped and expanded, thus rendering this wash column pressure totally independent of the rest of the process.
- nitrogen-enriched gas flow 21 at the outlet of the wash column 15 is almost equal to the air flow 4 at the inlet of this column, thus maintaining the perfect balance of the gas turbine.
In the embodiment of Figure 4, the liquid nitrogen for the wash column 15 is derived from a second air separation unit comprising a double column with a high pressure column 25 and a low pressure column 27 thermally linked via a reboiler condenser 29 as in standard plants. The system may additionally include an argon separation column fed by the low pressure column. The operating pressures preferably vary from about 5 to about 25 bara for the high pressure column.
The air for the double column comes from a compressor 30 and is sent to the high pressure column 25 after cooling in exchanger 33.
Alternatively, the air for the double column may be derived at least in part from compressor 1 of the gas turbine or from an independent compressor feeding the single column, as shown in Figure 8.
Oxygen-enriched and nitrogen-enriched liquids 32, 34 are sent from the high pressure column to the low pressure column as reflux. The system may use a Claude turbine, a turbine feeding air to the low pressure column or a nitrogen turbine to produce refrigeration.
Gaseous oxygen 36 is produced from the low pressure column either directly or by vaporizing liquid oxygen. Waste nitrogen 38 is withdrawn from the low pressure column.
Liquid nitrogen 17 from the top of the high pressure column 25 is sent to the top of wash column 15, optionally following pumping in pump 35. Liquid 37 from the bottom of column 15 is expanded in a valve 39 and sent to the bottom of the high pressure column or to the low pressure column. It could for example be mixed with reflux stream 32.
A standard cryogenic oxygen plant has a double column including high pressure column with liquid nitrogen at the top and oxygen-rich liquid at the bottom. If one installs a gas turbine next to an oxygen plant to produce electric power (for the oxygen plant or not) or to produce a combination of power and steam (cogeneration), the existing air separation plant can operate in conjunction with an additional air separation plant so as to supply a new product to the gas turbine.
With the arrangement of Figure 4, some liquid nitrogen or poor liquid 17 can be withdrawn from the existing medium pressure column or any other point of the process such as the low pressure column. It can be pumped to the relevant pressure in order to feed the additional plant which is a nitrogen wash column. The corresponding rich liquid 37 will be returned to the low pressure column as the normal rich liquid. Thus some extra oxygen molecules will be fed to the column, allowing increased oxygen production (at the same or reduced purity, depending on the boosting ratio).
Obviously, this interesting process can be used in a grass root plant. In this case, a dedicated cold box will be better suited than a standard plant.
2o Because oxygen is to be replaced by nitrogen or air for the gas turbine, some additional compressed air is needed. As illustrated in Figure 5, it can be either :
- injected into the cold box 41 of the air separation unit via compressor 30.
The necessary pressure will be lower but a second air purification 38 is necessary.
- injected at the inlet of the expander 9 (before or after the hot exchanger 8).
No purification is necessary but the corresponding oxygen will be wasted (which is not a problem if the by-pass flow is sufficient for oxygen demand).
- mixed with the by-pass air 4 before the nitrogen wash step (before or after the hot exchanger 8). In that case the existing purification 14 can be used to purify the air.
In certain cases and depending on the final oxygen pressure required, a nitrogen (or air) recycle compressor 43 fed by nitrogen-enriched gas from the high pressure and/or low pressure columns may be required to adjust the separation power requirement of the oxygen separation and compression cycle.

To maintain the advantages of the global pressurized cycle, this compressor 43 will preferably receive air or nitrogen at medium pressure (above about 3 bar).
Refrigeration from oxygen will be recovered in the cold box 41 or within the cold exchanger 13.
Because the gas at the top of nitrogen wash column is nitrogen, it can be used partly to help the final distillation instead of the recycle compressor.
Thus nitrogen-enriched gas 45 from a column 25, 27 of the air separation unit can be sent to compressor 47 and thence to the expander 9. The flow to the turbine can be readjusted as before with air or waste nitrogen recompression 47. It might have an advantage over a nitrogen recycle compressor as this compressed nitrogen will not need any final cooling (Figure 6).
It will be appreciated that the external source for the liquid nitrogen could be a remote storage tank periodically replenished by tanker trucks or a liquefier in which gaseous nitrogen, e.g. from a pipeline is condensed rather than an air separation unit. The oxygen-enriched liquid from the first air separation unit may then be sent to another column or another user, or to liquefy after expansion the gaseous nitrogen from the pipeline.
In the case where the external source is a second air separation unit, this may be a single column air separator generating liquid nitrogen, a standard double column with or without minaret an external condenser of an air separation column, a double column in which oxygen-enriched liquid from the bottom of the low pressure column is fed to a top condenser of the low pressure column, a triple column in which rich liquid from a high pressure column feeds a medium pressure column and liquid from the medium pressure column feeds the low pressure column for example of the type shown in FR1061414 or EP538118.
The second air separation unit serving as an external source may produce other liquids in addition to the nitrogen and other gaseous products. Gases may be produced at high pressure by pumping and vaporizing liquids withdrawn from columns of the second air separation unit.
One advantage of the present system is that the first air separation unit and the second air separation unit can operate independently by providing storage tanks for the liquid nitrogen from the second air separation unit and the oxygen-enriched liquid from the first air separation unit.
Thus, when the second air separation unit is not operational, the first air separation unit draws liquid nitrogen from the storage. Similarly, when the first air separation unit is not operational the oxygen-enriched liquid is removed from 1o the storage and sent to the second air separation unit.
In the process of Figure 7, air stream 4 is purified in purifying unit 14 and then cooled in heat exchanger 13 to a temperature suitable for cryogenic distillation. It is then sent to a first air separation unit, in this case a wash column which is a single column fed at the top by a nitrogen-enriched liquid wash 15 stream 17 which may be pure or contain up to about 5 mol.% oxygen. Wash column 15 operates at a pressure from about 4 to about 25 bara.
Liquid 37 containing from about 27 to about 40 mol.% oxygen is removed from the bottom of column 15.
Gaseous nitrogen 21 is removed from the column at a pressure from about 8 to about 25 bar, warmed in exchangers 13, 8, reactivates air purification 14 and is compressed in a booster 16 at ambient temperature but may be compressed at sub-ambient or super-ambient temperatures so as to make up for the pressure drop in the exchangers and column.
An air separation unit which may be a source of the liquid 17 is shown in Figure 8. It will of course be appreciated that this air separation process and that of Figure 7 are not necessarily integrated with a gas turbine in these particular cases.

An existing plant fed by 1000 Nm3/h of air consists of a double column where all the refrigeration is supplied by a high pressure nitrogen turbine (not shown) fed by 210 Nm3/h nitrogen-enriched gas from column 25 which provides the refrigeration for liquid production and an air turbine 28 sending 80 Nm3/h air to the low pressure column which provides refrigeration for the apparatus. The amount of oxygen-enriched gas 36 initially produced from low pressure column 27 is 210 Nm3/h and this can be increased by adding a wash column 15 as described above to produce a plant as shown in Figure 8, no longer using the nitrogen turbine and increasing the amount of air flowing in the other turbine by 20% to cover thermal losses.
In the version of Figure 8, the nitrogen-enriched liquid 17 for the further wash column 15 is derived from an air separation unit comprising a double column with a high pressure column 25 and a low pressure column 27 thermally linked via a reboiler condenser 29 as in standard plants. The system may additionally include an argon separation column fed by the low pressure column.
The operating pressures preferably vary from about 5 to about 25 bar for the high pressure column.
The 1000 Nm3/h of air for the double column come from a dedicated compressor 30 and are sent partly to the high pressure column 25 after cooling in exchanger 33 and partly (100 Nm3/h) to the turbine 28 which feeds the low pressure column 27. Oxygen-enriched and nitrogen-enriched liquids 32, 34 are sent from the high pressure column to the low pressure column as reflux. The system may additionally use a Claude turbine or a nitrogen turbine to produce refrigeration.
210 Nm3/h of gaseous impure oxygen 36 is produced from the low pressure column either directly or by vaporizing liquid oxygen. 735 m3/h of waste nitrogen 38 is withdrawn from the low pressure column.
180 Nm3/h of nitrogen-enriched liquid 17 from about 0 to about 10 theoretical trays below the top of the high pressure column 25 is sent to the top of wash column 15 following pumping in pump 35. 180 Nm3/h of liquid 37 containing 55 Nm3/h oxygen from the bottom of column 15 is expanded in a valve 39 and sent to the bottom of the high pressure column or alternatively to the low pressure column. This liquid typically contains from about 30 to about 40 mol.%
oxygen. 300 Nm3 /h of air is sent to the bottom of the further column 15 from a separate compressor 40, another source of compressed air or the main compressor 30 and 300 Nm3/h of nitrogen-enriched gas 42 is removed from the top. This nitrogen may be used as a product stream.
With the arrangement of Figure 8, some liquid nitrogen or poor liquid 17 can be withdrawn from the top of the medium pressure column or a few ,,..

theoretical trays below the top of that column or any other point of the process such as the low pressure column. It can be pumped or expanded to the relevant pressure in order to feed the nitrogen wash column. which may operate at a pressure which is equal to, greater than or less than the pressure of the high pressure column 25. The corresponding rich liquid 37 will be returned to the low 1o pressure column as the normal rich liquid. Thus some extra oxygen molecules will be fed to the column, allowing increased oxygen production (at the same or reduced purity, depending on the boosting ratio).
In this way, the nitrogen molecules sent from the double column to the wash column are replaced by oxygen molecules. This means that the amount of impure oxygen which can be produced by the double column is increased by up to 25%.
The pressure drop for nitrogen waste gas 38 from the low pressure column reduces because less nitrogen enters the double column when the wash column 15 is used. The pressure drop for the oxygen 36 is substantially increased and it may be necessary to use additional heat exchangers for the heat exchange between the air and the oxygen or to reallocate the existing passages in the heat exchanger 33.
In certain cases and depending on the final oxygen pressure required, a nitrogen (or air) recycle compressor 43 may be required to adjust the separation power requirement of the oxygen separation and compression cycle. To maintain the advantages of the global pressurized cycle, this compressor will preferably receive air or nitrogen at medium pressure (above 3 bar).
Refrigeration from oxygen will be recovered in the cold box 41 or within the cold exchanger 13.

The further column may be contained in a second cold box together with the exchanger 44 in which the feed liquid nitrogen is heated following pressurization against the bottom liquid of the further column and the exchanger 46 in which the feed air for the further column is cooled against the product gaseous nitrogen from the further column.

Because the gas at the top of nitrogen wash column is nitrogen, it can be used partly to help the final distillation instead of the recycle compressor.
The air may be cooled using the gaseous nitrogen from the top of the further column.
The air separation unit may be a single column air separator generating liquid nitrogen, a standard double column with or without minaret, an external condenser of an air separation column, a double column in which oxygen-enriched liquid from the bottom of the low pressure column is fed to a top condenser of the low pressure column or a triple column in which rich liquid from a high pressure column feeds a medium pressure column and liquid from the medium pressure column feeds the low pressure column for example of the type shown in FR1061414 or EP538118.
The air separation unit may produce other liquids in addition to the nitrogen and other gaseous products. Gases may be produced at high pressure by pumping and vaporizing liquids withdrawn from columns of the second air separation unit.
In particular, it may include an argon column or a mixing column.
One advantage of the present system is that the air separation unit and the further column can operate independently by providing storage tanks for the liquid nitrogen from the air separation unit and the oxygen-enriched liquid from the further column unit.

Thus, when the air separation unit is not operational, the further column draws liquid nitrogen from the storage. Similarly, when the further column is not operational, the oxygen-enriched liquid is removed from the storage and sent to the air separation unit.

With an apparatus of this sort, it becomes possible to increase the capacity of the existing air separation unit (i.e. the double or triple column) by 25% for impure oxygen by adding a further air separation column.

Further optional aspects of an integrated apparatus for generating power and/or oxygen-enriched fluid of the present invention are:

- the single column has no bottom reboiler and no top condenser.
- the apparatus comprises a second compressor and means for sending air from the further compressor to the single column.
- the external source of nitrogen-enriched liquid is a second air separation unit comprising at least one distillation column.
1o - the second air separation unit comprises a high pressure column and a low pressure column which are thermally linked.
- there are means for withdrawing the nitrogen-enriched liquid from the high pressure column or the low pressure column, where necessary pressurizing it and sending it to the top of the single column in liquid form and/or means for sending the oxygen-enriched liquid from the bottom of the single column to the high pressure column and/or the low pressure column.
- there are means for sending air to the double column from one of the first, second or a third compressor.
Alternatively there may be means for sending nitrogen-enriched gas from the single column to the double column and/or means for sending nitrogen-enriched gas from the double column to a point upstream of the expander.
The apparatus may additionally include a gasifier, means for sending oxygen from the air separation unit and a carbon containing substance to the gasifier and means for sending fuel from the gasifier to the combustor.
Further optional aspects of a process for generating power and/or oxygen-enriched fluid of the present invention are:
- the column having no bottom reboiler and no top condenser.
- sending air from a second compressor to the single column.
- the external source being a second air separation unit comprising at least one column -the external source comprises a high pressure column and a low pressure column which are thermally linked.
- withdrawing the nitrogen-enriched liquid from the high pressure column, pressurizing and sending it to the top of the column of the first air separation unit.

- sending the liquid from the bottom of the single column to the second air separation unit, optionally to the high pressure column or low pressure column of the second air separation unit.
- sending air to the second air separation unit from one of the first, second or a third compressor.
1o - sending nitrogen-enriched gas from the column of the first air separation unit to the second air separation unit.
- means for sending nitrogen-enriched gas from the second air separation unit to a point upstream of the expander.
- wherein the column of the first air separation unit operates at from about 8 to about 35 bara.
- the highest pressure of a column of the second air separation unit is from about 5 to about 25 bara.
- the volume of air sent from the first compressor to the first air separation unit and the volume of nitrogen-enriched gas sent upstream of the expander differ by no more than 10%, preferably 5%.
- all the nitrogen originates from the first air separation unit or alternatively the nitrogen originates from the first air separation unit and the external source.
- the external source being preferably the second air separation unit.
Further optional aspects of an air separation apparatus of the present invention are:

- the further column has no bottom reboiler and/or no top condenser.

- the apparatus comprises a second compressor and means for sending air from the second compressor to the further column.

- the apparatus comprises means for pressurizing the nitrogen-enriched liquid from the high pressure column, and sending it to the top of the column of the first air separation unit.

- the air separation unit is a double column comprising a high pressure column and a low pressure column and the nitrogen-enriched liquid comes from the high pressure column.

- there are means for sending the liquid from the bottom of the further column to the bottom of the high pressure coiumn.

- the air separation unit is a triple column comprising a high pressure column, an intermediate pressure column and a low pressure column and the nitrogen enriched liquid comes from the high pressure column or the intermediate pressure column.

- there are means for sending the liquid from the bottom of the further column to the bottom of the high pressure column or the middle of the intermediate pressure column.

Further optional aspects of an air separation process of the present invention are:
- the further column is a single column having no bottom reboiler and no top condenser.
- the process comprises sending air from a second compressor to the further column.
- the process comprises pressurizing the nitrogen-enriched liquid from the air separation unit, and sending it to the top of the column of the further column.
- the further column operates at from about 8 to about 25 bara.
- the pressure of the higher or highest pressure column of the air separation unit is from about 5 to about 25 bara.
- the oxygen-enriched liquid at the bottom of the further column contains from about 30% to about 40 mol.% oxygen.
- the air separation unit is a double column comprising a high pressure column and a low pressure column and the nitrogen-enriched liquid comes from the high pressure column.
- the process comprises sending the liquid from the bottom of the further column to the bottom of the high pressure column.
- the process comprises removing a stream containing at least 80 mol.%
oxygen from the low pressure column.

- the air separation unit is a triple column comprising a high pressure column, an intermediate pressure column and a low pressure column and the nitrogen-enriched liquid comes from the high pressure column or the intermediate pressure column.
- the process comprises sending the liquid from the bottom of the further column to the bottom of the high pressure column or the middle of the intermediate pressure column.
- the process comprises removing a stream containing at least 80 mol.%
oxygen from the low pressure column.
In particular the process may be an integrated gasification combined cycle process in which oxygen-enriched fluid from the air separation unit is sent to gasify a carbon containing substance thereby producing fuel for the combustor.

The combined air separation unit and further column will produce a greater proportion of oxygen and consequently a lesser proportion of waste nitrogen than the air separation unit alone. For this reason, more oxygen can be produced with less waste nitrogen. In general, the waste nitrogen circuits are the bottleneck for increased oxygen production by simple feed air flow boosting.

There are new separation power requirements for purifying the additional oxygen introduced in the air separation unit. This extra power can be obtained, either by decreasing the purity of part or all of the oxygen produced; or by reducing the total amount of gas expanded in one or more turbines to produce less refrigeration (thus possibly reducing liquid production), taking into account that the further column will require additional cooling.

Claims (21)

1. An air separation apparatus comprising a first compressor, means for sending air from the first compressor to the air separation unit following cooling and purification, an air separation unit, means for removing a nitrogen-enriched fluid and an oxygen-enriched fluid from the air separation unit, wherein the apparatus comprises a further column, means for sending nitrogen-enriched liquid from the air separation unit to the top of the further column, means for sending compressed air to the bottom of the further column and means for removing nitrogen-enriched gas from the top of the further column and for removing oxygen-enriched fluid from the bottom of the further column and sending it to the air separation apparatus.
2. An apparatus as claimed in Claim 1 wherein said further column has no bottom reboiler and/or no top condenser.
3. An apparatus as claimed in Claim 1 or 2 comprising a second compressor and means for sending air from the second compressor to the further column.
4. An apparatus as claimed in Claim 1, 2 or 3 comprising means for pressurizing the nitrogen-enriched liquid from the first air separation unit, and sending it to the top of the column of the first air separation unit.
5. An apparatus as claimed in Claim 1 wherein the air separation unit comprises at least a double column comprising a high pressure column and a low pressure column and the nitrogen-enriched liquid comes from the high pressure column.
6. An apparatus as claimed in Claim 5 comprising means for sending the liquid from the bottom of the further column to the bottom of the high pressure column or to the low pressure column.
7. An apparatus as claimed in any one of Claims 1 to 6 wherein the air separation unit is a triple column comprising a high pressure column, an intermediate pressure column and a low pressure column and the nitrogen-enriched liquid comes from the high pressure column or the intermediate pressure column.
8. An apparatus as claimed in Claim 7 comprising means for sending the liquid from the bottom of the further column to the bottom of the high pressure column or the middle of the intermediate pressure column or to the low pressure column.
9. An air separation process comprising compressing air in a first compressor, sending air from the first compressor to a first air separation unit, removing a nitrogen-enriched fluid and an oxygen enriched fluid from the first air separation unit and feeding the bottom of a further column with air, wherein the process comprises sending nitrogen-enriched liquid from the first air separation unit to the top of the further column, and removing nitrogen enriched gas from the top of the further column and an oxygen-enriched liquid from the bottom of the further column and sending the oxygen-enriched liquid to the air separation unit.
10. A process as claimed in Claim 9 wherein said further column is a single column having no bottom reboiler and no top condenser.
11. A process as claimed in Claim 9 or 10 comprising sending air from a second compressor to the further column.
12. A process as claimed in Claim 9, 10 or 11 comprising pressurizing the nitrogen-enriched liquid from the air separation unit, and sending it to the top of the column of the further column.
13. A process as claimed in any one of Claims 9 to 12 wherein the further column operates at a pressure from about 8 to about 25 bara.
14. A process as claimed in any one of Claims 9 to 12 wherein the pressure of the higher or highest pressure column of the air separation unit is from about 5 to about 25 bara.
15. A process as claimed in any one of Claims 9 to 14 wherein the oxygen-enriched liquid at the bottom of the further column contains from about 30% to about 40 mol.%
oxygen.
16. A process as claimed in any one of Claims 9 to 15 wherein the air separation unit is a double column comprising a high pressure column and a low pressure column and the nitrogen-enriched liquid comes from the high pressure column.
17. A process as claimed in Claim 16 comprising sending the liquid from the bottom of the further column to the bottom of the high pressure column or to the low pressure column.
18. A process as claimed in any one of Claims 9 to 17 comprising removing a stream containing at least about 80 mol.% oxygen from the low pressure column.
19. A process as claimed in any one of Claims 9 to 15 wherein the air separation unit is a triple column comprising a high pressure column, an intermediate pressure column and a low pressure column and the nitrogen-enriched liquid comes from the high pressure column or the intermediate pressure column.
20. A process as claimed in Claim 19 comprising sending the liquid from the bottom of the further column to the bottom of the high pressure column or the middle of the intermediate pressure column.
21. A process as claimed in Claim 19 or 20 comprising removing a stream containing at least about 80% oxygen from the low pressure column.
CA 2589334 1999-04-05 2000-04-03 Air separation process and apparatus Abandoned CA2589334A1 (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
US09285794 US6202442B1 (en) 1999-04-05 1999-04-05 Integrated apparatus for generating power and/or oxygen enriched fluid and process for the operation thereof
US09/285,794 1999-04-05
US09481681 US6276171B1 (en) 1999-04-05 2000-01-12 Integrated apparatus for generating power and/or oxygen enriched fluid, process for the operation thereof
US09/481,681 2000-01-12
CA 2303668 CA2303668C (en) 1999-04-05 2000-04-03 Integrated apparatus for generating power and/or oxygen enriched fluid, process for the operation thereof and air separation process and apparatus

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CA2589334A1 true true CA2589334A1 (en) 2000-10-05

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CA (1) CA2589334A1 (en)

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