US20230314069A1

US20230314069A1 - Flexible asu for variable energy cost

Info

Publication number: US20230314069A1
Application number: US18/130,542
Authority: US
Inventors: Michael A. Turney; Alain Guillard
Original assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2022-04-04
Filing date: 2023-04-04
Publication date: 2023-10-05

Abstract

A process for the production of at least liquid oxygen and/or liquid nitrogen in cryogenic rectification. During a first period, during which electrical power prices are low, a process stream utilized by the ASU is liquefied and stored. During a second period, during which electrical prices high, at least a portion of the stored, liquefied process stream is withdrawn and introduced into the ASU. Wherein the MAC has a discharge pressure of greater than 10 bara during the first period, a first molar flowrate (LF) and a first pressure (LP) during the first period, a second molar flowrate (HF) and a second pressure (HP) during the second period. Wherein C=(LF/HF)/(LP/HP). And wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and C is between 0.9 and 1.05.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to U.S. Provisional Patent Application No. 63/326,950, filed Apr. 4, 2022, the entire contents of which are incorporated herein by reference.

BACKGROUND

It is known that the cost of power varies significantly daily, weekly and seasonally due to supply and demand and limited ability to store power on the grid. These cost variations are increasing due to greater uses of renewable energy such as wind and solar. FIG. 1 is one representative example of the typical range of power cost. As shown in FIG. 1 , during periods of higher electrical prices, it is desirable to avoid running air separation systems which typically consume fairly large amounts of electricity. However, during periods of lower electrical prices, it is then more desirable to operate these air separation systems. The dilemma is how to accomplish these operating parameters.
The cost of power is a key design parameter for an air separations unit (ASU). Numerous methods are known in the existing art for ASU design to manage variations in power cost. A few examples include:

- For gaseous O2 and/or N2 customers, liquid oxygen (LOX) and/or liquid nitrogen (LIN) can be produced during times of low power cost. The LOX and/or LIN produced is pumped and vaporized to deliver product at times of high power cost.
- So-called Bascule systems are known for their ability to vary production rates with constant feed air (constant power) by producing and storing liquid air (LAIR) at times of low production demand and then consuming the LAIR produced at times of high production demand. (FIGS. 2-3 )

In FIG. 2 , one operating mode of a Bascule system is indicated. During periods of high electrical costs, the volume flowrate of inlet air 201 entering main air compressor 202 is reduced. This requires a portion of the liquid air stored in buffer tank 203 to be withdrawn and sent to distillation column 204. This results in the total oxygen production 206 being at the desired level, and a net increase in liquid nitrogen production, at least a portion of which is then stored in buffer tank 205.
In FIG. 3 , another operating mode of a Bascule system is indicated. During periods when electrical costs are not high, the volume flowrate of inlet air 201 entering main air compressor 202 is maintained at the best efficiency point. A portion of the liquid air produced is then stored in buffer tank 203. In order to satisfy the system refrigeration requirement, liquid nitrogen is then removed from buffer tank 205. This results in the total gaseous oxygen production 206 being at the desired level.
Prior art U.S. Pat. No. 7,228,715 describes an ASU process where when power price is low the main air compressor (MAC) and booster air compressor (BAC) are operating at high load and LAIR is accumulated. Conversely, when power price is high, the BAC can be stopped and the MAC can be reduced by 20-55% and LAIR is consumed resulting in a sharp drop in power consumption.
The power variations often occur on daily or twice daily basis. It is not desirable to start/stop large compressors and/or turboexpanders on such a frequent basis which will result in equipment damage and short equipment fife. Also, U.S. Pat. No. 7,228,715 does not describe how this equipment can achieve significant turndown without stopping. In the processes described, the MAC discharge pressure is fixed at 6 bara due to the vaporization of O2 and condensation of N2 in main vaporizer. Similarly, the BAC discharge pressure is fixed by the vaporization of production GOX in the main exchanger.
There is a need in the industry for an air separation system that can more efficiently and economically move between periods of high electricity prices and low electricity prices.

SUMMARY

A process for the production of at least liquid oxygen and/or liquid nitrogen in cryogenic rectification, During a first period, during which electrical power prices are low, a process stream utilized by the ASU is liquefied and stored. During a second period, during which electrical prices high, at least a portion of the stored, liquefied process stream is withdrawn and introduced into the ASU. Wherein the MAC has a discharge pressure of greater than 10 bara during the first period, a first molar flowrate (LF) and a first pressure (LP) during the first period, a second molar flowrate (HF) and a second pressure (HP) during the second period. Wherein C=(LF/HF)/(LP/HP). And wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and C is between 0.9 and 1.05.

BRIEF DESCRIPTION OF THE FIGURES

For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein;

FIG. 1 is one representative example of the typical range of power cost.

FIG. 2 is a schematic representation of one operating mode of a Bascule system is indicated, as known to the art.

FIG. 3 is a schematic representation of another operating mode of a Bascule system is indicated, as known to the art.

FIG. 4 is a schematic representation of an HP air cycle with a lost air, accordance with one embodiment of the present invention.

FIG. 5 is a schematic representation of one scheme utilizing a battery to store electricity to operate the MAC during short duration high energy price, accordance with one embodiment of the present invention.

FIG. 6 is a schematic representation of another scheme utilizing a battery to store electricity to operate the MAC during short duration high energy price, accordance with one embodiment of the present invention.

FIG. 7 is a schematic representation of a typical compressor inlet guide vane map.

FIG. 8 is a schematic representation of a typical compressor turndown map, accordance with one embodiment of the present invention.

FIG. 9 is a schematic representation of the range of operation as it relates to a defined coefficient, in accordance with one embodiment of the present invention.

FIG. 10 is a schematic representation of a BAC recycle system, in accordance with one embodiment of the present invention.

Element Numbers

- 201=inlet air
- 202=main air compressor
- 203=liquid air buffer tank
- 204=distillation column
- 205=liquid nitrogen buffer tank
- 206=total gaseous oxygen production
- 401=inlet air
- 402=main air compressor
- 403=front end purification
- 404=Claude compressor
- 405=lost air compressor
- 406=main heat exchanger
- 407=first portion (of cooled inlet air)
- 408=distillation column
- 409=second portion (of cooled inlet air)
- 410=Claude expander
- 411=expanded second air stream
- 412=first fraction (of expanded second air stream)
- 413=second fraction (of expanded second air stream)
- 414=warmed second fraction
- 415=lost air expander
- 416=xpanded second air stream
- 417=waste stream
- 418=liquid nitrogen product stream
- 419=waste nitrogen stream
- 420=iquid oxygen stream
- 421=warmed waste nitrogen stream
- 422=LAIR storage vessel
- 501=typical ASU
- 502=MAC (and/or BAC)
- 503=liquid nitrogen
- 504=liquid oxygen
- 505=liquid air
- 506=electrical power
- 507=renewable power
- 508=local electrical storage system (battery)
- 901=inlet air
- 902=main air compressor
- 903=front end purification
- 904=booster air compressor
- 905=boosted air stream
- 906=first portion (of boosted air stream)
- 907=second portion (of boosted air stream)
- 908=Claude compressor
- 909=boosted first portion
- 910=main heat exchanger
- 911=air compressor
- 912=compressed second portion
- 913=combined air stream
- 914=third portion (of cooled inlet air)
- 917=air expander
- 918=expanded air
- 920=air stream to front end purification (1^st)
- 922=second portion (of cooled inlet air)
- 924=Claude expander
- 925=expanded second air stream
- 926=first portion (of cooled inlet air)
- 927=LAIR storage vessel
- 928=LAIR stream (from LAIR storage vessel)
- 932=distillation column
- 933=liquid nitrogen product stream
- 934=waste nitrogen stream
- 935=liquid oxygen stream
- 926=air stream to front end purification (2^nd)

DESCRIPTION OF PREFERRED EMBODIMENTS

Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms. specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
One objective of the current application is to have an efficient feasible process to produce LOX (or LOX and LIN) for purpose of merchant liquid, rocket propellant. If one skilled in the art performs a mass and energy balance around the cold end of an ASU (distillation columns+sub-cooler) he would find that it indicates that the energy to produce LOX and/or LIN products may be from MAC flow and pressure, turbo-expanders, stored LAIR.
The inventive process may be utilized by any process which utilizes an air expansion cycle. Examples include, but are not limited to, an HP air cycle, an HP air cycle with a lost air turbine, and low-pressure MAC+HP air recycle. For purpose of describing the concept an HP air cycle with a lost air is used in FIG. 4 .
Turning now to FIG. 4 , the process scheme for a high-pressure air feed (GOK) cycle, which also has a lost air turbine to generate additional refrigeration, accordance with one embodiment of the present invention is illustrated. Inlet air stream 401 enters main air compressor 402 wherein the pressure is increased. The compressed air stream is then directed to front end purification 403, wherein the inlet air stream is purified, The purified inlet air is then compressed in Claude compressor 404 and then further compressed in lost air compressor 405, after which it enters main heat exchanger 406.
First portion 407 of the cooled inlet air exits main heat exchanger 406 and, if necessary, is combined with LAIR from LAIR storage vessel 422. First portion 407, with or without additional LAIR from LAIR storage vessel 422, then enters distillation column 408. Second portion 409 of the cooled inlet air exits main heat exchanger 406 and then enters Claude expander 410. Expanded second air stream 411 is then split into two fractions. First fraction 412 then enters distillation column 408. Second fraction 413 is reintroduced into main heat exchanger 406. Warmed second fraction 414 then exits main heat exchanger 406 and enters lost air expander 415. Further expanded second air stream 416 then reenters main heat exchanger 406, wherein it is warmed and exits as waste stream 417.
Distillation column 408 produces at least liquid nitrogen product stream 418 waste nitrogen stream 419, and liquid oxygen stream 420. In the interest of simplicity, a single column system is illustrated herein, but one of ordinary skill in the art will recognize that such a column may comprise two or more separate columns. Also in the interest of simplicity, only liquid oxygen and liquid nitrogen are shown being produced. In some embodiments, such a system may also produce liquid argon, gaseous argon, gaseous oxygen and/or gaseous nitrogen. The overarching principles discussed here would apply to these cycles equally well. In order to produce the desired flowrate in liquid oxygen stream 420, it is necessary to introduce additional refrigeration duty. Many methods of generating additional refrigeration duty are known in the art such as adding cycle compression with turbo-expansion, LIN assist from external sources as well as utilizing lost air compressor 405 and lost air expander 415 as shown in FIG. 4 , After passing through main heat exchanger 406, waste nitrogen stream 419 exits the system as warmed waste nitrogen stream 421. An example of the results of this process scheme is illustrated in Table 1.

	TABLE 1

	BASE	WITH LAIR BUFFER

LOW	HIGH		LOW	HIGH
ELECTRICAL	ELECTRICAL	WEIGHTED	ELECTRICAL	ELECTRICAL	WEIGHTED
PRICES	PRICES	AVERAGE	PRICES	PRICES	AVERAGE

MAC VOLUME FLOWRATE	129400	129400		137000	50000
MAC ELECTRICAL CONSUMPTION	19529	19529	19529	20676	7546	19582
LOX VOLUME FLOWRATE	17695	17695	17695	18180	12360	17695
LOX ELECTRICAL CONSUMPTION	15446	15446		16401	5583
LIN VOLUME FLOWRATE	7703	7703	7703	8067	3703	7703
LIN ELECTRICAL CONSUMPTION	4083	4083		4276	1963
$/MW-h	20	80	30	20	80
$/MT LOX	11.21	4.08		11.58	2.11
$/MT LIN	7.77	2.83		7.77	2.83
OPEX M$/YEAR			4.28			3.92
DELTA OPEX M$/YEAR						−0.4

In one embodiment, a significant turndown of refrigeration production is made during high power cost times by operating only 1 of the 2 50% capacity installed compressors and shutting down one of two turbines (e.g. shutting down the warm turbine). The installed compressors may include auxiliary compressors such as booster air compressor, refrigeration cycle compressor, and recycle compressor. These auxiliary compressors may compress air or nitrogen. In order to maintain a distillation column profile, the LOX and LIN production rates are either maintained or only somewhat reduced (column turndown is less than refrigeration turndown) compared to the refrigeration turndown. The refrigeration balance is maintained by consumption of liquid, preferably LAIR, which is produced and stored at least part of the time during the low power cost times.
The operating expense (OPEX) cost may be further reduced by utilization of a battery to store electricity to operate the MAC during short duration high energy price. This is illustrated in FIGS. 5 and 6 .
Turning to FIG. 5 , a typical ASU 501 is fed air through MAC (and/or BAC) 502, thereby producing LIN 503, LOX 504, and possibly LAIR 505. During periods of low electricity prices, electrical power 506 for MAC (and/or BAC) 502 may be received from some renewable source 507, such as wind power or solar power. Additionally, electrical power may be stored in a local electrical storage system 508, such as a battery.
Turning to FIG. 6 , during periods of high electricity prices, renewable source 507 electrical power may be discontinued, and electrical power 506 for MAC (and/or BAC) 502 may come directly from local electrical storage system 508, such as a battery. An example of this process scheme is illustrated in Table 2.

	TABLE 2

	BASE	WITH LAIR BUFFER and BATTERY

MAC VOLUME FLOWRATE	129400	129400		137000	50000
MAC ELECTRICAL CONSUMPTION	19529	19529	19529	20676	7546	19582
LOX VOLUME FLOWRATE	17695	17695	17695	18180	12360	17695
LOX ELECTRICAL CONSUMPTION	15446	15446		16401	5583
LIN VOLUME FLOWRATE	7703	7703	7703	8067	3703	7703
LIN ELECTRICAL CONSUMPTION	4083	4083		4276	1963
$/MW-h	20	80	30	20	20
$/MT LOX	11.21	4.08		11.58	0.53
$/MT LIN	7.77	2.83		7.77	0.71
OPEX M$/YEAR			4.28			3.4
DELTA OPEX M$/YEAR						−0.9

Turning to FIGS. 7 and 8 , it is shown that the refrigeration turndown may be achieved without completely stopping the machinery (i.e. MAC and/or turbines). In this case, turndown is achieved by reducing both MAC flow and pressure by either dosing Inlet Guide Vane angle (IGV) or reducing the compressor speed. In this case, turndown is achieved by reducing both MAC flow and pressure by either reducing the compressor speed or dosing Inlet Guide Vane angle (IGV). By adjusting the compressor speed it is possible to reduce both MAC flow and pressure to achieve operating range from 100% to less than 30%.
As indicated in FIG. 7 , it is possible to reduce both the mass flowrate and the pressure ratio in the MAC by adjusting the IGVs. In this generic representation of a centrifugal compressor curve, Point A is the design point. The prior art would maintain the pressure ratio as the compressor mass flowrate was reduced. In this figure, as the IGVs are “opened” from an angle of approximately 0° (Point A) to an angle of approximately 40° (Point C) the compressor throttle mass flowrate is reduced to about 55% of the design mass flowrate and the pressure ratio is maintained at about 100% of the design pressure ratio.
In the current invention, as the IGVs are “opened” from an angle of approximately 0° (Point A) to an angle of approximately 60° (Point B) the compressor throttle mass flowrate is reduced to about 55% of the design mass flowrate and the pressure ratio is reduced to about 70% of the design pressure ratio. Thus, allowing the controlled reduction in both mass flowrate and pressure ratio. One of ordinary skill in the art will recognize that each compressor will have its own inlet guide vane map, and FIG. 7 is merely a typical representation.
As indicated in FIG. 8 , it is possible to reduce both the volume flowrate and the pressure ratio in the MAC by adjusting the compressor speed. In this generic representation of a centrifugal compressor curve, Point A is the design point. As mentioned above, the prior art would maintain the pressure ratio as the compressor mass flowrate was reduced. In this figure, as the compressor speed is reduced from approximately 100% (Point A) to approximately 95% (Point C) the compressor throttle volume flowrate is reduced to about 65% of the design volume flowrate and the pressure ratio is maintained at about 100% of the design pressure ratio.
In this figure, as the compressor speed is reduced from approximately 100% (Point A) to approximately 80% (Point B) the compressor throttle volume flowrate is reduced to about 90% of the design volume flowrate and the pressure ratio is reduced to about 60% of the design pressure ratio. One of ordinary skill in the art will recognize that each compressor will have its own compressor speed map, and FIG. 8 is merely a typical representation. By adjusting the compressor speed, it is typically possible to reduce both MAC flow and pressure ratio to achieve operating range from 100% to less than 30%. This not only directly reduces the flow but also allows for further reduction in power.
Turning to FIG. 9 , during a first period, during which electrical power prices are below a first predetermined threshold, the air compressor has a first molar flowrate (LF) and a first outlet pressure (LP). During a second period, during which electrical power prices are above a second predetermined threshold, the air compressor has a second molar flowrate (HF) and a second outlet pressure (HP). The first predetermined threshold may be approximately equal to the second predetermined threshold. The coefficient C=(LF/HF)/(LP/HP). When HF is less than 90% of LF, then C is be between 0.9 and 1.05. When HF is less than 80% of LF, then C is between 0.8 and 1.15. VVhen HF is less than 70% of LF, C is between 0.6 and 1.3.
As indicated in FIG. 9 , the current state of the art is to turn down the molar flowrate of the compressor while maintaining the outlet pressure at or near 100%. This control approach leads to the conditions indicated within shaded box A. As can be seen, in such an operating mode the coefficient C increases as the flowrate decreases.
The current invention requires that the molar flowrate of the compressor as well as the outlet pressure are both reduced, by the above described adjustments of the IGVs and/or compressor speed. This control approach leads to the conditions indicated within shaded box B. As can be seen, in such an operating mode the coefficient C remains approximately constant as the flowrate decreases.
In one example of combined daily, and seasonal energy price variation.

TABLE 3

Period A 7 Months at 25 to 110 $/MWh

7 months	Period A	1	5 months	Period B

120	5		120
80	35		80	20
40	35		40	35
25	25		25	35
−30			−30	10

BASE

WITH LAIR BUFFER and COMPRESSOR ADJUSTMENT

	LOW	HIGH		LOW	HIGH
	ELECTRICAL	ELECTRICAL	WEIGHTED	ELECTRICAL	ELECTRICAL	WEIGHTED
	PRICES	PRICES	AVERAGE	PRICES	PRICES	AVERAGE

MAC VOLUME FLOWRATE	129400	129400		169000	103000
MAC ELECTRICAL CONSUMPTION	19529	19529	19529	25459	14021	19740
LOX VOLUME FLOWRATE	17695	17695	17695	18180	17210	18099
LOX ELECTRICAL CONSUMPTION	15446	15446		21270	10046
LIN VOLUME FLOWRATE	7703	7703	7703	7905	7500	7703
LIN ELECTRICAL CONSUMPTION	4083	4083		4190	3975
$/MW-h	25	110	68	25	110
$/MT LOX	7.64	33.63		10.24	22.49
$/MT LIN	5.30	23.32		5.30	23.32
OPEX M$/YEAR			11.55			9.66
DELTA OPEX M$/YEAR						−1.89
DELTA OPEX M$/15 YEARS						−28.4

TABLE 4

Period B 5 Months at −30 to 90 $/MWh

BASE

WITH LAIR BUFFER and COMPRESSOR ADJUSTMENT

MAC VOLUME FLOWRATE	129400	129400		169000	103000
MAC ELECTRICAL CONSUMPTION	19529	19529	19529	25459	14021	19740
LOX VOLUME FLOWRATE	17695	17695	17695	18180	17210	18099
LOX ELECTRICAL CONSUMPTION	15446	15446		21270	10046
LIN VOLUME FLOWRATE	7703	7703	7703	7905	7500	7703
LIN ELECTRICAL CONSUMPTION	4083	4083		4190	3975
$/MW-h	−30	90	30	−30	90
$/MT LOX	−9.17	27.52		−12.29	18.40
$/MT LIN	−6.36	19.08		−6.36	19.08
OPEX M$/YEAR			5.13			2.42
DELTA OPEX M$/YEAR						−2.71
DELTA OPEX M$/15 YEARS						−40.6

This concept also applies to other air separation unit processes where the main air compressor discharge pressure is not directly linked to the pressure of the high-pressure column. For example, the process below has a main air compressor discharge between 9 to 15 bar followed by further compression in a booster air compressor. It is conceivable that both compressor discharge pressures can be reduced significantly in combination with flow rate reductions. The air separation unit may include rotating devices such as booster air compressor, recycle compressor, refrigeration compressor, and expanders. AH of which may be adjusted as discussed herein. In one embodiment none of the rotation devices are stopped when transitioning between the first period (of low electrical power prices) and the second period (of high electrical power prices), In another embodiment one or more of the rotation devices are stopped when transitioning between the first period (of low electrical power prices) and the second period (of high electrical power prices). In another embodiment one or more of the rotation devices are stopped at least a portion of the time during the second period (of high electrical power prices).
Key concepts pertinent to the present invention are as follows: First, a process for the production of LOX and/or LIN by the cryogenic rectification of feed air utilizing a reduction of compression power input to <70% (preferably <50%) of nominal by reducing flow and discharge pressure. Where compression power reduction is by either A) reducing compressor speed (rpm) [preferred] or B) closing IGVs (inlet guide vanes). Wherein power reduction is without shutting down compression equipment. (Note: Add separate claim for option to shut down compressor and/or turbine machine.)
The present invention may also include the storage of LAIR, where LAIR is produced mostly during low power cost times and LAIR is consumed mostly during high power cost times. LOX and LIN production rates may be either maintained or only somewhat reduced compared to the refrigeration turndown (either by shutting down machines or reducing load without shutting down machines). In one embodiment the combined LOX and LIN production rates during high power cost times is approximately equal to that during low power cost times. In one embodiment, the combined LOX and LIN production rate during the high power cost times is approximately 75%, preferably 90%, of those during low power cost times. In one embodiment, at least one stream comprising a hydrocarbon is introduced into the air separation unit and liquefied by indirect heat exchange there.
Specifically, total LOX and LIN molar flow production may be either maintained or reduced by less than 50% (preferably less than 10% and ideally <5%) of the reduction of power input of compression equipment. For example MAC power is reduced from 100% (during low power cost) to 50% (during high power cost) to yield a reduction in total molar LOX and LIN flow of less than 0.5×0.5=25% (preferably less 0.5×0.1=5%). LOX production rates may be either maintained or only somewhat reduced compared to the refrigeration turndown, either by shutting down machines or reducing load without shutting down machines.
Specifically, total LOX molar flow production may be either maintained or reduced by less than 50% (preferably less than 10% and ideally <5%) of the reduction of power input of compression equipment. For example MAC power is reduced from 100% (during low power cost) to 50% (during high power cost) to yield a reduction in total molar LOX flow of less than 0.5×0.5=25% (preferably less 0.5×0.1=5%)
LIN production rates may be either maintained or only somewhat reduced compared to the refrigeration turndown (either by shutting down machines or reducing load without shutting down machines). (column turndown is less than refrigeration turndown). Specifically, total LIN molar flow production may be either maintained or reduced by less than 50% (preferably less than 10% and ideally <5%) of the reduction of power input of compression equipment. For example MAC power is reduced from 100% (during low power cost) to 50% (during high power cost) to yield a reduction in total molar LIN flow of less than 0.5×0.5=25% (preferably less 0.5×0.1=5%)
During periods of low electricity cost: Adding energy from an energy source (from grid, wind, solar, . . . ) to a battery as well as to the ASU compression equipment. During periods of high electricity cost: removing energy from the batter to power the compression equipment.
Possible configurations include: the MAC has a pressure higher than 10 bara with no BAC; the MAC has a pressure higher than 10 bara with BAC, may optionally shut down 1 MAC in case of multiple MACs
A similar known system is the so-called BAC recycle system, as illustrated in FIG. 10 . Turning now to FIG. 10 , the process scheme for a BAC recycle system in accordance with one embodiment of the present invention is illustrated. Inlet air stream 901 enters main air compressor 902 wherein the pressure is increased. The compressed air stream is then directed to front end purification 903, wherein the inlet air stream is purified. The purified inlet air is then further compressed in booster air compressor 904. Boosted air stream 905 is then split into two portions. First portion 906 is then compressed in Claude compressor 908 thus producing boosted first portion 909. Second portion 907 is compressed in air compressor 911, thus producing compressed second portion 912. Boosted first portion 909 and compressed second portion 912 are combined to form stream 913, which then enters main heat exchanger 910.
First portion 926 of the cooled inlet air exits main heat exchanger 910 and, if necessary, is combined with LAIR stream 928 from LAIR storage vessel 927. First portion 926, with or without additional LAIR from LAIR storage vessel 927, then enters distillation column 932. Second portion 922 of the cooled inlet air exits main heat exchanger 932 and then enters Claude expander 924. Expanded second air stream 925 then enters distillation column 932, Third portion 914 of the cooled inlet air exits main heat exchanger 932 and enters air expander 917. Expanded air stream 918 then reenters main heat exchanger 910, wherein it is warmed and exits as stream 920. Stream 920 then enters front end purification 903.
Distillation column 932 produces at least liquid nitrogen product stream 933 waste nitrogen stream 934, and liquid oxygen stream 935. In order to produce the desired flowrate in liquid oxygen stream 935, it is necessary to introduce additional refrigeration duty, in the form of air compressor 911 and air expander 917. After passing through main heat exchanger 910, waste nitrogen stream 934 exits as stream 936. Stream 920 and stream 936 then enter front end purification 903. An example of this process scheme is illustrated in Table 5.

	TABLE 5

	BASE	WITH LAIR BUFFER

MAC VOLUME FLOWRATE	88475	88475		93200	65000	88500
MAC ELECTRICAL CONSUMPTION	7011	7011	7011	7385	5151	7013
BAC VOLUME FLOWRATE	154875	154875		161400	112950	153325
BAC ELECTRICAL CONSUMPTION	12590	12590	12590	13252	9274	12589
LOX VOLUME FLOWRATE	176950	176950	176950	17900	17080	17763
LOX ELECTRICAL CONSUMPTION	15518	15518		16500	10502
LIN VOLUME FLOWRATE	7703	7703	7703	7805	7400	7738
LIN ELECTRICAL CONSUMPTION	4083	4083		4137	3922
$/MW-h	25	110	39	25	110
$/MT LOX	12.80	11.26		13.45	7.90
$/MT LIN	8.84	7.77		8.84	7.77
OPEX M$/YEAR			6.72			6.15
DELTA OPEX M$/YEAR						−0.58

Turing to the current application, with the high-pressure air process, the MAC discharge pressure can be reduced with the flow. This not only directly reduces the power but also allows for further reduction in flow. Thus, applying the IGV control and compressor speed control, to the process illustrated in FIG. 4 , results in the numbers shown in Table 6.

	TABLE 6

	BASE	WITH LAIR BUFFER and COMPRESSOR ADJUSTMENT

MAC VOLUME FLOWRATE	129400	129400		146000	73700
MAC ELECTRICAL CONSUMPTION	19529	19529	19529	21959	9021	19803
LOX VOLUME FLOWRATE	17695	17695	17695	17818	17080	17695
LOX ELECTRICAL CONSUMPTION	15446	15446		17845	5099
LIN VOLUME FLOWRATE	7703	7703	7703	7763	7400	7703
LIN ELECTRICAL CONSUMPTION	4083	4083		4114	3922
$/MW-h	25	110	39	25	110
$/MT LOX	12.74	11.21		14.61	3.83
$/MT LIN	8.84	7.77		8.84	7.77
OPEX M$/YEAR			6.7			5.48
DELTA OPEX M$/YEAR						−1.22

The IGV and compressor speed adjustments utilized with the high-pressure air process as shown above in FIG. 4 , the MAC discharge pressure can be reduced with the flow. This not only directly reduces the power but also allows for further reduction in flow. This is illustrated below in Table 7. And likewise, the IGV and compressor speed adjustments may be utilized with the MAC+BAC cycle shown above in FIG. 10 . The results of this is presented below in Table 8.

	TABLE 7

	BASE	WITH IGV AND COMPRESSOR SPEED ADJUSTMENTS

AVERAGE HOURS PER DAY	20	4		20	4
MAC VOLUME FLOWRATE	100%	100%		112%	57%	100%
MAC PRESSURE
	100%	100%	100%	100%	50%
LOX SPECIFIC POWER (KW/MT)	100%	100%		115%	34%
$/MW-h	25	110		25	110
$/MT LOX	12.74	11.21	23.95	14.61	3.83	18.45
$/MT LIN	8.84	7.77	16.61	8.84	7.77	16.61
OPEX M$/YEAR			6.70			5.48
DELTA OPEX M$/YEAR						−1.22

	TABLE 8

	BASE	WITH IGV AND COMPRESSOR SPEED ADJUSTMENTS

AVERAGE HOURS PER DAY	20	4		20	4
MAC VOLUME FLOWRATE	100%	100%		105%	73%	100%
MAC PRESSURE
	100%	100%	100%	100%	100%
BAC VOLUME FLOWRATE	100%	100%		104%	73%	100%
BAC PRESSURE
	100%	100%	100%	100%	100%
LOX SPECIFIC POWER (KW/MT)	100%	100%		105%	70%
$/MW-h	25	110		25	110
$/MT LOX	12.80	11.26	24.06	13.45	7.90	21.35
$/MT LIN	8.84	7.77	16.61	8.84	7.77	16.61
						\
OPEX M$/YEAR			6.72			6.15
DELTA OPEX M$/YEAR						−0.58

Paragraph 1. A process for the production of at least liquid oxygen and/or liquid nitrogen in the cryogenic rectification of feed air, comprising an air separation unit and a main air compressor, the process comprising:

- during a first period, during which electrical power prices are below a first predetermined threshold, a process stream utilized by the air separation unit is liquefied and stored at least a part of the time of this period,
- during a second period, during which electrical prices are at, or above a second predetermined threshold, at least a portion of the stored, liquefied process stream is withdrawn and introduced into the air separation unit at least a part of the time of this period,
  wherein the main air compressor has a discharge pressure of greater than 10 bara during the first period,
- wherein the main air compressor has a first molar flowrate (LF) and a first pressure (LP) during the first period,
- wherein the main air compressor has a second molar flowrate (HF) and a second pressure (HP) during the second period,
- wherein C=(LF/HF)/(LP/HP), and
- wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and C is between 0.9 and 1.05.

Paragraph 2. The process of paragraph 1, wherein second molar flowrate (HF) is <80% of first molar flowrate (LF) and C is between 0.8 and 1.15.
Paragraph 3. The process of paragraph 1, wherein second molar flowrate (HF) is <70% of first molar flowrate (LF) and C is between 0.6 and 1.3.
Paragraph 4. The process of paragraph 1, wherein the first predetermined threshold is approximately equal to the second predetermined threshold.
Paragraph 5. The process of paragraph 1, wherein the process stream that is liquefied and stored in at least a portion of the first period and withdrawn and introduced into the air separation unit in the second period, is liquid air.
Paragraph 6. The process of paragraph 5, wherein the air separation unit produces a mass flowrate of liquid oxygen and a mass flowrate of liquid nitrogen, and

- wherein the combined mass flowrate of the liquid oxygen and the mass flowrate of liquid nitrogen of the first period and the second period are approximately equal at least a portion of the time.

Paragraph 7. The process of paragraph 5, wherein the air separation unit produces a mass flowrate of liquid oxygen and a mass flowrate of liquid nitrogen, and

- wherein the combined mass flowrate of the liquid oxygen and the mass flowrate of liquid nitrogen of the second period is less than 75% (preferably less than 90%) of the first period at least a portion of the time.

Paragraph 8. The process of paragraph 7, wherein the ratio of the mass flowrate of liquid oxygen to the mass flowrate of liquid nitrogen during the first period is within 20% of the ratio of the mass flowrate of liquid oxygen to the mass flowrate of liquid nitrogen during the second period.
Paragraph 9. The process of paragraph 7, wherein the ratio of the mass flowrate of liquid oxygen to the mass flowrate of liquid nitrogen during the first period is approximately equal to the ratio of the mass flowrate of liquid oxygen to the mass flowrate of liquid nitrogen during the second period.
Paragraph 10. The process of paragraph 1, wherein the air separation unit does not have a booster air compressor.
Paragraph 11. The process of paragraph 1, wherein the air separation unit comprises a booster air compressor.
Paragraph 12. The process of paragraph 1, wherein the air separation unit further comprises one or more rotating devices selected from the group consisting of a booster air compressor, recycle compressor, refrigeration compressor and expanders.
Paragraph 13. The process of paragraph 12, wherein none of the rotating devices are stopped when transitioning from the first period to the second period.
Paragraph 14. The process of paragraph 12, wherein one or more of the rotating devices are stopped when transitioning from the first period to the second period.
Paragraph 15. The process of paragraph 12, wherein one or more of the rotating devices are stopped at least a portion of the time during the second period.
Paragraph 16. The process of paragraph 1, wherein at least one stream consisting of a hydrocarbon is introduced into the air separation unit and liquefied by indirect heat exchange therein.
Paragraph 17. A process for the production of at least liquid oxygen and/or liquid nitrogen in the cryogenic rectification of feed air, comprising an air separation unit and a main air compressor, and an auxiliary compressor the process comprising:

- during a first period, during which electrical power prices are below a first predetermined threshold, a process stream utilized by the air separation unit is liquefied and stored at least a part of the time of this period,
- during a second period, during which electrical prices are at, or above a second predetermined threshold, at least a portion of the stored, liquefied process stream is introduced into the air separation unit at least a part of the time of this period,
  wherein the auxiliary compressor has a pressure ratio of greater than 6 during the first period,
- wherein the auxiliary compressor has a first molar flowrate (LF) and a first pressure ratio (LPR) during the first period,
- wherein the auxiliary compressor has a second molar flowrate (HF) and a second pressure ratio (HPR) during the second period,
- wherein CR=(LF/HF)/(LPR/HPR), and
- wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and CR is between 0.9 and 1.05.

Paragraph 18, The process of paragraph 17, wherein the auxiliary compressor is one or more of the devices selected from the group consisting of a booster air compressor, refrigeration cycle compressor, a recycle compressor. (and may be air, nitrogen).
Paragraph 19. The process of paragraph 17, wherein second molar flowrate (HF) is <80% of first molar flowrate (LF) and CR is between 0.8 and 1.15.
Paragraph 20. The process of paragraph 17, wherein second molar flowrate (HF) is <70% of first molar flowrate (LF) and CR is between 0.6 and 1.3.
Paragraph 21. The process of paragraph 17, wherein the first predetermined threshold is approximately equal to the second predetermined threshold.
Paragraph 22. The process of paragraph 17, wherein the process stream that is liquefied and stored in at least a portion of the first period and withdrawn and introduced into the air separation unit in the second period, is liquid air.
Paragraph 23. The process of paragraph 22, wherein the air separation unit produces a mass flowrate of liquid oxygen and a mass flowrate of liquid nitrogen, and

Paragraph 24. The process of paragraph 22, wherein the air separation unit produces a mass flowrate of liquid oxygen and a mass flowrate of liquid nitrogen, and

Paragraph 25. The process of paragraph 24, wherein the ratio of the mass flowrate of liquid oxygen to the mass flowrate of liquid nitrogen during the first period is within 20% of the ratio of the mass flowrate of liquid oxygen to the mass flowrate of liquid nitrogen during the second period.
Paragraph 26. The process of paragraph 24, wherein the ratio of the mass flowrate of liquid oxygen to the mass flowrate of liquid nitrogen during the first period is approximately equal to the ratio of the mass flowrate of liquid oxygen to the mass flowrate of liquid nitrogen during the second period.
Paragraph 27. The process of paragraph 17, wherein the air separation unit does not have a booster air compressor.
Paragraph 28. The process of paragraph 17, wherein the air separation unit comprises a booster air compressor.
Paragraph 29. The process of paragraph 17, wherein the air separation unit further comprises one or more rotating devices selected from the group consisting of a booster air compressor, recycle compressor, refrigeration compressor and expanders.
Paragraph 30. The process of paragraph 29, wherein none of the rotating devices are stopped when transitioning from the first period to the second period.
Paragraph 31. The process of paragraph 29, wherein one or more of the rotating devices are stopped when transitioning from the first period to the second period.
Paragraph 32. The process of paragraph 29, wherein one or more of the rotating devices are stopped at least a portion of the time during the second period.
Paragraph 33. The process of paragraph 17, wherein at least one stream consisting of a hydrocarbon is introduced into the air separation unit and liquefied by indirect heat exchange.
Paragraph 34. The process of paragraph 18, wherein none of the rotating devices are stopped when transitioning from the first period to the second period.
Paragraph 35. The process of paragraph 18, wherein one or more of the rotating devices are stopped when transitioning from the first period to the second period.
Paragraph 36. The process of paragraph 18, wherein one or more of the rotating devices are stopped at least a portion of the time during the second period.
Paragraph 37. A process for the production of at least gaseous oxygen in the cryogenic rectification of feed air, comprising an air separation unit and a main air compressor, the process comprising:

- during a first period, during which electrical power prices are below a first predetermined threshold, a process stream utilized by the air separation unit is liquefied and stored at least a part of the time of this period.
- during a second period, during which electrical prices are at, or above a second predetermined threshold, at least a portion of the stored, liquefied process stream is introduced into the air separation unit at least a part of the time of this period,
  wherein the main air compressor has a discharge pressure of greater than 10 bara during the first period,
- wherein the main air compressor has a first molar flowrate (LF) and a first pressure (LP) during the first period,
- wherein the main air compressor has a second molar flowrate (HF) and a second pressure (HP) during the second period,
- wherein C=(LF/HF)/(LP/HP), and
- wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and C is between 0.9 and 1.05.

Paragraph 38. The process of paragraph 37, wherein second molar flowrate (HF) is <80% of first molar flowrate (LF) and C is between 0.8 and 1.15.
Paragraph 39. The process of paragraph 37, wherein second molar flowrate (HF) is <70% of first molar flowrate (LF) and C is between 0.6 and 1.3.
Paragraph 40. The process of paragraph 37, wherein the first predetermined threshold is approximately equal to the second predetermined threshold.
Paragraph 41. The process of paragraph 37, wherein the process stream that is liquefied and stored in at least a portion of the first period and withdrawn and introduced into the air separation unit in the second period, is liquid air.
Paragraph 42. The process of paragraph 41, wherein the air separation unit produces a mass flowrate of gaseous oxygen and/or a mass flowrate of gaseous nitrogen, and

- wherein the combined mass flowrate of the gaseous oxygen and the mass flowrate of gaseous nitrogen of the first period and the second period are approximately equal at least a portion of the time.

Paragraph 43. The process of paragraph 41, wherein the air separation unit produces a mass flowrate of gaseous oxygen and/or a mass flowrate of gaseous nitrogen, and

- wherein the combined mass flowrate of the gaseous oxygen and the mass flowrate of gaseous nitrogen of the second period is less than 75% (preferably less than 90%) of the first period at least a portion of the time.

Paragraph 44. The process of paragraph 43, wherein the ratio of the mass flowrate of gaseous oxygen to the mass flowrate of gaseous nitrogen during the first period is within 20% of the ratio of the mass flowrate of gaseous oxygen to the mass flowrate of gaseous nitrogen during the second period.
Paragraph 45. The process of paragraph 43, wherein the ratio of the mass flowrate of gaseous oxygen to the mass flowrate of gaseous nitrogen during the first period is approximately equal to the ratio of the mass flowrate of gaseous oxygen to the mass flowrate of gaseous nitrogen during the second period.
Paragraph 46. The process of paragraph 37, wherein the air separation unit does not have a booster air compressor.
Paragraph 47. The process of paragraph 37, wherein the air separation unit comprises a booster air compressor.
Paragraph 48. The process of paragraph 37, wherein the air separation unit further comprises one or more rotating devices selected from the group consisting of a booster air compressor, recycle compressor, refrigeration compressor and expanders.
Paragraph 49. The process of paragraph 48, wherein none of the rotating devices are stopped when transitioning from the first period to the second period.
Paragraph 50. The process of paragraph 48, wherein one or more of the rotating devices are stopped when transitioning from the first period to the second period.
Paragraph 51. The process of paragraph 48, wherein one or more of the rotating devices are stopped at least a portion of the time during the second period.
Paragraph 52. The process of paragraph 37, wherein at least one stream consisting of a hydrocarbon is introduced into the air separation unit and liquefied by indirect heat exchange.
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.

Claims

What is claimed is:

1. A process for the production of at least liquid oxygen and/or liquid nitrogen in the cryogenic rectification of feed air, comprising an air separation unit and a main air compressor, the process comprising:

during a first period, during which electrical power prices are below a first predetermined threshold, a process stream utilized by the air separation unit is liquefied and stored at least a part of the time of this period,

during a second period, during which electrical prices are at, or above a second predetermined threshold, at least a portion of the stored, liquefied process stream is withdrawn and introduced into the air separation unit at least a part of the time of this period,

wherein the main air compressor has a discharge pressure of greater than 10 bara during the first period,

wherein the main air compressor has a first molar flowrate (LF) and a first pressure (LP) during the first period,

wherein the main air compressor has a second molar flowrate (HF) and a second pressure (HP) during the second period,

wherein C=(LF/HF)/(LP/HP), and

wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and C is between 0.9 and 1.05.

2. The process of claim 1, wherein second molar flowrate (HF) is <80% of first molar flowrate (LF) and C is between 0.8 and 1.15.

3. The process of claim 1, wherein the first predetermined threshold is approximately equal to the second predetermined threshold.

4. The process of claim 1, wherein the process stream that is liquefied and stored in at least a portion of the first period and withdrawn and introduced into the air separation unit in the second period, is liquid air.

5. The process of claim 4, wherein the air separation unit produces a mass flowrate of liquid oxygen and a mass flowrate of liquid nitrogen, and

wherein the combined mass flowrate of the liquid oxygen and the mass flowrate of liquid nitrogen of the first period and the second period are approximately equal at least a portion of the time.

6. The process of claim 1, wherein the air separation unit further comprises one or more rotating devices selected from the group consisting of a booster air compressor, recycle compressor, refrigeration compressor and expanders, and

wherein none of the rotating devices are stopped when transitioning from the first period to the second period.

7. A process for the production of at least liquid oxygen and/or liquid nitrogen in the cryogenic rectification of feed air, comprising an air separation unit and a main air compressor, and an auxiliary compressor the process comprising:

during a second period, during which electrical prices are at, or above a second predetermined threshold, at least a portion of the stored, liquefied process stream is introduced into the air separation unit at least a part of the time of this period,

wherein the auxiliary compressor has a pressure ratio of greater than 6 during the first period,

wherein the auxiliary compressor has a first molar flowrate (LF) and a first pressure ratio (LPR) during the first period,

wherein the auxiliary compressor has a second molar flowrate (HF) and a second pressure ratio (HPR) during the second period,

wherein CR=(LF/HF)/(LPR/HPR), and

wherein second molar flowrate (HF) is <90% of first molar flowrate (LF) and CR is between 0.9 and 1.05.

8. The process of claim 7, wherein second molar flowrate (HF) is <80% of first molar flowrate (LF) and CR is between 0.8 and 1.15.

9. The process of claim 7. wherein the first predetermined threshold is approximately equal to the second predetermined threshold.

10. The process of claim 7, wherein the process stream that is liquefied and stored in at least a portion of the first period and withdrawn and introduced into the air separation unit in the second period, is liquid air.

11. The process of claim 10, wherein the air separation unit produces a mass flowrate of liquid oxygen and a mass flowrate of liquid nitrogen, and

12. The process of claim 7. wherein the air separation unit further comprises one or more rotating devices selected from the group consisting of a booster air compressor, recycle compressor, refrigeration compressor and expanders, and

13. A process for the production of at least gaseous oxygen in the cryogenic rectification of feed air, comprising an air separation unit and a main air compressor; the process comprising:

during a first period; during which electrical power prices are below a first predetermined threshold, a process stream utilized by the air separation unit is liquefied and stored at least a part of the time of this period.

wherein C=(LF/HF)/(LP/HP), and

14. The process of claim 13, wherein second molar flowrate (HF) is <80% of first molar flowrate (LF) and C is between 0.8 and 1.15.

15. The process of claim 13, wherein the first predetermined threshold is approximately equal to the second predetermined threshold.

16. The process of claim 13, wherein the process stream that is liquefied and stored in at least a portion of the first period and withdrawn and introduced into the air separation unit in the second period, is liquid air.

17. The process of claim 16, wherein the air separation unit produces a mass flowrate of gaseous oxygen and/or a mass flowrate of gaseous nitrogen, and,

wherein the combined mass flowrate of the gaseous oxygen and/or the mass flowrate of gaseous nitrogen of the first period and the second period are approximately equal at least a portion of the time.

18. The process of claim 17, wherein the air separation unit further comprises one or more rotating devices selected from the group consisting of a booster air compressor, recycle compressor, refrigeration compressor and expanders, and