Patent Application
20230314069
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.
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:
In
In
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.
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a second period, during which electrical prices high, at least a portion of the stored, liquefied process stream is withdrawn and introduced into the ASU.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.
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;
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
Turning now to
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
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
Turning to
Turning to
Turning to
As indicated in
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
As indicated in
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
Turning to
As indicated in
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.
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
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.
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
The IGV and compressor speed adjustments utilized with the high-pressure air process as shown above in
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:
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
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
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:
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:
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
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
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 63326950 | Apr 2022 | US |
