METHOD FOR OBTAINING ONE OR MORE AIR PRODUCTS AND AIR SEPARATION SYSTEM

Abstract

A method for obtaining one or more air products, wherein an air separation system having a rectification column system is used, in which pressurized air is processed in an adjustable total air volume, wherein the total air volume is set to a first value during a first operating period and set to a second value that is different from the first value during a second operating period, and wherein the setting of the total air volume is changed from the first value to the second value in a third operating period from a first time to a second time. The second operating period is after the first operating period, the third operating period is between the first operating period and the second operating period. In the third operating period, a setting of a volume of a fluid, is changed from a third time up to a fourth time.

Claims

1. A method for obtaining one or more air products, wherein an air separation system having a rectification column system is used in which pressurized air is processed in an adjustable total air volume, wherein the total air volume is set to a first value during a first operating period and set to a second value that is different from the first value during a second operating period, wherein the setting of the total air volume is changed from the first value to the second value in a third operating period from a first time and to a second time, and wherein the second operating period is after the first operating period, and the third operating period is between the first operating period and the second operating period, characterized in that, in the third operating period, a setting of a volume of a fluid, which is formed via rectification using the pressurized air and transported into or out of the rectification column system, is changed from a third time and up to a fourth time, wherein the third time is before or after the first time and before the second time, and the fourth time is after the first time and the third time and before or after the second time, and a time period between the first time and the second time is set to not differ by more than 20% from a time period between the third time and the fourth time.

2. The method according to claim 1, wherein the rectification column system has a high-pressure column operated at a first pressure level and a low-pressure column operated at a second pressure level below the first operating pressure, wherein a gaseous, nitrogen-rich overhead product is formed in the low-pressure column.

3. The method according to claim 2, wherein the liquid, whose amount is changed in the third operating period, is a fraction of the gaseous, nitrogen-rich overhead product of the high-pressure column, which is liquefied and fed as a return flow to the low-pressure column.

4. The method according to claim 2, wherein the first pressure level is 5 to 12 bar absolute pressure, and the second pressure level is 1.3 to 3.5 bar absolute pressure.

5. The method according to claim 2, wherein a time period between the first time and the second time is set by changing the first time and/or the second time.

6. The method according to claim 5, wherein a time period between the first time and the third time is set by changing the third time as a function of the setting of the time period between the first time and the second time.

7. The method according to claim 6, wherein the third time is after the first time, and the fourth time is after the second time, wherein the time period between the first time and the third time is lengthened when the period between the first time and the second time is shortened.

8. The method according to claim 2, wherein one or more air products are formed in an adjustable product quantity, wherein the product quantity is set to a first value during the first operating period and to a second value which differs from the first value during the second operating period, and wherein the setting of the product quantity is changed from the first value to the second value during the third operating period from the first time and up to the second time point.

9. The method according to claim 8, wherein the one or more air products is or are at least partially formed from the gaseous, nitrogen-rich overhead product of the high-pressure column.

10. The method according to claim 1, wherein the first total air volume differs from the second total air volume by more than 5 percent and up to 30 percent.

11. The method according to claim 10, wherein the total air volume in the third operating period changes stepwise or continuously.

12. The method according to claim 11, wherein an average rate of change, during the stepwise change, or a rate of change, during the continuous change, of the total air volume in the third operating period is from 0.1 to 10 percent per minute.

13. The method according to claim 1, wherein the rectification column system has one or more rectification columns designed to obtain an argon-rich air product, and wherein the argon-rich air product is formed in the process.

14. An air separation system which is configured for obtaining one or more air products and has a rectification column system, wherein the air separation system is configured to process pressurized air in an adjustable total air volume in the rectification column system and to set the total air volume to a first value during a first operating time period and to a second value different from the first value during a second operating time period, and to change the setting of the total air volume from the first value to the second value in a third operating period from a first time and up to a second time, wherein the second operating period is after the first operating period, and the third operating period is between the first operating period and the second operating period, characterized in that the air separation system has a control unit that, in the third operating period, is programmed to change a setting of a volume of a fluid which is formed via rectification using the pressurized air and transported into or out of the rectification column system from a third time and up to a fourth time, wherein the third time is before or after the first time and before the second time, and the fourth time is after the first time and the third time and before or after the second time, and to set a time period between the first time and the second time such that it does not differ by more than 20% from a time period between the third time and the fourth time.

15. The air separation system according to claim 14, wherein the control unit is programmed to execute a method for obtaining one or more air products, wherein an air separation system having a rectification column system is used in which pressurized air is processed in an adjustable total air volume, wherein the total air volume is set to a first value during a first operating period and set to a second value that is different from the first value during a second operating period, wherein the setting of the total air volume is changed from the first value to the second value in a third operating period from a first time and to a second time, and wherein the second operating period is after the first operating period, and the third operating period is between the first operating period and the second operating period, characterized in that, in the third operating period, a setting of a volume of a fluid, which is formed via rectification using the pressurized air and transported into or out of the rectification column system, is changed from a third time and up to a fourth time, wherein the third time is before or after the first time and before the second time, and the fourth time is after the first time and the third time and before or after the second time, and a time period between the first time and the second time is set to not differ by more than 20% from a time period between the third time and the fourth time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 shows an air separation system which can be operated in the form of a simplified process flow diagram, according to one embodiment of the invention.

[0044] FIG. 2 shows changes in material flows and compositions thereof in a method that is not according to the invention, in the form of a graph.

[0045] FIG. 3 shows changes in material flows and their compositions in a method according to one embodiment of the invention, in the form of a graph.

[0046] FIG. 4 shows changes in material flows and their compositions in a method according to one embodiment of the invention, in the form of a graph.

DETAILED DESCRIPTION OF THE DRAWINGS

[0047] In FIG. 1, an air separation system that can be operated according to one embodiment of the invention is illustrated in the form of a process flow diagram, and is identified as a whole by 100. With regard to the components of the shown air separation system 100 which are not explained below, reference is made to the relevant professional literature—in particular, the aforementioned chapter by Häring. The air separation system 100 has a distillation column system 10 comprising a high-pressure column 11 and a low-pressure column 12.

[0048] In the air separation system 200, feed air (A) is suctioned and compressed by means of a main air compressor 1 via a filter 2. A correspondingly-formed compressed-air flow “a” is precooled and purified in a precooling device 3 operated with cooling water (B) and a purification device 4 in a basically known manner. Air of the precooled and purified pressurized air flow “a” is supplied to a main heat exchanger 5 in the form of two partial flows “b” and “c.”

[0049] The partial flow “b” is taken from the main heat exchanger 5 at an intermediate temperature level and is expanded (blown in) in the low-pressure column 12 by means of a blowing turbine 6 that can be coupled to an oil brake or a generator, which is not designated separately. In contrast, the partial flow “c” is taken from the main heat exchanger 5 at the cold side, guided through a secondary condenser 7, and fed into the high-pressure column 11 via a valve, which is not separately identified.

[0050] In the high-pressure column 11, an oxygen-enriched, liquid bottom product and a nitrogen-enriched or nitrogen-rich, gaseous overhead product forms. The bottom product of the high-pressure column 11 is guided through a cooling counter-flow heat exchanger 8 in the form of a material flow “d” and fed into the low-pressure column 12. The overhead product of the high-pressure column 11 is liquefied partly in the form of a material flow “e” in a main condenser 13, which interconnects the high-pressure column 11 and the low-pressure column 12 for exchanging heat, and is partially heated in the form of a material flow “f” in the main heat exchanger 5 and discharged from the system as a gaseous, compressed nitrogen product. The liquefied fraction is partly returned as reflux to the high-pressure column 11 in the form of a material flow “g” and, in particular, fed into a tank 20 in additional, adjustable fractions, on the one hand, in the form of a material flow “h,” and, on the other, is guided in the form of a material flow “i” through the counter-flow heat exchanger 8 and added to the low-pressure column 12.

[0051] In the low-pressure column 12, an oxygen-rich, liquid bottom product is formed and pressurized in a liquid state in the form of a material flow “k” in an internal compression pump 9. At least a part thereof can be supplied to the secondary condenser 7 in the form of a material flow “1” and heated there. If necessary, another fraction in the form of a material flow “m” can be fed back into the low-pressure column 12 by a valve that is not separately identified.

[0052] In the secondary condenser 7, the material flow “1” is, at least predominantly, evaporated. A correspondingly evaporated material flow “n” is heated in the main heat exchanger 5, converted from a liquid to a gaseous or supercritical state, and discharged from the air separation system 100 as a gaseous, compressed oxygen product (C). A fill-level in a liquid container of the secondary condenser 7 is regulated by the feed flow “1.” If necessary, liquid in the form of a material flow “o” can be released to the atmosphere (D). A liquid level in the liquid container of the secondary condenser 7, but also a liquid level in the low-pressure column 12, and thus in a liquid container of the main condenser 13, should, as mentioned, be kept constant for safety reasons. Thus, in the air separation system 100 illustrated here, basically, the sump of the high-pressure column 11 remains as a possible fluid reservoir for load changes.

[0053] In the air separation system illustrated here, overhead gas in the form of a material flow “p” is drawn off from the head of the low-pressure column 12 and guided partly in the form of a material flow “q” through the counter-flow heat exchanger 8 and the main heat exchanger 5, and heated thereby. The same applies to so-called impurities which are withdrawn from the low-pressure column 12 in the form of a material flow “r.” The last-mentioned material flows can be used in different ways in the air separation system 100, provided as a product, and/or released to the atmosphere (D).

[0054] The tank 20 can be used, in particular, to buffer a reflux to the low-pressure column 12. In other words—particularly if the nitrogen-rich liquid which can be provided in the form of the material flow “i” is not sufficient for operating the low-pressure column 12 in certain operating states—corresponding supplementation can occur with a material flow “s” from the tank 20, and, if the quantity of such nitrogen-rich liquid exceeds the demand for product or the demand in the air separation system 100, feeding into the tank 20 can be undertaken.

[0055] FIG. 2 shows changes in material flows and their compositions in a method not according to the invention in the form of a graph, wherein a time in minutes is plotted on the x-axis against a standardized range of values from 0 to 100% on the y-axis. The depiction in FIG. 1 corresponds to that of FIGS. 3 and 4, wherein, in the latter, corresponding changes in material flows and their compositions are illustrated in a method according to one embodiment of the invention.

[0056] As can be seen from FIG. 2, an air quantity 101 fed into a distillation column system of an air separation system, e.g., the air separation system 100 according to FIG. 1, and processed there is set, during a first operating period T1, to a first value and, during a second operating period T2, to a second value differing from the first value. The corresponding guide vane position of the main air compressor is designated 101′, and the default (ramp) for the guide vane position is designated 101″. The same also applies to the amount of a gaseous, nitrogen-rich overhead product of a high-pressure column of a corresponding system, which is liquefied and fed as a return flow to the low-pressure column In FIG. 1, such a material flow is designated “i.” Its quantity is set by a default (ramp) with respect to the position of a valve 111 which is arranged downstream of a subcooler 110 (see FIG. 1 in each case). This default is designated 102 in FIG. 2. There is no measurement. It goes without saying that the values used in each case differ from one another. Other material flows are also changed in a corresponding manner, but are not illustrated separately here.

[0057] As can be seen here, the change in the nitrogen-rich reflux quantity according to the default 102 is ramp-like here, from the same time at the end of the first operating time period T1 as the ramp-like change of the fed and processed air quantity 101. This disadvantageously results here in a temporarily greatly increased oxygen content 103 in an overhead product of the high-pressure column. This is accompanied by a temporary increase in the column temperature 104 of the high-pressure column and a reduction in the column temperature 105 of the low-pressure column. A quantity of an oxygen product withdrawn from the air separation system is designated 106.

[0058] During the operation, illustrated in FIG. 3, according to one embodiment of the present invention, a third operating time period T3 is therefore provided in this case. During this time period, as was the case, in principle, beforehand, the air quantity 101 fed into the distillation column system and processed there is changed from the first value to the second value from a first time X1 and up to a second time X2.

[0059] In addition, however, it is provided in this case that, in the third operating time period T3, a setting of an amount of a fluid which is formed by rectification using pressurized air and transported into or out of the rectification column system—in this case, namely, the gaseous, nitrogen-rich overhead product of the high-pressure column, which is liquefied and supplied according to the default 102 as a reflux to the low-pressure column—be changed to be slower than the fed and processed air quantity 101—specifically, in this case, starting at a third time X3 and up to a fourth time X4. In this case, the third time X3 is after the first time X1 and before the second time X2, and the fourth time X4 is after the first time X1 and the third time X3 and after the second time X2.

[0060] The depiction according to FIG. 4 corresponds to the depiction according to FIG. 3 over an extended period of time. As further illustrated here, “purge” oxygen 107 is periodically vented into the atmosphere (see flow “o” in FIG. 1) to prevent accumulation of unwanted components. This can, in principle, also be injected into the compressed oxygen product (C).

[0061] As can be seen from FIGS. 3 and 4, when the present invention is used in the depicted embodiments, there is, in particular, no deterioration in the purity of a nitrogen product (see in each case the oxygen content 103 in the overhead product of the high-pressure column).