阅读说明：本技术 用于提取一种或多种空气产物的方法和空气分离设备 (Method and air separation plant for extracting one or more air products ) 是由 D·施文克 D·戈卢别夫 于 2019-10-08 设计创作，主要内容包括：本发明提出一种用于提取一种或多种空气产物的方法,其中使用具有精馏柱系统(10)的空气分离设备(100),在所述空气分离设备中处理空气总量可调节的压缩空气,其中所述空气总量在第一运行时间段(T1)期间被设置为第一值并且在第二运行时间段(T2)期间被设置为与所述第一值不同的第二值,并且其中所述空气总量的所述设置在第三运行时间段(T3)内从所述第一时间点(X1)起并且直至所述第二时间点(X2)从所述第一值变为所述第二值。所述第二运行时间段(T2)在所述第一运行时间段(T1)之后,所述第三运行时间段(T3)在所述第一运行时间段(T1)与所述第二运行时间段(T2)之间。设置为,使得使用所述压缩空气通过精馏形成的且运输至所述精馏柱系统(10)内或从所述精馏柱系统运出的液体的量的设置在所述第三运行时间段(T3)内从第三时间点(X3)起并且直至第四时间点(X4)发生变化,其中所述第三时间点(X3)在所述第一时间点(X1)之前或之后并且在所述第二时间点(X2)之前并且所述第四时间点(X4)在所述第一时间点(X1)和所述第三时间点(X3)之后并且在所述第二时间点(X2)之前或之后。所述第一时间点(X1)与所述第二时间点(X2)之间的时间段设置得跟所述第三时间点(X3)与所述第四时间点(X4)之间的时间段基本上相同。本发明还涉及一种对应的空气分离设备(100)。(The invention relates to a method for extracting one or more air products, wherein compressed air is treated in an air separation plant (100) having a rectification column system (10), the total amount of air being adjustable, wherein the total amount of air is set to a first value during a first operating period (T1) and to a second value, different from the first value, during a second operating period (T2), and wherein the setting of the total amount of air is changed from the first value to the second value from the first time point (X1) and up to the second time point (X2) within a third operating period (T3). The second operating period (T2) is subsequent to the first operating period (T1), the third operating period (T3) is between the first operating period (T1) and the second operating period (T2). Is configured such that the setting of the amount of liquid formed by rectification using the compressed air and transported into or out of the rectification column system (10) changes within the third operating period (T3) from a third point in time (X3) and up to a fourth point in time (X4), wherein the third point in time (X3) precedes or follows the first point in time (X1) and precedes the second point in time (X2) and the fourth point in time (X4) succeeds the first point in time (X1) and the third point in time (X3) and precedes or follows the second point in time (X2). A time period between the first time point (X1) and the second time point (X2) is set to be substantially the same as a time period between the third time point (X3) and the fourth time point (X4). The invention also relates to a corresponding air separation plant (100).)

1. A method for extracting one or more air products, wherein compressed air with an adjustable total air quantity is treated in an air separation plant (100) having a distillation column system (10), wherein the total air quantity is set to a first value during a first operating period (T1) and to a second value different from the first value during a second operating period (T2), wherein the setting of the total air quantity changes from the first value to the second value within a third operating period (T3) from a first point in time (X1) and up to a second point in time (X2), and wherein the second operating period (T2) follows the first operating period (T1) and the third operating period (T3) is between the first operating period (T1) and the second operating period (T2), characterized in that the setting of the amount of liquid formed by rectification using the compressed air and transported to or from the rectification column system (10) is made to vary within the third operating period (T3) from a third point in time (X3) and up to a fourth point in time (X4), wherein the third point in time (X3) is before or after the first point in time (X1) and before the second point in time (X2) and the fourth point in time (X4) is after the first point in time (X1) and third point in time (X3) and before or after the second point in time (X2), and a time period is thus set between the first time point (X1) and the second time point (X2), such that the difference between the time period and the time period between the third time point (X3) and the fourth time point (X4) is not more than 20%.

2. The process according to claim 1, wherein the rectification column system (10) has a high pressure column (11) operated at a first pressure level and a low pressure column (12) operated at a second pressure level lower than the first operating pressure, wherein a gaseous nitrogen-rich column overhead is formed in the low pressure column (11).

3. Method according to claim 2, wherein the amount of liquid, which varies within the third operating period (T3), is part of the gaseous nitrogen-rich column overhead of the high-pressure column (11), which is liquefied and given off as reflux to the low-pressure column (12).

4. The method of claim 2 or 3, wherein the first pressure level is 5 to 12bar absolute and the second pressure level is 1.3 to 3.5bar absolute.

5. The method according to one of claims 2, 3 or 4, wherein the time period between the first point in time (X1) and the second point in time (X2) is set by altering the first point in time (X1) and/or the second point in time (X2).

6. The method of claim 5, wherein the time period between the first point in time (X1) and the third point in time (X3) is set by altering the third point in time (X3) according to the setting of the time period between the first point in time (X1) and the second point in time (X2).

7. The method of claim 6, wherein the third point in time (X3) is after the first point in time (X1) and the fourth point in time (X4) is after the second point in time (X2), wherein the period of time between the first point in time (X1) and the third point in time (X3) is extended when the period of time between the first point in time (X1) and the second point in time (X2) is shortened.

8. Method according to one of claims 2 to 7, wherein one or more air products are formed, the product quantity of which is adjustable, wherein the product quantity is set to a first value during the first operating period (T1) and to a second value, which is different from the first value, during the second operating period (T2), and wherein the setting of the product quantity changes from the first value to the second value from the first point in time (X1) and until the second point in time (X2) within the third operating period (T3).

9. The method of claim 8, wherein the one or more air products are formed at least in part from the gaseous nitrogen-rich column overhead of the high pressure column (11).

10. The method according to one of the preceding claims, wherein the difference between the first total amount of air and the second total amount of air is between 5 percentage points and 30 percentage points.

11. The method according to claim 10, wherein the total amount of air is varied stepwise or continuously within the third operating period (T3).

12. The method according to claim 11, wherein the average rate of change of the total amount of air when changing stepwise or continuously over the third running time (T3) is 0.1 to 10 percentage points per minute.

13. The method according to one of the preceding claims, wherein the rectification column system (10) has one or more rectification columns adapted for extracting an argon-rich air product and wherein the argon-rich air product is formed during the method.

14. An air separation plant (100) adapted for extracting one or more air products and having a rectification column system (10), wherein the air separation plant (100) is adapted for treating compressed air in the rectification column system (100) with an adjustable total amount of air, and where the total amount of air is set to a first value during a first operating period (T1) and to a second value different from the first value during a second operating period (T2), and the setting of the total amount of air changes from the first value to the second value from a first point in time (X1) and until a second point in time (X2) within a third operating period (T3), wherein the second operating period (T2) follows the first operating period (T1) and the third operating period (T3) is between the first operating period (T1) and the second operating period (T2), characterized in that the air separation plant (100) has a control unit (50) which is program-technically adapted such that the setting of the amount of liquid formed by rectification and transported into or out of the rectification column system (10) using the compressed air changes within the third operating time period (T3) from a third point in time (X3) and up to a fourth point in time (X4), wherein the third point in time (X3) is before or after the first point in time (X1) and before the second point in time (X2) and the fourth point in time (X4) is after the first point in time (X1) and the third point in time (X3) and before or after the second point in time (X2), and a time period is thus set between the first point in time (X1) and the second point in time (X2), such that the difference between the time period and the time period between the third time point (X3) and the fourth time point (X4) is not more than 20%.

15. Air separation plant (100) according to claim 14, wherein the control unit (50) is programmatically adapted to perform a method according to one of claims 1 to 13.

Background

The production of liquid or gaseous air products by cryogenic separation of air in air separation plants is known and is for example published by Wiley-VCH, inc 2006, by h.The editorial published "Industrial Gases Processing" book is described in particular in section 2.2.5 "CryogenicRection".

The air separation plant has rectification column systems which can be designed, for example, as double column systems, in particular as typical linde double column systems, but also as three-column or multi-column systems. In addition to the rectification column for extracting liquid and/or gaseous nitrogen and/or oxygen, i.e. for nitrogen-oxygen separation, a rectification column for extracting other air components, in particular krypton, xenon and/or argon, can also be provided. Even though the rectification columns for extracting other air components are not discussed in detail below, an air separation plant with corresponding rectification columns can at any time be the subject of the present invention.

The rectification columns of the rectification column system are operated at different pressure levels. A two-column system has a so-called high-pressure column (also called pressure column, medium-pressure column or lower column) and a so-called low-pressure column (also called upper column). The pressure level of the high-pressure column is, for example, 4.7 to 6.7bar, preferably about 5.5 bar. The low-pressure column is operated, for example, at a pressure level of 1.3 to 1.8bar, preferably about 1.4 bar. The pressure levels described here and below are in each case the absolute pressure at the top of the respectively given column. The values given are merely examples and may be changed as necessary.

US 4251248A discloses a method and an apparatus for automatically modifying the operational flow in an air separation plant to increase or decrease the amount of product. In each case, an expected change value, including an expected change value of the intake air, is calculated from the value corresponding to the increased or decreased product amount.

In US 5901580 a, the purity of the air product is held substantially constant at the demand for one of the products or at the intake air flow or intake pressure fluctuations by: introducing excess nitrogen-rich liquid into the rectification column system when the demand for products or the intake air amount is increased; when the demand for product or the intake air amount is reduced, the excess nitrogen-rich liquid is extracted from the distillation unit and stored.

The subject of US 6006546 a is a cryogenic air separation plant that can be subjected to periods of severe changes in product demand. The apparatus is specifically controlled during these periods to minimize the effect of transient operation on product purity.

According to US 5224336 a, rapid changes in oxygen demand and inlet gas pressure are compensated for by the net transfer of cold in the form of liquid nitrogen into and out of the distillation system. This cold transfer is performed using a liquid nitrogen storage vessel connected to the reflux path of the distillation system.

In the process for producing gaseous products under pressure by cryogenic separation of air presented in US 6185960B 1, the process sometimes takes place in gas operation and sometimes in combined operation using an internal compression device and a corresponding refrigeration device.

Regardless of the particular embodiment of the air separation plant, it is often desirable to be able to operate flexibly, i.e., a corresponding air separation plant should be able to provide significantly greater or lesser amounts of certain air products at correspondingly higher or lower air intakes over a period of time. In this context, it is also generally desirable to switch rapidly between these operating states, which differ in their respective throughputs. The corresponding handover procedure is also referred to as "load change" in the following. It is thus believed that rapid load changes will result in an overall improvement in the efficiency of the air separation plant. Furthermore, in the case of rapid load changes, backup storages of lower capacity are required, since less or no liquid is drawn from such backup storages in order to support the load changes. It is thus possible to consider that the manufacturing cost of the corresponding air separation plant is reduced.

The aim of the invention is to design the extraction of the air product using the air separation plant more flexibly and to enable overall faster load changes.

Disclosure of Invention

This object is achieved by a method for extracting one or more air products and a corresponding air separation plant having the respective features of the independent claims. Preferred embodiments are subject matter of the respective independent claims and the following description.

Some terms used in describing the present invention and its advantages and the basic technical background will be further explained below.

For Air separation, a so-called Main Compressor/secondary Compressor (MAC-BAC) process or a so-called High Air Pressure (HAP) process may be used. The primary/secondary compressor process is a more traditional process and in recent years, the high pressure process has been increasingly used as an alternative. The invention is applicable to both of these applications.

The main compressor/secondary compressor process is characterized in that only a part of the inlet air quantity supplied as a whole to the rectification column system is compressed to a pressure level at least 3, 4, 5, 6, 7, 8, 9 or 10bar higher than the pressure level of the high-pressure column. Another part of the intake air amount is then compressed only to the pressure level of the high-pressure column, or a pressure level which differs from the pressure level of the high-pressure column by no more than 1 to 2bar, and is fed into the high-pressure column at this lower pressure level. One example of a primary compressor/secondary compressor process isShown in figure 2.3A of the book (see above).

In contrast, in a high pressure process, the entire amount of inlet air supplied to the rectification column system as a whole is compressed to a pressure level at least 3, 4, 5, 6, 7, 8, 9 or 10bar higher than the pressure level of the high pressure column. The pressure difference may be, for example, up to 14, 16, 18 or 20 bar. High-pressure processes are known, for example, from EP 2980514 a1 and EP 2963367 a 1.

The invention can be used in air separation plants with so-called Internal Compression (IC) but also with external Compression. For the internal compression means, at least one product provided by means of the air separation plant is formed by: the ultra-low temperature liquid is withdrawn from the rectification column system, undergoes a pressure rise in the liquid state, and is converted into a gaseous or supercritical state by heating depending on the existing pressure. The internally compressed gaseous oxygen (GOX IC), the internally compressed gaseous nitrogen (GAN IC) or the internally compressed gaseous argon (GAR IC) can be generated, for example, by means of an internal compression device. Internal compression brings a series of technical advantages compared with external compression, which is likewise possible in principle, of the corresponding product and has been explained in the specialist literature, for exampleSection 2.2.5.2 of the book (see above).

In the language used herein, fluids and gases may be enriched or depleted in one or more components, where "enriched" may mean a content of at least 90%, 95%, 99%, 99.5%, 99.9%, or 99.99% on a molar, weight, or volume basis, and "depleted" may mean a content of up to 10%, 5%, 1%, 0.1%, or 0.01%.

In the language used herein, liquids and gases may be enriched or depleted in one or more components, where these concepts refer to the content in the initial liquid or initial gas from which the liquid or gas in question is extracted. A liquid or gas is "enriched" if it contains at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times, 100 times or 1,000 times the content of the corresponding component relative to the initial liquid or initial gas, and "depleted" if it contains at most 0.9 times, 0.5 times, 0.1 times, 0.01 times or 0.001 times the content of the corresponding component. If, for example, "oxygen" is mentioned here, this is also to be understood as a liquid or gas which is rich in oxygen, but not necessarily consists entirely of oxygen.

The present application uses the two concepts "pressure level" and "temperature level" to characterize pressure and temperature, thereby indicating that the concept of the present invention need not be implemented in a corresponding device using pressure and temperature in the form of precise pressure or temperature values. However, such pressures and temperatures typically move within a range, for example, of the mean ± 1%, 5%, 10%, or 20%. The respective pressure and temperature levels can be in non-intersecting ranges or in overlapping ranges. In particular, for example, the pressure level includes an unavoidable or expected pressure loss. The corresponding applies to the temperature level. The pressure level in bar here is absolute pressure.

THE ADVANTAGES OF THE PRESENT INVENTION

Depending on the "direction" of the aforementioned load change (from high to low production or vice versa), in conventional air separation plants, excess or deficiency of cryogenic liquid is produced in the rectification section, i.e. the rectification column system, on the basis of the respective subsequently set load state. The reason for this is the amount of cryogenic liquid stored on the separation plate or in the liquid distributors and packings of the rectification column, in particular of the high-pressure column and of the low-pressure column, respectively. This liquid amount depends on the load: the lower the load, the less liquid is distributed over the separation plate. Thereby releasing excess liquid when the load is reduced. This excess liquid should be stored in the device so that it can be reused to compensate for the deficiency that exists at that time when the load rises.

In conventional air separation plants that do not produce argon, only the bottom of the high pressure column serves as a liquid reservoir. For safety reasons, the further liquid containers present in the respective air separation plants, for example the main condenser or the so-called auxiliary condenser for connecting the high-pressure column and the low-pressure column in a heat-exchanging manner, should generally be operated with a constant liquid level, and therefore should not be considered as storage containers for load variations. This is further explained below with reference to fig. 1, which shows a corresponding air separation plant. It will be appreciated that for rapid load changes an equally "fast" regulator is required, which leads to only small deviations between the set value and the actual value.

Rapid load changes can result in changes in product composition. For example, if the air separation plant shown in fig. 1 is operated at an increased load change rate (from 75% load to 100% load at a rate of 4% per minute) while the other operating conditions are unchanged, an increase in the oxygen content in the gaseous overhead product of the high-pressure column can additionally be observed, as is also shown in fig. 2 (see trace 103 in the figure). This rise is considered negative because the purity of at least two air products, namely the liquid pressurized nitrogen product (LIN) formed by liquefaction from the overhead product of the high-pressure column and the portion of the overhead product which is output in a non-liquefied state from the air separation plant in the form of the gaseous pressurized nitrogen Product (PGAN), is thereby affected.

In order to avoid a corresponding reduction in the product purity, one obvious solution is to operate the plant with a product purity that includes a certain buffer margin for such operating conditions, so that the required purity is always maintained. However, this has the disadvantage that for most operating states a higher product purity than is actually required has to be provided. This may therefore lead to higher investment costs (more separation stages in the high-pressure column) or higher operating costs (due to excessive feed gas).

It is known in the context of the present invention that the stated problems can be solved by: the set point adjustment of the regulators in the air separation plant affecting the amount of streams being led into or out of the rectification column system is delayed or advanced in accordance with the change in the amount of air being processed in the air separation plant or its rectification column system. In particular, as described with emphasis below, this can be done in the form of a delay in adjusting the set point, and in particular in relation to the amount of nitrogen-rich liquid formed from the overhead product of the high pressure column. However, the present invention is not limited to this particular case. More precisely, the basic idea of the invention is that, in a corresponding application scenario, an early or late adjustment of the corresponding fluid flow or its quantity can be particularly advantageous.

Against this background, the invention proposes a process for extracting one or more air products, in which an air separation plant with a rectification column system is used in which compressed air is treated in an amount which is adjustable. The term "total air quantity" as used herein is to be understood throughout as the total air quantity which is processed in the respective device at the respective point in time, i.e. the total air quantity which has undergone the rectification process. In this case, no air other than the total amount of air is processed in each case in the air separation plant or its rectification column system.

In the context of the present invention, the total amount of air is set to a first value during a first operating period and to a second value different from the first value during a second operating period. Thus, different total amounts of air are present in the two operating periods, wherein the first total amount of air can be greater or smaller than the second total amount of air. The respective air separation plants are thus operated in different load states in the first and second operating periods, wherein in particular a full-load operation can be present or carried out in one of the two operating periods. In other words, the invention relates to the case of a load increase and a load decrease.

In the context of the present invention, as is basically known, in the third operating period, starting from the first point in time and up to the second point in time, the setting of the total air quantity is changed from the first value to the second value, i.e. a load change is carried out. It is to be understood here that the second operating period follows the first operating period and the third operating period is between the first and second operating periods. As mentioned before, this may lead to said negative effects if no further measures are taken. The load change can be a load increase or a load decrease, depending on whether the first total amount of air is lower or higher than the second total amount of air. The first, second and third operating time periods are operating time periods which do not overlap one another in time and the third operating time period is always between the first and second operating time periods or between the second and first operating time periods in time. This does not exclude the presence of other periods of operation.

According to the invention, the setting of the amount of liquid formed by rectification using compressed air and transported into or out of the rectification column system is varied within a third operating period from a third point in time and up to a fourth point in time, wherein the third point in time is before or after the first point in time and before the second point in time and the fourth point in time is after the first point in time and after the third point in time and before or after the second point in time. The first, second, third and fourth time points are each within a third operating time period, wherein, for example, the third time point may precede the first time point or the fourth time point may follow the second time point, i.e. the third operating time period does not necessarily have to start at the first time point and end at the second time point. The third operating time period may be between the earliest and latest of these points in time, but may also extend over a longer time period. According to the invention, the time period between the first time point and the second time point is set such that it differs from the time period between the third time point and the fourth time point by no more than 20%, 10%, 5% or 1%. The time periods mentioned can be set to be the same or substantially the same. The setting can be carried out in particular by using corresponding set values or predetermined values in the regulating device or the control device.

Thus, in the context of the present invention, it is suggested that the change in the amount of fluid formed by rectification using compressed air and transported into or out of the rectification column system is not synchronized in time with the change in the total amount of air. Such a change takes place in particular by a corresponding setpoint specification of a control system or a regulating system of the air separation plant and takes place by means of suitable control elements, in particular valves, slide valves, etc. In particular, corresponding control or regulation can be carried out as a function of the actual values detected, and all measures known in the art of control or regulation can be included here, provided they are suitable and effective for the present invention.

In particular, the change in the amount of fluid formed by rectification using compressed air and transported into or out of the rectification column system can take place using a corresponding setpoint booking. In some cases, for example in the air separation plants shown in fig. 1 to 4, it may furthermore be provided that the respective regulator output is additionally (usually within a range of not more than ± 5%) additionally controlled by a fine-tuning control. This can in the extreme case result in the actual value at the end of the adjustment being slightly different from the respectively predetermined set value (but maximally 5%).

In particular, the invention can be used in an air separation plant whose rectification column system has a high-pressure column which is operated at a first pressure level and a low-pressure column which is operated at a second pressure level which is lower than the first pressure level, wherein the amount of liquid which changes over a third operating period, as previously described, is part of the gaseous nitrogen-rich column overhead of the high-pressure column, which is liquefied and given back to the low-pressure column as reflux. In particular, the present invention may be used in an air separation plant having an auxiliary condenser for heating an internally compressed oxygen product. Internal or external compression of the air product can be carried out in the corresponding air separation plant and process technology wiring with nitrogen and air circuits can be used. Air separation plants having multiple high pressure columns may also be used.

Irrespective of the number of high-pressure columns and low-pressure columns, in the context of the present invention the first pressure level may in particular be 5 or 7 to 12bar absolute and the second pressure level may in particular be 1.3 or 1.8 to 3.5bar absolute. The invention is thus particularly useful in so-called "pressure-boosting" air separation plants in which the operating pressure of the rectification column system is above the conventional values as described hereinbefore. Nevertheless, the present invention can also be used in conjunction with conventional pressure levels in distillation column systems.

In the context of the present invention, flexible load change speeds can be achieved in particular. In other words, the time period between the first point in time and the second point in time may be set by altering the first point in time and/or the second point in time. In this context, this proves to be particularly advantageous when, for example, the delay time set in the context of the invention is adapted to the change, i.e. when the time period between the first point in time and the third point in time is set by modifying the third point in time in accordance with the time period setting between the first point in time and the second point in time. In this way, the advantages according to the invention are achieved even when the load change speed changes. In this case, it can be provided in particular that the third time point is after the first time point and the fourth time point is after the second time point, wherein the time period between the first time point and the third time point is extended when the time period between the first time point and the second time point is shortened. In other words, a longer delay time may be selected, for example, when the load change speed increases.

In particular, in the context of the present invention, a load change can also comprise a change in the amount of air product formed in each case. One or more air products with adjustable product quantities can thus be formed, wherein the product quantity is set 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 wherein the setting of the product quantity changes from the first value to the second value within a third operating time period starting from the first time point and up to the second time point. In particular, the corresponding air product may be an air product which is at least partially formed from a gaseous nitrogen-rich column overhead of the high-pressure column. The product may be provided in liquefied or unliquefied form.

The present invention may be used in conjunction with different load variation ranges. In this case, for example, the difference between the first total air quantity and the second total air quantity can be set to 5 percentage points to 30, 40 or 50 percentage points. In particular, the change in the total amount of air can take place here in steps or continuously over a third operating period, and preferably at an average rate of change (reference step change) or rate of change (in the case of continuous change) of the total amount of air of 0.1 (in the case of argon extraction) or 1 to 10 percentage points per minute.

In general, it is possible in the context of the present invention to provide for extraction of argon, i.e. in which the rectification column system may in particular have one or more rectification columns adapted for extraction of an argon-rich air product and in which an argon-rich air product may be formed. Herein, an "argon-rich" air product has at least 50, 60, 70, 80, or 90 mole percent argon.

The invention also relates to an air separation plant which is adapted to extract one or more air products and has a rectification column system, wherein the air separation plant is adapted to process compressed air in which the total amount of air is adjustable and in which the total amount of air is set to a first value during a first operating period and to a second value different from the first value during a second operating period, and to change the total amount of air from the first value to the second value within the set third operating period from a first point in time and up to a second point in time. As previously described, the second operating period is subsequent to the first operating period, and the third operating period is between the first and second operating periods.

According to the invention, the air separation plant is equipped with a control unit which is program-technically adapted such that the setting of the amount of liquid formed by rectification using compressed air and transported into or out of the rectification column system changes within a third operating period from a third point in time and up to a fourth point in time, wherein the third point in time is before or after the first point in time and before the second point in time and the fourth point in time is after the first and third points in time and before or after the second point in time. Furthermore, the air separation plant is adapted to set the time period between the first point in time and the second point in time such that the difference between the time period and the time period between the third point in time and the fourth point in time does not exceed 20% or the other of the aforementioned difference values.

In particular, the control unit is programmably adapted to carry out a method as described above in the various embodiments.

With regard to the corresponding air separation plant and further advantages of embodiments according to the invention, reference is explicitly made to the above explanations regarding the method according to the invention and its different advantageous embodiments. An air separation plant provided according to the invention is particularly adapted to carry out a corresponding method and has tools which are each specially constructed for this purpose.

The invention is further explained below with reference to the accompanying drawings, which primarily show air separation plants operable in accordance with embodiments of the invention.

Drawings

FIG. 1 illustrates, in simplified process flow diagram form, an air separation plant that may be operated in accordance with an embodiment of the present invention.

Fig. 2 shows, in diagrammatic form, the variation of the substance flow and its composition in a method not according to the invention.

Fig. 3 shows, in diagrammatic form, the variation of the substance flow and its composition in a method according to an embodiment of the invention.

Fig. 4 shows, in diagrammatic form, the variation of the substance flow and its composition in a method according to an embodiment of the invention.

Detailed Description

An air separation plant, which may be operated in accordance with an embodiment of the present invention, is illustrated in simplified process flow diagram form in FIG. 1 and designated in its entirety by 100. The components of the illustrated air separation plant 100 not illustrated below are referred to in the relevant artDocuments, especially as mentioned hereinbeforeThe book of (1). Air separation plant 100 has a distillation column system 10 that includes a high pressure column 11 and a low pressure column 12.

The intake air (a) is sucked and compressed in the air separation plant 200 by means of the main air compressor 1 via the filter 2. The correspondingly formed compressed air flow a is subjected to pre-cooling and cleaning in a well-known manner in a pre-cooling device 3 and a cleaning device 4, which are propelled by cooling water (B). The air of the precooled and cleaned compressed air stream a is conveyed from the hot side to the main heat exchanger 5 in the form of two partial streams b and c.

The partial stream b is drawn off from the main heat exchanger 5 at an intermediate temperature level and is relieved of pressure (blown into) the low-pressure column 12 by means of the injection turbine 6, which can be coupled to an oil brake or generator, which is not separately indicated. In contrast, the partial stream c is drawn off from the main heat exchanger 5 on the cold side, is conducted through the auxiliary condenser 7 and is fed via a valve, not separately indicated, into the high-pressure column 11.

An oxygen-rich liquid bottoms and a nitrogen-rich gaseous overhead are formed in the high pressure column 11. The bottom product of the high-pressure column 11 is conducted in the form of a stream d through the ultra-low-temperature counter-current heat exchanger 8 and into the low-pressure column 12. The overhead product of the high-pressure column 11 is partly liquefied in the form of a stream e in a main condenser 13 which connects the high-pressure column 11 and the low-pressure column 12 in a heat-exchanging manner and partly heated in the main heat exchanger 5 in the form of a stream f and is discharged from the plant as gaseous pressurized nitrogen product. A part of the liquefied fraction is returned as reflux to the high-pressure column 11 in the form of stream g and is fed, in particular in a further adjustable proportion, on the one hand in the form of stream h to the tank 20 and, on the other hand, in the form of stream i through the ultralow-temperature countercurrent heat exchanger 8 and is passed to the low-pressure column 12.

An oxygen-rich liquid bottom product is formed in the low-pressure column 12 and is pressurized in the liquid state in the internal compression pump 9 in the form of a stream k. At least a part of which can be conveyed in the form of a stream 1 to the auxiliary condenser 7 and heated there. If necessary, a further portion can be fed back into the low-pressure column 12 in the form of a stream m via a valve which is not separately indicated.

In the auxiliary condenser 7, the substance stream 1 is at least largely evaporated. The corresponding evaporated stream n is heated in the main heat exchanger 5, where it is converted from the liquid state into the gaseous or supercritical state and is output from the air separation plant 100 as a gaseous pressurized oxygen product (C). The liquid level in the liquid container of the auxiliary condenser 7 is regulated by the intake air flow 1. If necessary, the liquid can be discharged to the atmosphere (D) in the form of a stream o. As mentioned before, the liquid level in the liquid container of the auxiliary condenser 7, but also in the low pressure column 12 and thus in the liquid container of the main condenser 13, should be kept constant for safety reasons. Thus, in the air separation plant 100 shown here, the bottom of the high-pressure column 11 remains essentially as a possible liquid reservoir for load changes.

In the air separation plant shown here, the overhead gas is withdrawn from the top of the low-pressure column 12 in the form of a stream p and a portion is conducted in the form of a stream q through the ultra-low-temperature counter-current heat exchanger 8 and the main heat exchanger 5 and is heated in this way. The corresponding applies to what is called impure nitrogen which is withdrawn from the low-pressure column 12 in the form of a substance flow r. These last-mentioned streams may be used in various ways in the air separation plant 100, provided as products, and/or vented to the atmosphere (D).

Tank 20 is particularly useful for buffering the reflux to low pressure column 12. In other words, in particular when the nitrogen-rich liquid which can be provided in the form of stream i under certain operating conditions is not sufficient to support the operation of the low-pressure column 12, a corresponding replenishment can be carried out with the aid of stream s from the tank 20 and can be fed into the tank 20 if the amount of this nitrogen-rich liquid exceeds the product demand or the demand in the air separation plant 100.

Fig. 2 shows, in a diagram form, the variation of the substance flow and its composition in a method not according to the invention, wherein time in minutes is plotted on the abscissa and a standard value range of 0 to 100% is plotted on the ordinate. The display of fig. 1 corresponds here to the display of fig. 3 and 4, wherein the latter each shows a corresponding change in the flow of substances and their composition in a method according to an embodiment of the invention.

As can be seen from fig. 2, the amount of air 101 which is fed into the air separation plant, for example the distillation column system of the air separation plant 100 according to fig. 1, and is treated there during a first operating period T1 is set to a first value and to a second value which is different from the first value during a second operating period T2. The corresponding turbine blade position of the main air compressor is indicated by 101' and the predetermined (slope) of the turbine blade position is indicated by 101 ". The corresponding applies also to the amount of gaseous nitrogen-rich column overhead of the high-pressure column of the corresponding plant, which is liquefied and given as reflux to the low-pressure column. In fig. 1, such a material flow is denoted by i. The amount of this substance flow is set via a predetermined (ramp) on the basis of the position of a valve 111, which is arranged downstream of the subcooler 110 (see fig. 1 each). This reservation is indicated at 102 in fig. 2. No measurement is performed. It is to be understood that the values used in each case differ from one another. The other material flows are also modified in a corresponding manner, but are not shown separately here.

From this it can be seen that, as well as the ramped variation of the amount 101 of air fed and treated, the nitrogen-rich reflux flow takes place in a ramped manner according to the variation of the predetermined 102 from the same point in time until the end of the first operating period T1. This disadvantageously results in a temporarily large increase in the oxygen content 103 in the column head 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 decrease in the column temperature 105 of the low-pressure column. The amount of oxygen product withdrawn from the air separation plant is indicated at 106.

Therefore, during operation according to the embodiment of the present invention shown in fig. 3, there is provided a third operating period T3. In this operating period, as is the case in principle above, the amount of air 101 which is fed into the distillation column system and is treated there changes from the first value to the second value from the first point in time X1 and up to the second point in time X2.

However, it is also provided here that the setting of the amount of fluid which is formed by rectification using compressed air and is transported into or out of the rectification column system, i.e. the setting of the amount of gaseous nitrogen-rich column overhead which is liquefied in the high-pressure column and is passed as reflux to the low-pressure column according to the predetermined value 102, is used, which changes in a delayed manner in relation to the amount of air 101 which is fed into and subjected to the treatment in the third operating period T3, and in this way from the third point in time X3 and up to the fourth point in time X4. The third time point X3 is here after the first time point X1 and before the second time point X2, and the fourth time point X4 is after the first time point X1 and the third time point X3 and after the second time point X2.

The display content according to fig. 4 corresponds to the display content according to fig. 3 over an extended period of time. As also shown herein, "purge" oxygen 107 is periodically vented to atmosphere (see stream o in FIG. 1) to prevent the enrichment of undesirable constituents. This oxygen can in principle also be injected into the pressurized oxygen product (C).

As can be seen from fig. 3 and 4, in particular no reduction in the purity of the nitrogen product occurs in the respective illustrated embodiment when using the present invention (see respective oxygen content 103 in the high-pressure column top product).