RU2722074C2 - Method of producing liquid and gaseous oxygen-enriched air separation product in an air separation plant and an air separation plant - Google Patents

Abstract

FIELD: water and air purification technology.SUBSTANCE: invention relates to an air separation plant. Air separation unit (100) includes high pressure column (61), low pressure column (62) and mixing column (7). First flow (h) of compressed air, which is cooled to the first temperature level and expanded in first turbine (4), is supplied to mixing column (7). High pressure column (62) is supplied with the second flow (g) of compressed cooled to the first level temperature and expanded in the first air turbine (4). At the same time, a third compressed air flow (f) is supplied to the low pressure column (62), which is then cooled to a second temperature level, expanded in second turbine (5) and further cooled in main heat exchanger (3). Air expelled in the first and second turbines (4, 5) is supplied to first turbine (4) at the first and second turbine (5) at the second temperature level. Liquid oxygen-enriched air separation product is discharged from unit (100).EFFECT: technical result is providing process flexibility at variable demand for liquid and gaseous oxygen-enriched air separation products.15 cl, 1 dwg

Description

The invention relates to a method for producing a liquid and gaseous, oxygen-enriched air separation product in an air separation unit, and to an air separation unit for performing a similar method.

State of the art

The preparation of air separation products in a liquid or gaseous state by low-temperature air separation in air separation plants is known and described, for example, in the publication “Industrial Gases Processing”, edited by H.-W. Häring, Wiley-VCH, 2006, especially section 2.2.5, “Cryogenic Rectification”.

Some industrial applications require at least not exclusively pure oxygen. This opens up the possibility of optimizing air separation plants in relation to the costs of their manufacture and operation, in particular, their energy consumption. For details, reference should be made to specialized literature, for example, F.G. Kerry, Industrial Gas Handbook: Gas Separation and Purification, (CRC Press, 2006, chapter 3.8, "Development of Low Oxygen-Purity Processes" purity ").

To obtain gaseous compressed oxygen of reduced purity, inter alia, air separation units with so-called mixing columns can be used, which have been known for a long time and are described in a number of publications, for example, DE 2 204 376 A1 (according to US Pat. No. 4,022,030 A ), US 5 454 227 A, US 5 490 391 A, DE 198 03 437 A1, DE 199 51 521 A1, EP 1 139 046 B1 (US 2001/052244 A1), EP 1 284 404 A1 (US 6 662 595 B2 ), DE 102 09 421 A1, DE 102 17 093 A1, EP 1 376 037 B1 (US 6 776 004 B2), EP 1 387 136 A1 and EP 1 666 824 A1. An air separation unit with a mixing column is also presented in patent document FR 2 895 068 A1.

An oxygen-enriched liquid is supplied to the mixing column near the top, and gaseous compressed air, the so-called mixing column air, is supplied near the bottom part, and passed countercurrently to each other. As a result of intense contact, a certain part of the more volatile nitrogen from the air of the mixing column passes into the oxygen-enriched liquid. At the same time, the oxygen-enriched liquid evaporates in the mixing column, and can be removed from the top of the mixing column in the form of so-called "crude" oxygen. Crude oxygen can be taken from the air separation unit as a gaseous product. For its part, the air of the mixing column is liquefied as it moves through the mixing column, is enriched with oxygen to a certain extent, and can be removed from the bottom of the mixing column. This liquefied stream may then be routed to the distillation column system used in a place suitable for separation by energy and / or process conditions. Thanks to the use of the mixing column, the energy necessary for the separation of substances can be significantly reduced due to the purity of the gaseous oxygen product.

A disadvantage of known air separation plants, including those that operate with mixing columns, is limited operational flexibility. The need for cold in such installations is usually satisfied by the expansion of air in the so-called turbocharger. Such a turbocharger expands the air from a pressure level, for example, from 5.0 to 6.0 bar to a pressure level, for example, from 1.2 to 1.6 bar (in this case we are talking about absolute pressure values; used in the framework of the present invention specific pressure levels are given below). In appropriate installations, a distillation column system is provided with (at least) one high pressure column and one low pressure column. In the exemplary case explained, the high pressure column is operated at said pressure level from 5.0 to 6.0 bar, the low pressure column operates at said pressure level from 1.2 to 1.6 bar. The air expanded in the turbocharger is supplied to the low pressure column. Expansion is possible due to the indicated pressure difference between the high pressure column and the low pressure column. However, the air expanded in this way in the low-pressure column prevents the rectification, as a result of which the amount of air expanded in the turbocompressor and thereby the cooling capacity of the installation as a whole are very limited. Therefore, noteworthy quantities of liquid products cannot be selected from plants with similar connection configurations.

The maximum amount of liquid nitrogen and liquid oxygen taken off in conventional plants with mixing columns, as in other typical air separation plants for producing gaseous air separation products (so-called gas plants), is therefore limited to no more than about 0.5% of the introduced air amount .

Although the method, as described in patent document WO 2014/037091 A2, allows to increase the amount of liquid produced, however, for reasons explained below, it does not always provide sufficient technological flexibility with the variable demand for liquid and gaseous oxygen-enriched air separation products.

Therefore, there is a need for improved capabilities for efficiently and flexibly producing liquid and gaseous oxygen enriched air separation products in air separation units with corresponding mixing columns.

SUMMARY OF THE INVENTION

The present invention, based on the foregoing, provides a method for producing a liquid and gaseous oxygen enriched air separation product in an air separation unit, and an air separation unit for performing a similar method, with the features of the independent claims. Preferred embodiments are the subject of the dependent claims, as well as the following description.

In air separation plants, turbochargers are used to compress air. This is true, for example, for the “main air compressor”, which differs in that it compresses the entire amount of air supplied to the system of distillation columns, that is, all supplied air. Accordingly, a “booster compressor” may also be provided, by which a portion of the amount of air compressed in the main air compressor is brought to an even higher pressure. It can also be shaped like a turbocharger. Additional turbocompressors, which are also called boosters, are usually provided for compressing partial amounts of air, however, compared to the main air compressor or booster compressor, only a relatively small degree of compression is performed.

In many places in air separation plants, in addition, the air can be expanded, for which, among other things, expansion machines in the form of turbo expanders, here also briefly called “turbines,” can be used. Turbo expanders can also be connected to and driven by turbochargers. If one or many turbocompressors are driven without supplying energy from the outside, that is, only through one or many turbo-expanders, then the term “turbo booster” also applies to this configuration. In a turbo booster, a turbo expander and a turbocharger are mechanically connected.

In this application, for the characterization of pressures and temperatures, the terms “pressure level” and “temperature level” are used, in connection with which it should be noted that the pressures and temperatures in the corresponding installation should not be applied in the form of exact values of pressure and, accordingly, temperature in order to realize concept of the invention. However, such pressures and temperatures typically vary within certain ranges that deviate, for example, by ± 1%, 5%, 10%, 20%, or even 50% of the average. As a rule, values within one “level” diverge from each other by no more than 5% or 10%. In this case, the corresponding pressure levels and temperature levels can be in isolated areas or in ranges that overlap with each other. In particular, pressure levels include, for example, unavoidable pressure drops or expected pressure losses, for example, due to cooling effects or losses in pipelines. This is also true for temperature levels. In relation to the pressure levels given in units of bar, this is an absolute pressure value.

As part of this application, we are talking about obtaining products from air, in particular, oxygen-enriched and nitrogen-enriched air separation products, and, accordingly, oxygen and nitrogen as products. The “product” is derived from the installation in question and, for example, is stored in a tank or consumed. Thus, it participates not only exclusively in the circulation circuits inside the unit, but before leaving the unit can be used accordingly, for example, as a refrigerant in a heat exchanger. Thus, the term “product” does not include such fractions or streams that as such remain in the installation and are used exclusively there, for example, as reflux, refrigerant or purge gas.

In addition, the term “product” contains an indication of quantity. A “product” corresponds to at least 1%, in particular at least 2%, for example at least 5% or at least 10% of the amount of air supplied to the respective installation. Smaller quantities, as usual, also generated in the gas plants under discussion, and due to the circumstances of the liquid fractions taken in such a plant, do not constitute “products” in the sense of this application. For example, in known distillation column systems, small amounts of the liquid fraction collected in the bottom portion of the liquid fraction are always removed from the low pressure column to avoid saturation with undesirable components such as methane. But at the same time, we are not talking about “products” in the sense of this application, on the basis of quantity. When liquid products are removed from the air separation unit, a significant amount of cold is “taken away”, which otherwise could be partially compensated by the evaporation of these liquid products. However, such a withdrawal has an effect only up to a certain output quantity, that is, only when the “product” is actually displayed in the sense of the above definition.

The liquid or gaseous "oxygen-enriched air separation product" in the terminology of this application is a fluid in an appropriate state of aggregation, which has an oxygen content of at least 75%, in particular at least 80%, on a molar, weight or volume basis. Therefore, the “crude oxygen” that is discharged from the mixing column is an oxygen enriched air separation product.

Advantages of the Invention

The present invention provides a low-temperature air separation method in which an air separation unit with a main heat exchanger and a distillation column system is used, which includes one high pressure column operating at a first pressure level, one low pressure column operating at a second pressure level, and a mixing column. The second level of pressure is lower than the first.

As, for example, it is already known from the aforementioned patent document WO 2014/037091 A2, in such a method, an oxygen-enriched liquid stream with a first oxygen content that is not removed from the air separation unit directly by liquid or vapor can be taken out of the low pressure column, in particular, after heating, it is supplied in liquid with a first oxygen content to the mixing column, in particular to the upper region, for example, to the head. In addition, a first gaseous stream of compressed air is introduced into the mixing column, and is passed in a countercurrent countercurrent flow towards the oxygen-rich liquid stream with a first oxygen content. The supply of the first stream of compressed air to the mixing column is preferably carried out directly above the still bottom.

As a result of this action of the mixing column, an oxygen-enriched stream with a second oxygen content below the first oxygen content can be withdrawn from its head, and removed from the air separation unit in the form of a gaseous oxygen-enriched air separation product. With respect to the oxygen-enriched stream with a second oxygen content, we are talking about the said “crude” oxygen, however, the oxygen content (second) in which is sufficient for certain applications and allows the said optimization of energy consumption.

In an appropriate installation, a liquid stream of pure oxygen can be diverted from the low pressure column, in particular from its bottom part, and with its oxygen content in the form of a liquid oxygen-enriched air separation product is removed from the air separation unit. The corresponding situation is shown in patent document WO 2014/037091 A2. The pure oxygen stream has an oxygen content higher than the first oxygen content. Thus, in this case, an additional liquid oxygen-enriched air separation product is obtained which has a high oxygen content. The thus achieved removal of two oxygen enriched streams from the low pressure column (namely, an oxygen enriched stream with a first oxygen content and optionally a pure oxygen stream) is a technological option if, in addition to the gaseous oxygen enriched air separation product, a liquid oxygen enriched separation product is required air in the form of pure liquid oxygen. If such a liquid oxygen-enriched air separation product in the form of pure liquid oxygen is not required, or if the required purity of the liquid oxygen-enriched air separation product is about one to two percentage points higher than the desired purity of the gaseous oxygen-enriched air separation product, then the low only one liquid oxygen enriched stream can also be removed from the pressure. Then, for example, part of this, as explained earlier, is fed into the mixing column, and part in liquid form is removed from the air separation unit, that is, it is used as a liquid oxygen-enriched air separation product.

In each case, in the present invention, also from the air separation unit, the liquid oxygen-enriched air separation product is withdrawn, at least periodically, in a liquid state, for example, the corresponding liquid oxygen-enriched air separation product from the low pressure column with a first oxygen content or the corresponding pure oxygen. Other oxygen enriched liquid air separation products may also be removed from the air separation unit. Their quantity as products includes at least the above values with respect to “products”. The amount in which the corresponding liquid oxygen-enriched air separation product can be removed from the liquid separation plant is highly variable based on the measures proposed according to the invention.

If the oxygen-enriched streams are discussed above, namely, in particular the oxygen-enriched stream with a first oxygen content, and, as the case may be, a stream of pure oxygen with a higher oxygen content, and additional oxygen-enriched streams that are removed from the low pressure column in a liquid state at this refers to the streams that are used to produce the corresponding oxygen enriched air separation products. Therefore, they, as mentioned above in relation to the term “products”, are removed from the low pressure column in an amount that is clearly different from streams that are not obtained as products, for example, washing streams that are used only to remove impurities, for example, from the bottoms low pressure columns. Thus, the oxygen enriched stream with the first oxygen content and, as the case may be, the pure oxygen stream and other oxygen enriched streams in each case are taken from the low pressure column in an amount that is within the range mentioned above with respect to the “product”.

In the framework of the present invention, the first stream of compressed air that is supplied to the mixing column is formed using air that has been compressed to an initial pressure level above the first pressure level, and then cooled, in particular in the main heat exchanger, to the first temperature level and expanded in the first turbine. As will also be explained later, the present invention is applied in particular in the so-called HAP-method HAP (“High Air Pressure”), that is, a method in which the entire amount of air that is supplied to the distillation column system is first compressed to a pressure that is definitely higher than the highest working pressure used in the distillation column system. In this case, the term "definitely higher" in this case should be understood as a pressure difference of at least 1.0 bar (0.1 MPa), especially more. By using the corresponding first turbine, additional cold can be generated that compensates for the loss of cold, in particular due to the selection of liquid oxygen-enriched air separation products from the air separation unit. Thus, in the framework of the present invention, part of the need for cold is covered by the expansion of the air used to produce the first stream of compressed air, which expands in the first turbine.

In addition, the present invention provides a second stream of compressed air, which is also formed using compressed to the original pressure level and then cooled, in particular in the main heat exchanger, to the first temperature level and expanded air in the first turbine, is supplied to the high-pressure column. Thus, a portion of the air expanded in the first turbine after being expanded in the first turbine is supplied to the mixing column, and the other part is sent to the high pressure column.

In addition, the present invention proposes the introduction into the low-pressure column of a third stream of compressed air, which is formed using air that has been compressed to an initial pressure level, and then cooled, in particular in the main heat exchanger, to a second temperature level, expanded in a second turbine, and then again cooled in the main heat exchanger to a third temperature level.

In the framework of the present invention, air expands in the first turbine to the first, that is, the pressure level of the high pressure column, and in the second turbine to the second, that is, the pressure level of the low pressure column. The mixing column in the framework of the present invention is operated at a first pressure level, that is, a pressure level of a high pressure column, or at a third pressure level that differs from the first pressure level by no more than 1 bar.

The air expandable in the first turbine and in the second turbine in the framework of the present invention is supplied to the first turbine at the first temperature level, and to the second turbine at the second temperature level, the first temperature level of at least 20 K, in particular at least 30 K or at least 40 K, lies below the second temperature level. In particular, the first temperature level of 25 to 35 K or 28 to 32 K, more preferably of about 30 K, is lower than the second temperature level. Data in each case temperature levels will also be referenced in the explanations below. Moreover, in relation to the first turbine we are talking about a "cold" turbine, in relation to the second turbine it is about a "warm" turbine.

If, in conventional methods and, accordingly, installations in which the HAP method is performed as explained above, and a mixing column is used, it is desirable to reduce the formation of liquid, that is, the amount in which the products of air separation in the liquid state are removed from the air separation unit, then the pressure of the main air compressor should be reduced with a constant amount of air flowing through the main air compressor. However, a correspondingly reduced pressure with a constant amount of air increases the actual volume of compressed air. Therefore, in standard installations, located in the warm part of the device, in particular, air purification and pre-cooling units, should have clearly increased sizes. This is undesirable for economic reasons. In addition, the pressure reduction with a constant amount of air, as a rule, is not optimal in relation to the efficiency of the main air compressor used.

For a method in which the pressure in the mixing column, which is adapted to the required pressure of the gaseous oxygen product, is definitely lower or higher than the pressure in the high pressure column, a technology is proposed as described in the aforementioned patent document WO 2014/037091 A2.

On the contrary, if the required pressure of the compressed product is at or near the pressure of the high pressure column of about 5 bar, that is, at the first pressure level or at the third pressure level, which differs from the first pressure level by at most 1 bar, as in the framework of the present invention then the HAP method using a medium-pressure turbine as well as a turbocharger presents advantages in terms of the technological flexibility of the apparatus for producing a liquid oxygen product and operating costs, as was discovered according to the invention.

With respect to the “medium pressure turbine”, this is referred to in the first turbine, while the “turbocharger” in the framework of the present application is formed by the second turbine. Since the method according to the invention has the configuration of the HAP method, only a single main air compressor is required, which significantly reduces capital costs. The inlet pressures of both turbines are preferably at the same level, in particular at the same level as the outlet pressure of the main air compressor.

If a relatively large amount of liquid oxygen product (“increased liquid production”) is to be obtained, then within the framework of the present invention, the initial pressure level (that is, the pressure level created by the main air compressor) can be increased and at the same time the amount of air which in the form of a third stream of compressed air is supplied to the low pressure column (that is, “pumped air”, which expands in the second turbine, that is, “turbocharger”). The increased amount of air expanded in the second turbine thereby increases the so-called "excess air coefficient", that is, the amount of air required for rectification as a whole.

The aforementioned simultaneous increases in pressure and quantity result in higher plant uptime, the main air compressor provides higher productivity, and fluid production can be increased. At the same time, in the framework of the present invention, the actual air volume in the warm part remains approximately constant, since both pressure and quantity increase. In the characteristic of the main air compressor, this way increases both the quantity and pressure of compressed air, which, as a rule, has a beneficial effect on the efficiency of the main air compressor.

If, on the contrary, a relatively small amount of liquid oxygen product is to be obtained (“reduced liquid production”), the initial pressure level decreases and, at the same time, the amount of air, which in the form of a third stream of compressed air, is supplied to the low-pressure column. A reduced amount of air expandable in the second turbine reduces the excess air ratio.

Thus, a simultaneous decrease in pressure and quantity leads to less exergy of the installation, the main air compressor provides lower productivity, and the liquid production is reduced. Again, at the same time, the actual volume of air in the warm part remains approximately constant. In the characteristic of the main air compressor, this way reduces both the quantity and pressure of compressed air, which, as a rule, is more favorable for the efficiency of the main air compressor than a simple decrease in pressure.

In the framework of the present invention, a fourth stream of compressed air is advantageously applied, which is supplied to the high pressure column and is formed using air which is compressed to the initial pressure level and then cooled to the third temperature level and expanded by means of a throttle. The corresponding fourth stream of compressed air corresponds to a throttled stream in a conventional air separation method.

The method according to the invention preferably includes a first technological mode and a second technological mode, moreover, in the first technological mode, from the air separation unit, the liquid oxygen-enriched air separation product is discharged in a liquid state in a larger quantity than in the second technological mode, and moreover, in the second technological mode a larger amount of air expands in the turbine than in the second process mode, and thereby along with this, the third stream of compressed air in the first process mode includes the same increased amount of air as in the second process mode. In other words, in order to select more liquid oxygen enriched air separation product in the framework of the present invention, the amount of pumped air is increased, which expands in the second turbine and is supplied to the low pressure column. This satisfies the additional need for cold, which arises due to the selection of a liquid oxygen product.

The liquid oxygen enriched air separation product, which in each case is discharged from the air separation unit, is taken from the low pressure column. In this case, either pure oxygen, as explained above, or a liquid oxygen product with a lower oxygen content can be used. If such an oxygen-enriched air separation product “is discharged in a liquid state”, this means that no evaporation is performed inside the air separation unit. If it is indicated above that in the first technological mode from the air separation unit the liquid oxygen-enriched air separation product is discharged in a liquid state in a larger quantity than in the second technological mode, this may also mean that in the second technological mode the liquid oxygen-enriched air separation product is generally not displayed. The amount of liquid oxygen-enriched air separation product that is discharged from the air separation unit in the liquid state in the first process mode may be, for example, 1.5 times, 2 times, 3 times, 4 times or 5 times the value of the corresponding quantities in the second technological mode.

The increase in the amount of air expanded in the second turbine and at the same time contained in the third stream of compressed air is preferably carried out taking into account the so-called discharge equivalent. The discharge equivalent primarily includes the amount of air expanded by the second turbine, which at the same time corresponds to the amount of air contained in the third compressed air stream, and additionally the amount of nitrogen-rich streams that are also taken from the high pressure column. These nitrogen-rich streams are liquid nitrogen and compressed nitrogen, which, as nitrogen-enriched air separation products, are supplied by an appropriate air separation unit. These nitrogen-rich streams are not used as liquid reflux in a high pressure column and in a low pressure column. The total amount expanded in the second turbine and at the same time contained in the third stream of compressed air and such nitrogen-rich streams in the first process mode is preferably from 12 to 18%, and in the second process mode from 0 to 8% of the total supplied to the system distillation columns of the total amount of air. This cumulative amount of air supplied to the distillation column system also includes the air expanded in the second turbine.

Such variability is achieved, in particular, by the fact that the first turbine is made and, accordingly, is operated adjustable in number of revolutions, so that correspondingly different air flow rates can be achieved in different operating conditions. The term “speed-controlled” turbine in the framework of this application is used only for delimiting from turbines, the speed of which, for example, by means of suitably adjustable brake systems, is set at a fixed speed of rotation. This is also true for the second turbine.

As already mentioned, the method according to the invention is preferably applied in connection with the so-called HAP method, in which all the air supplied to the distillation column system is compressed using a main air compressor to a pressure level that is higher than the pressure level in the high pressure column. Thus, all air supplied to the system of distillation columns is brought to the initial pressure level using the main air compressor.

In the framework of the present invention, as already explained above in other words, in the first process mode, the excess air coefficient, that is, the amount of air introduced to obtain a fixed amount of product, is clearly higher than in the second process mode, since the amount expanded in the second turbine and at the same time contained in the third stream of compressed air and supplied to the low pressure column of air is greater than in the second process mode. In the first technological mode, as mentioned, a larger amount of liquid products is selected than in the second technological mode. Therefore, more air must be passed through the main air compressor than in the second process mode. But at the same time, due to the higher coefficient of excess air, the final pressure of the main air compressor, that is, the pressure level referred to here as the "initial pressure level", still remains lower than with a reduced coefficient of excess air.

In contrast, in the second process mode, the excess air coefficient is clearly lower than in the first process mode, since the amount of compressed air expanded in the second turbine and simultaneously contained in the third stream and supplied to the low pressure column is lower than in the first process mode. In the second technological mode, as mentioned, fewer liquid products are selected than in the first technological mode. This leads to a decrease in the amount of air passed through the main air compressor at a simultaneously lower final pressure (that is, the pressure level referred to herein as the "initial pressure level") compared to the first process mode. In contrast, as mentioned, in conventional methods, the amounts of air passed through the main air compressor are maintained at reduced pressure, resulting in increased actual volumes of these quantities of air. In the framework of the invention, this no longer takes place, that is, the design load in the second technological mode is no longer a factor determining the dimensions in the warm part of the air separation unit. At the same time, the pressure difference relative to the final pressure of the main air compressor (that is, the "initial pressure level") in the first and second technological mode becomes smaller than would be typical in traditional methods, since, as mentioned, due to the high coefficient of excess air, the final pressure of the main the air compressor in the first technological mode remains smaller than with a reduced coefficient of excess air. Since both the amount of air compressed in the main air compressor and the pressure used there are reduced, this design load, as a rule, is more consistent with the characteristics than with a constant amount of compressed air and a more reduced pressure.

The air expandable in the first turbine and in the second turbine is preferably supplied to the first turbine and to the second turbine at the same pressure level, in particular at the initial pressure level. Moreover, in the framework of the present invention, the initial pressure level in the first technological mode is preferably 1 to 10 bar higher than the initial pressure level in the second technological mode. In general, within the framework of this application, at an initial pressure level of 6 to 15 bar, the first pressure level can be from 4.3 to 6.9 bar, in particular about 5.4 bar, and the second pressure level can be from 1 , 3 to 1.7 bar, in particular about 1.4 bar. The third pressure level, if the mixing column does not operate at the first pressure level, differs, as mentioned, by no more than 1 bar from the first. The first temperature level is preferably from 110 to 140 ° C., the second temperature level is from 130 to 240 ° C., and the third temperature level is from 97 to 102 ° C.

The turbines used in the framework of the present invention can be braked in various ways. In particular, a generator, a booster and / or an oil brake may be used.

The process according to the invention is particularly suitable in situations in which the first oxygen content is below 99 molar percent, for example, from 98 to 99 molar percent, and the second oxygen content is from 80 to 98 molar percent. The oxygen content in the stream of pure oxygen, if formed, is preferably from 99 to 100 molar percent. In these cases, the method using the mixing column proved to be particularly energy efficient.

In addition, the present invention extends to an air separation unit with one main heat exchanger and one distillation column system, which includes a high pressure column designed for operation at a first pressure level, a low pressure column designed to operate at a second, lower pressure level, and a mixing column .

In an appropriate installation, devices are provided which are designed to discharge an oxygen-enriched stream with a first oxygen content in a liquid state from a low-pressure column and to supply a first column of oxygen in a liquid state to a mixing column, in particular to the upper region, in addition in order to bring the first stream of compressed air in a gaseous state into the mixing column, in particular, near the bottom part, and in the mixing column to pass the oxygen-enriched stream with the first oxygen content in countercurrent mode, to select the oxygen-enriched stream with the second oxygen content on the head of the mixing column below the first oxygen content, and withdraw from the air separation unit, and form a first stream of compressed air using air that is compressed to an initial pressure level above the first pressure level, and then cooled to the first temperature level and expanded into moat turbine.

As mentioned, a stream of pure oxygen in a liquid state can also be taken from a low-pressure column and removed from the air separation unit in a liquid state. In one such case, there are adapted for this device. In any case, devices are provided which are designed to withdraw from the air separation unit, at least in part, the liquid oxygen-enriched air separation product in the liquid state.

According to the invention, devices are provided which are designed to supply a second stream of compressed air to the high pressure column and also to form it using compressed pressure to the initial pressure level and then cooled to the first temperature level and expanded in the first air turbine, to supply it to the column low-pressure third stream of compressed air and form it using air, which is compressed to the initial pressure level and then cooled to the second temperature level, then expanded in the second turbine and further cooled in the main heat exchanger to the third temperature level, and expand the air into the first turbine to the first pressure level, and in the second turbine to the second pressure level, and operate the mixing column at the first pressure level or at the third pressure level, which differs from the first pressure level by no more than 1 bar.

In addition, these devices according to the invention are designed to allow air to be expanded in the first turbine and in the second turbine to the first turbine at the first temperature level, and to the second turbine at the second temperature level, the first temperature level being lower than the second temperature level at least 20 K.

In particular, such an air separation unit is designed for operation in the first technological mode and in the second technological mode, for which devices are provided that are designed to remove a larger amount of oxygen-enriched liquid air separation product from the air separation unit in a larger quantity, than in the second technological mode, and in the first technological mode to expand a larger amount of air in the second turbine than in the second technological mode, so that as a result the third compressed air stream in the first technological mode includes the same large amount of air as in the second technological mode .

The invention is further explained in more detail with reference to the accompanying drawings, which clearly illustrate preferred embodiments of the present invention.

Brief Description of the Drawings

Figure 1 shows an air separation unit according to one embodiment of the invention in the form of an installation flow chart.

Detailed Description of Drawings

In Figure 1, an air separation unit according to one particularly preferred embodiment of the invention is presented and generally indicated by code number 100.

Installation 100 separation of air using the main air compressor 2 through the filter 1 sucks in the flow of supplied air, and in the presented example compresses to a pressure level of 6 to 15 bar (absolute). After compression, drying, cooling and purification steps of a known type may follow, which are not shown in Figure 1 for the sake of clarity.

The corresponding stream b of compressed and purified air is divided into two partial streams c and d, which are supplied at the indicated pressure level to the main heat exchanger 3 from the warm side, are cooled in it and are selected at different temperature levels.

From the partial stream c, after removal from the main heat exchanger 3 at two temperature levels, two partial streams e and f are formed. The partial stream e expands in the expansion machine 4, the partial stream f in the expansion machine 5. Since the partial stream e is cooled to a lower temperature than the partial stream f, the expansion machine 4 is also called a “cold” expansion machine, on the contrary, the expansion machine 5 is called " warm "expansion machine.

The expansion of both partial flows e and f in each case is performed on the basis of the mentioned pressure level from 5 to 15 bar (absolute). The partial flow e in the presented example expands to a pressure level of about 5.4 bar (absolute), while the partial flow f to a pressure level of about 1.4 bar (absolute). In each case, the generators 41 and, respectively, 51 are connected to the expansion machines 4 and 5.

The partial stream e after its expansion in the expansion machine 4 is once again divided into two partial streams g and h. Partial flow g is introduced near the bottoms in the high-pressure column 61, which is configured as part of the double column 6. Partial flow h expands near the bottoms in the mixing column 7. The high-pressure column 61 operates at the pressure level of about 5.4 bar (absolute) , the mixing column 7 is operated at a slightly lower pressure level of about 5.0 bar (absolute).

The partial stream f after expansion in the expansion machine 5 at an intermediate temperature level is returned to the main heat exchanger 3, is removed from it on the cold side and fed to the low pressure column 62, which is also made as part of the double column 6. The low pressure column 62 acts on the aforementioned pressure level of about 1.4 bar (absolute).

Partial flow d is discharged from the cold side of the main heat exchanger 3 and, based on the pressure level mentioned above from 6 to 15 bar (absolute), expands in the high pressure column 61.

In the high-pressure column 61, a liquid, oxygen-enriched fraction is deposited on the bottom side and is discharged in the form of stream i. Stream i is passed through a counterflow cooler 8 and then expanded in the low pressure column 62.

The nitrogen-rich overhead product is discharged from the top of the high-pressure column 61, and partly in the form of stream k is passed through the main condenser 63 of the double column 6, and there, at least partially, is liquefied. A portion of the liquid nitrogen-rich head product of the high-pressure column 61 (see Bundle A) in the form of stream l is passed through a counter-current supercooler, and is discharged outside the unit as a liquid nitrogen-rich product of separation. An additional portion of the liquefied nitrogen rich head product of the high pressure column 61 is returned to the high pressure column 61 as a reflux.

A nitrogen-enriched stream m is discharged from the intermediate bottom of the high-pressure column 61, is also passed through a counter-current supercooler 8, and expands in the low-pressure column 62 near its head.

A liquid, oxygen-enriched fraction is formed in the bottom part of the low-pressure column, which is discharged (see bundle B) in the form of stream n, partially passed through a counterflow supercooler 8, and is discharged outside the unit in the form of a liquid oxygen-enriched air separation product.

An oxygen-enriched stream o is discharged from the intermediate bottom of the low-pressure column 62, using the pump 9 it acquires increased pressure in the liquid state, is passed through a counter-current supercooler 8, heated in the main heat exchanger 3, and fed to the mixing column 7 near its head. The mixing column acts as explained many times. From the top of the mixing column 7 is depleted of oxygen depleted, compared with stream o, stream p is heated in the main heat exchanger 3, and is discharged outside the installation in the form of a gaseous oxygen product.

From the top of the low pressure column 62, a crude nitrogen stream q is discharged, passed through a counterflow supercooler 8 and a main heat exchanger 3, and, for example, is used in a device for cleaning stream a.

The nitrogen-enriched stream r is formed from a low-pressure column 61 that is not enriched in nitrogen through the main condenser 63 of the overhead product.

Illustratively illustrated in Figure 1, the air separation unit 100 is designed to operate in two process modes that were previously explained. In the first technological mode, the amount of liquid, here in the form of stream n in the liquid state, from the air separation unit 100 of the liquid air separation product is larger than in the second technological mode. At the same time, in the first technological mode, with the help of the turbine 5, a larger amount of air expands than in the second technological mode, so that the coefficient of excess air increases. In the second technological mode, due to the reduced coefficient of excess air, the pressure and the amount of flow b, that is, the final pressure of the main air compressor 2 and the amount of air conducted through it, are reduced.

Claims (39)

1. The method of low-temperature air separation, which uses the installation (100) of air separation with the main heat exchanger (3) and a distillation column system (6, 7), which includes one high-pressure column (61) operating at the first pressure level, one acting on a second, lower pressure level, the low pressure column (62) and the mixing column (7), in which - an oxygen-enriched stream (n) with a first oxygen content and with this first oxygen content in a liquid state is fed to a mixing column (7) from a low pressure column (62) in a liquid state, - in addition, in the mixing column (7) serves the first stream (h) of compressed air in a gaseous state and is passed in the mixing column (7) in countercurrent mode towards the oxygen-rich stream (n) with the first oxygen content, - an oxygen-enriched stream (o) with a second oxygen content below the first oxygen content is taken from the head of the mixing column (7) and removed from the air separation unit (100), - form the first stream (h) of compressed air using air, which is compressed to the initial pressure level above the first pressure level, and then cooled to the first temperature level, at the first temperature level they are brought into the first turbine (4) and expanded in the first turbine ( 4), and - from the installation (100) of air separation, at least partially, the liquid oxygen-enriched air separation product is removed, characterized in that - a second stream (g) of compressed air is supplied to the high-pressure column (61), which is also formed using compressed to the initial pressure level, and then cooled to the first temperature level and expanded in the first turbine (4) air, - a third stream (f) of compressed air is supplied to the low pressure column (62), which is formed using air, which is compressed to the initial pressure level, and then cooled to the second temperature level, at the second temperature level, it is supplied to the second turbine (5 ), expand in the second turbine (5) and additionally cool in the main heat exchanger (3) to the third temperature level, - air is expanded in the first turbine (4) to the first and in the second turbine (5) to the second pressure level, and the mixing column (7) is operated at the first pressure level or at the third pressure level, which differs from the first pressure level by no more than 1 bar (0.1 MPa), and - wherein the first temperature level is at least 20 K lower than the second temperature level. 2. The method according to claim 1, wherein a fourth stream (f) of compressed air is supplied to the high pressure column (61), which is formed using air that is compressed to the initial pressure level, and then cooled to a third temperature level and expanded with using a throttle. 3. The method according to p. 1 or 2, which includes a first technological mode and a second technological mode, and - in the first technological mode from the air separation unit (100), a liquid oxygen-enriched air separation product is discharged in a larger quantity than in the second technological mode, and - in the first technological mode, a larger amount of air is expanded in the second turbine (5) than in the second technological mode, and at the same time, the third compressed air stream (f) in the first technological mode includes the same large amount of air as in the second technological mode. 4. The method according to p. 3, in which one or more nitrogen-rich streams (l, q) are taken from the high pressure column (61) and removed from the air separation unit (100), the amount of air expanded in the second turbine (4) and at the same time contained in the third stream (f) of compressed air, is controlled so that the sum of the amount expanded in the second turbine (4) and at the same time contained in the third stream (f) of compressed air and the amount enriched or enriched with nitrogen flow (s) (l, q) in the first technological mode corresponds to 12-18 percent, and in the second technological mode - 0-8 percent of the total amount of air supplied to the system of distillation columns (6, 7). 5. The method according to p. 3, in which all the air supplied to the system of distillation columns (6, 7) is brought to the initial pressure level using the main air compressor (2). 6. The method according to p. 5, in which in the first technological mode, a larger amount of air is passed through the main air compressor (2) at a higher pressure than in the second technological mode. 7. The method according to claim 1, wherein the air expandable in the first turbine (4) and in the second turbine (5) is supplied to the first turbine (4) and to the second turbine (5) at the same pressure level. 8. The method according to p. 3, in which the initial pressure in the first technological mode by 1 to 10 bar exceeds the initial pressure in the second technological mode. 9. The method according to claim 1, wherein the initial pressure level is from 6 to 15 bar (abs.), The first pressure level is from 4.3 to 6.9 bar (abs.) And the second pressure level is from 1.3 to 1 7 bar (abs.). 10. The method according to p. 1, wherein the first temperature level is preferably from 110 to 140 ° C., The second temperature level from 130 to 240 ° C and the third temperature level from 97 to 102 ° C. 11. The method according to claim 1, wherein the first turbine (4) and / or the second turbine (5) is braked using a generator, a booster and / or an oil brake. 12. The method according to claim 1, wherein the first oxygen content is from 99 to 100 molar percent, and the second oxygen content is from 80 to 98 molar percent. 13. The method according to claim 1, wherein the first turbine (4) and the second turbine (5) are turbines with a variable speed. 14. An air separation unit (100) with a main heat exchanger (3) and a distillation column system (6, 7), which includes one high pressure column (61) designed for operation at the first pressure level, one designed for operation at a second, lower the pressure level of the low pressure column (62) and the mixing column (7), and in which devices are provided that are designed to - discharge from the low pressure column (62) in a liquid state an oxygen-enriched stream (n) with a first oxygen content and, with this first oxygen content in a liquid state, feed to a mixing column (7), - in addition, in the mixing column (7) to supply the first stream (h) of compressed air in a gaseous state and pass in the mixing column (7) in countercurrent mode towards the oxygen-rich stream (n) with the first oxygen content, - from the head part of the mixing column (7), select the oxygen-enriched stream (o) with a second oxygen content below the first oxygen content and withdraw from the air separation unit (100), - to form the first stream (h) of compressed air using air that has been compressed to the initial pressure level above the first pressure level, and then cooled to the first temperature level, at the first temperature level it is brought into the first turbine (4) and expanded in the first turbine (4), and - from the installation (100) of the separation of air, at least partially, to remove the liquid oxygen-enriched product of the separation of air, characterized in that it contains devices that are designed to - in the high pressure column (61) to supply a second stream (g) of compressed air, which is also formed using compressed to the original pressure level, and then cooled to the first temperature level and expanded in the first turbine (4) air, - feed a third stream (f) of compressed air into the low-pressure column (62), which is formed using air that has been compressed to the initial pressure level, and then cooled to the second temperature level; at the second temperature level, it is supplied to the second turbine (5 ), expands in the second turbine (5) and is additionally cooled in the main heat exchanger (3) to the third temperature level, - expand the air in the first turbine (4) to the first and second turbine (5) to the second pressure level, and the mixing column (7) is operated at the first pressure level or at the third pressure level, which differs from the first pressure level by no more than 1 bar, and - wherein the first temperature level is at least 20 K lower than the second temperature level. 15. Installation (100) of air separation according to claim 14, which is designed for operation in the first technological mode and in the second technological mode, for which there are devices that are designed to - in the first technological mode, from the air separation unit (100) to withdraw the liquid oxygen-enriched air separation product in a larger quantity than in the second technological mode, and - in the first technological mode in the second turbine (5) to expand a larger amount of air than in the second technological mode, so that the third stream (f) of compressed air in the first technological mode includes the same large amount of air as in the second technological mode.

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