Air separation apparatus and air separation method

Abstract

The present invention provides an air separation plant and method. In the air separation plant, a feed line is used to feed at least a portion of a total feed gas from a main compressor to a rectifier column system via a main heat exchanger, and a waste line is used to remove waste gas from the rectifier column system via the main heat exchanger. The air separation plant further includes an additional line and an additional expander. The additional line is tapped from the feed line at a location before the main heat exchanger and leads to the waste line at a location between the main heat exchanger and the rectifier column system. The additional expander is disposed in the additional line such that a stream in the additional line is expanded via the additional expander and fed into the waste line. The air separation plant and method described above can accommodate different operating conditions with varying amounts of air product.

Description

Technical Field

[0001] This invention belongs to the field of air separation and relates to an air separation device and an air separation method. Background Technology

[0002] Air separation equipment is widely used in various industries. Users of air separation equipment often face varying demands for air products, especially gaseous products, at different times. For example, in the early stages of plant construction, due to incomplete supporting facilities, users may only need a low output of gaseous products. Later, as supporting facilities mature, the required amount of gaseous products increases. The design operating condition is based on the longer later period, while the shorter earlier period is considered the low-production operating condition. Sometimes, the amount of air products, such as oxygen, required under the low-production condition is less than half of the amount required under the design operating condition.

[0003] The inventors analyzed that when the required air product volume differs significantly between design and low-production operating conditions, the amount of feed air will also differ significantly between the two conditions. In this situation, under design conditions, the main compressor can normally compress the feed air with a larger mass flow rate. However, under low-production conditions, for feed air with a significantly reduced mass flow rate, the main compressor may fail to operate normally, for example, experiencing surge problems.

[0004] In response, the inventors further analyzed that, under low-production conditions, the feed air with a mass flow rate exceeding the required amount can be fed to the main compressor, and this excess feed air will not be sent to the distillation column system.

[0005] Therefore, how to effectively utilize this excess feed air is a problem that needs further investigation. Summary of the Invention

[0006] The purpose of this invention is to provide an air separation device and method that can adapt to different operating conditions, especially those with significant changes in air product quantity.

[0007] Another object of the present invention is to provide an air separation device and method that can effectively utilize all the feed air.

[0008] This invention provides an air separation unit. The air separation unit includes a feed line and a waste gas discharge line. The feed line is used to supply at least a portion of the total feed gas from the main compressor via the main heat exchanger to the distillation column system. The waste gas discharge line is used to discharge waste gas from the distillation column system via the main heat exchanger. The air separation unit also includes an auxiliary line and an auxiliary expander. The auxiliary line extends from the feed line before the main heat exchanger and leads to the waste gas discharge line between the main heat exchanger and the distillation column system. The auxiliary expander is disposed in the auxiliary line such that the stream in the auxiliary line is expanded by the auxiliary expander and then fed into the waste gas discharge line.

[0009] In one embodiment, the air separation unit further includes a regulating device for regulating the mass flow rate of the stream flowing from the feed line to the auxiliary line.

[0010] In one embodiment, the air separation unit further includes an auxiliary compressor. The auxiliary compressor is located in the auxiliary pipeline and upstream of the auxiliary expander, such that the stream in the auxiliary pipeline is pressurized by the auxiliary compressor before entering the auxiliary expander for expansion.

[0011] In one embodiment, the auxiliary piping extends downstream of the auxiliary compressor via the first and second positions of the main heat exchanger to the auxiliary expander, wherein the first position is a hotter position relative to the second position.

[0012] In one embodiment, the air separation unit further includes an aftercooler. The aftercooler is located in the additional piping and between the additional compressor and the main heat exchanger.

[0013] In one implementation, the first position is the hot end of the main heat exchanger; and / or, the second position is the middle position of the main heat exchanger.

[0014] In one embodiment, the auxiliary compressor and the auxiliary expander are the pressurizing end and the expanding end of the expander, respectively, which are mechanically connected in the expander.

[0015] The present invention also provides an air separation method using an air separation unit. The air separation method includes feeding at least a portion of the total feed gas from the main compressor of the air separation unit via a main heat exchanger to a distillation column system as the feed stream for the distillation column system, and discharging waste gas from the distillation column system via the main heat exchanger. The air separation method further includes, under predetermined operating conditions, drawing a portion of the total feed gas as an additional stream before the main heat exchanger, and causing the additional stream to undergo expansion treatment before merging into the waste gas at a location between the main heat exchanger and the distillation column system.

[0016] In one implementation, the additional stream is pressurized before undergoing expansion.

[0017] In one implementation, the additional stream is cooled via the main heat exchanger between the pressurization and expansion processes.

[0018] In one implementation, the additional stream is first cooled by an aftercooler after being pressurized, and then by the main heat exchanger.

[0019] In one embodiment, when the additional stream is cooled by the main heat exchanger, the additional stream enters from the hot end of the main heat exchanger and exits from the middle position of the main heat exchanger; such that after expansion treatment, the pressure and temperature of the additional stream are reduced to be comparable to the pressure and temperature of the exhaust gas.

[0020] In one implementation, the ratio of the mass flow rate of the additional stream to the total feed gas mass flow rate is 5% to 20%. The ratio of the mass flow rate of the feed stream in the distillation column system under predetermined operating conditions to the mass flow rate under other operating conditions is 40% to 60%.

[0021] In the aforementioned air separation equipment and method, when the required amount of air product, especially gaseous product, is large, auxiliary piping can be omitted, and almost all of the total feed gas can be fed into the distillation column system as the feedstock. When the required amount of air product decreases, a portion of the total feed gas fed into the feed line can be drawn off through auxiliary piping. Therefore, in addition to the feed gas required as feedstock, the total feed gas passing through the main compressor also includes this portion drawn off from the auxiliary piping. This prevents the mass flow rate of the total feed gas passing through the main compressor from becoming too low and causing a malfunction. Therefore, the aforementioned air separation equipment and method can adapt to different operating conditions with varying air product quantities, especially those where significant changes in air product quantity could lead to malfunctions.

[0022] In the aforementioned air separation equipment and method, under conditions where the amount of air product decreases, a portion of the feed gas drawn from the auxiliary pipeline is expanded and cooled before being incorporated into the exhaust gas. This allows the feed gas and exhaust gas to absorb heat together in the main heat exchanger, thereby providing additional cooling capacity to the entire air separation equipment, specifically the distillation column system. This results in the production of more liquid products. These liquid products can be converted into the required amount of air product or directly into liquid products for easy storage. Therefore, this portion of the feed gas drawn from the auxiliary pipeline is also utilized to provide additional cooling capacity, thus enabling the aforementioned air separation equipment and method to effectively utilize all the feed air.

[0023] Furthermore, in the aforementioned air separation equipment and method, the portion of feed gas drawn from the auxiliary pipeline is merged with the exhaust gas and then sent together to the main heat exchanger. That is, this portion of feed gas directly utilizes the passage in the main heat exchanger used for exhaust gas passage, thus minimizing changes to the structure of the main heat exchanger and reducing overall equipment costs. Attached Figure Description

[0024] The advantages and spirit of this invention can be further understood through the following detailed description of the invention and the accompanying drawings.

[0025] Figure 1 This is a schematic diagram of an exemplary air separation device according to the present invention.

[0026] Figure 2 This is a schematic diagram of an exemplary air separation unit used as a comparative example. Detailed Implementation

[0027] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, it should be understood that the present invention is not limited to the embodiments described below, and the technical concept of the present invention can be implemented in combination with other known technologies or functions, or with other technologies similar to those known technologies.

[0028] The terms "first" and "second" are used for descriptive purposes only and do not refer to a limitation on time sequence, quantity, or importance. They should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated, but are merely used to distinguish one technical feature from another in this technical solution. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "multiple" means two or more, unless otherwise explicitly specified. Similarly, qualifiers such as "one" appearing in the text do not refer to a limitation on quantity, but describe technical features not mentioned above. Likewise, unless a noun is modified by a specific quantifier, the text should be considered to include both singular and plural forms; the technical solution may include either a singular or plural number of that technical feature. Similarly, modifiers such as "approximately" or "approximately" appearing before numerals generally include the number itself, and their specific meaning should be understood in conjunction with the context.

[0029] It should be understood that in this invention, "at least one time" means one or more times. "And / or" is used to describe the relationship between related objects, indicating that there can be three relationships. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural.

[0030] As used herein, the term "and / or" includes any and all combinations of one or more of the related listed items. Unless otherwise stated, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood in the art to which this invention pertains. It should also be understood that terms, such as those defined in common dictionaries, should be understood to have the meaning consistent with their meaning in the context of this specification and in the relevant field, and should not be interpreted in an idealized or overly formal sense unless expressly stated herein. For the sake of brevity and / or clarity, well-known functions or constructions may not be described in detail.

[0031] In practical engineering, the demand for air products, especially gaseous products, produced by an air separation unit often varies. Typically, the required air product volume varies within the range of 75% to 105% of the design operating conditions. In this case, the load capacity or performance requirements of the individual units within the air separation unit are not very high, and the air separation unit can usually adapt to these variations.

[0032] However, sometimes the amount of air products required by users fluctuates significantly within the design operating range. For example, in the early stages of plant construction, due to incomplete supporting facilities, the amount of air products required by users may be very low, later increasing or ramping up to a much higher level to meet the design operating conditions with mature supporting facilities. This initial operating condition with low air product demand can be called a low-production (turndown) condition or a ramp-up condition. As an example, the air product demand under a low-production condition may be only about 50% of that under the design condition. As a more specific example, users may require the air separation unit to initially operate at a low oxygen production capacity stage, then gradually transition or suddenly jump to a stage with a higher oxygen production capacity stage. The low production capacity stage can be considered as the air separation unit 10 operating under a low-production condition (or low-production mode), while the high production capacity stage can be considered as the air separation unit 10 operating under the design condition (or design mode).

[0033] The main compressor, which compresses the feed gas, is designed for the operating conditions and can therefore handle the larger mass flow rate of the feed gas under those conditions. However, under low-production conditions, the required amount of air product is significantly reduced, and the mass flow rate of the feed gas as the raw material will also be significantly reduced accordingly. In this case, for feed gas with an excessively low mass flow rate, the main compressor will experience surge, which not only increases the energy consumption of the air separation unit but also hinders machine operation and may even cause the entire air separation unit to malfunction and become inoperable.

[0034] "Low-production condition" can refer to a specific operating condition where the air output is lower than the design condition, or it can refer to any one of several operating conditions where the air output is lower than the design condition. In actual engineering, the low-production condition can gradually transition to the design condition, that is, the air output can be gradually increased from a lower value to a higher value, either continuously or intermittently. Alternatively, the low-production condition can be abruptly upgraded to the design condition, that is, the air output can suddenly jump from a lower value to a higher value. This can be specifically controlled according to the actual situation.

[0035] "Air products" refers to various products separated from air using the distillation column system of an air separation unit that can be directly used or stored, including oxygen, nitrogen, and argon products. Air products include "gaseous products" existing in gaseous form and "liquid products" existing in liquid form, thus facilitating storage. Gaseous products can include oxygen, nitrogen, and argon products. Liquid products can include liquid oxygen, liquid nitrogen, and liquid argon products. "Liquid products" refers to all liquid intermediate products directly produced from the distillation column system of an air separation unit, such as liquid oxygen, liquid nitrogen, and liquid argon products. It should be understood that "liquid products" includes the first portion of liquid products that are directly produced as liquid products, and also includes the second portion of liquid products that will vaporize and convert into gaseous products in the main heat exchanger. Figure 1 Taking liquid oxygen as an example of the liquid products, the liquid oxygen products include a second portion (represented by streams c31 and c32, corresponding to low-pressure oxygen and high-pressure oxygen respectively) that will eventually vaporize and be converted into oxygen in the main heat exchanger 1b, and a first portion (represented by stream c33) that can be directly sent to a storage tank for storage as liquid oxygen. As previously mentioned, the second portion of liquid product will eventually recover its cooling energy to the distillation column system through heat exchange in the main heat exchanger, while the first portion of liquid product needs to have its cooling energy removed from the distillation column system. Therefore, the first portion of liquid product, which is directly a liquid product, actually requires a high level of cooling energy to be delivered to the distillation column system, making it difficult to obtain. In other words, the yield or output of the liquid product places high demands on the construction of the entire air separation unit and method.

[0036] The "yield" of a liquid product refers to, for example, the ratio of the number of moles of liquid product obtained per unit time to the number of moles of the corresponding feed stream (i.e., the feed air entering the distillation column system). In other words, it can be used to characterize the conversion rate of the total feed gas stream into liquid product through a cryogenic air separation unit. Yield is expressed as a percentage of moles in this text. The number of moles of liquid product obtained per unit time can be converted or characterized by the mass flow rate of the liquid product, and the number of moles of the feed stream per unit time can be converted or characterized by the mass flow rate of the feed stream. For example, the mass flow rate of the feed stream or liquid product can be expressed as the standard volume of the fluid fed or flowing per unit time, for example, in Nm³ / h (standard cubic meters per hour). The mass flow rate of the liquid product can also be referred to as the output of the liquid product. It can be understood that, for a roughly constant total feed gas volume, different yields of liquid products directly translate to different outputs of liquid products.

[0037] Based on the analysis and consideration of the above circumstances, the present invention aims to provide an air separation device and method that can solve the above problems.

[0038] The inventors analyzed that when the required air product volume differs significantly between design and low-production operating conditions, the amount of feed air also differs significantly between the two conditions. In this situation, under design conditions, the main compressor can normally compress a large mass flow rate of feed air. However, under low-production conditions, because the mass flow rate of feed air passing through the main compressor is too small, the main compressor may experience surge and other problems, leading to malfunction. Therefore, this invention provides the following air separation equipment and method to solve the above problems.

[0039] It is understood that the accompanying drawings in this article are merely examples and are not necessarily drawn to scale, and should not be used as a limitation on the scope of protection of the present invention.

[0040] Figure 1 An exemplary air separation unit 10 according to the present invention is shown. The air separation unit 10 includes a feed line 81 and a waste line 82. The feed line 81 is used to feed at least a portion of the total feed gas f0 from the main compressor 61 via the main heat exchanger 1 to the distillation column system 2. The waste line 82 is used to discharge waste gas W0 from the distillation column system 2 via the main heat exchanger 1.

[0041] A compressor is a device assembled for compressing a stream of gaseous or at least partially gaseous fluid. During compression, the device pressurizes and heats the stream. A compressor may include multiple compression stages, all housed in the same housing or connected to the same drive shaft. The stream may be compressed through all or only a portion of the compression stages. Each compression stage of the compressor may be, for example, a piston, screw, or turbine type. An expander is a device assembled for expanding a stream of fluid. During expansion, the device cools and depressurizes the stream. An expander may be, for example, a piston, screw, or turbine type. Typically, the stream is gaseous or at least partially gaseous. An expander may be coupled to other expanders or energy converters such as hydraulic brakes, generators, or auxiliary compressors via a common shaft. When an expander is coupled to a compressor, the assembly consisting of the expander, compressor, etc., is called an expander-boost compressor. In an expander-boost compressor, the compressor is driven by one or more expanders; that is, the expansion work done in the expander is converted into the compression work of the compressor. At this point, the expander and compressor can be referred to as the expansion end and boosting end of the expander-booster, respectively, and the compressor is often called a booster. The expansion end and boosting end are mechanically connected in a suitable manner. This "mechanical connection" can be understood as achieving a fixed or adjustable speed relationship between these rotating components through mechanical parts such as drive shafts, gears, and belts.

[0042] The "main compressor," also known as the main air compressor (MAC), is, as the name suggests, a compressor. The main compressor compresses all or most of the feed air entering the air separation unit, and is typically located before the purification unit within the air separation unit that purifies the feed air. This entire or most of the feed air can be referred to as the total feed gas. For example, in the MAC / BAC method, the main compressor typically compresses the total feed gas to a pressure comparable to the highest operating pressure of the distillation column system. The highest operating pressure of the distillation column system is also the operating pressure of the high-pressure column. As another example, in the HAP method, the main compressor typically compresses the total feed gas to a pressure significantly higher than the highest operating pressure of the distillation column system. The main compressor is usually a compressor driven by external energy.

[0043] A distillation column system is used to separate feed air into air products of various compositions. A distillation column system includes distillation columns, which utilize cryogenic distillation technology to separate air into gaseous or liquid products of varying purities, such as nitrogen (GAN), liquid nitrogen (LIN), oxygen (GOX), and liquid oxygen (LOX). Distillation column systems can be single-column or multi-column, commonly, for example, in a two-column configuration. Multi-column distillation column systems typically also include a condenser / evaporator to facilitate heat exchange between the streams flowing between the two columns.

[0044] A "main heat exchanger" is used to cool feed air, such as warm compressed air and one or more cold streams, or low-temperature liquid air products and one or more warm streams, when indirectly exchanging heat with the return streams from the distillation column system of an air separation unit. The main heat exchanger can be formed by a single heat exchanger section or multiple heat exchanger sections connected in parallel and / or in series. Each heat exchanger section, for example, consists of one or more plate heat exchanger blocks. The plate heat exchanger blocks can have channels that are separated from each other and have heat exchange surfaces, through which different streams flow, thereby being cooled or heated separately. Commonly, the main heat exchanger can be an aluminum brazed plate-fin heat exchanger (BAHX). "Complete cooling" means that the stream being cooled enters the main heat exchanger at the hot end and is then cooled to the cold end temperature of the main heat exchanger; that is, the stream being cooled exits from the cold end of the main heat exchanger. "Partial cooling" means that the cooled stream is cooled to an intermediate temperature between the hot and cold ends of the main heat exchanger; that is, the cooled stream exits from the middle position between the hot and cold ends of the main heat exchanger. Similarly, "complete heating" means that the heated stream exits from the hot end of the main heat exchanger and is heated to the hot end temperature. "Partial heating" means that the heated stream exits from the middle position of the main heat exchanger and is heated to an intermediate temperature.

[0045] Figure 2 An air separation unit 10a is shown as a comparative example. Compared to... Figure 2The comparative example of the air separation unit 10a also includes an additional pipeline 83 and an additional expander 3. Figure 2 and Figure 1 In this context, identical or similar components are labeled with the same or similar designations to omit parts of the description and make the overall description more concise.

[0046] It is understandable that the text uses "upstream" and "downstream" to describe relative positions, both of which are relative to the flow direction of the corresponding stream in the pipeline. The corresponding stream flows to a relatively upstream position and then to a relatively downstream position. Therefore, the text sometimes refers to "upstream" as "before" and "downstream" as "after".

[0047] It can also be understood that the terms "pipeline," "pipeline," and "pipe segment" used in the text all refer to the route through which the flow stream passes, without limiting the physical form of the corresponding components. Taking "pipeline" as an example, a pipeline can refer to a segment of a complete pipeline. A pipeline can also be a combination of multiple pipelines connected sequentially. These multiple pipelines can be connected by pipe fittings or other pipeline components such as valves. The space through which the flow stream passes in the pipe fittings or other pipeline components can also be considered part of the pipeline. For example, Figure 2 Taking feed line 81 as an example, feed line 81 can substantially include the main feed line 810 located before position Z31, or it can include two branch feed lines 811 and 812 branching off downstream of position Z31. Taking feed line 811 as an example, feed line 811 includes not only pipe sections located upstream and downstream of the main heat exchanger 1, but also the space within the main heat exchanger 1 for the corresponding flow stream to pass through.

[0048] The auxiliary pipeline 83 extends from position Z31 of the feed pipeline 83 before the main heat exchanger 1 and leads to position Z32 of the waste discharge pipeline 82 between the main heat exchanger 1 and the distillation column system 2. That is, the upstream end of the auxiliary pipeline 83 connects to position Z31 of the feed pipeline 83 upstream of the main heat exchanger 1, and the downstream end connects to position Z32 of the waste discharge pipeline 82 between the main heat exchanger 1 and the distillation column system 2. In other words, the auxiliary pipeline 83 can ultimately channel a portion f3 of the total feed gas f0 in the feed pipeline 83 into the waste gas W0 in the waste discharge pipeline 82. To distinguish it from other subsequent sections, this portion f3 of the total feed gas f0 can be referred to in this text as the third portion f3 of the total feed gas f0. For ease of description and understanding, it is sometimes also referred to as the third portion feed gas f3 or the auxiliary stream f3.

[0049] An auxiliary expander 3 is installed in the auxiliary pipeline 83, so that the stream f3 in the auxiliary pipeline 83 is expanded by the auxiliary expander 3 and then sent to the waste discharge pipeline 82. That is, the auxiliary pipeline 83 can send the third part of the feed gas f3 from the upstream position Z31 of the main heat exchanger 1 of the feed pipeline 83 into the inlet of the auxiliary expander 3, and then send the expanded and cooled third part of the feed gas f3 from the outlet of the auxiliary expander 3 into the waste discharge pipeline 82.

[0050] It is understood that when the text describes a stream entering the first and second elements sequentially, or uses similar descriptions, it only indicates the order in which the stream enters the first and second elements. It does not preclude the possibility that the stream passes through a third element between the first and second elements, nor does it preclude the possibility that the stream passes through a third element before or after the first element. For example, describing the auxiliary pipe 83 from position Z31 to position Z32 does not preclude the possibility that the auxiliary pipe 83 mentioned above passes through the auxiliary expander 3 between positions Z31 and Z32, nor does it preclude the possibility that, as will be described later, the auxiliary compressor 4, main heat exchanger 1, etc., may pass before the auxiliary expander 3.

[0051] It is understood that, as mentioned above, the description of each component or process only indicates that the stream passes through or sequentially passes through the aforementioned components or processes, and does not exclude the possibility of other components or processes passing through before, after, or in between. For example, before being fed into the distillation column 81, the feed stream s0 can be dried, purified, etc., using specific processes or devices, such as through an absorber, filter, or additional heat exchanger.

[0052] Compared to Figure 2 As a comparative example, in the air separation unit 10a, under low-production conditions, a total feed gas f0 exceeding the required mass flow rate (corresponding to the sum of the mass flow rates of feed gases f1 and f2) can be fed into the main compressor 61. This excess feed gas f3 is then led out through an auxiliary pipeline 83 instead of being sent to the distillation column system 2. Therefore, a relatively large mass flow rate of the total feed gas f0 can be maintained through the main compressor 61 without causing surge or other malfunctions. Specifically, the mass flow rate of the total feed gas f0 passing through the main compressor 61 can be greater than or equal to the minimum mass flow rate that the main compressor 61 can withstand, which can be determined based on the actual performance of the main compressor 61.

[0053] Furthermore, in the aforementioned air separation unit 10, after the feed gas f3 in the auxiliary pipeline 83 is subjected to expansion and refrigeration treatment, it is sent to the main heat exchanger 1a for heat absorption and vaporization, and can then be fed to other parts of the feed gas that serve as raw material flow. Figure 1In this system, the feed gases f1 and f8 provide cooling. That is, through the above arrangement, the additional feed gas f3 (excess amount compared to actual demand) can provide cooling to the distillation column system 2, thus producing more liquid products, more specifically, more liquid products. Specifically, "more liquid products" essentially refers to a higher yield of liquid products; after all, it is inappropriate to discuss liquid product output without considering the mass flow rate of the feedstock (i.e., the feed rate of distillation column system 2). It is understood that users typically prefer to obtain larger quantities of liquid products because they are easy to store and expensive.

[0054] Furthermore, in the aforementioned air separation unit 10, the third portion of the feed gas f3 in the auxiliary pipeline 83 merges with the exhaust gas W0 and flows in the exhaust pipeline 83, following the exhaust gas W0 into the main heat exchanger 1a. Therefore, it is unnecessary to design a separate channel in the main heat exchanger 1a for the flow of the third portion of the feed gas f3. Consequently, no structural modifications to the main heat exchanger 1a are required, significantly reducing costs.

[0055] Furthermore, in the aforementioned air separation unit 10, a larger portion of the feed gas can be separated into liquid products, such as liquid oxygen. Therefore, in reality, even considering only the amounts of the first portion of feed gas f1 and the second portion of feed gas f2 fed to the distillation column system 2, this amount of feed gas can be higher than the amount of feed gas required for the comparative proportion, which has a small amount or does not convert to liquid products, under the unimproved design. Consequently, it is easier to achieve the minimum mass flow rate that the main compressor 61 can withstand.

[0056] Figure 1 The air separation unit 10 may also include a regulating device 51. The regulating device 51 is used to regulate the mass flow rate of the stream f3 flowing from the feed line 81 to the auxiliary line 83. For example, the regulating device 51 may be a regulating valve provided in the auxiliary line 83, which can, for example, regulate the mass flow rate of the stream f3 to zero.

[0057] Figure 1 In this process, the air separation unit 10 may further include an auxiliary compressor 4. The auxiliary compressor 4 may be located in the auxiliary pipeline 83 and upstream of the auxiliary expander 3, so that the stream f3 in the auxiliary pipeline 83 is pressurized by the auxiliary compressor 4 and then enters the auxiliary expander 3 for expansion. The increased pressure of the third portion of feed gas f3 after being compressed by the auxiliary compressor 4 can increase the expansion ratio of the auxiliary expander 3. Moreover, the volumetric flow rate of the third portion of feed gas f3 after being compressed by the auxiliary compressor 4 will be smaller, making it easier for it to enter the auxiliary expander 3.

[0058] Figure 1In this configuration, the auxiliary pipeline 83 can reach the auxiliary expander 3 downstream of the auxiliary compressor 4 via the first Z11 and the second Z12 of the main heat exchanger 1. The first Z11 is a hotter position relative to the second Z12. That is, when the auxiliary stream f3 in the auxiliary pipeline 83 flows through the main heat exchanger 1, it changes from the hotter stream to the colder stream as it flows from the first Z11 to the second Z12. In other words, the auxiliary stream f3 first enters the auxiliary compressor 4 for pressurization, then enters the main heat exchanger 1 for cooling, and finally enters the auxiliary expander 3 for expansion. Furthermore, Figure 1 In this configuration, the first Z11 can be the hot end of the main heat exchanger 1. The second Z12 can be the middle position of the main heat exchanger 1. In other words, Figure 1 In the process, the auxiliary stream f3 is partially cooled by the main heat exchanger 1. After being cooled by the main heat exchanger 1, the auxiliary stream f3, at a lower temperature, expands through the auxiliary expander 3, resulting in higher efficiency for the auxiliary expander 3. Furthermore, the auxiliary stream f3, after being cooled by the main heat exchanger 1 and expanded by the auxiliary expander 3, can easily reach an even lower temperature, thus making it not significantly different from the temperature of the exhaust gas W0.

[0059] like Figure 1 As shown, the third feed gas f3, after passing through the auxiliary compressor 4, can be cooled by the aftercooler 52. That is, the aftercooler 52 is located downstream of the auxiliary compressor 4 and upstream of the auxiliary expander 3, more precisely, upstream of the main heat exchanger 1, which will be mentioned later. In this way, more cooling capacity can be provided through the aftercooler 52.

[0060] An aftercooler is used to cool the high-temperature gas exiting the compressor to below 40°C. Under certain operating conditions, the aftercooler can also help condense large amounts of water vapor and deteriorated oil mist into liquid water and oil droplets for removal. Commonly, aftercoolers are water-cooled types that use coolant at lower temperatures. The structure of an aftercooler can be, for example, a tubular type, with the cooling water flowing inside the pipes.

[0061] Figure 1 In this configuration, the auxiliary compressor 4 and the auxiliary expander 3 can be the pressurizing end and the expansion end of the expander-booster compressor 30, respectively, which are mechanically connected. That is, the work done by the expansion of the auxiliary stream f3 in the downstream auxiliary expander 3 is directly converted into the work done by the upstream auxiliary compressor 4 in pressurizing the auxiliary stream f3. In this case, the auxiliary compressor 4 is usually referred to as a booster.

[0062] Combination Figure 1 The present invention also provides an air separation method M0. Air separation method M0 uses an air separation device 10. Essentially, it can also be considered that the air separation device 10 operates by using air separation method M0.

[0063] Air separation method M0 includes feeding at least a portion (the branch feed gases f4 and f8 in the first portion f1 and the second portion f2) of the total feed gas f0 from the main compressor 61 of the air separation unit 10 via the main heat exchanger 1 into the distillation column system 2 as the feed stream of the distillation column system 2. Furthermore, air separation method M0 includes discharging waste gas W0 from the distillation column system 2 via the main heat exchanger 1.

[0064] The air separation method M0 also includes, under predetermined operating conditions, drawing a portion (third part f3) from the total feed gas f0 before the main heat exchanger 1 as an additional stream f3, and causing the additional stream f3 to be expanded and then merged into the waste gas W0 at position Z32 between the main heat exchanger 1 and the distillation column system 2.

[0065] The aforementioned air separation method M0, under the predetermined operating conditions, not only separates the first portion of feed gas f1 and the second portion of feed gas f2, but also separates the total feed gas f0 into a third portion of feed gas f3. This third portion of feed gas f3, after expansion treatment, merges into the waste gas W0, thus providing additional cooling as it vaporizes along with the waste gas W0 through the main heat exchanger 1, thereby increasing the yield or output of liquid products. This predetermined operating condition corresponds to the previously mentioned low-yield operating condition.

[0066] In another operating condition, the total feed gas f0 is only split into the first part feed gas f1 and the second part feed gas f2, without the third part feed gas f3 being drawn out. In this case, the cooling capacity supplied to the system is less, resulting in a lower yield of liquid products. This other operating condition corresponds to the design condition mentioned earlier. Therefore, in the design condition, the auxiliary pipeline 83 and some components on it, such as the auxiliary expander 3 and the auxiliary compressor 4, are essentially inactive, almost disappearing. The auxiliary expander 3 and the auxiliary compressor 4 can be low-pressure air expanders, low-pressure air compressors, etc.

[0067] Figure 1 In the air separation method M0, the additional stream f3 can be pressurized before undergoing the aforementioned expansion process. That is, the additional stream f3 is pressurized first and then expanded.

[0068] Figure 1 In the air separation method M0, the additional stream f3 can be cooled by the main heat exchanger 1a between the aforementioned pressurization process and the aforementioned expansion process. That is, the additional stream f3 is first pressurized, then cooled by the main heat exchanger 1a, and finally undergoes the aforementioned expansion process.

[0069] In the air separation method M0, when the additional stream f3 is cooled by the main heat exchanger 1a, the additional stream f3 can enter from the hot end Z11 of the main heat exchanger 1a and exit from the middle position Z12 of the main heat exchanger 1a. In other words, the additional stream f3 is partially cooled by the main heat exchanger 1a.

[0070] In the air separation method M0, the additional feed gas f3, after being pressurized as described above, can first be cooled by the aftercooler 52 and then by the main heat exchanger 1a. That is, after being pressurized by the auxiliary compressor 4, the third part of the feed gas f3 will be initially cooled by the aftercooler 52 and then further cooled by the main heat exchanger 1a.

[0071] This allows the pressure and temperature of the additional stream f3 to be reduced to a level comparable to the pressure and temperature of the exhaust gas W0 after the aforementioned expansion treatment. In other words, it ensures that the pressure and temperature of the additional stream f3 match the pressure and temperature of the exhaust gas W0 that will flow into it. Here, "comparable" does not require absolute mathematical equality, but rather allows for a certain degree of difference. For example, the temperature difference between the additional stream f3 and the exhaust gas W0 is within 20°C, preferably within 5°C or even 2°C; the pressure difference between the additional stream f3 and the exhaust gas W0 is within 0.1 bar, preferably 0.01 bar.

[0072] In air separation method M0, the ratio of the mass flow rate of the additional stream f3 to the mass flow rate of the total feed gas f0 can be 5% to 20%, for example, 7%. That is, under the aforementioned predetermined operating conditions, the third portion of feed gas f3 accounts for 5% to 20% of the total feed gas f0. The ratio of the mass flow rate of the feed stream (i.e., feed gases f1, f4, f8) of distillation column system 2 under the aforementioned predetermined operating conditions to the mass flow rate under other operating conditions is 40% to 60%, for example, 50%. It can be understood that "other operating conditions" refers to operating conditions other than the aforementioned predetermined operating conditions. For the case where the aforementioned predetermined operating conditions are low-yield operating conditions, other operating conditions are, for example, design operating conditions. It can be understood that, unless otherwise stated, the range values ​​indicated in this text include endpoint values.

[0073] The following is combined with Figure 1 A detailed description of an exemplary process for the air separation unit 10 is provided. Figure 1 In this air separation unit 10, there are two main heat exchangers 1. Main heat exchanger 1a, for example, can heat and vaporize low-pressure product gas, and is often referred to as a low-pressure heat exchanger, while main heat exchanger 1b, for example, can heat and vaporize high-pressure product gas, and is often referred to as a high-pressure heat exchanger. Constructing the main heat exchangers 1 as separate low-pressure and high-pressure heat exchangers can save on the manufacturing cost of the entire main heat exchange unit.

[0074] Feed line 81 may include feed lines 810, 811, 812, 813, 814, 815, 816, 817, 818, etc., for ease of description. It is understood that natural pressure loss is generally not considered when describing pressure in this text. If the pressure difference between corresponding locations is not greater than the natural line loss caused by pressure losses in pipes, heat exchangers, coolers, adsorbers, ordinary regulating valves (non-throttle valves), etc., even if such natural line loss is not insignificant, the pressure is still considered "equal" here. For example, the second portion of feed gas f2 before the recompressor 62 and the first portion of feed gas f1 before the distillation column system 2 are both described as being at a first pressure P1. However, in reality, because the flow paths are not the same, the actual pressure drops experienced by the first portion of feed gas f1 and the second portion of feed gas f2 are not substantially the same; for example, their pressures may be ±1%, 5%, 10%, 20%, or even 50% of the average value. Conversely, the pressure of a stream downstream of certain process steps is described as "lower" or "higher" than the pressure upstream of those process steps only when the corresponding pressure differential is higher than natural line losses, particularly through pressurization by at least one compression stage or depressurization by at least one throttle valve and / or at least one expander. The same applies to the description of temperature. Furthermore, in this case, the corresponding pressure and temperature can be in non-intersecting or overlapping ranges. Specifically, pressure includes, for example, unavoidable or anticipated pressure drops, and temperature includes, for example, unavoidable or anticipated temperature drops.

[0075] Figure 1 In this system, the MAC / BAC method is adopted. In addition to the main compressor 61, the air separation unit 10 also includes a re-compressor 62. The re-compressor 62 further compresses at least a portion of the total feed gas f0, which has already been compressed once by the main compressor 61, to a higher pressure, which can also be referred to as BAC. Figure 1 In this compressor, both the main compressor 61 and the re-compressor 62 are compressors driven by external energy, and are the booster end of the non-expansion booster.

[0076] It is understandable that after various treatments, the feed gas in the text may be in a liquid or gas-liquid mixed state in some locations. However, considering that the various treatments do not change the composition of the corresponding streams, it is sometimes still referred to as gas. For example, the third portion of feed gas f3 after passing through the throttle valve 53, although called gas, is actually a gas-liquid mixed state.

[0077] After being compressed by the main compressor 61, the total feed gas f0 in the feed line 810, such as ambient air at normal pressure and temperature, reaches a first pressure P1 equivalent to the operating pressure of the high-pressure tower 21. Corresponding to the pressure change, the temperature of the stream may also change. Therefore, in some descriptions, when the stream is at a predetermined pressure after a certain treatment, the stream must also be at a corresponding temperature.

[0078] The feed line 810 branches into feed lines 811 and 812 downstream. The total feed gas f0 is divided into a first part f1 (also called the first part feed gas f1), a second part f2 (also called the second part feed gas f2), and a third part f3 (also called the third part feed gas f3). The first part feed gas f1 is cooled by the main heat exchanger 1a after passing through the feed line 811, and then enters the distillation column system 2.

[0079] The distillation column system 2 includes a high-pressure column 21, a low-pressure column 22, and a main condenser-evaporator 23 located between the high-pressure column 21 and the low-pressure column 22. The first part of the feed gas f1 can enter the lower part of the high-pressure column 21 of the distillation column system 2 through the feed line 811.

[0080] After being partially compressed by the compressor 62, a portion of the second feed gas f2, f3 (also referred to as the first branch feed gas f8), reaches the second pressure P2. The second pressure P2 is greater than the first pressure P1.

[0081] After being partially compressed by compressor 62, a portion of the second feed gas f2, f3 (also referred to as the first branch feed gas f8), reaches the second pressure P2. After being completely cooled in the main heat exchanger 1a, the first branch feed gas f8 continues to be fed to the bottom position H3 of the high-pressure tower 21 via feed line 813. As will be described later, after the main heat exchanger 1a, the first branch feed gas f8 in feed line 813 merges with the first branch feed gas f5 into the downstream feed line 818, thus entering the high-pressure tower 21 via feed line 818.

[0082] Figure 1 In this process, a throttling valve 53 is installed on the feed line 813 after the main heat exchanger 1a. That is, the feed gas f8 of the first branch expands and is depressurized and cooled after passing through the throttling valve 53.

[0083] Figure 1 In the process, after being fully compressed by the recompressor, another portion of the second feed gas f2, f4 (also called the second branch feed gas f4), reaches the third pressure P3. The third pressure P3 is greater than the second pressure P2. For example, the recompressor may include multiple compression stages. The first branch feed gas f8 may be compressed only by the previous compression stage or the first few compression stages (not all compression stages) of the recompressor, while the second branch feed gas f4 may have been compressed by all compression stages of the recompressor.

[0084] Figure 1 It is also shown that, similar to the first branch feed gas f8, another part fi of the second part feed gas f2 (also referred to as the third branch feed gas fi) is also extracted after being partially compressed by the recompressor. Figure 1 In the process, the third branch feed gas fi, after being compressed by the recompressor, also reaches the second pressure P2 and temperature T2. The third branch feed gas fi can be used as instrument gas.

[0085] See also Figure 1 The second branch feed gas f4 in feed line 814 branches into feed lines 815 and 816 at downstream position Z56. That is, the second branch feed gas f4 in feed line 814 splits into the first branch feed gas f5 and the second branch feed gas f6 downstream. In other words, the first branch feed gas f5 and the second branch feed gas f6 are both part of the second branch feed gas f4.

[0086] Feed line 815 can lead to the high-pressure column 21 of distillation column system 2 via main heat exchanger 1b (from the hotter to the colder position of main heat exchanger 1b). That is, the feed gas f5 in the first branch of feed line 815 enters the main heat exchanger 1b for example to be completely cooled, and then, for example, is sent to the high-pressure column 21 of distillation column system 2 at a lower position H12.

[0087] Before passing through the main heat exchanger 1b, the feed line 815 can first pass through the compressor 63. That is, the feed gas f5 in the first branch of the feed line 815 can be compressed by the compressor 63, thus increasing the pressure to pressure P31 and the temperature to temperature T31. Then, the feed gas f5 in the first branch at pressure P31 and temperature T31 is completely cooled by the main heat exchanger 1b, and the temperature drops to temperature T32.

[0088] After passing through the main heat exchanger 1b, the feed line 815 first passes through the expander 72 and then reaches the distillation column system 2. That is, the first branch feed gas f5 in the feed line 815, after being cooled by the main heat exchanger 1b, enters the expander 72 for expansion, thus reducing its pressure to pressure P33 and its temperature to temperature T33. As mentioned earlier, after passing through the expander 72, the feed line 815 merges with the feed line 813, which has passed through the throttle valve 53, to form the downstream feed line 817. That is, the first branch feed gas f5 in the feed line 815 and the first branch feed gas f8 in the feed line 813 merge and are jointly sent into the high-pressure column 21 at position H12. Figure 1 In this case, the expander 72 is not the expansion end of the expansion compressor, but rather supplies energy to the outside, for example, it can be connected to a generator.

[0089] Feed line 816 can lead to the high-pressure column 21 of distillation column system 2 via main heat exchanger 1b (from the hotter to the colder position of main heat exchanger 1b). That is, the second branch feed gas f6 in feed line 816 enters the main heat exchanger 1b for example, for partial cooling, and then, for example, is sent to the high-pressure column 21 of distillation column system 2 at a lower position H11.

[0090] After passing through the main heat exchanger 1b, the feed line 816 first passes through the expander 71 and then reaches the distillation column system 2. That is, the second branch feed gas f6 in the feed line 816, after being cooled by the main heat exchanger 1b, enters the expander 71 for expansion, thus reducing its pressure to pressure P62 and its temperature to temperature T62. After passing through the expander 71, the feed line 816 merges with the feed line 811 that has passed through the main heat exchanger 1a. That is, the second branch feed gas f6 in the feed line 816 merges with the first part of the feed gas f1 in the feed line 811 and is jointly sent into the high-pressure column 21 at position H11. Figure 1 In the middle, position H11 is lower than position H12. Figure 1 In this design, expander 71 and compressor 63 can be the expansion end and pressure boosting end of the expander-booster, respectively. This allows for full utilization of expansion work and saves energy.

[0091] Figure 1 In this system, the distillation column system 2 may include a high-pressure column 21, a low-pressure column 22, and a main condenser-evaporator 23. It is understood that the pressures of the high-pressure column 21 and the low-pressure column 22 are relatively high and low, respectively. For example, in some engineering projects, the high-pressure column 21 is also referred to as the medium-pressure column, and the medium-pressure column operates at a higher pressure than the low-pressure column 22.

[0092] The feed line 3, through branching and merging, eventually sends at least a portion of the total feed gas f0 into the high-pressure tower 21 at lower positions H11 and H12, as the raw material flow for the distillation tower system 2.

[0093] Waste discharge line 82 leads from the low-pressure tower 22 to the main heat exchanger 1a (from the colder end to the hotter end). In other words, the waste gas W0 in waste discharge line 82 exits from the low-pressure tower 22, is completely heated by the main heat exchanger 1a, and then discharged. The waste gas W0 discharged from waste discharge line 82 after being heated by the main heat exchanger 1a can be directly discharged into the atmosphere or reused in other devices. Other devices can be, for example, a pre-cooling and purification unit of the air separation unit 10, which can be located between the main compressor 61 and the re-compressor 62, specifically after the main compressor 61 and before the main feed line 810 branches into feed lines 811 and 812.

[0094] Figure 1In this configuration, before reaching the main heat exchanger 1a, the waste gas discharge line 82 passes through a subcooler 91 (from a colder position to a hotter position). In other words, the waste gas W0 in the waste gas discharge line 82, after exiting the low-pressure tower 22, is first fully heated by the subcooler 91, and then heated a second time by the main heat exchanger 1a. Position Z32 is located between the main heat exchanger 1a and the subcooler 91.

[0095] Figure 1 In the middle, between the subcooler 91 and the main heat exchanger 1a, and further between the subcooler 91 and position Z32, the waste discharge pipe 82 also has a branch waste discharge pipe 821 leading out, which introduces a portion of the waste gas W0 (marked as W1 in the figure) into the main heat exchanger 1b, where it is heated into a gaseous state. Additionally, it is worth noting that, as... Figure 1 As shown, the waste discharge pipeline 82 branches into multiple branches at the downstream branch point. Figure 1 In the case of two branches, the location Z32 where the third feed gas f3 merges is set downstream of the branch point to merge into one of the multiple branches, making parameter matching easier. In addition, compared to the upstream main pipeline that has not yet branched, the branch pipe diameter is smaller, so even if merging the third feed gas f3 causes a change in pipe diameter, the pipe diameter will not be too large.

[0096] Figure 1 and Figure 2 Other exemplary piping involved in the distillation column system 2 is also shown. (See attached diagram.) Figure 1 The exemplary construction is described in further detail.

[0097] The oxygen-enriched liquid f50 accumulated at the bottom of the high-pressure tower 21 can be sent to the subcooler 91 for cooling from the bottom position H0, and then after being throttled and expanded by the throttling valve 57, it is sent to the low-pressure tower 22 at position H7. Figure 1 In the middle, between the throttle valve 71 and the subcooler 91, a portion of the liquid flow f501 from the oxygen-enriched liquid f50 can be directed to the dummy argon tower 24, specifically the top condenser in the dummy argon tower 24.

[0098] Under the distillation action of high-pressure tower 21, a nitrogen-rich stream f52 can be drawn from position H2 of high-pressure tower 21. After being cooled by subcooler 91, the nitrogen-rich stream f52 is expanded by throttling valve 52 and then sent to low-pressure tower 22 at position H91 as reflux liquid.

[0099] Under the distillation action of high-pressure tower 21 and the condensation action of main condenser-evaporator 23, nitrogen-rich streams c1 and c2 can be obtained at the top positions H31 and H32 of high-pressure tower 21. Positions H31 and H32 can be approximately at the same height. Nitrogen-rich stream c2 can be cooled by subcooler 91 and then expanded by throttling valve 55, directly as liquid nitrogen product (LIN), for example, stored in a storage tank. Nitrogen-rich stream c1 can be divided into two parts: a first part, nitrogen-rich stream c11, and a second part, nitrogen-rich stream c12. The first part, nitrogen-rich stream c11, can be pressurized and pumped to main heat exchanger 1a by pump 65, thus heating it to a gaseous state to form low-pressure nitrogen product (LPGAN), for example, at a pressure of 9 bara. The second nitrogen-rich stream C12 can be pressurized by pump 66, then expanded by throttling valve 56, and then sent to the main heat exchanger 1a, thus being heated to a gaseous state to form a high-pressure nitrogen product with a higher pressure than the low-pressure nitrogen product. Figure 1 In this implementation, the high-pressure nitrogen product is actually 31 bara, often referred to as MPGAN in engineering. It can be understood that bar is a unit of pressure, while bara indicates that the pressure is absolute.

[0100] Under the evaporation action of the main condenser-evaporator 23, an oxygen-enriched stream c3 can be drawn out at position H4 of the main condenser-evaporator 23. The oxygen-enriched stream c3 can be divided into three parts: a first part c31, a second part c32, and a third part c33. The first part c31 can be pressurized by pump 67 and pumped to the main heat exchanger 1b, thus heating it to a gaseous state to form a low-pressure oxygen product (LPGOX), for example, at a pressure of 14 bara. The second part c32 can be pressurized by pump 68 to a higher pressure than the aforementioned low-pressure oxygen product and pumped into the main heat exchanger 1b, thus heating it to a gaseous state to form a high-pressure oxygen product (HPGOX), for example, at a pressure of 31 bara. The third part c33 can be cooled by subcooler 91 and then expanded by throttling valve 54, directly serving as a liquid oxygen product (LOX).

[0101] Figure 1 In the process, feed line 817, formed by the convergence of feed lines 813 and 815, branches off at position Z17 before reaching distillation column system 2 (specifically, position H12). The stream f18 in branch line 818 (a portion of the stream formed by the convergence of feed gas f3 and feed gas f5) is cooled by subcooler 91, then expanded by throttling valve 58, and finally sent to low-pressure column 22 at position H8.

[0102] Figure 1The diagram also shows oxygen-enriched gas f71 drawn from position H5 of low-pressure tower 22 and sent to dummy argon tower 24, and crude argon gas f72 produced from dummy argon tower 24. The crude argon gas f72 from dummy argon tower 24 is heated by subcooler 91 and then enters main heat exchanger 1b for further heating.

[0103] Figure 1 The diagram also shows oxygen-enriched purge stream f61 and oxygen-enriched stream f62 fed from the dummy argon column 24 into the low-pressure column 22 at positions H61 and H62. The oxygen-enriched purge stream f61 can exit from the bottom of the top condenser in the dummy argon column 24.

[0104] See also Figure 1 In high-pressure tower 21, from lowest to highest, the positions are H0, H11, H12, H2, and H31, with positions H31 and H32 at approximately the same height. In low-pressure tower 22, from lowest to highest, the positions are H5, H61, H62, H7, H8, H9, and H10.

[0105] The following provides a specific example of the application of the air separation unit 10 and air separation method M0 described above. Before being compressed by the main compressor 61, the total feed gas f0 in the feed line 810 is at normal pressure and temperature. For example, the temperature is 32°C and the pressure is 1 bara. The operating pressures of the low-pressure tower 22 and the high-pressure tower 21 are 1.2 bara and 5.5 bara, respectively.

[0106] In the design mode, the total feed gas f0 in feed line 810 has a mass flow rate of 213,500 Nm3 / h. The mass flow rate of the feed stream (f1+f4+f8) in distillation column system 2 is 209,500 Nm3 / h. After compression by the main compressor 61, the total feed gas f0 reaches 5.6 bara and 100°C. After the total feed gas f0 is split, the mass flow rates of the first part feed gas f1 and the second part feed gas f2 are 54,400 Nm3 / h and 159,100 Nm3 / h, respectively. That is, the mass flow rate of the third part feed gas f3 can be made zero by adjusting device 5. After the second part feed gas f2 is split, the mass flow rates of the first branch feed gas f8, the second branch feed gas f4, and the third branch feed gas f1 are 24,000 Nm3 / h, 131,100 Nm3 / h, and 4,000 Nm3 / h, respectively.

[0107] In low-production mode, the mass flow rate of the total feed gas f0 in feed line 810 is 161,900 Nm3 / h. After compression by the main compressor 61, the total feed gas f0 reaches 5.5 bara and 100°C. After the total feed gas f0 is split, the mass flow rates of the first part feed gas f1 and the second part feed gas f2 are 7,600 Nm3 / h and 140,500 Nm3 / h, respectively. That is, by adjusting device 5, the mass flow rate of the third part feed gas f3 can be made 13,800 Nm3 / h. After the second part feed gas f2 is split, the mass flow rates of the first branch feed gas f8, the second branch feed gas f4, and the third branch feed gas f1 are 12,000 Nm3 / h, 124,500 Nm3 / h, and 4,000 Nm3 / h, respectively. Therefore, the mass flow rate of the feed stream (f1+f4+f8) in distillation column system 2 is 144100 Nm3 / h.

[0108] After being compressed by the auxiliary compressor 4, the third-section feed gas f3 is pressurized and heated to 9.2 bara and 80°C. After being cooled by the aftercooler 52, the third-section feed gas f3 is cooled to 36°C. Then, after being partially cooled by the main heat exchanger 1a, the third-section feed gas f3 is cooled to -90°C. After being expanded by the auxiliary expander 3, the third-section feed gas f3 is depressurized and cooled to 1 bara and -165°C. Among them, the waste nitrogen W0 is 1 bara and -177°C before entering the main heat exchanger 1a.

[0109] Table 1 below lists the comparison of the parameters generated under the two modes in the specific examples above.

[0110] Table 1

[0111]

[0112]

[0113] In the example above, compared to the design mode, HPGOX's mass flow rate did not decrease in low-production mode. This poses a significant challenge to the variable loads of all units in the air separation unit.

[0114] Table 1 above shows that, in low-production mode, the yield of liquid oxygen (LOX) and even liquid nitrogen (LIN) can be significantly increased. In practice, the control system can be used to adjust the yield of liquid oxygen and liquid nitrogen products in low-production mode.

[0115] Unless otherwise clearly indicated, each aspect or embodiment defined herein may be combined with any other aspect or embodiment. In particular, any feature indicated as preferred or advantageous may be combined with any other feature indicated as preferred or advantageous.

[0116] The embodiments described in this specification are merely preferred embodiments of the present invention. These embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the invention. Any technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation should be within the scope of the present invention.

Claims

1. An air separation unit, comprising a feed line and a waste discharge line, wherein the feed line is used to supply at least a portion of the total feed gas from a main compressor via a main heat exchanger to a distillation column system, and the waste discharge line is used to discharge waste gas from the distillation column system via the main heat exchanger, characterized in that, The air separation equipment also includes: An additional pipeline extends from the feed line upstream of the main heat exchanger and leads to the exhaust line between the main heat exchanger and the distillation column system; and An additional expander is installed in the additional pipeline so that the stream in the additional pipeline is expanded by the additional expander and then sent into the waste discharge pipeline.

2. The air separation equipment as described in claim 1, characterized in that, Also includes: A regulating device for regulating the mass flow rate of the stream flowing from the feed line to the auxiliary line.

3. The air separation equipment as described in claim 1, characterized in that, Also includes: An auxiliary compressor is provided in the auxiliary pipeline and upstream of the auxiliary expander, such that the stream in the auxiliary pipeline is pressurized by the auxiliary compressor and then enters the auxiliary expander for expansion.

4. The air separation equipment as described in claim 3, characterized in that, The additional pipeline extends downstream of the additional compressor, passing sequentially through the first and second positions of the main heat exchanger to the additional expander, wherein the first position is a hotter position relative to the second position.

5. The air separation equipment as described in claim 4, characterized in that, Also includes: An aftercooler is provided in the additional piping and between the additional compressor and the main heat exchanger.

6. The air separation equipment as described in claim 4, characterized in that, The first position is the hot end of the main heat exchanger; and / or The second position is the middle position of the main heat exchanger.

7. The air separation equipment as described in claim 3, characterized in that, The auxiliary compressor and the auxiliary expander are the pressurizing end and the expanding end of the expander, respectively, which are mechanically connected in the expander.

8. An air separation method using an air separation unit, the air separation method comprising feeding at least a portion of a total feed gas from the main compressor of the air separation unit via a main heat exchanger to a distillation column system as a feed stream for the distillation column system, and discharging waste gas from the distillation column system via the main heat exchanger, characterized in that, The space separation method further includes: Under predetermined operating conditions, a portion of the total feed gas is drawn off as an additional stream before the main heat exchanger, and this additional stream is expanded and then merged into the waste gas at a location between the main heat exchanger and the distillation column system.

9. The space separation method as described in claim 8, characterized in that, This causes the additional stream to be pressurized before undergoing the expansion process.

10. The space separation method as described in claim 9, characterized in that, This allows the additional stream to be cooled via the main heat exchanger between the pressurization process and the expansion process.

11. The space separation method as described in claim 10, characterized in that, This causes the additional stream to be cooled first by an aftercooler after the pressurization process, and then by the main heat exchanger.

12. The space separation method as described in claim 10, characterized in that, When the additional stream is cooled by the main heat exchanger, the additional stream enters from the hot end of the main heat exchanger and exits from the middle position of the main heat exchanger. This causes the pressure and temperature of the additional stream to decrease to a level comparable to the pressure and temperature of the exhaust gas after the expansion treatment.

13. The air separation method according to any one of claims 8 to 12, characterized in that, The ratio of the mass flow rate of the additional stream to the mass flow rate of the total feed gas is 5% to 20%. The ratio of the mass flow rate of the feed stream in the distillation column system under the predetermined operating conditions to the mass flow rate under other operating conditions is 40% to 60%.

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