An air separation system and a method of controlling an air separation system
By using two air separation units working in tandem, the operation of the air separation system is optimized, solving the problem of high power consumption of the air turbine compressor and achieving energy savings and cost reduction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NINGXIA SHENYIN TEGANG CORP
- Filing Date
- 2022-09-20
- Publication Date
- 2026-05-29
Smart Images
Figure CN115574543B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of cryogenic oxygen production technology, and in particular to an air separation system and a control method for the air separation system. Background Technology
[0002] The air turbine compressor system is a crucial component of an air separation unit. It employs isothermal compression to compress filtered air to the pressure required by the unit, providing the feed gas for operation. Air separation units primarily consume electrical energy, with the air turbine compressor accounting for approximately 95% of the total power consumption during startup. Therefore, in oxygen production using an air separation unit, the continuous operation of the air turbine compressor leads to excessive energy consumption, impacting oxygen production costs. Summary of the Invention
[0003] This application provides an air separation system and a control method for the air separation system to solve the problem of high power consumption in the cryogenic oxygen production process.
[0004] This application provides an air separation system, comprising: a first air separation unit and a second air separation unit, each having a compressor outlet; the compressor outlets of the first and second air separation units are connected; the compressor outlet of the second air separation unit is provided with a first connecting valve; an air-cooled tower, the inlet of which is connected to the compressor outlet of the first air separation unit; a heat exchanger assembly connected to the air-cooled tower; and an air separation tower connected to the heat exchanger assembly, such that air flows into the air separation tower after passing through the heat exchanger assembly, the air separation tower being used to separate a first gas and a second gas from the air.
[0005] In some embodiments, the two ends of the molecular sieve are connected to an air-cooled tower and a heat exchanger assembly, respectively; the molecular sieve consists of two sets.
[0006] In some embodiments, the molecular sieve includes a first inlet port, a second inlet port, and a first outlet port; the heat exchanger assembly includes a first heat exchanger and a second heat exchanger; the first outlet port is connected to the first heat exchanger and the second heat exchanger, and a second connecting valve is provided between the first outlet port and the first heat exchanger, and a third connecting valve is provided between the first outlet port and the second heat exchanger; the first inlet port is connected to the outlet of the air-cooled tower, and the second inlet port is connected to the first heat exchanger.
[0007] In some embodiments, the air separation system further includes a booster turbine expander; the booster turbine expander includes a booster inlet, a booster outlet, an expansion inlet, and an expansion outlet; the gas discharged from the first outlet port enters the booster turbine expander through the booster inlet; the gas in the booster turbine expander enters the first heat exchanger and the second heat exchanger through the booster outlet; the gas in the first heat exchanger and the second heat exchanger enters the booster turbine expander through the expansion inlet; the gas in the booster turbine expander enters the upper air separation column through the expansion outlet.
[0008] In some embodiments, the air separation tower includes an upper air separation tower and a lower air separation tower; the heat exchanger assembly further includes a third heat exchanger; the upper air separation tower includes a second outlet port, a third outlet port, and a fourth outlet port; the air separation system further includes a fourth connecting valve and a fifth connecting valve, the fourth connecting valve being disposed on the outlet pipeline from the second outlet port to the second heat exchanger; so that the gas discharged from the second outlet port, after passing through the third heat exchanger and the second heat exchanger, is connected to the fourth connecting valve; the fourth connecting valve is used to connect the first gas obtained by the air separation tower after opening; the gas discharged from the third outlet port, after passing through the third heat exchanger, is connected to the first heat exchanger, and the third outlet port is used to connect the gas back to the second inlet port; the fifth connecting valve is disposed on the outlet pipeline from the fourth outlet port to the second heat exchanger, so that the gas discharged from the fourth outlet port, after passing through the second heat exchanger, is connected to the fifth connecting valve, and the fifth connecting valve is used to connect the second gas obtained by the air separation tower after opening.
[0009] In some embodiments, the air separation system further includes: a sixth connecting valve, which is disposed between a first flow path and a second flow path, wherein the first flow path is a flow path from the third outlet port through the third heat exchanger to the first heat exchanger; the second flow path is a flow path from the booster turbine expander to the upper air separation column; and the sixth connecting valve is used to guide the gas from the second flow path to the first flow path after being opened.
[0010] In some embodiments, the lower air separation column includes a fifth outlet port, which is connected to the upper air separation column via a third heat exchanger, and a seventh connecting valve is provided between the third heat exchanger and the upper air separation column.
[0011] In some embodiments, the air separation system further includes an eighth connecting valve, a ninth connecting valve, a tenth connecting valve, an eleventh connecting valve, and a twelfth connecting valve; the eighth connecting valve is disposed in the flow path from the first heat exchanger to the second inlet port; the air separation system further includes a third flow path, which is disposed in the exhaust flow path from the third outlet port to the first heat exchanger; the inlet of the third flow path is disposed in the pipeline between the first heat exchanger and the eighth connecting valve, and the outlet of the third flow path is provided with the ninth connecting valve; the upper air separation column further includes a sixth outlet port, after the gas flows out from the sixth outlet port, one flow path enters the lower air separation column through the tenth connecting valve, and the other flow path returns to the upper air separation column through the third heat exchanger, and the eleventh connecting valve is disposed between the third heat exchanger and the upper air separation column; the twelfth connecting valve is disposed in the pipeline between the first heat exchanger, the second heat exchanger, and the expansion inlet of the booster turbine expander.
[0012] In some embodiments, the number of turboexpanders is two, and the two turboexpanders are connected in parallel.
[0013] The second aspect of this application provides a control method for an air separation system, used in the air separation system provided in the first aspect, comprising:
[0014] Start the second air separation unit and its compressor. After the second air separation unit is running normally, open the first connecting valve, control the pressure of the first air separation unit to the first preset pressure, and then start the air-cooled tower.
[0015] After controlling the pressure of the molecular sieve to the second preset pressure, the molecular sieve is turned on;
[0016] Open the second connecting valve. When the gas flow rate in the air-cooled tower reaches the preset flow rate, start a booster turbine expander, close the sixth connecting valve, and adjust the opening of the twelfth connecting valve.
[0017] After air enters the air separation tower, control the tenth and ninth connecting valves to close, adjust the opening of the seventh and eleventh connecting valves according to the pressure of the lower air separation tower and the air intake, adjust the fourth and fifth connecting valves according to the pressure of the upper air separation tower, and open the eighth connecting valve.
[0018] The third connecting valve is adjusted according to the air intake of the first air separation unit and the pressure of the second air separation unit.
[0019] After liquefied gas appears in the air separation tower, adjust the opening of the seventh connecting valve;
[0020] When the amount of liquefied gas in the upper air separation tower exceeds a preset value, the compressor of the first air separation unit is turned on to bring the air separation system into normal operation.
[0021] The air separation system provided in this application uses two air separation units to work together. In the initial stage of use, the second air separation unit is run first, followed by the first air separation unit. At the same time, the compressor of the first air separation unit is not turned on. When the system reaches the point where a certain amount of liquid has accumulated in the air separation tower, the compressor of the first air separation unit is turned on to enable the system to operate normally. This greatly reduces the power consumption while ensuring normal production efficiency, thus achieving the goal of saving electricity. Attached Figure Description
[0022] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0023] Figure 1 This is a schematic diagram of the air separation system in the embodiments of this application;
[0024] Figure 2 This is a flowchart of the air separation system control method in the embodiments of this application.
[0025] Illustration:
[0026] Wherein, 1-first air separation unit, 2-second air separation unit, 3-air-cooled tower, 4-heat exchanger assembly, 41-first heat exchanger, 42-second heat exchanger, 43-third heat exchanger, 5-air separation tower, 51-upper air separation tower, 511-second outlet port, 512-third outlet port, 513-fourth outlet port, 514-sixth outlet port, 52-lower air separation tower, 521-fifth outlet port, 6-first connecting valve, 7-molecular sieve, 71-first inlet port, 72-second inlet port, 73-first outlet port, 8-second connecting valve, 9-third connecting valve, 10-boosting turboexpander, 11-fourth connecting valve, 12-fifth connecting valve, 13-sixth connecting valve, 14-seventh connecting valve, 15-eighth connecting valve, 16-ninth connecting valve, 17-tenth connecting valve, 18-eleventh connecting valve, 19-twelfth connecting valve. Detailed Implementation
[0027] The embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described below do not represent all embodiments consistent with this application. They are merely examples of systems and methods consistent with some aspects of this application as detailed in the claims.
[0028] The basic principle of distillation separation is to separate the components in liquefied air by utilizing their different boiling points. Oxygen has a boiling point of -183℃, and nitrogen has a boiling point of -195.8℃. Air distillation occurs during the heat and mass exchange between the gas and liquid phases of an oxygen-nitrogen mixture. The gas flows from bottom to top, while the liquid flows from top to bottom. This process is accomplished by sieve plates (packing). Because nitrogen evaporates more easily than oxygen and oxygen condenses more easily than nitrogen in an oxygen-nitrogen mixture, the nitrogen concentration increases continuously as the gas passes through each plate (section). With enough plates (packing), high-purity nitrogen can be obtained at the top of the column. Conversely, as the liquid passes through each plate (section), the oxygen concentration increases continuously, resulting in oxygen-rich liquid air at the bottom of the lower column and high-purity liquid oxygen at the bottom of the upper column.
[0029] Example 1:
[0030] See Figure 1 This is a schematic diagram of the structure of an air separation system in this embodiment.
[0031] The air separation system provided in this application includes a first air separation unit 1 and a second air separation unit 2. The compressor outlet of the first air separation unit 1 is connected to the compressor outlet of the second air separation unit 2. The compressor outlet of the second air separation unit 2 is provided with a first connecting valve 6. The air separation system also includes an air-cooled tower 3. The inlet of the air-cooled tower 3 is connected to the compressor outlet of the first air separation unit 1. That is, when the first connecting valve 6 is open, the air discharged from the second air separation unit 2 can flow into the air-cooled tower 3 together with the air discharged from the second air separation unit 2 through the first connecting valve 6. The air discharged from the second air separation unit 2 is controlled by adjusting the opening degree of the first connecting valve 6. The air separation system also includes a heat exchanger assembly 4 and an air separation tower 5. After passing through the air-cooled tower 3, the gas temperature is lower than before entering the air-cooled tower 3. It then enters the heat exchanger assembly 4 for further cooling. Since different gases in the air have different liquefaction temperatures, cooling facilitates the liquefaction of these gases. After entering the heat exchanger assembly 4, the gas enters the air separation tower 5, which is used to collect the first and second gases separated from the air. For example, the first gas is nitrogen, and the second gas is oxygen.
[0032] Specifically, since a first connecting valve 6 is installed at the compressor outlet of the second air separation unit 2, when using this system, the second air separation unit 2 is started first to supply cold air. After the second air separation unit 2 is running stably, the first air separation unit 1 is then started. In this way, the two air separation units work together to provide the air source required for separating the first and second gases in the air separation system. At the same time, when the first air separation unit 1 is started, its compressor is not started temporarily; only ambient temperature air is introduced through the first air separation unit 1. It is understandable that in the field of cryogenic oxygen production, the compressor needs to work constantly, and the compressor's power consumption can reach about 95% of the entire air separation unit. By using the two air separation units in conjunction, and initially running the second air separation unit 2 before running the first air separation unit 1, while temporarily not starting the compressor of the first air separation unit 1, and starting the compressor of the first air separation unit 1 when a certain amount of liquid accumulates in the air separation tower 5, the system can operate normally. This ensures normal production efficiency while greatly reducing power consumption, achieving the goal of saving electricity.
[0033] It is worth noting that the gas referred to in this embodiment includes both gaseous gas and liquefied gas. Since both states coexist during the reaction, they are collectively referred to as gas in the description. Furthermore, the compressors of the first air separation unit 1 and the second air separation unit 2 in this embodiment are air turbine compressors.
[0034] It is understandable that the air-cooled tower 3 cools the air and further removes dust and mechanical impurities by using ambient temperature water and chilled water. The temperature of the gas extracted from the air-cooled tower 3 is usually around 12°C.
[0035] In a feasible embodiment, the first air separation unit 1 has an oxygen production capacity of 30,000 cubic meters per hour, and the second air separation unit 2 has an oxygen production capacity of 40,000 cubic meters per hour. That is to say, during the start-up phase of the air separation units, without affecting the normal operation of the air separation units, the air required for the cooling capacity produced by the booster turbine expander 10 is provided by another large air separation unit (the second air separation unit 2). By adjusting the start-up air separation units, the cooling operation conditions of the air separation units are met, achieving cooling and liquid accumulation in the air separation units. The air turbine compressor is started at the end of the liquid accumulation stage before purification, shortening the start-up time of the air turbine compressor and reducing start-up power consumption. This not only saves electricity but also effectively saves costs.
[0036] In some embodiments, the air separation system further includes a molecular sieve 7 connected between the air-cooled tower 3 and the heat exchanger assembly 4. This allows air exiting the air-cooled tower 3 to pass through the molecular sieve 7 before entering the heat exchanger assembly 4. The function of the molecular sieve 7 is to filter impurities in the gas to be separated, such as water, carbon dioxide, and other hydrocarbons from the air. Because the molecular sieve 7 separates impurities from the air, the gas temperature will slightly rise during operation. Typically, the temperature of the gas exiting the molecular sieve 7 is around 17°C before entering the heat exchanger assembly 4 for heat exchange.
[0037] Specifically, the molecular sieves are in two sets. When the system is running, one set is used for application and the other set is used for regeneration.
[0038] In some embodiments, the molecular sieve 7 includes two inlet ends and one outlet end. The inlet ends are respectively connected to the air-cooled tower 3 and the heat exchanger assembly 4, and the outlet end is connected to the heat exchanger assembly 4. The reason for providing two inlet ends is mainly to realize the gas circulation (simultaneously regenerating a set of molecular sieves) process. Specifically, the heat exchanger assembly 4 includes a first heat exchanger 41 and a second heat exchanger 42. A first outlet port 73 is connected to the first heat exchanger 41 and the second heat exchanger 42, and a second connecting valve 8 is provided at the inlet of the first heat exchanger 41, and a third connecting valve 9 is provided at the inlet of the second heat exchanger 42. It is understandable that the first outlet port 73 of the molecular sieve 7 is connected in parallel with the first heat exchanger 41 and the second heat exchanger 42. That is, when the second connecting valve 8 is open, the gas in the first outlet port 73 can enter the first heat exchanger 41 through the second connecting valve 8. When the second connecting valve 8 is closed, the gas discharged from the first outlet port 73 is directed toward the second heat exchanger 42 and enters the second heat exchanger 42 when the third connecting valve 9 is open. During operation, the opening degree of the second connecting valve 8 and the third connecting valve 9 is adjusted according to the gas temperature at the outlet of the first heat exchanger 41 and the second heat exchanger 42. The second connecting valve 8 is opened first to meet the gas source required for the regeneration of another set of molecular sieves 7. The first air inlet port 71 is connected to the air-cooled tower 3, thereby guiding the gas in the air-cooled tower 3 to the molecular sieve 7 in use. The second air inlet port 72 is connected to the first heat exchanger 41, thereby circulating the gas in the system back to the regenerated molecular sieve 7 through the first heat exchanger 41. On the one hand, the process of removing impurities from the gas is realized, and on the other hand, the desorption process of the regenerated molecular sieve 7 is realized.
[0039] In some embodiments, the air separation system further includes a booster turbine expander 10, which includes a booster inlet, a booster outlet, an expansion inlet, and an expansion outlet. That is, the booster turbine expander 10 pressurizes and expands the gas through these four gas flow ports. Specifically, the gas discharged from the first outlet port 73 enters the booster turbine expander 10 through the booster inlet; the gas inside the booster turbine expander 10 enters the first heat exchanger 41 and the second heat exchanger 42 through the booster outlet; the gas inside the first heat exchanger 41 and the second heat exchanger 42 enters the booster turbine expander 10 through the expansion inlet; and the gas inside the booster turbine expander 10 enters the upper air separation column 51 through the expansion outlet.
[0040] Specifically, the gas discharged from the first outlet port 73 of the molecular sieve 7 flows towards the first heat exchanger 41 in one direction, and is diverted from the above-mentioned flow path to the booster turbine expander 10 in another direction.
[0041] It is understood that any one of the first heat exchanger 41, the second heat exchanger 42, and the third heat exchanger 43 in this application can be a single heat exchanger or a heat exchanger composed of multiple heat exchange tanks. That is, the first heat exchanger 41 can be a single heat exchanger or multiple heat exchange tanks. For example, the first heat exchanger 41 consists of two independent heat exchange tanks, used for heat exchange between the air exiting the molecular sieve 73 and the returned waste nitrogen gas from the third outlet port 512. This is regulated by the second connecting valve 8, which needs to be fully opened to ensure the regeneration gas supply for the regenerated molecular sieve 7. For example, the second heat exchanger 42 consists of seven heat exchange tanks, used for heat exchange between the air exiting the molecular sieve 7 and the nitrogen gas from the second outlet port 511 and the oxygen gas from the fourth outlet port 513. This is regulated by the third connecting valve 9, which only needs to be slightly opened for adjustment at this stage. The third heat exchanger 43 is used for heat exchange between nitrogen and waste nitrogen returned from the second outlet port 511 and the third outlet port 512 of the upper air separation column at low temperature and liquid nitrogen and liquid air from the sixth outlet port 514 and the fifth outlet port 521. In some embodiments, the air separation column 5 includes an upper air separation column 51 and a lower air separation column 52, and the heat exchanger assembly 4 further includes the third heat exchanger 43. The upper air separation column 51 includes multiple outlet ports, specifically including a second outlet port 511, a third outlet port 512, and a fourth outlet port 513. The air separation system also includes a fourth connecting valve 11 and a fifth connecting valve 12. The fourth connecting valve 11 is located on the outlet pipeline from the second outlet port 511 to the second heat exchanger 42. That is, the liquefied gas in the upper air separation column 51 can be discharged through the second outlet port 511, and then through the third heat exchanger 43 and the second heat exchanger 42 before being connected to the fourth connecting valve 11. When the fourth connecting valve 11 is open, the first gas produced can be discharged.
[0042] The fifth connecting valve 12 is installed on the outlet pipeline in the direction of the fourth outlet port 513 and the second heat exchanger 42. That is to say, the liquefied gas in the upper air separation tower 51 can be discharged through the fourth outlet port 513, and after passing through the second heat exchanger 42, the gas is conducted to the fifth connecting valve 12. When the fifth connecting valve 12 is open, the second gas produced can be discharged.
[0043] The gas discharged from the third outlet port 512 can be conducted to the first heat exchanger 41 through the third heat exchanger 43, and then back to the second inlet port 72 through the first heat exchanger 41, thereby realizing the process of gas circulation into the molecular sieve 7 for regeneration.
[0044] Specifically, the fourth connecting valve 11 is a pure nitrogen vent valve, and the fifth connecting valve 12 is a pure oxygen vent valve.
[0045] In some embodiments, the air separation system is further provided with a sixth connecting valve 13, which is located between the first flow path and the second flow path. The first flow path is a flow path in which gas is conducted from the third outlet port 512 through the third heat exchanger 43 to the first heat exchanger 41. The second flow path is a flow path in which gas flows from the booster turbine expander 10 to the upper air separation column 51. The sixth connecting valve 13 is located between the first flow path and the second flow path. When the sixth connecting valve 13 is open, the gas in the second flow path flows into the first flow path. That is, the gas exported from the booster turbine expander 10 enters the upper air separation column 51 directly, and flows to the first heat exchanger 41. After being heated by the first heat exchanger 41, it is conducted back into the molecular sieve 7 and then vented, thereby realizing the gas circulation process inside the system.
[0046] For example, the sixth connecting valve 13 is an expansion air bypass valve into the nitrogen-contaminated pipeline.
[0047] In some embodiments, the lower air separation column 52 includes a fifth gas outlet port 521, which is connected to the upper air separation column 51 via a third heat exchanger 43. A seventh connecting valve 14 is provided in the direction from the third heat exchanger 43 to the upper air separation column 51. That is, when the seventh connecting valve 14 is open, the gas in the lower air separation column 52 is conducted to the upper air separation column 51 after heat exchange by the third heat exchanger 43.
[0048] For example, the seventh connecting valve 14 is the liquid air inlet valve for the upper tower.
[0049] In some embodiments, the air separation system further includes an eighth connecting valve 15, a ninth connecting valve 16, a tenth connecting valve 17, an eleventh connecting valve 18, and a nineteenth connecting valve 19. The eighth connecting valve 15 is located on the return gas (regeneration gas) pipeline of the molecular sieve 7, specifically on the return gas path from the first heat exchanger 41 to the second inlet port 72. This allows gas passing through the first heat exchanger 41 to be conducted back into the molecular sieve 7 via the second inlet port 72 when the eighth connecting valve 15 is open. Simultaneously, the air separation system is provided with a third flow path, located on the exhaust flow path from the third outlet port 512 to the first heat exchanger 41. The inlet of the third flow path is located on the flow path between the first heat exchanger 41 and the eighth connecting valve 15. In other words, the flow path between the first heat exchanger 41 and the eighth connecting valve 15 branches outward to form the third flow path, and the outlet end of the third flow path is provided with the ninth connecting valve 16. The ninth connecting valve 16 is used to discharge impure gas. Specifically, the ninth connecting valve 16 is a waste nitrogen to cooling tower valve, which mainly introduces waste nitrogen into the cooling tower.
[0050] For example, the eighth connecting valve 15 is the valve for sending waste nitrogen to the molecular sieve 7 regeneration gas, the ninth connecting valve 16 is the valve for sending waste nitrogen to the water cooling tower, the tenth connecting valve 17 is the valve for liquid nitrogen reflux to the lower tower, and the eleventh connecting valve 18 is the valve for liquid nitrogen to the upper tower. The twelfth connecting valve 19 is installed on the pipeline between the first heat exchanger 41 and the second heat exchanger 42 and the expansion inlet of the booster turbine expander 10.
[0051] The upper air separation column 51 also includes a sixth outlet port 514, which is located at the bottom of the upper air separation column 51, near the lower air separation column 52. After the gas flows out of the sixth outlet port 514, one flow path passes through the tenth connecting valve 17 into the lower air separation column 52. That is, when the tenth connecting valve 17 is open, the gas in the upper air separation column 51 can enter the lower air separation column 52 through the tenth connecting valve 17. Another flow path returns the gas to the upper air separation column 51 through the third heat exchanger 43, and the eleventh connecting valve 18 is located on this flow path. The eleventh connecting valve 18 is located on the pipeline between the third heat exchanger 43 and the upper air separation column 51. That is, when the eleventh connecting valve 18 is open, the gas at the bottom of the upper air separation column 51 passes through the third heat exchanger 43 and then flows back to the upper part of the upper air separation column 51 through the eleventh connecting valve 18.
[0052] In some embodiments, the number of booster turbine expanders 10 is two, and the two booster turbine expanders 10 are arranged in parallel. The use of two booster turbine expanders 10 ensures the stability of the air separation system operation.
[0053] Example 2:
[0054] This application provides a control method for an air separation system, such as... Figure 2The diagram shown is a flowchart of this control method. Specifically, it includes:
[0055] Step S102: Start the second air separation unit and its compressor, and after the second air separation unit is running normally, open the first connecting valve, control the pressure of the first air separation unit to the first preset pressure, and then start the air-cooled tower.
[0056] After the second air separation unit is turned on and is running normally (the compressor of the second air separation unit is turned on normally), the first connecting valve is opened to increase the pressure of the first air separation unit to the first preset pressure, where the first preset pressure is the working pressure of the first air separation unit. At this time, the compressor of the first air separation unit is not turned on while the first air separation unit is turned on, and the air-cooling tower is turned on for pre-cooling. At this time, attention should be paid to the opening of the air guide vanes at the inlet of the compressor of the second air separation unit to ensure that the air pressure entering the tower of the second air separation unit is stable.
[0057] Step S104: Start the molecular sieve operation program, control the pressure of the molecular sieve to the second preset pressure, and then turn on the molecular sieve.
[0058] This step is mainly to ensure the operational stability of the molecular sieve. The second preset pressure is the working pressure of the molecular sieve.
[0059] Step S106: Open the second connecting valve. When the gas flow rate in the air-cooled tower reaches the preset flow rate, start a booster turbine expander, close the sixth connecting valve, and adjust the opening of the twelfth connecting valve.
[0060] Open the second connecting valve to allow the air in the molecular sieve to enter the first heat exchanger for heat exchange. This process is slow and synchronized with the load of the compressor in the second air separation unit. At this time, the second connecting valve is open and the sixth connecting valve is closed. One stream of gas enters the first heat exchanger from the molecular sieve, while the other stream of gas is diverted from the above-mentioned flow path to the booster turbine expander and then enters the upper air separation tower.
[0061] In one feasible embodiment, the preset flow rate is 20000m³ / h. 3 / h, of course, the preset flow rate can be adaptively adjusted according to the parameters of the first air separation unit and the second air separation unit.
[0062] Step S108: After air enters the air separation tower, control the tenth and ninth connecting valves to close, adjust the opening of the seventh and eleventh connecting valves according to the pressure of the lower air separation tower and the air intake volume, adjust the fourth and fifth connecting valves according to the pressure of the upper air separation tower, and open the eighth connecting valve.
[0063] At this point, the tenth and ninth connecting valves are closed. The pressure in the lower air separation column is now greater than the pressure in the upper air separation column. Gas from the lower column is regulated and enters the upper air separation column via the seventh and eleventh connecting valves. This gas is now cold, gaseous air. Simultaneously, the fourth and fifth connecting valves are adjusted according to the pressure in the upper air separation column. The eighth connecting valve is opened to ensure the flow of regenerated gas for the molecular sieve and maintain a stable temperature decrease within the column. When the eighth connecting valve is opened, the liquid in the upper air separation column, after passing through the third and first heat exchangers, becomes ambient-temperature gas and is returned to the regenerated molecular sieve.
[0064] Step S110: Adjust the third connecting valve according to the air intake of the first air separation unit and the pressure of the second air separation unit.
[0065] As the temperature inside the air separation tower decreases, the intake air volume of the first air separation unit increases, and the compressor of the second air separation unit slowly increases its load. At this time, the temperature of the first air separation unit drops, and the intake air volume gradually increases. To maintain the stability of the system pressure and ensure that it does not exceed the design current, the second and third connecting valves are mainly opened for adjustment. This ensures the molecular sieve regeneration gas volume and the temperature difference of each heat exchanger after adjustment, reduces cold loss, and accelerates the cooling process of the system.
[0066] Step S112: After liquefied gas appears in the air separation tower, adjust the opening of the seventh connecting valve.
[0067] Specifically, liquefied air in the upper air separation column enters the lower air separation column. The seventh connecting valve is opened as the liquefied air level rises to accelerate liquid accumulation, while the tenth connecting valve remains closed.
[0068] Step S114: When the amount of liquefied gas in the upper air separation tower is greater than the preset value, start the compressor of the first air separation unit to bring the air separation system into normal operation.
[0069] Once the air separation liquid level stabilizes and rises above the preset value, the compressor of the first air separation unit is started. At this time, the air intake volume increases, sending air into the air-cooling tower. The compressor of the second air separation unit reduces its load to the opening of the guide vanes during normal production. The operating conditions of the first air separation unit are adjusted so that the air separation system enters normal operating condition and the quality of the oxygen and nitrogen products is qualified. The method of using the two air separation units in this embodiment in combination and starting the compressor of one air separation unit first can effectively save energy and achieve cost savings.
[0070] For example, the preset value is 3000mm. Of course, the preset value can be adjusted according to the parameters of the first air separation unit and the second air separation unit.
[0071] Taking the first air separation unit with an air intake of 30,000 cubic meters per hour and the second air separation unit with an air intake of 40,000 cubic meters per hour as an example, using the method in this embodiment, the compressor start-up time of the first air separation unit is shortened by 22 hours, the rated power of the motor is 14,000 kW / h, the operating power is 11,200 kW / h, and the power consumption is reduced by 123,200 yuan per start-up.
[0072] Similar parts between the embodiments provided in this application can be referred to mutually. The specific implementation methods provided above are only a few examples under the overall concept of this application and do not constitute a limitation on the scope of protection of this application. For those skilled in the art, any other implementation methods extended from the solution of this application without creative effort shall fall within the scope of protection of this application.
Claims
1. An air separation system, characterized in that, include: The first air separation unit (1) and the second air separation unit (2) are provided with compressor outlets. The compressor outlet of the first air separation unit (1) and the compressor outlet of the second air separation unit (2) are connected. The compressor outlet of the second air separation unit (2) is provided with a first connecting valve (6). Air-cooled tower (3), the inlet of which is connected to the compressor outlet of the first air separation unit (1); A heat exchanger assembly (4) is connected to the air-cooled tower (3); An air separation tower (5) is connected to the heat exchanger assembly (4) so that air flows into the air separation tower (5) after passing through the heat exchanger assembly (4). The air separation tower (5) is used to separate a first gas and a second gas from the air. The air separation tower (5) includes an upper air separation tower (51), which includes a second outlet port (511), a third outlet port (512), and a fourth outlet port (513). Molecular sieve (7), the molecular sieve is in two groups. When the system is running, one group is used for use and the other group is used for regeneration. Each group of molecular sieve (7) includes a first inlet port (71), a second inlet port (72) and a first outlet port (73). The heat exchanger assembly (4) includes a first heat exchanger (41), a second heat exchanger (42) and a third heat exchanger (43). The first outlet port (73) is connected to the first heat exchanger (41) and the second heat exchanger (42) respectively, and a second connecting valve (8) is provided between the first outlet port (73) and the first heat exchanger (41), and a third connecting valve (9) is provided between the first outlet port (73) and the second heat exchanger (42). The first air inlet port (71) is connected to the outlet of the air-cooled tower (3), and the second air inlet port (72) is connected to the first heat exchanger (41); A turboexpander (10) includes a turbo inlet, a turbo outlet, an expansion inlet, and an expansion outlet; The gas discharged from the first outlet port (73) enters the booster turbine expander (10) through the booster inlet; The gas inside the turboexpander (10) enters the first heat exchanger (41) and the second heat exchanger (42) through the pressurization outlet; The gas in the first heat exchanger (41) and the second heat exchanger (42) enters the booster turbine expander (10) through the expansion inlet; The gas inside the turboexpander (10) enters the upper air separation tower (51) through the expansion outlet; The gas discharged from the third outlet port (512) is conducted to the first heat exchanger (41) after passing through the third heat exchanger (43). The third outlet port (512) is used to conduct the gas back to the second inlet port (72). The sixth connecting valve (13) is located between the first flow path and the second flow path. The first flow path is the flow path from the third outlet port (512) through the third heat exchanger (43) to the first heat exchanger (41). The second flow path is the flow path from the booster turbine expander (10) to the air separation upper column (51). The sixth connecting valve (13) is used to guide the gas in the second flow path to the first flow path after it is opened. The gas exported from the booster turbine expander (10) enters the air separation upper column (51) directly in one path and flows to the first heat exchanger (41) in the other path. After being heated by the first heat exchanger (41), it is guided back to the molecular sieve 7 and then vented, thereby realizing the circulation process of the gas inside the system. The eighth connecting valve (15) is disposed in the flow path from the first heat exchanger (41) to the second air inlet port (72).
2. The air separation system according to claim 1, characterized in that, The air separation tower (5) also includes a lower air separation tower (52); the air separation system also includes a fourth connecting valve (11) and a fifth connecting valve (12); The fourth connecting valve (11) is installed on the outlet pipeline from the second outlet port (511) to the second heat exchanger (42) so that the gas discharged from the second outlet port (511) is connected to the fourth connecting valve (11) after passing through the third heat exchanger (43) and the second heat exchanger (42); the fourth connecting valve (11) is used to connect the first gas obtained by the air separation tower (5) after it is opened; The fifth connecting valve (12) is installed on the outlet pipeline from the fourth outlet port (513) to the second heat exchanger (42) so that the gas discharged from the fourth outlet port (513) is connected to the fifth connecting valve (12) after passing through the second heat exchanger (42). The fifth connecting valve (12) is used to connect the second gas obtained by the air separation tower (5) after it is opened.
3. The air separation system according to claim 2, characterized in that, The lower air separation tower (52) includes a fifth outlet port (521), which is connected to the upper air separation tower (51) through the third heat exchanger (43), and a seventh connecting valve (14) is provided between the third heat exchanger (43) and the upper air separation tower (51).
4. The air separation system according to claim 3, characterized in that, It also includes the ninth connecting valve (16), the tenth connecting valve (17), the eleventh connecting valve (18), and the twelfth connecting valve (19). The air separation system further includes a third flow path, which is provided on the exhaust flow path from the third outlet port (512) to the first heat exchanger (41); the inlet of the third flow path is provided on the pipeline between the first heat exchanger (41) and the eighth connecting valve (15), and the outlet of the third flow path is provided with the ninth connecting valve (16). The upper air separation tower (51) also includes a sixth gas outlet port (514). After the gas flows out from the sixth gas outlet port (514), one flow path enters the lower air separation tower (52) through the tenth connecting valve (17), and the other flow path returns to the upper air separation tower (51) through the third heat exchanger (43). The eleventh connecting valve (18) is located between the third heat exchanger (43) and the upper air separation tower (51). The twelfth connecting valve is installed on the pipeline between the first heat exchanger (41), the second heat exchanger (42) and the expansion inlet of the booster turbine expander (10).
5. The air separation system according to claim 4, characterized in that, The number of the booster turbine expanders (10) is two, and the two booster turbine expanders (10) are connected in parallel.
6. A control method for an air separation system, characterized in that, For use in the air separation system of claim 5, comprising: Turn on the second air separation unit and its compressor, and after the second air separation unit is running normally, open the first connecting valve, control the pressure of the first air separation unit to the first preset pressure, and then turn on the air-cooled tower. Start the molecular sieve operation program, control the pressure of the molecular sieve to the second preset pressure, and then turn on the molecular sieve; Open the second connecting valve. When the gas flow rate in the air-cooled tower reaches the preset flow rate, start one of the booster turbine expanders, close the sixth connecting valve, and adjust the opening of the twelfth connecting valve. After air enters the air separation tower, the tenth and ninth connecting valves are closed, the opening of the seventh and eleventh connecting valves is adjusted according to the pressure and air intake of the lower air separation tower, the fourth and fifth connecting valves are adjusted according to the pressure of the upper air separation tower, and the eighth connecting valve is opened. The third connecting valve is adjusted according to the air intake of the first air separation unit and the pressure of the second air separation unit. After liquefied gas appears in the air separation tower, adjust the opening of the seventh connecting valve; When the amount of liquefied gas in the upper air separation tower exceeds a preset value, the compressor of the first air separation unit is turned on to bring the air separation system into normal operation.