Air purification method and air purification device

Abstract

The flow rate of the purge gas used when regenerating the adsorbent is reduced to improve the yield of the product gas. [Solution] A method and apparatus for purifying raw air in cryogenic air separation, which continuously purifies raw air G1 by switching between at least two or more adsorption towers 10a, 10b, includes an adsorption process in which pressurized raw air G1 is introduced into an adsorption tower and at least water and carbon dioxide are removed from the raw air G1, a depressurization process in which the pressure inside one of the adsorption towers pressurized in the adsorption process, which adsorption tower is used for thermal regeneration of the adsorbent, is reduced to atmospheric pressure, a heating process in which heated purge gas G3 is introduced into the adsorption tower that has completed the depressurization process and the adsorbent is thermally regenerated, a charging process in which the adsorption tower that has completed the heating process is pressurized with air that has passed through the adsorption tower and is purified, and a cooling process in which the air that has passed through the adsorption tower and is purified is introduced into the adsorption tower that has completed the charging process and the adsorbent is cooled.

Description

[Technical Field]

[0001] The present invention relates to an air purification method and an air purification device. [Background technology]

[0002] BACKGROUND ART An adsorption tower for purifying raw air is provided in the upstream stage of the distillation section of a cryogenic air separation unit that separates and purifies nitrogen, oxygen, argon, etc. from air as a raw material (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-137639 [Patent Document 2] Patent No. 5577044 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 proposes that the cooling step be completed at a temperature higher than that of the gas treated in the adsorption step, thereby reducing the flow rate of the purge gas used in the regeneration step and improving the productivity of the plant. However, completing the cooling step at a high temperature results in high-temperature gas being introduced from the adsorber into the distillation section at the start of the subsequent adsorption step, causing fluctuations in the operation of the distillation section and resulting in fluctuations in the purity of the nitrogen, oxygen, argon, etc. produced.

[0005] Patent Document 2 proposes that unpurified compressed air containing moisture and carbon dioxide, in addition to the purge gas, be used to regenerate the moisture adsorbent, thereby reducing the flow rate of the purge gas used in the regeneration process and improving the productivity of the plant. However, there remain issues with stable pre-purification, such as the amount of moisture remaining in the moisture adsorbent at the end of the regeneration process changing due to fluctuations in the amount of moisture contained in the compressed air.

[0006] An object of the present invention is to provide an air purification method and an air purification apparatus that can improve the yield of product gas by reducing the flow rate of purge gas used when regenerating an adsorbent. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following means.

[0008] [1] A method for purifying feed air in cryogenic air separation, which is a method for continuously purifying feed air by switching between at least two or more adsorption towers, and which comprises the following steps: an adsorption step in which pressurized feed air is introduced into the adsorption towers and at least water and carbon dioxide are removed from the feed air; a depressurization step in which the pressure inside one of the adsorption towers pressurized in the adsorption step, which adsorption tower is used for thermal regeneration of the adsorbent, is depressurized to atmospheric pressure; a heating step in which heated purge gas is introduced into the adsorption tower that has completed the depressurization step and thermally regenerates the adsorbent; a pressurization step in which the adsorption tower that has completed the heating step is pressurized with air that has passed through the adsorption tower and is purified; and a cooling step in which the air that has passed through the adsorption tower and is purified is introduced into the adsorption tower that has completed the pressurization step and the adsorbent is cooled. [2] The air purification method according to [1], characterized in that a heat exchanger is provided to exchange heat with a low-temperature gas to cool the purified air that has passed through the adsorption tower, and an additional heat exchanger is provided between the adsorption tower and a cryogenic air separation unit that distills and separates the purified air that has passed through the adsorption tower. [3] The air purification method according to [1] or [2], characterized in that in the heating step, the purge gas is introduced into the adsorption tower after the depressurization step in a direction opposite to the flow direction of the feed air. [4] The air purification method according to any one of [1] to [3], characterized in that in the cooling step, the air purified through the adsorption tower is introduced into the adsorption tower after the pressurization step has been completed from the same direction as the flow direction of the feed air.

[0009] [5] A raw air purification device for cryogenic air separation, which continuously purifies raw air by switching between at least two or more adsorption towers, and which is characterized by carrying out the following steps: an adsorption process in which pressurized raw air is introduced into the adsorption towers and at least water and carbon dioxide are removed from the raw air; a depressurization process in which the pressure inside one of the adsorption towers pressurized in the adsorption process, which adsorption tower is used for thermal regeneration of the adsorbent, is depressurized to atmospheric pressure; a heating process in which heated purge gas is introduced into the adsorption tower that has completed the depressurization process and the adsorbent is thermally regenerated; a pressurization process in which the adsorption tower that has completed the heating process is pressurized with air that has passed through the adsorption tower and is purified; and a cooling process in which the air that has passed through the adsorption tower and is purified is introduced into the adsorption tower that has completed the pressurization process and the adsorbent is cooled. [6] The air purification system according to [5], characterized in that a heat exchanger is provided to exchange heat with a low-temperature gas to cool the purified air that has passed through the adsorption tower, and an additional heat exchanger is provided between the adsorption tower and a cryogenic air separation unit that distills and separates the purified air that has passed through the adsorption tower. [7] The air purification apparatus according to [5] or [6], characterized in that in the heating step, the purge gas is introduced into the adsorption tower after the depressurization step in a direction opposite to the flow direction of the feed air. [8] The air purification apparatus according to any one of [5] to [7], characterized in that in the cooling step, the air purified through the adsorption tower is introduced into the adsorption tower after the pressurization step has been completed from the same direction as the flow direction of the raw air. [9] The air purification device according to any one of [5] to [7], characterized in that it is provided with a pipeline for introducing purified air that has passed through one of at least two adsorption towers that performs the adsorption step into an adsorption tower that has completed the pressurization step from the same direction as the flow direction of the raw air. [Effects of the Invention]

[0010] According to the present invention, the flow rate of the purge gas used when regenerating the adsorbent can be reduced, thereby improving the yield of the product gas. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing an example of an air purification device according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing a first example of a process when two adsorption towers are used. [Figure 3] FIG. 10 is a diagram showing a second example of the process when two adsorption towers are used. [Figure 4] 10A and 10B are diagrams illustrating an example of valve operation in the second process example. [Figure 5] FIG. 2 is a schematic diagram showing the configuration of an air purification device used in a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described below based on preferred embodiments.

[0013] The air purification method of this embodiment is a method for purifying feed air in cryogenic air separation, which continuously purifies feed air by switching between at least two or more adsorption towers, and includes the following steps a to e. The air purification device of this embodiment is a device for purifying feed air in cryogenic air separation, which continuously purifies feed air by switching between at least two or more adsorption towers, and performs the following steps a to e.

[0014] Step a: An adsorption step in which pressurized feed air is introduced into an adsorption tower to remove at least water and carbon dioxide from the feed air. Step b: A depressurization step in which the pressure inside the adsorption tower in which the adsorbent is thermally regenerated is reduced to atmospheric pressure, out of the adsorption towers pressurized in the adsorption step. Step c: A heating step in which the heated purge gas is introduced into the adsorption tower after the depressurization step, and the adsorbent is heated and regenerated. Step d: A pressurizing step in which the inside of the adsorption tower after the heating step is pressurized using purified air that has passed through the adsorption tower. Step e: A cooling step in which the purified air that has passed through the adsorption tower is introduced into the adsorption tower after the pressure charging step is completed, and the adsorbent is cooled.

[0015] When two or more adsorption towers are used in an alternating manner, at least one adsorption tower needs to perform step a (adsorption step), and two or more adsorption towers can simultaneously perform step a (adsorption step). When it becomes necessary to thermally regenerate the adsorbent in any of the adsorption towers, steps b to e are sequentially performed for that adsorption tower.

[0016] FIG. 1 is a schematic diagram showing an example of an air purification apparatus according to this embodiment. This air purification apparatus includes at least two or more adsorption towers 10a and 10b that can be switched between, a pipeline 101 into which feed air G1 is introduced, and a pipeline 102 through which purified air G2 is supplied to a cryogenic air separation unit (not shown). The system also includes a pipeline 103 through which purge gas G3 is supplied from the cryogenic air separation unit, and a pipeline 104 through which exhaust gas G4 is discharged from the air purification unit to the outside. Other pipelines, valves, and the like (described in detail below) can be arranged as needed.

[0017] Feed air G1 is air taken in from the atmosphere and compressed by an air compressor (not shown) before being introduced into the adsorption towers 10a and 10b. The compressed air is preferably cooled using an aftercooler or a refrigerator (not shown), and the moisture condensed by cooling is preferably separated by a drain separator (not shown). Depending on the humidity of the atmosphere, the feed air G1 may be saturated with moisture.

[0018] The state of the feed air G1 when introduced into the adsorption towers 10a and 10b may be, for example, a pressure of 300 to 2000 kPa (G) and a temperature of 5 to 45°C. The moisture contained as a component to be removed in the adsorption towers 10a and 10b may include saturated moisture at the introduction temperature of the feed air G1. The carbon dioxide concentration contained in the feed air G1 may be, for example, 1000 ppm or less.

[0019] The purified air G2 is liquefied by heat exchange with low-temperature gas in a heat exchanger (not shown) housed in a cryogenic air separation unit (not shown), and then supplied to a distillation column in the cryogenic air separation unit to be separated and purified into nitrogen, oxygen, argon, etc. At this time, the water content of the purified air G2 is generally 1 ppm or less, and the carbon dioxide content is 0.1 ppm or less. At these contents, no problems arise in the heat exchange or distillation operations within the cryogenic air separation unit.

[0020] The purge gas G3 is a gas other than the product gas, which is generated in the distillation operation to obtain product gases such as nitrogen, oxygen, and argon. By reducing the required flow rate of the purge gas G3 in the regeneration process (processes b to e), it is possible to improve the yield of the product gas and improve the unit consumption. The conditions under which the purge gas G3 is introduced into the air purification device include a temperature of 5 to 45°C and a pressure that takes into account the pressure loss that occurs when it flows through the adsorption towers 10a and 10b in the regeneration process.

[0021] The exhaust gas G4 contains components such as moisture and carbon dioxide that are desorbed from the adsorbent when the purge gas G3 passes through the adsorption towers 10a and 10b in the heating step. The exhaust gas G4 is generally released into the atmosphere.

[0022] The adsorber in the illustrated air purification system is composed of two adsorption towers 10a and 10b. The feed air is continuously purified by alternately repeating an adsorption process (step a) and a regeneration process (steps b to e). The regeneration process here consists of a depressurization process, a heating process, a pressurization process, and a cooling process. Similar processes are alternately performed in the adsorption towers 10a and 10b.

[0023] The adsorption towers 10a and 10b in the illustrated example are equipped with valves 11a to 17a and 11b to 17b.

[0024] Valves 11a and 11b used to introduce the feed air G1 are provided in a pipe 111 that branches off from the pipe 101 toward each of the adsorption towers 10a and 10b. Valves 12a and 12b used for exhausting the purge gas G3 (discharging the exhaust gas G4) are provided in a conduit 112 that joins the adsorption towers 10a and 10b toward the conduit 104. Valves 13a and 13b used to introduce purified air used in the cooling step are provided on a pipe 113 connected to the pipe 110c.

[0025] The pipes 111, 112, and 113 are arranged to connect the inlet pipes 110a and 110b through which the feed air G1 is introduced into the adsorption towers 10a and 10b. The order in which the pipes 111, 112, and 113 are arranged relative to the inlets of the adsorption towers 10a and 10b is arbitrary.

[0026] Valves 14a and 14b used to discharge purified air used in the cooling step are provided on a pipe 114 connected to the pipe 110c. Valves 15a and 15b used to introduce purge gas G3 are provided in a pipe 115 that branches from pipe 103 to each of adsorption towers 10a and 10b. Valves 16a and 16b used to introduce purified air G2 in the pressurizing step are provided in a pipe 116 that branches from pipes 102 and 122 to each of the adsorption towers 10a and 10b. Valves 17a and 17b used to extract purified air G2 to be supplied to the distillation columns are provided in a pipe 117 that branches from pipes 102 and 122 to adsorption columns 10a and 10b.

[0027] The pipes 114, 115, 116, and 117 are arranged to connect the outlet pipes 120a and 120b through which the purified air G2 is discharged from the adsorption towers 10a and 10b. The order in which the pipes 114, 115, 116, and 117 are arranged relative to the outlets of the adsorption towers 10a and 10b is arbitrary.

[0028] In the illustrated example, the pipeline 102 used to introduce and extract purified air G2 between the air purification device and the cryogenic air separation device is divided into a pipeline 121 equipped with a heat exchanger 21 and a pipeline 122 not equipped with a heat exchanger 21.

[0029] The supply system for purge gas G3 is equipped with valves 18 and 19 and a heater 20. Valve 19 is used when supplying purge gas G3 heated by heater 20 to adsorption towers 10a and 10b. Valve 18 is used when supplying unheated purge gas G3 to adsorption towers 10a and 10b. Pipe 103 used to supply purge gas G3 is divided into pipe 119 equipped with heater 20 and pipe 118 not equipped with heater 20.

[0030] The outlet temperature of the heater 20 when heating the purge gas G3 is preferably 100 to 250° C. If it is below 100° C., the adsorbent cannot be sufficiently regenerated, and if it is above 250° C., the capacity of the heater 20 becomes too large, which is uneconomical.

[0031] In the illustrated example, a heat exchanger 21 is provided between the adsorption towers 10a, 10b and a cryogenic air separation unit (not shown). In the heat exchanger 21, the purified air G2 exchanges heat with a heat medium such as cooling water. For example, even if the temperature of the purified air G2 temporarily rises during the cooling process, the temperature of the purified air G2 introduced into the cold box can be kept constant, enabling stable distillation operation. In this case, the temperature of the purified air G2 at the outlet of the heat exchanger 21 is preferably 5 to 50°C.

[0032] The duration of each of the adsorption step, depressurization step, heating step, pressurization step, and cooling step can be determined based on the operating conditions of the apparatus. For example, the duration of the adsorption step can be 60 to 1000 minutes. If the duration is shorter than 60 minutes, the required flow rate of the purge gas increases, while if the duration is longer than 1000 minutes, the size of the adsorber becomes large, which is uneconomical.

[0033] Components to be removed from the feed air G1 in each of the adsorption towers 10a and 10b include moisture and carbon dioxide. A moisture adsorbent is packed on the side of each of the adsorption towers 10a and 10b where the feed air G1 is introduced, and a carbon dioxide adsorbent is packed in the subsequent stage. Activated alumina, silica gel, and zeolite are commonly used as moisture adsorbents, and they may be composed of a single type or multiple types. Zeolite is commonly used as a carbon dioxide adsorbent. Additional adsorbents or catalysts may also be packed to remove other components, such as hydrogen, carbon monoxide, and nitrous oxide. The same can be done when there are three or more adsorption towers.

[0034] Figure 2 shows the progression of processes in each adsorption tower 10a, 10b when two adsorption towers 10a, 10b are used. While the adsorption process is performed in the adsorption tower 10a, the regeneration process is performed in the adsorption tower 10b, and while the regeneration process is performed in the adsorption tower 10a, the adsorption process is performed in the adsorption tower 10b. Details of each process for the adsorption tower 10a are explained below. As for the adsorption tower 10b, the processes are similar except for the symbols a and b being interchanged, and therefore explanations of each process will be omitted.

[0035] (Adsorption process) In the adsorption process using adsorption tower 10a, feed air G1 is introduced into adsorption tower 10a by opening valve 11a. When adsorption tower 10b is in the depressurization step, heating step, or pressurization step, purified air G2 is discharged through valve 17a. When adsorption tower 10b is in the cooling step, valve 17a is closed and valves 14a, 13b, and 17b are opened, so that the air purified through adsorption tower 10a is introduced into adsorption tower 10b via valves 14a and 13b and then supplied to the cryogenic air separation unit via valve 17b and heat exchanger 21.

[0036] (Decompression process) When the adsorption process in the adsorption tower 10a is completed and the regeneration process of the adsorbent installed in the adsorption tower 10a is started, the valves 11a, 14a, and 13b are closed and the valve 12a is opened as a depressurization process. As a result, exhaust gas G4 is discharged and the pressure inside the adsorption tower 10a is reduced to near atmospheric pressure. During the depressurization process of the adsorption tower 10a, the valves 14a, 15a, 16a, and 17a on the outlet side of the adsorption tower 10a are all closed.

[0037] Before or simultaneously with the start of the depressurization step in adsorption tower 10a, valve 11b is opened to introduce feed air G1 into adsorption tower 10b, thereby starting the adsorption step using adsorption tower 10b. The air purified through adsorption tower 10b is supplied to the cryogenic air separation unit via valve 17b and heat exchanger 21.

[0038] (Heating process) After the depressurization step of the adsorption tower 10a is completed, the heating step of the adsorption tower 10a begins by opening valves 19 and 15a to supply purge gas G3 heated by heater 20 to the adsorption tower 10a. The gas that has passed through the adsorption tower 10a is released into the atmosphere as exhaust gas G4 via valve 12a. As the temperature of each adsorbent increases, the adsorbed moisture and carbon dioxide are desorbed. When sufficient moisture is desorbed from the moisture adsorbent, the temperature of the moisture adsorbent and the temperature of the gas flowing out from the moisture adsorbent increase. When the measured values ​​of these temperatures reach predetermined values, the heating step is completed.

[0039] In the illustrated adsorption tower 10a, the purge gas G3 in the heating step passes through the adsorption tower 10a in the opposite direction to the flow direction of the feed air G1. Therefore, the purge gas G3 comes into contact with the carbon dioxide adsorbent and then the moisture adsorbent, raising the temperature of each adsorbent. Zeolite, which is generally used as a carbon dioxide adsorbent, also strongly adsorbs moisture. If the purge gas G3 passes through in the same direction as the flow direction of the feed air G1, moisture desorbed from the moisture adsorbent may be re-adsorbed by the carbon dioxide adsorbent. By passing the purge gas G3 in the opposite direction to the flow of the feed air G1, it is possible to prevent moisture adsorbed by the moisture adsorbent from being re-adsorbed by the carbon dioxide adsorbent.

[0040] (Charging process) After the heating step of adsorption tower 10a is completed, heating by heater 20 is stopped. During the pressurization step of adsorption tower 10a, valves 12a, 15a, and 19 are closed, and valve 16a is opened. As a result, the adsorption tower 10a is pressurized to the operating pressure of the adsorption step using a portion of the air purified through the other adsorption tower 10b. At this time, the purified air produced in adsorption tower 10b passes through valve 17b, heat exchanger 21, and valve 16a and reaches adsorption tower 10a. During the pressurization step of adsorption tower 10a, valves 11a, 12a, and 13a on the inlet side of adsorption tower 10a are all closed.

[0041] (cooling process) After the pressurization step of adsorption tower 10a is completed, valves 16a and 17b are closed and valves 13a, 14b, and 17a are opened during the cooling step of adsorption tower 10a. This allows purified air produced in the other adsorption tower 10b to be introduced into adsorption tower 10a via valves 14b and 13a. The adsorbent in adsorption tower 10a is cooled to a temperature at which the adsorbent can perform at its full potential in the next adsorption step. When the measured value of the adsorbent temperature or the temperature of the gas exiting adsorption tower 10a reaches a predetermined value, the cooling step is completed. Valves 13a and 14b are closed, and valve 11a is opened, and adsorption tower 10a begins the next adsorption step.

[0042] In the illustrated example, during the cooling process of the adsorption tower 10a, purified air is introduced into the adsorption tower 10a from the side where the feed air G1 is introduced. Because the purified air passes through the moisture adsorbent and then the carbon dioxide adsorbent in the adsorption tower 10a, even if trace amounts of moisture or carbon dioxide components remain in the piping at the bottom of the adsorption tower 10a, the inclusion of impurities in the purified air can be suppressed.

[0043] The air purification method of this embodiment is not limited to the above, and may include the following two-tower adsorption steps and / or a pre-cooling step. Figure 3 shows the progress of the steps in each tower when two-tower adsorption steps and a pre-cooling step are included.

[0044] When a pre-cooling step is provided during the regeneration of the adsorption tower 10b, regeneration steps (depressurization step, heating step, pre-cooling step, pressurization step, and cooling step) are performed in the adsorption tower 10b while the adsorption step is performed in the adsorption tower 10a. Furthermore, when a pre-cooling step is provided during the regeneration of the adsorption tower 10a, regeneration steps (depressurization step, heating step, pre-cooling step, pressurization step, and cooling step) are performed in the adsorption tower 10a while the adsorption step is performed in the adsorption tower 10b.

[0045] When the adsorption steps for both adsorption towers are performed after the regeneration step of the adsorption tower 10b is completed, the adsorption steps are performed simultaneously in both adsorption towers 10a and 10b before the regeneration step of the adsorption tower 10a is started. Also, when the adsorption steps for both adsorption towers are performed after the regeneration step of the adsorption tower 10a is completed, the adsorption steps are performed simultaneously in both adsorption towers 10a and 10b before the regeneration step of the adsorption tower 10b is started.

[0046] The pre-cooling step and the adsorption steps for both adsorption towers will be described in detail below for the adsorption tower 10a. The adsorption tower 10b is similar except for the symbols a and b being interchanged, so a description of each step will be omitted.

[0047] (Pre-cooling process) After the heating step of the adsorption tower 10a is completed, but before the pressurization step, the heater 20 is stopped, the valve 19 is closed, and the valve 18 is opened. As a result, unheated purge gas G3 is supplied to the adsorption tower 10a via the valve 15a. By bringing the unheated purge gas G3 into contact with the adsorbent, cooling of the adsorbent provided in the adsorption tower 10a begins. By providing this pre-cooling step, it is possible to prevent an excessive amount of heat from being input from the heater 20. The gas that has passed through the adsorption tower 10a is released into the atmosphere as exhaust gas G4 via the valve 12a.

[0048] (Both tower adsorption process) After the cooling process of the adsorption tower 10a is completed, the valves 13a and 14b are closed and the valves 11a and 17b are opened. This allows the feed air G1 to be introduced into both the adsorption towers 10a and 10b. At this time, the purified air G2 is discharged from both the adsorption towers 10a and 10b through the valves 17a and 17b.

[0049] In order to suppress fluctuations in the pressure of the purified air G2 during the cooling process and other processes, an orifice or an additional valve (not shown) may be provided between the downstream of the valves 17a, 17b that discharge the purified air G2 and the heat exchanger 21, or between the adsorption towers 10a, 10b and the valves 17a, 17b that discharge the purified air G2.

[0050] FIG. 4 shows an example of valve operation in each step when the system shown in FIG. 1 is used and includes a pre-cooling step and two-tower adsorption steps.

[0051] The air purification apparatus used in the comparative example is shown in Figure 5. The method for purifying the feed air in the comparative example is described below. The conditions required for the feed air G1, purified air G2, purge gas G3, and exhaust gas G4, the duration of the adsorption step, the components to be removed, the adsorbent used, etc. are the same as in the above embodiment.

[0052] The adsorption towers 30a and 30b are equipped with valves 31a to 35a and 31b to 35b. The valves 31a and 31b are used to introduce raw air G1. The valves 32a and 32b are used to exhaust purge gas G3 (discharge exhaust gas G4). The valves 33a and 33b are used to introduce purge gas G3. The valves 34a and 34b are used to introduce purified air G2 in the pressurization step. The valves 35a and 35b are used to discharge purified air G2 to be supplied to the cryogenic air separation unit.

[0053] The supply system for the purge gas G3 is equipped with valves 36 and 37 and a heater 38. The valve 37 is used when supplying the purge gas G3 heated by the heater 38 to the adsorption towers 30a and 30b. The valve 36 is used when supplying the unheated purge gas G3 to the adsorption towers 30a and 30b.

[0054] Valves 31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b, 36, and 37 in Figure 5 correspond to valves 11a, 11b, 12a, 12b, 15a, 15b, 16a, 16b, 17a, 17b, 18, and 19 in Figure 1, respectively. Pipes 130a, 130b, 131, 132, 133, 134, 135, 136, 137, 140a, 140b, 141, and 142 in Figure 5 correspond to pipes 110a, 110b, 111, 112, 115, 116, 117, 118, 119, 120a, 120b, 121, and 122 in Figure 1, respectively.

[0055] The air purification apparatus of Figure 5 does not have components corresponding to valves 13a, 13b, 14a, and 14b, pipes 110c, 113, and 114, and heat exchanger 21 of Figure 1. Pipes 110c, 113, and 114 of Figure 1 are pipes for introducing purified air that has passed through another adsorption tower from the same direction as the flow of the feed air during the cooling step of the adsorption tower that has completed the pressurization step.

[0056] The following describes in detail each step of the adsorption tower 30a. The adsorption tower 30b is similar except for the symbols a and b being interchanged, so a description of each step will be omitted.

[0057] (Adsorption process) In the adsorption step using the adsorption tower 30a, the feed air G1 is introduced into the adsorption tower 30a by opening the valve 31a. The air purified through the adsorption tower 30a is discharged through the valve 35a and supplied to the cryogenic air separation unit.

[0058] (Decompression process) After the adsorption step using the adsorption tower 30a is completed, the valves 31a and 35a are closed and the valve 32a is opened in the depressurization step of the adsorption tower 30a, whereby the exhaust gas G4 is discharged and the pressure inside the adsorption tower 30a is reduced to near atmospheric pressure.

[0059] (Heating process) After the depressurization step of the adsorption tower 30a is completed, in the heating step of the adsorption tower 30a, the valves 37 and 33a are opened to supply the purge gas G3 heated by the heater 38 to the adsorption tower 30a. The gas that has passed through the adsorption tower 30a is released into the atmosphere as exhaust gas G4 via the valve 32a.

[0060] (cooling process) After the heating step of the adsorption tower 30a is completed, the heating of the heater 38 is stopped, the valve 37 is closed, and the valve 36 is opened in the cooling step of the adsorption tower 30a. As a result, unheated purge gas G3 is supplied to the adsorption tower 30a. The gas that has passed through the adsorption tower 30a is released into the atmosphere as exhaust gas G4 via the valve 32a.

[0061] (Charging process) After the cooling step of adsorption tower 30a is completed, the adsorption tower 30a is pressurized by closing valves 32a, 33a, and 36 and opening valve 34a. This allows the adsorption tower 30a to be pressurized to the operating pressure for the adsorption step using a portion of the purified air that has passed through the other adsorption tower 30b. After the pressurization step is completed, adsorption tower 30a resumes the adsorption step.

[0062] In the air purification method of the comparative example, it is necessary to heat and cool the adsorption tower 30a using only the purge gas G3. In contrast, in the air purification method of the present embodiment, the adsorption tower 10a is cooled using air purified through the other adsorption tower 10b. This allows for a higher flow rate than the purge gas G3, enabling cooling to be completed more quickly than in the comparative example. This allows for an extended heating time when operating for the same regeneration time, and the flow rate of the supplied purge gas G3 can be reduced, resulting in an improved product gas yield compared to the comparative example.

[0063] Furthermore, it is preferable to provide a heat exchanger that cools the purified air G2 by heat exchange with a low-temperature gas, and to provide an additional heat exchanger between the cryogenic air separation unit and the adsorption tower, so that even if the temperature of the purified air G2 temporarily rises during the cooling process, the temperature of the purified air G2 introduced into the cold box can be kept constant, enabling stable distillation operation.

[0064] In the cooling step of the adsorption tower after the pressurization step, the air purification apparatus shown in Figure 5 can also be used if purified air that has passed through the other adsorption tower is introduced from the opposite direction to the flow of the feed air. In this case, the regeneration step consists of a depressurization step, a heating step, a pressurization step, and a cooling step in that order. The pressurization step and cooling step for adsorption tower 30a can be performed as follows. The description of adsorption tower 30b is omitted because it is similar except for the interchange of the symbols a and b.

[0065] (Charging process) After the heating step of adsorption tower 30a is completed, heating by heater 38 is stopped. During the pressurization step of adsorption tower 30a, valves 32a, 33a, and 37 are closed, and valve 34a is opened. As a result, the inside of adsorption tower 30a is pressurized to the operating pressure for the adsorption step using a portion of the air purified through the other adsorption tower 30b.

[0066] (cooling process) After the pressurization step of adsorption tower 30a is completed, valve 32a is opened during the cooling step of adsorption tower 30a. Following the pressurization step, a portion of the air purified through the other adsorption tower 30b is introduced into adsorption tower 30a via valves 35b and 34a. The adsorbent in adsorption tower 30a is cooled to a temperature at which the adsorbent can demonstrate its performance in the next adsorption step. The gas that has passed through adsorption tower 30a is released into the atmosphere as exhaust gas G4 via valve 32a. [Example]

[0067] The present invention will be specifically described below with reference to examples.

[0068] Example 1 Adsorber conditions: Tower diameter 1.4 m, total height of adsorbents (moisture adsorbent, carbon dioxide adsorbent) packed in each tower: 1.8 m Adsorption conditions: 1000 kPaA, 40°C, 5000 Nm 3 / h, moisture content 40℃ saturated, carbon dioxide content 450ppm Regeneration conditions: 100 kPaA, heating gas temperature 230°C, moisture content in product gas <1 ppm, carbon dioxide content <0.1 ppm Switching time: Adsorption time 120 min, regeneration time (decompression + heating + pressure increase + cooling) total 120 min (time breakdown shown in Table 1)

[0069] In the regeneration process of Example 1, a depressurization process, a heating process, a pressurization process, and a cooling process are performed. Under the above operating conditions, when using the system shown in Figure 1 and flowing the same flow rate of purge gas in both the heating process and the cooling process, the minimum flow rate of purge gas that can stably perform pre-treatment purification is 1750 Nm 3 At this time, the temperature of the purified air G2 entering the cold box was stable at below 50°C, and the impurity (oxygen + argon) concentration in the product nitrogen gas extracted from the cold box was continuously below 0.1 ppm.

[0070] Example 2 In Example 2, the system shown in Figure 1 was used under the same operating conditions as in Example 1, except that the regeneration step included a pre-cooling step. When the same flow rate of purge gas was used in both the heating step and the cooling step, the minimum flow rate of purge gas that could stably perform pre-treatment purification was 1800 Nm 3 / h. As in Example 1, the temperature of the purified air G2 entering the cold box was stable at 50°C or less, and the impurity (oxygen + argon) concentration in the product nitrogen gas extracted from the cold box was continuously 0.1 ppm or less.

[0071] Example 3 Under the same operating conditions as in Example 1, when using an apparatus in which the heat exchanger 21 is omitted from the system shown in FIG. 1 and the same flow rate of purge gas is used in both the heating step and the cooling step, the minimum flow rate of purge gas that can stably perform pre-treatment purification is 1750 Nm 3 / h. The temperature of the purified air G2 entering the cold box was above 100°C for 30 minutes during the 120-minute switching time. As a result, the impurity (oxygen + argon) concentration in the product nitrogen gas extracted from the cold box temporarily rose to a maximum of 10 ppm.

[0072] (Comparative Example 1) Under the same operating conditions as in Example 1, using the system of FIG. 5, and flowing the same flow rate of purge gas in both the heating and cooling steps, the minimum purge gas flow rate at which stable pre-treatment and purification can be performed is 2050 Nm 3 At this time, the temperature of the purified air G2 entering the cold box was stable at below 50°C, and the impurity (oxygen + argon) concentration in the product nitrogen gas extracted from the cold box was continuously below 0.1 ppm.

[0073] [Table 1]

[0074] The above Example 1 (purge gas flow rate 1750 Nm 3 / h) and Comparative Example 1 (purge gas flow rate 2050 Nm 3 / h), the required purge gas flow rate was reduced to 300 Nm by introducing purified air through the other adsorption tower in the adsorbent cooling process. 3 / h (feed air supply rate 5000 Nm 3 This is understood to contribute to improving the yield of product gas and improving the unit consumption.

[0075] By comparing the above Example 1 and Example 2, it can be seen that when the regeneration process includes a pre-cooling process, the amount of purge gas required increases slightly, but the time for the heating process can be shortened, and therefore the amount of heat input in the heating process can be reduced.

[0076] By comparing the above Example 1 and Example 3, it can be understood that providing a heat exchanger between the adsorption tower and the cold box enables stable operation of the distillation section. [Industrial Applicability]

[0077] According to the present invention, in the purification of feed air in cryogenic air separation, the flow rate of the purge gas used in regenerating the adsorbent can be reduced, thereby improving the yield of the product gas. [Explanation of symbols]

[0078] G1...feed air, G2...purified air, G3...purge gas, G4...exhaust gas, 10a, 10b, 30a, 30b...adsorption tower, 11a, 11b, 12a, 12b, 13a, 13b, 14a, 14b, 15a, 15b, 16a, 16b, 17a, 17b, 18, 19, 31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b, 36, 37...valves 20,38...heater, 21...heat exchanger, 101,102,103,104,110a,110b,110c,111,112,113,114,115,116,117,118,119,120a,120b,121,122,130a,130b,131,132,133,134,135,136,137,140a,140b,141,142...pipes.

Claims

1. A method for purifying feed air in cryogenic air separation, comprising: A method for continuously purifying feed air by switching between at least two adsorption towers, an adsorption step of introducing pressurized feed air into the adsorption tower and removing at least water and carbon dioxide from the feed air; a depressurization step of depressurizing the pressure inside one of the adsorption towers pressurized in the adsorption step, which is one of the adsorption towers where the adsorbent is thermally regenerated, to atmospheric pressure; a heating step of introducing the heated purge gas into the adsorption tower after the depressurization step has been completed, and heating and regenerating the adsorbent; a pressurizing step of pressurizing the adsorption tower after the heating step with purified air that has passed through the adsorption tower; a cooling step of introducing the purified air that has passed through the adsorption tower into the adsorption tower after the pressurizing step has been completed, and cooling the adsorbent; An air purification method comprising:

2. 2. The air purification method according to claim 1, further comprising providing a heat exchanger for exchanging heat with a low-temperature gas to cool the purified air that has passed through the adsorption tower, and providing an additional heat exchanger between the adsorption tower and a cryogenic air separation unit that distills and separates the purified air that has passed through the adsorption tower.

3. 2. The air purification method according to claim 1, wherein in the heating step, the purge gas is introduced into the adsorption tower after the depressurization step in a direction opposite to the flow direction of the feed air.

4. 2. The air purification method according to claim 1, wherein in the cooling step, the purified air that has passed through the adsorption tower is introduced into the adsorption tower that has completed the pressurizing step from the same direction as the flow of the feed air.

5. A purification apparatus for feed air in cryogenic air separation, comprising: This is an apparatus that continuously purifies raw air by switching between at least two adsorption towers. an adsorption step of introducing pressurized feed air into the adsorption tower and removing at least water and carbon dioxide from the feed air; a depressurization step of depressurizing the pressure inside one of the adsorption towers pressurized in the adsorption step, which is one of the adsorption towers where the adsorbent is thermally regenerated, to atmospheric pressure; a heating step of introducing the heated purge gas into the adsorption tower after the depressurization step has been completed, and heating and regenerating the adsorbent; a pressurizing step of pressurizing the adsorption tower after the heating step with purified air that has passed through the adsorption tower; a cooling step of introducing the purified air that has passed through the adsorption tower into the adsorption tower after the pressurizing step has been completed, and cooling the adsorbent; An air purification device characterized by performing the above.

6. 6. The air purification system according to claim 5, further comprising a heat exchanger for exchanging heat with a low-temperature gas to cool the purified air that has passed through the adsorption tower, and an additional heat exchanger for separating the purified air that has passed through the adsorption tower by distillation, between the adsorption tower and a cryogenic air separation unit.

7. 6. The air purification apparatus according to claim 5, wherein in the heating step, the purge gas is introduced into the adsorption tower after the depressurization step in a direction opposite to the flow direction of the feed air.

8. 6. The air purification apparatus according to claim 5, wherein in the cooling step, the purified air that has passed through the adsorption tower is introduced into the adsorption tower that has completed the pressurizing step from the same direction as the flow of the feed air.

9. 6. The air purification system according to claim 5, further comprising a pipeline for introducing purified air that has passed through one of the at least two adsorption towers performing the adsorption step into the adsorption tower that has completed the pressurization step from the same direction as the flow of the feed air.

Images