Drying operation recovery method in drying adsorbent in adsorption tower

Abstract

To provide a method for recovering a drying operation in drying of an adsorbent in an adsorption tower capable of preventing movement of the adsorbent downstream during restoration of a drying operation after stop of drying the adsorption tower and thereby enhancing safety.SOLUTION: A method for recovering a drying operation, in which a vacuum pump 13 is connected downstream of an adsorption tower 10 via piping to reduce pressure inside the adsorption tower 10 by sucking air containing water vapor W1, for restoring, upon stop of a drying operation for drying an adsorbent in an adsorption tower 10 that adsorbs radioactive substances contained in contaminated water, includes: restarting the vacuum pump 13 so that the internal pressure of the adsorption tower becomes a set degree of vacuum on the basis of an operating condition under which the adsorbent inside the adsorption tower 10 does not flow; and the vacuum pump 13 operating for a running time of 45 minutes or more and 60 minutes or less from the start of the restart so that the internal pressure of the adsorption tower becomes 2.4 kPa.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for restoring a drying operation in an adsorption tower when the drying operation is stopped during drying of an adsorbent that adsorbs radioactive substances contained in contaminated water in the adsorption tower. [Background technology]

[0002] Conventionally, in decommissioning work of nuclear reactors installed in nuclear facilities, etc., contaminated water and decontamination waste liquid containing radioactive materials (hereinafter collectively referred to as contaminated water) are discharged as waste (primary waste). One treatment method for removing (reducing) the radioactive materials in contaminated water is to use an adsorption tower containing an adsorbent, as disclosed in Patent Document 1, for example.

[0003] The adsorption towers used to remove radioactive materials from contaminated water are treated as secondary waste. To remove the treated water (residual water) remaining in the adsorption towers, a method is adopted in which adsorbent material that adsorbs the radioactive materials contained in the contaminated water is dried inside the adsorption towers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5236835 Summary of the Invention [Problem to be solved by the invention]

[0005] A conventional method for drying adsorbents in adsorption towers involves vacuum drying the adsorbents using a vacuum pump. However, if an unexpected interruption, such as a power outage, occurs during drying, the drying operation must be restarted to restore the operation. This restoration method involves restarting the vacuum pump and heater, but this can lead to the adsorbent in the adsorption tower migrating downstream. If the radioactive adsorbent migrates downstream of the adsorption tower, the radiation can be transferred to the condenser or condensation tank located downstream of the adsorption tower, requiring cleaning or replacement, creating safety issues. Therefore, a drying operation restoration method that does not cause downstream migration of the adsorbent during restoration operation is needed, and there is room for improvement in this regard.

[0006] The present invention aims to provide a method for restoring drying operation in an adsorption tower when drying operation is resumed after drying in the adsorption tower has been stopped, which can prevent the adsorbent from migrating downstream and thereby increase safety. [Means for solving the problem]

[0007] One aspect of the present invention is a method for restoring drying operation in an adsorbent tower when the drying operation stops during drying of an adsorbent that adsorbs radioactive substances contained in contaminated water in the adsorption tower, the method comprising: a vacuum pump connected via piping to the downstream side of the adsorption tower and sucking in air containing water vapor to reduce the pressure inside the adsorption tower; and restarting the vacuum pump so that the pressure inside the adsorption tower reaches a set vacuum level based on operating conditions in which the adsorbent does not flow inside the adsorption tower.

[0008] According to the present invention, when the drying operation of the adsorption tower is resumed after the drying stop, the evaporation amount can be adjusted by restarting the adsorption tower while adjusting the vacuum force of the vacuum pump so that the pressure inside the adsorption tower reaches a set vacuum level based on operating conditions that prevent the adsorbent from flowing inside the adsorption tower. This prevents the adsorbent from flowing inside the adsorption tower due to an increase in the vapor velocity of water vapor. Therefore, the present invention prevents the adsorbent from migrating downstream, further improving safety.

[0009] The present invention is also characterized by comprising the steps of restarting the vacuum pump, measuring the vapor flow rate in the adsorption tower to determine the vapor velocity, determining a minimum fluidization velocity in the adsorbent, determining whether a value obtained by dividing the vapor velocity by the minimum fluidization velocity reaches a criterion of 1.5 times, and maintaining the decompression by the vacuum pump when the determination indicates that the value is less than 1.5 times, and stopping the decompression by the vacuum pump when the value is 1.5 times or more.

[0010] According to the present invention, the vapor flow rate in the adsorption tower is compared with the minimum fluidization velocity calculated by the judgment formula, and the evaporation rate can be adjusted by adjusting the vacuum of the vacuum pump so that the vapor flow rate does not exceed 1.5 times the judgment standard. This prevents the adsorbent in the adsorption tower from flowing due to an increase in the vapor velocity of water vapor. Therefore, the present invention can prevent the adsorbent from migrating downstream, further improving safety.

[0011] In the present invention, it is preferable to adjust the amount of condensation by a condenser that condenses water vapor in the adsorption tower by cooling.

[0012] According to the present invention, in this case, the condensation force is promoted by lowering the cooling temperature at which the water vapor is cooled in the condenser to increase the condensation capacity (condensation amount), and the steam equivalent to the volume of the condensed water flows from the adsorption tower into the condenser. In other words, the steam from the adsorption tower flows more easily into the reducer, and the steam velocity increases. Therefore, the vapor velocity in the adsorption tower can be adjusted by adjusting the condensation capacity of the condenser in addition to adjusting the degree of vacuum using the vacuum pump.

[0013] In the present invention, the vacuum pump is preferably operated for an operating time of 45 minutes to 60 minutes from the start of restarting the adsorption tower so that the pressure inside the adsorption tower reaches 2.4 kPa.

[0014] According to the present invention, the evaporation rate can be adjusted by adjusting the vacuum level of the vacuum pump so that the pressure inside the adsorption tower reaches 2.4 kPa over an operating time of 45 to 60 minutes from the start of restart. This prevents the adsorbent from flowing inside the adsorption tower due to an increase in the vapor velocity of water vapor. Therefore, the present invention prevents the adsorbent from migrating downstream, further improving safety.

[0015] In the present invention, it is preferable that an air intake valve capable of taking in air is provided in a pipe between the adsorption tower and the vacuum pump.

[0016] According to the present invention, when the vacuum capacity of the vacuum pump is large, the vacuum capacity can be reduced by the air intake valve to reduce the vacuum and adjust the degree of vacuum, thereby adjusting the amount of evaporation and preventing the adsorbent from migrating downstream.

[0017] In the present invention, it is preferable that the vacuum pump has a variable pressure reducing force that can be controlled by an inverter.

[0018] According to the present invention, the motor rotation speed of the vacuum pump can be changed by inverter control to vary the pressure reducing force and adjust the degree of vacuum, thereby adjusting the amount of evaporation and preventing the adsorbent from migrating downstream. [Effects of the Invention]

[0019] According to the method for restoring drying operation in an adsorbent drying tower of the present invention, when the drying operation of the adsorption tower is resumed after drying has stopped, the migration of the adsorbent to downstream can be prevented, thereby further increasing safety. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing a schematic configuration of a vacuum drying apparatus 1 equipped with an adsorption tower 10 to which a method for restoring a drying operation for drying an adsorbent material in an adsorption tower according to a first embodiment of the present invention is applied. [Figure 2]FIG. 10 is a graph showing the change over time in the amount of condensed water during a drying test according to the first test of the example. [Figure 3] FIG. 10 is a graph showing the change in pressure in the adsorption tower over time when the vacuum drying system is restarted in the first test of the embodiment. [Figure 4] 1A and 1B show the state of adsorbent collection by the strainer in the first test of the example, where (a) is a photograph before the test and (b) is a photograph after the test. [Figure 5] FIG. 10 is a graph showing the change in pressure in the adsorption tower over time when the vacuum drying system is restarted in the second test of the embodiment. [Figure 6] 10 is a flowchart showing a method for restoring the drying operation in drying the adsorbent in the adsorption tower according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, a method for restoring drying operation in an adsorbent drying chamber in an adsorption tower according to an embodiment of the present invention will be described with reference to the drawings. The dimensions, materials, and other specific values ​​shown in the embodiment are merely examples for facilitating understanding of the invention and, unless otherwise specified, do not limit the present invention. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant description, and elements not directly related to the present invention are not shown.

[0022] (First embodiment) FIG. 1 is a diagram showing a schematic configuration of a vacuum drying apparatus 1 equipped with an adsorption tower 10 to which a method for restoring a drying operation for drying an adsorbent material in an adsorption tower according to a first embodiment is applied. 1, an adsorbent that adsorbs radioactive materials such as cesium is filled to a height of, for example, about 90% of the internal space of the adsorption tower 10. Zeolite or silicate titanate, for example, can be suitably used as the adsorbent.

[0023] First, the configuration of the vacuum drying device 1 will be specifically described. The vacuum drying apparatus 1 includes an adsorption tower 10, a condenser 11, a condensed water tank 12, a vacuum pump 13, and a cooling device 14. The adsorption tower 10 is connected to the vacuum pump 13 via a drain pipe 15, and the inside of the adsorption tower is maintained in a vacuum state during drying.

[0024] The adsorption tower 10, condenser 11, condensed water tank 12, and vacuum pump 13 are connected to the drain pipe 15 in this order from the upstream side. That is, water vapor W1 flows from the adsorption tower 10 to the upstream side of the drain pipe 15, and the water vapor W1 is cooled in the condenser 11 to become condensed water W2, which is collected in the condensed water tank 12. The vacuum pump 13 is disposed downstream of the condensed water tank 12, and maintains a vacuum state not only inside the adsorption tower 10 but also inside the condenser 11 and the condensed water tank 12 through the drain pipe 15. In FIG. 1 , the symbol "L" represents a water level gauge, the symbol "T" represents a thermometer such as a thermocouple, and the symbol "P" represents a pressure gauge.

[0025] The drain pipe 15 includes a first pipe 15A, a second pipe 15B, and a third pipe 15C. The first pipe 15A connects the adsorption tower 10 and the condenser 11, and mainly allows water vapor W1 to flow from the adsorption tower 10 toward the condenser 11. The second pipe 15B connects the condenser 11 and the condensed water tank 12, and allows condensed water W2 cooled in the condenser 11 to flow toward the condensed water tank 12. The third pipe 15C connects the condensed water tank 12 and the vacuum pump 13, and reduces the pressure inside the adsorption tower 10, the condenser 11, and the condensed water tank 12, as well as inside the drain pipe 15, to maintain a vacuum state.

[0026] The cooling device 14 passes the cooling water W3 through the condenser 11 and the condensed water tank 12. That is, the cooling water W3 of the cooling device 14 passes through the condenser 11 via the first cooling pipe 141, then passes through the condensed water tank 12 via the second cooling pipe 142, and then returns to the cooling device 14 through the third cooling pipe 143.

[0027] The top of the adsorption tower 10 is provided with a water supply pipe 101 connected to an inlet header (not shown) that functions as a water supply inlet, and the aforementioned drain pipe 15 connected to an outlet header (not shown) that functions as a drain outlet. Contaminated water is supplied to the adsorption tower 10 from the water supply pipe 101 via the inlet header. The contaminated water supplied from the water supply pipe 101 passes through the inside of the adsorbent, whereby radioactive substances are adsorbed by the adsorbent, producing treated water from which radioactive substances have been removed (or reduced). The treated water is discharged to the outside from the outlet header through the drain pipe 15. When the adsorption tower 10 reaches the end of its performance life and is replaced, compressed air is supplied from the water supply pipe 101 to air-blow and discharge the treated water, and the treated water remaining in the adsorbent is discharged from the outlet header through the drain pipe 15.

[0028] The adsorption tower 10 is provided with a hydrogen vent pipe 102 to prevent hydrogen generated by the radioactivity adsorbed on the adsorbent radiolytically decomposing the treated water from remaining inside the tower, and a hydrogen vent valve (not shown) is provided at the end of the pipe.

[0029] The adsorption tower 10 comprises a cylindrical, bottomed inner container (not shown) filled with an adsorbent, and an outer container 103 disposed outside the inner container with an air layer interposed therebetween to shield radiation from the outside. The upper opening of the inner container is sealed by an upper lid 104. A heater 105 is provided on the outer surface of the outer container 103. Furthermore, a heat insulating material (not shown) is provided to cover the heater 105 from the outside. A split band heater is used as the heater 105, and the pair of band heaters sandwich the outer container 103 to cover the entire circumference of the container.

[0030] When water evaporates in the adsorption tower 10, the water temperature drops due to latent heat, making evaporation difficult. Therefore, by supplying heat to the adsorption tower 10 using the heater 105, the latent heat is compensated for and the drop in water temperature is prevented. This suppresses a decrease in the evaporation rate and increases the evaporation efficiency of the treated water. Furthermore, by covering the heater 105 with a heat insulating material, the heat of the heater 105 can be efficiently supplied to the adsorption tower 10.

[0031] The condenser 11 cools the air sucked from the adsorption tower 10 to condense the moisture. A drain pipe 15 (first pipe 15A) extending from the adsorption tower 10 is connected to the condenser 11. The water condensed in the condenser 11 is drained into the condensed water tank 12 through the second pipe 15B. A water meter is provided on the first pipe 15A, and the amount of water condensed in the condenser 11 (condensed water W2) is measured by this water meter.

[0032] The first pipe 15A is provided with a mesh strainer 151 at a position upstream of the condenser 11. The strainer 151 captures particles of the adsorbent that migrate along with the water vapor W1.

[0033] A drain pipe 15 is connected to the vacuum pump 13, and the vacuum pump 13 sucks in the water vapor-containing air inside the adsorption tower 10, which is supplied from the hydrogen vent pipe 102, through the drain pipe 15, thereby reducing the pressure inside the adsorption tower 10. The vacuum pump 13 and the condenser 11 are connected by the drain pipe 15 via the condensed water tank 12. The air sucked in by the vacuum pump 13 is sent to the condenser 11 through the drain pipe 15.

[0034] An air intake valve 17 capable of taking in air is provided in the third pipe 15C between the condensed water tank 12 and the vacuum pump 13. The air taken in by the air intake valve 17 is sucked by the vacuum pump 13, so the amount of vacuum of the vacuum pump 13 can be adjusted to be small.

[0035] The vacuum drying apparatus 1 is also provided with a control unit 16 that controls the above-mentioned adsorption tower 10, condenser 11, condensed water tank 12, vacuum pump 13, cooling device 14, heater 105, etc. The control unit 16 acquires various operating data of the vacuum pump 13, the heater temperature of the heater 105, the internal pressure of the adsorption tower 10 (adsorption tower pressure), the steam flow rate, etc., and performs control based on these data.

[0036] If the drying operation is stopped due to a power outage or the like during drying of the adsorbent in the adsorption tower using the vacuum drying apparatus 1 configured as described above, the vacuum pump 13 is restarted so that the pressure inside the adsorption tower reaches the set vacuum level under operating conditions that prevent the adsorbent from flowing inside the adsorption tower 10. Specifically, the vacuum pump 13 is operated for an operating time of 45 to 60 minutes from the start of restart so that the pressure inside the adsorption tower reaches 2.4 kPa. The operating time of the vacuum pump 13 is preferably 60 minutes.

[0037] At this time, the vacuum pump 13 can be operated by gradually decreasing or gradually increasing the degree of vacuum, or by providing a plurality of vacuum pumps with different rated capacities and adjusting the vacuum force by switching between them as appropriate.

[0038] As another method for operating the vacuum pump 13, when the vacuum capacity of the vacuum pump 13 is large, the vacuum capacity may be reduced by the air intake valve 17 to reduce the amount of vacuum drawn. It is also possible to use a method in which the motor rotation speed of the vacuum pump 13 is changed by inverter control to vary the pressure reduction force.

[0039] Next, the operation of the method for restoring the drying operation in drying the adsorbent in the adsorption tower will be described in detail with reference to FIG. The method for restoring drying operation in an adsorption tower for drying an adsorbent material according to this embodiment includes a vacuum pump 13 connected via piping to the downstream side of the adsorption tower 10, and sucking in air containing water vapor W1 to reduce the pressure inside the adsorption tower 10. This method is for restoring drying operation when the drying operation stops when drying an adsorbent that adsorbs radioactive materials contained in contaminated water inside the adsorption tower 10. In the method for restoring drying operation in an adsorption tower for drying an adsorbent material, the vacuum pump 13 is restarted based on operating conditions under which the adsorbent inside the adsorption tower 10 does not flow, so that the pressure inside the adsorption tower reaches a set vacuum level.

[0040] As described above, in this embodiment, when the drying operation of the adsorption tower 10 is resumed after the drying operation has been stopped, the evaporation amount can be adjusted by restarting the adsorption tower 10 while adjusting the vacuum force of the vacuum pump 13 so that the pressure inside the adsorption tower reaches the set vacuum level based on the operating conditions under which the adsorbent does not flow inside the adsorption tower 10. This prevents the adsorbent from flowing inside the adsorption tower 10 due to an increase in the vapor velocity of the water vapor W1. Therefore, in this embodiment, the adsorbent can be prevented from migrating downstream, further improving safety.

[0041] Furthermore, according to the method for restoring drying operation for drying the adsorbent material in the adsorption tower according to this embodiment, the vacuum pump 13 is operated for an operating time of 45 minutes to 60 minutes from the start of restart so that the pressure inside the adsorption tower becomes 2.4 kPa. Therefore, the evaporation amount can be adjusted by adjusting the vacuum level of the vacuum pump 13 so that the pressure inside the adsorption tower becomes 2.4 kPa over an operation time of 45 to 60 minutes from the start of restart. This makes it possible to prevent the adsorbent in the adsorption tower 10 from flowing due to an increase in the vapor velocity of water vapor. Therefore, in this embodiment, it is possible to prevent the adsorbent from migrating downstream, further improving safety.

[0042] In this embodiment, an air intake valve 17 capable of taking in air is provided in the third pipe 15C between the adsorption tower 10 and the vacuum pump 13. Therefore, when the vacuum capacity of the vacuum pump 13 is large, the vacuum capacity can be reduced by the air intake valve 17, thereby reducing the vacuum and adjusting the degree of vacuum. This makes it possible to adjust the amount of evaporation and prevent the adsorbent from migrating downstream.

[0043] In this embodiment, the vacuum pump 13 is inverter-controlled to vary the pressure reduction force. Therefore, the motor rotation speed of the vacuum pump 13 is changed by inverter control to vary the pressure reduction force and adjust the degree of vacuum. This makes it possible to adjust the amount of evaporation and prevent the adsorbent from migrating downstream.

[0044] Next, an example will be described below that was carried out to verify the method for restoring the drying operation in drying the adsorbent in the adsorption tower according to the first embodiment described above.

[0045] (Example) In the examples, the effectiveness of the method for restoring the drying operation in drying the adsorbent in the adsorption tower according to the first embodiment described above was confirmed by drying tests in the first and second tests. In the second test, the operating conditions of the vacuum pump were found to solve the problem confirmed in the first test.

[0046] Fig. 2 is a diagram showing the change in the amount of condensed water over time during the drying test in the first test of the example. In Fig. 2, Test C shows the test results using the vacuum drying apparatus according to the first embodiment described above. Fig. 2 shows a graph of the change over time, with the horizontal axis representing time (hours) and the vertical axis representing the amount of water stored in the condensed water tank (L). The adsorption tower of the vacuum drying device used in the first test was a cesium removal device (SARRY) manufactured by SARRY. The drying operation in this example was performed with the heater temperature set to 80°C and the pressure inside the adsorption tower set to 2.4 kPa, and vacuum drying was carried out. Figure 2 shows the state in the first test where, as drying progressed over time, steam was generated inside the adsorption tower, and the steam sucked in by the vacuum pump was cooled in the condenser, resulting in an increase in condensed water.

[0047] In the first test shown in Figure 2, when a power outage occurred during drying (reference symbol P1 in Figure 2), the heater and vacuum pump were turned off, and approximately 24 hours later, the heater and vacuum pump were turned on (reference symbol P2 in Figure 2). As shown in Figure 2, it can be seen that condensation generation stopped from the time of the power outage P1. Then, by turning on the heater and vacuum pump (at P2), the pressure inside the adsorption tower decreased, and water vapor inside the adsorption tower moved to the reducer side, generating condensation water at a maximum rate of 7 L / h. Note that because the adsorption tower is equipped with a shielding container (outer container), even if the heater is not turned on when restarting, residual heat from the shielding container will generate water vapor from the adsorbent inside the adsorption tower within approximately 24 hours after the power outage.

[0048] Figure 3 shows the change in the degree of vacuum (pressure inside the adsorption tower) over time when the vacuum drying was restarted in Test 1. Figure 3 shows a graph of the change over time, with the horizontal axis representing time (hours) and the vertical axis representing the pressure inside the adsorption tower (kPa). During the restart shown in Figure 2, the vacuum pump was operated at rated speed from the time of restart. As shown in Figure 3, it was confirmed that the pressure inside the adsorption tower reached 2.4 kPa, which was almost the set vacuum level, after 15 to 20 minutes had elapsed (hereinafter referred to as the recovery time).

[0049] Figure 4 shows the state of adsorbent collection by the strainer installed in the piping between the adsorption tower and the reducer in the first test, where (a) is a photograph before the test and (b) is a photograph after the test. As shown in Figure 4(a), before the test, no adsorbent was detected, and it was confirmed that the adsorbent had not migrated downstream from the adsorption tower to the reducer. On the other hand, as shown in Figure 4(b), after the test, i.e., after restarting operation, it was confirmed that the adsorbent had been detected, and it was confirmed that the adsorbent had migrated downstream from the adsorption tower to the reducer.

[0050] Therefore, in this example, a second test was conducted to confirm the conditions under which the adsorbent would not migrate when the system was restarted. The test equipment used in the second test was a drying test equipment equipped with an adsorption tower that was half the height of the adsorption tower of the vacuum drying equipment used in the first test.

[0051] Figure 5 shows the change in the degree of vacuum (pressure inside the adsorption tower) over time when the vacuum drying was restarted in the second test. Figure 5 shows a graph of the change over time, with the horizontal axis representing time (hours) and the vertical axis representing the pressure inside the adsorption tower (kPa). As shown in Figure 5, in the second test, the vacuum pump was restarted and then the internal pressure of the adsorption tower was evacuated to a set vacuum level of 2.4 kPa over a recovery time of approximately 60 minutes. In other words, in the first test described above, the recovery time to reach the set vacuum level of 2.4 kPa was 15 to 20 minutes, as shown in Figure 3. In contrast, in the second test, the capacity of the vacuum pump was adjusted so that the recovery time was approximately three times longer, at 60 minutes, as shown in Figure 5.

[0052] As a method for operating the vacuum pump in the second test, for example, a vacuum pump with a small vacuuming capacity may be used, or a method may be adopted in which the vacuum capacity is kept low by using an air intake valve in the piping connecting the vacuum pump and the adsorption tower. Alternatively, if a vacuum pump that can be controlled by an inverter is used, the vacuum capacity can be adjusted more precisely.

[0053] After restarting the plant for the second test, the condition inside the adsorption tower and the state of adsorbent capture by the strainer installed in the piping between the adsorption tower and the reducer were visually inspected to confirm downstream migration of the adsorbent. As a result, no evidence of adsorbent flow was found inside the adsorption tower. Furthermore, when adsorbent flows inside the adsorption tower, evidence of roughening of the surface (top surface) of the adsorbent accumulated inside the adsorption tower can be confirmed, but after restarting the plant for the second test, no such roughening was found. Furthermore, no adsorbent capture was confirmed on the strainer. Therefore, it was confirmed that there was no migration of adsorbent downstream (towards the condenser).

[0054] In this example, it was confirmed that by using a drying operation recovery method in which the vacuum pump was operated to increase the pressure inside the adsorption tower to the set vacuum level of 2.4 kPa over a period of 60 minutes from the start of restart, it was possible to prevent the adsorbent from migrating downstream of the adsorption tower, thereby increasing safety.

[0055] In Figure 5, the pressure inside the adsorption tower reaches 2.4 kPa from 100 kPa at shutdown after 60 minutes of recovery. Therefore, a vacuum capacity of 97.6 kPa / h is sufficient for the dry operation condition of the vacuum pump. The graph in Figure 5 also shows that the pressure inside the adsorption tower reaches 2.4 kPa from 100 kPa at shutdown after 45 minutes of recovery. Since the pressure inside the adsorption tower remains almost constant from 45 minutes to 60 minutes, a recovery time of at least 45 minutes is sufficient. In this case, a vacuum capacity of 130 kPa / h (97.6 kPa / 45 minutes) is sufficient for the dry operation condition of the vacuum pump. Therefore, the vacuum capacity range, which is the dry operation condition of the vacuum pump, can be set to a range of 97.6 kPa / h to 130 kPa / h.

[0056] (Second embodiment) The second embodiment of the method for restoring drying operation in drying an adsorbent in an adsorption tower is a method for restarting a vacuum pump so that the pressure inside the adsorption tower reaches a set vacuum level based on operating conditions in which the adsorbent does not flow inside the adsorption tower when the drying operation is stopped due to a power outage or the like during drying of an adsorbent in an adsorption tower using a vacuum drying device 1 (see Figure 1) having a configuration similar to that of the first embodiment, and is a drying operation restoration method that uses a discriminant equation for the minimum fluidization rate (equation (1) described below).

[0057] FIG. 6 is a flowchart showing a method for restoring the drying operation in the adsorbent drying in the adsorption tower according to the second embodiment. 6, in the drying operation recovery method, first, the vacuum pump is restarted when it was stopped (step S1). The operation method of the vacuum pump at this time can be set appropriately, and for example, a method of gradually decreasing the degree of vacuum or a method of gradually increasing the degree of vacuum can be adopted. As another method for operating the vacuum pump, when the vacuum capacity of the vacuum pump is large, a method of reducing the vacuum capacity by using an air intake valve to reduce the vacuuming power may be adopted. Also, a method of varying the pressure reduction power of the vacuum pump by inverter control may be adopted.

[0058] Next, in step S2, the vapor flow rate in the adsorption tower is measured to determine the vapor velocity (A). Furthermore, in step S3, the minimum fluidization velocity (B) in the adsorbent is determined using the discriminant formula (1) below. Formula (1) will be described later. Note that either the step of calculating the vapor velocity in step S2 or the step of calculating the minimum fluidization velocity in step S3 may precede the other, or they may be performed simultaneously or in parallel.

[0059] Next, it is determined whether the value ((A) / (B)) obtained by dividing the vapor velocity (A) calculated in step S1 by the minimum fluidization velocity (B) calculated in step S3 reaches the determination criterion of 1.5 (step S4). If the determination in step S4 is that the value is less than 1.5 (step S4: NO), the depressurization by the vacuum pump is maintained. If the value is 1.5 or more (step S4: YES), the pumping capacity of the vacuum pump is reduced or the depressurization by the vacuum pump is stopped (step S5). If (A) / (B) does not reach 1.5 in step S4, the process returns to step S2, and the vapor velocity (A) in the adsorption chamber is calculated again.

[0060] After reducing or stopping the decompression by the vacuum pump in step S5, a determination is made in step S6 as to whether the pressure inside the adsorption tower has reached 2.4 kPa. If the pressure inside the adsorption tower has reached 2.4 kPa in step S6 (step S6: YES), the process proceeds to step S7, where normal operation by the vacuum pump (maintaining 2.4 kPa) is initiated, and the recovery operation is terminated. On the other hand, if the pressure inside the adsorption tower has not reached 2.4 kPa in step S6 (step S6: NO), the pumping capacity of the vacuum pump is increased or the vacuum pump is restarted in step S8, and the process returns to step S2, where the vapor velocity (A) inside the adsorption tower is calculated again.

[0061] Next, the minimum fluidization velocity u calculated in step S3 described above m (Equivalent to (B) above) The discriminant will now be explained. Minimum fluidization speed u m (m / s) can be calculated using the well-known discriminant (1). Here, D pv is the particle diameter, ε is the void fraction in the minimum fluidized state, P (kPa) is the pressure in the adsorption column, μ (Pa s) is the viscosity coefficient, L (m) is the diameter of the adsorbent, ρ (kg / m 3 ) is the vapor density, ρ p is the density of the adsorbent, g (m / s 2 ) is the gravitational acceleration, Cm is the proportionality constant, Re is the Reynolds number, and k is the correction coefficient. Re is calculated based on equation (2).

[0062]

number

[0063]

number

[0064] (An example of a method for restoring dry operation using a judgment formula) Next, the minimum fluidization velocity u obtained by the above equation (1) m This section explains an example of a method for restoring drying operation, in which the minimum fluidization velocity (B) calculated using the discriminant equation is compared with the vapor velocity (A) in the adsorption tower at the time of restoration. Table 1 shows various parameters required for comparing the calculated values ​​of the minimum fluidization velocity (B) and the vapor velocity (A) in the adsorption tower at the time of restoration. These parameters include the adsorption tower pressure (kPa), saturation temperature (°C), vapor density (kg / m 3 ), viscosity (Pa s), liquid density (kg / m 3 ), weight of adsorbent (kg / m 3 ), diameter of the adsorbent (m), gravitational acceleration g (m / s 2 ), minimum fluidization velocity (B) um (m / s), Reynolds number Re, proportionality constant Cm, adsorption tower diameter (m), adsorption tower cross-sectional area (m 2 ), drainage per hour during adsorbent flow (L / h), drain flow rate (kg / s), steam flow rate (m 3 / s), and vapor velocity (A) (average over the surface of the adsorbent) (m / s).

[0065] The vapor velocity (m / s) is calculated from the amount of condensed water to determine the volumetric flow rate of the vapor before condensation, and then divided by the cross-sectional area of ​​the adsorption tower vessel to obtain the average vapor flow velocity within the adsorption tower (average over the surface of the adsorbent).

[0066] [Table 1]

[0067] As shown in Table 1, the ratio (A) / (B), which is the condition for fluidization, increased by 4.5 times. In other words, it was confirmed that the vapor flow rate when downstream migration of the adsorbent occurred after power outage recovery was 4.5 times the minimum fluidization rate. Therefore, by adjusting the vacuum pump's evacuation speed and limiting the condensation rate to 7 (L / h) / 4.5 = 1.5 (L / h) in the case of this example adsorption tower, it was confirmed that the adsorbent would not migrate from the adsorption tower to the condenser side.

[0068] Furthermore, in the example shown in Figure 5 above, using a vacuum pump for 60 minutes of operation is a good method for preventing the adsorbent from migrating downstream, so in the example of Table 1 where vacuuming is performed for 20 minutes of operation, the condition for flow to occur, (A) / (B), which is 4.5 times, can be set to 1.5 times, or 1 / 3.

[0069] As described above, in the second embodiment, the vapor flow rate in the adsorption tower is compared with the minimum fluidization velocity calculated by the judgment formula, and the evaporation rate can be adjusted by adjusting the vacuum level of the vacuum pump so that the vapor flow rate does not exceed 1.5 times the judgment standard. This prevents the adsorbent in the adsorption tower from flowing due to an increase in the vapor velocity of water vapor. Therefore, in the present invention, downstream migration of the adsorbent can be prevented, further improving safety.

[0070] Furthermore, in the second embodiment of the method for restoring the drying operation of the adsorbent in the adsorption tower, in addition to adjusting the operating conditions of the vacuum pump, the amount of condensation by the condenser that condenses the water vapor in the adsorption tower by cooling may be adjusted. In this case, the condensation force is promoted by lowering the cooling temperature at which the water vapor is cooled in the condenser to increase the condensation capacity (condensation amount), and the amount of steam equivalent to the volume of the condensed water flows from the adsorption tower into the condenser. In other words, the steam from the adsorption tower flows more easily into the reducer, increasing the vapor velocity. Therefore, the vapor velocity in the adsorption tower can be adjusted by adjusting the condensation capacity of the condenser in addition to adjusting the degree of vacuum using the vacuum pump described above.

[0071] Furthermore, the vacuum pump may be operated for an operating time of 45 to 60 minutes from the start of restart so that the pressure inside the adsorption tower reaches 2.4 kPa.

[0072] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

[0073] For example, the configurations such as the shapes and sizes of the adsorption tower 10, the condenser 11, and the condensed water tank 12 of the vacuum drying apparatus 1 are not limited to those in this embodiment, and can be changed as appropriate. [Explanation of symbols]

[0074] 1 vacuum drying device, 10 adsorption tower, 11 condenser, 12 condensed water tank, 13 vacuum pump, 14 cooling device, 15 drain pipe, 15A first pipe, 15C third pipe, 151 strainer, 17 air intake valve, W1 water vapor, W2 condensed water

Claims

1. A method for restoring an adsorbent drying operation in an adsorption tower, the method comprising the steps of: (a) providing a vacuum pump connected to a downstream side of the adsorption tower via a pipe and sucking air containing water vapor to reduce the pressure inside the adsorption tower; and (b) restoring an adsorbent drying operation in the adsorption tower when the adsorption tower stops drying the adsorbent that adsorbs radioactive materials contained in contaminated water, the method comprising the steps of: A method for restoring drying operation in drying an adsorbent in an adsorption tower, comprising restarting the vacuum pump so that the pressure inside the adsorption tower reaches a set vacuum level based on operating conditions in which the adsorbent in the adsorption tower does not flow.

2. restarting the vacuum pump; measuring the vapor flow rate in the adsorption tower to determine the vapor velocity; determining a minimum fluidization velocity in the adsorbent; determining whether a value obtained by dividing the vapor velocity by the minimum fluidization velocity reaches a determination criterion of 1.5 times; maintaining the reduced pressure by the vacuum pump when the determination is less than 1.5 times, and stopping the reduced pressure by the vacuum pump when the determination is 1.5 times or more; The method for restoring the drying operation of an adsorbent drying tower according to claim 1, further comprising:

3. The method for restoring a drying operation for drying an adsorbent material in an adsorption tower according to claim 1 , further comprising adjusting an amount of condensation by a condenser that condenses water vapor in the adsorption tower by cooling.

4. 2. The method for restoring drying operation in an adsorption tower for drying an adsorbent material according to claim 1, wherein the vacuum pump is operated for an operating time of 45 minutes to 60 minutes from the start of restart so that the pressure inside the adsorption tower becomes 2.4 kPa.

5. 5. The method for restoring a drying operation in an adsorption tower for drying an adsorbent material in an adsorption tower according to claim 1, further comprising providing an air intake valve capable of taking in air in a pipe between the adsorption tower and the vacuum pump.

6. 5. The method for restoring a drying operation for drying an adsorbent in an adsorption tower according to claim 1, wherein the vacuum pump has a variable pressure reducing force controlled by an inverter.

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