Method for starting a rotary calciner for radioactive liquid waste

Abstract

Embodiments of the present application relate to the technical field of radioactive waste liquid treatment, and particularly relate to a starting method of a rotary calcining furnace for radioactive waste liquid. The method comprises: delivering water into the rotary calcining furnace to make the part of the rotary calcining furnace close to the inlet end reach heat balance; after the water is delivered for a first predetermined time, increasing the flow of the water, and continuing to deliver the water into the rotary calcining furnace to make the rotary calcining furnace reach heat balance; after the water is delivered for a second predetermined time, stopping the delivery of the water, and starting to deliver a salt solution into the rotary calcining furnace; after the outlet end of the rotary calcining furnace normally discharges solid calcined products, stopping the delivery of the salt solution; and starting to input the radioactive waste liquid to be calcined into the rotary calcining furnace to calcine the radioactive waste liquid. The method provided by the embodiments of the present application can make the rotary calcining furnace smoothly and stably transit from the suspended state to the stable running stage, and meanwhile, the quality of the calcined products is ensured, and the starting time is saved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of radioactive waste liquid treatment technology, specifically to a method for starting up a rotary calciner for radioactive waste liquid. Background Technology

[0002] The statements herein are merely background information relating to the present invention and do not necessarily constitute prior art. In the treatment of radioactive waste liquids, a two-step cold crucible glass solidification method is typically used. First, the radioactive waste liquid is calcined in a rotary kiln to obtain solid calcined products. These calcined products are then vertically dropped into a cold crucible to melt with base glass beads, forming a solidified glass body. When calcining radioactive waste liquids in a rotary kiln, the waste liquid enters the furnace from the inlet end, undergoes evaporation, denitrification, and calcination to form oxide particles, which are then discharged from the outlet end of the rotary kiln. Summary of the Invention

[0003] A brief overview of this application is provided below to offer a basic understanding of certain aspects thereof. It should be understood that this overview is not an exhaustive summary of the application. It is not intended to identify key or essential parts of the application, nor is it intended to limit its scope. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0004] An embodiment of the present invention provides a method for starting up a rotary calciner for radioactive waste liquid. The rotary calciner has an inlet end and an outlet end. Radioactive waste liquid continuously enters the rotary calciner from the inlet end for calcination. After calcination, the radioactive waste liquid forms a solid calcination product and is discharged from the outlet end. The startup method provided in the embodiments of the present invention is used to restart the feeding and calcination of radioactive waste liquid after the feeding of a rotary calciner has been suspended. The rotary calciner remains heated after the feeding has been suspended. The method includes: step S10, supplying water into the rotary calciner to achieve thermal equilibrium in a portion of the rotary calciner near its inlet; step S20, increasing the water flow rate after a first predetermined time and continuing to supply water into the rotary calciner to achieve thermal equilibrium; step S30, stopping the water supply after a second predetermined time and starting to supply a salt solution into the rotary calciner; step S40, stopping the supply of the salt solution after the solid calcined material is normally discharged from the outlet of the rotary calciner; and step S50, starting to feed the radioactive waste liquid to be calcined into the rotary calciner for calcination.

[0005] The startup method in this embodiment of the invention, when restarting the rotary calciner after a pause in feeding, lowers the temperature inside the calciner by supplying water to the furnace for a predetermined time and flow rate. This allows the calciner to achieve thermal balance, enabling a smooth and stable transition from a paused state to a stable operating stage. This prevents water or radioactive waste from flowing out of the calciner's outlet, while also ensuring the quality of the calcined product. Furthermore, restarting the rotary calciner using this method eliminates the need to stop heating and wait for the furnace to cool to room temperature, saving startup time and improving calcination efficiency. Attached Figure Description

[0006] Other objects and advantages of the invention will become apparent from the following description of embodiments of the invention with reference to the accompanying drawings, and will help to provide a comprehensive understanding of the invention.

[0007] Figure 1 This is a flowchart of a method for starting up a rotary calciner for radioactive waste liquid according to an embodiment of the present invention.

[0008] It should be noted that the accompanying drawings are not necessarily drawn to scale, but are shown only in a schematic manner without affecting the reader's understanding. Detailed Implementation

[0009] Exemplary embodiments of the invention will be described below with reference to the accompanying drawings. For clarity and brevity, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the development of any such actual embodiment to achieve the developer's specific goals, such as complying with constraints related to the system and business, and these constraints may vary depending on the implementation. Furthermore, it should be understood that while development work can be very complex and time-consuming, such development work is merely a routine task for those skilled in the art who benefit from the content of this application.

[0010] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the device structure and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0011] The rotary calciner is used to calcine radioactive waste liquid. It has an inlet end and an outlet end. The radioactive waste liquid continuously enters the rotary calciner from the inlet end for calcination. After calcination, the radioactive waste liquid forms solid calcination products and is discharged from the outlet end.

[0012] The inventors of this invention discovered that in some situations, such as during the cold crucible unloading stage or when components need to be replaced in the rotary calciner, the rotary calciner needs to pause feeding without stopping heating. When unloading or component replacement is completed and the rotary calciner is restarted for feeding and calcining radioactive waste, the high furnace tube temperature causes the Leidenfrost effect upon entry, resulting in some liquid being discharged from the outlet. Furthermore, if the low-temperature start-up method in related technologies is used to start the rotary calciner, heating must be stopped first, and the furnace must be allowed to cool down before restarting, which requires a long wait and is inefficient.

[0013] Based on this, embodiments of the present invention provide a method for starting up a rotary calciner for radioactive waste liquid. This method is used to restart the feeding and calcination of radioactive waste liquid after the rotary calciner has paused its feeding, wherein the rotary calciner remains heated after the feeding has paused. Figure 1 As shown, the method includes the following steps.

[0014] Step S10: Water is supplied into the rotary calciner to achieve heat balance in a portion of the rotary calciner near its inlet.

[0015] Step S20: After the water has been supplied for the first predetermined time, increase the water flow rate and continue to supply water into the rotary calciner to achieve heat balance in the rotary calciner.

[0016] Step S30: After the water continues to be supplied for a second predetermined time, the water supply is stopped and the salt solution is started to be supplied into the rotary calciner.

[0017] Step S40: After the solid calcined material is discharged normally from the outlet end of the rotary calciner, stop conveying the salt solution.

[0018] Step S50: Begin feeding the radioactive waste liquid to be calcined into the rotary calciner to calcine the radioactive waste liquid.

[0019] In embodiments of the present invention, when restarting the rotary calciner after a pause in feeding, water is supplied to the furnace for a predetermined time and flow rate to lower the actual temperature inside the furnace. This allows the furnace to achieve thermal balance, enabling a smooth and stable transition from a paused state to a stable operating state. This prevents water or radioactive waste from flowing from the furnace's outlet, ensuring the quality of the calcined product and meeting performance requirements. Furthermore, restarting the rotary calciner using this method eliminates the need to wait for the furnace to cool down for a low-temperature start-up, saving start-up time and improving calcination efficiency.

[0020] In some embodiments, in steps S20 and S30, a first predetermined time and a second predetermined time can be determined based on the temperature change of the rotary calciner to ensure that the temperature inside the rotary calciner can stabilize and achieve heat balance after water is supplied for the first and second predetermined times.

[0021] In some embodiments, the first predetermined time may be the time it takes for the temperature of a portion of the rotary calciner near its inlet to stabilize. Once the temperature in this portion of the rotary calciner near its inlet has stabilized, a higher flow rate of water continues to be supplied to the furnace, thereby continuing to remove excess heat from the remaining areas of the furnace and achieving thermal equilibrium. In some embodiments, the first predetermined time may be the time it takes for the temperature of the first half of the rotary calciner to stabilize. For example, the first predetermined time may be set in the range of 20-30 minutes.

[0022] In some embodiments, in step S10, the rotational speed of the rotary calciner can be reduced before water is introduced into the rotary calciner to prevent the water from flowing out of the outlet end of the rotary calciner due to excessive rotational speed, thus causing all the water entering the rotary calciner to evaporate. For example, the rotational speed of the rotary calciner can be reduced from 20-30 r / min at the start of operation to a range of 10-15 r / min.

[0023] In some embodiments, in step S10, water can be supplied to the rotary kiln at a predetermined flow rate to ensure that the water can remove excess heat from certain areas of the kiln, achieving thermal equilibrium in those areas, while also ensuring that water does not flow out of the kiln's outlet even in the event of the Leidenfrost effect. For example, the predetermined flow rate can be set to 50-60 L / h.

[0024] In some embodiments, a pipe connected to the inlet of the rotary calciner can be provided, and a flow regulating device can be installed on the pipe to input water, brine solution, or radioactive waste liquid into the rotary calciner, while simultaneously controlling and regulating the input flow rate. The pipe is made of a material resistant to acid corrosion. For example, the flow regulating device can be a pump or similar device with flow regulating function.

[0025] In some embodiments, in step S30, the second predetermined time can be the time from the start of increasing the water flow rate until the temperature of the remaining area of ​​the rotary kiln stabilizes, to ensure that all areas within the rotary kiln reach thermal equilibrium after the water has been supplied for the second predetermined time. In some embodiments, the second predetermined time is the time from the start of increasing the water flow rate until the temperature of the latter half of the rotary kiln stabilizes. For example, the second predetermined time can be set in the range of 30-40 minutes.

[0026] In some embodiments, in step S20, the rotation speed of the rotary calciner can be increased while increasing the water flow rate, so as to prevent the high flow rate of coolant from being thrown off as the rotary calciner rotates, resulting in the coolant not being able to fully contact and evaporate with the inner wall of the furnace tube, thereby preventing water from flowing out from the outlet end of the rotary calciner.

[0027] In some embodiments, the rotary calcining furnace can employ a zoned heating method. The rotary calcining furnace includes a first heating zone, a second heating zone, a third heating zone, and a fourth heating zone, arranged sequentially along the direction from the inlet to the outlet of the rotary calcining furnace. Furthermore, during the start-up process of the rotary calcining furnace, the temperature of each heating zone is monitored in real time to determine whether the temperature of each heating zone has reached a stable state.

[0028] Further, in step S10, the first predetermined time is the time it takes for the temperatures of the first and second heating zones to stabilize; in step S20, the second predetermined time is the time it takes for the temperatures of the third and fourth heating zones to stabilize after the flow rate is increased. In step S20, after the temperatures of the first and second heating zones are detected to be stable, the water flow rate is increased to continue stabilizing the temperatures of the third and fourth heating zones, thereby achieving heat balance throughout the rotary calciner and promptly balancing the temperature distribution within the rotary calciner.

[0029] In some embodiments, in step S20, the increased water flow rate can be determined based on the target calcination temperature, critical point temperature, and parameters of the rotary calciner tubes, so that the water can carry away excess heat from the tubes, thereby preventing water from flowing out of the rotary calciner's outlet. The critical point temperature is the lowest temperature at which the Leidenfrost effect occurs in the tubes.

[0030] The critical point temperature can be determined based on the material of the furnace tube. Since the temperature at which the coolant undergoes the Leidenfrost effect varies when different materials are used for the furnace tubes of the rotary calcining furnace, the critical point temperature needs to be determined based on the material of the furnace tubes to ensure that the Leidenfrost effect does not occur after the coolant is introduced into the furnace tubes.

[0031] For example, when the furnace tubes of the rotary calcining furnace are made of Inconel 690 stainless steel, the temperature at which the coolant exhibits the Leidenfrost effect is 300°C. To reduce the actual temperature inside the rotary calcining furnace below this temperature, the water flow rate can be increased to 60-80 L / h, and the rotation speed of the rotary calcining furnace can be increased to the range of 20-30 r / min.

[0032] Specifically, when the rotary calcining furnace is in a suspended state, the temperature of each heating zone is maintained at the target calcination temperature set for each heating zone. When the rotary calcining furnace is restarted, the temperature of each heating zone needs to be reduced to the temperature at which the Leiden Frost effect will not occur, i.e., the critical point temperature.

[0033] Furthermore, based on the law of conservation of heat, the amount of heat required to be removed when the actual temperature of each heating zone in the rotary calciner decreases from the target calcination temperature to the critical temperature, the specific heat capacity of the furnace tubes, and the size of the furnace tubes can be determined. Combined with the temperature difference before and after water is heated and evaporated, the specific heat capacity and heat of vaporization of water, the increased water flow rate can be determined using the expression Q = CmΔT. This ensures that the water can remove excess heat from the furnace tubes, preventing the Leidenfrost effect from occurring, and even if the Leidenfrost effect does occur, the water will not flow to the outlet.

[0034] In this embodiment, the target calcination temperatures of the first heating zone, the second heating zone, the third heating zone, and the fourth heating zone can be set to 600℃, 640℃, 850℃, and 880℃, respectively. When the rotary calcining furnace is in a paused state, the temperature of each heating zone is maintained at the above-mentioned target calcination temperature.

[0035] In some embodiments, in step S30, after the temperatures of the third and fourth heating zones are detected to be stable, the water supply is stopped, and a salt solution is supplied to the rotary calciner so that the salt solution is calcined in the rotary calciner to form solid particles. For example, the flow rate of the salt solution can be set to 80 L / h.

[0036] In some embodiments, the salt solution can be one of diluted radioactive waste liquid, nitrate solution, and sodium chloride solution. In this embodiment, the above solution is selected as the salt solution and input into the rotary calciner to generate some particulate matter in the third and fourth heating zones of the rotary calciner. When the rotary calciner is in operation and radioactive waste liquid is transported into it, the flow resistance of the generated calcined material is increased, the flow velocity of the calcined material is slowed down, thereby increasing the residence time of the calcined material in the furnace and ensuring that the quality and performance of the calcined product meet the preset requirements. For example, it ensures that the moisture content, denitrification rate, and other indicators of the calcined product meet the preset requirements.

[0037] In this embodiment, the diluent for the radioactive waste liquid can be a diluent obtained by diluting the radioactive waste liquid by 1-3 times.

[0038] In some embodiments, in step S40, after the solid calcined material is normally discharged from the outlet of the rotary calciner, the conveying of salt solution is stopped, and the rotary calciner is restarted after the feeding is suspended, in order to convey radioactive waste liquid into the furnace.

[0039] In some embodiments, in step S50, the radioactive waste liquid to be calcined can be fed into the rotary calciner at a predetermined flow rate. For example, the predetermined flow rate can be set to 80 L / h. This ensures that the radioactive waste liquid is fully calcined in the rotary calciner, guaranteeing the quality of the calcined product.

[0040] In some embodiments, in steps S30 and S50, the flow rate of the salt solution can be set to be the same as the flow rate of the radioactive waste liquid, so that the rotary kiln can adapt to the flow rate in advance, thereby ensuring that the rotary kiln can quickly enter the stable operation stage and improving the start-up efficiency.

[0041] The process of starting the rotary kiln using the method of the present invention is further illustrated below with specific embodiments.

[0042] Example 1

[0043] When the rotary calcining furnace is in a paused state, the temperatures of the first heating zone, the second heating zone, the third heating zone and the fourth heating zone are maintained at their respective target calcining temperatures, which are 600℃, 640℃, 850℃ and 880℃, respectively. At this time, the rotation speed of the rotary calcining furnace is 30 r / min.

[0044] The first step is to prepare two 500L feed tanks and two 500L waste liquid tanks. The feed tanks contain deionized water and diluted radioactive waste liquid, respectively. The waste liquid tanks contain radioactive waste liquid. They are connected to the inlet of the rotary kiln through acid corrosion resistant pipes. The pipes are equipped with pumps that can adjust the flow rate.

[0045] In this embodiment, the water is deionized water, and the composition of the radioactive waste liquid to be calcined is shown in Table 1.

[0046] Table 1 Composition of Radioactive Waste Liquid

[0047]

[0048] The second step is to reduce the rotation speed of the rotary calciner to 15 r / min before starting to supply water into the rotary calciner, and supply water into the rotary calciner at a flow rate of 50 L / h. After 30 minutes of supplying water, the first heating zone and the second heating zone reach thermal equilibrium and the temperature is maintained at about 150℃.

[0049] The third step is to increase the flow rate of water supplied to the rotary calciner to 80L / h. After 40 minutes of supplying water, the third and fourth heating zones reach thermal equilibrium and the temperature is maintained at around 250℃. At this point, the water supply is stopped.

[0050] The fourth step is to start feeding the diluted radioactive waste liquid into the rotary calciner at a flow rate of 80 L / h and increase the rotation speed of the rotary calciner to 30 r / min. After 5 minutes, the calcined material is discharged from the outlet of the rotary calciner, and the discharge is smooth. At this point, the feeding of the diluted radioactive waste liquid is stopped.

[0051] The fifth step involves feeding radioactive waste liquid into the rotary calciner at a flow rate of 80 L / h to calcine the radioactive waste liquid to be treated. Once the rotary calciner has started up, it enters a stable operation phase.

[0052] During the startup of the rotary calciner, no water flowed out of the outlet. When water was supplied to the furnace at a low flow rate, the dry-wet interface was located at the rear of the second heating zone, indicating that the Leidenfrost effect did not occur and the evaporation efficiency was high. When the flow rate of water supplied to the furnace was increased, the dry-wet interface was located in the middle of the third heating zone, indicating that the Leidenfrost effect also did not occur. After the rotary calciner entered the operation phase and radioactive waste was supplied, the solid-liquid interface was located at the rear of the second heating zone. After 5 minutes, the calcined products began to flow out from the outlet. By collecting and analyzing the calcined products discharged from the outlet of the rotary calciner, it was found that the moisture content of the calcined products was <5% and the denitrification rate was >95%, which met the quality and performance requirements of the calcined products.

[0053] Regarding the embodiments of the present invention, it should also be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to obtain new embodiments.

[0054] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for starting up a rotary calciner for radioactive waste liquid, wherein the rotary calciner has an inlet end and an outlet end, the radioactive waste liquid continuously enters the rotary calciner from the inlet end for calcination, and the radioactive waste liquid forms a solid calcination product after calcination and is discharged from the outlet end; characterized in that, The startup method is used to restart the feeding and calcination of the radioactive waste liquid after the rotary calciner has stopped feeding. The rotary calciner is still heating after the feeding has stopped, and it includes the following steps: Step S10: Water is supplied into the rotary calcining furnace to achieve heat balance in a portion of the rotary calcining furnace near its inlet. Step S20: After the water has been transported for a first predetermined time, the water flow rate is increased, and the water is continued to be transported into the rotary calciner to achieve heat balance in the rotary calciner. Step S30: After the water continues to be delivered for a second predetermined time, the water delivery is stopped, and the salt solution is started to be delivered into the rotary calcining furnace. Step S40: After the solid calcined material is normally discharged from the outlet end of the rotary calciner, the supply of the salt solution is stopped. Step S50: Start feeding the radioactive waste liquid to be calcined into the rotary calciner to calcinate the radioactive waste liquid.

2. The startup method according to claim 1, characterized in that, The first predetermined time and the second predetermined time are determined based on the temperature change of the rotary calcining furnace.

3. The startup method according to claim 2, characterized in that, The first predetermined time is the time it takes for the temperature of the partial area to stabilize.

4. The startup method according to claim 3, characterized in that, In step S10, before water is introduced into the rotary calciner, the rotation speed of the rotary calciner is reduced to prevent the water from flowing out of the outlet end of the rotary calciner.

5. The startup method according to claim 3, characterized in that, The second predetermined time is the time from the start of increasing the water flow rate until the temperature in the remaining area of ​​the rotary kiln becomes stable.

6. The startup method according to claim 5, characterized in that, In step S20, the water flow rate is increased, and the rotation speed of the rotary calciner is increased at the same time to prevent the water from flowing out of the outlet end of the rotary calciner.

7. The startup method according to claim 1, characterized in that, In step S20, the increased water flow rate is determined based on the target calcination temperature, critical point temperature, and furnace tube parameters of the rotary calciner. The critical point temperature is the lowest temperature at which the water undergoes the Leidenfrost effect inside the furnace tube.

8. The startup method according to claim 3, characterized in that, The rotary calcining furnace employs a zoned heating method; wherein, the rotary calcining furnace includes a first heating zone, a second heating zone, a third heating zone, and a fourth heating zone, which are arranged sequentially along the direction from the inlet end to the outlet end of the rotary calcining furnace; During the startup process of the rotary calcining furnace, the temperature of each heating zone is monitored in real time; In step S20, after the temperature of the first heating zone and the second heating zone is detected to be stable, the water flow rate is increased.

9. The startup method according to claim 8, characterized in that, In step S30, after the temperature of the third heating zone and the fourth heating zone is detected to be stable, the water supply is stopped and the salt solution is supplied to the rotary calcining furnace.

10. The starting method according to any one of claims 1-9, characterized in that, The salt solution is one of the following: diluted radioactive waste liquid, nitrate solution, and sodium chloride solution.

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