A flue gas cooling device for plasma treatment of low-level radioactive waste

Abstract

The present invention discloses a flue gas cooling device for plasma treatment of low-level radioactive waste, which relates to the technical field of radioactive waste treatment and solves the problems of poor cooling effect, low device integration, high investment cost, etc. of conventional flue gas cooling devices. The device comprises a cylinder, which is divided into an upper cylinder, a lower cylinder and an ash hopper from top to bottom. A water cooling device is arranged in the upper cylinder, a tube-and-tube heat exchange device is arranged in the lower cylinder, and the bottom of the ash hopper is opened and closed by a valve; a flue gas inlet pipe located above the water cooling device and a flue gas exhaust pipe located below the tube-and-tube heat exchanger are connected to the cylinder, and the water cooling device comprises a plurality of cylindrical membrane water-cooled walls nested inside and outside in sequence. By adjusting the heat exchange area according to the flue gas volume, the flue gas temperature can be reduced from 1150°C to about 200°C, achieving the effects of small footprint, low investment cost, automatic cleaning of radioactive fly ash, simple and convenient operation, and high device integration.

Description

Technical Field

[0001] The invention relates to the technical field of radioactive waste treatment, and in particular to a flue gas cooling device for low-level radioactive waste treated with plasma. Background Art

[0002] At present, domestic nuclear power plants generate a large amount of low-level radioactive waste during operation and maintenance. The low-level waste mainly includes plastic sheets, plastic bags, absorbent paper, waste wood, rags, scrap metal parts, building materials, etc. Most of the low-level waste is combustible waste; a small part is non-combustible waste. Plasma gasification melting technology has the characteristics of high temperature, high energy density and strong compatibility. It can dispose of all low-level waste and completely destroy dioxins. Heavy metals and nuclides are solidified in molten glass. Plasma gasification melting technology has the advantages of more thorough harmlessness, high degree of volume reduction, and small footprint. The ash produced by traditional incineration still needs to be solidified and stabilized (volume increase), while the glass produced by plasma melting treatment has stable physical and chemical properties and can be directly landfilled.

[0003] However, the flue gas generated during the plasma treatment of low-level radioactive waste has a high temperature (the flue gas temperature at the outlet of the secondary combustion chamber is generally around 1150°C) and contains a large amount of radioactive nuclides and particulate matter. In the hazardous waste industry, the high-temperature flue gas is often cooled before the pollutants in the flue gas are treated. Conventional flue gas cooling devices often have problems such as poor cooling effect, low device integration, high investment cost, difficulty in cleaning fly ash, and a sharp increase in flue gas volume. Therefore, there is an urgent need for a new flue gas cooling device that can effectively reduce the flue gas temperature while having the characteristics of small footprint, low investment cost, simple and convenient fly ash cleaning, and high device integration. Summary of the invention

[0004] The purpose of the present invention is to provide a flue gas cooling device for plasma treatment of low-level radioactive waste, and proposes a flue gas cooling method combining "multi-circle membrane water cooling structure + shell and tube heat exchanger". The flue gas can be cooled from 1150°C to about 200°C by adjusting the heat exchange area according to the flue gas volume, and has a good cooling effect; and has the characteristics of small footprint, low investment cost, automatic cleaning of radioactive fly ash, simple and convenient operation, and high degree of device integration. The discharged flue gas temperature is low, which brings convenience to the subsequent removal of pollutants in the flue gas.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions:

[0006] A flue gas cooling device for plasma treatment of low-level radioactive waste, comprising a cylinder, which is divided into an upper cylinder, a lower cylinder and an ash hopper from top to bottom, a water cooling device is arranged in the upper cylinder, a tube-in-tube heat exchange device is arranged in the lower cylinder, and the bottom of the ash hopper is opened and closed by a valve;

[0007] The cylinder is connected with a flue gas inlet pipe located above the water cooling device and a flue gas exhaust pipe located below the tube-in-tube heat exchanger. The water cooling device includes a plurality of cylindrical membrane water-cooled walls which are nested in sequence inside and outside.

[0008] Furthermore, the water cooling device reduces the flue gas temperature to 500-600°C, and then the shell and tube heat exchanger reduces the flue gas temperature to no more than 200°C in <1s.

[0009] Furthermore, the membrane water-cooled wall includes a plurality of vertical cooling water tubes and fins welded to each other.

[0010] Furthermore, the membrane water-cooled wall includes spiral cooling water coils and fins welded to each other.

[0011] Furthermore, a dust cleaning device is provided above the upper cylinder and the lower cylinder.

[0012] Furthermore, the cleaning device includes a shock wave cleaning device.

[0013] Furthermore, both ends of the water-cooling device and the shell-and-tube heat exchange device are connected to a cooling water inlet pipe and a cooling water outlet pipe, respectively.

[0014] Furthermore, the ash hopper is in a cone shape that is larger at the top and smaller at the bottom, and the bottom is opened and closed by an electric double-disc valve.

[0015] Furthermore, the ash hopper is connected to the ash bucket via a flange.

[0016] Furthermore, the ash hopper is also provided with an air hammer or a mechanical vibration device.

[0017] In summary, the present invention has the following beneficial effects:

[0018] (1) The flue gas cooling method combining "membrane water cooling structure + shell and tube heat exchanger" is adopted, and the cooling effect of the whole device is obvious; the membrane water cooling structure can reduce the flue gas temperature from about 1150℃ to about 500-600℃, and the shell and tube heat exchange structure can not only reduce the flue gas temperature from 500℃ to 200℃, but also control the cooling time of 500℃-200℃ to less than 1s, avoiding the re-synthesis of dioxins during the cooling process, thereby achieving the purpose of controlling the pollutant concentration in the outlet flue gas;

[0019] (2) The membrane water-cooling structure is composed of multiple membrane water-cooling walls stacked and nested inside and outside (a single membrane water-cooling wall can be composed of two methods: "vertical cooling water pipes and fins welded" or "spiral cooling water coils and fins welded"); the membrane structure can effectively reduce fly ash deposition, and a suitable gap is designed between the membrane walls for easy cleaning; an online cleaning device is arranged at the upper end of the tube-in-tube heat exchanger to facilitate regular cleaning of fly ash adhering to the tube wall; an air hammer or mechanical vibration device is also arranged at the conical ash hopper to regularly knock the area to prevent the fly ash from forming a bridge above the electric double-gate valve and being unable to fall, thereby achieving the effect of simple and convenient cleaning of the device;

[0020] (3) The entire set of inverted cone cylinder device is made of heat-resistant and corrosion-resistant metal materials; it not only has better heat resistance but also can withstand the corrosion of acidic gases such as SO2 and HCl in the flue gas, ensuring that the device will not crack, break, corrode or deform during the flue gas treatment process;

[0021] (4) The diameter and height of the inverted cone cylinder are determined by the actual heat exchange cooling effect. The flue gas flow rate, cylinder diameter, and cylinder height should be appropriately designed to improve the flue gas cooling effect and reduce pressure loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of the first embodiment of the present invention;

[0023] Figure 2 yes Figure 1 Top view of the middle membrane water cooling structure;

[0024] Figure 3 It is a structural side view of the shell and tube heat exchanger part;

[0025] Figure 4 It is a schematic diagram of the overall structure of the second embodiment of the present invention;

[0026] Figure 5 yes Figure 4 Top view of the middle membrane water cooling structure.

[0027] In the figure, 1. Cylinder; 2. Water-cooling device; 3. Flue gas inlet pipe; 4. Flue gas exhaust pipe; 5. Cooling water inlet pipe; 6. Cooling water outlet pipe; 8. Shock wave cleaning device; 9. Mechanical vibration device; 10. Shell-and-tube heat exchange device; 11. Electric double-disc valve; 12. Ash receiving bucket. DETAILED DESCRIPTION

[0028] The specific implementation manner of the present invention is further described below in conjunction with the accompanying drawings, and this embodiment does not constitute a limitation of the present invention.

[0029] Embodiment 1:

[0030] A device for cooling flue gas from plasma treatment of low-level radioactive waste, such as Figure 1 As shown, it comprises a cylinder 1, which is divided into an upper cylinder 1, a lower cylinder 1 and a conical ash hopper from top to bottom. A water cooling device 2 is provided in the upper cylinder 1, a tube-in-tube heat exchange device 10 is provided in the lower cylinder 1, and the bottom of the ash hopper is opened and closed by a valve;

[0031] The cylinder 1 is connected with a flue gas inlet pipe 3 (on the cylinder wall of the upper cylinder 1) located above the water-cooling device 2 and a flue gas exhaust pipe 4 (on the cylinder wall of the lower cylinder 1) located below the shell-and-tube heat exchanger. The flue gas inlet pipe 3 and the flue gas exhaust pipe 4 are respectively located on opposite sides of the cylinder 1 and are connected to the upstream and downstream equipment through flanges. The cylinder 1, the flue gas inlet pipe 3 and the flue gas exhaust pipe 4 are all made of the same high-temperature resistant and corrosion-resistant metal material and are welded together.

[0032] like Figure 1 and Figure 2 As shown, the water-cooling device 2 includes a plurality of cylindrical membrane water-cooling walls nested in sequence (the spacing between adjacent water-cooling walls is equal, which is convenient for designing an automatic cleaning robot to clean them in the future), and the membrane water-cooling wall includes a plurality of vertical cooling water pipes and fins welded to each other. The fins are of arc cross-section, arranged vertically, and welded between adjacent cooling water pipes;

[0033] Both ends of the water-cooling cooling device 2 and the shell-and-tube heat exchange device 10 are respectively connected to the cooling water inlet pipe 5 and the cooling water outlet pipe 6; in this embodiment, the water-cooling cooling device 2 also includes a plurality of concentric circular water distribution pipes welded and fixed at the top and the bottom, the cooling water inlet pipe 5 supplies water to the top water distribution pipe, and the top water distribution pipe supplies water to each cooling water pipe in the membrane water-cooled wall with the same diameter; similarly, each cooling water pipe in the corresponding membrane water-cooled wall is collected to the cooling water outlet pipe 6 through the bottom water distribution pipe for drainage, and the flow rate is fast and the cooling effect is good.

[0034] like Figure 3 As shown, the cooling water pipes of the shell-and-tube heat exchange device 10 are made of high-temperature resistant and corrosion-resistant metal materials; a cleaning device is provided above the upper cylinder 1 and the lower cylinder 1. In this embodiment, the cleaning device includes a shock wave cleaning device 8. A plurality of openings and closing ports located above the water-cooling device 2 can also be provided on the outer periphery of the upper cylinder 1. The openings and closing ports are closed during operation, and are opened during cleaning to allow a cleaning device (such as a blowing pipe, a spray pipe or a knocking device, etc.) to pass through or a cleaning robot, etc. to be placed in.

[0035] like Figure 1 As shown, the ash hopper is a cone with a larger top and a smaller bottom. The bottom is connected to the ash bucket 12 through a flange, and an electric double-disc valve 11 is connected between the two flanges to control opening and closing.

[0036] A material level transmitter is arranged on the wall of the ash hopper and is interlocked with the opening and closing of the electric double-disc valve 11. When a certain amount of fly ash is deposited in the ash hopper and the material level reaches a certain height, the electric double-disc valve 11 automatically opens. Conversely, when the material level in the ash hopper drops below the detection value, the electric double-disc valve 11 automatically closes.

[0037] like Figure 1 As shown, an air hammer or a mechanical vibration device 9 is also connected to the outside of the ash hopper. The hammer body is controlled to swing through hydraulic or cam connecting rod mechanisms. It can also use existing vibration and cleaning devices such as vibrators to regularly beat the area to prevent the fly ash from forming a bridge above the gate valve and being unable to fall.

[0038] Working process:

[0039] When the flue gas cooling device is in operation, high-temperature flue gas of about 1150°C (generally not exceeding 1200°C) will enter the cylinder 1 horizontally through the air inlet pipe on the cylinder wall of the upper cylinder 1. When the flue gas moving downward passes through the membrane water cooling device 2, the high-temperature flue gas and the cooling water are heat exchanged through the convection of the cold and hot fluids on the wall.

[0040] The temperature of the flue gas in this heat exchange section is reduced from 1150°C to about 500°C-600°C by means of the cooling liquid velocity and the length of the membrane water cooling device 2;

[0041] When the flue gas moves to the lower cylinder 1, the flue gas will contact the tube heat exchanger, and the flue gas will exchange heat with the cooling water of the heat exchanger again. The tube heat exchange structure can not only reduce the temperature of the flue gas from about 500-600℃ to 200℃, but also control the time of the 500℃-200℃ cooling section to less than 1s to avoid the re-synthesis of dioxins during the cooling process, thereby achieving the purpose of controlling the concentration of pollutants in the outlet flue gas. After the device has been used for a period of time, the online cleaning device will be started to clean the fly ash adhering to the tube wall;

[0042] Finally, the cooled flue gas will be discharged from the exhaust pipe on the wall of the lower cylinder 1, and the fly ash falling to the bottom of the cylinder 1 will accumulate above the electric double-gate valve along the conical ash hopper. When a certain amount of fly ash is accumulated and the material level reaches a certain height, the electric double-gate valve 11 will automatically open. When the material level drops, the electric double-gate valve 11 will automatically close, and the fly ash will eventually fall into the ash receiving bucket 12, thereby completing the collection of fly ash by the entire device;

[0043] After the high-temperature flue gas is treated by a flue gas cooling method that combines "membrane water cooling structure + shell-and-tube heat exchanger", the flue gas is finally discharged at a relatively low temperature, completing the purpose of the device to significantly cool the high-temperature flue gas; at the same time, the device cleans and captures the fly ash adhering to the pipe wall in an efficient and simple way, with the characteristics of small footprint, low investment cost, automatic cleaning of radioactive fly ash, simple and convenient operation, and a high degree of device integration. The exhaust flue gas temperature is relatively low, which facilitates the subsequent removal of pollutants in the flue gas.

[0044] Embodiment 2:

[0045] The structure of this embodiment is roughly the same as that of the first embodiment, except that:

[0046] like Figure 4 and Figure 5 As shown, the membrane water-cooled wall includes spiral cooling water coils and fins welded to each other. The cooling water coils can be formed by welding multiple pipes end to end. The fins are spiral and welded between the upper and lower pipes to form a water-cooled wall. The cooling water inlet pipe 5 is located on one side of the cylinder 1 and is connected to the water inlet on the top of the spiral cooling water coils of different diameters. The cooling water outlet pipe 6 is located on the other side of the cylinder 1 and is connected to the water outlet at the bottom of the spiral cooling water coils of different diameters. Its structure and connection method are simpler, and the amount of on-site welding is small.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions should also be deemed to fall within the protection scope of the technical solution of the present invention.

Claims

1. A flue gas cooling device for plasma treatment of low-level radioactive waste, characterized in that: It includes a cylinder, which is divided into an upper cylinder, a lower cylinder and an ash hopper from top to bottom. A water cooling device is provided in the upper cylinder, a tube-in-tube heat exchange device is provided in the lower cylinder, and the bottom of the ash hopper is opened and closed by a valve; The cylinder is connected with a flue gas inlet pipe located above the water-cooling device and a flue gas exhaust pipe located below the tube-in-tube heat exchanger, and the water-cooling device includes a plurality of cylindrical membrane water-cooling walls nested in sequence inside and outside; The membrane water-cooled wall comprises a plurality of vertical cooling water tubes and fins welded to each other, or comprises spiral cooling water coils and fins welded to each other.

2. The device for cooling flue gas from plasma treatment of low-level radioactive waste according to claim 1, characterized in that: The water cooling device reduces the flue gas temperature to 500-600°C, and then the shell and tube heat exchanger reduces the flue gas temperature to no more than 200°C in <1s.

3. A plasma treatment low-level radioactive waste flue gas cooling device according to claim 1 or 2, characterized in that: Dust cleaning devices are arranged above the upper cylinder and the lower cylinder.

4. The device for cooling flue gas from plasma treatment of low-level radioactive waste according to claim 3, characterized in that: The cleaning device comprises a shock wave cleaning device.

5. The device for cooling flue gas from plasma treatment of low-level radioactive waste according to claim 1, characterized in that: Both ends of the water-cooling device and the tube-in-tube heat exchange device are connected to a cooling water inlet pipe and a cooling water outlet pipe respectively.

6. The device for cooling flue gas from plasma treatment of low-level radioactive waste according to claim 1, characterized in that: The ash hopper is in a cone shape with a larger top and a smaller bottom, and the bottom is opened and closed by an electric double-disc valve.

7. A flue gas cooling device for plasma treatment of low-level radioactive waste according to claim 1 or 6, characterized in that: The ash hopper is connected to the ash bucket via a flange.

8. A flue gas cooling device for plasma treatment of low-level radioactive waste according to claim 1 or 6, characterized in that: The ash hopper is also provided with an air hammer or a mechanical vibration device.

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